Correlating Cryptosporidium removal using dissolved air flotation in water treatment

Cryptosporidium parvum behaves similarly to other low density colloidal particles in water. Their physical removal requires destabilization and subsequent separation. Removal as high as 4.9 log-units has been reported for gravity sedimentation but the average removal tends to be less than 2 log-units. Dissolved air flotation (DAF) is a method of water treatment that has been used primarily for sludge thickening to remove low density particles that are generally missed by gravity sedimentation treatment. Dissolved air flotation process has been found to be effective for removal of fragile floc particles such as found in water treatment. This method has been reported to be effective in removing up to 4 log-units of C. parvum in pilot-scale studies. There were 138 data points found in the literature that were used to estimate the model parameters from the temperature, turbidity and pH of the water source as well as the flocculation time, coagulant concentration and recycle ratio of the DAF process. The statistical analysis suggested that there was a strong positive correlation with the recirculation ratio for the recycle feed and a slightly weaker positive correlation with the coagulant concentration, water temperature and the time of flocculation. Both the pH and the turbidity demonstrated a strong negative correlation. The model presented here can be used as an aid for regulators, water utilities, and engineers who are considering designing DAF processes as an alternative to gravity flocculation and sedimentation processes.