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.

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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

 

1.     
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:

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

v  n (moles): stoichiometry
factors of the redox reaction

v  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