Intensification Of Groundwater Nitrate Removal With Electrical Stimulation From Microbial Fuel Cells

Nitrate can transform to nitrite and nitrosamines, which may cause cancer. Compared with physical and chemical methods, biological denitrification is more effective and environmental friendly, but improving the efficiency of biological method is the focus of nitrate removal. This study utilized the low voltage from MFC to power the bio-electrical reactor(BER) to promote denitrification. The experiments were including three aspects: feasibility, mechanism and influencing factors. This research aims at improving the nitrate removal performance in the BER, and realizing the in-situ utilization of biological electricity, further providing the reference for groundwater nitrate removal.The results showed that:(1) In the feasibility research part, the MFC as the power supply, powered the BER.The voltage, nitrate nitrogen, nitrite nitrogen, ammonia and chemical oxygen demand(COD) were measured in 5 h intervals. A biological reactor without electricity was set as the control to explore the voltage effect for BER. The results indicated that, when voltage maintained between 500 m V to 700 m V by refreshing the nutrient solution of MFC, the nitrate removal rate of the BER with power supply was faster than the ones without voltage addition, and the intermediates decreased after voltage addition. But nitrate in the electrical reactor did not show obvious variation, so that the low voltage may stimulate the microbes.(2) In the mechanism research part, the ability and amounts of microbes in the BER with and without power were measured by the ATP analysis and most probable number(MPN) methods. By measuring and calculating the electrical indicators, the physical-chemical effects were eliminated. The results showed that compared with the one without power, the amounts in the BER with power supply increased one order of magnitude, and the microbe ability increased to 1.5 folds of the one without power.(3) Based on the results we have got, the voltage of MFC was maintained in the range of 500 m V to 700 m V. The factors including influent nitrate nitrogen concentration, COD concentration and hydraulic retention time(HRT) were optimized by response surface methodology(RSM), and with the target of the maximum nitrate nitrogen removal efficiency, and the minimum intermediates accumulation, we got the optimal results of COD=849.66 mg/L,NO3--N=60mg/L,HRT=3.92 h.In conclusion, the low voltage from MFCs can improve the ability and amounts of denitrification bacteria, which can improve the nitrate nitrogen removal efficiency and decrease the intermediates accumulation. And by using RSM, we got the optimal results. The influencing factors research and optimization promote the practical application of the system.