Screening Of Flocculant-producing Microbe And Study On The Flocculability

Microbial flocculant is a kind of high molecular substance which is produced bymicroorganisms. It is nontoxic, high-efficient and widely-used. Nowadays, much moreresearches focus on microbial flocculant. The main content of this paper and the results areas follows:Thirty strains produce flocculant were selected from the activated sludge and soil, andthe flocculating rate were over70%. Among them,13strains showed high flocculatingactivity more than80%. In this research, one fungus （designated M9） exhibited agreeableflocculating activity was selected as the research material. According to its morphologicaland culture characters, as well as rDNA-ITS sequence homology comparison, this strainwas identified as Aspergillus aculeatus.Submerged fermentation conditions affect flocculant production were studied usingthe classical “change-one-factor-at-a-time” method. The results showed that the optimalcarbon source was dextrin （4.0%）, the optimum nitrogen source were soybean peptone（0.1%） and NH4Cl （0.2%）, while the best inorganic salts were NaCl （0.025%）, KCl（0.025%）, K₂HPO₄（0.05%） and MgSO₄·7H₂O （0.05%）. The optimal initial pH value,cultivation temperature, rotation rate, inoculum size and liquid volume of the cultures were7.5,30℃,150r/min,1×10⁶spores/mL and50mL, repectively. Under the optimizedconditions, the highest flocculating acitiviy was97.67%obtained in the3th day.The bioflocculant was simply purified. It was secreted by Aspergillus aculeatus M9into the extracellular and present in the fermentation liquid mainly. The supernatant waspoured into three volumes of cold anhydrous ethanol to precipitate the bioflocculantovernight at4℃. The resulting precipitate was collected by centrifugation at7,000rpm,4℃for20min, and finally lyophilized to obtain crude bioflocculant. The production of thecrude bioflocculant was16.6g/L. Composition of the crude flocculant was studied by colorreaction, UV-spectrophotometry and quantitative analysis. The proportion of thepolysaccharide and protein was98.51%and0.88%, repectively. The results of theexperiment on the flocculating characteristics of the bioflocculant produced by strainAspergillus aculeatus M9showed that the bioflocculant had good pH stability and thermalstability. The optimal dosage of bioflocculant was2mL. Multiple metallic ions could promote the flocculating effects. Among these metallic ions, Ca²⁺showed the best effect,and the optimum dosage was2mL at a concentration of1%. The flocculant kept highflocculation activity in a wide pH range2～5of kaolin suspension.