A standard method for analyzing 22 off-flavors in drinking water was developed. It includes chemical analysis - CLSA and SDE coupled with GC-MS, and sensory techniques - FPA and sensory GC analysis. Trans, trans-2,4-Heptadienal, a newly found fishy causing compound, was studied for its detection limit and OTC. Two grassy causing compounds, cis-3-hexen-1-ol and cis-3-hexenyl acetate, were also evaluated.
β-Cyclocitral and geosmin have been identified as the chemicals responsible for causing hay/woody and earthy odors in Lake Winnebago, respectively. Initial identifications of off-flavors were made by the GC-MS with an MS spectral library and sensory-GC analysis and the identifications were confirmed by GC retention time and MS spectral matches to the known standard compounds. A Weber-Fechner plot has been developed for β-cyclocitral and its three odor descriptors, fresh grass, hay/woody, and tobacco-like, which were observed at different concentration ranges.
The City of Appleton, Wisconsin operates an 800 l/s Drinking Water Treatment Plant (WTP). Lake Winnebago serves as the source water which experiences algae blooms that are typically accompanied by severe taste and odor (T&O) episodes. Historically, raw water quality in the summer months prevents the full capacity from being achieved despite the use of potassium permanganate, powdered activated carbon (PAC) and granular activated carbon (GAC) filters. Thus, the City proceeded with a study of various treatment processes to mitigate the T&O problems experienced during the summer months. The relatively short duration of T&O episodes and extensive experimental plan necessitated a bench-scale testing for rapid evaluation of various oxidation and adsorptive processes.
This paper presents a review of the effect of carbon type, dosage, contact time, and application point on the performance of PAC in controlling odors. In addition, the effect of GAC type and empty bed contact time (EBCT) on removal of T&O compounds were evaluated using a rapid small scale column test (RSSCT).
Three odorants, geosmin (earthy), MIB (2-methylisoborneol) (musty), and IPMP (2-isopropyl-3-methoxypyrazine) (decaying vegetation/musty) were spiked into raw water taken from the Detroit River and subjected to bench-scale ozonation (with and without hydrogen peroxide). Statistical experiment design was employed to investigate operating variables such as ozone dose, ozone addition point, temperature, odorant spike level, and presence of hydrogen peroxide. Two additional odorants, cis-3-hexenyl acetate (grassy) and trans,trans-2,4-heptadienal (fishy) were also tested. Results showed that ozonation was capable of mitigating the spiked odorants in the Detroit source water. Ozone dose was the single most important factor in removing the odorants. Presence of hydrogen peroxide (without dose optimization) had a limited effect on odorant removal at tested pH and alkalinity conditions. Ozone application point and water temperature had significant impacts on ozone residual, but not on odorant removal. MIB was most difficult to remove by ozonation among the five spiked odorants.
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