Improving Granular Media Filtration Performance by Media Roughness

摘要

Engineered filtration media have an inherent advantage over conventional media (mined aggregates) in that their physical properties are more uniform and other attributes may be optimized. Pilot- and lab-scale studies were conducted to examine the impacts of media roughness on particle removal and turbidity spike dampening by filtration. Preliminary pilot-scale experiments evaluated filtration performance of various media (of differing surface roughness), including anthracite/sand, GAC/sand, and engineered ceramic media. Filter media performance was assessed based on turbidity, particle count reduction, Cryptosporidium oocyst, and oocyst-sized microsphere removal at different operational conditions. It was observed that engineered ceramic media with "rough" surfaces generally achieved greater particle/turbidity removal and dampening relative to anthracite and GAC filters under all investigated conditions. Lab-scale experiments were conducted to: 1) elucidate the role of surface roughness on particle removal and turbidity dampening; and 2) define the most effective surface roughness characteristics to ensure particle entrapment. The colloid particle removal ability of 6 types of media with varied surface roughness under different operational conditions (favorable and unfavorable, with and without coagulation, high and low flow rate, etc.) was assessed by particle count and turbidity reductions (including response to sudden influxes of particles). The results presented in this paper and the associated presentation clearly and reproducibly demonstrate that 1.1 and 4.5 μm particle removal by rough engineered ceramic media do not remove particles in a manner that is consistent with conventional filtration theory and are equivalent to or greater than those obtained with conventional anthracite and GAC media, depending on operational conditions.