Study On The Process And Mechanism Of Nitrogen Conversion In Bioelectrochenlical Systems

Nitrogen removal is important for wastewater treatment,especially for some wastewater with low C/N,which also has become one of the most important indicator for water quality.Traditional biological denitrification contains two processes of nitrification and denitrification,which is the most mature and widespread method for nitrogen-containing wastewater treatment.Nitrification produces a large number of protons that need to be neutralized with alkali,and denitrification requires the addition of carbon source and acid to maintain the effective nitrogen removal,which not only increases the cost but also causes secondary pollution.Aim to solve the low return of traditional biological denitrification,bioelectrochemistry systems(BESs)was introduced for self-supplying protons to maintain the efficient nitrogen removal,which is also a potential application for wastewater treatment.Recently,BESs technology for low C/N wastewater treatment,especially ammonium-containing wastewater treatment,generally separated the nitrogen removal from organic matter removal,which resulted in the COD degradation incompletely and autotrophical denitrification rate slowly.Meanwhile,electricity performance was affected by the performance of cathodic denitrification,making the denitrification with BES difficult for practical wastewater treatment.In this study,a composited cathode coated both bacteria and platinum(Pt)catalyst was in situ prepared for simultaneous cathodic nitrification and oxygen reduction,while electricity performance mantained stable.Nitrate as the nitrification product migrated from the cathode chamber into the anode chamber,was gradually reduced by hetertrophic denitrifers.Complete denitrification and COD degradation were enhanced for the high C/N in the anode chamber.A three-chambered denitrifying microbial fuel cell(MFC)was developed to maintain the proton balance,making high efficiency of energy recovery,carbon and nitrogen removal.The results as follows:Firstly,nitrate reduction and its kinetic process in the anode chamber of MFC was investigated.Organic degradation rate was improved by anodic denitrification and anode respiration was relatively enhanced,which making the voltage output and power density improved.With the addition of nitrate,the percent of denitrifying bacteria in the anodic bio films increased,while the proportion of electrogenic bacteria relatively decreased.In a dual-chamber denitrifying MFC with acetate as electron donor,the COD consumption for anodic denitrification was 3.7 ± 0.3 g COD/g NO3--N,which is lower than that with the traditional hetertrophic denitrification.Furthermore,the factors of electrode material,electronic donor,and MFC configuration also changed the contribution of functional bacteria,resulting in the electrical performance decreased.But nitrogen removal was slightly affected.Based on the kinetic equation of Michaelis Equation,the maximum denitrification rate of323.5 mg/L/h was obtained in denitrifying MFC.Voltage and denitrification rate affected by external resistance and nitrate concentration,demonstrating the competition-cooperation mode between denitrifying bacteria and electrongenic bacteria in the anodic biofilms.Then,a composited bifunctional cathode contained nitrifying bacteria and Pt/C was in situ prepared,combining two reactions of biological nitrification by nitrifiers and oxygen reduction by Pt.It is a promising method due to the nitrification as a proton source supply the consumption of proton for oxygen reduction,maintaining the proton balance in the cathode chamber.The limited growth of biofilm on the cathode surface could maintain the high-efficiency of denitrification and oxygen reduction activity for a long period of time,attributing to the long period of aerobic autotrophic microorganisms loaded on the cathode.Furthermore,a three-chambered MFC with anode-cathode-anode structure was constructed for nitrogen-containing wastewater treatment,simultaneously achieving high efficient nitrogen removal and energy recovery.Finally,a novel strain EB-1 isolated from the anodic biofilm of denitrifying MFC,gram-positive,concurrent anaerobic,has the ability of electricity generation and denitrification.Strain EB-1 was belonged to Mycobactria sp.after identifying through cell morphological characteristics and 16S rRNA sequence analysis.The maximum power density of 0.84 W/m2 was obtained when MFC inoculated with strain EB-1.Based on SEM and CV analysis,a direct electron transfer mechanism by nanotubes or direct contact was confirmed in MFC with EB-1.Strain EB-1 can use many substrates as electron donors.It can provide as a promising source and theoretical basis for MFC with nitrogen-containing wastewater treatment.