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Methylisoborneol (MIB)

Actinomycetes Oscillatoria

Geosmin

Actinomycetes Anabaena Oscillatoria issue either in terms of affecting raw water quality or during subsequent dissemination of these waters via distribution piping.

Excessive biological growth of any sort, whether algal, bacterial, or other, can lead to elevated levels of turbidity (i.e., cloudiness) that would complicate subsequent treatment efforts. However, one of the largest biological problems in potable processing of surface waters is that of the formation of various taste- and odor-inducing chemicals. Two such compounds, geosmin and methylisoborneol (often referred to as MIB), are depicted in le 16.14, and it is these particular biochemical products that are most frequently cited as the chemical culprits behind serious aesthetic complaints. These compounds are produced biochemically by a variety of cyanobacteria (including Oscillatoria and Anabaena), actinomycetes (including Streptomyces, Micromonospora, and Nocardia), and algae (e.g., Asterionella), leading to taste and odor complaints that have been likened to "musty" or "fishy" (Darleym, 1982).

The ability of either compound to create problems is readily demonstrated by their respective aqueous-phase "threshold odor" values, which quantifies the concentration value at which humans may perceive their presence. As shown in Figure 16.52, geosmin and methylisoborneol have remarkably low "threshold" values, in the single-digit parts per trillion range. This level is nearly 1000 times lower than that of the next-highest compound (i.e., methyl sulfide, otherwise known as methyl mercaptan, which as described earlier, has a considerable odor of its own!).

The typical circumstance of these two products creating a problem is that of seasonal blooms of cyanobacteria and algae in reservoirs, lakes, and rivers, tied to changes in water temperature and nutrient availability. One such commonplace trigger is that of diurnal fall and spring overturns in deeper reservoirs and lakes, at which point the underlying phosphate-rich hypolimnion waters are returned to the surface to stimulate phototrophic microbial growth. Even without the bacterial release of geosmin or MIB, algal activity stimulated in much the same fashion may also result in the release of various phenolic-type organics, which can then react with chlorine during the treatment process to produce the strong taste- and odor-causing chlorinated phenols.

A second biological problem in potable water systems that may occur is that of bacterial colonization along the interior surfaces of distribution piping (Bitton and Gerba,

Geosmin Methylisoborneol (MIB) Crotyl mercaptan Tert-butyl mercaptan Thiocresol Indole Diphenyl sulfide Allyl mercaptan Benzyl mercaptan Phenyl mercaptan Ethyl mercaptan Amyl mercaptan Trimethylamine Propyl mercaptan Methyl mercaptan Hydrogen sulfide Skatole Ammonia

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