A workshop of international drinking water experts was convened in Sedona, Arizona, March 26-27, 2001 for the purpose of developing a method for testing drinking water system components for their potential to contribute to taste-and-odor problems in drinking water. The workshop participants derived a method using provisions from European Standards as well as newly developed approaches. It is intended that this method can serve as a temporary procedure for water utilities, as well as a recommended template to derive an official standard. Materials to be tested may include pipes, fittings, ancillaries, joints, lubricants, tanks, and reservoirs. The recommended method includes a migration (leaching) test with chlorinated water, followed by sensory analysis of the samples from the migration test after dechlorination. Sensory analyses use both statistical (e.g., triangle test) and descriptive (e.g. Flavor Profile Analysis) techniques. A decision tree for the results is provided.
The presence of grassy-type odors in drinking water has frequently been determined by flavor-profile analysis (FPA). Previous work (Khiari et al., 1995) has identified cis-3-hexen-1-ol and cis-3-hexenyl acetate as the causes of these odors in laboratory experiments. Both chemicals possess very similar characteristics; however, cis-3-hexenyl acetate has a much lower odor threshold concentration (OTC) than its corresponding alcohol. In this study, both chemicals were identified by both sensory and chemical analyses separately or in combination in natural and treated waters. It was also found that the sensory and chemical characteristics of samples with grassy odors have a tendency to change upon storage and shipment. Hydrolysis was determined to be a major controlling mechanism for the degradation of cis-3-hexenyl acetate and the formation of cis-3-hexen-1-ol in aqueous solution. The kinetics of the hydrolysis of cis-3-hexenyl acetate to cis-3-hexen-1-ol was evaluated in bench-scale experiments. These studies showed the concentration of cis-3-hexen-1-ol and cis-3-hexenyl acetate to be strongly pH-dependent. This study shows that preservation by refrigeration and adjustment of pH to 4.6 were important steps to be taken when quantitation of the compounds is needed. However, the samples should be analyzed as quickly as possible.
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.
A comprehensive nutrient removal evaluation to meet extremely low nutrient limits was performed for the South District Water Reclamation Plant (SDWRP) in Miami, Florida. Several alternatives were originally identified by the project team as possible candidates to complement SDWRP's proposed membrane filtration / reverse osmosis (RO) / ultraviolet disinfection and advanced oxidation processes to meet the required limits. A preliminary screening of these alternatives resulted in the selection of chemical phosphorus removal coupled with biologically active filters, movable bed biofilm reactors, second pass RO, ion exchange (IX), and breakpoint chlorination as the most viable nutrient removal processes for complementing SDWRP's originally anticipated three-stage RO system to meet the low nutrient limits required for the project. A comprehensive evaluation of the final alternatives resulted in the selection of chemical phosphorus removal and IX as the best processes for SDWRP. Decision factors included significant sustainable advantages compared to the other alternatives.
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