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.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 360 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 13 |
| Published : | 06/15/2003 |
