The Influence Of Chitosan Flocculant On Sludge Dewatering Ability

As the rate of municipal wastewater treatment going up in our country, the amount of sludge produced in the treatment process increase a lot. Since the sludge contain larege proportion of water,about 95-99%, resulting in enlarged sewage volume,which bring too much trouble when disposing sludge, bring a number of problems in process of treating the sludge. Accordingly getting rid of the containing water will greatly decrease the sludge amount and enormously increase the ability of sludge proposal afterwards.Normally, due to its bad dewateringability, the sludge is difficult to be dewatered. Therefore, increasing the dewateringability of sludge is very important. Employing the chemical coagulants to pretreating the sludge can greatly increase the sludge dewater ability and then make the sludge lose a great deal liquid in the subsequent mechanical dewatering processs.At present, many sewage plants adopt PAM,PAC etc, to conditioning the sludge. These man-made coagulants have the venomousness and are difficult to decomposing, harm to environment and human health. Macromolecular Chitosan flocculant is nontoxic, and harmless to human health, easy to decomposing,and does not cause secondary pollution besides.This paper provides a study concerning the effect of Chitosan (CTS) flocculant to sludge dewater ability. Dewaterability was mainly evaluated by specific resistance to filtration (SRF). Sludge dewatering behaviors conditioned with CTS, cation polyacrylamine (CPAM) and AlCl₃ coagulants were compared. Effects of pH,chitosan characteristics such as molecular weight, degree of deacetylation and dosage have been studied. As following, CTS composite flocculants (with AlCl₃) were also used in sludge conditioning of two stages. The sludge dewater ability is studied with this composite flocculants. The main conclusions of this study are as follows.Under the experimental condition, the optimum dosage rate for CTS was2.0% of dry solids in the sludge feed, while SRF was reduced by 93.7% and moisture content of cake was 70.8%.It was found that the sludge conditioned with CTS has better dewaterability than that with AICI3 and the dosage of CTS is less than AICI3. The similar result was obtained when CPAM was employed in the range of experimental dosage. The better result could be achieved with CTS out of this range.pH, chitosan characteristics such as molecular weight, degree of deacetylation and dosage have taken parts in sludge conditioning to different points. The literature review finds that the optimum condition is pH 6-8.As CTS is employed together with AICI3, the dewaterability was improved better in the case of that when AICI3 was followed by CTS. CTS composite flocculants was found to be more effective than single flocculant in sludge conditioning.