Testing of Diatomaceous Earth Filtration for Removal of Cryptosporidium Oocysts

Abstract

Because previous studies of diatomaceous earth (DE) filtration for Cryptosporidium oocyst removal have been conducted on a relatively small scale, this study was designed to determine the performance capability of DE at the pilot‐scale level and at a flow rate greater than that permitted by many state regulatory agencies. This study used DE of moderate permeability that is commonly used by smaller water systems to provide economical water treatment. It found that Cryptosporidium oocyst removals at a flow rate of 1 gpm/sq ft (2.5 m/h) averaged 6.25 logs and removals at 2 gpm/sp ft (5 m/h) averaged 6.31 logs. In addition, average turbidity levels and particle concentrations were lower at 2 gpm/sp ft (5 m/h). These findings of equal or better performance at 2 gpm/sp ft (5 m/h) are significant because many regulatory agencies ‐ and consequently municipal water suppliers ‐ have historically restricted operation of DE filters to 1 gpm/sp ft (2.5 m/h). The findings are also important because they clearly show that DE filtration is capable of providing far greater reduction in Cryptosporidium oocyst concentrations than is provided by conventional or direct granular media filtration. The data summarized in this article support consideration of DE as a more broadly applicable alternative for Cryptosporidium control; they also support including DE filtration as a serious alternative for a much broader range of applications that include larger plant sizes, higher filtration rates, and backwash treatment applications.