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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.

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With funding from the European Commission, a consortium of members of the European Water Research Institutes is carrying out a programme of work with the objective of optimising and standardising a method for determining the presence in water of (oo)cysts of Cryptosporidium and Giardia. Each of the stages of the conventional analysis procedure (initial concentration, recoveryand identification and enumeration) are being investigated and the relative merits of existing and new methods are being assessed. Newly developed filters (Envirochek and Filta-Max) have been shown to be more efficient for initial recovery of (oo)cysts from water than the previously used Cuno cartridge filters. In addition, for the analysis of raw waters, flocculationwith ferric sulphate has been shown to give recoveries similar to the Envirochek and Filta Max. Modern purification systems such as immunomagnetic separation have also been assessed and found to offer some advantages over flotation although optimisation of the latter has brought improved efficiency. Preliminary assessment of solid phase cytometry has indicated that this technique could offer significant time savings compared to conventional microscopic counting. The results of the study will be used to propose a revised standard method to CEN.

To determine the removal efficiency of ultrafiltration (UF) membranes for nano-particles in the size range of viruses the state of the art uses challenge tests with virus-spiked water. This work focuses on bench-scale and semi-technical scale experiments. Different experimental parameters influencing the removal efficiency of the tested UF membrane modules were analyzed and evaluated for bench- and semi-technical scale experiments. Organic matter in the water matrix highly influenced the removal of the tested bacteriophages MS2 and phiX174. Less membrane fouling (low ΔTMP) led to a reduced phage reduction. Increased flux positively affected phage removal in natural waters. The tested bacteriophages MS2 and phiX174 revealed different removal properties. MS2, which is widely used as a model organism to determine virus removal efficiencies of membranes, mostly showed a better removal than phiX174 for the natural water qualities tested. It seems that MS2 is possibly a less conservative surrogate for human enteric virus removal than phiX174. In bench-scale experiments log removal values (LRV) for MS2 of 2.5-6.0 and of 2.5-4.5 for phiX174 were obtained for the examined range of parameters. Phage removal obtained with differently fabricated semi-technical modules was quite variable for comparable parameter settings, indicating that module fabrication can lead to differing results. Potting temperature and module size were identified as influencing factors. In conclusion, careful attention has to be paid to the choice of experimental settings and module potting when using bench-scale or semi-technical scale experiments for UF membrane challenge tests.