The growth of bacteria on organic compounds in drinking water

Abstract Growth (“regrowth”) of bacteria In drinking water distribution systems results in a deterioration of the water quality. Regrowth of chemoheterotrophic bacteria depends on the presence of organic. compounds that serve as a nutrient source for these bacteria. A batch-culture technique was developed to study the growth of bacteria in drinking water. The maximum colony counts of selected pure cultures of bacteria grown in drinking water were used as a measure for the concentration of easily assimilable organic carbon compounds (AOC). Three strains of bacteria isolated from drinking water were selected for AOC determinations: (1) Pseudomonas fluorescens strain P17, an organism with a very great nutritional versatility, for general use; (2) a Flavobacterium sp. strain S12, to determine the concentration of maltose and starch-like compounds, and (3) a Spirillum sp. strain NOX to determine the concentration of carboxylic acids. Including oxalic acid. The properties of these bacteria were extensively studied in batch-culture experiments with drinking water supplemented with very low amounts of selected organic compounds. The obtained results prove that growth and growth kinetics of bacteria at concentrations between 1 and 1000 μg of C per liter can be determined in simple experiments using simple equipment. The strains mentioned above were well adapted to growth at concentrations of a few micrograms of substrate C per liter; their substrate saturation constants (K s ) were below 1 μM for many compounds tested. K s values below 0.1 μM were also obtained. Growth measurements with strain P17 in water sampled from various treatment stages revealed that the AOC concentrations in these water types usually varied between 10 and 100 μg of acetate C equivalents per liter. Ozonation caused a strong increase of the AOC concentration. Strain NOX was better suited for the determination of the AOC concentration in ozonated water because of its ability to utilize oxalate. Filtration processes caused significant reductions of the AOC concentrations, at low AOC concentrations (< 25 μg of acetate C equivalents per liter) this reduction was less than 50 %. The use of starch-based coagulant aids in water treatment gave increased AOC concentrations an determined with Flavobacterium strain S12. The concentration of these compounds was reduced to non-detectable levels ( < 1 μg of starch C equivalents per liter) by biological filtration processes. These findings demonstrate that biological filtration processes are effective in reducing AOC concentrations to levels where excessive regrowth is not possible. This conclusion is supported by the very poor growth of Pseudomonas aeruginosa in the filtrate of slow sand filters, and the inability of Aeromonas hydrophila to multiply in this water type.