Study On Production Performance And Coupling Mechanism In Nitrogen And Phosphorus In SMFC Under Different DO Concentrations

With the rapid development of our country economy,a large number of sewage and industrial waste water flows into the natural water bodies,causing organic matter pollution and eutrophication of lakes,frequently between water and sediment in material cycle,a large amount of oxygen consumption of organic matter and nitrogen and phosphorus nutrient accumulating in river sediment,lead to serious destruction of ecological system of lakes water black smelly occur.Sediment microbial fuel cell?SMFC?is a new method to restore water body by using electrogenic microorganisms to oxidize and decompose pollutants such as sediment organic matter and obtain electric energy at the same time.In this study,the SMFC system was constructed by using the sediment of black and smelly river bottom as the substrate,to explore the effect of electricity generation and pollutant removal of SMFC system under different DO concentrations of overlying water,and to further analyze the coupling competition between nitrogen and phosphorus in SMFC system.The main conclusions are as follows:?1?In this study,SMFC system was constructed with the sediments of black and smelly river bottom as the substrate.There were 4 experimental groups:1#anaerobic group?DO<1mg/L?,2#anoxic group?DO=3±0.5mg/L?,3#natural group?DO=5±0.5mg/L?,and 4#highly dissolve oxygen group?DO>7mg/L?.Connect the data acquisition system and investigate the electrical performance of SMFC.In about 20days,the output voltage of four groups of SMFC reactors reached the peak value,which was 377 mV,417 mV,533 mV and 568 mV,respectively.The maximum power density was 12.31 mW/m²,15.39 mW/m²,25.14 mW/m² and 28.55 mW/m²,respectively.The stable power generation cycle was about 20d.The results showed that the electrical properties of 4 groups of SMFC were positively correlated with the DO concentration of the overlying water.?2?The introduction of electrodes in SMFC system can promote the organic matter,nitrogen and phosphorus nutrient pollutants in sediments.The removal rates of organic matter from reactor sediments in the four groups were 13.08%,18.56%,27.61%and29.34%.The removal rates of total nitrogen were 26.48%,32.13%,40.86%and 35.21%.The reduction rates of total phosphorus were 8.98%,8.06%,6.98%and 6.29%.Under the condition of DO=5±0.5mg/Lin overlying water,the removal rate of total nitrogen in sediments was the highest.Under the overlying water DO<1mg/L,the sediment has the highest total phosphorus reduction rate,which is mainly by released to overlying water.?3?This study found the coupling relationship between nitrogen and phosphorus in SMFC:at the initial start-up stage of SMFC system,ammonifying bacteria responded first,and ammonifying bacteria oxidized organic nitrogen into ammonia nitrogen,providing raw materials for the process of nitrification and denitrification.With higher output voltage,microbial gradually adapt to the new environment,PAOs began to actively absorb carbon source synthesising PHB stored energy,electric bacteria near anode oxidated organic matter to produce electrons,NO₃^-inside the battery under the action of electric field to the anode,promote the anode denitrification,this phase electricity production bacteria,phosphorus accumulating bacteria,denitrifying bacteria compete carbon source.As the output voltage of SMFC system drops,the sediments are easily consumed by bioavailable organic matter,and PHB in the cells is consumed by phosphorus-accumulating bacteria,which release energy to maintain their metabolism.Meanwhile,NO₂^-and NO₃^-lose cathodic electrochemical reduction and the internal electric field of the battery,resulting in the increase of NO₂^-and NO₃^-in the sediments,while ammonifying bacteria dominate,and the ammonia nitrogen content in the sediments continues to rise.?4?The dissolved oxygen concentration in the overlying water and SMFC system caused significant differences in the sediments'microbial community.The microbial abundance in the 3#experimental group was the highest,and at the DO=5±0.5mg/L condition was the most conducive to microbial reproduction.Among the phylum horizontal bacteria classification,Chloroflexi,Actinobacteria,and Firmicutes were the dominant species in all the four experimental groups.In the genus horizontal bacterial classification,the common dominant bacteria in the sediments of the four experimental groups were Propionicicella,Pseudomonas and Anaerolineaceae.It was found that the microbial abundance of nitrifying bacteria and denitrifying bacteria in the 3#reactor was higher than that in the other three reactors.?5?High-throughput sequencing found the presence of denitrifying phosphorus removal bacteria in the sediments,and with the increase of the overlying water dissolved oxygen,the abundance of denitrifying phosphorus removal bacteria in the sediments increased,indicating that the overlying water dissolved oxygen can promote the occurrence of denitrifying phosphorus removal phenomenon in the sediments to a certain extent.