| Coal chemical industry wastewater is with complex components and difficult to be degraded. It has characteristics of high concentration of suspended solids and high chroma, so that it needs to be treated by adding flocculant. However, the conventional chemical flocculant in the treatment also brought secondary pollution, therefore microorganism was considered to be used as flocculant to deal with coal chemical wastewater.In this study, 6 strains of bacteria were screened out from the domestic sewage of North University of China and the coal chemical wastewater from a coal mine in Beijing city. Through testing the flocculating activity of the six cells, two kinds of microbial flocculant producing bacteria were selected and used to conduct the endurance experiment with different concentration of coal chemical wastewater, and screened out one of the plant--flocculant producing bacteria MBFS1 that can flocculate coal chemical wastewater and survive in it. What’s more, in this study, the effects of different single factors on the culture conditions and the treatment conditions of wastewater was investigated. In addition, aiming at the problem of high cost of microbial culture, carbon and nitrogen sources were added suitably to be used as the culture solution of the strain in different organic wastewater. After that, the flocculation mechanism of MBFS1 will be discussed.By the optimization of the single factor conditions and response surface analysis. The results showed that the optimized culture conditions of MBFS1 were: p H of the medium was 7, culture time was 24 h, culture temperature was 25℃, the flocculation rate was 98.86%; and optimum conditions for the treatment of coal chemical industry wastewater were: s trains dosage was 2mL, pH was 5, cationic coagulant aid was Ca2+, help agent best dosage added amount was 5mL, flocculation rate reached 99.13% and COD removal rate was 72.56%. With beer wastewater as low-cost culture medium: the volume fraction was 60%, the best nitrogen source was urea without adding carbon source. With acetic acid wastewater as low-cost culture medium: the volume fraction was 80%, the best nitrogen source was ammonium chloride without adding of carbon source. With soybean curd wastewater as low-cost culture medium: the volume fraction was 100%, and no carbon and nitrogen sources were added. In consideration of the overall cost, soybean curd wastewater was selected to be used as culture medium for treating coal chemical wastewater with flocculation rate of 98.08%, meanwhile, the removal rate of COD was found to be 72.05%, and the color removal rate was 97.25%.By analysis, the main components of the extracellular secretion of MBFS1 was found to affect mainly in the flocculation system MBFS1 cell were protein and polysaccharide. Bioflocculant contained functional groups, such as-OH and –COOH by infrared spectrum. The Zeta potential was measured before and after coal chemical wastewater treatment, and it was found that the Zeta potential value was decreased, which was the result of the compression of the double layer. By comprehensive analysis the flocculation process was a combined effect of adsorption bridging, charge neutralization, the compression process of electric double layer and precipitation net interaction. This study made organic wastewater as culture medium and cultured strains treating the coal chemical industry wastewater and it had made certain effect: reaching the purpose of using waste to treat waste, and making progress for mixed coagulation in coal chemical industry wastewater treatment. |
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