Operation Performance And Membrane Fouling Of AnMBR+AO-MBR Process For Treating High-salt Mustard Wastewater

High salt mustard wastewater is a typical representative of high salt organic wastewater in food industry,which presented the characteristics of high salinity,high concentration of organic matter and nitrogen and high phosphorus.The water quality fluctuates greatly.However,in the treatment of high-salt organic wastewater,high salinity will have a certain inhibitory effect on the activity and metabolic function of microorganisms,which will seriously affect the efficiency of the system’s treatment of pollutants and even lead to a breakdown of the biological treatment system.Anaerobic Membrane Bioreactor（AnMBR）is often used for the treatment of ultra-high concentration organic wastewater,which has high volume load and strong impact resistance.Anacrobic/Oxic-Membrane Bioreactor（AO-MBR）exhibited high nitrogen removal efficiency and good effluent quality.Both of them can achieve complete interception of microorganisms,which is benefit for the accumulation and reproduction of the salt-tolerant microorganisms.Thus,they can maintain high microbial biomass in the reacotor and improve the treatment efficiency.In this study,the operation performance of the AnMBR+AO-MBR combined process for treating high salt mustard wastewater had been studied,and the optimal operation parameters of AnMBR and AO-MBR were determined through reasonable process control.In addition,the changes of sludge properties during the operation of the combined process were tracked,and the changes of microbial community structure in AnMBR were analyzed.Finally,the fouling of AnMBR and AO-MBR was analyzed by SEM-EDX,FTIR and EEM.The main results are showed as follows:（1）The effect of four kinds of inoculated sludge（anaerobic sludge of food processing wastewater,landfill leachate,kitchen wastewater and excess sludge）on the anaerobic digestion for high salinity mustard wastewater was compared by testing the biological methane potential（BMP）.The results showed that when the inoculated sludge was anaerobic sludge of kitchen wastewater,the methane yield was 223.6 m L·g COD^-1,the COD removal rate was 79.5%.The production and digestion rate of volatile organic acids（VFAs）in the system was high.And the anaerobic microorganism could maintain high dehydrogenase activity in high salt environment.Therefore,the anaerobic sludge of kitchen wastewater was determined as the inoculated sludge of AnMBR.（2）The anaerobic digestion performance,sludge properties and membrane fouling of AnMBR were investigated for three stages of salinity elevation,organic loading rate（OLR）increase and sludge discharge.In the stage of salinity increasing（0-34 d）,when the OLR maintained at 0.5-1.0 kg COD·（m³·d）^-1,the salinity gradually elevated from 12.9 g·L^-1 to 33.5g·L^-1,COD removal efficiency first decreased and then increased,finally stabilized at about75%.In the stage of OLR increasing（35-99 d）,when the OLR increased from 0.9kg COD·（m³·d）^-1 to about 7.6 kg COD·（m³·d）^-1,the COD removal efficiency reached 80%,and the biogas yield was stable at 330-380 m L·g COD^-1,while the VFA in the effluent was less than300 mg·L^-1.In the operation stage of sludge discharge（100-120 d）,the average OLR was 0.5-1.0 kg COD·（m³·d）^-1,COD removal efficiency and biogas yield increased significantly,reaching 83%and 400 m L·g COD^-1,respectively.The sludge discharge improved the digestion performance of AnMBR.During the operation period,it was found that the sludge concentration decreased briefly due to the impact of high salinity.The SMP and BEPS increased to 74.0 and 114.3 mg·g VSS^-1,while the sludge particle size decreased from 20.97μm to 4.23μm.Long term domestication in high salt environment changed the composition of microbial community.The dominant bacteria in the system changed from Bacteroidetes、Firmicutes and Actinobacteria to Synergistetes,and the dominant archaea changed from Methanoculleus、Methanobacterium to Methanosaeta.The methanogenic pathway changed from hydrogen trophic type to acetic acid type.The membrane assembly showed good performance in the long-term operation of AnMBR,which was demonstrated by the low membrane cleaning frequency.SEM-EDX showed that there were a lot of organic fouling and inorganic salt crystals on the membrane surface.FTIR and EEM showed that the main substances causing membrane fouling were polysaccharide,protein and humic acid.（3）The removal effects of AO-MBR on nitrogen and phosphorus of the effluent from AnMBR were studied under different Hydraulic Retention Time（HRT）and nitrification liquid reflux ratio（Ro）.The optimal operation parameters of the reactor are HRT=4 d and Ro=200%.Under this condition,the COD removal rate is 85.4%,the ammonia nitrogen removal rate is96.4%,and the total nitrogen removal rate is 89.1%.AO-MBR has limited removal capacity of total phosphorus,which needs to be combined with chemical phosphorus removal.The results showed that the sludge properties in the system had changed greatly due to the long-term domestication of high salt environment,the concentrations of SMP and BEPS increased from5.1 and 36.9 mg·g VSS^-1 to 18.3 and 62.5 mg·g VSS^-1,and the particle size of sludge increased slightly.SEM-EDX showed that there were a lot of organic fouling and inorganic salt crystals on the membrane surface.FTIR and EEM showed that the main substances causing membrane fouling were polysaccharide,protein.