THE IMPACT OF UV-ABSORBING WASTEWATER FROM A PRINTED CIRCUIT BOARD MANUFACTURING FACILITY ON THE PERFORMANCE OF A MUNICIPAL UV DISINFECTION SYSTEM

A city in the Northwest recently installed ultraviolet (UV) disinfection equipment as part of the expansion of its municipal wastewater treatment plant (WWTP) from a design capacity of 2 MGD to 4 MGD. In its first few months of operation, the UV disinfection system experienced problems disinfecting WWTP effluent to the required standards. It is believed that constituents in an industrial discharge from a printed circuit board manufacturer (PCBM) were contributing to the difficulties in achieving adequate disinfection. This paper discusses the methodology used and the steps taken to research and address the problems with the performance of this UV disinfection system. The research included measuring transmittance and absorbance and acquiring ultraviolet spectra for industrial wastestreams and WWTP influents and effluents. In order to obtain some perspective on the issues facing the WWTP and PCBM, three other PCBMs and two of the WWTPs to which they discharge were visited. Factors thought to affect UV disinfection were compared among the four PCBMs and the three WWTPs. During the investigation, premature scaling of quartz UV lamp sleeves was also found to be a cause of disinfection problems. This premature scaling was examined through effluent analysis, in-situ scale analysis, and comparison of factors affecting sleeve scaling rates to similar parameters at other WWTPs.