Coupling Of Electricity Generation And Denitrification In Three-phase Single-chamber MFCs In High-salt Conditions

Microbial fuel cell(MFC)is a device that uses electricigens as an anode catalyst to directly convert chemical energy stored in organic matter into electrical energy.MFC has broad application prospects in wastewater treatment and new energy development.When MFC uses high-salt wastewater as a substrate for electric ity generation and wastewater purification coupling operation,high salt can increase the conductivity of the solution,thereby reducing the internal resistance of MFC,which is conducive to MFC electricity generation.However,high salt will also inhibit the growth and metabolism of microorganisms,resulting in a decline in the electricity generation performance of MFC and the purification function of wastewater.Therefore,the coupling technology of MFC electricity generation and wastewater purification under high salt needs to solve the problem of high salt inhibition of electrode microbial growth and metabolism.This article intends to integrate the salt-tolerance and salt-tolerance assist functions of Halomonas and the simultaneous nitrification and denitrification(SND)function into MFC to build a "salt-tolerant generation-transfer-acquisition" system to improve the salt-tolerance of the MFC electrode microorganisms and enhance the electricity generation efficiency and the SND efficiency under high salt.In this paper,the addition of 1 g/L CaCl2 promotes the accumulation of microorganisms on the anode of MFC,accelerates the maturation of biofilm,and greatly shortens the startup cycle of MFC.By increasing the concentration of NaCl in conventional bipolar single-chamber MFC(Common MFC)from 0 to 15,30,45 and 60g/L,the average voltage within 24 hours was reduced by 5.6%,37.1%,45.9%and 52.7%,respectively.It was verified that high salt could inhibit microbial activity and significantly reduce the electricity generation efficiency of MFCs.Then the strain Halomonas alkaliphila DSM 16354T,which was used to improve the salt-tolerance of electrode microorganisms in MFCs and enhance the efficiency of SND and electricity generation under high-salt conditions,was screened.The strain has a high ectoine secretion rate(82.0%)and strong SND capacity(96.7%)at the same time.According to the measurement results of TTC-dehydrogenase activity,the ratio of 100 g/L polyvinyl alcohol and 7.5 g/L sodium alginate was selected to prepare the immobilized cell carrier.And a three-phase single-chamber MFC(TP-MFC)was constructed by setting an immobilized cell phase in Common MFC.According to the results of internal resistance and power density curve of MFC,the influence of the amount of immobilized pellets on the power generation of TP-MFC was characterized.When NaCl concentration was increased from 0 to 30 g/L,the voltage recovery speed of TP-MFC was significantly faster than that of Common MFC,and the average voltage in the stable period was 439.3 mV,which was also 55.2%higher than that of Common MFC.When running for 72 hours,the nitrogen removal rate of TP-MFC was 63.4%,Which was 17.6%higher than that of Common MFC.The effect of carbon-nitrogen ratio(C/N)on the electricity generation of TP-MFC under high salt was investigated,the results show that the voltage stability period of TP-MFC increases with the increase of C/N in the range of 0.25:1 to 5:1.The 16S rRNA diversity of common MFC and TP-MFC was analyzed.The results showed that the addition of immobilized Halomonas improved the relative abundance of Pseudomonas,Acinetobacter,Alcaligenes and Halomonas in the anode flora of TP-MFC,which indicated that Halomonas had good growth adaptability under high salt substrate conditions.At the same time,the ectoine secreted by immobilized Halomonas conferred substantial salt-tolerance on the electrogenic bacteria growing in a high-salt environment.The metabolic function analysis based on the Illumina platform showed that the xenobiotics biodegradation and metabolism,lipid metabolism,carbohydrate metabolism and amino acid metabolism functions of TP-MFC were significantly enhanced,which indicated that TP-MFC could significantly promote the metabolic activity of microbial population and improve the efficiency of electricity production and nitrogen removal due to the salt tolerance assistance of immobilized Halomonas.The TP-MFC based on immobilized Halomonas for the first time constructed in this paper has not been reported so far.This is a novel,convenient,and efficient technology to improve the electricity generation and denitrification performance of MFCs under high salt,which has great significance in the theory and application of MFC power generation and purification coupling technology in the treatment of high-salt wastewater.