The objectives of this study on the qualitative and quantitative effects of rate changes made during a filter run were to determine: the relation between magnitude of the rate disturbance and resulting change in effluent quality; the relation between the duration of the disturbance and resulting change in effluent quality; and, whether gradual or sudden rate increases have greater effect on effluent quality. The investigation was conducted using three types of influent suspensions and two filtering facilities. The pilot plant consisted of a mixing and aeration tank, a pump which pumped to a constant‐head tank, and three plexiglass tube sand filters, 6 in. ID, with flowmeter and photoelectric turbidimeter attached to each filter. Twelve experimental runs were made with the three pilot plant filters, resulting in 36 separate filter tests. Hydrous ferric oxide floc suspension was filtered in twelve filter tests. The results of each pilot plant run were evaluated to determine the maximum iron concentration passed by the filter following the rate change disturbance. Several conclusions were drawn from an analysis of the collected data, and the article provides a discussion of these conclusions, and their relationship to the stated objectives.

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More and more water plants are using higher filtration rates. Several factors should be considered in selecting the design filtration rate. The consequences of higher rates in terms of water quality, filter run length, and percentage of product used in backwashing are important factors. This article, based on 3 years of pilot scale research, attempts to demonstrate how higher filtration rates affect these factors.

For many years, municipal water treatment facilities have been producing potable water using coliform organisms as an index of water disinfection. In individual water supplies, where constant supervision is unavailable and where the physical and biological character of the raw water fluctuates rapidly, a more stringent standard of disinfection is needed. Superchlorination is recommended to provide a factor of safety for these fluctuations and to reduce the necessary chlorine contact time. This study recommends the use of Coxsackie virus as a criterion of chlorine resistivity in the disinfection of individual water supplies.

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