Impact of Upstream Process on Ozone Demand and Disinfection Effectiveness

Ozone's use in wastewater treatment has experienced new interest with additional disinfection requirements and the potential to remove compounds of emerging concern. One of the most critical aspects of its application is determining the ozone demand, which is important in sizing the system. The most significant factors that influence the ozone demand of wastewater effluent are chemical oxygen demand (soluble COD), inorganic oxidant demand (e.g. nitrite), influent bacteria density, and target effluent bacteria density. As regulations have been tightened and nutrient limits have been lowered, ozone demand has decreased and dosages as low as 5 mg/L can be used to meet a high-level of disinfection. The lower dosages, coupled with the advances in ozone generating and dissolution technology, have made ozone as a disinfectant for wastewater cost-competitive with UV. Results of an economic analysis of disinfection systems for a large midwestern WWTP indicated that the cost of ozone was only 17 percent higher than the cost of UV on a present worth basis.