INTERNATIONAL a direct recovery of electric energy and

INTERNATIONAL UNIVERSITY HCMC

 

SCHOOL
OF BIOTECHNOLOGY

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REPORT FINAL PROJECT

 

 

 

 

Microbial Fuel Cell

 

For Wastewater Treatment

 

 

CONTENTS
 
 
I.                INTRODUCTION.. 2
II.              WASTEWATER
COMPOSITION.. 4
III.            PROCESS. 5
IV.            ROLE
OF MFCS. 13
V.              ADVANTAGE
& DISADVANTAGE: 15
VI.            APPLICATION
OF MFC IN BEER BREWERY WASTEWATER.. 15
VII.          CONCLUSION.. 19
VIII.        REFERENCES. 19
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                                                                                                            

 

 

 

 

 

 

 

 

 

 

 

      
I.           
INTRODUCTION

 

1.     
General information:

Contaminated wastewater
sources give rise to environmental pollution (on the surface or underground
water bodies). Wastewater treatment has become a major concern in many
countries due to its benefit as drinking source for human and this is a crucial
solution, a basic sanitation to protect environment.

Many phenomenon
including eutrophication of surface waters, hypoxia, and algal blooms impairing
potential drinking water sources are specific consequences of direct disposal
of unprocessed water generating from domestic, agricultural, industrial and
small-scale facilities. Yet the ways to overcome these environmental impacts
have not much yielded desired efficiency.

Rapid industrialization
and overgrowth of population are two main causes that current wastewater
treatment technologies are not sustainable to meet the ever-growing water because
those energy- and cost-intensive techniques is dominant over for development of
technologies that are energy-conservative or energy-yielding.

For the present and
future context, microbial fuel cells (MFCs) technology, which present a
sustainable and an environmental friendly route to solve the water sanitation
problems, may become one of most noticeable technique for wastewater treatment.
The newly wastewater treatment –  Microbial
fuel cell (MFC) – employ the concept of bioelectrochemical catalytic activity
in which microbes/bacteria are main characters that produce electricity from
the oxidation reaction of organic (in most cases), inorganic (some cases), and
substrates collected from any urban sewage, agricultural, dairy, food and industrial
wastewaters.

As shown in many
researches, MFC technology could be highly adaptable to a sustainable pattern
of wastewater treatment for several reasons:

(1)  
Ability
to have a direct recovery of electric energy and value-added products

(2)  
Combination
of biological and electrochemical processes

 => Achieve a good effluent quality and low
environmental footprint

(3)  
Inherent
of real-time monitoring and control

=>
Benefit operating stability.

Fig.
1.
Microbial Fuel Cells produce energy while consume food sources from wastewater

 

2.     
Objective of a project:

The potential for energy
generation and comprehensive wastewater treatment in microbial fuel cells are discussed.

An overview of MFC
application on brewery wastewater treatment is mentioned with two specific
aims:

1)     
Provide
a background of current energy needs for wastewater treatment and potential
energy recovery options followed by a nutrient content in wastewater and a
comprehensive review of the principles of wastewater treatment, substrate
utilization (organic removal).

2)     
Present
process performance, organic removal capacities.

 

 

 

 

 

 

 

 

 

Fig.2.Cleaning Okinawan pig
farm wastewater with MFCs containing
treated and untreated wastewater from the Okinawa Prefecture Livestock and
Grassland Research Center MFCs in the OIST Biological Systems Unit lab

II.               
WASTEWATER COMPOSITION

The composition of the
microbial fuel cell for waste water treatment are shown detail following this
figure:

 

Fig.3. MFC for wastewater treatment with two chambers of cathode-anode.
Microbes fed on various compounds in wastewater sources and transfer electron
to the cathode chamber to be used to produce useful chemicals or remove environmental
pollutants.

For
example:
Brewery Wastewater Treatment

Brewery and food
manufacturing wastewater can be processed by MFCs because there is a rich
content in organic compounds that can serve as food for the microorganisms.
Breweries are ideal for the implementation of microbial fuel cells, as they
remain a steady and stable conditions for easily bacterial adaptations due to their
sane wastewater composition and thus is more efficient. Moreover, organic
substances in brewery unprocessed water are biodegradable, highly concentrated
which helps to improve the performance of fuel cells.

 

III.            
PROCESS

·        
MFC is bioreactor that undergoes the
catalytic reaction to convert chemical energy in the chemical bonds in organic
compounds to electrical energy by microorganisms under anaerobic condition or
capture electrons from electron transport chains by inorganic mediator forming.

 

 

 

Fig.4. Typical type of
microbes can utilize almost any chemical as a food source. In the MFC system,
bacteria form a biofilm, a living community that is attached to the electrode
by a sticky sugar and protein coated biofilm matrix. When grown in an anaerobic
condition, the byproducts of bacterial metabolism of waste comprise of carbon
dioxide molecules, electrons and hydrogen ions. Electrons generated by the
bacteria are shuttled onto the electrode by the biofilm matrix, creating a
thriving ecosystem called the biofilm anode and producing electricity.

 

·        
As opposed to excess sludge and energy issues in conventional
wastewater treatment systems, a better solution to eliminate is to convert directly waste into clean
electricity with high value energy or chemical products. This biological
system is known as bioelectrochemical system (BES).

·        
Bioelectrochemical
systems produce clean energy from waste organic sunstances by applying
indigenous exoelectrogenic bacteria, in which the energy is extracted in the
form of bioelectricity in MFCs or valuable biofuels such as ethanol, methane,
hydrogen, and hydrogen peroxide in case of microbial electrolysis cells.

·        
A cation
exchange membrane also known as proton exchange membrane (PEM) is used for anode
and cathode compartments separation and permeability of proton ions to anode
chamber.

·        
Electrons
releasing in anode chamber will combine with
hydrogen ions and oxygen forming water through electrical circuit.

·        
Where are the microbes
in a Microbial Fuel Cell?

o  
Microbes
accept electrons from organic matter


Electron donors (e.g. acetate: a reducing agent)

o  
Microbes
donate electrons to reducible chemicals


Electron Acceptors (e.g. oxygen: an oxidizing agent)

o  
In
MFC, anode is an electron acceptor

o  

This
below figure shows thick biofilm on wastewater fed microbial fuel cell

 

 

 

 

 

 

The principle of MFC: mostly based on redox reaction

o  
MFC system includes:
an anode, a cathode, a PEM and an electrical circuit. 

o  
Substrates act as
microbial feed that use in MFC are glucose, acetate, acetic acid etc and
influence the overall performance which can be justified sby CE (coulombic
efficiency) and P (power density) parameters.

o  
Wastewaters providing
a good source of organic matter for electricity production and wastewater
treatment accomplishment simultaneously have been used for MFC system to
effectively offset the operation costs for treatment processing.

o  
An MFC is a galvanic cell and the based system is exergonic from electrochemical
reactions.

o  
Energy is released from the reaction and thus it possesses negative
free reaction energy (Gibb’s free energy). The standard free energy can easily
be converted into a standard cell voltage (or electromotive force, emf) DE0 as shown in
Eq. (1).

 

§ 
Where:


DG0 (J/mol): free
energies of respective products and reactants formation.


n (moles): stoichiometry factors of the redox reaction


F Faraday’s constant (96,485.3 C/mol).

§ 
The Gibbs free energy of a reaction measures the maximum amount of
useful work obtained from a thermodynamic reaction.

§ 
The theoretical cell voltage or electromotive force (emf) of the
overall reaction indicates anode and cathode potential differences, leading to
determination the electricity generation capacity in a system in Eq (2).

 

o  
As shown in Eq.
(3), negative free reaction energy leads to a
positive standard cell voltage. This distinguishes a galvanic cell from an
electrolysis cell, as the latter, associated with a positive free reaction
energy and thus with a negative cell voltage, requires the input of electric
energy. The standard cell voltage can also be obtained from the biological
standard redox potentials of the respective redox couples

o  
In an MFC, the Gibbs free energy of the reaction is negative.
Therefore, the emf is positive, indicating the potential for spontaneous
electricity generation from the reaction. For example, if acetate is used as
the organic substrate (CH3COO- = HCO3-
=10 mM, pH 7, 298.15 K, pO2= 0.2 bar), with oxygen reduction, the
combined redox reaction would be shown in Eqs. (3)- (5):

·        
Oxidation – reduction reactions (ORR) in MFCs

o  
Pollutants in the wastewater such as organic substances and other
nutrient products and metals can be used to produce clean and direct
electricity.

o  
Electricity production in MFCs is the result of
oxidation-reduction reactions that result in electron release, transfer and
acceptance through biochemical or electrochemical reactions at the electrodes
in the anode and cathode chambers. One acts as an electron donor while the
other essentially serves as an electron acceptor. The chemical compounds that
are responsible for accepting electrons are called terminal electron acceptors
(TEA).

o  
The following oxidation reduction reactions (Eqs. (6) – (18)) represent possible bioelectrochemical reactions in
microbial fuel cells generating electricity utilizing wastewater as a substrate
(electron donor) and other pollutants such as nitrates, phosphates, and others
as electron acceptors.

o  
Oxidation reactions (anode)

o  
Reduction reactions (cathode)

 

·        
Materials and methods

o  
For
example: Beer brewery
wastewater

Ø 
Wastewater and Organic Substrates.

ü 
Brewery
wastewater was collected from the regulating reservoir of the wastewater
treatment system

ü 
Wastewater
use as the inoculums for the reactor and as substrates.

ü 
Organic
Substrates will use glucose  

ü 
In a
medium containing nutrients, minerals, vitamins stock solution and a phosphate
buffer (PBS)

Ø  Operation

ü  The system will operate in a temperature
controlled room

ü  The reactor will inoculate with wastewater and
operate in continuous flow mode.

Ø  Analyses

ü 
The COD
of the wastewater and other organic compounds will measure according to
standard method:

ü 
The cell
voltage change and the power generation over the resistor at a constant
resistance are continuously will monitor during the period of digestion using
digital millimeter.

Ø  Electric
power calculation

ü 
Unit of
electric power in MFC usually using power density: are of anode unit (W/m²) and
power density per volume of MFC unit (W/m³)

ü 
Coulombic
efficiency (CE) value that should calculate because CE value is show
performance of electricity producing and performance of electron transfer from
substrate to electrode give the energy as product .

 

Ø  Enrichment
of the microbial community in the MFC

ü 
Electron
microscopic observations showed that the fuel cell electrode had a microbial
biofilm attached to its surface with loosely associated microbial clumps.

                            •
Microscopy

                            •
Low-vacuum electron micrographs (LVEM)

                            •
Scanning electron micrographs (SEM)

                            •
Transmission electron microscopy (TEM)

• Confocal scanning laser
microscope (CSLM). The samples were stained with LIVE BacLight bacterial gram
stain kit (L-7005; Molecular Probes)

ü 
Imaging
of MFC biofilms

Ø  Community
structure of the MFC

ü 
Community
structure of the MFC determined by analyses of bacterial 16S rRNA gene
libraries and anaerobic cultivation showed excellent agreement with community
profiles from denaturing gradient gel electrophoresis (DGGE) analysis.

Ø 
Expected results

ü 
MFCs will
be able to degrade biological waste as well as generate electricity products of
wastewater from brewery production.

ü 
MFCs
application on wastewater treatment from brewery processing will be able to
improve the research on invention has high efficiency to treat wastewater which
is possible to scale-up for practical application.

 

IV.            
 ROLE OF MFCS

·        
Organic removal in MFCs

o  
MFCs with synthetic wastewater as substrates: high percentages of
carbon removal (>90%) from wastewaters. Synthetic wastewaters used in the
MFCs include acetate, glucose, sucrose and xylose and many other organic
substrates for microbial oxidation in the anode chamber.

o  
MFCs with actual wastewater as substrates: Municipal wastewaters
have lower BOD concentrations usually less than 300 mg/L which are categorized
as low energy density carriers or feedstocks for MFCs. However MFCs are also
capable of treating high strength wastewaters (high energy density) with BOD
concentrations exceeding 2000 mg/L due to the anaerobic condi- tions in the
anode chamber. These high strength wastewater sources generate from food
processing industry, brewer plants, dairy farms and animal feeding operations
and other industrial waste streams.

o  
Effect of process parameters: the efficiency of MFCs is reported
in terms of substrate conversion rate which depends on

§ 
Biofilm establishment, growth, mixing and mass transfer trends in
the reactors

§ 
Bacterial substrate utilization-growth-energy gain kinetics (mmax, the
maximum specific growth rate of the bacteria, and Ks, the bacterial affinity constant for
the substrate)

§ 
Biomass organic loading rate (g substrate per g biomass present
per day)

§ 
The efficiency of the proton exchange membrane for transporting
protons (Liu
and Logan, 2004; Jang et al., 2004)

§ 
Parameters influencing the overpotentials are the electrode
surface, the electrochemical characteristics of the electrode, the electrode
potential, and the kinetics together with the mechanism of the electron
transfer and the current of the MFC.

§ 
 internal resistance of the
electrolyte between the electrodes and the membrane resistance to proton
migration

·        
Nutrient removal in MFCs

o  
Wastewater leaving the anode chamber is rich in nitrogen and
phosphorous compounds. However, these nutrient compounds can be efficiently
removed in MFCs especially in biocathode chambers to enhance the effluent water
quality or they can be recovered as ammonia or magnesium ammonium phosphate
(MgNH4PO4.6H2O)
known as struvite.

·        
Metal removal in MFCs

o  
Metal ions present in wastewater do not biodegrade into harmless
end products and therefore require special methods for treatment. Moreover,
some of these heavy metal-containing groups have high redox potentials, and
these could, therefore, be utilized as electron acceptors in order to reduce
and precipitate. If incorporated, this method could equip MFCs not only to
serve the function of removing heavy metal ions in wastewater, but also as a
method for recovering heavy metals.

 

V.               
ADVANTAGE & DISADVANTAGE

 

1.     
Advantages:

There are several
advantages that are concerned:

§  MFC technology
contributes to sustainable wastewater treatment

§  Electric energy can directly extract from organic matters in
wastewater

§  Achieving the power while wastewater is
treat

§  Show a better decontamination performance, especially for
removal of aqueous recalcitrant contaminants including many persistent
contaminants.

§  Have a low carbon footprint, arising from less fossil-related
CO2 production as a result of low energy
consumption as well as ability for CO2 sequestration in some reactors with a
specifically designed cathode.

§  Microorganisms typically
develop into a biofilm on electrodes in MFC, which confers their good resistance
to toxic substances and environmental fluctuations.

 

2.     
Disadvantages:

§ 
Bacterial
metabolic losses

§ 
Low
power density

§ 
High
initial cost

§ 
Limited
use, only use for dissolved substrate

 

VI.            
APPLICATION OF MFC IN BEER BREWERY WASTEWATER

 

1.     
Characteristics of beer brewery wastewater:

2.     
Set up double chambers:

MFC consisted of two chambers that are constructed with 6 cm×5 cm×6 cm
in size, each chamber contained a liquid working volume of 0.1 L and separated
by a proton exchange membrane (PEM).

Anode: three parallel groups of carbon fibers, which were wound on two
graphite rods (?8 mm, 5 cm long) to form 3-sheet structures (4 cm×3 cm);

Cathode: plain carbon felt (6 cm×6 cm, 3 mm thick with biofilm). In the
bottom, an aerator was inserted to supply air and mixing.

Inlet and outlet with respect to every side constructed at both anode
and cathode, while on the top, six electron tip jacks with a diameter of 9mm
were set up. Associations between two electrodes were aggravated for copper
wires through a rheostat (0. 1–9999 ?).

The external resistance
(R): 100 ?.

The cell voltage (V) of
the MFCs: 50mV

The MFC was worked in continuous flow at room temperature. Raw brewery
wastewater was pump to the anode chamber with the up-flow rate (13.6 ml/h),
matching to a hydraulic retention time (HRT) of 7.35 h.

Effluent of anode was joined by a beaker, and then it was pumped into
the cathode chamber with the same flow rate with HRT 7.35 h and overall HRT of
this system was 14.7h

3.     
Calculations:

a.      Electrical parameters in practical at normal condition
R=100?:

§ 
According
to Ohm’s law, the current density and power density were calculated as:

 

§ 
The
recorded of current and power
generation details during MFC operation with the function of resistance,
followed by this diagram:

b.      Data of wastewater on seven days:

Data showed that:

§  Influent COD fluctuated from 1249 to 1 359 mg/L corresponding to organic
loading rates (OLRs) of 4.08–4.43 kg COD/(m3·d)

§  91.7%–95.7% 3.87–4.24
kg COD/(m3·d) for substrate degradation rates, SDRs is the overall removal
efficiencies value that were reached, while donations of anode chamber were 45.
6%–49. 4% 1. 86–2. 12 kg COD/(m3·d) to SDRs, which represent over a half
extent.

§  At HRT of 60h, in the cathode, COD removal of 79% was obtained when
brewery wastewater concentration was 1333 mg COD/L.

? Sequential anode-cathode MFC in this experiment can greatly improve
the effluent quality at a much lower HRT. This showed that sequential
anode-cathode MFC has a well capacity in brewery wastewater treatment.

§  In this study, since the influent COD of cathode was high (650–710 mg/L),
the excessive COD entering the cathode may be caused the inferior
electrochemical performance of the MFC. In addition, the low cathodic open
circuit possibility for ?0.034 V also pointed a sign of incipient COD
carry-over. Thus, optimization should be carried out further to improve the
performance of this sequential anode-cathode MFC.

c.      
Discussion:

§  Effluent of anode was connected by a beaker, which kept an HRT of 7.35 for
each chamber => overall HRT of this system was 7.35+7.35 = 14.7 h.

§  Flow rate was 13.6 ml/h=13.6 x 157.73 = 2145.128 gal/day, the same rate
with influent and effluent.

§  Overall influent in 7-days is 1292 mg/L (an average value of influent
COD). Overall effluent in 7-day is 682 mg/L (an average value of effluent COD
of anode, because the treated water was released in anode column) ? % removal
efficiency in anode chamber ={(1292 x 2145.128×8.34)- (682 x2145.128×8.34)/(1292×2145.128×8.34)}
x 100% = 47.2%

§   At an external resistance of 100
?, a steady COD removal efficiency of both chambers (91.7%–95.7% 3.87–4.24 kg
COD/(m3·d) for SDR) was attained.

§  Moreover, at an external resistance of 300 ?, an open circuit voltage of
0.434 V and a maximum power density
of 830 mW/m3 (including
23.1 mW/m2 vs.
cathodic area and 7.5 mW/m2 vs.
anodic area) were attained.

§  With a high COD removal efficiency, it is concluded that the sequential
anode-cathode MFC constructed with bio-cathode in this experiment could provide
a new approach for brewery wastewater treatment.

VII.         
CONCLUSION

Microbial fuel cells
show the potential for a sustainable route to mitigate the growing energy
demands for wastewater treatment and environmental protection. The indigenous
exoelectrogenic microbial communities in the MFCs are capable of degrading various
forms of wastewaters. However, until now, researchers are trying to improve
this system to get highest effectiveness and reducing as much as limitation.
The following issues should be given priority for significant developments in
MFC technology such as incorporating effectively between low cost materials and
cost-effective electricity production in MFCs; wastewaters should be
the focus of future research and process development activities; more in-depth
studies focusing on life cycle impact analysis of the microbial fuel cell technology
should be developed to identify critical areas of development.

 

VIII.      
REFERENCES

1.   
Wastewater treatment in
microbial fuel cells – an overview Veera Gnaneswar Gude, Department of Civil
& Environmental Engineering, Mississippi State University, Mississippi
State, MS 39762, USA

2.   
Wastewater Treatment
with Microbial Fuel Cells: A Design and Feasibility Study for Scale-up in
Microbreweries,
Ellen Dannys, Travis Green, Andrew Wettlaufer, Chandra Mouli R Madhurnathakam
and Ali Elkamel

3.      Electricity generation and brewery wastewater treatment from sequential
anode cathode microbial fuel cell, Qing Wen, Ying Wu,Li-xin Zhao,Qian Sun,and Fan-ying Kong

 

 

 

 

 

 

 

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