OZONE DISINFECTION OF FISH HATCHERY WATERS: PILOT PLANT RESULTS, PROTOTYPE DESIGN AND CONTROL CONSIDERATIONS

Abstract

For over two years, ozone pilot plant studies have been conducted examining the efficacy of disinfecting makeup water entering the Dworshak National Fish Hatchery at Orofino, Idaho. The major pilot plant equipment consisted of a 1.12 kg/day Union Carbide Ozone Generator and contacting column. Plate counts for total bacteria were taken at various points in the pilot plant. Similar plate counts were taken from existing ultraviolet disinfection equipment. Also monitored were ozone residual levels entering and within the recycle system, ammonia, nitrate, nitrite, total organic nitrogen, suspended solids, turbidity and biochemical oxygen demand. Analysis of the plate counts shows ozone consistently provides more effective disinfection of the makeup water than the existing ultraviolet system. Nitrite levels after ozonation show a significant decrease, while nitrate levels increased. Ozone disinfection of recycle water was also satisfactorily demonstrated. Additionally, batch studies indicate ozone effectively destroyed algae. The pilot work established Dworshak ozone requirements to disinfect both makeup and recycle water. Experimental ozone demand, residual ozone removal rates, and ozone decay rates make it possible to design equipment and controls that will protect the fish from unsafe ozone concentrations. An ozone disinfection system preliminary design for a typical recycle fish hatchery is presented.