| Nonylphenol polyethoxylates (NPnEO, n=1-20), which are widely used in people’s daily life and are closely related to human life, are the second major category of commercial nonionic surfactant in the world. After being discharged into the environment, NPnEO would be degraded step by step into short-chain nonylphenol polyethoxylates (SCNPnEO, n=1-2) and nonylphenol (NP) by microorganisms. SCNPnEO can also be abbreviated to NPnEO1～2 or NPnEO (n=1～2). As the degradation products of NPnEO, NPnEO1～2 are difficult to be further degraded because of their stable property. NPnEO0～2 are kinds of environmental hormone, and are similar to endogenous estrogen 17 β-estradiol in structure. If they enter animals’ bodies, the estrogen-like effect as macrocephaly, cancer and mutationwill occur. Currently, NPnEO0～2 distribute all over the world and can be detected in most of the countries and regions. The harms of NPnEO0～2 to human and animals are growing. It has great significance to find proper bacteria to fully degrade NPnEO0～2 and to avoid its deposition in environment.Dispersive liquid-liquid micro-extraction and high performance liquid chromatography (DLLME-HPLC) were used as the detection method in this study. The degradation properties of pseudomonas putida, rhodococcus erythropolis and citrobacter freundion NPnEO (n≈2) were investigated. The optimal degradation parameters under 36 h were bacterial culture temperature of 30 ℃, pH of 6-7, initial NPnEO (n≈2) concentration of 6 μg/mL, initial strains dosing of 2%(v/v), and co-metabolic substrate of 0.5 g peptone. Under this condition, the NPnEO (n≈2) degradation efficiencies of three bacteria achieved 97.9%,98.9% and 97.6%, respectively. The mixed bacteria degradation efficiency was also studied. The mixed bacteria (1:1:1) degradation efficiency was higher than each single bacterium and presented obvious synergistic effect.The anoxic/oxic membrane bioreactor (A/O-MBR) was performed to degrade the artificial NPnEO (n≈2) waste water. The previous research showed that the temperature was the most important factor of A/O-MBR on NPnEO (n≈2) degradation. In this study, the A/O-MBR was run under different temperatures of 25,30,35 and 40 ℃ to find the optimal temperature for NPnEO (n≈2) degradation. The results showed that the optimal temperature was 35 ℃. The pH, mixed liquor suspended solids (MLSS),mixed liquor volatile suspended solids(MLVSS), chemical oxygen demand (COD), total phosphorus (TP), NH4+-N, NO3--N and NO2--N were also monitored to ensure the stable operation of A/O-MBR. The results showed that the pH was between 6.5～7.8, MLSS was between 6221-7792 mg/L and MLVSS was between 5011～6588 mg/L, respectively. The removal efficiencies of COD、TP were 96.5% and 95.4%. The variation of NH4+-N, NO3--N, NO2--N conformed to the nitrogen theory and the system ran stably.The plating method was used to purify the dominant degradation bacteria from the A/O-MBR running at 35℃.The purified bacteria were cultivated to degrade NPnEO (n-2) for 24 h to seeking the optimal degradation parameters. The resulted showed that the optimal parameters were bacteria culture temperature of 30 ℃, pH of 7, the initial NPnEO (n≈2) concentration of 15μg/mL for anoxic bacteria and 20 μg/mL for oxic bacteria, the strains dosing of 4%, and the peptone dosage of 0.5 g. Under this optimal parameters, the NPnEO (n≈2) degradation efficiencies of anoxic bacteria and oxic bacteria achieved 88.7% and 87.4%, respectively.The results showed that the A/O-MBR process and the five kinds of bacterium could degrade NPnEO (n≈2) efficiently. The bacteria separated from the A/O-MBR process presented higher degradation ability for high NPnEO (n≈2) concentration than pseudomonas putida, rhodococcus erythropolis and citrobacter freundi. The NPnEO (n≈2) degradation efficiency of A/O-MBR process was higher than purified bacterium and proved that appropriate mixed bacteria could improve NPnEO (n≈2) degradation efficiency effectively. This study can offer support for the further research. |
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