The toxicity of composts from sewage sludges evaluated by the direct contact tests phytotoxkit and ostracodtoxkit

Limitations relating to permissible standards of undesirable substances in sweage sludges make it necessary to optimize sludge properties. On of the methods to achieve the above goal is the use of composting process. The aim of this study was to determine the toxicity of composts obtained from sewage sludges composted for 76 days. Dewatered sewage sludges were collected from the four wastewater treatment plants located in the south-eastern part of Poland (Krasnik, Lublin, Bilgoraj and Zamose). The sludges were mixed with standard OECD soil at doses of 6% and 24%. Phytotoxkit (with Lepidium sativum) and ostracodtoxkit (with Heterocypris incongruens) tests were used to evaluate toxicity. The results obtained showed different toxicity of sewage sludge depeending on the sludge dose and bioassay used. H. incongruens mortality ranged from 0% to 90% and depended on the sewage sludge. The greatest inhibition of test organism growth was noted at a level of 55% In the case of the Phytotoxkit test, a clearly negative influence of the sewage sludges oil seed germination wits observed at a dose of 24%. Root growth inhibition was noted in the case of most sewage sludges and was at a level of 20-100%. The influence of the composting oil the toxicity of biosolids also showed various trends depending oil the sludge type. Sludge composting often resulted in a toxicity increase in relation to H. incongruens. In the case of plants (Phytotoxkit test) and most sewage sludges, however, the composting process influenced both the seed germination and root growth in a positive way. (c) 2007 Elsevier Ltd. All rights reserved.