Mechanism Of Simultaneous Nitrogen And Sulfur Removal By Dual-Anode Methane Microbial Fuel Cells

In recent years,nitrate and sulfate pollution in water has become increasingly serious,causing eutrophication and ecosystem destruction.Microbial fuel cell(MFC),as a new biological wastewater treatment technology,can effectively complete the removal of nitrogen and sulfur..Methane is the world’s second largest greenhouse gas and an important fossil fuel.Recent studies have shown that gas(methane)can also act as a carbon source for MFCs.Anaerobic oxidation of methane(AOM)is an important method for its removal.AOM-MFC provides a new technology for wastewater treatment and greenhouse effect mitigation.However,the feasibility of simultaneous nitrogen and sulfur removal of AOM-MFC and information on microbial diversity are still unclear,and further studies are needed,and the mechanism of microbial action in the reaction process needs to be further revealed.In this study,multiple microbial fuel cells were constructed,and methane was used as the only carbon source in the anode chamber to explore the performance and feasibility of simultaneous nitrogen and sulfur removal.The mechanism of simultaneous nitrogen and sulfur removal of MFCs was revealed through microbial diversity analysis,and the maximum tolerance of MFCs was studied.Specific experimental results are as follows:Two dual chamber MFCs(N-MFC,S-MFC)and one dual anode chamber MFC(AOM-MFC-1)were domesticated under the same conditions.After the successful start of the three reaction units,they all showed the ability to remove nitrogen and sulfur.The removal rates of nitrate and sulfate in AOM-MFC-1 were 90.91% and 18.46%,respectively.A voltage of 180.76 m V is generated at the same time.The removal rate of nitrate was higher than that of N-MFC,and the removal rate of sulfate was little different from that of S-MFC.The overall performance of the AOM-MFC-1 system was the best.Although methanotrophes were enriched,they accounted for a small proportion.AOM-MFC-2 was started by incubating methanotrophs followed by removing nitrogen and sulfur.In the first stage of acclimatization,the maximum voltage reached 249 m V,and the enrichment of electroactive microorganisms promoted the generation of electricity in the system.In the second stage,nitrate and sulfate were added by gradient concentration.When the influent nitrate and sulfate concentrations were 110 mg/L and 1700 mg/L,the removal rates were 92.54% and 15.33%,respectively,and the maximum voltage was 75.42 m V at this time.AOM-MFC-2’s successful start-up time was 70 days longer than AOM-MFC-1.By comparison,the overall performance of the AOM-MFC-1 reaction device was the best,while the AOM-MFC-2 domestication method was conducive to methanotrophes enrichment.The maximum tolerance of AOM-MFC-1 was studied by increasing the concentration of nitrate and sulfate in the anode chamber.As the influent nitrate concentration increased,the average amount of nitrate removal first increased and then decreased.Nitrite accumulation occurred during the experiment,and its accumulation showed a trend of first increasing and then decreasing.The maximum nitrate tolerance concentration of the system was 160 mg/L.The maximum tolerated concentration of sulfate was 2000 mg/L.As the experiment went on,the microorganisms attached to the electrode surface increased,and the bacterial community structure changed significantly.At the genus level,a large number of methanotrophes(Methylomicrobium,unclassified＿Methylophilaceae)were enriched.Halobacterota and Euryarchaeota accounted for the largest proportion,accounting for more than 95% of the total.There are many methanogenic archaea at the genus level,which play an important role in DAMO and SAMO processes.In conclusion,AOM-MFC has the feasibility of simultaneously removing nitrogen and sulfur,which can not only effectively remove pollutants,but also make methane resource utilization and generate electricity.This study provides a new perspective on the control of methane energy conservation and emission reduction,and provides effective theoretical and technical support for the application of methane MFC in simultaneous nitrogen and sulfur removal from wastewater.