Evaluation of Ecotoxicity of Wastewater from the Full-Scale Treatment Plants
Ewa Liwarska-Bizukojć
Abstract
In this work, the influence of wastewater from full-scale wastewater treatment plants (WWTPs) on aquatic and soil biota was reviewed and presented. Moreover, the methods and model organisms used in testing the ecotoxicity of wastewater were shown. It was found that wastewater usually affected the biochemical activity and growth of organisms such as bacteria, algae and protozoa. They contributed to the immobilization and death of inter alia crustaceans and fishes. The values of degree of inhibition or lethality widely varied dependent on the type of wastewater, the sampling point (influent or effluent) and the model organisms applied in the biotests. Thus, a battery of ecotoxicity tests using model organisms of different sensitivities should be employed. So far, bacteria (e.g., Vibrio fischeri), green microalgae (e.g., Raphidocelis subcapitata) and crustaceans (Daphnia magna) have been frequently used organisms in the biological assessment of wastewater. They were applied in almost half (bacteria) or more than half (microalgae, crustaceans) of papers analyzed in this study. In almost all studies, the reduction of wastewater toxicity after treatment processes was found. It was proven that the conventional activated sludge systems were efficient in the removal of wastewater toxicity from both municipal and industrial wastewater, while the tertiary stage of treatment, in particular chlorination or ozonation, contributed to the increase in wastewater toxicity.