Study On The Removal Of Aromatic Compounds In Oil Refinery Wastewater By Membrane Bioreactors

A large quantity of wastewater containing a high concentration of toxic and refractory organic compounds is discharged in the petroleum refining industry.With the higher refining amount of heavy oil and the more complexity refinery processes,it is more difficulty to treat oil refinery wastewater.Otherwise,the wastewater treatment process must be upgraded due to the more stringent discharge standard.Membrane bioreactor(MBR)combines biodegradation and membrane filtration,achieving some advantages,including high effluent quality,high volumetric loading rate.However,the removal efficiency of refractory pollutants in MBR and the effect of refractory pollutants on membrane fouling were unclear.In this work,removal pathways of aromatic compounds in MBR were analyzed,membrane fouling mechanism was studied and the method of membrane fouling control was proposed,which provide guidelines for the popularization and application of MBR and the control of membrane fouling.The study on the effects of solid retention time(SRT)on the removal efficiencies of aromatic hydrocarbons and the membrane fouling in MBR showed,MBR could effectively remove toluene and anthracene,the longer SRT the higher removal efficiencies and biodegradation rates of toluene and anthracene.Increasing SRT reduced the content of loosely bound extracellular polymeric substances(LB-EPS)including the protein and polysaccharide and the relative abundances of the biofilm-forming bacteria Deinococcus and the bulking and foaming bacteria Caldilineaceae which were both correlated well with membrane fouling rate.The study on the effect of aniline on MBR performance and membrane fouling showed,the initial shock loading of aniline significantly reduced the removal efficiencies of TOC and NH4+-N in MBR.The membrane fouling rate increased with the increasing concentration of aniline due to the higher contents of soluble microbial products(SMP)and EPS,especially the polysaccharide concentration in SMP,in activated sludge.Compare to the absence of aniline in the influent,the membrane fouling rate increased 1.7 times when the aniline concentration was 50 mg/L.The increased aniline concentration significantly reduced the abundance and diversity of the microbial community.After long-time acclimatization,Comamonas which is capable of degrading aromatic compounds enriched in MBR,with the relative abundances increased from 0.3%to 16.4%.Comparing the relationship of the membrane fouling and three different membrane materials including PTFE,PVDF,and Ceramic.The results showed that the membrane fouling rates of three membranes can be ordered as follows:PTFE>PVDF>Ceramic.The hydrophilic of the membrane has a great influence on the membrane fouling,and the low roughness membrane was effective to antifouling.Tryptophan and tyrosine in SMP and LB-EPS were the key components leading to membrane fouling.Adding activated carbon significantly mitigated membrane fouling.Adding powder activated carbon(PAC)and granular activated carbon(GAC)prolonged the membrane cleaning cycle to 2.6 times and 1.5 times,respectively.Activated carbon increased sludge floc size and improved the dewaterability of activated sludge.PAC was effective to reduce the contents of SMP and LB-EPS,decreasing initial membrane fouling rater and increasing the filterability of the cake layer on the membrane.Adding GAC reduced contents of polysaccharide and protein in LB-EPS and mitigated membrane fouling by scouring membrane surface to suppress the formation of the cake layer.