Occurrence and Removal of Earthy-Musty Odorants in Two Waterworks in Kinmen Island, Taiwan

摘要

In this study, the occurrence and treatment of two earthy-musty odorants, geosmin and 2-MIB, produced by cyanobacteria is investigated at two conventional drinking-water treatment plants (WTPs) at Kinmen Island, Taiwan. Samples of the source, processed, and finished waters and tap water at the two WTPs were collected and analyzed. Both geosmin and 2-MIB were commonly detected in most water samples, with the 2-MIB concentration much higher than the geosmin concentration. About 78% of the source water samples and 35% of the finished and tap water samples showed detected 2-MIB levels higher than the odor threshold concentration (OTC, ～10 ng/L). Sampling and analysis of the reservoir water indicated that 2-MIB is uniformly distributed in the reservoir, with ～70% of which existing in the dissolved phase. The chlorination study of the raw water indicates that both geosmin and 2-MIB are resistant to chlorine. However, the cyanobacterial cells in raw water were effectively ruptured within 15 min of the contact time when a chlorine dosage of 6.4 mg/L was applied at the WTPs. A monitoring of the processed water at WTPs shows that the flotation process is most effective to the removal of cyanobacteria, with about 77-79% efficiency, compared to ～99.4% achieved with the whole treatment train. Removal of 2-MIB by the treatment processes before flotation was only about 17-28%, which may be limited to the low ratio of cell-bound 2-MIB. The two sand filtration processes removed 23-47% of 2-MIB, due probably to the biological degradation of dissolved 2-MIB. For the two WTP studied, the removal of 2-MIB was about 74%. It is shown that 2-MIB is a major odorant in the drinking water source and the finished water at Kinmen Island. The current processes are not sufficient to remove 2-MIB to a level below the OTC. Advanced processes are needed to effectively remove the odorant.