Development and Operational Implementation of a Modified and Simplified Method for Determination of Assimilable Organic Carbon (AOC) in Drinking Water

Abstract

The concept of using a bioassay technique to measure the proportion of dissolved organic carbon in drinking water that is readily assimilable by micro-organisms (AOC), was first introduced by Van der Kooij. The approach has subsequently been adapted by a number of research laboratories, but in general the methods used have been relatively expensive in equipment, materials and/or time. We report here the development of a modified and simplified assay procedure for AOC. The method is based on incubation of the sterilised water sample with a defined mixed inoculum comprising 4 characterised bacterial species. At the end of a 6 day incubation period the amount of AOC present is directly related to the bacterial growth yield measured by a simple plate count. It is not necessary to determine growth curves for every sample, nor is it essential to calibrate each time the assay is used. The method has been shown to give a linear response for mixed organic substrates between 0 and 1 × 10⁶ µgC/l. We report on preliminary investigations into the AOC content of a range of different drinking waters both at treatment works and within distribution systems.