Bio-Electrochemical Treatment of Wastewater Organic Load: Comparison of Microbial Electrolysis, Microbial Fuel Cell and Microbial Electrochemical Snorkel Performances

The removal of the total organic load (COD) from urban wastewater was studied in different bio-electrochemical systems (BES): microbial electrolysis, microbial fuel cell (MFC), and microbial electrochemical snorkel (MES). Here is presented the concept of MES [1], a simplified design of a “short-circuited” MFC.

The MES cannot provide current but it is optimized for wastewater treatment. Technically, the MES concept can simply consist of a single piece of conductive material on which there are (i) one end colonised by an electro-active biofilm acting as a microbial anode (anaerobic zone), and (ii) one end covered with oxygen (bio- or not) electro-catalyst that ensures electron removal to the final electron acceptor and allows bacteria “snorkelling” to oxygen. Unlike MFCs, a MES does not divert energy to produce electricity but it ensures maximum efficiency for the oxidation of organic matter.

COD removal comparison with the different BES was made starting from optimized graphite based microbial anodes already working at steady state rate of oxidation. Optimization of microbial anodes consisted of immersing a microbial anode already colonized with electoactive microorganisms together with a second polarized clean electrode resulting in the formation of an electroactive biofilm on the clean electrode that became more effective than the initial one. This strategy multiplied the current provided by the second electrode by a factor ranging from 2 to 20 in respect to the initial one. Comparative analysis of microbial diversity on electrodes was performed by pyrosequencing technology. Then, the comparative study using microbial anodes in different BES for the treatment of urban wastewater validated the MES concept since the MES process ensured about 75% of wastewater COD removal in less than 24 hours as well as a “short-circuited” MFC.

In conclusion, the MES technology, which aims at maximizing the reaction rates by elimination of current generation, provided degradation performance far higher than the MFCs that operated at optimum power. This demonstration opens a new route for the design of extremely simple electro-microbial devices for wastewater treatment.

 [1] B. Erable et al., 2011. Biofouling 27(3):319-326. doi: 10.1080/08927014.2011.564615.