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.