Thermal treatment of municipal wastewater sludge containing heavy metals

Summary

In the process of municipal wastewater sludge incineration ash is generated that contains concentrations of heavy metals which limits its further practical use and requires land filling on industrial waste dumps. The carried out research was aiming at the development of detoxification of wastewater sludge in the process of thermal destruction with the production of a product of useful quality. In the course of studies the samples of dewatered wastewater sludge from the Perm municipal treatment facilities were used. The wastewater treatment facilities receive domestic wastewater and industrial effluents from machinery works that provide for the increased concentration of heavy metals both in wastewater and in sludge. During thermochemical processing of the Perm municipal wastewater sludge wastes from potash fertilizer production (flotation potash chloride, sodium chloride) can be used as an agent that provides for utilizing heavytonnage wastes and reducing the costs of wastewater sludge utilization. It was stated that wastewater sludge pretreatment with concentrated potassium chloride or calcium chloride solutions with the subsequent incineration at 900–1000 °C provided for heavy metals transfer to gaseous phase in the form of metal chloride aerosols that were further absorbed by alkaline agent solution. The generated mineral residue contains 5–7% phosphorus (as Р₂О₅) in the form of calcium phosphate or potassium phosphate and trace elements that allow using it as a compound fertilizer.

Key words

reagent treatment , sludge , heavy metals , thermochemical sludge utilization , mineral residue , mineral fertilizer