Elemental Analysis of Composted Source Separated Municipal Solid Waste

? Samples from composted source separated municipal solid waste were analyzed for 25 elements, including heavy metals and trace nutrients. The results were compared to a rural soil. The precision and recoveries for the various analytes using microwave digestion and atomic spectroscopic methods were determined. The recoveries ranged from 30 percent to 130 percent, depending on the analyte. The concentrations of the regulated elements were all well below proposed EPA 503 limits. The average values (mg/kg, dry weight) were 2.1(As), 1.2(Cd), 20(Cr), 173(Cu), <2(Hg), <22(Mo), 17(Ni), 92(Pb), <1(Se), and 395(Zn). The sampling strategy followed a two-stage nested design, allowing for assignment of the errors to the various sampling components. The average errors were 7.2% (samples), 3.5% (sub-samples), and 3.6% (replicates) for the compost, and 10.8% (samples) and 4.7% (replicates) for the rural soil. Reducing the grind size dramatically reduced the error between replicates. The implication of these errors, in terms of estimating the number of samples needed for analysis, is demonstrated.