Study On Development And Application To Sludge Dewatering Of Microbial Flocculant

Microbial flocculant(MBF) is a kind of natural macro-molecular organic substances with flocculating activity produced by microorganism. In recent years, For its high performance , biodegradability and safety for the environment et al, microbial flocculants has drawn more and more attentions. This paper cultures all of the organisms which can survive in the experimental condition together and then extractes the flocculant from the culture broth. The MBF is applied to the concentrated sludge from the forth wastewater treatment of Kunming to improve the ability of its dewatering.In this study, the flocculating activity is the best when the activated sludge in the culture broth is 0 ml. The favorable medium for production of the flocculant is 1% glucose, 0.5% K₂HPO₄, 0.2% KH₂PO₄, 0.02% MgSO₄.7H₂O, 0.01%NaCl, 0.05% urea, and 0.05% yeast extract with initial pH 8.5, culture temperature 30 °C and aeration rate 0.008 m³/h.The productivity of the flocculant is about 5.39 g/L. Its major ingredient is protein and polysaccharide.From the study of the flocculating efficiency, we can conclude that (1)its flocculating activity on kaolin clay suspension is very weak in the acid condition, but the MBF exhibits significant flocculating activity when the pH value is in the range of 7 8;(2)Most of the flocculant distributes in the culture broth and a few of it distribute in the cell;(3)MBF has a optimum concentration range, when the dosage of culture broth ranges from 0.5ml to 3ml, the flocculating activity increases. The flocculating activity increases to 98.8% when the dosage is 3ml, but when the dosage is more than 3ml ,the flocculating activity is lower and lower. (4)When the dosage of CaCl₂ solution(1%) raises from 0ml to 5ml, the flocculating activity raises from 0 to 98.3%, but the flocculating activity decreases when the dosage is more than 5ml. (5)The MBF exhibits much higher flocculating activity in the presence of divalent and trivalent cations. This indicates that multivalent cations can stimulate the flocculating activity of MBF.The flocculating experiment of concentrated sludge shows that MBF almost can not improve the dewatering ability of concentrated sludge without the CaCl₂ solution. In thesame centrifugation condition, the dosage of MBF is the least among PAM, PAC andbut the flocculating effect is the best.