A Practical Case Study for Wastewater UV Disinfection:Evaluation of a Quartz Sleeve Mechanical Wiping SystemPerformance Resultant Fouling Factor

摘要

It is well documented that Quartz sleeve fouling can adversely impact the efficacy of a UV disinfection system by absorbing a large fraction of the emitted UV-C output. Fouling is an issue that is more predominant with the UV disinfection of wastewater although drinking water applications can also experience significant fouling depending on the mineral content of the water source and the type of UV lamp used. Accordingly, UV reactors are typically equipped with a cleaning system to provide operators with a means of controlling Quartz sleeve fouling and thereby preserving optimum disinfection performance.In 2008, an extensive test campaign was undertaken to evaluate and optimize the performance of an automated mechanical wiping system for a wastewater UV reactor that uses low-pressure high-output amalgam lamps arranged in a vertical array. Initially, several wiper technologies were evaluated in terms of drag force generated and consistency of drag over the length of the Quartz sleeves. The optimal wiper design was selected and utilized to conduct an initial fouling test using a commercial UV reactor submerged in "synthetic wastewater". After one month of continuous operation at two wipes per day, the transmittance of the sleeves without wipers dropped by 40% while that of the wiped sleeves remained at 95% of the baseline obtained with new / clean sleeves. The result from this initial study yields a fouling factor of 0.92 representing a clear improvement from the NWI default fouling factor of 0.80 that is currently used to size UV systems.A third party fouling study has now been initiated at a full-scale plant in order to validate the cleaning performance of this new wiper technology in accordance with the 2003 UV Guidelinesin.