Assessment of Heavy Metal Contamination and Macro-nutrient Content of Composts for Environmental Pollution Control in Ghana

This study examined macro-nutrient content of solid waste compost to determine the potential of the compost for soil fertility amelioration in Ghana. Heavy metal concentrations in the compost were also examined to assess the potential health implication of compost application in urban and peri-urban agriculture. It was observed that the overall NPK concentration was low in the different compost types, but generally, total N and K were greater in agricultural waste compost compared to municipal solid waste (MSW) composts. The agricultural waste compost was also richer in organic carbon. In terms of toxicity concerns, heavy metals concentrations (Ni, Zn, Cu and Cd) were generally low in the different types of composts and within permissible Australian standards for compost products. However, lead (Pb) concentration in mixed MSW composts was significantly high in the dry season, exceeding the Australian limit of 150 mg/kg Pb, required for unrestricted compost use. There was considerable seasonal variation in the heavy metal levels in the composts made from open windrows process, with reduced levels in the rainy season. It appeared that seasons affected mixed waste characteristics, which affected compost quality. It was therefore concluded that seasons and composting processes, to some extent, were important determinants of the levels of toxic metal concentrations in final compost products in Ghana.