| Nonylphenol Polyethoxylates(NPnEO), which is widely used in industry, agriculture and daily life, is currently the second largest commercial nonionic surfactant in the world. Abandoned Nonylphenol Polyethoxylates(NPnEO) enter into the municipal sewage treatment plants or natural waters through the city sewer system, which are converted into Short-Chain Nonylphenol Polyethoxylates(SC-NPnEO), such as Nonylphenol Monoethoxylate (NP2EO), Nonylphenol Diethoxylate(NP1EO) and Nonylphenol(NP) by the degradation micro-organisms. These substances(collectively called NPEC2～0) have the difficult degradability, toxic and the biological accumulation, which also exhibit estrogenic activity to organisms, and they are environmental hormone substance. The massive research indicated that these substances can be found in the air, the soil and the water.A wastewater treatment system combined with anoxic/oxic (A/O) activated sludge process and membrane bioreactor (MBR), which is A/O-MBR, was developed to treat NPnEO (a mixture containing NP and NPEO5～1,n≈3). Activated sludge of this system was cultivated and domesticated firstly, and then key operational parameters were changed to optimize the treatment process. The removal efficiencies of COD, ammonia(NH4+-N), total nitrogen (TN), total phosphorus (TP), and even pH, mixed liquor suspended solids(MLSS) and mixed liquor volatile suspended solids(MLVSS) of activated sludge were monitored. During the study, the concentrations of the short-chain nonylphenol polyethoxylates were detected in water sample by High Performance Liquid Chromatography and were analyzed to the treatment effect of this system. Orthogonal experiment was designed by four parameters:Temperature(T), Dissolved Oxygen(DO), Hydraulic Retention Time(HRT) and Solids Retention Time(SRT). The concentrations of SC-NPnEO in effluent and the removal efficiencies of SC-NPnEO were used as the evaluation index for the orthogonal experiment. According to the results of orthogonal experiment and range analysis, the effect of each parameter and the optimum operation parameters were obtained.In anoxic and oxic reactors, pH was between7.0and8.0, MLVSS/MLSS was in 88.00%～94.00%, and MLSS kept in3500～5000mg/L. The removal efficiencies of COD was stable and wre more than85.00%, even more than95.00%in the sludge cultivation period. good removal efficiencies of NH4+-N were also obtained and the average removal efficiency was92.30%. TN removal efficiencies were not very good and were varied from50.00%to90.00%. TP removal efficiencies were bad and less than50.00%during the experiment. After the addition of SC-NPnEO to influent, the system shared certain resistance to impact lood and could remain stable.According to the orthogonal experimental results under different operating parameters and the analysis of parameters to the degradation effect of the short-chain nonylphenol polyethoxylates, we obtained optimal value of system operation parameters:T-32℃, DO-4mg/L, HRT-24h, SRT-20d. We also obtained the influence order of various parameters fpr the degradation of NP, NP1EO, NP2EO. |
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