Self-startup Of Microbial Electrochemical Snorkel And Its Application For Pollutant Removal And Monitoring

Microbial fuel cell is an electrochemical device with the dual functions of productivity and decontamination,which has been developed in recent years.However,due to the disadvantages of low output power,high raw material cost and complex operating conditions,the application of MFC in actual sewage treatment is greatly limited.From the current research results,MFC in the improvement of power output progress is relatively slow.Compared with power output,the collaborative decontamination of MFC is easier to realize in sewage treatment and more likely to be applied in practice.Therefore,at present,the main development direction of MFC has shifted from decontamination and productivity to decontamination and energy saving,and on this basis,a new microbial electrochemical system,microbial electrochemical snorkel,has been developed.MES is actually a single-electrode short-circuit MFC,whose electrodes can grow electroactive microorganisms to oxidize and degrade organic pollutants in water,as well as redox reactions using oxygen in the air or other electron receptors in solution.Although MES cannot output electric energy,it can utilize the electrochemical reaction of microorganisms to oxidize and remove organic pollutants and reduce and remove nitrate and other pollutants to the maximum extent.As reported in the current literature,the enrichment and growth of EAM of MES mainly depends on the pre-cultivation of constant-potential method.In order to further reduce the cost of MES and promote its practical application,this paper carries out the research on MES self-startup and decontamination application.In this paper,three kinds of MESs are constructed with electrodes of different structures,and the self-startup and decontamination and monitoring properties of MESs under different conditions are studied.The main research content is as follows:In the first part of this paper,the self-startup and coordinated decontamination of rotating MES with oxygen reduction reaction as the cathode reaction was studied.In this part,nitrogen and phosphorus co-doped graphite brush is used as the electrode.The electrode is placed horizontally along the axis,partially immersed in the solution and partially exposed to the air.GB/NPC rotates under the drive of the motor,alternately contacting with the air and the solution,promoting the oxygen in the air to fully spread to the solution and creating an aerobic environment.The results showed that under aerobic conditions,the in situ growth of aerobic bacteria on the electrode surface provided a local anaerobic environment for the enrichment and growth of electricity-producing bacteria.GB/NPC electrode surface catalyzed ORR to accept the electrons released by EAM and provide electron respiration for EAM,thus promoting the enrichment and growth of EAM and realizing the self-startup of R-ORR-MES.It is found that the system has the function of synergistically removing COD and NO₃^--N in sewage.When the carbon/nitrogen ratio?C/N ratio?is 2.4,the removal rate of COD and NO₃^--N is the fastest.This R-ORR-MES is expected to combine with the traditional aerobic wastewater biological treatment technology to achieve the coordinated and efficient removal of COD and NO₃^--N.In the second part,the self-startup and NO₃^--N sensing of MES with nitrate reduction as the cathode reaction are studied.In this part,an unmodified graphite brush was used as an electrode,which was directly immersed in a solution containing sodium acetate and sodium nitrate to study the self-startup of the DN-MES system and the NO₃^--N sensing behavior.The cyclic voltammetry curves under different substrate conditions showed that both EAM and denitrifying bacteria grew on the electrode surface at the same time.The protons and electrons generated by the oxidation reaction of organic matter catalyzed by EAM were directly received by nitrate,and the reduction reaction took place under the action of denitrifying bacteria,realizing the self-startup of DN-MES.When the concentration of NO₃^--N was in the range of 10⁶0 mg L^-1,the MES response potential showed a linear relationship with the concentration of NO₃^--N.Therefore,this DN-MES can be used as NO₃^--N sensor to realize real-time monitoring of NO₃^--N in sewage.In the third part,the self-startup,decontamination and sensing of MES driven by oxygen reduction reaction as the cathode reaction transpiration were studied.T-ORR-MES uses carbon material with micro-channel pore structure as the electrode and ORR as the cathode reaction.The MC was placed axially along the microchannel hole,partially immersed in solution and partially exposed to air.The study showed that EAM grew in MC terminal in the immersed solution.Driven by capillarity,the solution rises automatically along the microchannel of MC,transferring ions.The oxygen in the air diffuses to the electrode along the microchannel,and dissolves in the microchannel solution to generate ORR,accepting the electrons released by EAM,thus realizing the self-startup of MES.The T-ORR-MES system can not only remove COD in sewage,but also realize real-time monitoring of COD.The results showed that the COD degradation rate of T-ORR-MES could reach 93%within 22 h.When the substrate concentration ranges from 0.4 to 1.1mM,the MES response potential has a linear relationship with the concentration.The micro-channel electrode material used by T-ORR-MES can be obtained from the direct carbonization of natural plants with micro-pore structure?such as wood?.Due to the abundant and sustainable material sources,the operating conditions are simpler after being assembled into batteries.Therefore,it can be used not only for sewage treatment,but also for in-situ remediation of pollutants.