Bioreactor performance and quantitative analysis of methanogenic and bacterial community dynamics in microbial electrolysis cells during large temperature fluctuations

The use of microbial electrolysis cells (MECs) for H ₂ production generally finds H ₂ sink by undesirable methanogenesis at mesophilic temperatures. Previously reported approaches failed to effectively inhibit methanogenesis without the addition of nongreen chemical inhibitors. Here, we demonstrated that the CH ₄ production and the number of methanogens in single-chamber MECs could be restricted steadily to a negligible level by continuously operating reactors at the relatively low temperature of 15°C. This resulted in a H ₂ yield and production rate comparable to those obtained at 30°C with less CH ₄ production (CH ₄% < 1%). However, this operation at 15°C should be taken from the initial stage of anodic biofilm formation, when the methanogenic community has not yet been established sufficiently. Maintaining MECs operating at 20°C was not effective for controlling methanogenesis. The varying degrees of methanogenesis observed in MECs at 30°C could be completely inhibited at 4 and 9°C, and the total number of methanogens (mainly hydrogenotrophic methanogens) could be reduced by 68-91% during 32-55 days of operation at the low temperatures. However, methanogens cannot be eliminated completely at these temperatures. After the temperature is returned to 30°C, the CH ₄ production and the number of total methanogens can rapidly rise to the prior levels. Analysis of bacterial communities using 454 pyrosequencing showed that changes in temperature had no a substantial impact on composition of dominant electricity-producing bacteria (Geobacter). The results of our study provide more information toward understanding the temperature-dependent control of methanogenesis in MECs. (Figure Presented).