Deteriorating drinking water quality, including the presence of cyanobacteria-derived
taste and odor-causing compounds and algal toxins, continues to be a major concern for
municipal drinking water suppliers. For many utilities ultraviolet disinfection (UV) is the best option to comply with the treatment
requirements of the US Environmental Protection Agency's Long Term 2 Enhanced Surface
Water Treatment Rule (LT2). In
addition, there is a growing awareness of UV light-based advanced oxidation processes for
treating micropollutants in water, including treatment of taste and odor-causing compounds and
associated algal toxins.
Several municipalities have installed or are in the process of installing full-scale UV-oxidation
systems for simultaneous disinfection and treatment of taste and odor and algal
toxins. 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 UV
disinfection/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 UV
system is operated at lower energy levels sufficient for inactivation of microorganisms. During a
T&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 the
UV system. The combination of UV light and hydrogen peroxide initiates an oxidation reaction
that destroys T&O-causing chemicals and increases the level of disinfection.
Data from selected performance validation studies demonstrates the ability of full-scale
UV-oxidation systems to remove T&O-causing compounds. For example, at typical operating
conditions at Cornwall, Ontario, 90% reduction of geosmin was achieved. Actual T&O reduction
data collected compares well to results of predictive models. Data is presented that demonstrates that other cyanobacteria-derived compounds that
lead 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 to
MIB and geosmin.
Finally, to demonstrate that the UV-oxidation process is effective for the destruction of
algal toxins, bench-scale studies were performed. Algal toxins, including microcystin-LR,
cylindrospermopsin, anatoxin-a, and saxitoxin, can be released into the water through the lysis
of cyanobacteria cells in pre-UV treatment steps and have been proven to cause acute and
chronic health effects in humans and animals. Results indicated that these compounds absorb UV
light in the UV-C range and are also degraded rapidly through the oxidation initiated by the
hydroxyl radical. Therefore, a UV-oxidation system designed to remove T&O compounds will
also accomplish treatment of algal toxins. Includes 4 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 670 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/01/2008 |
