Nitrite-depeadent Anaerobic Methane Oxidation Process Enhanced By Bio-electrochemical System With Nano-MnO₂ Modified Carbon Felt Electrode

The nitrite-dependent anaerobic methane oxidation（n-damo）process,which can convert nitrite（NO₂-）to nitrogen（N2）,with methane as the electron donor under anaerobic conditions,has been emerging as a novel and attractive denitrification strategy because it can simultaneously reduce the environmental impact of nitrogen compounds and utilize greenhouse gases as a carbon source.In addition,compared with the traditional denitrification process,the n-damo process has a broad application prospect due to no N2O emission.However,the application and promotion of n-damo process for wastewater treatment suffered from limitation of its long doubling time,harsh requirement of environmental conditions and low reaction rates.Microbial electrolysis cell（MEC）is a new method of wastewater treatment composed of biological anode and cathode electrode.The implement of electron transfer driven by impressed voltage enhanced the electron transport of microorganisms.promoted the metabolism of substances and accelerated microbial enrichment.Moreover,the use of denitrifying-MEC provides a mode for accelerating the enrichment culture of n-damo bacteria and enhancing the metabolic rate of nitrogen.Meanwhile,in the process of microbial metabolism driven by extracellular electron transfer,the efficiency of electron transfer between microorganism and electrode is one of the important factors affecting the overall performance.Manganese dioxide（MnO₂）as a cheap transition metal material,the application of modified electrode combined with carbon base electrode in MEC system improves the efficiency of wastewater treatment,and the addition of appropriate nano-level manganese dioxide（Nano-MnO₂）into anaerobic system promoted the activity of key enzymes and enhanced the treatment effect.Based on this,this paper intends to strengthen the n-damo metabolic process by MEC system composed of Nano-MnO₂ electrodes.The main conclusions are as follows:（1）Nano-MnO₂ electrode modified by hydrothermal synthesis has better surface morphology and electrochemical properties compared with electroplating synthesis and daub synthesis.Hydrothermal synthesis method was used to obtain tubular nanoparticles with crystal type of a-MnO₂ with diameter of<100 nm,which were uniformly distributed in flower shape and loaded on the inside and outside of carbon felt.In addition,it shows good electrochemical activity in electrochemical test and stable electron transfer resistance after cycle life test,which is more suitable for microbial electrode carriers under long-term culture conditions.（2）Nano-MnO₂ particles in large quantities can slightly inhibited the nitrogen metabolism process,but interestingly,DAMO archaea can form associated bacteria consortium to participate in the biological manganese reduction process.The Nano-MnP2 particles with 100mg/g VSS reduced the metabolic rate of NO₂-by 51.87%and diminished the biodiversity.However,in the presence of Nano-MnO₂ particles alone,XPS results showed that the valence state of insoluble manganese oxides was 3.04-3.54,and relevant microbial data supported the biological reduction/oxidation process of manganese oxides exist in the n-damo enrichment system.（3）The rate of nitrogen metabolism in the n-damo system was increased by electrochemical techniques.Compared with the control group,the removal of NO₂-in the n-damo+MEC+ Nano-MnO₂ group increased by 79.89%.The decrease of EPS content and the increase of microbial load indicated that electrochemical technology promoted the formation of an alternate community that was conducive to the communication between electrodes and microorganisms.The REDOX peaks in the cyclic voltammetry results demonstrate that there is a direct bioavailability pathway for the electrons on the electrode.The increase of NC10 bacterial abundance proved that electrochemical technology promoted the enrichment of n-damo bacteria.