AWWA ACE68715

Deteriorating drinking water quality, including the presence of cyanobacteria-derivedtaste and odor-causing compounds and algal toxins, continues to be a major concern formunicipal drinking water suppliers. For many utilities ultraviolet disinfection (UV) is the best option to comply with the treatmentrequirements of the US Environmental Protection Agency's Long Term 2 Enhanced SurfaceWater Treatment Rule (LT2). Inaddition, there is a growing awareness of UV light-based advanced oxidation processes fortreating micropollutants in water, including treatment of taste and odor-causing compounds andassociated algal toxins.Several municipalities have installed or are in the process of installing full-scale UV-oxidationsystems for simultaneous disinfection and treatment of taste and odor and algaltoxins. Selected examples include the cities of Groesbeck, Texas (2 million gallons per day[MGD] peak flow), Lucerne, California (1 MGD) and Cornwall, Ontario, Canada (26 MGD). Each UVdisinfection/UV-oxidation system operates in two modes, Disinfection-Only Mode and T&O Control+ Disinfection Mode. In Disinfection-Only Mode during the majority of the year, the UVsystem is operated at lower energy levels sufficient for inactivation of microorganisms. During aT&O event, the UV system is operated in T&O-Control + Disinfection Mode. In this mode,additional UV lamps are energized and hydrogen peroxide dosed into the water upstream of theUV system. The combination of UV light and hydrogen peroxide initiates an oxidation reactionthat destroys T&O-causing chemicals and increases the level of disinfection.Data from selected performance validation studies demonstrates the ability of full-scaleUV-oxidation systems to remove T&O-causing compounds. For example, at typical operatingconditions at Cornwall, Ontario, 90% reduction of geosmin was achieved. Actual T&O reductiondata collected compares well to results of predictive models. Data is presented that demonstrates that other cyanobacteria-derived compounds thatlead to fishy, swampy and grassy (FSG) tastes and odors are eliminated by UV-oxidation.These FSG compounds include dimethyl trisulfide, (cis) 4-heptanal, cis-3-hexenyl acetate, and(trans, trans) 2,4-heptadienal. FSG compounds are treated with efficiencies that are similar toMIB and geosmin.Finally, to demonstrate that the UV-oxidation process is effective for the destruction ofalgal toxins, bench-scale studies were performed. Algal toxins, including microcystin-LR,cylindrospermopsin, anatoxin-a, and saxitoxin, can be released into the water through the lysisof cyanobacteria cells in pre-UV treatment steps and have been proven to cause acute andchronic health effects in humans and animals. Results indicated that these compounds absorb UVlight in the UV-C range and are also degraded rapidly through the oxidation initiated by thehydroxyl radical. Therefore, a UV-oxidation system designed to remove T&O compounds willalso accomplish treatment of algal toxins. Includes 4 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2008

Number of Pages:

12

File Size:

1 file , 670 KB