When engineers evaluate an ozone system, maximum ozone production usually receives the most attention. The first question is often simple: how many grams per hour or kilograms per hour can the generator produce? Maximum capacity is important, but most water and wastewater plants do not operate at one fixed condition. Flow changes throughout the day. Source-water quality changes seasonally. Ozone demand rises and falls. Industrial production schedules change. Treatment objectives can also change with operating conditions. That means an ozone system must do more than meet the peak design point. [...]