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Whole systems thinking for sustainable water treatment design

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Title:
Whole systems thinking for sustainable water treatment design
Creator:
Huggins, Mitchell Tyler ( author )
Place of Publication:
Denver, Colo.
Publisher:
University of Colorado Denver
Publication Date:
Language:
English
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1 online resources (58 pages). : ;

Thesis/Dissertation Information

Degree:
Master's ( Master of Engineering)
Degree Grantor:
University of Colorado Denver
Degree Divisions:
Department of Engineering, CU Denver
Degree Disciplines:
Civil Engineering
Committee Chair:
Ren, Zhiyong
Committee Members:
Karunanithi, Arunprakash
Rorrer, Ron

Subjects

Subjects / Keywords:
Microbial fuel cells ( lcsh )
Sewage disposal plants -- Design and construction ( lcsh )
Microbial fuel cells ( fast )
Sewage disposal plants -- Design and construction ( fast )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis (M.Eng.)--University of Colorado Denver. Civil engineering
Bibliography:
Includes bibliographic references.
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System requirements: Adobe Reader.
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Mitchell Tyler Huggins.

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|University of Colorado Denver
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|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
868583851 ( OCLC )
ocn868583851

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Full Text
WHOLE SYSTEMS THINKING FOR SUSTAINABLE WATER TREATMENT
DESIGN
by
Mitchell Tyler Huggins
B.S., University of Montana, 2007
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Master of Engineering
Civil Engineering
2013


This thesis for the Master of Engineering degree by
Mitchell Tyler Huggins
has been approved for the
Civil Engineering Program
by
Zhiyong Ren, Chair
Zhiyong Ren, Advisor
Arunprakash Karunanithi
Ron Rorrer
April 4, 2013


Mitchell Tyler Huggins (M.Eng, Civil Engineering)
Whole Systems Thinking for Sustainable Water Treatment Design
Thesis directed by Assistant Professor Zhiyong Ren
ABSTRACT
Microbial fuel cell (MFC) technology could provide a low cost alternative to
conventional aerated wastewater treatment, however there has been little comparison
between MFC and aeration treatment using real wastewater substrate. This study
attempts to directly compare the wastewater treatment efficiency and energy consumption
and generation among three reactor systems, a traditional aeration process, a simple
submerged MFC configuration, and a control reactor acting similar as natural lagoons.
Results showed that all three systems were able to remove >90% of COD, but the
aeration used shorter time (8 days) then the MFC (10 days) and control reactor (25 days).
Compared to aeration, the MFC showed lower removal efficiency in high COD
concentration but much higher efficiency when the COD is low. Only the aeration system
showed complete nitrification during the operation, reflected by completed ammonia
removal and nitrate accumulation. Suspended solid measurements showed that MFC
reduced sludge production by 52-82% as compared to aeration, and it also saved 100% of
aeration energy. Furthermore, though not designed for high power generation, the MFC
reactor showed a 0.3 Wh/g COD/L or 24 Wh/m3 (wastewater treated) net energy gain in
electricity generation. These results demonstrate that MFC technology could be
integrated into wastewater infrastructure to meet effluent quality and save operational
cost.


The high cost and life-cycle impact of electrode materials is one major barrier to
the large scale application of microbial fuel cells (MFC). We also demonstrate that
biomass-derived black carbon (biochar), could be a more cost effective and sustainable
alternative to granular activated carbon (GAC) and graphite granule (GG) electrodes. In
a comparison study, two biochar materials made from lodgepole pine sawdust pellets
(BCp) and lodgepole pine woodchips (BCc), gassified at a highest heat temperature
(HHT) of 1000C under a heating rate of 16C/min, showed a satisfactory power density
of 532 18 mW m-2 and 457 20 mW/m-2 respectively, compared to GAC with 674
10 mW m-2 and GG with 566 5 mW m-2 (normalized to cathode projected surface
area), as an anode material in a two-chamber MFC. BCc and BCp had BET-N2 surface
area measurements of 429 cm2 g-1 and 470 cm2 g-1 respectively, lower than industrial
GAC with 1248 cm2 g-1 but several orders of magnitude higher that GG with 0.44 cm2
g-1. BCc and BCp had a lower surface resistance of 31Q mm-1 and 61 Q mm-1 than
82Q mm-1 for GAC, but higher that GG with 0.40.5 Q mm-1. We also investigated
the life-cycle impact and estimated cost of biochar as an electrode material. Although
there is no well-established market price for biochar, conservative estimates place the
costs around 51-356 US$/tonne, up to ten times cheaper that GAC (500-2500 US$/tonne)
and GGs (500-800 US$/tonne) with significantly greater life-cycle advantages.
The form and content of this abstract are approved. I recommend its publication.
Approved: ZhiyongRen


ACKNOWLEDGMENTS
I would like to thank all members of the Ren lab, for their support and
encouragement. I would also like to thank Dr. Ren for his financial support and
mentorship through my graduate studies.


TABLE OF CONTENTS
CHAPTER
I. INTRODUCTION...........................................................11
II. ENERGY AND PERFORMANCE COMPARISON OF MICROBIAL FUEL CELL
AND CONVENTIONAL AERATION TREATMENT OF INDUSTRIAL
WASTEWATER..........................................................12
Abstract............................................................12
Introduction........................................................13
Materials and Methods...............................................16
Reactor Configuration and Construction..........................16
Reactor Start-up and Operation..................................16
Analyses and Calculations.......................................16
Results and Discussion..............................................17
Organic Removal.................................................17
Ammonia and Nitrate Removal Efficiencies........................19
Solids Production...............................................20
MFC Electricity Production Using Wastewater as the Substrate....21
Conclusion..........................................................23
III. BIOCHAR AS A SUSTAINABLE ELECTRODE MATERIAL IN MICROBIAL
FUEL CELLS.............................................................24
Abstract............................................................24
Introduction........................................................25
Anode Electrode Material Manufacturing..........................28
MFC Construction and Operation..................................29
Statistical and Electrochemical Analyses........................29
Results and Disussion
31


Power Production from Electrode Materials
31
Surface Characteristics of Electrode Materials.....................32
Resistance Characteristics of Electrode Materials..................36
Biochar Electrode Life-Cycle and Cost Analysis.....................38
Conclusion............................................................43
IV. BIOCHAR LCA AND CARBON ACCOUNTING........................................44
Introduction..........................................................44
Goal and Scope.....................................................45
Research Methodology...............................................46
Case Study: Biochar Production in Golden Colorado.....................46
Company Description................................................46
Technology Description.............................................46
System Boundary.......................................................47
Data Collection Methodology...........................................48
Forestry Residue Processing........................................48
Pyrolysis Emissions................................................48
Transportation Emissions...........................................48
On-site Decomposition and Combustion of Forestry Residue...........49
Biochar Stable Carbon Content......................................49
GHG Inventory and Carbon Accounting...................................50
Results and Discussion................................................51
Global Warming-GHG Emissions......................................51
Carbon Accounting..................................................51
Process Refinement Recommendations.................................51
Conclusion
52


V. CONCLUSION..........................................53
REFERENCES.............................................54


LIST OF TABLES
Table
I. Electrode characteristics used in this study............................................28
II. List of MFC reactors in this study and their specifications............................40


LIST OF FIGURES
Figure
I. Reactor configurations..........................................................15
II. Comparison of COD removal efficiency between MFC, aeration, and control reactors
18
III. COD removal rates and COD removal rates at COD concentrations > 200 mg/L.... 19
IV. Ammonia and nitrate removal comparison between the MFC, aeration, and control
reactors..........................................................................20
V. Final TSS concentration comparison between the MFC, aeration, and control reactors
21
VI. Power analysis for the MFC and aeration reactors...............................22
VII. Four electrode materials used in this study.................................27
VIII. Power density curve normalized by cathode projected area (A) and electrode
potentials (cathode, filled symbols; anode, open symbols) versus Ag/AgCl reference
electrode as a function of current density in two-chamber reactors packed with GAC, GG,
BCp and BCc.......................................................................32
IX. Incremental pore area with the distribution of pore size........................33
X. Temperature profile and residence time of BCp and BCc gasification...............35
XI. System resistance of the reactors filled with four different anode materials.37
XII. Flow chart of manufacturing methods of electrode materials used in this study.41
XIII. Flow Diagram for Biochar production.........................................47
XIV. Carbon accounting of biochar production with avoided carbon loss due to
combustion of forestry residue....................................................50
XV. Carbon accounting during the production of biochar with avoided carbon loss due to
decomposition of forestry residue.................................................50


CHAPTERI
INTRODUCTION
The current global wastewater infrastructure system has several major limitations.
In the developed world the wastewater infrastructure provides for adequate treatment, but
can be extremely expensive and energy intensive. In the developing world there is a
serious lack of wastewater infrastructure, which can lead to pollution and the spread of
infectious diseases. In both cases the wastewater stream is treated as a separate system
and does not generally tie into other civil processes. This thesis is an attempt to use
microbial fuel cell technology and biochar electrodes to lower the cost, decrease energy
use, and integrate wastewater treatment into agricultural production and land reclamation.


CHAPTER II
ENERGY AND PERFORMANCE COMPARISON OF MICROBIAL FUEL CELL
AND CONVENTIONAL AERATION TREATMENT OF INDUSTRIAL
WASTEWATER
Abstract
Microbial fuel cell (MFC) technology could provide a low cost alternative to
conventional aerated wastewater treatment, however there has been little comparison
between MFC and aeration treatment using real wastewater substrate. This study
attempts to directly compare the wastewater treatment efficiency and energy consumption
and generation among three reactor systems, a traditional aeration process, a simple
submerged MFC configuration, and a control reactor acting similar as natural lagoons.
Results showed that all three systems were able to remove >90% of COD, but the
aeration used shorter time (8 days) then the MFC (10 days) and control reactor (25 days).
Compared to aeration, the MFC showed lower removal efficiency in high COD
concentration but much higher efficiency when the COD is low. Only the aeration system
showed complete nitrification during the operation, reflected by completed ammonia
removal and nitrate accumulation. Suspended solid measurements showed that MFC
reduced sludge production by 52-82% as compared to aeration, and it also saved 100% of
aeration energy. Furthermore, though not designed for high power generation, the MFC
reactor showed a 0.3 Wh/g COD/L or 24 Wh/m3 (wastewater treated) net energy gain in
electricity generation. These results demonstrate that MFC technology could be
integrated into wastewater infrastructure to meet effluent quality and save operational
cost.


Introduction
Traditional activated sludge or aerated lagoon wastewater treatment processes
can efficiently remove organic pollutants, but operating such systems are cost and energy
intensive, mainly due to the aeration and sludge treatment associated processes. The
United States spends approximately $25 billion annually on domestic wastewater
treatment and another $202 billion is needed for improving publicly owned treatment
works 1. Wastewater treatment accounts for about 3% of the U.S. electrical energy load,
which is approximately 110 Terawatt hours per year, or equivalent to 9.6 million
households annual electricity use 2 Traditional activated sludge based treatment
processes employ aerobic heterotrophic microorganisms to degrade organic matters. Such
types of microbes have high metabolic kinetics, so they can process substrates faster than
anaerobic bacteria, but they also require sufficient supply of oxygen and generate
significant amount biomass. Aeration can amount to 45-75% of wastewater treatment
plant (WWTP) energy costs, while the treatment and disposal of sludge may count up to
60% of the total operation cost.
The next generation of wastewater infrastructure should consider transforming
current energy-intensive, treatment-focused processes into integrated systems that
recover energy and other resources. It was estimated that the energy content embedded in
wastewater is estimated about 2-4 times the energy used for its treatment2, so it is
possible to make wastewater treatment self-sufficient, if new technologies can recover the
energy while simultaneously achieving treatment objectives. Microbial fuel cells (MFCs)
recently emerged as a novel technology to fulfill this mission because they directly
convert biodegradable materials into renewable energy with minimal sludge production 3.


MFCs employ exoelectrogenic bacteria to extract electrons from (in)organic substrates
and transfer them to the anode, and the electrons then form electric currents when
flowing from the anode to the cathode, where they then combine with oxygen and
protons to produce water 4 MFCs have been shown effective in treating almost all kinds
of waste streams, including municipal, brewery, agricultural, refinery, paper cycling
wastewater, and even landfill leachate 5. The power output is dependent on the
biodegradability of the substrate, conversion efficiency, and loading rate. For example,
261 mW/m2 was obtained using swine wastewater6 while other studies have
demonstrated that a maximum power output of 205mW/m2 can be achieved using
brewery wastewater7 and 672 mWm2 using paper recycling wastewater 8.
The functional bacteria in MFCs are generally anaerobic or facultative
microorganisms, so the operation of MFCs may not use any active aeration 9 In addition,
the cell yield of exoelectrogenic bacteria (0.07-0.16 gVSS/gCOD) was much less than the
activated sludge (0.35-0.45 0.16 gVSS/gCOD), so sludge production can be significantly
reduced 10. However, most studies have focused on energy production from MFCs while
very few compared the energy use/generation and sludge production between MFCs and
traditional aeration based processes. In this study, we used liter-scale reactors to
quantitatively audit the power generated or consumed during the operation of an MFC, an
aeration tank, and a control reactor during the treatment of wastewater. We also
compared system performance in terms of COD and ammonia removal, and the
concentration changes in nitrate, suspended solids, and dissolved oxygen. We aim to
provide side-by-side quantitative information in evaluating the potential energy and


treatment benefits of MFCs as compared to traditional aeration processes such as
activated sludge or aerated lagoon systems.
Figure I. Reactor configurations


Materials and Methods
Reactor Configuration and Construction
Three reactors including an MFC, an aeration reactor, and a control reactor,
were constructed using a 15 L container. The single-chamber submerged MFC reactor
was configured using graphite brush as the anode (Chemviron Carbon) and carbon cloth
(1% Pt) as the air-cathode (Fuel Cell Earth LLC) (Figure I). The same 15 L container
was used for the aeration reactor, with an aquarium pump air diffuser at the bottom
(Figure I). The control reactor used a same type of container but without any aeration
equipment or electrode installed (Figure I). All reactors were operated in fed-batch mode
at room temperature and exposed to the ambient air.
Reactor Start-up and Operation
Industrial wastewater was collected from the effluent of the primary clarifier from
the Coors Wastewater Treatment Plant in Golden, Colorado. The wastewater was used as
the inoculum and sole substrate for all three reactors. No extra medium or buffer solution
was added. The MFC reactor went through an initial 7 day inoculation period before the
wastewater was replaced and measurements taken. All reactors were operated until
>90% COD reduction was achieved then the wastewater was replaced for a series of three
trials.
Analyses and Calculations
Closed circuit voltage (V) and amps (A) were measured and recorded using a data
acquisition system (Keithley Instruments, Inc. OH) across an external resistance (R) of 10


Q in a time interval of 3 minutes. Power in watts (W) was calculated from the equation
W = V-A. Power generation or consumption was measured during a specific time
measured in hours (h), expressed in watt hours (Wh) and calculated using the equation
Wh = W'h. The wattage for the aeration pump was determined from the manufacturers
specification, while the wattage generated from the MFC was determined from the data
acquisition system and the equation described above. Polarization curve was normalized
by cathode surface area and was determined by conducting a linear sweep voltammetry
test using a potentiostat (G 300, Gamry Instruments). Dissolved oxygen concentration
was measured with a standard DO probe (DO50-GS, Hach Co.) COD, DCOD, NH4+-N,
and NO3' concentrations were measured with digester vials (Hach Co.) according to
APHA standards. The solid retention time (SRT) was calculated based on the amount of
time in days (d) each reactor was operated.
Results and Discussion
Organic Removal
All three reactors were fed with the same wastewater with a COD concentration
of 124763.9 mg/L. The reactors were operated in batch mode till reaching >90% of
COD removal. While all reactors were able reach the same treatment goal, the average
retention time for achieving similar treatment efficiency varied significantly (Figure II).
The MFC reactor took 15 days to reach to 90% removal, which is 10 days shorter than
the control reactor without aeration but 2 days longer than the aeration reactor. The
shorter retention time for the aeration reactor is similar to the extended aeration activated
sludge systems and can be attributed to the readily available oxygen supply and rapid
metabolisms of aerobic respiration 10. The SRT of the control is around 25 days, close to


traditional stabilization lagoons, which do not employ mechanical aeration and may
create aerobic, anoxic, and anaerobic layers of environment for different microbial
community and metabolisms. The absence of mechanical aeration in the MFC reactor
also provided an anoxic environment but experienced much shorter retention time than
the control. These results suggest that by providing a submerged anode and a floating
cathode, the MFC configuration significantly facilitated substrate oxidation rate close to
aeration operation but without any external oxygen supply.
1400.0
0 5 10 15 20 25 30
SRT (Day)
Figure IE. Comparison of COD removal efficiency between MFC, aeration, and
control reactors
Such variations can also be presented by COD removal rates. As shown in Figure
III, the COD removal rates from the three systems varied significantly and changed
depending on the COD concentrations. During the initial stage of operation, when the
COD concentration was high, COD removal rate for the aeration reactor averaged around
12.1 mg/L'h, which was 3.6 times and 9.7 times higher than that of the MFC or control
reactor treating the similar COD concentrations. However, when the COD concentration


COD Kcmoviil Rutc (mg/L-li)
decreased to around 200 mg/L or less, the removal rate for the aeration reactor decreased
to 0.6 mg/L'h. This rate was similar to that of the control but significantly less than that
of the MFC reactor, which had an average COD reduction rate of 2.0 mg/L'h. This
observation may be interpreted using the different degradation natures between
suspended growth systems and attached growth systems. Many studies and models
showed that compared to attached growth systems, such as trickling filters, completely
mixed suspended growth systems such as activate sludge were able to treat high
concentrated organics more efficiently but the effluent COD was highly depending on the
solid retention time 10.
Figure III. COD removal rates and COD removal rates at COD concentrations > 200 mg/L
120.0 35
Ammonia and Nitrate Removal Efficiencies
Because the same wastewater was used as the influent for all three reactors, all
systems were fed with the same ammonia concentration of 10 mg/L. However, because
the aeration reactor provided a completely aerobic environment for nitrification, it
showed nearly 100% ammonia removal within 11 days, after an initial concentration
increase due to organic ammonification (Figure IV). This nitrification process is also
confirmed by the accumulation of nitrate in the aeration reactor, where the increase of


nitrate concentration from 2 mg/L to 12 mg/L perfectly accompanied the ammonia
decrease (Figure IV). No denitrification was observed in the aeration reactor due to the
highly aerobic environment. In contrast, neither MFC or control reactor showed
significant ammonia removal or nitrate accumulation during the operation, presumably
due to inhibition of nitrification in the anoxic to anaerobic condition in such reactors.
However, other studies have shown that MFC, supplemented with nitrate, experienced
94.1 0.9% nitrogen removal u. Our MFC reactor did show a slight nitrification process
after 14 days of operation, as shown in Figure 3A-B, but we had to change the solution at
the time because the reactor had reached the 90% organic removal threshold.
Figure IV. Ammonia and nitrate removal comparison between the MFC, aeration,
and control reactors.
Solids Production
Preliminary characterization on total suspended solid (TSS) at different solid
retention time shows that the aeration reactor produced much more solids than the other
two reactors. The final TSS concentration from the aeration reactor was 202 50 mg/L in
the reactor at the corresponding SRT of 13 days. By comparison, the MFC reactor
maintained the lowest TSS concentration, with 20 10 mg/L, and the control reactor had


a TSS of 45 10 mg/L. The low TSS concentration in the MFC reactor can be attributed
to two reasons. First, the MFC is a biofilm based system, and the accumulation of
biomass mainly resides on the electrode except of occasional biofilm falloff, so the
suspended solid is low. Another reason is due to the low cell yield of the anoxic to
anaerobic microorganisms in the MFC compared to the activated sludge. This finding
confirms that sludge reduction can be a main benefit of MFC to replace activated sludge
and reduce plant operation cost by 20-30%. When converting aeration basin into an MFC
system, second clarifiers may be reduced in size, converted to solid contact basin, or even
eliminated due to the reduced biomass generation 12
250 -r
MFC Aeration Control
Figure V. Final TSS concentration comparison between the MFC, aeration, and
control reactors
MFC Electricity Production Using Wastewater as the Substrate
The MFC reactor was operated under a 10 Q external resistance during operation.
Low resistance was used in this study because under this condition more electrons can be
transferred freely and substrate degradation can be maximized 13. The MFC generated a
maximum output voltage of 135 mV and a current density of 193 mA/m2 The total MFC
power output during a 15-day SRT was 0.36 Wh, equivalent to 0.32 Wh/g COD/L, or 24


Wh per cubic meter wastewater treated. With an average SRT of 13 days, the aeration
reactor consumed approximately 624 Wh of electricity, which transfers to about
547 Wh/g COD/L. The aeration pump could have been more efficient and adjusted to
aerate less during lower levels of COD, however it was maintained as the same level in
order to allow for complete nitrification and ensure oxygen was not the limiting factor.
Figure 6 shows a comparison between power consumption in the aeration reactor and
energy saving and production in the MFC reactor. Though this MFC was mainly
designed for COD removal not for high power production, it still saves 100% of the
aeration energy and produce extra energy while achieving the same treatment goal. Due
to the high energy consumption of aeration in this study, it is not representative to
directly calculate how much percentage of extra energy can be produced from MFC, but
based on many other studies, MFC may produce 10% of extra electricity on top of
aeration energy savings, if the aeration energy consumption is assumed as 1 kWh/kg-
COD 12
50
Figure VI. Power analysis for the MFC and aeration reactors.


Conclusion
The results in this study showed that microbial fuel cell can be a viable
technology to treat wastewater at the same level as traditional aeration process does, and
it carries great potential as an energy positive process, because it saves 100% of aeration
energy with extra electricity output. It also significantly reduces sludge production, which
may reduce the size of secondary clarifier and save the cost of sludge disposal.


CHAPTER III
BIOCHAR AS A SUSTAINABLE ELECTRODE MATERIAL IN MICROBIAL
FUEL CELLS
Abstract
The high cost and life-cycle impact of electrode materials is one major barrier to
the large scale application of microbial fuel cells (MFC). We demonstrate that biomass-
derived black carbon (biochar), could be a more cost effective and sustainable alternative
to granular activated carbon (GAC) and graphite granule (GG) electrodes. In a
comparison study, two biochar materials made from lodgepole pine sawdust pellets
(BCp) and lodgepole pine woodchips (BCc), gassified at a highest heat temperature
(HHT) of 1000C under a heating rate of 16C/min, showed a satisfactory power density
of 532 18 mW m-2 and 457 20 mW/m-2 respectively, compared to GAC with 674
10 mW m-2 and GG with 566 5 mW m-2 (normalized to cathode projected surface
area), as an anode material in a two-chamber MFC. BCc and BCp had BET-N2 surface
area measurements of 429 cm2 g-1 and 470 cm2 g-1 respectively, lower than industrial
GAC with 1248 cm2 g-1 but several orders of magnitude higher that GG with 0.44 cm2
g-1. BCc and BCp had a lower surface resistance of 31Q mm-1 and 61 Q mm-1 than
82Q mm-1 for GAC, but higher that GG with 0.40.5 Q mm-1. We also investigated
the life-cycle impact and estimated cost of biochar as an electrode material. Although
there is no well-established market price for biochar, conservative estimates place the
costs around 51-356 US$/tonne, up to ten times cheaper that GAC (500-2500 US$/tonne)
and GGs (500-800 US$/tonne) with significantly greater life-cycle advantages.


Introduction
Microbial fuel cell (MFC) is a new platform technology that can simultaneously
achieve (in)organic biodegradation and electricity generation14-16. MFC reactors utilize
the metabolic activity of exoelectrogenic bacteria to catalyze redox reactions on the
anode and promote the flow of elections from anode to cathode for direct current
harvesting12. Compared to current energy and cost intensive wastewater treatment
processes, MFC is considered a next generation technology for wastewater industry,
because it can be an energy positive system with net energy output, and it significantly
reduces sludge production by more than 60%317. Over the past decade the MFC power
output has been improved by several orders of magnitudes, but one main challenge for
MFC to be used in large scale applications is the high cost compared to other wastewater
treatment alternatives18.
One of the major contributors to the high cost of MFCs is the electrode materials,
which is estimated to amount to 20-50 % of the overall cost19. However, electrodes play
a fundamental role in facilitating exoelectrogenic biofilm growth and electrochemical
reactions and are essential in improving the functionality and efficiency of MFCs. Ideal
electrode materials should possess key characteristics such as high surface area, high
conductivity, low cost, and biocompatibility20. Most electrode materials used in MFCs
are carbon based granular activated carbon (GAC) or graphite granules (GGs)20,
especially in larger scale systems, because GAC has high degree of microporosity and
catalytic activities, and GGs are less expensive with higher conductivity, even though the
surface area density is lower. The costs of GAC or GG electrodes range from 500-2500
US$ per US tonne, which is significantly lower than carbon cloth or carbon paper


(100,000-500,000 US$ per tonne), but it is still considered high for large scale
applications. In addition to the cost, the life-cycle impact of these materials can be
significant depending on feedstock choice, manufacturing, and disposal methods. For
example, GAC is most commonly manufactured from the pyrolysis of coal along with
secondary thermal or chemical activation21,22. GGs can be mined from natural deposits or
synthetically manufactured through the thermal treatment (>3000C) of carbon based
materials. Such feedstock extraction and manufacturing methods used for industrial
GAC and GG can be highly energy intensive and result in the release of environmental
pollutions, including CO2 and other greenhouse gases. Furthermore, the recycle and
reuse rate of GAC and GG are low, and the waste materials are traditionally landfilled
after several times of usage.
In order to promote sustainable and cost-effective electrode materials, the
feedstock, manufacturing, and end-of-life alternatives all need to be investigated. In this
context, biomass-derived black carbon (biochar) could be a more sustainable option,
because it is produced from locally available biowastes, such as agricultural and forestry
residue, which helps lower the cost and environmental impact while ensuring a steady
regional supply. Manufacturing is carried out through pyrolysis or gasification, which
utilizes the internal chemical energy of the feedstock to fuel the carbonization process
and produce harvestable bioenergy. In addition, unlike GG or GAC, biochar can be
reused as agricultural soil amendment, which has been shown to increase crop
production23,24, increase microbial diversity and abundance, lower emissions such as
NO2, and remain environmentally stable for thousands of years. Moreover, the cost of
biochar is low, ranging from 51-381 US$ per ton25, nearly ten times less than GAC and


GGs. Based on different purposes of usage, tailored biochar can be manufactured to have
different physical properties26-28. For example, by using elevated temperatures (>800-
1000C), biochars can have a wide range of pore sizes and high service area, which can
also cause internal graphitization and increased conductivity293031.
Although the unique features of biochar have been demonstrated for some time in
other areas, to our best knowledge few study investigated the feasibility and performance
of biochar as electrode material in MFCs. In this study, we tested the performance of two
different types of biochar materials made from compressed lodgpole pine sawdust pellets
(BCp) and lodgepole pine woodchips (BCc) and compared them to GAC and GG as the
anode materials in two-chamber MFCs. Performance was comprehensively characterized
through electrochemical and statistical analyses, in terms of power production, resistivity,
and total surface area. Furthermore, we also investigated the manufacturing process,
feedstock selection, and cost of biochar electrodes.
Figure VII. Four electrode materials used in this study


Experimental Section
Anode Electrode Material Manufacturing
The main physical characteristics and costs of the four anode materials used in this
study are shown in Table 1, and their images are shown in Fig. la. Fig. lb illustrates the
general outlines of the manufacturing process for the electrode materials. The GAC was
purchased from Cameron-Yakima, Inc, (Yakima, WA, USA), and it was manufactured
from coal using industrial standard methods21, resulting in 100% of activated carbon.
Activation was achieved using thermal activation procedures. GG were purchased from
Graphite Sales, Inc, (Nova, OH, USA). GG material is comprised of 100% synthetic
graphite made from petroleum coke using temperatures exceeding 3000C. BCc and
BCp were both manufactured using a custom made top-lit up-draft biomass gasifier with
an external fan, as described by Kerns et.al. 201232. Biomass was carbonized using a
HHT of 1000C, residence time of 1 hr, and a ramp rate of 16C/min (figure X) and
temperature reading were measured using a programmable thermocouple. BCp used
compressed lodgepolepine sawdust pellets and BCc used lodgepole pine woodchips
gathered from local forestry residue as the biomass feedstock
Table I Electrode characteristics used in this study
Electrode Material Particle size (mm3) Surface Resistance (O mnr *) Average Pore Diameter (A) BET SA (cm2 g1) Cost ($ Ton'
GAC 26-36 82 26.8 1247.8 500-2500
GG 350-450 0.40.5 71.0 0.44 500-800
BCp 60-74 61 37.6 428.6 100-199
BCc 160-700 31 29.4 470.0 51-384


MFC Construction and Operation
MFCs were constructed using two polycarbonate cube-shaped blocks separated by a
cation exchange membrane (38 cm2, CMI-7000, Membrane International, NJ, USA). A
37 cm diameter hole was drilled at the center of each block forming the internal anode
and cathode33 Plain carbon cloth (38 cm2, Fuel Cell Earth) was used as the common
cathode material for all reactors. Each anode material (GAC, GG, BCp or BCc) was
packed into one side of anode chamber to a volume of 75mL and held by a plastic mesh
to tighten anode packing. A twisted titanium wire was used as a current collector and
was buried in the packed anode. The total empty volumes were 150ml and 200ml for
cathode chamber and anode chamber, respectively. MFCs were inoculated using
anaerobic sludge from Longmont Wastewater Treatment Plant (Longmont, CO, USA).
The anolyte growth medium contained 1.25g of CFbCOONa, 0.31 g of NH4CI, 0.13 g of
KC1, 3.32 g of NaH2P04-2H20, 10.32 g of Na2HP0412H20, 12.5 mL of mineral
solution, and 5 mL of vitamin solution per liter13,34. The catholyte was potassium
ferricyanide solution dissolved in 50 mM phosphate buffer, which aims to provide a
stable cathode potential and minimize cathode limitation on system comparison35. Each
MFC was operated in fed-batch mode under a 400 ohm external resistor. When voltage
dropped below 20 mV, both anolyte and catholyte were replaced with fresh media. All
the tests were conducted at room temperature and repeated for at least 3 times.
Statistical and Electrochemical Analyses
The surface resistance measurement was determined by randomly selecting 35
electrode samples and measuring the ohmic resistance across a 4 mm distance with a
programmable multimeter. The t-distribution was used to calculate confidence intervals


(CIs). The 95% CIs were calculated by X + 2.0325/Vriwhere X = 'L%1Xjn was
sample mean, 5 = y; (Z= X)r)/(n l)was sample standard variation, and n was
the sample size33.
The cell voltage (E, volt) and electrode potentials for each MFC were measured
continuously using a data acquisition system (Keithley Instrument, OH) every 66 sec.
Polarization curves were obtained by varying external resistances from 50,000 to 30 ohm
with each resistor stabilized for 30 min13. The anode potential and cathode potential were
measured against an Ag/AgCl reference electrode (RE-5B, Bioanalysis) inserted in the
anode chamber and cathode chamber, respectively. During both acclamation and fed-
batch periods, circuits were operated under a fixed load (Re, ohm) of 400 Q. Current(I,
amp) was calculated according to / = El Re. Power (P, watt) was calculated according
to P = El. Current density and power density were normalized by cathode projected
surface area of 38 cm2. Electrochemical impedance spectroscopy (EIS) was conducted by
a potentiostat (PC 4/3000, Gamry Instruments, NJ, USA) to determine total internal
resistance using the anode as the working electrode, where the cathode served as the
counter electrode and reference electrode14,34.
Brunauer-Emmett-Teller (BET) method that uses a five-point N2 gas adsorption
technique (ASAP 2020; Micromeritics, Norcross, GA) was used to measure specific
surface area and pore size distribution of the electrode materials. Average pore size and
pore size distribution were determined from desorption of N2 according to the method
developed by Barrett, Joyner, and Halenda (BJH)33,36.


Results and Disussion
Power Production from Electrode Materials
The maximum power output and Columbic efficiency (CE) are two major
measures to evaluate the performance of MFC systems. The CEs and maximum power
densities from MFCs occupied with the 4 different anode materials (BCp, BCc, GAC,
and GG) are summarized in Table 2 and Fig. 2, and the power densities are normalized
by cathode surface area. Results showed that the GAC anode achieved the highest CE at
around 47%, and GG had the lowest CE at 35%. The CEs from BCc and BCp were
comparable at 41-43%. GAC had the highest power density of 674 10 mWm"2 followed
by GG with 566 5 mWm"2, BCp with532 18 mWm"2, and BCc with 457 20 mW/m"
2(Table 2). The power output from BCp and BCc was 21% and 32% lower than the
GAC, and 6% and 19% lower than the GG anodes. Fig. 2B shows that the cathode
potentials among all 4 reactors were comparable as designed, because ferricyanide
cathode was used to minimize the cathode effects. The anode potential of BCc increased
to around 0 mV at 1.8 Am"2, which resulted in lower power output. It was hypothesized
that the difference in power densities can be attributed to the difference in both surface
area density and system internal resistance, which will be explained in more detail in the
following sections. It must be noted that the power density differences are not an
intrinsic value of the biochar material, and it could be manipulated through variations in
manufacturing. As research in this field matures, biochar electrodes could be
manufactured in such a way to mimic the beneficial properties of both GAC and GG,
while maintaining its integrity as a sustainable electrode material option. More detailed
synopses of the manufacturing alternatives will also be discussed in the following


sections. Moreover, when material costs were added into consideration, Table 2 shows
that to generate the same amount of 1 W electricity, the biochar based electrodes (BCp
and BCc) were much more cost effective than GAC and GG, in fact more than ten times
cheaper, indicating a good potential in larger scale applications.
Figure VIEL Power density curve normalized by cathode projected area (A) and
electrode potentials (cathode, filled symbols; anode, open symbols) versus
Ag/AgCl reference electrode as a function of current density in two-chamber
reactors packed with GAC, GG, BCp and BCc.
Surface Characteristics of Electrode Materials
High surface area and low resistance are two fundamental characteristics to define
good electrode materials and affect MFC power output performance. While this section
discusses the characteristics of surface area and porosity of the four materials, the next


section elucidates the effects of resistance. Table 1 and Figure IX show the pore
distribution of the materials using the Brunauer-Emmett-Teller (BET) test. Results show
that GAC has the highest BET surface area of 1247.8 cm2/g followed by BCp and BCc
with 469.9 cm2/g and 428.6 cm2/g respectively. GG had the lowest BET surface area of
0.44 cm2/g. The pore size distribution for GAC is concentrated around 20-30 A, while
the BCp and BCc samples had an average pore diameter of 30-40 A range.
Figure IX Incremental pore area with the distribution of pore size
While the high surface area can explain why GAC obtained a higher power density,
as it presumably has high microbial attachment and therefore more electron transfer, it is
hard to directly correlate the low surface area of graphite with low power output. As
shown in the Figure VIII, graphite electrode generated higher power density than the
biochar electrode despite its low surface area, and it is believed mainly due to the high
conductivity of graphite.


Studies show that surface area and pore size can be due to a variety of factors
including the manufacturing process and feedstock material. The higher surface area of
GAC is primarily caused by the secondary activation process carried out during
manufacturing, in which reactive components of the feedstock material were burn away
by the use of oxidizing agents, such as steam or carbon dioxide, leaving behind a pitted
and porous char21,37. The biochar samples used in this study and GGs did not undergo
this activation step, but the gasification process used to manufacture both biochar
samples is thought to promote the formation of higher BET surface area similar as GAC.
The gasification process reached a highest treatment temperature (HTT) of 1000C with a
heating rate of 16.6C/min (figure 5), and in the process lignocellulosic materials are
converted to a primarily aromatic carbon-based char38. The HTT and heating rate are
reported to significantly influence the physical structure of the feedstock material during
carbonization. For example, studies showed that higher surface area was achieved at
temperatures between 650C and 850C,394041but sintering and deformation may occur at
higher temperatures41. Brown, et. al. provides further evidence that higher surface area is
achieved with higher heating rate and is primarily due to cracking at low temperatures by
unevenly heating the feedstock material. These cracks provided access to internal pores
that could not be as easily effected by melting and deformity of the feedstock material at
high temperatures. Brown, et. al.42provides further evidence that higher surface area is
achieved with higher heating rate, because such process leads to cracking at low
temperatures by unevenly heating the feedstock material, and these cracks provided
access to more internal pores.


1200
Figure X Temperature profile and residence time of BCp and BCc gasification
Along with HTT and heating rate, the inherent porosity and structure of the
feedstock material can also affect the surface area density. Several studies showed that
biomass based chars possess high surface area so can be cheaper surrogates for GAC type
electrode materials39,42. In many cases, the archetypal cellular structure of the parent
feedstock material is identifiable in chars derived from botanical origin, resulting in a
honeycomb-like structure that significantly contributes to the majority of macroporosity.
Although there is a growing body of literature on the effects of manufacturing methods
on the chemical and physical properties of biochar and other biomass based absorbance
materials, there is little understanding of how surface area density and pore size
distribution effects microbial growth, abundance, and adhesion. This study highlights
that microporosity is important for increased power density, but additional research is
needed to refine the manufacturing of biochar in order to increase the desired


characteristics as MFC electrodes while maintaining the economic and environmental
benefits.
Resistance Characteristics of Electrode Materials
Similar as surface area, internal resistance (Ri) is one of the major factors effecting
power density in MFCs. The total Ri can be separated into activation resistance (Rp),
ohmic resistance (Rs) and concentration resistance14. Rp occurs when electrons are
transferred to or from a compound, primarily during oxidation/reduction reactions and
relates to the catalytic efficiency near or on the electrode surface. The concentration
resistance is due to the rate of mass transport to or from the electrode. While Rs occurs
due to the resistance of electron and ion transfer through the solution, electrodes, and
membrane. Electrochemical impedance spectroscopy (EIS) is a techniqueused to
measure chemical and physical processes in solution and can help to separate out the
different internal resistances in MFC reactors. By graphing the data collected from EIS
and constructing a Nyquist plot,Ri, and Rs can be calculated (Figure XI). According to
our EIS results, GG has the lowest Rs of 24 0.6 Q, followed by BCc with 29 0.7 Q,
BCp with 34 0.3 Q, and GAC with 34 0.9 Q (Table 2). The surface resistance results
can be seen in Table 1 with GG having 0.4 0.5 Q mm"1, followed by BCc with 3 1 O
mm'1, BCp with 6 1 Q mm"1, and GAC with the highest surface resistivity of 8 2 Q
mm"1. However, GG and GAC had a similar total Ri of 39 9 Q and 40 3 Q
respectively, while BCp and BCc had a higher R; of 46 2 Q and 43 3 Q respectively
(Table II).
The Rs is responsible for nearly 86%, 62%, 74%, and 68% of the total Ri in the
GAC, GG, BCp, and BCc, reactors respectively, but cannot account entirely for the


difference in the observed power densities. The Rp for BCp and BCc was 7 0.9 O and
8 0.1 Q respectively, much higher than GAC with 4 0.6 Q and GG with 4 0.2 Q.
Because of the biochars lower Rs compared to GAC, it is believed that the Rp is the
primary reason for the differences in power density. It is generally accepted that the
catalytic activity of the anode is due primary to microbial biomass density and surface
area density and combined have been shown to positively correlate with Rp. GACs
lower Rp and lower R, can thus be explained by its higher surface area density, which
makes up for its higher Rs. When comparing BCp with BCc, the differences in power
density can also be attributed to differences in surface area density. Although BCp has
higher BET surface area and a lower surface resistance, its larger particle size limits its
surface area density, which results in a higher Rp and resulting higher R,.
Figure XI System resistance of the reactors filled with four different anode
materials


Our results further emphasis the need to develop electrodes with high surface area
density and low resistance. However, this should not come at higher costs or
environment impact. The development of graphitic structures in biomass-based electrode
material is due to the thermal treatment of the carbonaceous feedstock material, where
carbon rearranges into small graphitic crystallites at temperature 700C-800C3031.
These graphitic zones have delocalized pi electrons that facilitate the flow of electrical
current. Resistance through the graphitic zones is based on the degree of purity and
orientation. Other studies have shown that biomass treated at high temperatures can have
both high surface area and low resistance and could function as electrodes or
supercompasitors43'44. Converting non-conductive biomass into electrode materials has
been demonstrated and because of the stored chemical energy in the feedstock material
could be energy positive, but further research is needs to develop the optimal
methodology to achieve maximum surface area and conductivity while reducing the
amount of energy and environmental impact. Doing so could help to lower the cost of
electrode material, increase the feasibility of scaling up MFC technologies, and reduce
environmental impact.
Biochar Electrode Life-Cycle and Cost Analysis
There are a variety of feedstock materials and manufacturing technologies used to
make biochar, but it is generally accepted that high-yield, low emission pyrolysis and
gasification biochar manufacturing and land application is as a way to simultaneously
sequester carbon, produce energy and increase crop production. The methods employed
to make biochar with high surface area density and low resistance could be emphasized to
produce electrodes materials for MFCs while maintain its environmental and economic


benefits. Moreover, the use of biochar as an electrode material in MFC reactors,
especially for wastewater treatment, could add an additional step to further expand its
life-cycle benefits and in doing so could also reduce the cost and increasing the feasibility
of large-scale deployment of MFCs.
Biochars carbon (C) sequestration potential is largely due to conversion of
biomass C to biochar C, a much more recalcitrant form which slows the rate at which
photosynthetically fixed C returns to the atmosphere45. This conversion process
sequesters around 50% of the biomass C, significantly greater than that retained from
burning (3%) or biological decomposition (<10-20% after 5-10 years)46. Using higher
temperatures (>800C), such as those employed to make high surface area and
conductive chars increases fixed C ratio and stability of the material47. Although the
yields from high temperature treatments are often lower, much of the loss in weight is
due to the off gassing of volatile organic components of the feedstock. GAC and GG
also have high concentrations of C, but when coal is used as the feedstock material, the C
is derived from fossil sources and is not part of the current cycle. The pyrolysis of coal
only increases the total atmospheric C concentration, along with other toxic substances
such a mercury and sulfur. This further emphasizes the importance of feedstock material
and manufacturing methods when determine the impact of electrode materials.
Similar to GAC, any carbonaceous material could be used as a feedstock in the
production of biochar electrodes. Biowastes, such as forestry, milling, and agricultural
residue, along with yard clippings and construction waste are the feedstock of choice
because of their reliable supply, low cost, high lignin content, and high surface area and
conductivity when manufactured at high temperatures48. Coal is most commonly used in


GAC manufacturing because of its lower cost and high carbon content. However, using
biowaste with little to no commercial value and local availability greatly reduces the cost
of feedstock purchasing compared to coal. In this study we used lodgepole pine chips
and lodgepole pine sawdust pellets as the feedstock material. Both of these materials are
locally available and are either considered biowaste or made from biowaste. Data on
U.S. supplies suggest that 0.012 Pg C yr"1 and 0.024 Pg C yr"1 of biochar could be
produced from forestry residue and mill residue46. This is a stark comparison when you
consider that there are no graphite mines in the U.S. and few globally49. Although
feedstock characteristics and availability are important to ensure a high quality product
and to maintain a steady supply, manufacturing methodology also contributes
significantly to the environmental impact, final characteristics and cost of manufacturing
biochar electrodes.
Table II List of MFC reactors in this study and their specifications
Anode Material Total BET SA (m2) Rs (O) Ri(0) Maximum Power Density mW/m2 \Y/m3 CE (%) Material Cost(US$)/Wa
GAC 3.68 34.9 40.3 67410 7.3210 470.7 $402.80
GG 0.002 24.9 39.9 5665 6.155 350.1 $392.62
BCp 0.52 34.3 46.2 53218 5.7818 410.4 $23.88
BCc 0.32 29.7 43.4 45720 4.9720 430.1 $35.79
a Material cost per Watt produced was calculated by dividing electrode material cost in anode chamber by maximum power density
As described above, biochar is the result of the pyrolysis or gasification of
biomass. The elevated temperatures needed to carbonize the feedstock material are
general produced by the combustion of the syngas released during pyrolysis of the
feedstock. In this way, the chemical energy stored in the feedstock material is used to


fuel the carbonization process. The manufacturing of GAC also uses a similar technique
but often times an additional energy source is used to control the reaction rate and fuel
thermal activation. Biochar does not traditionally undergo activation, but air flow
through the reactor during gasification can perform similar purposes. The biochar
samples used in this experiment were manufacturing using a top-lit up-draft gasifier
(TLUD). In a TLUD the pyrolysis front moves downward through the mass of fuel,
converting the biomass to char. The syngas is directly combusted at the top of the kiln,
increasing the internal temperature and passively pulling air up through the bottom. The
air flowing through the reactor is thought to react with the surface of the char material,
similar to the activation step in GAC, increasing the surface area density. This is
achieved with minimal external energy. TLUD gasifier is just one example of variety
technologies that can be used to manufacture biochar electrodes, pyrolysis, gasification,
hydrothermal, and flash carbonization being the most thoroughly study25. No matter
what technology is employed, high yield, low emissions, and parameters that increase the
surface area and conductivity should be emphasized to produce the most sustainable and
cost effective electrode materials possible.
Figure XII Flow chart of manufacturing methods of electrode materials used in this
study


Along with energy production, land application of biochar has shown additional C
offsets and cost reductions. The benefits of biochar addition to agricultural soils includes
improved water and nutrient retention, increase crop yield, suppressed N2O emissions,
reduce fertilizer requirements, and increased soil organic carbon content50. We suggest
that composting and soil application of spent MFC electrode material, especially in the
case of wastewater treatment, could also have similar, if not increased, beneficial effects
on agricultural production. Several studies have shown that high surface area biochars
have increased absorbance capabilities51,52. When used as an electrode material in MFCs
treating wastewater, valuable micronutrients could be adsorbed and slowly released in
agricultural field after application. The thick exoelectrogenic biofilm established on the
biochar electrode surface during wastewater treatment could also help to increase the
biological diversity and abundance in agricultural soils. If sorbed contaminates or
pathogens are of concern, composting could be utilized to allow ample time for elevated
temperatures and enhanced microorganism activity to biodegrade any pollutants.
However, recent research on biochar and carbon absorbents has shown little migration of
pathogens or leaching form contaminated materials53. If sufficient evidence is collected
to demonstrate the beneficial use of spent biochar electrodes as agricultural amendments,
it could significantly offset the cost of MFC construction and operation.
It is evident that additional research is needed to refine the production method and
full life-cycle use of biochar electrode materials. Great care should be taken to select
feedstock material with little economic value, while maximizing the energy output during
manufacturing. Manufacturing parameters should also be set to produce chars with
increased surface area density and conductivity to increase their performance in MFCs.


Additional research is also needed to test the feasibility of land application of spent
biochar electrodes.
Conclusion
High temperature biochar materials, made form lodgepole pine chips (BCc) and
lodgepole pine sawdust pellets (BCp), were tested for the first time as an electrode
materials in a microbial fuel cell. BCp and BCc should satisfactory power density of 532
18 mW m"2 and 457 20 mW/m"2 respectively compared to 674 10 mW m"2 and 566
5 mW m"2 for GAC and GG respectively. Differences in power density can be
attributed to the lower surface area density than GAC and high surface resistance than
GG. However, biochar electrode material cost have been estimated at 51-356 US$/tonne,
up to ten times cheaper that GAC (500-2500 US$/tonne) and GGs (500-800 US$/tonne).
Biochar electrode manufacturing also carries additionally environmental benefits,
including biowaste feedstock, energy positive manufacturing, and carbon sequestration
potential. We also suggest spent biochar electrode material could be used as an
agricultural amendment, further increasing its life-cycle benefits and subsidizing its cost.
Although further research is needed to optimize the manufacturing method of biochar
electrode production and increase its performance, the use of biomass-derived electrode
materials ring in a new era of material use in MFCs with additional economic and
environmental benefits.


CHAPTER IV
BIOCHAR LCA AND CARBON ACCOUNTING
Introduction
Global atmospheric greenhouse gas (GHG) concentrations are rapidly increasing
and concerns about anthropogenic climate change are sparking interest in carbon
sequestering technologies. Although there are several methodologies being explore,
biochar production and its use as a soil amendment has been gaining worldwide attention
due to its carbon sequestering potential, benefits to the agricultural sector, co-energy
generation, and its use of waste-biomass as a feedstock material.
Biochar is a crude form of activated carbon produced through the combustion of
biomass, in a limit oxygen environment, with the attentional use as an agricultural
amendment. Pyrolysis and gasification are the most widely used and thoroughly studied
methods of manufacturing, where high temperatures and controlled oxygen exposer are
used to convert biomass into primarily recalcitrant carbon. Biochar is comprised mostly
of carbon (97%), ash (3%) and some trace minerals (<1%), although the physical and
chemical features vary greatly depending on feedstock and manufacturing methods. The
volitization of organic matter from the original feedstock material creates syngas that can
be further combusted, for co-energy generation, or refined to produce bio-oils.
Traditionally biochar has been used as an agricultural amendment, in most cases,
increasing crop yield and decreasing the need for fertilizers47. Depending on soil type,
biochar can help mitigate N20 emissions from agricultural soil54. It is also used in land
reclamation projects, because of its water and nutrient absorption capabilities55. And


more recently, biochar is being investigated as a low cost electrode material in microbial
fuel cells.
Biochar has the potential to sequester carbon because of its biomass feedstock
use, high carbon content, and stability during use45. However, there have been few case
studies investigating that real-world production of biochar. More research needs to be
done in order to quantify the total GHG emissions during the production of biochar
compared to the amount of carbon being sequestered in its final use and that of the
traditional fate of the biomass. There have been several LCA conducted on
biochar455056, but they have only focused on hypothetical examples and theoretical
models. In this study we take direct emissions data from field based slow-pyrolysis
biochar production using forestry residue, and compare it to the more common treatment
methods, field burning and decomposition.
Goal and Scope
The goal of this study is to calculate the total carbon balance and GHG emissions
of biochar production compared to the more traditional fate of forestry residue. Using 1
kg of biomass as the functional unit, a process-based LCA analysis is used to inventory
total GHG emissions (CO2, N2O, and CH4) released during biochar production and
transportation. The carbon content of the biochar and the GHGs associated with the
alternative fate scenarios is also subtracted from the GHG inventory of production and
the carbon sequestration potential is assessed.


Research Methodology
An LCA analysis is conducted according to commonly excepted procedure. The
entire life cycle of biochar production is evaluated from cradle to grave. The
transportation data was collected and compiled from EPA emission reports57. The
emissions and technical process specifications was collected from reports and
consultations given by the facility managers themselves. Emissions associated with the
alternative fate of forestry residue were taken from a Stockholm Environmental Institute
CO
report .
Case Study: Biochar Production in Golden Colorado
Company Description
Biochar Engineering Corporation (BEC) is a design fabrication company in
Golden Colorado that focuses on biochar and co-energy production. BEC optimizes its
biochar production for high sorption properties and fixed carbon content. Their pyrolysis
machines are designed for mobility and can be transported on-site of biomass storage
locations, reducing the need to transport the biomass feedstock.
Technology Description
BEC uses a two-stage process with their Beta Base Unit (a mobile 'A ton/hr
production unit). During the first stage the material is carbonized in an aerobic
environment. Temperatures at this stage range between 700-750C, for a duration of less
than one minute. By controlling the ratio of air to biomass, they can ensure that it is kept
below the combustion ratio. Using this process they can also ensure the preservation of
solid carbon. During the second stage the material is kept in a sweep gas environment at


temperatures between 200-500C for approximately ten to fifteen minutes. The gas
produced by the pyrolysis of biomass in the first stage, which is mostly composed of N2,
H2, CO, CH4 and higher VOCs and trace gases, is used as the sweep gas in second stage.
Biochar ranging from 1.5 cm long by 1 cm wide and .5 cm thick is produced.
System Boundary
The system boundary includes the on-site collection and processing of forestry
residue to chip, the processing of chip to biochar, and the transportation of biochar to
end-use customers. This process is consistent with the real world production of biochar
using BEC technology. We did not include the GHG mitigation associated with the end-
use of biochar in our LCA because there is no consistent scientific data and depends on
several variables including soil type, application rate, and local climate.
For comparison, we used GHG emissions data on more tradition forestry residue fates59.
In most cases the residue left behind after a forestry operation is collected, piled, and
burned (11). In some cases the residue is scattered and left to decompose. For the
purpose of this analysis we compare the GHG emissions from the on-site decomposition
and combustion of forestry residue.
GHG emissions
associated with
transportation
(VMT)
/ \
Transportation to
end-user

Figure XIII. Flow Diagram for Biochar production


Data Collection Methodology
Forestry Residue Processing
Forestry residue is mostly comprised of small diameter trees, branches, and the
tops of commercial timber collected during logging operations. We assumed that the
material has dried and all of the needles have fallen off. This method is consistent with
other forestry residue analyses58,60,61. Collection and processing operation was modeled
after the current operations of Grays Harbor Paper and Hermann Bros. GHG emissions
associated with the collection and processing of the forestry residue was collected from
the Stockholm Environmental Institute report, Greenhouse gas and air pollution
emissions of alternatives for woody biomass residues.
Pyrolysis Emissions
Stack emissions were collected from BEC, using methods that are required by the
EPA for air pollution reporting. The biomass feedstock used during the emissions
testing was comprised of chipped forestry residue, mostly lodgepole pine chip. Some
propane and electricity use for the pyrolysis process is also calculated into the total
emissions.
Transportation Emissions
The emissions associated with the transportation of biochar to the end-user was
collected from the EPA vehicle emissions report57. Biochar was assumed to be
transported with a semi for 200 miles round trip with a 10 mpg average. 100 miles is the
average distance from forestry operations in the Rocky Mountains to agricultural field on
the front range of Colorado.


On-site Decomposition and Combustion of Forestry Residue
Emissions data associated with the on-site decomposition and combustion of
forestry residue was collected from the Stockholm report. Emission factors and data
resources relied on current published literature, reports, site visits, and air emissions data
reported by state agencies. For on-site decomposition it is assumed that the material is
scattered and left to decompose, emissions are associated with a decay period of over
100-yr. Although, some reports indicate methane emissions associated with
decomposition, this report assumes that residue piles do not facilitate anaerobic
conditions and there is no methane release. For the on-site combustion it is assumed
forestry residue is gathered into piles and ignited by hand.
Biochar Stable Carbon Content
Data on the stable carbon content was collected from laboratory elemental
analysis carried about by BEC.


GHG Inventory and Carbon Accounting
GHG Inventory
0.400
2 0.200
"aT 0.000
O -0.200
-0.400
-0.600
tC02e/t-l
Gath/Chipping 0.008
Pyrolysis 0.297
Transportation 0.076
Biochar -0.125
Avoided C02e (Combustion) -0.475
Total C -0.218
Figure XIV. Carbon accounting of biochar production with avoided carbon loss due
to combustion of forestry residue
GHG Inventory
t C02e/t-l
Gath/Chipping 0.008
Pyrolysis 0.297
Transportation 0.076
Biochar -0.125
Avoided C02e (Decomposition) -0.395
Total C -0.138
Figure XV. Carbon accounting during the production of biochar with avoided
carbon loss due to decomposition of forestry residue


Results and Discussion
Global Warming-GHG Emissions
The total avoided CO2Q is -333 t CChe/t"1 and -0.083 t CChe/t"1 for the combustion
and decomposition avoidance scenarios respectively. According to our results, the total
GHG emissions associated with the production and transportation of biochar is negative,
if you consider the avoided CChe due to combustion or decomposition of the feedstock.
Of the total GHG emissions during the processing of biochar, pyrolysis is responsible for
the majority or 79% of the total GHGs emitted. Much of the reduction in GHG emissions
can be contributed to the use of a waste feedstock that would otherwise be combusted or
decompose on-site. The mobile unit also allows the production of biomass on-site
without the additional need to transport the feedstock before processing.
Carbon Accounting
The total C sequestered during the processing of biochar is -.189 t C/t"1 and -.1091
C/t"1 for the combustion and decomposition avoidance scenarios respectively. This
indicates that there is more C sequestered during the processing of biochar than there is if
the fate of the forestry residue was on-site combustion or decomposition. Much of the
carbon sequestration can be attributed to the avoidance of on-site combustion or
decomposition; however the stable C content of the biochar contributes 20% of the total
carbon sequestration.
Process Refinement Recommendations
Although our results indicate that the production of biochar using forestry residue
is GHG and carbon negative there is room for further improvement, including co-


production of heat and power. Co-production of heat and electricity would off-set the use
of fossil fuel combustion and/or natural gas. Many pyrolysis machines incorporate co-
production into their systems. Utilizing the syngas and heat produced during the
pyrolysis process, electricity and heat can be used for domestic consumption. In the
Denver region, 1.75 lb or C02e is emitted per kWh62, depending on the pyrolysis
machine design; this would offset the amount of GHG released into the atmosphere if a
traditional method of electricity production is used.
Conclusion
The production of biochar using waste biomass material has great potential to
sequester C and mitigate GHG emissions. There have been several LCAs published
claiming this potential, however they use hypothetical models and do not have real-world
data. To our knowledge there has not been an LCA conducted on actual case studies of
the production of biochar. This report is the first to get direct emissions data on real-
world production and use of biochar. The findings of this report demonstrate that biochar
production can sequester C and mitigate GHG emissions if waste forestry residue is used
as feedstock instead of its alternative fates. Although the findings show GHG mitigation,
there is still room for improvement, including co-production of electricity and heat,
which would further improve the technology.


CHAPTER V
CONCLUSION
The goal of this thesis was to demonstrate the possibility of microbial fuel cells
(MFCs) for treating wastewater and to use biochar as a more sustainable electrode
material option in MFCs. These studies demonstrate that infact MFC technology can
treat wastewater as effectively as traditional aeration treatment, although further research
is needed to improve the process. The studies also show that biochar could effectively
serve as a surrogate for more traditional electrode materials with lower overall cost and
environmental impact. These results could be highly impactful with the potential to
change the current global wastewater treatment infrastructure from one that is costly,
energy intensive, or in the case of developing countries, lacking all together.


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Full Text

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WHOLE SYSTEMS THINKING FOR SUSTAINABLE WATER TREATMENT DESIGN by Mitchell Tyler Huggins B.S., University of Montana, 2007 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirem ents for the degree of Master of Engineering Civil Engineering 2013

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This thesis for the Master of Engineering degree by Mitchell Tyler Huggins has been approved for the Civil Engineering Program by Zhiyong Ren Chair Zhiyong Ren Advisor Arunprakash Karunanithi Ron Rorrer April 4, 2013

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Mitchell Tyler Huggins ( M.Eng Civil Engineering ) Whole Systems Thinking for Sustainable Water Treatment Design Thesis directed by Assistant Professor Zhiyong Ren ABSTRACT Microbial fuel cell (MFC) technolog y could provide a low cost alternative to conventional aerated wastewater treatment, however there has been little comparison between MFC and aeration treatment using real wastewater substrate. This study attempts to directly compare the wastewater treatm ent efficiency and energy consumption and generation among three reactor systems, a traditional aeration process, a simple submerged MFC configuration, and a control reactor acting similar as natural lagoons. Results showed that all three systems were able to remove >90% of COD, but the aeration used shorter time (8 days) then the MFC (10 days) and control reactor (25 days). Compared to aeration, the MFC showed lower removal efficiency in high COD concentration but much higher efficiency when the COD is low Only the aeration system showed complete nitrification during the operation, reflected by completed ammonia removal and nitrate accumulation. Suspended solid measurements showed that MFC reduced sludge production by 52 82% as compared to aeration, and i t also saved 100% of aeration energy. Furthermore, though not designed for high power generation, the MFC reactor showed a 0.3 Wh/g COD/L or 24 Wh/m 3 (wastewater treated) net energy gain in electricity generation. These results demonstrate that MFC technol ogy could be integrated into wastewater infrastructure to meet effluent quality and save operational cost.

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The high cost and life cycle impact of electrode materials is one major barrier to the large scale application of microbial fuel cells (MFC). We al so demonstrate that biomass derived black carbon (biochar), could be a more cost effective and sustainable alternative to granular activated carbon (GAC) and graphite granule (GG) electrodes. In a comparison study, two biochar materials made from lodgepol e pine sawdust pellets (BCp) and lodgepole pine woodchips (BCc), gassified at a highest heat temperature (HHT) of 1000C under a heating rate of 16C/min, showed a satisfactory power density of 532 18 mW m 2 and 457 20 mW/m 2 respectively, compared to GAC with 674 10 mW m 2 and GG with 566 5 mW m 2 (normalized to cathode projected surface area), as an anode material in a two chamber MFC. BCc and BCp had BET N2 surface area measurements of 429 cm2 g 1 and 470 cm2 g 1 respectively, lower than industr ial GAC with 1248 cm2 g 1 but several orders of magnitude higher that GG with 0.44 cm2 g 1 than 1. We also investigated the li fe cycle impact and estimated cost of biochar as an electrode material. Although there is no well established market price for biochar, conservative estimates place the costs around 51 356 US$/tonne, up to ten times cheaper that GAC (500 2500 US$/tonne) a nd GGs (500 800 US$/tonne) with significantly greater life cycle advantages. The form and content of this abstract are approved. I recommend its publication. Approved: Zhiyong Ren

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ACKNOWLEDGMENTS I would like to thank all members of the Ren lab, for t heir support and e ncouragement. I would also like to thank Dr. Ren for his financial support and mentor ship through my graduate studies

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TABLE OF CONTENTS CHAPTER I INTRODUCTION ................................ ................................ ................................ ........ 11 II ENERGY AND PERFORMANCE COMPARISON OF MICROBIAL FUEL CELL AND CONVENTIONAL AERATION TREATMENT OF INDUSTRIAL WASTEWATER ................................ ................................ ................................ .......... 12 Abstract ................................ ................................ ................................ ................. 12 Introduction ................................ ................................ ................................ ........... 13 Materials and Methods ................................ ................................ .......................... 16 Reactor Configuration and Construction ................................ ........................ 16 Reactor Start u p and Operation ................................ ................................ ...... 16 Analyses and Calculations ................................ ................................ .............. 16 Results and Discussion ................................ ................................ ......................... 17 Organic Removal ................................ ................................ ............................ 17 Ammonia and Nitrate Removal Efficienc ies ................................ .................. 19 Solid s Production ................................ ................................ ............................ 20 MFC E lectricity P roduction U sing W astewater a s the S ubstrate ................... 21 C onclusion ................................ ................................ ................................ ............ 23 III BIOCHAR AS A SUSTAINABLE ELECTRODE MATERIAL IN MICROBIAL FUEL CELLS ................................ ................................ ................................ ............. 24 Abstract ................................ ................................ ................................ ................. 24 Introduction ................................ ................................ ................................ ........... 25 Anode Electrode Material Manufacturing ................................ ...................... 28 MFC C onstructio n and O peration ................................ ................................ ... 29 Statistical and Electrochemical Analyses ................................ ....................... 29 Results and Disussion ................................ ................................ ........................... 31

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Power Production from Electrode Materials ................................ ................... 31 Surface Characteristics of Electrode Materials ................................ ............... 32 Resistance Characteristics of Electrode Materials ................................ .......... 36 Biochar Electrode Life Cycle and Cost Analysis ................................ ........... 38 C onclusion ................................ ................................ ................................ ............ 43 IV BIOCHAR LCA AND CARBON ACCOUNTING ................................ .................. 44 Introduction ................................ ................................ ................................ ........... 44 Goal and Scope ................................ ................................ ............................... 45 Research Methodology ................................ ................................ ................... 46 Case Study: Biochar Production in Golden Colorado ................................ .......... 46 Company Description ................................ ................................ ..................... 46 Technology Description ................................ ................................ .................. 46 System Boundary ................................ ................................ ................................ .. 47 Data Collection Methodology ................................ ................................ ............... 48 Forestry Residue Processing ................................ ................................ ........... 48 Pyrolysis Emissions ................................ ................................ ........................ 48 Transportation Emissions ................................ ................................ ................ 48 On site Decomposition and Combustion of Forestry Residue ....................... 49 Biochar Stable Carbon Content ................................ ................................ ...... 49 GHG Inventory and Carbon Accounting ................................ .............................. 50 Results and Discussion ................................ ................................ ......................... 51 Global Warming GHG Emissions ................................ ................................ .. 51 Carbon Accounting ................................ ................................ ......................... 51 Process Refinement Recommendations ................................ .......................... 51 C onclusion ................................ ................................ ................................ ............ 52

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V CONCLUSION ................................ ................................ ................................ ............ 53 REFERENCES ................................ ................................ ................................ ................. 54

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LIST OF TABLES T able I Electrode characteristics used in this study ................................ ................................ ... 28 II List of MFC reactors in this study and their specifications ................................ .......... 40

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LIST OF FIGURES Figure I. Reactor configurations ................................ ................................ ................................ ... 15 II. Comparison of COD removal efficiency between MFC, aeration, and control reactors ................................ ................................ ................................ ................................ ........... 18 III. C OD removal rates and COD removal rates at COD concentrations > 200 mg/L .... 19 IV. Ammonia and nitrate removal comparison between the MF C, aeration, and control reactors. ................................ ................................ ................................ ............................. 20 V. Final TSS concentration comparison between the MFC, aeration, and control reactors ................................ ................................ ................................ ................................ ........... 21 VI. Power analysis for the MFC and aeration reactors. ................................ .................... 22 VII. Four electro de materials used in this study ................................ ............................... 27 VIII. Power density curve normalized by cathode projected area (A) and electrode potentials (cathode, filled symbols; anode, open symbols) versus Ag/AgCl re ference electrode as a function of current density in two chamber reactors packed with GAC, GG, BCp and BCc. ................................ ................................ ................................ ................... 32 IX Incremental pore area with the distribution of pore size ................................ ........... 33 X Temperature profile and residence time of BCp and BCc gasification ....................... 35 XI System resistance of the reactors filled with four different anode materials .............. 37 XII Flow chart of manufacturing methods of electrode materials used in this study ...... 41 XIII. Flow Diagram for Biochar production ................................ ................................ ..... 47 XIV. Carbon accounting of biochar production with avoided carbon loss due to combustion of forestry residue ................................ ................................ .......................... 50 XV. Carbon accounting during the production of biochar with avoided carbon loss due to decomposition of forestry residue ................................ ................................ ..................... 50

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CHAPTER I INTRODUCTION The current global wastewater infra structure system has several major limitations. In the developed world the wastewater infrastructure provides for adequate treatment, but can be extremely expensive and energy intensive. In the developing world there is a serious lack of wastewater infra structure, which can lead to pollution and the spread of infectious diseases. In both cases the wastewater stream is treated as a separate system and does not generally tie into other civil processes. This thesis is an attempt to use microbial fuel cell technology and biochar electrodes to lower the cost, decrease energy use, and integrate wastewater treatment into agricultural production and land reclamation.

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CHAPTER II ENERGY AND PERFORMANCE COMPARISON OF MICROBIAL FUEL CELL AND CONVENTIONAL AERA TION TREATMENT OF INDUSTRIAL WASTEWATER Abstract Microbial fuel cell (MFC) technology could provide a low cost alternative to conventional aerated wastewater treatment, however there has been little comparison between MFC and aeration treatment using real wastewater substrate. This study attempts to directly compare the wastewater treatment efficiency and energy consumption and generation among three reactor systems, a traditional aeration process, a simple submerged MFC configuration, and a control reacto r acting similar as natural lagoons. Results showed that all three systems were able to remove >90% of COD, but the aeration used shorter time (8 days) then the MFC (10 days) and control reactor (25 days). Compared to aeration, the MFC showed lower removal efficiency in high COD concentration but much higher efficiency when the COD is low. Only the aeration system showed complete nitrification during the operation, reflected by completed ammonia removal and nitrate accumulation. Suspended solid measurement s showed that MFC reduced sludge production by 52 82% as compared to aeration, and it also saved 100% of aeration energy. Furthermore, though not designed for high power generation, the MFC reactor showed a 0.3 Wh/g COD/L or 24 Wh/m 3 (wastewater treated) n et energy gain in electricity generation. These results demonstrate that MFC technology could be integrated into wastewater infrastructure to meet effluent quality and save operational cost.

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Introduction Traditional activated sludge or aerated lagoon wast ewater treatment processes can efficiently remove organic pollutants, but operating such systems are cost and energy intensive, mainly due to the aeration and sludge treatment associated processes. The United States spends approximately $25 billion annuall y on domestic wastewater treatment and another $202 billion is needed for improving publicly owned treatment works 1 Wastewater treatment accounts for about 3% of the U.S. electrical energy load, which is approximately 110 Teraw att hour s per year, or equivalent to 9.6 million households annual electricity use 2 Traditional activated sludge based tre atment processes employ aerobic heterotrophic microorganisms to degrade organic matters. Such types of microbes have high metabolic kinetics, so they can process substrates faster than anaerobic bacteria, but they also require sufficient supply of oxygen a nd generate significant amount biomass. Aeration can amount to 45 75% of wastewater treatment plant (WWTP) energy costs, while the treatment and disposal of sludge may count up to 60% of the total operation cost. The next generation of wastewater infrastr ucture should consider transforming current energy intensive, treatment focused processes into integrated systems that recover energy and other resources It was estimated that the energy content embedded in wastewater is estimated about 2 4 times the ener gy used for its treatment 2 so it is possible to make wa stewater treatment self sufficient if new technologies can r ecove r th e energy while simultaneously achieving treatment objectives Microbial fuel cells (MFCs) recently emerged as a novel technology to fulfill this mission because they directly convert biodegradable materials into renewable energy with minimal sludge produc tion 3

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MFCs employ exoelectrogenic bacteria to extract electrons from (in)organic substrates and transfer them to the anode, and the electrons then form electric currents when flowing from the anode to the cathode where they then combine with oxygen and protons to produce water 4 MFCs have been shown effective in treating almost all kinds of waste streams, including municipal, brewery, agricultural refinery, paper cycling wastewater, and even landfill leachate 5 The power output is dependent on the biodegradability of the substrate, conversion efficiency, and loading rate. For example, 261 mW/m 2 was obtained using swine wastewater 6 while other s tudies have demonstrated that a maximum power output of 205mW/m 2 can be achie ved using brewery wastewater 7 and 672 mWm 2 using paper recycling wastewater 8 The functional bacteria in MFCs are generally anaerobic or facultative microorganisms, so the ope ration of MFCs may not use any active aeration 9 In addition, the cell yield of exoelectrogenic bacteria (0.07 0. 16 gVSS/g COD) was much less than the activated sludge (0.35 0.45 0. 16 gVSS/g COD), so sludge production can be significantly reduced 10 However, most studies have focused on energy production from MFCs while very few compared the energy use /generation and sludge production between MFCs and tradit ional aeration based processes. In this study, we used liter scale reactors to quantitatively audit the power generated or consumed during the operation of a n MFC, an aeration tank and a control re actor duri ng the treatment of wastewater. W e also compared system performance in terms of COD and ammonia removal, and the concentration change s in nitrate suspended solids, and dissolved oxygen. We aim to provide side by side quantitative information i n evaluating the potential energy and

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treatment benefits of MFCs as compared to traditional aeration processes such as activated sludge or aerated lagoon systems. Figure I Reactor configurations

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Materials and Methods Reactor Configuration and Constructio n Three reactors including an MFC, an aeration reactor, and a control reactor, were constructed usi ng a 15 L container. The single chamber submerged MFC reactor was configured using graphite brush as the anode (Chemviron Carbon) and carbon cloth (1% Pt) a s the air cathode (Fuel Cell Earth LLC) (Figure I ). The same 15 L container was used for the aeration reactor, with an aquarium pump air diffuser at the bottom (Figure I ). The control reactor used a same type of container but without any aeration equipme nt or electrode installed (Figure I ). All reactors were operated in fed batch mode at room temperature and exposed to the ambient air. Reactor Start up and Operation Industrial wastewater was collected from the effluent of the primary clarifier from the C oors Wastewater Treatment Plant in Golden, Colorado. The wastewater was used as the inoculum and sole sub strate for all three reactors. No extra medium or buffer solution was added. The MFC reactor went through an initial 7 day inoculation period before the wastewater was replaced and measurements taken. All reactors were operated until >90% COD reduction was achieved then the wastewater was replaced for a series of three trials. Analyses and Calculations Closed circuit voltage (V) and amps (A) were me asured and recorded using a data acquisition system ( Keithley Instruments, Inc. OH ) across an external resistance (R) of 10

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measured in hours (h), expressed in watt hours ( Wh) and calculated using the equation specification, while the wattage generated from the MFC was determined from the data acquisition system and the equation described abo ve. Polarization curve was normalized by cathode surface area and was determined by conducting a linear sweep voltammetry test using a potentiostat (G 300, Gamry Instruments). Dissolved oxygen concentration was measured with a standard DO probe (DO50 GS Hach Co.) COD, DCOD, NH 4 + N, and NO 3 concentrations were measured with digester vials (Hach Co.) according to APHA standards. The solid retention time (SRT) was calculated based on the amount of time in days (d) each reactor was operated. Results a nd Discussion Organic R emoval All three reactors were fed with the same wastewater with a COD concentration of 1 24763.9 mg/L. The reactors were operated in batch mode till reaching >9 0 % of COD removal While all reactors were able reach the same treatmen t goal, t he average retention time for achieving similar treatment efficiency varied significantly (Figure II ). T he MFC reactor took 15 days to reach to 90% removal, which is 10 days shorter than the control reactor without aeration but 2 days longer than the aeration reactor The shorter retention time for the aeration reactor is similar to the extended aeration activated sludge systems and can be attributed to the readily available oxygen supply and rapid metabolisms of aerobic respiration 10 The SRT of the control is around 25 days, c lose to

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traditional stabilization lagoons, which do not employ mechanical aeration and may create aerobic, anoxic, and anaerobic layers of environment for different microbial community and metabolisms. The absence of mechanical aeration in the MFC reactor also provided an anoxic environment but experienced much shorter retention time than the control. These results suggest that by providing a submerged anode and a floating cathode, the MFC configuration significantly facilitated substrate oxidation rate cl ose to aeration operation but w ithout any external oxygen supply. Such variations can also be presented by COD removal rates. As shown in Figure III the COD removal rates from the three systems varied significantly and cha nged depending on the COD concentrations. During the initial stage of operation, when the COD concentration was high, COD removal rate for the a eration reactor averaged around which was 3.6 times and 9.7 times higher than that of the MFC or control reactor treating the similar COD concentration s However, when the COD concentration Figure II Comparison of COD removal efficiency between MFC, aeration, and control reactors

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decreased to around 200 mg/L or less, the removal ra te for the aeration reactor decreased to This rate was similar to that of the control but significantly less than that of the MFC reactor which had This observation may be interpreted using the di fferent degradation natures between suspended growth syste ms and attached growth systems. Many studies and models showed that compared to attached growth systems, such as trickling filters, completely mixed suspended growth systems such as activate sludge were able to treat high concentrated organics more efficiently but the effluent COD was highly depending on the solid retention time 10 Ammonia and N itrate R emoval E fficiencies Because the same wastewater was used as the influent for all three reactors, all systems were fed with the same ammonia concentration of 10 mg/L. However, because t he aeration reactor provided a completely aerobic environment for nitrification, it showed nearly 100% ammonia removal within 11 days, after an initial concentration increase due to organic ammonif ication (Figure IV ). T h is nitrification process is also confirmed by the accumulation of nitrate in the aeration reactor, where the increase of Figure III COD removal rates and COD removal rate s at COD concentrations > 200 mg/L

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nitrate concentration from 2 mg/L to 12 mg/L perfectly accompanied the ammonia decrease (Figure IV ). No denitrif ication was observed in the aeration reactor due to the highly aerobic environment. In contrast, neither MFC or control reactor showed significant ammonia removal or nitrate accumulation during the operation, presumably due to inhibition of nitrification in the anoxic to anaerobic condition in such reactors. However, other studies have shown that MFC, supplemented with nitrate, experienced 94.1 0.9% nitrogen removal 11 Our MFC reactor did show a slight nitrification process after 14 days of operation, as shown in Figure 3A B, but we had to change the s olution at the time because the reactor had reached the 90% organic removal thre shold. Solid s P roduction Preliminary characterization on total suspended solid (TSS) at different solid retention time shows that the aeration reactor produced much more solids than the other two reactors. Th e final TSS concentration from the aeratio n reactor was 202 50 mg/L in the reactor at the corresponding SRT of 13 days. By comparison, the MFC reactor maintained the lowest TSS concentration, with 20 10 mg/L, and the control reactor had Figure IV Ammonia and nitrate removal comparison between the MFC, aeration, and control reactors.

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a TSS of 45 10 mg/L. The low TSS concentration in the MFC reactor can be attributed to two reas ons. First, the MFC is a biofilm based system, and the accumulation of biomass mainly resides on the electrode except of occasional biofilm falloff, so the suspended solid is low. Another reason is due to the low c ell yield of the anoxic to anaerobic microorganisms in the MFC compared to the activated sludge. This finding confirms that sludge reduction can be a main benefit of MFC to replace activated sludge and reduce plant operation cost by 20 30%. When converting aeration basin into an MFC system, second clarifiers may be reduced in size, converted to solid contact basin, or even eliminated due to the reduced biomass generation 12 MFC E lectricity P roduction U sing W astewater a s the S ubstrate The MFC reactor was operated under a 10 Low resistance was used in this study because under this condition more electrons can be transferred freely and substrate degradation can be maximized 13 The MFC generated a maximum output voltage of 135 mV and a current density of 193 mA/m 2 The total MFC power output during a 15 day SRT was 0.36 Wh, equivalent to 0.32 Wh/g COD/L, or 24 Figure V Final TSS concentration comparison between the MFC, aeration and control reactors

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Wh per cubic meter wastewater treated. With an average SRT of 13 days, the aeration reactor consumed approximately 624 Wh of electricity, which transfers to about 547 Wh/g COD/L. The aeration pump could have been more efficient and adjusted to aerate less during lower levels of COD, however it was maintained as the same level in order to allow for complete nitrification and ensure oxygen was not the limiting factor. Figure 6 shows a comparison between power consumption in the aeration reactor and energy saving and production in the MFC reactor. Though this MFC was mainly designed for COD removal not for high power production, it still saves 1 00% of the aeration energy and produce extra energy while achieving the same treatment goal. Due to the high energy consumption of aeration in this study, it is not representative to directly calculate how much percentage of extra energy can be produced fr om MFC, but based on many other studies, MFC may produce 10% of extra electricity on top of aeration energy savings, if the aeration energy consumption is assumed as 1 kWh / kg COD 12 Figure VI Power analysis for the MFC and aeration reactors.

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C onclusion The results in this study showed that microbial fuel cell can be a viable technology to treat wastewater at the same level as traditional aeration process does, and it carries great potential as an energy positive process, because it saves 100% of aeration energy with extra electricity output. It also significantly reduces sludge production, which may reduce the size of secondary clarifier and save the cost of sludge disposal.

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CHAPTER I I I BIOCHAR AS A SUSTAINABLE ELECTRODE MATERIAL IN MICROBIAL FUEL CELLS Abstract The high cost and life cycle impact of electrode materials is one major barrier to the large scale appli cation of microbial fuel cells (MFC). We demonstrate that biomass derived black carbon (biochar), could be a more cost effective and sustainable alternative to granular activated carbon (GAC) and graphite granule (GG) electrodes. In a comparison study, t wo biochar materials made from lodgepole pine sawdust pellets (BCp) and lodgepole pine woodchips (BCc), gassified at a highest heat temperature (HHT) of 1000C under a heating rate of 16C/min, showed a satisfactory power density of 532 18 mW m 2 and 457 20 mW/m 2 respectively, compared to GAC with 674 10 mW m 2 and GG with 566 5 mW m 2 (normalized to cathode projected surface area), as an anode material in a two chamber MFC. BCc and BCp had BET N2 surface area measurements of 429 cm2 g 1 and 470 c m2 g 1 respectively, lower than industrial GAC with 1248 cm2 g 1 but several orders of magnitude higher that GG with 0.44 cm2 g 1. BCc and BCp had a lower surface resi 1 than 1. We also investigated the life cycle impact and estimated cost of biochar as an electrode material. Although there is no well established market price for b iochar, conservative estimates place the costs around 51 356 US$/tonne, up to ten times cheaper that GAC (500 2500 US$/tonne) and GGs (500 800 US$/tonne) with significantly greater life cycle advantages.

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Introdu c tion Microbial fuel cell (MFC) is a new pla tform technology that can simultaneous ly achieve (in) organic biodegradation and electric ity generation 14 16 MFC reactors utilize the metabolic activity of exoelectrogenic bacteria to catalyze redox reactions on the anode and promot e the flow of elections from anode to cathode for direct current harvestin g 12 Compared to current energy and cost intensive wastewater treatment processes, MFC is considered a nex t generation technology for wastewater industry, because it can be an energy positive system with net energy output, and it significantly reduces sludge production by more than 60% 3,17 Over the past decade the MFC power output has been improved by several orders of magnitudes, but one main challenge for MFC to be used in large scale applications is the high cost compared to other wastewater trea tment alternatives 18 One of the major contributors to the high cost of MFCs is the elec trode materials, which is estimated to amount to 20 50 % of the overall cost 19 However, electrodes play a fundamental role in facilitating exoelectrogenic biofilm growth and ele ctrochemical reactions and are essential in improving the functionality and efficiency of MFCs. Ideal electrode materials should possess key characteristi cs such as high surface area, high conductivity, low cost, and biocompatibility 20 Most electrode materials used in MFCs are carbon based granular activated carbon ( G AC) or graphite granules (GGs) 20 especially in larger scale systems, because G AC has high degree of microporosity and catalytic activities, and G Gs are less expensive with highe r conductivity, even though the surface area density is lower. The costs of GAC or GG electrodes range from 500 2500 US$ per US tonne which is significantly lower than carbon cloth or carbon paper

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(100,000 500,000 US$ per tonne), but it is still consider ed high for large scale applications. In addition to the cost, the life cycle impact of these materials can be significant depending on feedstock choice, manufacturing, and disposal methods For example, GAC is most commonly manufactured from the pyrolys is of coal along with secondary thermal or chemical activation 21,22 G Gs can be mined from natural deposits or synthetically manufactured through the thermal treatme nt (>3000C) of carbon based materials. Such feedstock extraction and manufacturing methods used for industrial GAC and GG can be highly energy intensive and result in the release of environmental pollutions including CO 2 and other greenhouse gases Fur thermore, the recycle and reuse rate of GAC and GG are low, and the waste materials are traditionally landfilled after several times of usage. In order to promote sustainable and cost effective electrode materials, the feedstock, manufacturing and end o f life alternatives all need to be investigated. In this context, biomass derived black carbon (b iochar ) could be a more sustainable option, because it is produced from locally available biowastes, such as agricultural and forestry residue, which helps lo wer the cost and environmental impact while ensuring a steady regional supply. Manufacturing is carried out through pyrolysis or gasification, which utilizes the internal chemical energy of the feedstock to fuel the carbonization process and produce harve stable bioenergy. In addition, unlike GG or GAC, biochar can be reused as agricultural soil amendment, which has been shown to increase crop production 23,24 increase microbial diversity and abundance, lower emissions such as NO 2 and remain environmentally stable for thousands of years. Moreover, the cost of biochar is low, ranging from 51 381 US$ per ton 25 nearly ten times less than GAC and

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GGs. Based on different purposes of usage, tailored biochar can be manufactured to have diffe rent physical properties 26 28 For example, by using elevated temperatures ( >800 1000 C ), biochars can have a wide range of p ore sizes and high service area, which can also cause internal graphitization and increased conductivity 29 30 31 Although the unique features of biochar have been demonstrated for some time in other areas, to our best knowledge few study investigated the feasibility and performance of bioch ar as electrode material in MFCs. In this study, we tested the performance of two different types of biochar materials made from compressed lodgpole pine sawdust pellets ( BCp ) and lodgepole pine woodchips ( BCc) and compared them to GAC and GG as the anode materials in two chamber MFCs. P e rformance was comprehensively characterized t hrough electrochemical and statistical analys e s, in terms of power production, resistivity, and total surface area. Furthermore, we also investigated the manufacturing process feedstock selection, and cost of biochar electrodes. Figure VII Four electrode materials used in this study

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Experimental Section Anode Electrode Material Manufacturing The main p hysical characteristics and costs of the four anode materials used in this study are shown in Table 1, and their images are shown in Fig. 1a. Fig. 1b illustrates the general outlines of the manufacturing process for the electrode materials. The G AC was pu rchased from Cameron Yakima, Inc, ( Yakima, WA, USA ), and it was manufactured from coal using industrial standard methods 21 resulting in 100% of activated carbon. Activation was achieved using thermal activation procedures. GG were purchased from Graphite Sales, Inc, ( Nova, OH, USA ) GG material is comprised of 100% synthetic graphite made from petroleum coke using temperatures exceeding 3000C. BCc and BC p were both manufactured using a custom made top lit up draft biomass gasifier with an external fan, as described by Kerns et.al. 2012 32 B iomass was carbonized using a HHT of 1000C residence time of 1 hr, and a ramp rate of 16C/min (figure X) and temperature reading were measured using a prog rammable thermocouple. BCp used compressed lodgepole pine sawdust pellet s and BCc used lodgepole pine woodchips gathered from local forestry residue as the biomass feedstock Table I Electrode characteristics used in this study Electrode Material Particle size (mm 3 ) Surface mm 1 ) Average Pore Diameter () BET SA (cm 2 g 1 ) Cost ($ Ton 1 ) GAC 26 36 82 26.8 1247.8 500 2500 GG 350 450 0.4 0.5 71.0 0.44 500 800 B Cp 60 74 61 37.6 428.6 100 199 B Cc 160 700 31 29.4 470.0 51 384

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MFC C onstruction an d O peration MFCs were constructed using two polycarbonate cube shaped blocks separated by a cation exchange membrane (38 cm 2 CMI 7000, Membrane International, NJ, USA ) A 3 7 cm di ameter hole was drilled at the center of each block forming the internal anode and cathode 33 Plain c arbon cloth (38 cm 2 Fuel Cell Earth ) was used as the common cathode material for all reactors Each anode material (GAC, G G, BCp or BCc) was packed into one side of anode chamber to a volume of 75 mL and held by a plastic mesh to tighten anode packing. A twisted titanium wire was used as a current collector and was buried in the packed anode The total empty volumes were 150m l and 200ml for cathode chamber and anode chamber, respectively. MFCs were inoculated using anaerobic sludge from Longmont Wastewater T reatment P lant (Longmont, CO, USA). The anolyte growth medium contained 1. 25 g of CH 3 COONa, 0.31 g of NH 4 Cl, 0.13 g of KC l, 3.32 g of NaH 2 PO 4 2H 2 O, 10.32 g of Na 2 HPO 4 12H 2 O, 12.5 mL of mineral solution, and 5 mL of vitamin solution per liter 13,34 The catholyte was potassium ferricyanide solution dissolved in 50 mM phosphate buffer, which aims to provide a stable cathode potential and minimize cathode limitation on system com parison 35 Each MFC was operated in fed batch mode under a 400 ohm external resistor. W hen voltage dropped below 2 0 mV, both anolyte and catholyte were replaced with fresh media. All the tests were conducted a t room temperature and repeated for at least 3 times. Statistical and Electrochemical Analyses The surface resistance measurement was determined by randomly selecting 35 electrode samples and measuring the ohmic resistance across a 4 mm distance w ith a programmable multimeter. The t distribution was used to calculate confidence intervals

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(CIs). The 95% CIs were calculated by ,where was sample mean, was sample standard variation, and n was the sample size 33 The cell voltage (E, volt) and electrode potentials for each MFC w ere measured continuously using a data acquisition system (Keithley Instrument, OH) every 66 sec Polarization curves were obtained by varying external resista nces from 50,000 to 30 ohm with each resistor stabilized for 30 min 13 The anode potential and cathode potential were measured against an Ag/AgCl reference electrode (RE 5B, Bioanalysis) inserted in the anode chamber and cathode chamber, respectively. D uring both acclam ation and fed batch periods c ircuits were operated under a fixed load (Re ohm ) of 4 Current(I, amp) was calculated according to Power (P, watt) was calculated according to C urrent density and p ower density were normalized by cathode projected surface area of 38 cm 2 Electrochemica l impedance spectroscopy (EIS) was conducted by a potentiostat (PC 4/3000, Gamry Instruments, NJ, USA) to determine total internal resistance using the anode as the working electrode, where the ca thode served as the counter electrode and reference electrode 14,34 Brunauer Emmett Teller (BET) method that us es a five point N 2 gas adsorption technique (ASAP 2 020; Micromeritics, Norcross, GA) was used to measure specific surface area and pore size distribution of the electrode materials. Average pore size and pore size distribution were determined from desorption of N 2 according to the method developed by Barr ett, Joyner, and Halenda (BJH) 33 36

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Results and Disussion Power Production from Electrode Materials The maximum power output and Columbic efficiency (CE) are two major measures to evaluate t he performance of MFC systems. The CEs and maximum power densities from MFCs occupied with the 4 different anode materials (BCp, BCc, GAC, and GG) are summarized in Table 2 and Fig. 2, and the power densities are normalized by cathode surface area. Result s showed that the GAC anode achieved the highest CE at around 47%, and GG had the lowest CE at 35%. The CEs from BCc and BCp were comparable at 41 43%. GAC had the highest power density of 674 10 mWm 2 followed by GG with 566 5 mWm 2 BCp with 532 18 mWm 2 and BCc with 457 20 mW/m 2 (Table 2) The power output from BCp and BCc was 21% and 32% lower than the GAC, and 6% and 19% lower than the GG anodes. Fig. 2B shows that the cathode potentials among all 4 reactors were comparable as designed, becau se ferricyanide cathode was used to minimize the cathode effects. The anode potential of BCc increased to around 0 mV at 1.8 Am 2 which resulted in lower power output. It was hypothesized that the difference in power densities can be attributed to the di fference in both surface area density and system internal resistance, which will be explained in more detail in the following sections. It must be noted that the power density differences are not an intrinsic value of the biochar material, and it could be manipulated through variations in manufacturing. As research in this field matures, biochar electrodes could be manufactured in such a way to mimic the beneficial properties of both GAC and GG, while maintaining its integrity as a sustainable electrode m aterial option. More detailed synopses of the manufacturing alternatives will also be discussed in the following

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sections. Moreover, when material costs were added into consideration, Table 2 shows that to generate the same amount of 1 W electricity, th e biochar based electrodes (BCp and BCc) were much more cost effective than GAC and GG, in fact more than ten times cheaper, indicating a good potential in larger scale applications. Figure VIII Power density curve normalized by cathode projected area (A) and electrode potentials (cathode, filled symbols; anode, open symbols) versus Ag/AgCl reference electrode as a function of current density in two chamber reactors packe d with GAC, GG, BCp and BCc. Surface Characteristics of Electrode Materials High surface area and low resistance are two fundamental characteristic s to define good electrode materials and affect MFC power output performance. While this section dis cusses the characteristics of surface area and porosity of the four materials, the next

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section elucidates the effects of resistance. Table 1 and Figure IX show the pore distribution of the materials using the Brunauer Emmett Teller (BET) test Results s how that GAC ha s the highest BET surface area of 1247.8 cm 2 /g followed by BCp and BCc with 469.9 cm 2 /g and 428.6 cm 2 /g respectively. GG had the lowest BET surface area of 0.44 cm 2 /g The pore size distribution for GAC is concentrated around 20 30 , whil e the BCp and BCc samples had an average pore diameter of 30 40 range. While the high surface area can explain why GAC obtained a higher power density, as it presumably has high microbial attachment and therefore mor e electron transfer, it is hard to directly correlate the low surface area of graphite with low power output. As shown in the Figure VIII, graphite electrode generated higher power density than the biochar electrode despite its low surface area, and it is believed mainly due to the high conductivity of graphite. Figure IX Incremental pore area with the distribution of pore size

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Studies show that surface area and pore size can be due to a variety of factors including the manufacturing process and feedstock material. T he higher surface area of GAC is primarily caused by t he secondary activation process carried out during manufacturing, in which reactiv e components of the feedstock material were burn away by the use of oxidizing agent s such as steam or carbon dioxide leaving behind a pitted and porous char 21,37 The biochar samples used in this study and GG s did not un dergo this activation step, but the gasification process used to manufacture both biochar samples is thought to promote the formation of higher BET surface area similar as GAC. The gasification proc ess reached a highest treatment temperature (HTT) of 1000 C with a heating rate of 16.6C/min (figure 5), and in the process lignocellulosic materials are converted to a primarily aromatic carbon based char 38 The HTT and heating rate are reported to significantly influence the physical structure of the feedstock materi al during carbonization. For example, studies showed that higher surface area was achieved at temperatures between 650C and 850C, 39 40 41 but sintering and deformation may occur at higher temperatures 41 Brown, et. al. provides further evidence that higher surface area is achieved with higher heating rate and is primarily due to cracking at low temperatures by unevenly heating the feedstock material. These cracks provided access to internal pores that could not be as easily effected by melting and deformity of the feedstock material at high temperatures. Brown, et. al. 42 provides further evidence that higher surface area is achieved with higher heating rate, because suc h process leads to cracking at low temperatures by unevenly heating the feedstock material, and these cracks provided access to more internal pores.

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Along with HTT and heating rate, the inherent porosity and structure of th e feedstock material can also affect the surface area density. Several studies showed that biomass based chars possess high surface area so can be cheaper surrogates for GAC type electrode materials 39,42 In many cases, the archetypal cellular structure of the parent feedstock material is identifiable in chars derived from botanical origin resulting in a honeycomb like structure that significantly contributes to the majority of macroporosity. Although there is a growing body of literature on the effects of manufacturing methods on the chemical and physical properties of biochar and other biomass based absorbance materials, there is little understanding of how surface area density and pore size distribution effects microbial growth, abundance, and adhesion. This study highlights that microporosity is important for increased power density, but additional research is needed to refine the manufacturing of biochar in order to increase the desired Figure X Temperature profile and residence time of BCp and BCc gasification

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characteristics as MFC electrodes while maintaining the economic and environmental benefits. Resistance Characteristics of Electrode Materials Similar as surface area, internal resistance ( R i ) is one of the major factors effecting power density in MFCs. The total R i can be separated into activation resistance (R p ), ohmic resistance (R s ) and concentration resistance 14 R p occurs when electrons are transferred to or from a compound, primarily during oxidation/reduction reactions and relates to the catalytic effici ency near or on the electrode surface. The concentration resistance is due to the rate of mass transport to or from the electrode. While R s occurs due to the resistance of electron and ion transfer through the solution, electrodes, and membrane. E lectro chemical impedance spectroscopy (EIS) is a techniqueused to measure chemical and physical processes in solution and can help to separate out the different internal resistances in MFC reactors. By graphing the data collected from EIS and constructing a Nyq uist plot,R i and R s can be calculated ( F igure XI ). According to our EIS results, GG has the lowest R s can be seen in T able 1 with GG having 0.4 0. 5 mm 1 followed by BCc with 3 1 mm 1 BCp with 6 1 mm 1 and GAC with the highest surface resistivity of 8 2 mm 1 However, GG and GAC had a similar total R i respectively, while BCp and BCc had a higher R i (Table II ). The R s is responsible for nearly 86%, 62%, 74%, and 68% of the total R i in the GAC, GG, BCp, and BCc, reactors respectively, but cannot account entirely for the

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difference in the observ ed power densities. The R p Because of the biochars lower R s compared to GAC, it is believed that the R p is the primary reason for the dif ferences in power density. It is generally accepted that the catalytic activity of the anode is due primary to microbial biomass density and surface area density and combined have been shown to positively correlate with R p lower R p and lower R i ca n thus be explained by its higher surface area density, which makes up for its higher R s When comparing BCp with BCc, the differences in power density can also be attributed to differences in surface area density. Although BCp has higher BET surface ar ea and a lower surface resistance, its larger particle size limits its surface area density, which results in a higher R p and resulting higher R i Figure XI System resistance of the reactors filled with four different anode materials

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Our results further emphasis the need to develop electrodes with high surface area density and low resistance. However, this should not come at higher costs or environment impact. The development of graphiti c structures in biomass based electrode material is due to the thermal treatment of the carbonaceous feedstock mater ial, where carbon rearranges into small grap hitic crystallites at temperature 700C 800C 30,31 These graphitic zones have delocalized pi electrons that facilitate the flo w of electrical current. Resistance through the graphitic zones is based on the degree of purity and orientation. Other studies have shown that biomass treated at high temperatures can have both high surface area and low resistance and could function as electrodes or supercompasitors 43,44 Converting non conductive biomass into electrode materials has been demonstrated and because of the stored chemical energy in the feedstock material could be energy positive, but further research is needs to develop the optimal methodology to achieve maximum surface area and conductivity while reducing the amount of energy and environmental impact. Doing so could help to lowe r the cost of electrode material, increase the feasibility of scaling up MFC technologies, and reduce environmental impact Biochar Electrode Life Cycle and Cost Analysis There are a variety of feedstock materials and manufacturing techn ologies used to make biochar, but it is generally accepted that high yield, low emission pyrolysis and gasification biochar manufacturing and land application is as a way to simultaneously sequester carbon, produce energy and increase crop production. The methods employed to make biochar with high surface area density and low resistance could be emphasized to produce electrodes materials for MFCs while maintain its environmental and economic

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benefits. Moreover, the use of biochar as an electrode material in MFC reactors, especially for wastewater treatment, could add an additional step to further expand its life cycle benefits and in doing so could also reduce the cost and increasing the feasibility of large scale deployment of MFCs sequestration potential is largely due to conversion of biomass C to biochar C, a much more recalcitrant form which slows the rate at which photosynthetically fixed C returns to the atmosphere 45 This conversion process sequesters around 50% of the biomass C, significantly greater than that retained fro m burning (3%) or biological decomposition (<10 20% after 5 10 years) 46 Using higher temperatures (>800C), such as those employ ed to make high surface area and conductive chars increases fixed C ratio and stability of the material 47 Although the yields from high temperature treatments are often lower, much of the loss in weight is due to the off gassing of volatile organic components of the feedstock. GAC and GG also have high concentrations of C, but when coal is used as the feedstock material, the C is derived from fossil sources and is not part of the current cycle. The pyrolysis of coal only increases the total atmospheric C concentration, along with other toxic substances such a mercury and sulfur. This further emphasizes the importance of feedstock material and manufacturing methods when determine the impact of electrode materials. Si milar to GAC, any carbonaceous material could be used as a feedstock in the pro duction of biochar electrodes. Biowastes, such as forestry, milling, and agricultural residue, along with yard clippings and construction waste are the feedstock of choice beca use of their reliable supply low cost high lignin content, and high surface area and conductivity when manufactured at high temperatures 48 Coal is most commonl y used in

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GAC manufacturing because of its lower cost and high carbon content. However, using biowaste with little to no commercial value and local availability greatly reduces the cost of feedstock purchasing compared to coal. In this study we used lodg epole pine chips and lodgepole pine sawdust pellets as the feedstock material Both of these materials are locally available and are either considered biowaste or made from biowaste. Data on U.S. supplies suggest that 0.012 Pg C yr 1 and 0.024 Pg C yr 1 of biochar could be produced from forestry residue and mill residue 46 This is a stark comparison when you consider that there ar e no graphite mines in the U.S. and few globally 49 Although feedstock characteristics and availability are important to ensure a high quality product and to maintain a steady supply, manufacturing methodology also contributes significantly to the environmental impact, final characteristics and cost of manufacturing biochar electrodes. Table II List of MFC reactors in this study and t heir specifications Anode Material Total BET SA (m 2 ) R s R i Maximum Power Density mW/m 2 W/m 3 CE (%) Material Cost(US$)/W a GAC 3.68 34.9 40.3 674 10 7.32 10 47 0.7 $ 402.80 GG 0.002 24.9 39.9 566 5 6.15 5 35 0.1 $3 9 2.62 BCp 0.52 34.3 46.2 532 18 5.78 18 41 0.4 $ 23.88 BCc 0.32 29.7 4 3.4 457 20 4.97 20 43 0.1 $ 35.79 a Material cost per W att produced was calculated by dividing electrode material cost in anode chamber by maximum power density As described above, biochar is the result of the pyrolysis or gasification of biomass. Th e elevated temperatures needed to carbonize the feedstock material are general produced by the combustion of the syngas released during pyrolysis of the feedstock. In this way, the chemical energy stored in the feedstock material is used to

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fuel the carbo nization process. The manufacturing of GAC also uses a similar technique but often times an additional energy source is used to control the reaction rate and fuel thermal activation. Biochar does not traditionally undergo activation, but air flow through the reactor during gasification can perform similar purposes. The biochar samples used in this experiment were manufacturing using a top lit up draft gasifier converting th e biomass to char. The syngas is directly combusted at the top of the kiln, increasing the internal temperature and passively pulling air up through the bottom. The air flowing through the reactor is thought to react with the surface of the char material similar to the activation step in GAC, increasing the surface area density. This is achieved with minimal external energy. TLUD gasifier is just one example of variety technologies that can be used to manufacture biochar electrodes, pyrolysis, gasifica tion, hydrothermal, and flash carbonization being the most thoroughly study 25 No matter wha t technology is employed, high yield, low emissions, and parameters that increase the surface area and conductivity should be emphasized to produce the most sustainable and cost effective electrode materials possible. Figure XII Flow chart of manufacturing methods of e lectrode materials used in this study

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Along with energy production, land application of biochar has shown additional C offsets and cost reductions. The benefits of biochar addition to agricultural soils includes improved water and nutrient retention, increase crop yield, suppressed N 2 O emissions, reduce ferti lizer requirements, and increased soil organic carbon content 50 We suggest that compos ting and soil application of spent MFC electrode material, especially in the case of wastewater treatment, could also have similar, if not increased, beneficial effects on agricultural production. Several studies have shown that high surface area biochars have increased absorbance capabilities 51,52 When used as an elec trode material in MFCs treating wastewater, valuable micronutrients could be adsorbed and slowly released in agricultural field after application. The thick exoelectrogenic biofilm established on the biochar electrode surface during wastewater treatment c ould also help to increase the biological diversity and abundance in agricultural soils. If sorbed contaminates or pathogens are of concern, composting could be utilized to allow ample time for elevated temperatures and enhanced microorganism activity to biodegrade any pollutants. However, recent research on biochar and carbon absorbents has shown little migration of pathogens or leaching form contaminated materials 53 If sufficient evidence is collected to demonstrate the beneficial use of spent biochar electrodes as agricultural amendments, it could significantly offset t he cost of MFC construction and operation. It is evident that additional research is needed to refine the production method and full life cycle use of biochar electrode materials. Great care should be taken to select feedstock material with little economi c value, while maximizing the energy output during manufacturing. Manufacturing parameters should also be set to produce chars with increased surface area density and conductivity to increase their performance in MFCs.

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Additional research is also needed to test the feasibility of land application of spent biochar electrodes. C onclusion High temperature biochar materials, made form lodgepole pine chips (BCc) and lodgepole pine sawdust pellets (BCp), were tested for the first time as an electrode materia ls in a microbial fuel cell. BCp and BCc should satisfactory power density of 532 18 mW m 2 and 457 20 mW/m 2 respectively compared to 674 10 mW m 2 and 566 5 mW m 2 for GAC and GG respectively. Differences in power density can be attributed to t he lower surface area density than GAC and high surface resistance than GG. However, biochar electrode material cost have been estimated at 51 356 US$/tonne, up to ten times cheaper that GAC (500 2500 US$/tonne ) and GGs (500 800 US$/tonne) Biochar elect rode manufacturing also carries additionally environmental benefits, including biowaste feedstock, energy positive manufacturing, and carbon sequestration potential. We also suggest spent biochar electrode material could be used as an agricultural amendme nt, further increasing its life cycle benefits and subsidizing its cost. Although further research is needed to optimize the manufacturing method of biochar electrode production and increase its performance, the use of biomass derived electrode materials ring in a new era of material use in MFCs with additional economic and environmental benefits.

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CHAPTER I V BIOCHAR LCA AND CARBON ACCOUNTING Introduction Global atmospheric greenhouse gas (GHG) concentrations are rapidly increasing and concerns about anthr opogenic climate change are sparking interest in carbon sequestering technologies. Although t here are several methodologies being explore, biochar production and its use as a soil amendment has been gaining worldwide attention due to its carbon sequeste ring potential, benefits to the agricultural sector, co energy generation, and its use of waste biomass as a feedstock material Biochar is a crude form of activated carbon produced through the combustion of biomass, in a limit oxygen environment, with the attentional use as an agricultural amendment. P yrolysis and gasification are the most widely used and thoroughly studied methods of manufacturing, where high temperatures and controlled oxygen exposer are used to convert biomass into primarily recalcitra nt carbon. Biochar is comprised mostly of carbon (97%), ash (3%) and some trace minerals (<1%) although the physical and chemical features vary greatly depending on feedstock and manufacturing methods The volitization of organic matter from the origina l feedstock material creates syngas that can be further combusted, for co energy generation, or refined to produce bio oils. Traditionally biochar has been used as an agricultural amendment, in most cases, increasing crop yield and decreasing the need f or fertilizers 47 D epending on soil type, biochar can help mitigate N2O emissions from agricultural soil 54 It is also used in land reclamation projects, because of its water and nutrient absorption capabilities 55 And

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more recently biochar is being investigated as a low cost electrode material in microbial fuel cell s. Biochar has the potential to sequester carbon because of its biomass feedstock use, high carbon content, and stability during use 45 However, there have been few case ore research needs to be done in order to quantify the total GHG emiss ions during the production of biochar compared to the amount of carbon being sequestered in its final use and that of the traditional fate of the biomass. There have been several LCA conducted on biochar 45,50,56 but they have only focused on hypothetical examples and theoretical models. In this study we take direct emissions data from field based slow pyrolysis biochar production using forestry residue, and compare it to the more common treatment methods, field burning and decomposition. Goal and Scope The goal of this study is to calculate the total carbon balance and GHG emissions of biochar prod uction compared to the more traditional fate of forestry residue. Using 1 kg of biomass as the functional unit, a process based LCA ana lysis is used to inventory total GHG emissions ( CO 2 N 2 O, and CH4) released during biochar production and transportation The carbon content of the biochar and the GHGs associated with the alt ernative fate scenarios is also subtracted from the GHG inventory of production and the carbon sequestration potential is assessed.

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Research Methodology An LCA analysis is conducted a ccording to commonly excepted procedure. The entire life cycle of biochar production is evaluated from cradle to grave. The transportation data was collected and compiled from EPA emission reports 57 The emissions and technical process specifications was collected from reports and consultations given by the facility managers themselves Emissions associated with the alternative fate of forestry residue were taken from a Stockholm Environmental Institute report 5 8 Case Study: Biochar Production in Golden Colorado Company Description Biochar Engineering Corporation (BEC) is a design fabrication company in Golden Colorado that focuses on biochar and co energy production. BEC optimizes its biochar production for h igh sorption properties and fixed carbon content. Their pyrolysis machines are designed for mobility and can be transported on site of biomass storage locations, reducing the need to transport the biomass feedstock. Technology Description BEC uses a t wo stage process with their Beta Base Unit (a mobile ton/hr production unit). During the first stage the material is carbonized in an aerobic environment. Temperatures at this stage range between 700 750 o C, for a duration of less than one minute. By c ontrolling the ratio of air to biomass, they can ensure that it is kept below the combustion ratio. Using this process they can also ensure the preservation of solid carbon. During the second stage the material is kept in a sweep gas environment at

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temp eratures between 200 500 o C for approximately ten to fifteen minutes. The gas produced by the pyrolysis of biomass in the first stage, which is mostly composed of N 2 H 2 CO, CH 4 and higher VOCs and trace gases, is used as the sweep gas in second stage. Biochar ranging from 1.5 cm long by 1 cm wide and .5 cm thick is produced. System Boundary The system boundary includes the on site collection and processing of forestry residue to chip, the processing of chip to biochar, and the transportation of biochar to end use customers. This process is consistent with the real world production of biochar using BEC technology. We did not include the GHG mitigation associated with the end use of biochar in our LCA because there is no consistent scientific data and depends on several variables including soil type, application rate, and local climate. For comparison, we used GHG emissions data on more tradition forestry residue fates 59 In most cases the residue left behind after a forestry operation is collected, piled, and burned (11) In some cases the residue is scattered and left to decompose. For the purpose of this analysis we c ompare the GHG emissions from the on site decomposition and combustion of forestry residue. Figure XIII Flow Diagram for Biochar production

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Data Collection Methodology Forestry Residue Processing Forestry residue is mostly comprised of small diameter trees, branches, and the tops of commercial timber co llected during logging operations. We assumed that the material has dried and all of the needles have fallen off. This method is consistent with other forestry residue analyses 58,60,61 Collection and processing operation was modeled after the current operations of Grays Harbor Paper an d Hermann Bros. GHG emissions associated with the collection and processing of the forestry residue was collected from Pyrolysis Emissions Stack emissions were collected from BEC, using methods that are required by the EPA for air pollution reporting. The biomass feedstock used during the emissions testing was comprised of chipped forestry residue, mostly lodg e pole pine chip. Some propane and electricity use for the pyrolysis process is also calculated into the total emissions. Transportation Emissions The emissions associated with the transportation of biochar to the end user was collected from the EPA vehicle emission s report 57 Biochar was assumed to be transported with a semi for 200 miles round tri p with a 10 mpg average. 100 miles is the average distance from forestry operations in the Rocky Mountains to agricultural field on the front range of Colorado.

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On site Decomposition and Combustion of Forestry Residue Emissions data associated with the on site decomposition and combustion of forestry residue was collected from the Stockholm report. Emission factors and data resources relied on current published literature, reports, site visits, and air emissions data reported by state agencies. For o n site decomposition it is assumed that the material is scattered and left to decompose, emissions are associated with a decay period of over 100 yr. Although, some reports indicate methane emissions associated with decomposition, this report assumes that residue piles do not facilitate anaerobic conditions and there is no methane release. For the on site combustion it is assumed forestry residue is gathered into piles and ignited by hand. Biochar Stable Carbon Content Data on the stable carbon content wa s collected from laboratory elemental analysis carried about by BEC.

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GHG Inventory and Carbon Accounting Figure XIV Carbon accounting of biochar production with avoided carbon loss due to combustion of forestry residue Figu re XV Carbon accounting during the production of biochar with avoided carbon loss due to decomposition of forestry residue

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Results and Discussion Global Warming GHG Emissions The total avoided CO 2 e is 333 t CO 2 e/t 1 and 0.083 t CO 2 e/t 1 for the combustion and decomposition avoidance scenarios respectively. According to our results, the total GHG emissions associated with the production and transportation of biochar is negative, if you consider the avoided CO 2 e due to combustion or decomposition of the feedstock. Of the total GHG emissions during the processing of biochar, pyrolysis is responsible for the majority or 79% of the total GHGs emitted. Much of the reduction in GHG emissions can be contributed to the use of a waste f eedstock that would otherwise be combusted or decompose on site. The mobile unit also allows the production of biomass on site without the additional need to transport the feedstock before processing. Carbon Accounting The total C sequestered during the processing of biochar is .189 t C/t 1 and .109 t C/t 1 for the combustion and decomposition avoidance scenarios respectively. This indicates that there is more C sequestered during the processing of biochar than there is if the fate of the forestry re sidue was on site combustion or decomposition. Much of the carbon sequestration can be attributed to the avoidance of on site combustion or decomposition; however the stable C content of the biochar contributes 20% of the total carbon sequestration. Proc ess Refinement Recommendations Although our results indicate that the production of biochar using forestry residue is GHG and carbon negative there is room for further improvement, including co

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production of heat and power. Co production of heat and elect ricity would off set the use of fossil fuel combustion and/or natural gas. Many pyrolysis machines incorporate co production into their systems. Utilizing the syngas and heat produced during the pyrolysis process, electricity and heat can be used for dom estic consumption. In the Denver region, 1.75 lb or CO2e is emitted per kWh 62 depending on the pyrolysis machine design; this would offset the amount of GHG released into the atmosphere if a traditional method of electricity production is used. C onclusion The production of biochar using waste biomass material has great potential to sequester C and mitigate GHG emissions. There have been several LCAs published claiming this potential, however they use hypothetical models and do not have real w orld data. To our knowledge there has not been an LCA conducted on actual case studies of the production of biochar. This report is the first to get direct emissions data on real world production and use of biochar. The findings of this report demonstra te that biochar production can sequester C and mitigate GHG emissions if waste forestry residue is used as feedstock instead of its alternative fates. Although the findings show GHG mitigation, there is still room for improvement, including co production of electricity and heat, which would further improve the technology.

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CHAPTER V CONCLUSION The goal of this thesis was to demonstrate the possibility of microbial fuel cells (MFCs) for treating wastewater and to use biochar as a more sustainable electrod e material option in MFCs The se studies demonstrate that infact MFC technology can treat wastewater as effectively as traditional aeration treatment, although further research is needed to improve the p rocess. The studies also show that biochar could ef fectively serve as a surrogate for more traditional electrode materials with lower overall cost and environmental impact. These results could be highly impactful with the potential to change the current global wastewater treatment infrastructure from one that is costly, energy intensive, or in the case of developing countries, lacking all together.

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