Pilot‐Plant Studies of Slow‐Rate Filtration

Alternatives to conventional water filtration plants, which use coagulation, flocculation, sedimentation, and rapid filtration, may be appropriate for some small utilities. One such alternative is slow‐rate filtration. This article describes pilot‐plant studies that were undertaken to evaluate slow‐rate filtration for the removal of particulates, total coliforms, standard plate count bacteria, and organics (total organic carbon and trihalomethane formation potential). Two pilot‐scale filtration systems were used: a slow sand filter, operated for 800 days, and a second slow sand filter operated in parallel with a slow‐rate filter containing granular activated carbon, operated for 200 days. Results are presented for both systems.