Study On Performance And Membrane Fouling Control Of MBR Further Treating Leachate From MSW Incineration Plant

Incineration power generation has become a popular way for municipal solid waste （MSW） disposal. It has been demonstrated as an effective technology for its advantages in reduction, harmless and resource recovery. The fresh leachate generated during the MSW storing and aging can be treated by a combined "EGSB-anoxic/two-stage aerobic MBBR-MBR" process, however membrane fouling was observed in the MBR unit. In this paper, the operational parameters were optimized to mitigate the membrane fouling. The mechanisms involved in the membrane fouling of submerged and recirculated MBRs were disclosed, and a suitable cleaning method was proposed.Based on the performance on the removal of COD、NH₄（⁺）-N、TN、TP、SS and the flux and transmembrane pressure of the membrane, the optimized operation conditions of the recirculated MBR are controlled as the following:cross-flow rate,2.21 m/s, operating pressure,0.03 MPa, the MLSS, 2000-6000 mg/L. Both the submerged MBR and recirculated MBR were operated for 100 days under their optimal conditions. In the both MBRs, no obvious difference was observed on the pollutant removal by these two MBRs, the average removal efficiencies of COD, NH₄（⁺）-N, TN, TP and SS were 93%,97%,24%,15% and 100% respectively. Both the MBRs have demonstrated great on removal of volatile organic compounds and humus-like DOM, and the long-chain alkanes and protein-like substances in the influent were completely removed. The similar functional groups were observed according to the FT-IR spectra of the cake layer on the membrane surface. The inorganic CaCO3 and extracellular polymer substrates were determined as the main composition in the cake layer. Cake layer resistance was the main resistance in the submerged MBR, accounting for 63.89% of the total resistance, while the cake layer resistance and irreversible layer resistance accounted for 33.77% and 35.42% in the recirculated MBR. The bacterial community structure in the cake layers on the surface of membrane in submerged MBR and recirculated MBR were determined by high-throughput sequencing method. The results showed that bacterial diversity of cake layer in the recirculated MBR （Shannon=5.42） was much higher than that in the submerged MBR （Shannon=2.53） and the proportion of γ-proteobacteria in cake layer of submerged MBR was larger than that of submerged MBR. γ-proteobacteria can attach to the membrane surface easily, leading to the membrane fouling. It is the reason why the submerged MBR was contaminated more easily than the recirculated MBR.Physical （air wash+gas-water mixture wash+high-speed water wash） and chemical cleaning method （sodium hydroxide+citric acid） was used to recover the contaminated membrane, and it can make the membrane flux be recovered to more than 97.37%. The results based on the atomic force microscope and scanning electron microscope showed that the roughness and number of zoogloea on membrane surface decreased significantly after being cleaned. For the reuse of the recovered membrane, the membrane fouling rate of submerged MBR was more obvious than that of recirculated MBR, and the cumulative permeate volume of recirculated MBR was 93686.54 L/m2, much higher than that of the submerged MBR at 4246.71 L/m2, the costs by the recirculated MBR was 2.391 yuan/m3, less than 2.896 yuan/m3 by the submerged MBR, moreover, the recirculated MBR has other merits including the flexible operation, easy management, automatic control online.