Successful wastewater disinfection was achieved under stringent bacteriological standards with a 480 g/hr generator pilot facility. Optimization of the facility required an applied dose of 30 mg/1 (13 to 19 W–hr/g ozone produced) to obtain a 2.2 total coliform per 100 ml disinfection level of nitrified effluent. An applied dose of 20 mg/1 (18 W–hr/g) is optimal for a 70 total coliform per 100 ml disinfection level of secondary effluent. The approach to ozonation system optimization, including generator mapping and contactor evaluation, is presented.