| There is little knowledge about a reduction in a biological effect on aquatic organisms by wastewater treatment, and a biologically impactful chemical(s) contained in wastewater. The purpose of this study is to examine a seasonal variation of a biological effect caused by influent and final effluent obtained from a wastewater treatment plant employing conventional activated sludge process, and to characterize a biologically impactful chemical(s) in the wastewater based on an algal growth test. The influent in every season tested had a growth-infhibiting effect on Pseudokirchneriella subcapitata. The final effluent obtained in winter had the effect, although not obtained in other seasons.The grouth-inhibiting effect of the effluent in the winter may be due to the reduction in the bioligical treatment ability accompanied by a decrease in water temperature, which may lead to the residue of some biologically impactful chemicals in the effluent. It was suggested that the biologically impactful chemicals were non-polar organic toxicants and surfactants in the influent, and oxidants in the final effluent in a Toxicity Identification Evaluation test. |
