Isolation O F Microbial Flocculant-producing Strain And Its Application In Treatment Of Pb²⁺ Wastewater

Compared withinorganic flocculants and organicflocculants,microbial flocculants havemany advantages: no second pollution,easily degraded by microorganism, high flocculatingprecipitation, non-toxic,high efficiency andsafe. In water treatment,the technology of using flocculation is an important treatment method. That makes microbial flocculants become a hot field of research and have great development in our country and abroad.In this study, samples were used to isolate and screen polysaccharide producing strain via a selective medium containing Congo redstain. This method is novel and unique formicroorganisms. And it can significantly improve theculturability of strains, discovery and identifythe new strains. Based on its morphological observation and analysis of the partial sequences of its 16 S r DNA, it was found thatthe strain products capsular polysaccharide. In the study of microbial flocculants in our country and abroad, microbial flocculant product capsular polysaccharide is relatively rare. The main results are as follows:68 strains were isolated from activated sludge with oligoclonal medium including Congo-Red solution. After rescreening, 24 strains were obtained, and the strain LLin6 was obtained with the highest flocculating activity after double rescreening. By analyzing its morphological characteristics and the 16 S r DNA sequence,it was identified as Acinetobacter sp. Then the optimum culture medium was studied by orthogonal design test. The experimental results showed that the optimum culture medium of strain LLin6 isconsist of glucose 15 g/L, Sucrose 10 g/L, yeast extract 0.7 g/L, carbamide 0.1 g/L,(NH4)2SO4 0.5 g/L, KH2PO4 1 g/L, K2HPO4 2.5 g/L, Mg SO4 0.3 g/L and Na Cl 0.2 g/L.First of all, the optimum culture conditions were ascertained through single factor experiment,then, response surface methodology(RSM) was adopted to optimize culture conditions.Four response factors were selectedas response factors includingp H, cultivating temperature, cultivating time, shaking speed, and flocculation rate was used as response value. The optimum culture conditions were: p H of 6.59, cultivating time of 22.87 h, cultivating temperature 23.08 ℃, shaking speed of 150.34 r/min. Under such culture conditions, the theoretical value of the flocculation rate was 90.692% and the verifiedflocculation value was 90.33%. Itis demonstrated that the modelis convincible by confirmation experiments. The effective component of flocculant was determined through such method of ultraviolet spectroscope and infared spectra. The output of flocculant was 1.7 g/L, which including 2.553μg/μL of total glucideand 0.7028μg/μL of protein.By analysis of the effect on flocculation of the flocculation conditions,the results of experiments indicate that the optimum flocculation conditions are: bioflocculant of 10 ml/L,Ca Cl2 of 3 ml/L,p H of 7, temperature of 20 ℃.Bysimulating wastewater containing Pb2+ ions with biological flocculant, we explored the impact of various factors on the adsorption of heavy metal. The best p H range is 6, the optimum adsorption temperatureis 20 ℃ and 10 min-60 min is the optimum adsorption time. The optimal initial concentrationof Pb2+ range is 5 mg/L-20 mg/L. Under the optimum adsorption conditions,the maximum removal rate of Pb2+ reached to 95.98%.