Study On Effects Of Chitosan On Sludge Dewaterability

The most important feature of sludge is high content of water, up to 95%～99% of total quality. If water in sludge can be removed efficiently, then the volume of sludge can be reduced greatly, cost of management, transportation and treatment can be lowed and helping to latter disposal. Effect pretreatment could improve dewaterabilty of sludge. Adding flocculants is presently the most common method in sludge conditioning. However, flocculants always have some disadvantages on economic, quality and environment benefit. Therefore, this paper focuses on effects as well as mechanism of enzyme and chitosan that are broadly originated, nontoxic and biodegradable to sludge dewaterablity. The main conclusions of this paper are as follows:CSTs of activated sludge and digestion sludge were 9.8s and 41.6s respectively and this means that the dewaterability of digestion sludge is poorer than that of activated sludge. The reason is that digestion process results in degrading of solid EPS and releasing into sludge liquid. Analysis of EPS content of activated sludge and digestion sludge also illustrated that content of soluble EPS in digestion sludge was higher than that of activated sludge and content of solid EPS was reverse.Sludge was pretreated by chitosan and dewaterability of sludge treated was compared with that of sludge treated by polyscrylamide(PAM). Experiment results show when the dosage of chitosan and PAM were at their optimum dosage, for activated sludge, condition effect was comparative, whereas dosage of chitosan was 1.7 times than that of PAM; for digestion sludge, PAM could obtain a better condition effect with 44.2% lower dosage than that of PAM; for citric acid wastewater sludge, sludge conditioned by chitosan could get to better dewaterability after centrifuge dewatering, whereas dosage of chitosan was doubled.Chitosan as hypo-cationic polyelectrolyte, hydroxide radical and amido in their molecules act as both electricity neutralization and bridging in flocculation, therefore, they can be used to improve dewaterability of sludge. However, compared with PAM, molecular weight and charge density of chitosan are lower, so flocs formed in flocculation are smaller and less incompact.