Electrochemical To Strengthen A/O-MBR Process Of Oil Shale Retort Wastewater Treatment

Oil shale retort wastewater,which contains many types of pollutants with complex composition and high concentration,is currently acknowledged as the refractory organic wastewater.Common methods,including physical and chemical methods,chemical methods and biological methods,share the disadvantage of a high cost,instability of water quality and difficulties in reaching relevant standards.As a result,environmental issues have become a vital factor restricting the development and utilization of oil shale.Therefore,the key of oil shale retort wastewater treatment is discharge standards with a measure of lower-cost and efficiency by choosing and improving a reasonable processing technology.In order to achieve efficient treatment of oil retort wastewater and membrane fouling,an electrochemical A/O-MBR(EC-A/O-MBR)had been built by set iron plates in both sides of the membrane in aerobic tank of traditional A/O-MBR.The use of electrochemical interaction,biological treatment and membrane separation deal with oil shale retort wastewater.At the same time,the comparison system of traditional A/O-MBR was been established.Because of shale retort wastewater with high concentrations of organic matter and ammonia,low C/N and biodegradability,the method of gradually increasing the influent ratio of oil shale retort wastewater was adopted for sludge acclimation.The test studied sludge concentration,sludge setting properties,biological phase,the removal of COD,ammonia,TN,bacterial populations and transmembrane pressure conditions and Zeta Potential during acclimation period.The sludge characteristics,contaminant removal,microbial quantity of population change and membrane fouling were compared with the traditional A/O-MBR and EC-A/O-MBR.The effect of temperature,aeration and reflux ratio on the treatment was also discussed.Domestication conducted by influent added in oil shale retort wastewater volume was 0,5%,15%,30%and 50%.At 30%stage,MLSS in two reactors finally stabilized at 3070.5mg/L and 4535mg/L,MLVSS was 2679.5mg/L and 3243mg/L,respectively,sludge concentration in EC-A/O-MBR was higher than traditional A/O-MBR.Many sessile ciliates like Vorticella,a few swimming cilices,Rotifers and Nematodes were found by microscopic examination.Compared with traditional A/O-MBR,sludge structure was tighter and formed the slug,iron hydroxide as the core tightly connected to the sludge as a whole,then larger Zoogloea formed in EC-A/O-MBR.Two reactors both had a high removal rate of COD,ammonia nitrogen,TN and other pollutants.Respectively,COD removal were 70.85%and 74.16%,ammonia nitrogen removal were 84.26%and 97.14%,TN removal were 68.94%and 71.17%in traditional A/O-MBR and EC-A/O-MBR.The results showed that EC-A/O-MBR on pollutant treatment efficiency was stronger than traditional A/O-MBR.Thus electric field and iron could stimulate microbial growth in A/O-MBR,and electrocoagulation could promote the removal of pollutants.PCR high-throughput sequencing results showed that the major dominant species in each reaction cell throughout the acclimation period were organic degradation like Candidate_division_TM7,Chryseobacterium,Acinetobacter,Brevundimonas,Comamonadaceae,and heterotrophic nitrogen removal such as Flavobacterium,Enterobacteriaceae,Hydrogenophaga,Lactococcus,Paracoccus and Thauera.But autotrophic nitrifying bacteria failed to occupy the dominant position in the system.Compared with traditional A/O-MBR,biodiversity indicators were higher in EC-A/O-MBR.Also Fusibacter,Clostridium and Enterococcus which were associated with iron metabolism,and Ferruginibacter with electrochemically active were found.Fouling in membrane of two systems showed that the membrane module TMP in EC-A/O-MBR was lower 0.0181MPa on average when traditional membrane module TMP reached the critical TMP 0.04MPa and the average Zeta potential of sludge in EC-A/O-MBR was 5.451 mV higher than traditional A/O-MBR.Test results showed that electric field and electrocoagulation had a positive effect for membrane fouling.The effects of temperature,aeration rate and reflux ratio variable findings on pollutant removal showed that:traditional A/O-MBR for COD,ammonia nitrogen and TN removal rates were 71.25%?73.16%and 54.40%,respectively.EC-A.O-MBR for COD,ammonia nitrogen and TN removal rates were 87.24%,99.85%and 63.49%at 18?,respectively.It is indicating that the treatment effect in EC-A/O-MBR was stronger than traditional A/O-MBR at a low temperature.When the aeration rate was 0.2m3/h,the treatment reached the best.The removal of COD,ammonia and TN in traditional A/O-MBR were 66.40%,94.15%and 68.94%,respectively.The removal of COD,ammonia and TN in EC-A/O-MBR were 67.30%,98.26%and 71.17%,respectively.The treatment had the optimum state when reflux ratio was 200%.The removal of COD,ammonia and TN in traditional A/O-MBR were 81.20%,95.46%and 70.70%,respectively.The removal of COD,ammonia and TN in EC-A/O-MBR were 82.10%,99.40%and 72.73%.Studies have shown that,EC-A/O-MBR,as a new wastewater treatment system which combines of biological-electrochemical-membrane filtration,can improve the processing efficiency of traditional A/O-MBR and membrane fouling,effectively deal with oil shale retort wastewater.It will see a bright future for further development.