Giardia and Cryptosporidium removals by clarification and filtration underchallenge conditions

Used in drinking water treatment in Europe and South Africa since the late 1960s, dissolved-air flotation (DAF) technology is attracting increasing in terest in the United States as well. US drinking water regulations, however , have yet to recognize DAF capabilities, with both the Surface Water Treat ment Rule and the Interim Enhanced Surface Water Treatment Rule limiting th e definition of conventional treatment to clarification by sedimentation. B ecause of this, some states give DAF plants only direct filtration credit o r require collection of DAF pilot-plant data to demonstrate the technology' s capabilities. The authors compared removals of Giardia and Cryptosporidium by clarificati on (DAF or lamella [plate] sedimentation) and dual-media filtration. Under challenge conditions, DAF outperformed lamella sedimentation, providing con sistently higher removals of protozoa. Furthermore, DAF as a clarification process offered the advantage of providing a more effective barrier to the passage of Giardia and Cryptosporidium ahead of the filtration step. Given these findings, the authors argue that DAF plants should receive Giardia an d Cryptosporidium removal credits at least equal to those received by sedim entation plants.