Influence of Composting Methods on Heavy Metals and Nutrient Quality of Municipal Solid Waste

ABSTRACT Composting of municipal solid waste (MSW) is a sustainable approach for organic waste management; however, the performance of different methods varies considerably in terms of nutrient recovery and heavy metal stabilization. Integrated comparative studies that simultaneously evaluate nutrient quality, heavy metal behavior, seasonal variability, and overall compost suitability under identical conditions remain limited. In this study, source‐segregated MSW was collected from an urban residential area and processed under controlled conditions using windrow composting (WC), vermicomposting (VC), and inoculated microbial composting (IMC). Compost quality was evaluated through physicochemical parameters and composite quality indices within a multi‐parameter assessment framework. Fertilizing parameters, heavy metal concentrations, nutrient enrichment index (NEI), clean index (CI), fertilizing index (FI), and removal efficiencies were determined, and differences among treatments were statistically analyzed using one‐way analysis of variance (ANOVA) ( p < 0.05). The results demonstrated that VC achieved the most balanced compost quality, recording the highest FI score (6/6) due to optimal carbon‐to‐nitrogen (C:N) ratio, enhanced nutrient retention (N ≈ 1.9%, P ≈ 0.6%, K ≈ 1.6%), and biological stability. IMC exhibited rapid decomposition and exceptional removal efficiencies (>95%) for Pb, Cr, Cu, and Ni, resulting in the lowest CI value; however, substantial organic carbon depletion and reduced phosphorus levels led to a lower FI score (3/6). WC, although cost‐effective and operationally simple, showed moderate performance in both nutrient recovery and heavy metal stabilization. All composts complied with Indian regulatory standards, whereas comparative benchmarking against international standards indicated superior agronomic suitability for VC. Seasonal evaluation further revealed that the composting method exerted a stronger influence on final compost quality than climatic variability. Overall, the integrated assessment identifies VC as the most reliable technique for producing nutrient‐rich and agronomically valuable compost, whereas IMC shows strong potential for heavy metal remediation but requires nutrient optimization. WC remains a practical option for large‐scale municipal waste stabilization.