Study on the effect of sludge fermentation residue on soil remediation and plant growth in mining areas

Heavy metal contamination in mining-affected soils poses severe risks to ecosystems and crop productivity. In this study, sludge fermentation residue (SFR), derived from aerobic co-composting of municipal sewage sludge and straw, was evaluated as a soil amendment for remediating heavy-metal-contaminated soils from a mining region in Tibet, China. The effects of different SFR application rates (0%, 3%, 6%) on soil properties, heavy metal stabilization, plant growth, and metal migration were comprehensively investigated using Brassica chinensis and Lolium perenne under monoculture and intercropping conditions. The results showed that SFR significantly improved soil physicochemical properties, including cation exchange capacity (CEC), total organic carbon, ammonium nitrogen, available phosphorus, and potassium. At 6% application, SFR increased the residual fractions of Cu, Zn, and Pb by over 40%, thereby reducing their mobility and bioavailability. Simultaneously, SFR enhanced plant growth, with up to 72% increase in chlorophyll content and substantial improvements in biomass and plant height. Intercropping systems effectively redistributed metal loads between species, reducing heavy metal accumulation in Chinese cabbage while promoting uptake by ryegrass. This study demonstrates that SFR offers a sustainable, cost-effective strategy for stabilizing heavy metals and promoting vegetation recovery in contaminated soils.