Preozonation as a coagulant aid in drinking water treatment

The effects of preozonation on the treatment of Seine River water were evaluated in a pilot plant consisting of flocculation with basic aluminum polychloride (PAC) followed by sedimentation. Preozonation significantly increased the removals of turbidity, particle numbers and volumes, chemical oxygen demand, and UV absorbance at all treatment levels investigated (0.3–1.2 mg/L for ozone, and 15–60 mg/L for PAC), with the optimum ozone dose appearing to be about 0.8 mg/L. The favorable effects of ozone increased with pH and the particle count of the untreated water. The increases in particle removals appeared to stem partly from increases in floc size and settling velocity.