The Study Of Methanogenesis Performance Of Electrochemical Microbial Anaerobic System

Electrochemical microbial anaerobic system (EMAS) is based on modifying a microbial fuel cell (MFC) in two ways: adding a small amount of voltage (>0.2 V) to that produced by bacteria at the anode; and not using any oxygen at the cathode. The addition of the voltage makes it possible to produce pure gas at the cathode. Cubic air-Cathode microbial fuel cells were designed and operated,carbon cloth was used as the anode, the air-cathode was made of carbon cloth coated with 10% Pt catalysts on one side and PTFE waterproof layers on the other side. The system was inoculated with domestic wastewater (20% V/V) and operated under the external resistance of 1000Ω(30oC), 1g/L sodium acetate was used as the sole substrate. After the MFC reactors were started successfully, the cathode was changed to graphite fiber brush cathode, and a voltage was applied for methane generation. The effect of operating parameters (the applied voltage, DO, anode type, substate) on the EMAS performance were studied, and the EMAS reactors were compared with MAS reactors from several aspects.At the set voltage of -0.7V (vs Ag/AgCl), methane production was 260.0 mmol/(m~2·d) with current capture efficiency of 92.1%, while the maximum current of 3.25mA was obtained. At the set voltage of -0.6V and -0.5V, methane production were decreased about 55mmol/(m~2·d) with the current capture efficiency of 93.2% and 93.0%, while the maximum current were decreased to 1.63mA and 1.46mA with an decrease of 49.8% and 55.1%. When the nutrient solution was not aerated of nitrogen, methane production was decreased to 164.8mmoL/(m~2·d.) while the maximum current drop to 2.91mA with current capture efficiency of 89.60%, and the current curve drop 20 hours earlier compared with the current curve that the nutrient solution aerated of nitrogen. Carbon fiber cloth for anode, methane production was 359.2mmol/(m~2·d) with an increase of 100mmol/(m~2·d). The maximum current of 3.07 mA was obtained with a little decrease of 0.18 mA. When 20mL/L ethanol was used as the sole substrate, the current curve will appear two peaks. Methane production was 255.3mmol/(m~2·d) while the maximum current of 2.05mA was obtained. The current capture efficiency was drop to 61.2% with a decrease of 30.9% and current curve began to fall 16 hours earlier. When leachate was used as substrate, methane production was 126.4mmol/(m~2·d) while the maximum current of 4.08mA was obtained.The methane production of the MAS reactors was 84.5mmol/(m~2·d), about 1/3 of the EMAS, while COD removal efficiency was 78.1% with an decrease of 16.7%. The content of methane was up to 92.3% from the MAS reactors, but only 81.4% in EMAS reactors. After an average time of 28 days, the MAS reactors began to have a stable methane production, but in EMAS reactors, this state was got 10 days earlier. Furthermore, less sludge was produced in EMAS than MAS, and can got good methane production in low environmental temperature.