Relationship of pH and floc formation kinetics to granular media filtration performance

In drinking water treatment, destabilization of suspended particles through effective coagulation processes is critical for optimizing filtration performance. This study examined the impact of coagulation pH (6.0-7.4), zeta-potential, and floc formation kinetics on particle removal during settling and filtration. Increasing pH improved turbidity removal in the settling process and significantly increased the zeta-potential range in which filtration performance was optimized. Although it was possible to optimize filtration (i.e., attain total particles < 10/mL) at each of the three pH levels examined, the zeta-potential range in which this was possible was approximately +2 to +4 at pH 6.0 and -4 to +4 at pH 7.4. Overall, these results indicate that the use of a higher coagulation pH-and thus higher alum doses-may be particularly advantageous during periods of rapidly changing water quality conditions, such as high-NOM runoff events. Results from PDA experiments indicated that the rate of floc formation (measured immediately following coagulant addition) was indicative of overall process performance.