| It was known that the dewatering property of municipal sludge was worse and the general approaches of sludge conditioning show some disadvantages, such as high cost, secondary pollution and the influence caused by the overlooked of the treatment and disposal of conditioned sludge. To solve these problems, inorganic coagulant and chitosan(CTS) or biomass powder(wood as the raw material) and CTS as joint conditioner were investigated in the study, and the corresponding mechanisms were analysed.The sludge conditioning of CTS conditions were optimized by the estimate of sludge settling ratio, specific resistance to filtration(SRF) and filter cake moisture. The results showed that the sludge conditioning effectiveness was affected by the chitosan concentration and dosage, sludge p H and temperature. Under the optimum conditions that the CTS dosage was 3.0mg·(g DS)-1, the sludge SRF reduced by 83.13%, and filter cake moisture droped to 78.37%. According to the analysis of turbidity of sludge superatant, Zeta potential, EPS and COD contentas as well as microphotographs of sludge flocs, the conditioning mechanism of CTS conditions was discussed. The mechanisms of chitosan improving sludge dewaterability were to build bigger network structure flocs because of electrostatic neutralization, adsorption bridging and hydration, which could reduced the content of the LB-EPS sludge particle surface groups and improved sludge dewatering.Different inorganic coagulant were screened by assement of SRF and filter cake moisture in the same time. Inorganic coagulant which were to be selected out to the best-conditioning and CTS joint conditioning to improve sludge dewaterability. The results demonstrated that the effect of ferric chloride(PAFC) was best for dewatering sludge. The influence of the joint conditioning with PAFC and CTS sludge dewatering was better than single conditioning significantly under the same dosage, and inorganic coagulant followed by CTS performanced a better effect. Under the optimum conditions that PAFC dosage was 60mg·(g DS)-1and CTS dosage was 3.0mg(g DS)-1,the sludge SRF reduced by 90.28%, and filter cake moisture was 76.45%. Through the analysis of turbidity of sludge superatant, EPS and COD content as well as microphotographs of sludge flocs, the joint conditioning mechanism was discussed. Analysis results about the total quantity and morphological of heavy metal on joint conditioning sludge indicated that the cake heavy metal contamination belonged to a low risk, sludge could be considered for agriculture use.The conditioning effects of biomass powder under different particle size was discussed by assement of SRF, filter cake moisture and net sludge yield(YN), and the influence of biomass powder and CTS joint conditioning on the improvement of sludge dewatering were also explored. The results indicated that small size particles benefited the improvement of the effect of sludge dewatering. CTS followed by adding the biomass powder contributed to sludge dewatering. Under the optimum conditions of biomass powder dosage 60%DS and CTS dosage 3.0mg·(g DS)-1, the sludge SRF reduced by 92.8%, YN was 4.82kg·(m2·h)-1, and filter cake moisture was 72.11%. Through the analysis of turbidity of sludge superatant, and compressibility as well as microphotographs of sludge flocs, the joint conditioning mechanism was discussed which was based on the "skeleton" and "flocculation" effect. Under the optimum conditions, the calorific value of the sludge cake can achieved 14965 k J·kg-1, which could be burned as fuel for sludge disposal. |
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