TA5 Soil Ecotoxicology and Risk Assessment
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() Toxicity of digested, incinerated and pelletized sewage sludge.

Fjällborg, B.1, Gustafsson, N.1, 1 Applied Environmental Science, Göteborg University, Göteborg, Sweden

ABSTRACT- In order to make sewage sludge a better product for agricultural production by decreasing its toxicity, prevent spreading of pathogens and also to make it easier to handle, different treatment methods have been tried. The aim of this study was to investigate whether the two treatment methods incineration and pelletization of digested sewage sludge had any impact on the toxicity of the sludge, and on the leachability of metals present in the sludge. To investigate the impact of sludge treatment on the growth rate a three week growth tests with Triticum aestivum (spring wheat) was performed. The toxicity of the sludge leachates was investigated with Daphnia magna (24- and 48-h immobility) and seeds of Lactuca sativa (96-h root- and sprout-elongation). We tried to identify the toxicants by standard Toxicity Identification Evaluation (TIE) procedures, using EDTA and filtration through a CM-resin, combined with chemical analysis and calculation of toxic units. Sludge leachates were sampled and tested on D. magna and L. sativa (seeds) both before and after wheat harvest. Toxicity seemed to decrease over time in all leachates except leachates from pelletized sludge. In some of the leachates toxicity were caused by ammonia while in others TIE procedures indicated metals as a cause of toxicity. Incineration seemed to decrease toxicity, organic matter and phosphorous content and also to decrease the leachability of metals and phosphorous, while pelletization seemed to increase toxicity and to increase the leachability of metals and phosphorous. However, only a few of the toxic leachates had metals present in concentrations high enough to cause toxicity. It is possible that the toxicity was caused by interacting substances, present in the sludge. Our results suggest that neither, incineration nor pelletization of digested sewage sludge enhanced the quality of the sludge as a fertiliser.

Key words: metals, toxicity, leachability, sewage sludge

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