AWWA ACE58206

Natural organic matter (NOM) strongly affects water treatability (oxidant demand and micropollutant removal), water quality (disinfection byproduct [DBP] levels, taste, odor, and color) 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 of energy and carbon; and, nonbiodegradable (refractory to biodegradation), which has little effect on bacterial growth. Several biological tests have been developed to assess the level of BOM in water (Huck, 1990). These bioassays are based on two concepts: easily assimilable organic carbon (AOC) measures the growth of a bacterial inoculum in response to the amount of nutrient in the water; and, biodegradable dissolved organic carbon (BDOC) measures the fraction of DOC assimilated and mineralized by heterotrophic microorganisms. BOM in water promotes bacterial growth and may be related to the occurrence of coliform bacteria in distribution systems (Geldreich and LeChevallier, 1996; LeChevallier et al, 1991; LeChevallier, 1990). To comply with increasingly stringent regulation of DBPs and water quality, reducing the level of BOM during treatment may be an effective approach to controlling bacteria in finished water without using excessive levels of disinfectants or causing the formation of DBPs. AOC is a measure of the bacterial growth potential of finished water. To perform the test, an inoculum of pure bacterial strains, Pseudomonas fluorescens P17 and Spirillum strain NOX, are added to a pasteurized water sample (van der Kooij 1990, 1992). Bacterial growth is monitored in the water samples using colony counts, or ATP measurements. The maximum growth (Nmax) observed during the incubation is converted into AOC using the growth yield of the bacteria from calibration curves performed with known concentrations of standard organic compounds (acetate, oxalate). In general, AOC corresponds to the easily assimilable organic compounds and generally represent a relatively small portion of the BDOC. AOC levels (geometric means) in 94 North American drinking-water systems ranged from 20 to 214 ug/L, with a median of 100 ug/L (LeChevallier et al. 1996, Volk and LeChevallier 2000). AOC levels in North American drinking water systems typically range from 20 to 214 ug/L. The results also indicate that 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 in surface water supplies and lower in groundwaters, where microbial activity removes biodegradable organic matter as the water percolates through the soil. Includes 31 references, tables, figures.