Study On Preparation Of Bio-flocculant By Residual Of Sludge

The bio-flocculant, which is a kind of new natural organic compounds with high molecular weight, is highly valued by environmental scientists due to its high efficiency, no harm and non-toxicity. Although many kinds of bio-flocculants has been discovered, high cost of preparation limited its large-scale production, lowering the cost is an important issue for its pratical application. In this study, one low cost bio-flocculant was extracted from excess sludge by washing, cold acetone precipitation and freezing desiccation.The optimal condition for the bio-flocculant production were 100 g/L of residual concentration , washed 3 times by water while the best separating condition of bio-flocculant was 3 times volume acetone precipitation. The resulted the bio-flocculant production rate was 19.7 mg/g residual.The measurement results of partial properties indicated that the bio-flocculant had high storage stability, hot stability and pH stability. Infrared spectra analysis demonstrated that the bio-flocculant was mainly composed of polysaccharide and contained many hydroxyl, carbonyl, amide groups.The optimal condition for bio-flocculant to against kaolin clay suspension was listed as follows: pH 5.0, 3 mLMBF, 1.5 mL10 % I, 4 g/L kaolin clay suspension and 20°C. Under this situation, the flocculating activity could reach 96 %. The effect order on flocculating activity of bio-flocculant was : N >O> M> P>I> J>K >L.The acting force between bio-flocculant and kaolin suspension was hydrogen bond, which was determined by zeta potential, hydrogen bond and electrovalent bond determination, structure analysis of bio-flocculant. Bridge occured during flocculation. The results showed that the flocculation mechanism of bio-flocculant resulted from the combination of kaolin suspension with bio-flocculant by hydrogen bond at the active position. The major role of flocculation was compressed electric double layer, adsorption electrical neutralization and reducing electromotive force. The bio-flocculant had large amounts of hydroxyl and carboxyl, so the chains had longer useful length and promoted the bridge.The bio-flocculant had a high decoloration ability; it could be used in soil suspension with high flocculation rate; it could be used in activated carbon suspension , starch suspension, coking and phosphorus wastewater with poor effect.