Separation And Purification Of Compound Bioflocculant And Study On Decolorization Of Methylene Blue

Microbial flocculant is a new water treatment agent made of microbial cells, or cell structure, or the separation of metabolites, it is a new hot spot of flocculant researching. Compared with Organic and inorganic flocculants, microbial flocculant has the advantages of non-toxic, no secondary pollution, degradation, etc, but there are also many problems such as high medium cost, insufficient production, poor flocculation, more influence by environmental factors.In this study, the compound flocculation bacteria has been constructed with four flocculating strains DG2, DN1, H8, H13which were isolated and screened from activated sludge. Flocculating activity distribution test showed that the flocculant was mainly extracellular metabolites secreted by bacteria. Flocculant produced by the bacteria were isolated and extracted, the yield was0.923g·L-1. The flocculation rate can reach93.3%with the best dosage of0.06g·L-1on the kaolin suspension test. The extracted flocculant as pale pink powder has characteristics of strong water-soluble, heat resistance and suitable for the use of acid and neutral solution.To further improve the efficiency of the flocculant and analyze the flocculation mechanism, the extract of the flocculant was purified by ion-exchange chromatography and gel chromatography, and then the purified flocculant was tested by qualitative analysis, quantitative analysis and structure analysis. After purification flocculation rate can reach to98.4%and the recovery of flocculant was54%and. Property analysis showed the purified flocculant was mainly glycoprotein with sugar content81.6%and protein content17.8%, molecular weight5.2×106. Molecular structure contains a large number of mannose residues, hydroxyl and carboxyl, and combined with kaolin that was an interaction results of ionic bond and hydrogen bond.To test the treatment capacity of flocculant on printing and dyeing wastewater which is one difficult problem of wastewater treatment, decolorization capacity of flocculant had been test with object of study prepared by chemical dye methylene blue solution. Optimization by orthogonal experiments showed flocculant had the best effect that decolorization rate can reach to97.8%under pH9, flocculant dosage of0.07g·L-1, Ca2+concentration of1.4%, static precipitation time5min, the solution temperature of40℃. The flocculant had maintained more than85%of the decolorization rate at pH8～10, temperature20～50℃and it’s properties was significantly better than inorganic flocculants, organic flocculants and flocculant produced by single strain bacteria.