Dissolved air flotation has achieved a ______ removal of cryptosporidium, which compares to a removal rate of less than 0.5 log using conventional sedimentation.

Dissolved air flotation has achieved a ______ removal of cryptosporidium, which compares to a removal rate of less than 0.5 log using conventional sedimentation.

• A. 1.0-log
• B. 1.5-log
• C. 2.0-log
• D. 2.5-log

Answer: (C)

Log removal shows how much contaminant is taken out, using a base-10 reduction. So a two-log removal means the concentration is reduced by 10^2, leaving about 1% of the original — roughly 99% removed. Dissolved air flotation uses tiny air bubbles that attach to cryptosporidium and other fine particles, carrying them to the surface to be skimmed off. This flotation mechanism is much more effective for removing small, buoyant oocysts than gravity-based sedimentation, which typically achieves less than a 0.5 log removal (under about 68% removed). That contrast explains why the result for DAF is about a two-log removal: it yields far higher removal of cryptosporidium than conventional sedimentation.

Log removal shows how much contaminant is taken out, using a base-10 reduction. So a two-log removal means the concentration is reduced by 10^2, leaving about 1% of the original — roughly 99% removed. Dissolved air flotation uses tiny air bubbles that attach to cryptosporidium and other fine particles, carrying them to the surface to be skimmed off. This flotation mechanism is much more effective for removing small, buoyant oocysts than gravity-based sedimentation, which typically achieves less than a 0.5 log removal (under about 68% removed). That contrast explains why the result for DAF is about a two-log removal: it yields far higher removal of cryptosporidium than conventional sedimentation.