Neutral red as a mediator for the enhancement of electricity production using a domestic wastewater double chamber microbial fuel cell

Neutral red is an electron transport compound that is used in bacteria as a mediator for decolorization, degradation of different organic compounds and in electricity production using microbial fuel cells (MFCs). In this study, bacterial electron transport was followed by monitoring electricity production in a double chamber microbial fuel cell, and measured as current (mA). To enhance electron transfer and consequently increase electricity production, neutral red was added as a mediator. The optimal concentration that had minimal effect on bacterial growth was 15 mM. Spiking the culture with this concentration resulted in a maximal current of 1.36 mA and a power intensity that reached 467.6 mW/m2over 120 h, as compared to 0.74 mA and 209.5 mW/m2 over a period of just 24 h as a control. This was also confirmed by the increase in initial bacterial conductivity measured in the presence of neutral red as compared to low initial conductivity in the absence of a mediator. To prove that the process of electricity production is correlated to electron transfer, azole and azide were both used to inhibit membrane cytochrome complexes. The results showed a sharp decrease in electrical current production within less than 24 h, suggesting that the process takes place via membrane protein cytochromes. The predominant microorganism present under all previously mentioned conditions was Buttiauxella agrestis SW-1 (GenBank ID KP770022) as identified using 16S rRNA phylogenetic analysis, this bacterium was also studied morphologically to detect micropilli. Protein profiles of the membrane showed a distinct band close to that reported for cytochrome c; nevertheless, further investigation is required to highlight both its nature and its role.