Eco-Friendly Bioconversion of Sewage Sludge: Strategies for Nutrient Recovery and Pollutant Mitigation

Sewage sludge (SS), a byproduct of wastewater treatment, is rich in organic matter and nutrients but also harbors heavy metals, pathogens, and organic pollutants. Sustainable disposal and valorization of SS is critical to mitigate environmental and health risks. This review explores the potential of biological composting techniques including thermophilic composting; vermicomposting, co-composting, and black soldier fly larvae (BSFL) treatment as effective, low-cost alternatives to conventional methods such as incineration, pyrolysis, and wet oxidation. These biological approaches significantly reduce pathogenic load and heavy metal mobility, while enhancing nutrient recovery and producing high-quality compost. Microbial degradation during composting facilitates the breakdown of persistent organic pollutants such as PAHs and PCBs. Vermicomposting, in particular, promotes metal bioaccumulation and nutrient enrichment, making the final product suitable for agricultural use. Despite their promise, biological methods face challenges such as slower degradation rates and variability in pollutant removal efficiency. Future research should focus on optimizing composting conditions, microbial consortia, and bulking agents to improve the degradation of persistent pollutants like PPCPs and micro-plastics. Overall, biological composting represents a key strategy in circular waste management, turning SS from an environmental liability into a valuable resource for sustainable agriculture.