Research On The Performance Of Anoxic Biofilm-moving Bed MBR Hybrid System For Treating Wastewater From Maricultrue And The Membrane Fouling Mechanism

Membrane bioreactor has the advantages of complete biomass retention(beneficial to sludge acclimation),high effluent quality(satisfying water recycling need)and small footprint(low construction cost),which make it becoming the most promising technique for treating saline wastewater from mariculture.However,the low pollutants removing efficiency and deterioration of membrane fouling caused by high salinity stress limit its widely application.To this end,this research combined the biocarriers and MBR system to develop novel Anoxic biofilm-Moving bed MBR hybrid system,which employed the carriers to provide stable growing space for microbial,and promote the microbial activity and sludge mixed liqour properties,thus realizing the enhancement of pollutants removal and membrane fouling control under high salinity environment.Surrounding the developing process of the hybrid system,the variation of pollutants removing performance,the conversion of pollutants,the change of sludge bioactivity and evolution of microbial community structure were systematically investigated in order to clarify the enhanced pollutants removal performance of hybrid system;Based on this,the operational parameters of hybrid system was optimized;Meanwhile,the mechanism of membrane fouling mitigation in hybrid system was also investigated by analyzing the characteristics of three key fouling factors: sludge,EPS and SMP;Moreover,aiming at the features of membrane fouling in hybrid system,a method of membrane surface antifouling modification based on novel zwitterionic organosilica was developed to realize the control of membrane fouling in hybrid system.The hybrid system was gradually developed and its treatment performance on wastewater from mariculture and pollutants removing mechanism were investigated,the results showed that the use of salt-tolerance sludge endowed the hybrid system with high TOC removing ability under high salinity stress;And the employment of biocarriers in hybrid system significantly improved the nitrifying and denitrifying activities of sludge,resulting in a dramatically increase of TN removing efficiency(from 65.3% to 93.2%);Moreover,the mitigation of membrane fouling was also observed with fouling cycle was prolonged from 10 d to 44 d;Investigation on the nitrogen removal pathway found that with the help of selective inhibition effect of salinity on nitrifiers,stable shortcut nitrification-denitrification pathway was developed in the hybrid system.Influences of operational factors on system performance was investigated and results indicated that under the conditions of internal reflux ratio of 2.5:1,HRT of 8 h and DO of 2-3 mg/L,the hybrid system presented the best synergistic treatment performance.Furthermore,the hybrid system can even maintain a performance at high level even under low additional carbon resources or high influent C/N ratio condition,indicating its high robustness.The mechanism of membrane fouling mitigation in hybrid system was investigated and results showed that the mitigation of membrane fouling should be attributed to the effects of both fiber biofilter and polyurethane biocarriers.Fiber biocarrier in Anoxic unit induced decrease of organic load and suspended sludge in subsequent MBR unit and reduction of SMP fouling,thus resulting fouling mitigation in combined system with decrease of 96.3% on fouling rate.Polyurethane foam biocarriers in MBR alleviated membrane fouling(fouling rate decreased by 62.8%)mainly by its modification effects on suspended sludge(enlarging floc size,lessening hydrophobicity),EPS and SMP(reducing proteinaceous features and adsorption propensity).Evolution of microbial community in hybrid system was analyzed and results demonstrated that the acclimation process using seawater made a microbial community with marine and halotolerant micro-organisms as dominant species was developed in the salt-tolerance sludge;Moreover,biocarriers significantly prompted the community diversity of sludge in hybrid system;The abundance of nitrifiers and denitrifiers(such as Nitrosomonas,Sedimenticola)were significantly increased which explained the improvement of nitrogen removal in hybrid system;Otherwise,new species of Lucibacterium(12.17%),Cycloclasticus(3.51%),Lucibacterium(2.81%),etc.,that are capable of degrading refractory organics such as protein and polysaccharide,was found in biocarriers which could explain the changes of EPS and SMP characteristics induced by using biocarriers.Aiming at the membrane fouling characteristics in hybrid system,a novel surface antifouling modification method based on novel zwitterionic organosilica was developed;A smooth gel layer was formed on both modified membrane surface and pore wall,zwitterions were successfully introduced onto membrane surface via such sol-gel coating modifying process;The modified membrane exhibited excellent antifouling performance against EPS and SMP,the interfacial interaction energy between modified membrane surface and EPS/SMP was significantly repulsive;Employment of modified membrane in hybrid system led to obviously moderation of fouling propensity with fouling cycle increased from 42 d to 85 d.