The Effect of Temperature on the Performance of Anaerobic Membrane Bioreactors for Treatment of Domestic Wastewater

Anaerobic membrane bioreactors (AnMBRs) offer a potentially energy efficient means of treating domestic wastewater, but their performance with seasonal temperature variations must be understood to determine their feasibility in replacing conventional activated sludge processes. A bench-scale AnMBR treating primary clarifier effluent from a WWTP in Greenville, SC was found to achieve a similar chemical oxygen demand (COD) removal during operation at 35°C, 25°C, and 15°C, with average permeate COD concentrations of 70.5 mg/L, 60.7, and 77 mg/L respectively. Methane yields averaged 109 L CH4/kg CODremoved at 35°C, 114 L CH4/kg CODremoved at 25°C, and 64 L CH4/kg CODremoved at 15°C. Reduced methane yield is attributed to a decrease in methanogen abundance, seen by an almost 3-fold decrease in mcrA gene abundance during operation at 15°C. The conclusion that the AnMBR achieves similar methane yields at 35°C and 25°C is significant because substantial energy savings could be obtained from not heating the reactor to 35°C as is common in conventional anaerobic processes. Energy savings could especially be significant if the wastewater is already near 25°C for a portion of the year. By understanding the microbial components of AnMBR treatment through molecular microbial analysis and relating them with the performance of the AnMBR at different temperatures, we can better understand the functionality of specific microbial communities and therefore better inform, operate, and design anaerobic resource recovery processes for maximum effectiveness