Wastewater Remediation Using Microbial Fuel Cells and Bioenergy Production

Microbial Fuel Cells (MFCs) representing a promising technology for the extract of energy and resources through wastewater and it also offer an economic solution to the problem of environment effluent and energy crisis in near future. The advance device is rather appealing, due its potential benefits, its practical application is, however hindered by several drawbacks, such an internally competing microbial reaction, and low power generation. This report is an endeavor to address various design connected to the MFCs application to wastewater treatment, in particular cost effective bioelectricity from waste water are reviewed and discussed with a multidisciplinary approach. The conclusions drawn herein can be of practical interest to all new researchers dealing with effluent wastewater treatment using MFCs.


Background
Microbial fuel cells (MFC) technology is a rapidly evolving and an emerging technology in recent years and has attracted a lot of attention from researchers in the fields of wastewater treatment and bioenergy production (Logan and Rabaey, 2012;Malvankar and Lovley, 2012).These promising biotechnologies are capable of bio electrochemical systems that convert energy contained in organic matter substrates in wastewaters (e.g.municipal wastewater, food, industrial, landfill leachates, swine wastewater and urine into electrical energy (kan et al., 2011;Kiely et al., 2011a;Santoro et al., 2011 andSharma et al., 2011).A typical MFC is consisting of two chambers, i.e. the anaerobic anode chamber and the aerobic cathode.The two chambers are separated by a membrane (e.g., proton exchange membrane) where protons and other ions are transferred from the anode chamber to the cathode chamber, while electrons from the anode chamber are transferred to the cathode chamber through an external electrical circuit and a resistor for electricity production (Li et al., 2010).MFCs have been initially developed as a method for simultaneous wastewater treatment and electricity production.
While interesting, many researchers are realizing that the economic and environmental value of electricity from MFC cannot compete for that of other energy sources at this stage.Therefore, a development has been initiated recently that the researchers have even invented a new method expands the scope of MFCs from electricity production to an increasing number of other specialized applications and reduce its costs so that it can produce substantial amounts of electricity, in addition to treating wastewater, and be costeffective for industries.Many research attempted to understand MFCs, their structure based biosensor, and applications, for example microbial desalination cell (MDC) and microbial electrolysis cell (MEC), which can be applied in different environments for monitoring of organic matter, microbial activity, reduce the salinity of brackish water or seawater and rich chemicals production (e.g., hydrogen, methane, H2O2) from carbohydrate-rich wastes (Jiang et al., 2017;Chouler et al., 2015;Lian et al., 2017;Chen et al., 2015;Chen et al., 2016;El Mekawy et al., 2014;Sevda et al., 2015).

MFCs reaction:
In a fuel cell, a very simple reaction occurs; microbes oxidize pollutants substrates such as nitrates, phosphates, other nutrient products and metals in the wastewater under anaerobic conditions which is able to produce clean and direct electricity production in MFCs is the result of oxidation-reduction reactions (Behera and Ghangrekar, 2009;Hamelers et al., 2010).That result in electron release, transfer and acceptance through electrochemical reactions at the electrodes in the anode and cathode chambers.These electrons were generated via anaerobic respiration by microorganisms in the anode chamber then the flow of electrons from the anode to the cathode is driven by the voltage difference between the two electrodes and the concentrations of readily available electron donors and acceptors at the anode and cathode surfaces, respectively.pollutant + H2O → CO2 + NH + 4 + HCO − 3 + H + + e − (1.1) The bacteria in the anolyte or at the anode surface carry out this reaction.Liberated electrons travel through the anode to the cathode via the electrical circuit where they react with the electron acceptors at the cathode, as described by Equation 1.2: Where, QA = oxidized electron acceptor, QA− = reduced electron acceptor.
. The following oxidation-reduction reactions represent possible bioelectro-chemical reactions in microbial fuel cells generating electricity utilizing wastewater as a substrate and other pollutants such as nitrates, phosphates, and others as electron acceptors The typical reactions in the anode and cathode of MFCs were described below The pollution of wastewater effluents has gained worldwide attention due to their toxicity, difficult disposal, and accumulation in the living organisms.Therefore, treatment of wastewater is an important environmental issue.Several methods have been developed to treat wastewater, including ion exchange, chemical precipitation, electrolysis, and reverse osmosis.However, most of these methods required high operational and maintenance costs, and generated toxic sludge.Therefore, treating wastes with MFC would be an innovative method to reduce waste and harvest power at the same time (Zhang et al., 2015 andMateo-Sagasta et al., 2014).The organic components in some wastewaters plus microbial biomass generated in the activated sludge process can be used as substrate or feedstock to an MFC, acting as a resource and not simply a waste.
This approach can be considered a partial solution for wastewater treatment, or an integrated part of a larger waste treatment system.The benefit of the MFC is that the electricity it produces can offset some of the energy required to run the more conventional wastewater treatment operations.For example, fermented primary sludge from domestic wastewater treatment has been utilized for electricity generation using single-chamber air-cathode MFCs (Yang et al., 2013).An MFC has great potential for treating various wastewater sources like municipal agricultural, industrial, dairy and brewery/ food.For Example, Anode chamber fed with containing azo dyes for decolorization, and simultaneous production of electricity with the help of microorganisms as biocatalysts.Microbial fuel cell for treatment of azo dye Acid Orange 7 coloured removed 73.7 and 80.6 % and voltage density 38 mW/m2 and 167.4 Mv (Fernando et al., 2012 andThung et al., 2015) and Reactive Blue 221 dye decolourisation using dual chamber microbial fuel 84% coloured removed and voltage density as 28 mW/m2 (Bakhshian et al., 2011).Alizarin yellow R azo dye decolorization using Anaerobic baffled reactor coupled with biocatalyzed electrolysis system (ABR-BES) colored removed 96.4 % and voltage density as 24.1 A/m3 (Cui et al.,2014).Congo red azo dye decolorisation using air-cathode single-chamber microbial fuel cell 90 % colored removed and voltage density as 192 mW/m2 (Hou et al., 2011).Another abundant waste product worldwide is human waste urine/ Feces is which requires energy intensive treatment processes in modern wastewater treatment plants.Thus, urine/ Feces could be used to revolutionize the way we produce bioelectricity by harnessing the potential power A new-style microalgae MFC has appeared; it has the capacity to convert solar energy into electricity via the metabolism of photosynthetic microorganisms (Lee et al., 2015).The use of membrane-less MFCs based on biocathodes shows a remarkable achievement with a 24 h hydraulic retention time, in which the rate of the removal of COD and approached 90% and 99%, respectively (Zhang et al., 2015) wastewater treatment plant are ideal for the types of bacteria that can be used in an MFC.
Swine wastewater has been used for electricity generation with MFCs as well.
Exoelectrogens are more than happy to breakdown and metabolize the carbon rich sewage of a wastewater stream to produce electrons that can stream into a cheap conductive carbon cloth anode.The electricity generated from the MFC also offsets the energy cost of operating the plant.As an added bonus, the bacteria eat a lot of the sludge normally present in wastewater.Due to the characteristics of the MFC, it is considered to be a potential solution to the current global energy and environment crises, but its power output is still relatively low.Research on finding ways to improve performance is needed to elevate MFC technologies from the laboratory to commercialization (Logan, 2012).
Different types of applications have already been reported during the last decades.
Conversion of wastewater into bioenergy is one type of application of MFC that has been widely documented (Logan & Rabaey, 2012).Researchers studying in different disciplines are contributing to the development of the MFC.Material scientists and engineers study electrodes and membranes such as the effects of carbon electrode morphology on MFCs (Sanchez et al., 2015).Environmental engineers (Logan, 2008) study the treatment effectiveness of MFCs, and electrical engineers study the energy harvesting processes (Alaraj et al., 2014;Corbella et al., 2015).
Microbial communities involve in some wastewaters treatment by microbial fuel cell.electricity in MFCs with concomitant transfer of electrons to an MFC electrode.The power density output from MFCs might be improved by altering the design of MFC configuration or changing the physical/chemical environment.MFCs are based on using green fuels and on converting their latent chemical energy into electrical energy.
Therefore, various substrates including hydrocarbons, volatile fatty acids, alcohols, amino acids, proteins, and even inorganic materials have been used in this system.Egesta and real waste such as wastewater have also been treated successfully and generated suitable amounts of energy in this system.Of course, wastewater contain materials that are of different levels of bio-degradability, and the higher the percentages of materials with high levels of biodegradability are, the greater quantities of electricity will be generated.Therefore, these systems can be used in treatment plants and in factories for treating the outgoing wastewater and for recovering part of the energy consumed by the units.This will reduce costs and, more importantly, will protect the environment.
However, more applied research is needed to make this system operational and economically justifiable.Furthermore, for sustainable future growth and development in the economic world, MFCs are the best possible solution and an important field of research and innovation.
) -4 Cu2+ + 8 e-→ 4 Cu(s)    In this section of the review, we are mainly focused on the substrates for pollutant reduction with the help of MFC.The environmental and financial impacts of microbial fuel cell wastewater treatment systems could potentially be very significant, especially with a worsening energy crisis causing us to look more and more to alternative sources of electricity and summarizes almost all the relevant literature available in the field of MFC research till date.It also provides a better understanding of the processes that occur within these MFCs is thus very important to the sustainable energy and insight into the difficulties, challenges and future of this technology there by encouraging more research efforts towards commercialization of the technology.