Simultaneous Nitrification And Denitrification Based On Microbial Electrochemical Technology And The Denitrification Mechanism

Traditional biological denitrification technology plays an important role in the treatment of nitrogen-containing wastewater,but in the actual process of denitrification,when treating the wastewater with low C/N ratio,it is often necessary to add additional electron donors such as methanol and supplement the required alkalinity.With the development of new biological nitrogen removal processes,anaerobic ammonium oxidation?ANAMMOX?process has attracted much attention in recent years,due to its advantages in autotrophic nitrogen removal.However,the slow reproduction of ANAMMOX bacteria and its operating conditions limit the practical application of this process.In recent years,the extracellular electron transfer and have provided a new idea for the development of new denitrification technology.So this paper in view of the low C/N ratio wastewater treatment process of ammonia oxidation alkalinity and denitrification carbon source shortage problem,based on the electrical activity of the bacteria extracellular the characteristics of electron transfer.And we constructed a double chamber microbial electrochemical system,through two ways:the positive and negative electrode potential and Fe²⁺/Fe³⁺cycle,regulating the ammonia oxidation and denitrification process,discussed the electrode potential of ammonia oxidation alkalinity consumption and its influence on electrode ammonia oxidation and the electrode denitrification.And the process performance of the reactor,electrochemical characteristics,reaction mechanism and structure of the system functional microbial succession has carried on the related research.To provide technical support for the autotrophic denitrification treatment of nitrogenous wastewater with low C/N ratio.And the research contents and main results of this topic are follows:1)A double chamber MEC was constructed,then the electrode potential is set to regulate ammonia oxidation and electrochemical activity of biofilm for nitrogen removal.With the positive potential of+0.3 V,+0.4 V and+0.6 V?vs Ag/AgCl?applied to the working electrode with 1.0 g/L NaHCO₃ and 200 mg/L ammonia nitrogen,the efficiencies of ammonia oxidation were 54.59%,59.31%and 37.97%,respectively,and the maximum decreased to 46.24%of the control group without applying potential?70.79%?.While with the negative potential of-0.6 V,-0.8 V and-1.0 V?vs Ag/AgCl?,the removal efficiencies of ammonia increased to 93.41%,79.27%and83.23%,respectively,which maximum increased by 31.95%compared with control group without applying potential.However,the removal efficiency of total nitrogen is improved under both positive and negative potential conditions.The total nitrogen removal efficiency of the control experiment is only 9.38%,while the highest removal efficiencies of negative potential group raise to 23.47%,which reach to 2.5 times as much as the control experiment.What's more,the results of Cyclic Voltammetry analysis show that the working electrode biofilm has a reduction peak at the range of-0.25 V to-0.35 V after applied potential,while there was no obvious peak in control experiment,and the current was larger than the control group,indicating that potential applying could regulate the electrochemical activity of biofilm.According to 16S rRNA analysis,the relative abundance of Actinomycete phylum decrease in applied potential group compared with control experiment,while the phylum of Proteobacteria and Chloroforms increase,and the dominant bacteria with performance of ammonia oxidation and denitrification are enriched synchronously,such as Nitrosomonas sp.,Nitrosospira sp.,Bradyrhizobiaceae sp.and Rhodanobacter sp.Based on the microbial community and electrochemical activity of denitrification bacteria,it is speculated that there is a direct interspecific electron transfer?DIET?pathway for nitrogen conversion in nitrification/denitrification process,which improve nitrogen removal in ammonia–containing wastewater with low C/N ratio.2)A double chamber MFC reactor was constructed,using an iron rod as the working electrode,and coupling with the ammonia oxidation process through the Fe²⁺/Fe³⁺cycle.In the treatment of nitrogenous wastewater with low C/N ratio under anaerobic conditions,the removal efficiency of NH₄⁺-N reached 93.1%,and the total nitrogen removal efficiency was up to 63.61%.Compared with the control group,the participation of the iron electrode was beneficial to increase the efficiency of electron transfer,and had a external current density was 164.8 mW/m³.The 16S rRNA analysis found some anaerobic ammonium oxidation and denitrifying functional microbes in anodic electrode,such as Planctomycetes sp.,Thauera sp.In addition,combined with the concentration change regular of the substrate and the iron ions in the system,it was speculated that the Fe²⁺/Fe³⁺cycle drove the synchronous denitrification of ammonia oxidation,and the coupled denitrification process.