Critical elements of flocculation in drinking water treatment

Abstract

The specific focus of this study was on the effects of flocculation duration, intensity, and scheme (i.e., single or multistage) on floc formation (time and size) and treated turbidity (settled and filtered). The results showed that floc formation times were 2–8 times longer under charge neutralization conditions compared with sweep flocculation conditions for the low‐turbidity and low‐organics water studied. Settled turbidity removals were dependent on the applied mixing conditions. Filtered turbidity was found to be independent of the investigated flocculation conditions, which calls into question the true value of mixing conditions with substantial implications on facility design, operation, and regulation. While at least 9 min of flocculation time was necessary under some coagulation conditions, the intensity and scheme of flocculation were not critical to overall treatment efficiency under the studied conditions. These findings might offer potential savings to water utilities in terms of design, construction, operation, and maintenance costs.