The impact of separation on heavy metal contaminants in municipal solid waste composts

Increased composting of mixed municipal solid wastes has been accompanied by heightened concern about contaminants in compost products. This paper addresses the impacts of different separation strategies on trace metal concentrations. Separation strategies considered include source separation of either compostables or contaminants prior to collection, wet/dry collection schemes, and manual or mechanical separation at a centralized facility. Data from both experimental trials and operating facilities indicate that the lowest levels of contaminants are achieved by source separation of compostables. Wet/dry systems produce variable quality, depending on whether separation of recyclables or compostables is emphasized. Centralized separation can achieve moderate reductions in metal levels, and some evidence suggests this separation is most effective at early stages of processing. Further research is needed to document the potential for source separation of critical contaminants such as lead, and the effectiveness of various centralized separation technologies (individually or in combination) at minimizing contaminant levels.