Seminole County Markham Regional Water Treatment Plant Ozone Regulatory Compliance Considerations – Treatment Challenges and Solutions

This paper presents a case study of Ozone (O3) to oxidize hydrogen sulfide (H2S) from supply wells of Seminole County Markham Regional Water Treatment Plant (MRWTP). H2S, is now regulated by FDEP, and can lead to taste and odor complaints in the distribution system. Ozone oxidation was selected by the County as the preferred treatment process to oxidize H2S from the groundwater supply wells which will reduce the amount of applied chlorine in an effort to reduce Trihalomethanes (THM) formation.On-site pilot-scale ozone testing was performed to confirm design specifications, and to demonstrate whether the water quality compliance goals to reduce sulfide and control disinfection by-products (DBPs) can be achieved. The followings were the results of the ozone pilot-scale testing:Verified the bench-scale testing results (AECOM, 2008) and found that ozone dose is dependent on sulfide concentration with an Ozone to hydrogen sulfide demand ratio (O3:H2S) 3.9:1 to 4.4:1.Low O3 residuals (High O3 residuals (>1.0 mg/L) dissipated to less than 0.1 mg/L in 15 to 20 minutes.Formation of bromate was instantaneous and increased with increasing bromide and ozone residuals.THM formation was dependent upon source water bromide concentration.Oxidation reduction potential (ORP) was identified as being successful in being able to control ozone residual.