Research And Development Of Microbial Flocculants

Microbial flocculants are newly developed natural macromolecular organic substances. For their biodegradability, high performance and harmless to environment, microbial flocculants has draw more and more attentions. This paper summarized a series of research and development on preparation of microbial flocculants systematically. The isolation of flocculant-producing bacterium, optimization of culture condition for flocculants production, the composition, characteristics and flocculation mechanism of microbial flocculants were studied and discussed. The main contents of the research and the results are as follows:For the screening of microbial flocculant-produing microorganism, suspensions from activated sludge, soil solution were cultivated in given media with Kaolin clay suspension as the test sample for flocculating activity. In 17 screening bacteria, the two best strain with flocculating activity were isolated from soil and identified as Serratia ficaria and Klebsiella mobilis. It is first time to discover Serratia ficaria as flocculant-producing bacteria.The experiment conditions were optimized for Serratia ficaria. The strain could grow in wide situations and produce high-effect flocculants. The studies show that the optimum carbon source for this strain to producing flocculant is lactose and the nitrogen source are yeast cream and urea; the optimum pH is 6.0⁸.0; the optimum inoculability capacity is about 1.0 %; the salts are 0.2 % K₂HPO₄ and 0.5 % KH₂PO₄; the optimum culture time is 3 days. The flocculation could reach 97.0.% after 3 days' culture.The microbial flocculants produced by Serratia ficaria are excreted out of the cell, and the flocculants are mostly distributed in zymolytic medium. The flocculation and Zeta potential experiments were made. It is demonstrated that the microbial flocculants are a kind of anion macromolecular organic substances and the majormechanism are adsorption and bridging.The microbial flocculants are produced by using dairy wastewater instead of media. The flocculation effect of microbial flocculants on the treatment of wastewater is studied. Pilot tests show that COD_Cr, SS and chroma removal are high.