Physicochemical and biological assessment of legacy waste for application as soil conditioner

The study examines the recycling potential of fine fraction obtained from dumpsites for potential application as a soil conditioner. Legacy waste was excavated from Mulund dumpsite located in Mumbai, India, and < 4 mm fraction (fine fraction) was collected and tested for essential compost parameters like pH, electrical conductivity, total organic carbon (TOC), primary nutrients, and heavy metals. Further, the impact of fine fraction on plant growth was studied using phytotoxicity and vegetation test. The results show that except for TOC, fine fraction meets most of the physicochemical characteristics standard prescribed for Indian MSW-based compost. The fine fraction had significant nutrient content, i.e., 0.81% (N), 0.27% (P as P₂O₅), and 0.55% (K as K₂O), compared to local soil and meets the Indian MSW-based compost standards, except for phosphorous. However, the total heavy metals in fine fraction exceeded the standard limits for chromium, copper, nickel, lead, and zinc. The germination index of tomato seeds (Lycopersicon esculentum) for the fine fraction extract was more than that of the control for aged fine fraction (> 5 years old), whereas inhibition was observed for fine fraction less than 3 years old. The vegetation test on Napier grass (Pennisetum purpureum) showed that the fine fraction amended soil had a 53-56% increase in biomass yield compared to soil. Based on the characteristics of fine fraction, different potential applications, such as fertilizer, soil enricher, or substrate for remediation activity, are identified; however, caution will be desired on a case-to-case basis.