Study On The Efficacy Of Coupled MDC-MEC System For Treating High Concentration Ammonia Nitrogen Wastewater And Producing Hydrogen

Ammonia nitrogen wastewater comes from a wide range of sources and has a large volume of discharge.The production of petrochemical,non-ferrous metal chemical metallurgy,chemical fertilizer,MSG,meat processing and breeding industries as well as waste leachate all produce high concentration ammonia nitrogen wastewater,the concentration of which is generally between 100-5000mg/L.High concentration ammonia nitrogen wastewater has certain toxicity to human,animals and plants and can seriously harm the ecological environment.Therefore,how to effectively treat ammonia nitrogen wastewater has become an urgent problem.The common pretreatment methods（purging and chemical precipitation）have the problems of high operating costs and high energy consumption,which make the urgent need for energy in this field especially aggravated compared with other fields.Now we propose a new process without external power supply-Microbial Desalination Fuel Cell-Microbial Electrolytic Cell coupling system,which combines the above two principles to provide some theoretical basis for the operation of this coupling system.This system can combine the characteristics of MDC and use it for power generation,ammonia removal and ammonia recovery,and use MDC as an external power source for MEC to assist in hydrogen production.In this experiment,a coupled system of"ammonia removal-COD removal-hydrogen production"was constructed with high concentration of ammonia and nitrogen organic wastewater as the research object,and the effects of electrode spacing,anode COD concentration and different voltages on the removal of high concentration of ammonia and nitrogen,electrochemical performance,organic degradation performance and hydrogen production in the MDC-MEC coupled system were investigated,The effects of electrode spacing,anode COD concentration and different voltages on ammonia removal,electrochemical performance,organic degradation performance and hydrogen production in the coupled MDC-MEC system were investigated.The main findings are as follows:1.the MDC reactor used a mixed colony inoculation start,the 48thh reached the peak voltage,the start-up phase ran continuously for 4 cycles（1371h）,the voltage stabilization period output voltage between 600-700m V,at this time,the MDC start-up was considered successful;MEC reactor also used a mixed colony inoculation start,external DC power supply,connected to the MEC reactor,with the consumption of substrate,the current gradually reduced,the start-up period ran for a total of 12h.2.MDC has good electrochemical performance during operation,and it produces the best maximum power density of 6.04W/m³,the minimum internal resistance of 43.07Ω,and the highest average Coulomb efficiency of（4.67±0.15）%;in terms of ammonia nitrogen removal,the removal rate can reach up to 99%,and the removal rate can reach 8.71 mg/h（6000 mg/L ammonia nitrogen）;in terms of organic matter degradation In terms of organic matter degradation,the anode COD removal rate can reach up to 96.4%（300mg/LCOD）;meanwhile,the MEC can reach up to44.3%ammonia nitrogen removal rate and up to 71.2%anode COD removal rate during the operation,while the H₂production reaches up to 11.4m L.3.The optimization analysis of three key factors affecting the performance of the coupling system-electrode spacing,anode COD concentration and external voltage size-showed that the smaller the electrode spacing,the better the performance of the coupling system in all aspects,when the MDC electrode spacing was 3.5cm,the maximum power density was 6.04 W/m³,the ammonia nitrogen removal rate was3.17 mg/h,the highest COD removal rate was 96.4%（300mg/LCOD）,while the MEC had an ammonia removal rate of 11.78mg/h,a maximum COD removal rate of 73.1%（310mg/LCOD）and an H₂yield of 10.7m L at an electrode spacing of 1.0cm,although the reduced electrode spacing could improve the performance of the coupled system,however,too small a spacing would be detrimental to reactor scale-up and The smaller the anode feed water COD,the more optimal the coupling system in terms of ammonia nitrogen removal and electrochemical performance,when the anode liquid COD concentration was 200 mg/L,the maximum power density of MDC was 4.37W/m³and the ammonia nitrogen removal rate was 2.98 mg/h,while MEC had the fastest ammonia nitrogen removal rate of 10.78 mg/h when the anode feed water COD concentration was 300 mg/L.The highest hydrogen production was 11.5m L,but in terms of COD removal,the highest COD removal rate was 72.3%when the anode COD influent concentration was 800mg/L,so the anode organic degradation performance was also decreasing when the influent COD became smaller;when an external DC power supply was used to replace the MDC reactor as the MEC power supply,the ammonia nitrogen removal rate was 10.95mg/h when the MEC external power supply voltage was 0.8V.removal rate of 10.95mg/h,the highest COD removal rate of 67.1%,and H₂yield of 11.9m L.In this thesis,the MDC-MEC coupling system was applied to the treatment of organic wastewater with high concentration of ammonia and nitrogen,and the removal effect of high concentration of ammonia and nitrogen achieved more satisfactory results,and the removal of high concentration of ammonia and nitrogen while synergistic electricity production and degradation of organic matter and hydrogen production,providing a new method for the pretreatment of organic wastewater with high concentration of ammonia and nitrogen.The effects of electrode spacing,anode COD concentration,and different voltages on its performance were investigated,and the influencing factors were optimized to provide technical support for the stable operation of the coupled system for treating high concentration of ammonia nitrogen wastewater.