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| Occurrence and degradation of 2-methylisoborneol and geosmin in water supply reservoir in winter |
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Abstract The production of 2-MIB and geosmin by actinomycetes and cyanobacteria are causes of many musty/earthy odor complaints about the aesthetics of drinking water. These two compounds are noticeable at nanograms per liter levels, and for the lower TON, tastes and odours (T&O) are always ranked as one of the first three causes of complaints in developed countries. This study evaluated a water supply reservoir with bottom-release (hypolimnion) outlet structure in Baotou city. According to the plug flow reactor model, mass balance analyses on T&O compounds in the reservoir were used to calculate in situ field rates of net MIB and geosmin production and loss. Taste and odor compounds loss rates caused by volatilization was calculated from two-film theory. Experimental results indicated that under the ice which the thickness was 0.55m, and the surface photosynthetically active radiation (PAR) varied from 70to 636W/m2from November to March of next year. The average surface PAR was 114.8W/m2, and the lowest value was 70.57W/m2 (in December). The surface PAR in Huajiang reservoir satisfied the growth and geosmin production of the algae in winter. MIB/geosmin concentrations in the reservoir followed the same seasonal trend as concentrations increasing and decreasing according to ice freeze and melt. The loss rates followed a first-order relationship for all cases tested (R2ranged from 0.941to 0.989), with volatilization and outlet fluid carrying being the key mechanisms during the lower temperature period. Mass balance analyses on MIB/geosmin during ice freezing indicated that the rate of MIB/geosmin production was 4.119 and 2.146ng/(L×d), MIB/geosmin emission rate constant was 0.032d-1all due to outlet fluid carrying. During ice melting, MIB/geosmin production was 1.012, 1.638ng/(L×d), MIB/geosmin emission rate constant was 0.072, 0.083d-1caused by volatilization and outlet fluid carrying. Volatilization appeared more important than biodegradation, photolysis or adsorption in Huajiang reservoir in winter.
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Received: 23 August 2013
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