Compliance with chemical-based effluent standards does not always ensure ecological risk management of industrial effluent which contains a variety of chemicals used in a chemical manufacturer. To evaluate the biological effects of effluent discharged from our factories, we have applied Whole Effluent Toxicity (WET) test on effluent management system since 2007. Effluent samples were collected at least once a year from four factories and subjected to a battery of bioassays using fish, daphnids, algae, and luminescence bacteria. Our results showed that the most sensitive test species demonstrating toxic effects including annual changes were different for the four effluents. Considering the dilution factor of effluent after discharge, the ecological risk of all samples, which includes the highest toxic effluent from factory D, was assumed negligible in the receiving waters. To reduce effluent toxicity in factory D, we investigated the weekly and daily fluctuation of the effluent toxicity, suggesting that the effluent toxicity was different depending on products. Toxicity assessment of effluent samples collected from each drainage system inside the factory D identified the in-plant source of toxicity, which could be suppressed by reducing the amount of sodium hypochlorite. Moreover, C18 resin treatment in lab-scale reduced the toxicity of the effluent to the daphnids, indicating that at least some of the toxic chemicals were organic compounds.
