Biocathode Biofilm Regulation Of Microbial Separator MES And Research On Synergistic Removal Of Carbon And Nitrogen

Microbial Electrochemical System（MES）was considered as new generation wastewater treatment technology,for it combines the superiorities of pollutants degradation and in-situ utilization of chemical energy of pollutants in wastewater,which further supported a variety of cathode reactions based on this part of the energy to achieve multiple functions.In the past decade,great achievements were achieved in the analysis of extracellular electron transfer（EET）mechanism,innovation of materials,design and optimization of the structure,and function expansion.Recently,aimed to domestic wastewater treatment,the"intensive stack"mode of modularized construction depended on microbial separator combined with biocathode has been formed,which maximized the wastewater treatment efficiency and technical economy in MES.However,the pollutants degradation mechanisms,the MES performance limiting factors,and synergistic removal strategies of carbon and nitrogen,which involved in this established mode were still unclear.To overcome these bottlenecks,modularized MES with microbial separator combined with biocathode were constructed to evaluate its performance in removal efficiency and mechanism of pollutants degradation,and to explore enhancement strategies of synergistic pollution removal,and further promotes the development and application of MES.In this study,the biocathode MESs module with microbial separator were designed and constructed,the wastewater purification efficiency and pollution degradation mechanism were analyzed.Firstly,based on optimization results of matching ratio of the anode to cathode,the optimal ratio was obtained as a single set of anodes coupled with two sets of cathodes（1A2C mode）,which can maximize the efficiency of the MES module.Subsequently,based on the optimal ratio,modularized MESs were constructed.In this module,the MESs produced a maximum power density of 0.96±0.05 W m^–3 and achieved a volumetric loading of 1.1±0.2 kg-COD m^–3 day^–1.During the long-term operation process,monitoring results proved that microbial separator could well separate the anode and cathode compartments.Subsequently,the wastewater treatment efficiency of MES under different influent COD concentrations proved that the hydraulic retention time（HRT）is proportional to influent COD concentrations（effluent COD concentrations reach first-level A discharge standard of GB18918-2002）.Summarizing the results of energy conversion efficiency and COD removal rate,a range of 200–800 mg L^–1 was suggested as the most suitable COD range for this MES module.Furthermore,analyzing the COD and nitrogen removal contribution of key components,which suggested that biocathode was determining factor for MES power generation and pollutant removal.The 16S r DNA high-throughput sequencing results proved the conclusion that the microbial separator allied biocathode synergistically achieves nitrogen removal,and the predication of PICRUSt2 functional nitrogen metabolism genes further revealed the nitrogen metabolism mechanism that dominated by simultaneous nitrification and denitrification.In addition,there were two tricky questions were exposed,including the over-proliferation of filamentous bacteria in biocathode would cause degradation of the biofilm function and insufficient nitrogen removal efficiency of this kind of MES module.Aimed to solve the problem of function attenuation of biocathode caused by the over-proliferated filamentous bacteria,a periodic"starvation-anaerobic"regulation strategy based on restricted substrate regulation was proposed,and the mechanism of mass transfer limited ORR was clarified.During long-term operation,the fluctuation of current curves proved that the“starving and anaerobic”regulation could well recover the performance of MES.Meanwhile,the maximum output power density was increased from 0.59±0.03 W m^–3 to 1.33±0.06 W m^–3,and COD volumetric loading was also improved from 0.76 to 1.172 kg m^–3 day^–1.The electrochemical analysis before and after“AS”showed that over-proliferated filamentous bacteria would significantly increase oxygen mass transfer resistance（R_d）and charge transfer resistance(R_ct)of biocathode ORR,and“AS”regulation can reduce R_d from 357.2±20.6 to 151.8±5.5Ωand increase the specific catalytic activity(K_BSB)of the total cathode biomass from 3.2±0.4μA mg^–1 to 29.1±4.6μA mg^–1,which significantly promoted the rapid reaction of cathode ORR.In addition,16S r DNA high-throughput sequencing discerned that Sphaerotilus is the dominant genus that caused the over-proliferation of cathode biofilms,and“AS”regulation can effectively remove the filamentous bacteria and significantly improve the relative abundance of electroactive bacteria.Considering filamentous bacteria control and the enhancement of carbon as well as nitrogen synergistically removal,a new MES architecture of biocathode coupled with fluidized biocarriers was designed and developed,which significantly improves the wastewater treatment efficiency and energy conversion efficiency of MES.In terms of wastewater treatment,compared with MES without biocarriers（MES）or combined with non-conductive biocarriers（NCB）,MES with conductive biocarriers exhibited the highest COD removal rate(1.2±0.1 kg m^–3 day^–1),output power density(0.68±0.024 W m^–3),total nitrogen（TN）removal rate(0.18±0.012 kg m^–3 day^–1),and ammonia nitrogen（NH₄⁺–N）removal rate(0.17±0.007 kg m^–3 day^–1).The electrochemical impedance spectroscopy（EIS）of cathode ORR suggested that the combination of fluidized biocarriers obviously promoted the R_d reduction.Meanwhile,Cyclic voltammetry curves confirmed the compensation of carbonaceous biocarriers to cathode bio-capacitance,which avoided the risk of power overshoot in MES.The16S r DNA high-throughput sequencing results confirmed that the positive effect of the fluidized biocarrier on the enrichment of nitrifying and denitrifying bacteria in MES,which also achieved the improvement of nitrogen removal.The analysis of PICRUSt2 function genes prediction revealed that the carbonaceous biocarriers strengthened the expression of high-expressed genes,but the non-conductive biocarriers compensated the expression of weak-expressed genes.In addition,due to the aeration-produced shear force of biocarrier,the biomass adhesion ratio of cathode reduced by about 59%,which directly confirmed the positive effect of filamentous bacteria control in biocathode.Finally,the apparent sludge yield coefficients that represented the net synthesis rate of MES demonstrated that the promoting effect of the carbonaceous fluidized carriers on the promotion of metabolism in MES,which reduced the apparent sludge yield coefficients from 0.130±0.005 g-VSS g-COD^–1 in MES to 0.090±0.005 g-VSS g-COD^–1.