Characteristics of deposits of diatoms in filters and effective factors to filter clogging

摘要

Clogging problem of rapid sand filter has been occurred by eutrophication of water sources. Most of algae which affect the filter clogging are slender type diatoms. In this study, model mate-rials for diatoms and sand are used in the filtration experiment. The amount of 95 per cent of total deposit is captured within the layer as thick as 30 times of the diameter of a filter grain under the condition of size of a filter grain from 2 to 6 times of diatom length. The ratio of deposited amount on a grain to filter depth is a main factor to estimate the degree of the partial deposit at the upper layer of filter and decreases with larger diameter of filter grain and faster filtration rate. The result in this study shows useful points to design the depth of filter for protection of filter clogging.