Study on deep dewatering and heavy metal stabilization of stocked sludge

The stocked sludge has the characteristics of high moisture content and potential heavy metal pollution, which may pose potential ecological risks to the landfill site and the surrounding environment. Three solid waste materials, straw powder (SP), fly ash (FA) and phosphogypsum (PG), combined with two common dehydrators, quick lime (CaO) and polyaluminium chloride (PAC), were used to dehydrate the stocked sludge and study the stabilization effect of heavy metals. In addition, the microstructure and composition of the dehydrated sludge cake were studied by SEM-EDS. The results showed that the combined conditioner with solid waste materials had significant effects on sludge dewatering and heavy metal stabilization, and the group with PG was the best. When the addition of CaO, PAC and PG (dry basis ratio) were 20%, 25% and 23% respectively, the capillary water absorption time was 42.1 s and the moisture content of mud cake was 49.00%. The rich pore structure and phosphate impurities in PG had good adsorption and precipitation effects on heavy metals. The microstructure analysis showed that CaSO₄ or Al₂(SO₄)₃ formed the skeleton structure of treated sludge.