WF21 Treatment Process: CHEMICAL CLARIFICATION

Chemical clarification reduces turbidity, organics, trace metals, and phosphate, and elevates pH for disinfection and virus removal. The system includes separate rapid mixing, flocculation, and settling basins. Lime, at a dose of 375 to 500 mg/L, is added in slurry form into the rapid-mix basin as a primary coagulant and disinfectant (raising the pH to 11.3), and an anionic polymer, at a dose of 0.1 mg/L, is added as a settling aid in the third-stage flocculation basin.

Water flows from the bottom of the third flocculation basin into a settling basin where it flows horizontally into the notched weirs of collection troughs. Approximate detention time in the clarification basin is 117 minutes: one minute for each of the two rapid-mix basins, 30 minutes in the flocculation basins and 85 minutes in the settling basins.

OCWD is currently studying the possibility of using microfiltration (MF) as a replacement for chemical clarification. Benefits of MF may include reduction of space used for pre-treatment, less labor-intensive maintenance, and the possibility of producing even higher-quality water.