Plug-flow biofilm reactors colonized by microorganisms in streamwater were used to measure the concentration and composition of biodegradable dissolved organic C (BDOC) in White Clay Creek. During the 4-month study period, DOC ranged from 0.8 to 10.4 mg C liter-' and was, on average, composed of 75% humic substances, 13% carbohydrates, 2% amino acids, and 18% > 100 kDa. The carbohydrates were predominantly polysaccharides, nearly all amino acids were present in the combined form, and most carbohydrates and amino acids were humic bound. BDOC ranged from 0.2 to 2.9 mg C liter-', averaged 25% of the DOC, and was composed of 75% humic substances, 30% carbohydrates, 4% amino acids, and 39% DOC >lOO kDa. The carbohydrate portion of the BDOC was primarily polysaccharide or humic bound. Similarly, the amino acid portion of the BDOC was overwhelmingly present in the combined form and primarily humic bound. Glycine and aspartic acid were the dominant amino acids in White Clay Creek DOC and in the BDOC pool. Our data broaden the perspective on substrates important to microbial metabolism and energy flow in streams and provide the first direct evidence that humic substances, although largely refractory, are an important component of streamwater BDOC.Dissolved organic matter (DOM) comprises most of the reduced carbon in aquatic ecosystems and provides energy and carbon resources for the metabolism of heterotrophic bacteria. Not all DOM is biologically labile or even biodegradable. Although numerous investigations in both freshwater and marine environments have reported on the quantity and composition of DOM, fewer studies have addressed the biodegradable fraction. Identifying biodegradable DOM (BDOM) constituents and quantifying their contribution to heterotrophic metabolism can increase our understanding of ecosystem function and bacterial ecophysiology.From a limited number of studies we know that BDOM in streams and rivers includes both low-molecular-weight (Kaplan and Bott 1983) and high-molecular-weight (Meyer

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The presence of natural organic matter (NOM) strongly impacts drinking water treatment, water quality, and water behavior during distribution. Dissolved organic carbon (DOC) concentrations were determined daily over a 22 month period in river water before and after conventional drinking water treatment using an on-line total organic carbon (TOC) analyzer. Quantitative and qualitative variations in organic matter were related to precipitation and runoff, seasons and operating conditions. Following a rainfall event, DOC levels could increase by 3.5 fold over baseflow concentrations, while color, UV absorbance values and turbidity increased by a factor of 8, 12 and 300, respectively. Treated water DOC levels were closely related to the source water quality, with an average organic matter removal of 42% after treatment.

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A 16-month study was conducted on the presence of Aeromonas hydrophila in drinking water in Indiana, U.S.A. Enumeration was conducted in source water, in various sites within a water treatment plant, and in the distribution system in both bulk water and biofilm, as well as in a simulated (annular reactors) drinking-water distribution system. Presumptive Aeromonas spp. counts on source waters regularly approached 10(3)-10(4) CFU/100 mL, during summer months and granular activated carbon - filtered water counts ranged from <1 to 490 CFU/100 mL. In source water, presumptive Aeromonas levels were related to water temperature. Aeromonas hydrophila was never detected in the treatment plant effluent or distributed bulk water, showing disinfectant efficiency on suspended bacteria; however, isolates of A. hydrophila were identified in 7.7% of the biofilm samples, indicating a potential for regrowth and contamination of drinking-water distribution systems.

Biodegradable dissolved organic carbon (BDOC) in water is evaluated by the DOC reduction in the sample inoculated with a natural biomass, fixed on sand particles, within a few days incubation period. Recorded BDOC values are independent of the origin of the inoculum. This bioassay is accurate, precise, gives reproducible results and is sufficiently sensitive even for distributed water. A good relationship between BDOC values and the regrowth potential of presterilised samples of water reinoculated with Ps. fluorescens or mixed natural populations of bacteria is observed.

High temperature, high BOM concentration, and low disinfectant residual promote regrowth of coliforms in distribution systems. This article summarizes data collected during various surveys that assessed four aspects of biodegradable organic matter (BOM) in drinking water: (1) BOM concentrations entering distribution systems, (2) the relationship between concentrations of assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC), (3) field tests of a simple method of measuring BDOC using bioreactors, and (4) the effect of BOM on coliform occurrences in distribution networks. Overall, average concentrations of AOC and BDOC in plant effluent were 100 μg/L and 0.32 mg/L, respectively. A statistically significant but weak relationship between AOC and BDOC concentrations suggests that both parameters need to be monitored during biostability studies because they provide different pieces of information. BDOC bioreactors are useful for measuring BDOC concentrations at water utilities. However, they require a long time to colonize and must adapt to water at the site where they are used. Coliform occurrences were associated with three factors: temperature, disinfectant type and concentration, and AOC concentration. When threshold values for these factors were exceeded (15oC, AOC > 100 μg/L, and dead‐end disinfectant residuals < 0.5 mg/L for free chlorine or 1.0 mg/L for chloramines), the probability of coliform occurrences greatly increased.