Bed expansion affects performance

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Courtesy of Entech Design, Inc.

The experience of Pennsylvania Department of Environmental Protection staff over 14 years conducting filter plant performance evaluations led investigators to identify a coomon thread:'inadequate filter bed expansion eventually contributes to poor filter performance and reduced finished water quality.'

The article points our that and insufficiently expanded filter is insufficiently cleaned, and this can lead to numerous problems, specifically. 'poor post-backwash recovery, sensitivity to hydraulic surges (flow changes), shortend filter run times, and eventually mudball formation. All these problems can increase the likehood of a breakthrough of waterborne of waterborne disease-causing organisms' - with the final conclusion that 'proper filter bed expansion is a significant operational considerations.'

The examiners report that while plant-specific goals for filter bed expansion are recommended, plants that achieve a minimum of 20% expansion of the filter media perform better - 20% expansion is a good starting point for determining optimal media expansion. Noticeable filter performance problems are likely when expansion drops below 15%.

Finally, investigators recommend that bed expansion be measured in severla locations to better understand the effectiveness of the backwash - and, operators should take routine measurements for comparison with other filter performance paramters.

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