| With the municipal sewage sludge production increasing annually, the reduction, stabilization, harmless disposal and recycling use of sludge have been widely concerned. As high moisture content of the dewatered sludge is the bottleneck restricting sludge disposal, drying can furtherly reduce the water content. In conventional sludge drying process, slowly releasing of water and disgusting odor emission are the main problems to be solved. Compared with the drying performance of conventional polyacrylamide(PAM) conditioned sludge, this paper aims to study the drying characteristics of deep dewatering sludge which was conditioned by Fe Cl3 + coagulant aid(Ca O/Ca O+coal), as well as Fenton + coagulant aid(Ca O/Ca O+coal). The influence of composite conditioners on the water releasing and odor emission during the drying process were studied and the effects of drying atmosphere and temperatures were also investigated.The results showed that the conditioner can break sludge structure, releasing the internal water, and increase the pore volume and specific surface area of solids. Thus, the composite conditioned sludge had higher water emission rate and shorter drying time during the drying process compared with PAM conditioned sludge. H2 S, SO2, COS, CS2 and CH4 S were the main sulfur-containing gases, and the amount of H2 S, SO2 accounted for 82.4% of the total sulfur emission. The main nitrogen-containing gases were NH3 and HCN. The main polluting sulfur gases were reduced due to the oxidation of sulfur-containing group and unstable organic by the Fe3+ and Fenton reagent, as well as the combination reaction between the free H2S/SO2 with the Fe2+/Ca O. Meanwhile, strong alkaline surrounding formed by Ca O increased the emission intensity of NH3 by promoting the free NH3 emission and the interaction of NH4+ to NH3. The XPS result showed that compared to PAM conditioned sludge, the sulfate content of composite conditioned sludge increased, while the easier to release organic sulfur(sulfonic acid and sulfoxide) decreased as well as the ammonia, which indicates the composite conditioners could fix the sulfur and promote the NH3 emission in advance. The p H of the condensate were higher than that from PAM conditioned sludge due to more NH3 dissolution, on the contrary COD were much lower, due to the volatile organic destruction by the composite conditioners.H2S and SO2 capturing by Ca O was weakened by CO2, due to the reaction between CO2 and Ca O. The reaction between CO2 and NH3 under steam conditions can restrain the NH3 emission. O2 can oxidize H2 S to reduce its emission, but have no influence on SO2. O2 may promote the decomposition of organic matters in sludge and produce more NH3. The reaction between CO2 and NH3 in condensate lowered the p H, as well as decreased dissolution of the sulfur-containing gases, reducing the concentration of SO42-.The drying time decreased to 20%, while the drying temperature increased from 400 oC to 800 oC. The sulfur capture performance of the conditioners decreased with the increased drying temperature, which might result from the decomposition of the product at high temperature. The decomposition of nitrogen-containing organic at high temperature led to more NH3 releasing from composite conditioned sludge than PAM conditioned sludge. The organics in condensate turned from volatile fatty acids to tar with temperature rising, indicating that at low temperature volatile organics was released while more stable organics was decomposed at higher temperature. The content of the C, H, N, S in dried sludge showed that composite conditioned sludge had better thermostability. |
PDF Full Text Request