SITEL, Integrated Wastewater Treatment System of South Petrochemical Complex,has been processing liquid waste from this industrial area since November, 1982. The complex consists of an olefins plant and some second-generation plants that produce mainly thermoplastic resins. The raw industrial effluent is segregated in the plants in two main streams: organic and inorganic. The organic treatment consists of water-oil separator, equalization basin and dissolved air flotation (primary treatment), activated sludge and multi-media filters (secondary treatment) and stabilization ponds (tertiary treatment). The final effluent is applied on land by perforated PVC pipelines and sprinklers. In 1986, an aquatic toxicity test laboratory was implemented. It uses fish (Pimephales promelas) and crustaceans (Daphnia similis), according to methodology reported by EPA.

A three-step protocol has been developed to characterize the whole effluent toxicity reduction in a, treatment system as well as to identify the sources of toxicity in industrial plants. The first step consists of toxicity identification and characterization of effluents at several monitoring points of SITEL. After analysing the results of the first step, it is possible to evaluate the toxicity reduction obtained by the treatment system and environmental toxicity evaluation. The second step consists of identification of the sources of toxicity in industrial plants through comparative study of organic and inorganic effluents of the complex, prioritizing the most toxic effluents. The last step consists of a toxic fraction identification, based on sequential physico/chemical fractionations of the effluent with associated toxicity testing using aquatic organisms. This paper presents the results that have been obtained so far and a previous evaluation of the main contributors for the toxicity of the effluents.

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