I. to meet the water sanitation needs. Microbial fuel

 

I.                  
INTRODUCTION

1.     
General information:

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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.

Direct disposal of
wastewater generating from various sources such as domestic, agricultural and
industrial facilities is the major cause for various environmental impacts 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

Current wastewater
treatment technologies are not sustainable to meet the ever-growing water
sanitation needs due to rapid industrialization and population growth, simply
because they are energy- and cost-intensive leaving latitude for development of
technologies that are energy-conservative or energy-yielding.

For the present and
future context, microbial fuel cells technology may present a sustainable and
an environ- mentally friendly route to meet the water sanitation needs.
Microbial fuel cell (MFC) based wastewater systems employ bioelectrochemical
catalytic activity of microbes to produce electricity from the oxidation of
organic, and in some cases inorganic, substrates present in urban sewage,
agricultural, dairy, food and industrial wastewaters. Especially, MFC
technology could be highly adaptable to a sustainable pattern of wastewater
treatment for several reasons: (1) it enables direct recovery of electric
energy and value-added products; (2) good effluent quality and low
environmental footprint can be achieved because of effective combination of
biological and electrochemical processes; and (3) it is inherently amenable to
real-time monitoring and control, which benefits good operating stability.

2.     
Objective of a project:

This report presents the
potential for energy generation and comprehensive wastewater treatment in
microbial fuel cells. The article provides an overview of MFC application on
brewery wastewater treatment with two specific aims. First, it provides an
overview of current energy needs for wastewater treatment and potential energy
recovery options followed by a comprehensive review of the principles of
wastewater treatment, substrate utilization (organic removal), recent process
developments, nutrient and metal removal capacities in microbial fuel cells.
Several issues related to process performance, organic removal capacities and
potential environmental impacts were discussed in detail.

 

 

 

 

 

 

 

 

 

Fig.1.Cleaning Okinawan pig
farm wastewater with microbial fuel cells. MFCs in the OIST Biological Systems Unit lab
containing treated and untreated wastewater from the Okinawa Prefecture
Livestock and Grassland Research Center.

II.               
WASTEWATER COMPOSITION

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

Fig.2. Microbial fuel cell for wastewater treatment with a chemical
cathode: anode chamber can be fed with various wastewater sources while the
cathode chamber can be used to produce useful chemicals or remove environmental
pollutants.

For
example:
Brewery Wastewater Treatment

Brewery and food
manufacturing wastewater can be treated by microbial fuel cells because their
wastewater is rich in organic compounds that can serve as food for the
microorganisms. Breweries are ideal for the implementation of microbial fuel
cells, as their wastewater composition is always the same; these constant
conditions allow bacteria to adapt and become more efficient.

 

III.            
PROCESS

·        
MFC
is bioreactor that converts chemical energy in the chemical bonds in organic
compounds to electrical energy through catalytic reaction of microorganisms
under anaerobic condition.

 

Fig.3. Bacteria have evolved
to utilize almost any chemical as a food source. In the microbial fuel cell,
bacteria form a biofilm, a living community that is attached to the electrode
by a sticky sugar and protein coated biofilm matrix. When grown without oxygen,
the byproducts of bacterial metabolism of waste include carbon dioxide,
electrons and hydrogen ions. Electrons produced by the bacteria are shuttled
onto the electrode by the biofilm matrix, creating a thriving ecosystem called
the biofilm anode and generating electricity.

·        
Direct conversion of waste into clean electricity or high value
energy or chemical products was recognized as a better option to eliminate the
excess sludge and energy issues in conventional wastewater treatment systems.

·        
Biological systems that convert chemical energy (in the form of
organic substrate in wastewater) into electrical energy or other high value
products are known as bioelectrochemical sys-tems (BESs). Bioelectrochemical
systems harvest clean energy from waste organic sources by employing indigenous
exoelectrogenic bacteria. This 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 to
separate the anode and cathode compartments.

·        
Where
are the microbes in a Microbial Fuel Cell?

o  
Microbes
accept electrons from organic matter


Electron donors

o  
Microbes
donate electrons to reducible chemicals


Electron Acceptors (e.g. oxygen)

o  
In
MFC anode is an electron acceptor

o  

Thick
biofilm on wastewater fed microbial fuel cell

 

 

 

 

 

 

The principle of MFC

 

o  
MFC consists of an
anode, a cathode, a proton or cation exchange membrane and an electrical
circuit. 

o  
 A large number of substrates have been
explored as feed use in MFC such as glucose, acetate, acetic acid etc.

o  
Various of wastewater
have been used as substrates in MFCs which providing a good source of organic
matter for electricity production and accomplish wastewater treatment simultaneously,
thus may offset the operation costs of wastewater treatment plant.

o  
An MFC is a galvanic cell. The electrochemical reactions are
exergonic, i.e. the reaction possesses negative free reaction energy (Gibb’s
free energy) and this proceeds spontaneously with energy release (electric or
electron release). The standard free energy can easily be converted into a
standard cell voltage (or electromotive force, emf) DE0 as shown in Eq. (1).

o  
Here, the DG0 values
represent the free energies of formation of the respective products and
reactants (J/mol), n (moles) represents the stoichiometry factors of the redox
reaction, and F Faraday’s constant (96,485.3 C/mol). The Gibbs free energy of a
reaction measures the maximum amount of useful work that can be obtained from a
reaction of thermodynamic system. The theoretical cell voltage or electromotive
force (emf) of the overall reaction (the difference between the anode and
cathode potential) determines if the system is capable of electricity
generation 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

§  Directly extract electric energy from organic matters in
wastewater

§  Waste water treatment
and power generation at the same time

§  Show a better decontamination performance, especially for
removal of aqueous recalcitrant contaminants including many persistent
contaminants. This superior performance of MFC is likely due to the
co-existence of anaerobic and aerobic microenvironments, which allows many
reactions that are inherently incapable by strict anaerobic or aerobic
technologies.

§  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 was constructed by two chambers (6 cm×5 cm×6 cm, each with a liquid
working volume of 0.1 L) 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); plain
carbon felt (6 cm×6 cm, 3 mm thick with biofilm was used as cathode. An aerator
was inserted in the bottom of cathode chamber to supply air with an aquarium
pump and provide mixing.

Both anode and cathode chambers were constructed with a water inlet and
outlet on each side, while six electrode tip jacks with a diameter of 9 mm were
set up on the top. Connections between two electrodes were made with copper
wires through a rheostat (0.1–9999 ?).

The external resistance
(R) was set to 100 ?.

The cell voltage (V) of
the MFCs was measured 50mV

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

Effluent of anode was connected by a beaker, and then it was pumped into
the cathode chamber with the same flow rate, which kept an HRT of 7.35 h. Thus
the overall HRT of this system was 14.7 h.

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 between 1249 and 1 359 mg/L corresponding to
organic loading rates (OLRs) of 4.08–4.43 kg COD/(m3·d)

§  Overall removal efficiencies of 91.7%–95.7% 3.87–4.24 kg COD/(m3·d)
for substrate degradation rates, SDRs were achieved, while contributions of
anode chamber were 45.6%–49.4% 1.86–2.12 kg COD/(m3·d) for SDRs,
which account for about a half proportion.

§  Compare to the performance of an air-cathode MFC treating brewery
wastewater at an HRT of 60 h, and found a 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, indicating that sequential
anode-cathode MFC has a well capacity in brewery wastewater treatment.

§  Since the influent COD of cathode in this study was high (650–710 mg/L),
the inferior electrochemical performance of the MFC may be due to the excessive
COD entering the cathode. In addition, the low cathodic open circuit potential
of ?0.034 V in this experiment also indicated a sign of incipient COD
carry-over. Therefore, the performance of this sequential anode-cathode MFC can
be further improved by optimization.

c.      
Discussion:

§  With an HRT of 14.7 h (Raw brewery wastewater was fed by a peristaltic pump (Longer
BT100-1 J, China) to the anode chamber, corresponding to an HRT of 7.35 h.
Effluent of anode was connected by a beaker, which kept an HRT of 7.35 =>
overall HRT of this system was 7.35+7.35 = 14.7 h.

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

§  Overall influent in 7-day 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 e 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%

§   A steady COD removal efficiency (cathode
and anode chambers) of 91.7%–95.7% 3.87–4.24 kg COD/(m3·d) for SDR
was achieved at an external resistance of 100 ?.

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

§  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