AWWA ACE59931

Cyanobacteria, also called blue-green algae, are photosynthetic bacteria foundprimarily in surface waters. Eutrophic surface waters are at highest risk forcyanobacterial blooms; these include ponds, lakes, and water treatment plant reservoirsunder the influence of extraneous nutrients from agricultural runoff or sewage.Cyanobacteria are of interest to the water treatment community because they producecompounds which are toxic to humans and animals. This work reviews the current stateof water treatment for cyanotoxins and presents the results of a summer 2003 survey ofmicrocystin levels in 33 North American raw water supplies operated by AmericanWater. Recommendations to water treatment plants are made in view of the treatmentoptions and extent of toxin contamination.A commercially available immunoassay kit detected microcystins in 87% of 40-fold concentrated raw samples and 30% of concentrated effluent samples. The remainderin each case was below the enhanced assay detection limit of 0.031 ppb for raw samplesand 0.080 ppb for effluent samples. Raw water microcystin levels, expressed as the meanof six measurements, can be considered background when compared to the 1 ppb WorldHealth Organization (WHO) guideline. However, two raw water sources consistentlyshowed high microcystin concentrations. One of these was inactive, and the other wasremoved from service during testing due to odor problems. Plant effluent levels,expressed as the mean of two measurements, were only detectable at five of 28 samplingsites. All detectable plant effluent levels were below the WHO guideline.Because raw water microcystin levels are generally low across the AmericanWater system, source water protection measures should be adequate to control thedevelopment of algae problems. Existing water treatment regimens are sufficient tocontrol microcystins. In a context of increased source water eutrophication, theeffect of water treatment processes on higher levels of toxins will require additionalstudy. In the few instances where raw water contamination was a concern, the WorldHealth Organization method of microscopic cell enumeration is the recommendedmonitoring method for the months of July through September. In response to high cellnumbers, toxin levels may be conveniently quantified using methanol extraction of watersamples, evaporation under nitrogen at 45^oC, and reconstitution in 10% methanol forimmunological assay. Includes 32 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/17/2004

Number of Pages:

18

File Size:

1 file , 810 KB