Removal of heavy metals from runoff using grass clippings compost: effect of moisture content and ph in composting process

Abstract

Heavy metals are significant contaminants in stormwater runoff. Dissolved heary metals can be removed from the stormwater runoff primarily by physical and chemical processes. A compost stormwater filter is one of the devices used to remove heavy metals from runoff. Since composting is a biological process, the quality of the final product is controlled by factors, which affect microbial activities. Moisture content and initial pH were selected and studied for their effects on the characteristics and adsorption performance of the compost. Manila grass (Zoysia matrella Merrill) was composted at 25 different conditions: 5 moisture contents (30, 40, 50, 60 and 70% MC) and 5 initial pH values (5, 6, 7, 8 and 9). After 63 days of composting, the grass composted at 30% MC and initial pH 7 had the maximum volume reduction percentage. The 30% MC compost provided high cation exchange capacity. The results of the adsorption isotherm tests showed that the interactions trength of metals to the grass clippings was i the following order: Cd > Zn > Pb > Cu. The Freundlich coefficients and removal percentages were used to compare removal efficiencies of the compost. The Freundlich coefficients trends were distinct from the removal efficiency trends. However, the compost could remove Cu>Zn>Cd>Pb. The grass composte at the initial pH 9 and 30% MC had high removal for all metals. The noncomposted grass had much lower removal performances compared to the composted grass.