ALTERNATIVES FOR A DISINFECTION SYSTEM INCLUDING UV DISINFECTION ON EFLUENT CONTAINING IRON

摘要

The H.L. Mooney Advanced Wastewater Treatment Plant prepared a plan for improvements to meet future treatment requirements and capacity, which included evaluation of the existing chlorine disinfection system. Due to new Risk Management requirements the liquid chlorination/ dechlorination system was temporarily converted to a sodium hypochlorite and sodium bisulfite disinfection system. rnTo identify the final system for disinfection, various disinfection systems were researched. The evaluations considered performance and related costs. The disinfection alternatives evaluated included a sodium hypochlorite/sodium bisulfite system, an ultraviolet (UV) system and an ozone system. Based on lower construction and annual operating costs, a low pressure – high intensity UV system was recommended. rnThe plant uses ferric chloride for phosphorous removal and the effectiveness of the UV system in the presence of iron was a concern. High iron concentrations have been reported to increase the rate of lamp sleeve fouling and shield bacteria from UV light. Therefore, a side-by-side on-site pilot study was conducted employing low pressure – high intensity UV systems provided by two manufacturers. The pilot study was conducted for three months and tested flow from filtered effluent, secondary effluent, and a blend of primary effluent with the secondary effluent. The UV pilot systems were compared with regard to dose response, fouling rate, cleaning and maintenance requirements. rnThe studies addressed performance, costs and arrangements to retrofit existing facilities. Results showed UV capabilities to meet Virginia fecal coliform, E. Coli and Enterococci bacteria standards and provided guidance to the plant for converting from conventional chlorine disinfection to UV disinfection.