Determination of assimilable organic carbon in humus-rich drinking waters

The potential for microbial growth in drinking waters is considered to be associated with the content of easily assimilable organic carbon (AOC). The bacterial test for the determination of the AOC concentration presumes that microbial growth in the test is limited by the availability of organic carbon. However, in the northern latitudes inorganic nutrients, particularly phosphorus, may limit the microbial growth in drinking waters. In our studies, addition of an inorganic nutrient mixture (N, P, K, S, Ca, Mg) to soft, humus-rich drinking waters increased the AOC yield in most of the drinking waters. The assimilable organic carbon determined with the addition of nutrients describes that pool of organic carbon potentially available for microbial growth (AOCpotential). The AOC yield when there is no without addition of inorganic nutrients describes that part of organic carbon (AOCnative) which bacteria can utilize in the prevailing conditions and it is composed of the availability of both organic substrates and inorganic nutrients. We found that the bacterial strains, Pseudomonas fluorescens P 17 and Aquaspirillum NOX, used in the standard AOC method, can also be applied in humus-rich drinking waters.