Stabilization of Waste Sludge from Municipal Wastewater Treatment Plant

Abstract

Municipal wastewater treatment generates significant amounts of waste sludge that needs to be stabilized before disposal or reuse due to environmental and health risks. This study evaluated the effectiveness of microbiological, biological, and physical sludge treatment methods using physicochemical, microbiological, and ecotoxicological analyses. Microbiological treatment with a mixed microbial culture resulted in odor reduction and partial changes in organic matter content. Biological treatment with Eisenia fetida led to gradual structural transformation of the sludge and a reduction in pathogenic indicators, although a longer treatment time was required. Physical stabilization using pyrophyllite schist significantly increased total solids (from 17.75% to 48.32%), reduced volatile solids (to 2.26 %) due to combined stabilization and dilution effects, immobilized selected heavy metals, and eliminated fecal bacteria and other pathogenic microorganisms. Ecotoxicological assessment showed an increase in LC₅₀ values from 27% in raw sludge to 58% after physical treatment, indicating reduced toxicity. The results show that pyrophyllite schist is an effective natural material for improving the physicochemical stability and hygienic safety of wastewater sludge and highlight the potential of combining biological agents and natural mineral materials for sustainable sludge management.