UV DISINFECTION OPERATIONS AND MAINTENANCE OPTIMIZATION IN ALEXANDRIA

Cost effective operation and maintenance of an ultraviolet (UV) disinfection system requires careful evaluation of factors affecting life cycle costs including decisions for frequency of lamp cleaning and scheduling of equipment component replacements. This article discusses the fullscale operating and maintenance experience and control system troubleshooting of the UV disinfection system at the Alexandria Advanced Wastewater Treatment Plant (AWTP) through six years of operations that span a plant upgrade, several high-flow events and control system issues. Our experience shows that during a high flow event it is preferred to operate the UV system in a Local SCADA mode to prevent the package control system from removing channels from service. This lesson was learned during a high flow event when all channels were taken out of service by the control system resulting in flooding of the UV building and permit violation. Approximately 33% of capital cost was saved by putting out for bid the replacement of UV lamps and associated equipment. The Alexandria AWTP currently replaces UV lamps every three years. The lamp replacement costs can be better integrated into the budget by replacing one third of the bulbs annually. To achieve this goal the UV control system must be modified from the original manufacturer's strategy which equalizes the run-time of all lamps and replace them simultaneously.