Japanese Journal of Water Treatment Biology

This study aims to evaluate the toxic effect of influent and final effluent taken from a sewage treatment pilot plant, focusing on the effect of ammonia. Influent and final effluent were obtained in January and February from the pilot plant under little nitrification condition. The wastewater was examined based on the draft Japanese Whole Effluent Toxicity (WET) testing guidelines and a Toxicity Identification Evaluation (TIE) test using a green alga Pseudokirchneriella subcapitata. It was suggested that ammonia in the influent and final effluent, obtained in February, caused the toxic effect on P. subcapitata, although ammonia in those obtained in January seemed to do no toxic effect. It was also indicated that not only ammonia but also other chemicals like hydrophobic chemicals, oxidants and surfactants may cause the effect.

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In October 2014, a high concentration of 2－methylisoborneol （MIB） was confirmed in the Serikawa dam reservoir of the Oita River basin. Therefore, serious off-flavor problems with the drinking water occurred in Oita city located downstream of the reservoir. When it happened, we detected Phormidium tenue （P. tenue） and Oscillatoria agardhii （O. agardhii） in the dam water, these are reported that had the potential to produce musty/earthly odor compounds. We investigated the species by genetic analysis and musty/earthly odor-producing ability analysis, and determined that MIB was produced by P. tenue, and O. agardhii did not produce it. When we were faced with the problems, reduction of MIB in faucet water and providing information to customers are particularly pressing issues. Therefore, we improved the organizational response and coordinated closely with relevant organizations on water utilization. Furthermore, we purified the raw water to extensively reduce MIB, and carried out detailed water quality management. After overcoming, we are also trying to strengthen these countermeasures. We discussed a series of countermeasures against musty-odor problems.

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