Over 55,000 recorded particle counts, from February 21 through 27, 2000, at the PutnamStation Filter Plant, in Birmingham, Alabama provided the foundation for a study of filterparticle removal efficiency. Five anthracite/sand filters of identical constructioncontaining filter media differing in age by one year and were found to exhibitsignificantly different particle removal efficiencies. Filter 3, rebuilt in 1991, exhibitedthe lowest median particle removal efficiency of 99.1% while Filter 11, rebuilt in 1995,exhibited the highest median particle removal efficiency of 100%. To ensure consistentperformance from individual filters utility operators must be aware of the effect filtermedia age may have on particle removal efficiency and plan filter rebuilds and/ormaintenance accordingly.
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