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Access to safe drinking-water is a basic concern for human health and daily life, and biological stability of drinking water is becoming a focus in recent years. For conventional treatment processes there have been a lot of research of characteristics of bacterial regrowth and its influence factors on biological stability of drinking water, but for the water treated by ultrafiltration, it is not clear. Thus, it is necessary to study the major factors (such as temperature, particles, biofilm, nutrients, and retention time) affecting the biological stability in the water treated by UF.In this paper, according to synthetic water experiment, turbidity, heterotrophic plate counting, coliform, total number of bacteria, and microbial activity were investigated. The results showed that: There is a certain amount of bacteria in the water treated by UF, and it may continue growing because of the nutrients in the water; there is a certain amount of particles in the water treated by UF, and it can carry a lot of bacteria so that it can affect the microbiological examination; in water distribution pipes, bacteria could left biofilm which attached to pipes wall and suspended in bulk water in favorable conditions.Studied the growth characteristics of bacteria in the water treated by UF at different temperatures in the captive test, the results showed that: Regardless of the presence of biofilm, the HPC, total number of bacteria, microbial activity and turbidity at 22℃and 24℃are higher, at 14℃and 15℃are less, and at 4℃and 5℃are the lowest; and even at 4℃and 5℃, HPC also increased by two orders of magnitude. Temperature is a key factor in bacterial growth in water treated by UF.Studied the influence of nutrients on the biological stability in the water treated by UF, the results showed that: In the absence of disinfectants, when the limiting factor of bacterial growth is assimilable organic carbon, the biostability of water treated by UF with the assimilable organic carbon concentration less than 8μg /l was ideal and acceptable; when other nutrients are sufficient besides phosphorus, microbially available phosphorus can limit the growth of bacteria.Studied the influence of retention time on the biological stability in the water treated by UF, the results showed that: Retention time can affect the biostability of drinking water. As the time passed, the turbidity, total number of bacterial, heterotrophic plate counting, coliform increased, and the water quality deteriorated; when the retention time is longer than 5d, even at low temperature (4℃and 5℃) or low AOC concentration (8μg/l and 13μg/l), the biostability can not maintainable.
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