| 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(NP)EO) and Nonylphenol(NP) by the degradation micro-organisms. Numerous studies show that, SC-NPnEO those ethyl degree of polymerization was 1-2 (NP1EO and NP2EO) and NP(hereinafter collectively referred to as NPEO0～2) as degradation product of NPnEO widespread in nature, with a strong pro-lipid, accumulation and toxicity, is more difficult to be further degraded. Besides its structure is similar to endogenous estrogen 17β-estradiol, NPnEO can be directly combined with the estrogen receptor in the biological tissue to produce estrogen-like effects. However, due to the efficient decontamination ability and low price, NPnEO still as the main non-ionic surfactant mass production and use, resulting in the accumulation of large NPEOo-2 to the nature.A wastewater treatment system combined with anoxic/oxic (A/O) activated sludge process, membrane bioreactor (MBR) and contact oxidation process was developed to treat NPnEO (a mixture containing NP and NPEOO～5, 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 and mixed liquor suspended solids(MLSS) 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 three parameters:Temperature (T), Dissolved Oxygen (DO) and Hydraulic Retention Time (HRT). 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 the experiment, pH was between 7.0 and 8.5, and MLSS kept in 2500-6000 mg/L. The removal efficiencies of COD was stable and were more than 94.23%.Good removal efficiencies of NH4+-N were also obtained and the average removal efficiency was between 85.00% and 95.00%. TN removal efficiencies were not very good and were varied from 60.00% to 90.00%. Average removal rate of TP were 50.00% during the experiment. After the addition of SC-NPnEO to influent, the system shared certain resistance to impact 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:DO 5mg/L, T 33 ℃, HRT 24h. We also obtained the order of various parameters that influence the degradation of NPEO0～5. |
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