INTERNATIONAL WASTEWATER.. 14 VII. CONCLUSION.. 18 VIII. REFERENCES.

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.              ADVANTAGES
& DISADVANTAGES. 14
VI.            APPLICATION OF
MFC SYSTEM IN BREWERY WASTEWATER.. 14
VII.          CONCLUSION.. 18
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 phenomena 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 are 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 presents a sustainable and an
environmental friendly route to solve the water sanitation problems, may become
one of most noticeable technique for 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 substances 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 and so on,
influence the overall performance which can be justified by 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  
In an MFC, the Gibbs free energy of the reaction is negative. Thus,
the emf is positive, which represents the spontaneously potential electricity
generates from the reaction. For example, if acetate is used as the organic
substrate with oxygen reduction, the oxidation-reduction reaction would be
shown in Eqs. (3)- (5):

·        
Oxidation – reduction
reactions (ORR) in MFCs

o  
Pollutants in the wastewater composed of organic substances and
other nutrient products and also metals are sources to produce clean and direct
electricity through oxidation-reduction reactions

§ 
where electron release, transfer and acceptance under biochemical
or electrochemical processes at the anode and cathode electrodes occur.

§ 
one acts as an electron donor while the other must serve as an
electron acceptor.

§ 
the chemical compounds, that take responsibility for electrons
accepting, are known as terminal electron acceptors (TEA).

o  
The following redox reactions, a substrate (electron donor) and
other substances such as nitrates, phosphates, and others as electron
acceptors, as shown in (Eqs. (6) – (18)), introduce some possible bioelectrochemical reactions in MFCs electricity
generation and wastewater utilization spontaneously.

§ 

Oxidation reactions (anode)

 

§ 

Reduction reactions (cathode)

 

 

 

·        
Materials and methods

o  
For example: Beer brewery wastewater

Ø 
Wastewater and Organic Substrates.

ü 
Pollutants are
collected from brewery manufacturing wastewater.

ü 
Wastewater is used
as the inoculums for the reactor and as substrates.

ü 
Organic substrates
will consume glucose as a reducing agent.          

ü 
Nutrients, minerals,
vitamins stock solution and a phosphate buffer (PBS) are components in medium.

 

Ø 
Operation

ü 
The system will run
in a temperature controlled room (room temperature)

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

 

Ø 
Analyses

ü 
The COD measurements
of the wastewater and other organic compounds will be recorded, according to
standard method.

ü 
The chart below
summarizes the procedure for COD concentration.

 

ü 
The change in cell
voltage and the parameter for generating power over the resistor at a constant
resistance are continuously monitored during digestion time using digital
millimeter.

Ø 
Electric power calculation

ü 
Power density
(conversion of recorded voltage at an interval of time): unit of electric power
in MFC system

§ 
 Anode/cathode
unit (W/m²) = U x J current density = I / A (A/m2)

§ 
 Power density per
volume of MFC unit (W/m³) = 1000U x J x A / 0.1

§ 
Where:

v
A: surface area of
anode/cathode (m2)

v
P: power density
(W/m²), (W/m3)

v
J current density
(A/m2)

v
U: voltage yield (V)

v
R: external
resistance (?)

v
1000: unit change

v
0.1: volume of
anolyte (L)

 

ü 
Coulombic efficiency
(CE): displays electricity production and electron transfer from substrate to
electrode (generate energy as product) performance. It is estimated by
integrating the measured current to theoretical current based on the consumed
COD

§ 
CE = CE / CT x 100%

v
CT =
(Fxnxw)/M

v
CE = Ixt

§ 
Where:

v
CT:
theoretical current production

v
CE:
actual current production

v
I: current of MFC
(A)

v
t: time elapsed
between feedings of the anode (s)

v
M:
molecular
weight of substrate (g mol?1)

v
n:
number of moles of electrons exchanged per mole of substrate (n=4 in COD
wastewater)

v
F: Faraday’s constant (C/mol) (F= 96485 C/mol)

v
w: DCOD removed daily (mg/L)

 

Ø 
Microbial community in the MFC enrichment

ü 
As can be seen from
the electron microscopes, 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)

 

ü 
Images of MFC
biofilms in four micrographs

Ø  Community
structure of the MFC: Identify by

ü 
Bacterial 16S rRNA
gene libraries

ü 
Denaturing gradient
gel electrophoresis (DGGE) analysis => Anaerobic cultivation

Ø 
Expected results

ü 
Biological wastes
will be degraded in MFC system as well as electricity products from brewery
wastewater treatment.

ü 
Improvement on research
that yields high efficiency to treat wastewater

                            =>
A possible result to scale-up for practical application.

 

IV.            
 ROLE OF MFCS

 

·        
Organic removal

o  
Synthetic wastewater as substrates (acetate, glucose, sucrose,
xylose and other organic substrates for microbial oxidation): carbon removal
(>90%) is high from wastewaters in the anode chamber.

o  
Actual wastewater as substrates (low BOD, low energy density
carriers or feed stocks): still capable of treating high strength wastewaters
thanks to anaerobic conditions in the anode chamber.

o  
Effect of process parameters: in terms of substrate conversion
rate, depending on:

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

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

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

§ 
Proton exchange membrane efficiency

§ 
Overpotentials due to electrode surface, electrochemical
characteristics, electrode potential, kinetics, electron transfer mechanism and
the current.

§ 
 Internal resistance

§ 
Membrane resistance to proton migration

·        
Nutrient removal

o  
Efficiently removed in biocathode chambers

=>
Enhance the effluent water quality

o  
Recovered as NH4+ or MgNH4PO4.6H2O,
preferred to struvite.

·        
Metal removal

o  
Non-biodegradable: Utilized as electron acceptors

=> Reduce and
precipitate.

o  
If incorporated: Equip the ability to remove and recovery heavy
metal ions in wastewater.

 

V.               
ADVANTAGES & DISADVANTAGES

 

1.     
Advantages

There are several advantages that are concerned:

§ 
Application
of MFC technology to sustainable wastewater treatment yield positive efficiency

§ 
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

§ 
Typically
developing of microorganism into a biofilm on electrodes in MFC show 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 SYSTEM IN 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).

 

Fig.
5. Sequential
anode-cathode MFC diagram

 

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): 300 ?.

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

The MFC was worked in continuous flow at
room temperature. Raw brewery wastewater was pumped 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.

 

3.     
Calculations

a.      Electrical
parameters in practical

§ 
According
to Ohm’s law, the current density and power density were calculated at R=300?
and U= 0.02 V that yielded from MFC long-term operation

_ Current density:

At anode electrode: A = 6 cm×6 cmx3 = 108cm2 =
0.0108m2

J = I/A =
U/ (RxA) = 0.02 / (300×0.0108) = 0.006 (A/m2)

At cathode electrode: A’= 4 cm×3 cm = 12cm2 = 0.0012m2

J = I/A =
U/ (RxA) = 0.02 / (300×0.0012) = 0.056 (A/m2)

            _ Power density:

At anode electrode: A = 6 cm×6 cmx3 = 108cm2 =
0.0108m2

           P = 1000U x J x
A / 0.1 = 1000×0.02×0.019×0.006 / 0.1 = 0.0228 (W/m3)

At
cathode electrode: A’= 4 cm×3 cm =
12cm2 = 0.0012m2           

           P =
1000U x J x A / 0.1 = 1000×0.02×0.056×0.0012 / 0.1 = 0.01344 (W/m3)

§  Coulombic efficiency (CE) was determined by:

o  
 In day 1for NH3 – N in wastewater:  influent of COD was 1299 mg/L and effluent COD
of anode chamber was 657 mg/L. According to the practical, MFC operation was
recorded with the feed cycle time is 24 hour (86400s):

                               CE = CE/CT x 100% = (I
x t) / (F x n x w) / M x 100%

                   = (0.02/200 x 86400) / 96485 x 4 x (1299-657)
/ 17 x100%

                                     = 172800/14574910= 1.19%

b.      Data
of wastewater on seven days:

Data showed that:

§ 
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 /157.73 = 0.086 gal/day
= 13.6×0.024 = 0.3264 L/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 = (Removed/Influent x 100%)

       = (Influent-Effluent)/Influent x100%

 

ð 
%
Removal in anode chamber = (1292- 682/(1292) x 100% = 47.2%.

§ 
Influent COD fluctuated from 1249 to 1359 mg/L
corresponding to organic loading rates (OLRs) of 4.08–4.43 kg COD/(m3·d)
in 0.1L of working volume. The organic loading rates corresponding to 1249 mg/L
COD influent was calculated by:

 

ð 
Organic loading rate=COD in
(kg/L)xFlow rate (L/day)/Reactor volume (m3)

 

      = (1249×10-6×0.3264)
/ (0.1×10-3) = 4.08 kg COD/(m3.d)

§ 
91.7%–95.7%
is the overall removal efficiencies value that reached, while donations of
anode chamber were 45. 6%–49. 4% 1.86–2. 12 kg COD/(m3·d) to substrate
degradation rates (SDRs), which represent over a half extent. The substrate
degradation rate indicates the rate for COD removal during the cycle operation
corresponding to 1249 mg/L of COD influent that yielded 4.08 kg COD/(m3.d)
in OLR by 45.6% COD removal from anode contribution was measured by:

 

ð 
Substrate degradation rate=OLR x %
substrate removal efficiency at t time

 

    = 4.08 x 45.6% = 1.86 kg COD/(m3.d)

 

c.      
Discussion:

§ 
At an external resistance of 300 ?, a steady COD
removal efficiency of both chambers (91.7%–95.7%) was attained.

§ 
Moreover, R=300 ?, an open circuit voltage of
0.434 V and a power density includes 0.01344 (W/m3) vs. cathodic area and 0.0228 (W/m3)
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.

§ 
HRT value was 14.7h (>10 h) for the whole
system indicating the effectiveness of MFC 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.

 

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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