The fate of heavy metals in green waste composting

It has long been known that heavy metals, when in high enough concentration, have the potential to be both phytotoxic and zootoxic. Heavy metals are frequently found as contaminants in green waste. Any such waste that is subsequently segregated for composting theoretically has the potential to retain that possible contamination. To date, there have been a limited number of publications addressing this issue. Most reports have concentrated on the types of heavy metals found in compost and their acceptable levels, rather than the fate of heavy metal contaminants throughout the composting process. This investigation was aimed to identify the fate of cadmium (Cd), copper (Cu), chromium (Cr), lead (Pb) and zinc (Zn) concentrations throughout a fourteen week composting cycle. The results of this study showed a general increase in the removal of Pb, Cu, Cr, and to a much smaller extent Zn, manifested by a decrease in their overall concentrations within the solid fraction of the final product, by 93, 49, 43, and 20 percent respectively. By contrast, there was no decrease in the overall concentration of Cd.