Electroactive mixed culture biofilms in microbial bioelectrochemical systems: The role of temperature for biofilm formation and performance

In this paper we investigate the temperature dependence and temperature limits of waste water derived anodic microbial biofilms. We demonstrate that these biofilms are active in a temperature range between 5 °C and 45 °C. Elevated temperatures during initial biofilm growth not only accelerate the biofilm formation process, they also influence the bioelectrocatalytic performance of these biofilms when measured at identical operation temperatures. For example, the time required for biofilm formation decreases from above 40 days at 15 °C to 3.5 days at 35 °C. Biofilms grown at elevated temperatures are more electrochemically active at these temperatures than those grown at lower incubation temperature. Thus, at 30 °C current densities of 520 μA cm−2 and 881 μA cm−2 are achieved by biofilms grown at 22 °C and 35 °C, respectively. Vice versa, and of great practical relevance for waste water treatment plants in areas of moderate climate, at low operation temperatures, biofilms grown at lower temperatures outperform those grown at higher temperatures. We further demonstrate that all biofilms possess similar lower (0 °C) and upper (50 °C) temperature limits – defining the operational limits of a respective microbial fuel cell or microbial biosensor – as well as similar electrochemical electron transfer characteristics.