Trace Metals in Municipal Solid Waste Compost: Sources and Research Methodology

Abstract

A concern regarding MSW compost quality is the trace metal content. A study was initiated to assess the impact of various metal contaminants on compost quality. One critical step in the study was to estimate metal transfer during composting, which was achieved by measuring the corrosion rate of different contaminants during the high rate composting stage for 3 weeks using alfalfa hay and straw as composting substrate. A corrosion quantification technique, weight loss/gain of metal specimens, was employed to estimate metal release into composting substrate. Among the 7 types of contaminants, stainless steel screws, brass screws, and light bulb aluminum alloy thread contacts showed little weight changes. This suggests minimum concerns for these materials in terms of metal release during composting. The highest metal release per unit area was from light bulb foot contacts, which was 3.66 × 10⁻³ g cm⁻², while galvanized steel nails and zinc plated screw had a metal release rate in the range of 1.5 to 1.9 × 10⁻³ g cm⁻². Scanning Electron Microscope (SEM) was employed to determine the chemistry of corrosion products and change of surface morphology by corrosion and X-ray diffraction/spectrum to determine the type of corrosion products formed on the surface of some selected samples. As there is little literature on this subject, methodology and data from this work can be served as a scientifically sound reference to academics, industry and legislators.