UV Disinfection and Quartz Sleeve Fouling While Using Ferric Chloride for Nutrient Removal

A UV disinfection pilot study was conducted for ten weeks in 2013 at a 67-mgd wastewater treatment plant (WWTP) in Virginia. The pilot test was undertaken to assess the effectiveness of UV disinfection and of the pilot unit’s automated sleeve wiping system at this plant. The potential for rapid fouling of the quartz sleeves was a concern, because the WWTP adds ferric chloride upstream of tertiary clarification and filtration to enhance phosphorus removal, and some UV facilities report more rapid UV sleeve fouling when ferric chloride is used upstream.

Test conditions included planned changes in UV dose, pilot influent source, ferric chloride dose, and sleeve wiping frequency to represent both normal operating conditions and atypical conditions that could affect UV disinfection, such as high ferric chloride dose or filter bypasses. Data collected included pilot influent and effluent E. coli, and pilot UV transmittance, UV dose, UV intensity, total suspended solids, and total and soluble iron. Selected lamp sleeves were removed from the pilot unit periodically and were tested for changes in relative sleeve transmittance to estimate the degree of sleeve fouling and the effectiveness of the wipers. At the end of the test period on filter effluent, residue was scraped from selected lamp sleeves and was analyzed for chemical composition.

Based on the data collected during the UV pilot test period, UV disinfection was shown to be a viable option for effluent disinfection at the WWTP, even with the upstream addition of ferric chloride. The UV pilot test demonstrated UV lamp sleeve fouling following ferric chloride addition and filtration was well controlled with the UV system’s standard automatic wiper system. The WWTP is including UV technology as one of the options during a comprehensive evaluation of disinfection technologies.