It is my experience that the amount of electricity generated (watts) is too small for even large scale wastewater treatment to be productive from an electricity production stand point. We just do not have good enough catalysts for the oxygen reduction reaction to make it feasible at this point, and so the small voltage obtained is wasted as over potential. What you ask about, just doing it to treat waste water/nutrients/organic matter, seems to be the most feasible direction as we can probably do treatment more cost effectively by including microbial fuel (or electrolysis) cells than current methods. That's my two cents as someone who researched microbial electrochemical cells for six years.

Microbial fuel cells (MFCs) have mild operating conditions and using variety of biodegradable substrates as fuel. The traditional MFC consisted of anode and cathode compartments but there are single chamber MFCs. Microorganisms actively catabolize substrate, and bioelectricities are generated. MFCs could be utilized as power generator in small devices such as biosensor. Besides the advantages of this technology, it still faces practical barriers such as low power and current density.

Application of Microbial fuel cells (MFCs)

The main applications of MFCs developed in recent decades are classified in the following forms:  

Generation of bioelectricity

MFC is a fantastic technology that can use a wide variety of substrates, materials, and system architectures with bacteria to achieve bioenergy production despite the fact that power levels in all these systems were relatively low. It is particularly preferred for sustainable long-term power applications, with potential health and safety issues. Clytonbetin (2006) demonstrated if an MFC could convey 25mW of power, it would be suitable for cardiac stimulation; however, the amount of surface area needed is quite large. The main objective of MFCs is to achieve a suitable current and power for the application in small electrical devices. Rahimnejad and et al. turn on ten LED lamps and one digital clock with fabricated stacked MFC as power source and both devices were successfully operated for the duration of 2 days.

Biohydrogen production

MFCs can be readily adjusted to the harvest of biohydrogen, instead of producing electricity. Hydrogen can be accumulated for later application. MFCs supply a renewable hydrogen source that can be donated to the overall hydrogen demand in a hydrogen economy. To generate hydrogen gas in typical MFC, anodic potential must be increased with an additional voltage of about 0.23 V or more, and also the oxygen at the cathode chamber should be vanished.

Wastewater treatment

As energy source, large potential is kept in wastewaters including diverse types of organic substrate. Different kinds of Wastewaters such as sanitary wastes, food processing wastewater, swine wastewater and corn stover contain energy in the form of biodegradable organic matters. MFC technology that was considered to be used for wastewater treatment early in 1991 is favorable as a completely different method because of capturing energy in the form of electricity or hydrogen gas. For an efficient treating system, high operational sustainability and low material costs are worthwhile characteristics. Scientists have reported that to remove nitrogen and organic matters from leachate, biological treatment is prevalently used as a credible and highly cost-effective Method. Simultaneous methane and electricity generation from waste materials are anaerobic digestion processes with long detention time that are suitable for high-strength wastewaters. In 2006, Rabaey et al. demonstrated that MFCs using specific microbes were excellent techniques to remove sulfides from wastewater. Up to 90% of the COD can be removed in some cases and a columbic efficiency as high as 80% has been reported. The capability of MFC technology for simultaneous electricity generation and the removal of salinity from Se-containing wastewater were observed and it was concluded that at higher serenity concentration, both power output and CE are lower. Also MFC could be an efficient method of electricity generation and odor removal, and Kim et al. demonstrated MFC-based technology accelerates the rate of removing odor when the electricity generation reaches a maximum of 228 mW/m2. Puig et al. demonstrated that biofuel cells used landfill leachate as a method of treating biodegradable organic matter and electricity production even with high content of nitrogen and salinity. The amount of removal organic matter was 8.5 kgCODm−3 d−1when the power density was 344 mWm−3. A novel MFC-membrane bioreactor (MBR) for the treatment of wastewater has recently been reported to achieve a maximum power density of 6.0 W/m3 with the average current of 1.9 ± 0.4 mA and good pollutant removal performance attributed to the high biomass retention and solid rejection.

Application of MFCs in biosensor

Using MFC technology as sensor for pollutant analysis and process monitoring is another application of biofuel cells. Batteries have restricted lifetime and must be changed or recharged; thus, MFCs are suitable for powering electrochemical sensors and are small telemetry systems to transmit obtained signals to remote receivers. To design this type of system, having appropriate cathodic and anodic reactions is the first step. It is possible to use MFCs as biological oxygen demand (BOD) sensor, and it is exhibited that this type of BOD sensor has excellent operational sustainability and reproducibility and can be kept operating for 5 years. Different types of enzymatic glucose sensors have been developed. The first type measures the amount of produced hydrogen peroxide and the lack of oxygen with the advantages of being easily fabricated and assembling small sized systems. The another one uses chemical mediators such as ferrocene to convey electron to electrode. MFCs may have many other applications besides wastewater treatment and renewable energy. The first and practical application of MFC is using this system for energy recovery to sustainable water infrastructure. Also a potential of remediating toxicants, such as phenols and petroleum compounds is another application of MFC. Biological electricity from wastes produced onboard on a spaceship is also a possible applicability.

Limitations of the Method

Power generated by the cell may not be enough to run a sensor or a transmitter continuously. This is the principal problem with using microbial cells. It can be solved by increasing the surface area of the electrodes. Also the other solution is to use a suitable power management program: the data are transferred only when enough energy is stored and this occurs by using ultra capacitor. Finally, the other limitation of MFCs is that they cannot operate at extremely low temperatures due to the fact that microbial reactions are slow at low temperatures.

For more information, please use the following link which contains a recent review article on this topic:

http://www.sciencedirect.com/science/article/pii/S1110016815000484

Hoping this will be helpful,

Rafik

Maybe this article will be helpful also:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.546.276&rep=rep1&type=pdf

http://www.tandfonline.com/doi/abs/10.1080/09593330.2015.1077896?journalCode=tetr20

Here are a couple of our publications concerning this issue:

https://www.researchgate.net/profile/Ana_Cucu

Conference Paper Microbial Fuel Cells for Efficient Waste Water Treatment and...

Article Microbial Fuel Cell for Nitrate Reduction

Yes, microbial fuel can be an efficient method for wastewater treatment .

More details you can obtain from dr. Ana Cucu or Prof. Stamatin Ioan.

Dear All,

I would like to thank you very much for your answers and suggestions.

L Latrach

Agree with Rafik Karaman Sir.