Suchergebnisse

AbstractThe basic concept of chemical reaction engineering, as applied to the disinfection of water in a continuous flowing system, is summarized, and the effect of flow dispersion (i.e. the spread of residence time) on the efficiency of the process is highlighted. It is shown that deficiencies compared with the ideal batchwise situation can be offset by adjustments to the residence time or the disinfectant concentration, provided that the design is reasonable. The term 'compensation factor' is offered as a means of characterizing tanks which are intended for a specific duty.Reference is also made to recently available software which now enables tanks to be evaluated at the design stage without resorting to specialist computing services.

ABSTRACTA UK standard for the specification, approval and testing of filtering materials has recently been published by British Water (formed by the merger of the British Effluent and Water Association and the British Water Industries Group) in response to an identified need. This paper reviews the considerations during the preparation of the standard and provides a technical background. The approach has been to base the standard on parameters which affect the behaviour of the material during filtration, rather than to specify material composition and appearance, which are unimportant. Standards and specifications are a basis for testing, and the inclusion of irrelevant parameters can lead to unnecessary work.

ABSTRACT At present there is no generally accepted test available for characterizing the friability of granular filter media in the context of its ability to withstand handling and placing, as distinct from abrasion resistance during backwashing – which is the subject of other, existing, test methods. Most existing procedures tend to be grinding tests and have little meaning. The approach selected in this work was to adapt the ring shear test, in which a sample (large enough to be analysed by sieving) is subjected to shear under a known compression load and the change in the undersize fraction is assessed. A representative selection of dry media was submitted to the test and the results proved to be reproducible and capable of distinguishing (clearly) between friable and non‐friable resistant types. The procedure is likely to become the basis of a standard test.