Influence of Mechanical-Biological Pretreatment On the Toxicity of Municipal Solid Waste

Mechanical-biologically pretreated residual waste was tested for toxicity, chemical quality and reactional behavior. Samples were taken from different composting plants at different stages of treatment. Acute toxicity was determined using Daphnia magna (crustacean) and Vibrio fischeri (luminescent bacteria), chronic toxicity was tested with Selenastrum capricomutum (green algae) and Lepidium sativum (cress). Samples were analyzed for various physico-chemical parameters and for biological parameters (respiration activity, gas-generating potential). Toxicity tests were carried out from eluates and toxicity was expressed in German regulatory G-values. The results of this study indicate that high toxicity was observed in untreated MSW samples and in samples with a short treatment period. In most cases toxicity decreased significantly when the treatment period increased and marked differences were observed in the susceptibility among the species. Toxicity varied between a G-value of 1 and 256. For some tests a good relationship was noted between toxicity and high results of conductivity, TOC, COD, BOD5 and biological tests. It was found that high toxicity can influence biological tests, resulting in longer lag-phases and thus leading to misinterpretation.