| Octylphenol ethoxylates (OPnEO), next to the fatty alcohol ethoxylates, is the second largest and high performance nonionic surfactant. It has been widely used in washing, textile, leather, paper, pesticides and the like. However, OPnEO produces serious environmental pollution inevitably in its use because it is hard to natural degradation but easy to accumulate. And the low molecular weight oligomers have strong estrogenic effect from the progress of degradation. At present, OP, OPEO1 and OPEO2 have been detected in municipal wastewater, surface water, drinking water, industrial waste water, river and its sediment, ocean and coastal sediments. Therefore, the study is based on the four efficient degrading bacteria of octyl phenol ethoxylates (OPnEO) which filtered in the previous experiment; they are H1, TXBc10, OPQb11 and TXBa23. The study aims at enhancing the degradation ability of octyl phenol ethoxylates through competition and synergy among different strains, building a highly efficient mixed flora to degrade OPnEO, optimizing the conditions of mixed flora degradation OPnEO under the response surface methodology to improve the degradate efficiency. In addition, it tries to filter the best immobilized carrier of mixed flora degradation OPnEO by comparing the merits of three fixed carriers:sodium alginate (SA), polyvinyl alcohol (PVA) and PVA+SA. Moreover, the optimal condition for immobilization embedding is determined by orthogonal experiment. The main conclusions are as follows:(1) Structured efficient mixed bacteria L9 of OPnEO degradation. According to the research of growth characteristics and degradation characteristics of OPnEO degradation bacteria H1, TXBc10, OPQb11, and TXBa23, combination experiments are used to match four strains proportional ratio and obtain a set of mixed bacterium of OPnEO degradation, which was named L9 (H1: TXBc10: TXBa23 1:1:1). Under these circumstances:the total inoculum 4%,28 ℃, pH 7.0,180 r·min-1 for 7 d culture OPnEO initial concentration of 500 mg·L-1 degradation rate reached 56.44%, which improved 8.63% compare to the best single bacterial strain (table 1 test group 15 TXBa23,47.81%).(2) Optimized the degradation condition of mixed bacteria L9. Univariate tests are to investigate factors influence L9, initially determined the addional carbon resource and nitrogen sources of L9 degradation OPnEO were glucose and tryptone, optimum initial pH is 7.0, the optimum temperature is 28 ℃, the optimum inoculation amount is 4%. Plackett-Burman screening test gain three significant factors to influence OPnEO degradation, rate of L9 inoculation amount, temperature and initial pH. Steepest ascent experiment approaching three significant factors of the maximum response region, using the Box-Behnken experimental design and response surface method analysis to determine the optimal degradation conditions of L9 is in 50 mL reaction system, inoculation 4.16%, temperature 28.20 ℃, initial pH 7.13, the glucose concentration 2%, tryptone concentration 2%, OPnEO initial concentration 500 mg · L-1,180 r · min-1 cultured 7 d, the mixed bacteria L9 OPnEO degradation rate can reach 62.15%. This result is increased 4.82% than non-optimization conditions.(3) Filtered the best immobilized carrier of mixed bacteria L9. The experiment selects Sodium alginate (SA) and polyvinyl alcohol (PVA) as the carrier; OPnEO degrading mixed culture L9 is the target material, SA, PVA and PVA+SA are methods used to prepared immobilized mixed bacteria L9. The study probes into the mechanical stability of the particles and chemical stability of each immobilized mixed bacteria L9. The results show that the immobilized mixed bacteria L9 particles obtained by the use of PVA+S A have high mechanical and chemical stability.(4) Optimized the immobilization condition of mixed bacteria L9. PVA+SA immobilization conditions are optimized in Orthogonal Experiment. It obtained a polyvinyl alcohol (PVA) concentration of 8.0%, sodium alginate (SA) concentration of 1.0%,2% crosslinker saturated boric acid solution of calcium chloride, embedding medium and the amount of bacteria ratio is 1:2, crosslinking time 24 h are optimal conditions for immobilization of mixed bacteria L9 with PVA+SA. Based on the influence of different environmental conditions (temperature, pH and substrate concentration) to L9 degradation OPnEO between immobilized mixed bacteria L9 and dissociated mixed bacteria respectively, the results show that immobilized mixed bacteria L9 has wider tolerance range than dissociated mixed bacteria L9 in various environmental factors (temperature, pH and substrate concentration), which can keep stable biological activity in real environment application, and that will provide significant guidance to solve the OPnEO pollution problem made by leather, washing, pesticide and other industries. |
