Performance And Membrane Fouling Of Submerged Membrane Bioreactor Treating Tomato Processing Wastewater

In recent years,with the rapid development of tomato processing enterprises in Xinjiang,the discharge of wastewater has also been increasing significantly.Tomato paste processing wastewater was characterized by a dark color and was heavily polluted by organics.Conventional and easy-operating biological treatment was used for treating this kind of wastewater,while these methods exhibit limitations such as high cost and poor removal efficiency.Membrane bioreactor is an innovative and promising technology due to the complete solid-liquid separation and small footprint.However,the major obstacle for the application of membrane processes is the rapid decline of the permeate flux over time as a result of membrane fouling.In this paper,we applied submerged membrane bioreactor(sMBR)to tomato paste processing wastewater treatment and assessed the performance of sMBR process,particularly in terms of membrane fouling at different conditions.Firstly,the characteristics of sMBR at continuous operation of tomato paste processing wastewater treatment were studied.The results revealed that effluents from the sMBR could reach the standard in stable period.However,after the continuous 90-day operation,the membrane fouling was serious and the flux cannot be totally recovered by physical cleaning.It was found that the rapid trans-membrane pressure rise stage was mainly caused by the cake layer through resistance analysis.Moreover,the results indicated that the small particles had a strong deposit tendency on cake layer and would worsen membrane permeation significantly through the analysis of physicochemical properties of mixed liquor and membrane foulants.In addition,the results suggested that gel layer on membrane surface was not only governed by deposition of EPS,but also by organic substances.Though the proportion of inorganic elements to membrane foulants is small,the effect on membrane fouling could not be ignored.Secondly,the effect of aerobic granular sludge on tomato paste processing wastewater was investigated.The experimental results indicated that the aerobic granules have several advantages over conventional bioflocs on removing pollutants and delaying membrane fouling.However,the granular sludge appeared disintegration to some extent and led to severe membrane fouling.Therefore,it conducted to investigated this phenomenon,the results showed that the decrease of particle size and the release of EPS were responsible for aggravation of membrane fouling.In addition,the diversity variation of two biological process was analyzed and the results indicated that the structure and function succession of microbial community were occurred and the new dominant species and the corresponding functional bacteria appeared.Finally,the efficiency and membrane fouling mechanism of treating colloids and dissolved organic matters in tomato processing wastewater were compared in sMBR.The results showed that the removal efficiencies were nearly the same during the treatment of colloids and dissolved organic matters.In terms of membrane filtration resistance,the contribution of colloids to irreversible resistance is greater than that of dissolved organic matters.In the analysis of physicochemical properties,it was found that they had similar effects on the filtration resistance of mixed liquor,while that of cake layer was significant.The reason for this was the difference of small particle filtration resistance.The results showed that suspended solids in mixed liquor are the main reasons for the decline of membrane flux in early stage and colloid and dissolved organic matter are the main reasons for the later stage.