Identification and oxidation of 2-MIB and geosmin in source water

• Main Authors: Shu-Chu Tung, 童淑珠
• Other Authors: Tsair-Fu Lin
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/59063350407322382066

博士 === 國立成功大學 === 環境工程學系碩博士班 === 94 === Musty and earthy odor is present in the source water of Feng-Shen Waterworks (FSW) and Cheng-Chin Lake Waterworks (CCLW) south Taiwan year round. MIB concentrations were between 10ng/L and 200 ng/L, and higher concentrations happened in warm seasons, i.e. between May and October. In cooler seasons, from November to April, the concentrations were much lower. However the concentrations always exceed the odor threshold 2-10 ng/L. Although 2-methylisoborneol (2-MIB) and geosmin are responsible for the musty and earthy odor, respectively, the possible odor producers remained unknown. In this study four 2-MIB and geomsin producers were isolated for determining their odorant production, and release and destruction of the odorants under oxidation processes. The odorant producers, including a cyanobacterium and two actinomycetes were isolated from two source waters in southern Taiwan, and then identified using molecular biotechnology. Although the cyanobacterium, a 2-MIB producer, was only identified as Oscillatoria sp., the three actinomytecetes were identified as Streptomyces caelestis producing 2-MIB, S. roseoflavus producing geosmin and S. malaysiensis producing 2-MIB and geosmin after comparing the extracted DNA sequence with the NCBI database. Both the purified cyanobacterium and actinomycetes were incubated at 20, 25 and 30°C for the determination of 2-MIB and geosmin production ratios. At 20 and 25°C, a substantial proportion (around 80%) of 2-MIB retained intracellularly for the cyanobacterium at the logarithmic growth phase. The intracellular 2-MIB soon released into water once the cyanobacterium reached its stationary growth phase. The 2-MIB production ratio was about 300 ng/ug chl. a at three temperatures. For actinomycetes (except S. roseoflavus), about 50% of either geosmin or 2-MIB were present within cells at the logarithmic growth phase. The production ratio for 2-MIB and geosmin was around 1-5 ng/mg-biomass for the two actinomycetes. Two statistical methods, including principle component analysis and multiple linear regression technique were employed to correlate the 2-MIB concentrations with all the corresponding water quality and meteorological data collected from December 2000 to June 2001. The results suggested that 2-MIB concentration was highly correlated to water temperature or ambient temperature. Further analysis of ambient temperature with 2-MIB concentration suggested that a good correlation was observed between 2-MIB concentration and T1-9. The correlation equation, with regression coefficient = 0.90, is expressed as 2-MIB concentration (ng/L) = 0.3406+0.0579×T1-9 (R2=0.90, F=119.174, p<0.001) The equation was then employed to predict the 2-MIB concentrations for the period of July 2001 to July 2003. The data fits the predicted line closely, with about 70% of the observed 2-MIB concentrations falling into the 95% prediction intervals. These high correlations between 2-MIB concentration and environmental temperatures may provide a simple way for the utility to estimate the concentration of odorants, and serve as a means for the selection of control measure To understand the effect of oxidants used in waterworks on the dissolved and cell-bounded 2-MIB concentration, three oxidants, sodium hypochlorite, potassium permanganate, and ozone were tested. Chlorine and permanganate were much less effective, both removing only about 10% of the 2-MIB within 60 minutes with 10 mg/L addition in batch system. In semi-batch system, the overdose ozone applied, the 2-MIB decayed under 1st order reaction. Oxidation of the Oscillatoria sp. laden water was also conducted with addition of chlorine, permanganate, and ozone. As all the three oxidants might break the cell membrane of O. sp. and caused the release of almost all the MIB from cells into water, only ozone could effectively destroy dissolved MIB to a degree of higher than 50%.