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• The ceramsite was successfully produced using solid waste including MSWI fly ash. • The raw material ratio and sintering condition of ceramsite was optimized. • The heavy metals (HMs) were well immobilized in ceramsite. • HMs immobilization was mainly due to glass phase and formation of new crystal phases. With an increase in municipal solid waste incineration (MSWI) fly ash and its dangerous characteristics, the manner of its disposal has caused widespread concerns. In this study, ceramsite was prepared by using MSWI fly ash, civil sludge, and contaminated soil as the main raw materials; then, a certain proportion of clay was added as an additive. The optimum MSWI fly ash content and sintering conditions were investigated, and the immobilization mechanisms of heavy metals were explored. Based on the obtained results, the optimum preparation conditions were a preheating temperature of 400 °C, a preheating time of 10 min, a sintering temperature of 1150 °C, and a sintering time of 20 min. Moreover, the optimal raw material ratio of MSWI fly ash, civil sludge, contaminated soil, and flint clay was 30%:40%:15%:15%. Under these optimum preparation conditions, the obtained ceramsite showed the following excellent performance parameters: a 1-h water absorption of 0.97%, bulk density of 998.7 kg/m3, and cylindrical compressive strength of 37.84 MPa. Furthermore, the leaching of heavy metals was far less than the standard GB5085.3-2007. The immobilization of heavy metals in the ceramsite was mainly caused by the glass phase encapsulation and the formation of new crystal phase with the heavy metals. In addition, the generation of aluminosilicates played a positive role in the immobilization of heavy metals. Thus, the reuse of MSWI fly ash by preparing fly ash-based ceramsite is one of the effective methods for reducing solid wastes. [ABSTRACT FROM AUTHOR]

Sanitary landfill persists as a predominant sludge disposal method in particular in China. In this study, successive subsurface sludge samples (0.3 m deep) were collected from a bioreactor landfill unit where an anaerobic process took place during a 500 d period. The sludge samples were analyzed for total concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) and their species distributions, together with selected sludge chemical properties. In addition, the sludge samples were subjected to phytotoxicity testing. The results showed that the mobilities of Cd and Ni were decreased with landfill time, while the mobilities of Cr, Cu, Pb and Zn remained consistently low over the landfill period. The residual amounts of all these heavy metals were increased with landfill time, suggesting that the anaerobic sanitary landfill is an effective sludge stabilization method to reduce the ecological risk of these heavy metals. The increase in the sludge pH value with landfill time tended to promote the precipitation of heavy metals. Moreover, the sludge stabilization was found to be indicated by the formation of humic substance (HS) and volatilization of volatile matter (VM). The germination index (GI) values of barley ( Hordeum vulgare L.) and Chinese cabbage ( Brassica rapa chinensis ) seeds grown in the 500 d anaerobically stabilized sludge were approximately 5.2- and 4.1-times higher than the values of those grown in the fresh sludge. The final sludge extract did not cause any significant inhibitory effect on the germination of the two types of seeds. [ABSTRACT FROM AUTHOR]