Easily assimilable organic carbon (AOC) is frequently used for the assessment of the biological stability of drinking water, which is an important consideration in the control of bacterial growth in distribution networks. The first AOC bioassay was developed in 1982 and is based on growth of two bacterial strains (Pseudomonas fluorescens P17 and Spirillum spp. NOX) in drinking water relative to their growth on acetate. Much research was subsequently conducted to modify, simplify and increase the speed of the assay which resulted in a number of alternative AOC assays. Application of these assays raises legitimate questions about the comparison of AOC data from different studies. In the present study, a round-robin test was performed to evaluate the correlation between three established AOC methods. A total of 14 water samples, covering a wide range of AOC concentrations, were analyzed with the original ‘van der Kooij’ method, the ‘Werner & Hambsch’ method and ‘Eawag’ method. Good correlations were found between AOC concentrations measured with the various methods. The data suggest an acceptable compatibility between different AOC methods, although deviations between the methods call for careful interpretation and reporting of AOC data.
Biological activated carbon (BAC) filtration is an important treatment step in the production of drinking water especially if drinking water is produced from surface water. The performance and processes within a BAC filter have been of interest for researchers since the 1980's, mainly because of its ability to remove natural organic matter known as disinfection precursors. A malfunction of one of the pre-treatment steps might affect the feed water quality into the BAC filters. The main objective of this study was to determine the immediate response of the BAC filters to a rapid change in feed water quality. It was shown that with the studied setup it was possible to compare the effect of different pre-treatment steps and subsequent different water qualities on the performance of the BAC filters on the long term adaptation. However, especially the immediate response was not studied in detail before. All filters were able to mitigate a sudden change in feed water quality, either through improved adsorption or increased activity of the biomass on the filter. As a result of this resilience against sudden changes, it is therefore concluded that there is no direct need for very stringent on-line monitoring and continuous adjustments of the feed water quality of the BAC filters. The addition of phosphate resulted in the lowest dissolved organic carbon (DOC) concentration in the effluent of the BAC filters. In this study the influence of intact cells in the feed water on the performance of the BAC filters was shown to be limited.
The concentrations of dissolved ozone and assimilable organic carbon (AOC) are important performance parameters in drinking water production. For the measurement of ozone, a spectral algorithm was developed that allows quantification in situ using a UV/Vis spectrometer probe. Furthermore, a strong correlation between the change in the absorption spectrum after individual treatment steps and the formation or removal of AOC in that treatment step was observed. This allowed the development of a spectral algorithm that predicts AOC formation during ozonation and subsequent removal in further treatment steps. This method has been verified at one pilot plant of the Amsterdam drinking water supply.
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