| Membrane bioreactor (MBR) which is a new wastewater treatment technologyhas certain industrial applications in the process of domestic sewage and industrialwastewater. But the membrane fouling seriously affects the performance, shortens thelife of membrane and increases the economic running cost, therefore it is the mainbottleneck of restricting the popularization and application. Properties of the mixturein the MBR system especially the soluble microbial products (SMP) become theimportant influence factors of membrane fouling. Therefore, it’s important to studythe membrane fouling mechanism of SMP and to discuss the control methods ofmembrane fouling.This subject which regards pretreatment tungsten smelting wastewater as theresearch object study the effects of sludge characteristics, pollutants removal and theformation characteristics of SMP under different HRT and SRT,the results showed asfollows:（1）The removal of COD, TN were slightly poor,the SND process of sludgewas obvious and the SMP, protein and polysaccharide concentration were relativelylow with HRT. The results showed that when HRT was longer, a relative lack ofnutrients within the system caused by the enhanced endogenous metabolism ofmicrobial to meet their growing needs caused SMP, proteins and polysaccharidesrelatively low.（2）The increase of sludge loading with SRT decreasing will lead to less activityof sludge,it is not conductive to the remove of pollutants when SRT was too long ortoo short.There is an optimal SRT which can optimize the removal efficiency. SMP,protein and polysaccharide concentration gradually reduced with the decrease of SRT.It may be the combination of microbial metabolism and cell autolysis. Under thecondition of different SRT supernatant were analysed by fluorescence spectrum, theresults showed that PVDF membrane has a strong interception ability formacromolecular protein, however it was poorer interception effect for small moleculehumic acid.（3）The experimental results show that the resistance of membrane fouling ismainly caused by deposition layer resistance（Rc）, whose proportion is as high as91.7%in which the external pollution resistance (Ref) and gel polarization resistance (Rp) accounted for35.6%and35.6%,respectively. The gel polarization which causedby colloid substances and other products have been found to strongly impact themembrane pollution in the short-running process and belong to the primary pollutionfactors in membrane fouling. Internal contamination resistance (Rif) and membraneproportion resistance (Rm) are very small, at5.8%and2.5%, respectively. It showedthat deposits layer is the main cause of membrane fouling in the short-term membranefiltration process.（4）With the extension of operating time and the increase of the initialpressure, membrane pollution resistance increase and the membrane fouling rateaccelerated which form the gel layer and filter cake layer leading to membranefouling. There was a slight decrease in the proportion of Rcwith the extension of itsrunning time for a long-term operation,but still over80%.The proportion of RpandRifincreased because of the accumulation of SMP and small molecules adsorbed onthe membrane pores.（5）According to the different main pollutants of membrane,the differentcombinations of chemical cleaning and physical cleaning are adopted.The studiesfound that the cleaning combination of aeration+ultrasonic+sodium hypochlorite+sodium hydroxide+hydrochloric acid was better than simple combination ofaeration+hydrochloric acid+sodium hydroxide+sodium hypochlorite, the recoveringratio of flux was91.2%. The experiment analyzed the best cleaning time of variousstages of the cleaning combination of aeration+ultrasonic+sodium hypochlorite+hydrochloric acid+sodium hydroxide. The optimum time were: Aeration cleaning2h, ultrasonic cleaning1h, sodium hypochlorite cleaning1h, sodium hydroxidecleaning2h,hydrochloric acid cleaning1h. |
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