Study On Denitrification And Sludge Reduction Effect By Reflux Membrane-less Biological Cathode Microbial Fuel Cells

With the improvement of human living standard and the population expansion, thenitrogen pollution becomes a significant environmental pollution problems. One of thebiggest influence is attributed to water eutrophic. Among various kinds of wastewaterbiological treatment method,with the organic matter in wastewater removed,microorganisms will inevitably carry on quite a quantity of anabolism, a large numberof waste cells were generated, which lead to excess sludge accumulation. A largenumber of sludge can not get effective treatment, the sludge treatment is becoming anew social and environmental problems.In order to improve the efficiency ofdenitrification effectively、sludge reduction and reduce costs of MFC operation, wedesigned a new type of reflux PEM-less bio-cathode microbial fuel cell（sRPLB-MFC）.The study was based on RPLB-MFC system, and A²/O system was used as acontrol group.Start-up of RPLB-MFC、 sewage treatment effect and electricityproduction performance under stable operation were studied in this paper. To bothRPLB-MFC and the control group, for denitrification effect, we examined the changelaw of nitrogen under different load and the mechanism of denitrification by electricitypromotion. For sludge reduction, we studied the excess sludge reduction effect ofRPLB-MFC system under the conditions of different electricity production, andexplored the mechanism of reducing electricity promotion. Finally, the relationshipbetween the RPLB-MFC electricity production, denitrification and sludge reduction wasexplored.Study showed that, start-up of RPLB-MFC cost24h, and stable output voltage ofwas0.53V;after start-up for21d, removal efficiency of COD was stable, the process ofstart-up was related to microbial growth situation in the system. Anodic potentials keptat-0.46V after RPLB-MFC came into stability, while cathode potential was steady at0.7V;and internal resistance was406.8Ω under stable operation, the maximum powerdensity reached to201.9mW/m³, the coulombic efficiency was0.39%. RPLB-MFC wasprovided more than85%COD removal efficiency、75%NH3-N removal efficiency.RPLB-MFC operated steadily under zero load, NO₃^-N in effluent was reduced by19.46%on average than A²/O system,NO₂^-N was increased by16.67%than A²/O,TNremoval efficiency increased by8.17%than A²/O system. Electricity production processof RPLB-MFC system inhibited the accumulation of NO₃^-N and promoted theproduction of NO₂^-N, so ORP was reduced,which was conducive to denitrification.Changing the reflux ratio of MFC under zero load,with the increase of R,TN removalof RPLB-MFC system first increased and then decreased.TN removal rate reached amaximum of40.83%when R=1. Compared with the MFC system without reflux, whenR=1,the resistance reduced by27.3Ω, maximum power increased by23.4mW/m³. Change load of RPLB-MFC system to do the denitrification experiment by electricitypromotion, RexΩ=400,9999Ω represented the power transmission outside were0.2253W/m³and0.0062W/m³. When Rex=400Ω and9999Ω, NH3-N removal efficiency were93.6%,94.17%; in the Rex400Ω test group, the NO₃^-N emissions was inhibitied;theNO₂^-N formation efficiency was33.12%higher than the latter; the NO₃-N productionwas promoted by electricity production;the TN removal efficiency was49.52%, whichincreased by10.29%than the latter, and electricity production has promoted the TNremoval.In the RPLB-MFC and A²/O anoxia chamber,the living denitrifying bacterianumber in the mixed liquor were about5.5×10⁵/mL and3.5×10⁵/mL.ORP ofbackflow in RPLB-MFC system remained at about55mV, which was lower than A²/Osystem（75mv）, making the ORP of anoxic period in MFC system finally maintained atabout-90mv, significantly below the A²/O system （-40mv）, provided a betterdenitrification environment for MFC denitrifying bacteria.Under zero load, the RPLB-MFC cathode chamber was studied, and the dailyMLSS average increment was54mg/L, while the Yobs was0.1462KgCOD/KgVSS,synthetic rate Y was0.2548.RPLB-MFC system electricity production that promoted thecathode chamber sludge reduction effect was12.3%, inhibition of anabolic effect was7.21%,while the design process effect that promoted reduction was29.27%, and theeffect of inhibition of synthesis was29.11%. Changing the load, Rex400Ω and9999Ωthe output power were0.2253W/m³and0.0062W/m³respectively,average Yobs incathode chamber of RPLB–MFC were0.1291KgCOD/KgVSS,and0.1572KgCOD/KgVSS; Synthetic rate were0.2452and0.2708.The increasement of outputpower in RPLB–MFC could provide sludge reduction increment by17.88%andsynthesis inhibition by9.45%, while the best reduction effect of RPLB-MFC cathodechamber was45.23%,and the best inhibit sludge synthetic effect was38.72%.In Rex400Ω and9999Ω test, maximum output voltage were0.532V and0.471V; the maximumoutput power density were0.2483W/m³and0.1478W/m³; coulombic efficiency was0.46%and0.37%. When load was400Ω, the system resistance reduced by18.2Ω thanzero load and reduced by66.8Ω by maximum load respectively.Yobs of sludge in sludgecollection funnel mean total Yobs of RPLB-MFC was0.0809, and total decrement effectwas72.61%compared to a continuous flow reactor RPLB-MFC. Reduction reactionhappened in RPLB-MFC sludge collection funnel.The contribution of these reaction tothe system was31.04%. RPLB-MFC denitrification performance, sludge reductionperformance and production performance, the relationship of any promoted each other.Compared to A²/O, sludge EPS of RPLB-MFC increased, and the fluorescence inEBOM matter were soluble microbial products, and existing humic acid organic matterin HPO and TPI helped electron transport by bacteria in RPLB-MFC.