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This paper provides a broad overview of the various types of algae found in surface waters, theirrole in aquatic ecosystems, and the water-treatment problems they can cause. The focus is ontastes and odors and algal toxins. Algae can be regarded as "good" because they are the basis ofthe food chain. Some are "bad" when they grow excessively and create problems in watersupplies and at the water treatment plant. The author ascribes the term "ugly" to certain algaewhose physical form is not especially attractive, especially when they form blooms and scums inwater supplies, but recognizes that beauty is in the eye of the beholder. Algae most often causeproblems only when the aquatic ecosystem is unbalanced and one or more populations becomeover-productive. Typical water-treatment problems caused by excessive growth include cloggingof intake screens, production of taste-and-odor compounds, poor flocculation and settling, andfilter clogging. Blue-green algae produce taste-and-odor compounds that are offensive anddifficult to remove; in addition, some blue-greens produce toxins. The subject of algal toxins isnot new, but only since 1998 have they garnered attention in the United States because of theirpotential for causing human health effects. Diatoms and flagellated algae often produce taste-and-odor compounds that are more easily eliminated during water treatment than compoundsproduced by blue-greens, but these algae create problems at the water treatment plant other thanodors, notably interference with clarification process and filter clogging.Excessive algal growth in impoundments elevates pH and increases dissolved oxygen tosupersaturation levels during the daytime, both of which can cause water treatment problems. Inaddition, algal cells and the extracellular products they produce during photosynthesis increaselevels of disinfection byproduct precursors in the raw water. When algae die and settle inthermally stratified impoundments, they decay and cause depletion of dissolved oxygen near thebottom and set the stage for the release from the lake sediments of iron, manganese, ammonia,and other substances that degrade water quality. Includes 38 references, table.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 14File Size: 1 file , 300 KB