| Abstrakt: |
Sewage sludge samples were collected biweekly and analyzed for several components to determine the sampling procedures which should be required for the routine chemical monitoring of sewage sludge produced by a given treatment plant. While the composition varied significantly over time for every component and every plant, the standard deviation, expressed as a percentage of the mean for each treatment plant, indicated that two‐thirds of the values would be within the range of the true average value plus or minus 20 to 50%. Analyses for all samples collected in Pennsylvania, including those analyzed as a part of a service program, indicated that without chemical analysis the composition with respect to N, P, and K varied too much to establish an accurate prediction of the fertilizer value of unanalyzed sludge. In addition, the concentrations of the essential but phytotoxic elements, especially Zn and Cu, as well as trace elements harmful to the food chain, varied greatly among the treatment plants studied. |
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