The Effect Of PH On Power Generation And Denitrification In Microbial And Chemical Fuel Cells

Microbial fuel cells?MFCs?are wastewater treatment and energy recovery devices,which use electrochemically active microorganisms to convert chemical energy contained in wastewater into electrical energy.MFCs combined with biological denitrification technology can achieve simultaneous denitrification and power generation.Real wastewater involves different pH conditions and pH affects the metabolic activity of microorganisms.Therefore,it is very important to explore the influence of pH on the power generation and denitrification performance of MFC.In addition,wastewater containing high nitrogen produces toxicity to microorganisms,and struvite precipitation is an efficient technology for treating high ammonia-nitrogen wastewater.Based on this background,the effect of pH on electricity production and denitrification performance and the effect of electrochemically active microorganisms on denitrification were studied.What's more,electrochemical struvite precipitation system was developed as a pretreatment device,and the influencing factors of this system were studied.For the MFC reactors,the effects of pH on the electricity generation and anode biofilm under different electrode area ratios were studied.The results show that the power generation under alkaline conditions was higher than that under neutral and acidic conditions.The reactors with pH=10 had the best power generation performance and its maximum power density of carbon brush reactor was 1370.2 mW/m²,which was 103.7%higher than that under pH=7.The reason is that electrochemical activity of unit biomass under alkaline condition is higher than that under neutral and acidic conditions.When the area of cathode or anode was increased,the power of MFCs was increased and increasing cathode area was more effective than increasing anode area in improving power generation under neutral and alkaline conditions.For the denitrification MFC reactors,the effect of pH on denitrification and power generation and the effect of electrochemically active microorganisms on denitrification was studied.The results showed that the optimum pH for denitrification was within the range of pH=8-9.Under pH=8,the average nitrate degradation rate of denitrifying MFCs was 161.1 mg/?L·h?,which was 108.5%higher than that under pH=7.In terms of power generation,pH=9 reactors had the best power generation capacity,while pH=11 reactors couldn't produce electricity stably due to the toxicity of nitrite accumulated by denitrification.Moreover,the electrochemically active microorganisms were helpful for denitrification.The electrochemically active microorganisms cultured at pH=6 and pH=9 could electrochemical reduce nitrate and the electrochemically active microorganisms cultured at pH=6-11 could electrochemical reduce nitrite to N₂O.Therefore,the nitrite degradation rate of denitrifying MFC reactors was higher than traditional denitrifying reactors,and the increase of nitrite degradation rate was helpful for nitrate degradation.Electrochemical struvite precipitation system was conducted,which generated electricity and removed nitrogen and phosphorus simultaneously and improved pH through electrode reaction with lower cost.Moreover,effects of pH on the system performance were studied.The results showed that in the range of pH=7-10,pH=9reactors had the highest removal rate of nitrogen and phosphorus and the highest utilization rate of magnesium ion.The removal rate of ammonia nitrogen was 97.3%and the utilization rate of magnesium ion was 92.0%when influent involved 1000 mg/L ammonia nitrogen?the molar ratio of P/N is 1.05?under pH=9 with 60?external resistance.The cost of the system was?488.6 per ton of wastewater which is 39%lower than that of the system using MgCl₂,and the income of struvite was?36.9.