Technique Of Removing Turbidity From Raw Water By Microbial Flocculant Pullulan

This thesis summarizes the general research situation and development tendency of flocculant in domestic and international field. Combining the relevant theories of flocculation in removing turbidity, we have taken many experiments on removing the turbidity of raw water with a new flocculant in water treatment——microorganism polysaccharide pullulan, and have explored the flocculation mechanism primarily. The research results show that:(1)Pullulan has merit of security and it can be biodegraded. The common dosage is 1～3mg/L, and the flocculation effect is considerable, it can generates thick reticulation flocculate flower sediment which has strong frame and is not easy to crash. The separation of sludge and water is quick.(2)Pullulan has obvious merit of removing high turbidity water, the higher turbidity, the removing effect is better. The range of temperature it can adapt is: 5～35℃.(3)We should pay attention to the dosing sequence when we use pullulan as flocculant and some coagulant aid together, at the same time, we should control the dosage of coagulant aid within 10～20mg/L(such as aluminum sulfate), the primary stirring intensity is 200r/min(G=107s-1), the total value of GT is 30000. In addition, we should also notice the influence by pH value, it can generally be ignored when it's value is in 5.0～8.5.(4)At the same Initial condition, the effect is better when we use pullulan as flocculant and aluminum sulfate as coagulant aid together than use aluminum sulfate only. And the turbidity of effluent water has decreased 63%, the dosage has decreased 40%.(5)About the flocculation mechanism of pullulan, it mainly depends on the combination of the affine function between glucose(remnant base) and colloid particles, stuffing function inside the linear structure, physical adhesive effect outside, bridging by long molecular chain, electric neutralization and polymerizing electrolyte function.