Effects Of Filtration Aids (Sludge Incineration Slag, Sawdust)on Industrial Sludge Dewaterability

A large amounts of waste sludge are produced with the increase of wastewater. The most important part of sludge treatment prior to disposal is the reduction of the sludge volume by solid-liquid separation. The presence of organic components and colloidal particles in the sewage sludge makes the dewatering difficult even at the high pressures of mechanical dewatering. The addition of chemical conditioners such as polyacrylamide and surfactant is often necessary to help the sludge particles to agglomerate into larger particles or flocs prior to solid-water separation usually by mechanical dewatering. However, due to the highly compressible nature of the sludge solids, the sludge dewatering rate is often hindered by the blinding of filtration media and the filter cake. Therefore, it has become an urgent issue to seek an effective treatment for improve the sludge dewaterability.This study took the industrial sludge, including tannery sludge and textile dyeing sludge, as samples. The effects of sludge incineration slag, sawdust and microwave pretreatment on the sludge dewatering performance and its relevant mechanisms were investigated in this study. The main contents of this study could be summarized as following:Tannery sludge incineration slag (TSIS) was used as a skeleton builder, in combination with cationic polyacrylamide (CPAM), to condition tannery sludge. The results showed that pretreating the sludge with a combination of TSIS and CPAM considerably improved sludge dewaterability over CPAM conditioning alone. The optimum TSIS and CPAM dosages were150%dry solid (DS) and10kg/t DS, respectively, which generated a maximal net sludge solids yield (10.3kg/(m2·h)) and a minimal time to filter (7s). The negative charge of the sludge particles was neutralized by the positive charge of the dissolved metal ions of the TSIS, resulting in larger floc sizes. Compressibility and porosity measurements and scanning electron microscope (SEM) images indicated that the TSIS formed a porous and incompressible structure during mechanical dewatering.Sawdust was used as a filter aid for the textile dyeing sludge dewatering. Results showed that sawdust conditioning in conjunction with cationic polyacrylamide (CPAM) presented much better dewaterability than CPAM alone. The optimal sawdust and CPAM dosage for the best dewaterability was found to be60%wt (mass percent) and15kg/t DS (dry solid), the time to filter (TTF) and the yield at90%degree of the filtration completion (YN90) were5s and15.6kg/(m2·h) under the conditions, respectively. TTF and YN90were more appropriate parameters than specific resistance to filtration (SRF) for assessing the sludge dewaterability as affected by physical conditioners. The moisture content of various filter cake layers gradually became the same with the increase of sawdust dosage. The flocculated sludge cake became relatively incompressible after sawdust conditioning. Sawdust acts to maintain the permeability during the compressed filtration by resisting cake compression.The effects of microwave pretreatment on tannery sludge dewaterability were investigated. The results showed that the optimal pretreatment conditions were microwave output power at648W, radiation pretreatment time was60s and cationic polyacrylamide (CPAM) dosing was8mg/L. Comparing with the separate flocculating agents pretreatment, it was observed that the SV30, CST, SRF were separately decreased25%,48.9%and34.7%under the optimal conditions, respectively. It was also indicated that the dewatering performance was improved highly with the pretreatment of microwave and flocculent co-conditioning, while CPAM had played an important role during this process. Microwave radiation destroyed the floc structure of the sludge, which changed the water distribution and reduced the viscosity of the sludge, thus improved the dewatering performance of the tannery sludge.