AWWA ACE58206

Natural organic matter (NOM) strongly affects water treatability (oxidant demand andmicropollutant removal), water quality (disinfection byproduct [DBP] levels, taste, odor, andcolor) and water behavior during distribution (residual disinfectant stability, bacterial regrowth,corrosion, and growth of higher organisms). Organic matter can be divided into two fractions:biodegradable organic matter (BOM), which can be used by biofilm bacteria as a source ofenergy and carbon; and, nonbiodegradable (refractory to biodegradation), which has little effecton bacterial growth. Several biological tests have been developed to assess the level of BOM inwater (Huck, 1990). These bioassays are based on two concepts: easily assimilable organiccarbon (AOC) measures the growth of a bacterial inoculum in response to the amount of nutrientin the water; and, biodegradable dissolved organic carbon (BDOC) measures the fraction of DOCassimilated and mineralized by heterotrophic microorganisms. BOM in water promotes bacterialgrowth and may be related to the occurrence of coliform bacteria in distribution systems(Geldreich and LeChevallier, 1996; LeChevallier et al, 1991; LeChevallier, 1990). To complywith increasingly stringent regulation of DBPs and water quality, reducing the level of BOMduring treatment may be an effective approach tocontrolling bacteria in finished water without usingexcessive levels of disinfectants or causing the formationof DBPs.AOC is a measure of the bacterial growth potential offinished water. To perform the test, aninoculum of pure bacterial strains, Pseudomonasfluorescens P17 and Spirillum strain NOX, are added to apasteurized water sample (van der Kooij 1990, 1992).Bacterial growth is monitored in the water samples usingcolony counts, or ATP measurements. The maximumgrowth (Nmax) observed during the incubation isconverted into AOC using the growth yield of thebacteria from calibration curves performed with knownconcentrations of standard organic compounds (acetate,oxalate). In general, AOC corresponds tothe easily assimilable organic compoundsand generally represent a relatively smallportion of the BDOC.AOC levels (geometric means) in 94North American drinking-water systemsranged from 20 to 214 ug/L, with amedian of 100 ug/L (LeChevallier et al.1996, Volk and LeChevallier 2000). AOClevels in North American drinking watersystems typically range from 20 to 214ug/L. The results also indicatethat the majority of the total AOC results from the growth of the test organism, Spirillum sp.strain NOX. This AOCNOX fraction is influenced by disinfection practices (chlorine, ozone, etc.)and suggests that changes in these practices (i.e., the type of disinfectant, the point of application,dose) can impact AOC levels in finished drinking water. AOC levels tend to be higher insurface water supplies and lower in groundwaters, where microbial activity removesbiodegradable organic matter as the water percolates through the soil. Includes 31 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/15/2003

Number of Pages:

13

File Size:

1 file , 360 KB