Plant performance and leachate water quality enhancement using biochar-modified recycled concrete aggregates

The development of urbanization has increased the generation of construction waste, causing serious environmental problems. This study explores using recycled concrete aggregates (RCA) amended with biochar as a soil substrate in green roof applications. Column experiments were conducted to investigate the effects of three biochar types (wood biochar-WB, perishable waste biochar-PWB, and dairy manure biochar-DMB) at two application rates (5 % and 10 % w/w) on the growth of Miscanthus (a common green roof plant) and leachate water quality. Leachate was collected from three flushing events in each column to measure nutrient and heavy metal concentrations. Results showed that WB consistently enhanced plant shoot height regardless of application rate, while PWB at a 5 % application rate produced 31 % more leaves than at 10 % by the end of the growth period. Application rates did not significantly influence RCA pH when amended with WB or DMB. Nevertheless, biochar amendments substantially enhanced RCA fertility, with a significant (p < 0.05) increase in available phosphorus and potassium compared to conventional soil. DMB application consistently reduced leachate heavy metal concentrations compared to normal soil across all flushing events. Principal component analysis recommends using DMB at a 10 % application rate to optimize plant growth, enhance RCA nutrient content, and improve leachate quality. These findings demonstrate that biochar-amended RCA can effectively replace normal soil in green roofs.