The Screening And Culture Conditions Optimizing Of Flocculant-producing Strains And Study On Flocculation Characteristic Of The Flocculant

Organic and inorganic flocculants have been used widely due to their low prices and good effect.However,their disadvantages have drawn people's attention.Aluminium remaining in drinking water easily leads to senile dementia.The monomer of polyacrylamide(PAA) can't be degraded and it's both neurotoxic and oncogenic for human body.Thus,safe biodegradable flocculants that are both environment-friendly and effective are urgently needed.Microbial flocculants(MBF) are microorganism-produced special substance thatcan flocculate suspended solids,cells,and colloidal solids.With the advantages ofhigh efficiency,innocuity and biodegradability,MBF have been paid more and moreattention to recently.In this thesis,it was systematically researched,which includes the screening of the polymer-producing microorganism,the optimization of cultural conditions,droping down the cost of microbial flocculants,active ingredient,the characterization of mechanism of the microbial flocculants and application in wastewater treatment.Through preliminary researched,a strain of microbial flocculant named MBF- I with had high and stable flocculating activity was isolated from activated sludge.This strains was identified according to its morphological,physiological and biochemical characters,as well as 16S rDNA sequence homology comparison.The results are as follows:This flocculant composing microbe belong to Bacillus Brevis.The effects of carbon and nitrogen sources and initial pH on bioflocculant-producing properties of strain MBF-I were investigated respectively,and the optimum cultural conditions was confirmed:20g glucose,(NH₄)₂SO₄ 2g,1g MgSO₄.7H₂O,in 1000ml distilled water.When the initial pH value of themedium was adjusted to 7.0,and the microbe was cultured at 30℃and shaken at 150 rpm in a rotary shaker for 24 hours,the flocculating rate of the MBF- I can reach 83.43%The factors that affect efficiency of flocculation was tested systematically.The flocculant produced by strain MBF- I was found to be effective for flocculation of kaolin suspension when the dosage was 3ml/L,pH was 7 and temperature was 60℃,6%CaCl₂ in wastewater.Compared with other bioflocculants that were reported,this bioflocculant show a good quality of less dosage,commom pH range and higher thermal stability.The microbial flocculants produced by MBF-I was excreted out of the cell,the flocculating substances synthesized intracellularly which mainly existed in fermnt liquid.It is demonstrated that the microbial flocculant has negative charge,basis are complex polysaccharide by analyzing.The major mechanism are adsorption and bridging.When studying the application of bioflocculants.In order to reduce the cost of media the microbial flocculants are produced by using dairy soybean okara and currant instead of media. The flocculation effect of microbial flocculants on the wastewater is studied.Pilot tests show that CODcr,SS and chroma removal are high.