| At present,the discharge of urban sewage in our country is increasing year by year,and the composition of urban sewage is becoming more and more complex,which makes the demand of urban sewage treatment plant for effluent standard discharge and process transformation more and more intense.In the mainstream treatment process of urban sewage,the activated sludge process does not take into account the resource of urban sewage,with low energy recovery efficiency and large amount of residual sludge.Anaerobic digestion technology has little effect on removing ammonia nitrogen and suspended matter in urban sewage,and the effluent is not up to standard.Aiming at efficient treatment of urban sewage and energy recovery,a combined process of anaerobic fluidized bed and membrane technology is proposed to treat urban sewage,which can recover energy and improve the quality of effluent.Research was carried out on the membrane components,fillers and system regulation of the combined process.Conductive filter membranes with good conductivity and anti-pollution properties were prepared by doping modification,and fillers with high conductivity and specific surface area were prepared by loaded nanoparticles.The influence of conductive filter membranes and fillers on the operation efficiency of the combined process was investigated.The conductivity and anti-fouling performance of conductive filter membrane were improved by doping graphene,carbon nanotubes and carbon black.Among the three modified conducitve filter membrane,graphene conductive filter membrane exhibited better hydrophilicity,anti-fouling performance and interception property.The optimal doping ratio was 5 wt%(G5)of activated carbon.The contact angle and surface protein content of G5 were 77.5 ± 0.9° and 5.31 ± 0.02 mg-protein/cm2,which was 25.5% and 28.5% lower than that of the control.The interception rate of total chemical oxygen demand(t COD)was 60%,which was 42.9% higher than that of the control.G5 has the lowest flux attenuation rate(5.7 ± 0.1%),which was 37.4% lower than the optimal ratio of carbon nanotubes and 67.6% lower than the optimal ratio of carbon black.The magnetic active carbon loading ferric oxide(MAC)was prepared for improving the methane production rate and pollutant removal efficiency.The conductivity and specific surface area of MAC were 17.5 ± 0.6 m S/cm and 688 m2/g,which were 1.03 times and 93.3% higher than that of the GAC,respectively.After adding of the two particles to anaerobic bottle(influent t COD concentration was 400 mg/L),the effluent t COD concentration of the MAC bottle was 44.5 ± 1.5 mg/L,which was 42.9% and 31.0% lower than that of the control and GAC,respectively.The methane production of the MAC bottle was 0.32 ± 0.01 LCH4/gt CODremoved,which 2.7 times and 46.7% higher than that of the control and GAC,respectively.The effects of particles on the electron transfer in anaerobic digestion process with low-concentration influent were investigated by electrochemical means and high-throughput sequencing.The content of riboflavin in MAC(1.31 ± 0.06 mg/L)was increased by 31.0% compared with the control and 16.7% compared with GAC.The adding of MAC also increased the relative abundance of hydrogen-producing bacteria,hydromethanogens.The MAC also increased the relative abundance of bacteria that could release electrons and participate in interspecific electron transfer process.An anaerobic fluidized bed coupled conductive membrane bioreactor for treating low-concentration wastewater was constructed by using anti-pollution conductive filter membrane and MAC.The effects of starvation operation,reflux mode,functional particles and conductive filter membrane on pollutant removal efficiency were investigated.Under the conditions of taking the actual urban sewage as the inlet water and HRT as 0.92 hours,the operation efficiency of the reactor was improved by short-term starvation,gas driven fluidization and adding of fluidized particles.After short-term starvation,the t COD removal rate under gas driven fluidization(68.4%)was increased by 19.2% compared with that before short-term starvation,and the t COD removal rate under water driven fluidization was increased by 8.2% compared with that after short-term starvation.After adding MAC,t COD removal rate increased slightly(73.0%).Before short-term starvation,the total methane production under gas driven fluidization(0.84 ± 0.02 L/(L·d))was 11.0% higher than that under water driven fluidization(0.76 ± 0.02 L/(L·d)).After short-term starvation,the total methane production under gas driven fluidization(0.88 ± 0.01 L/(L·d))was 10.0% higher than that under water driven fluidization(0.80 ± 0.01 L/(L·d)).After adding of MAC,the total methane production was 0.91 ± 0.01 L/(L·d).The results of high throughput sequencing showed that the hungry operation and adding of MAC changed the microbial community structure of the system and affected the synthesis of functional enzymes.The conductive filter membrane improved the removal efficiency of coupling system,including the t COD removal efficiency,TN removal efficiency and SS removal efficiency.The effluent of the coupling system meets the pollutant discharge standard of urban urban sewage treatment plant(GB 18918-2016),grade A.After applying of the electric field,the composite conductive membrane exhibited stronger anti-fouling performance,the surface EPS(82.8 mg/cm2)was decreased by 17.4% and 33.1% compared with that of the conductive filter membrane without electric field and the basal membrane,respectively. |
