Ecotoxicological assessment of metal finishing effluents after real-scale treatments by conventional and advanced processes

摘要

This study assessed the ecotoxicity and physico-chemical composition of effluents derived from a metal finishing industry after treatments by a physico-chemical process (conventional system) followed by granular activated carbon and cationic exchange (advanced system). The assessment was developed to evaluate the effectiveness of the real-scale treatment systems routinely used by the industry to reduce the pollutant content of effluents and their high whole toxicity. The results showed continuously high effluent toxicity after conventional treatments, likely caused by high dissolved salt concentrations. Due to the low frequency of reactivation/regeneration performed in the advanced treatment system and the absence of a unit operation to promote cation and anion exchange, a high content of salts has remained in the effluents. Even so, when the granular carbon was newly reactivated for treatment, great reductions in algae toxicity were found. The previous regeneration of the cationic resin also favored a remarkable toxicity reduction for algae and fish. However, most advanced treatments were ineffective in reducing chronic algae toxicity. Although the acute harmful effect for daphnid and fish has tended to decrease after advanced treatments, none of them led to the complete removal of toxicity for the evaluated organism. Several trace metals were measured in residual concentrations above the toxicity thresholds reported by other studies for similar test organisms and indicated they are also possibly contributing to the observed toxicity.