When a filter is put back in service after backwash, a ripening period is experienced until the filter bed matures. Poor quality filtrate released during filter ripening may not be suitable for drinking. In this study, the ripening curve was characterised by the ripening flux, in addition to the turbidities and the time to reach the peaks and end of the filter ripening sequence (FRS). The end of the filter ripening was defined as the instant when a significant change in the filtrate turbidity reduction rate occurred, beyond which filtrate turbidity returned to normal filtration values. Results from pilot plant experiments indicated that the filtration rate generally governed the time parameters of the ripening curve, while the influent solid flux rate, rather than the influent turbidity, influenced the turbidity parameters. A starting filtration rate of 8 m/h minimised the length of the filter ripening sequence and the volume of water wasted during the filter-to-waste procedure.

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