PRACTICAL METHODS FOR DESCRIBING UV REACTOR PERFORMANCE FROM VALIDATION DATA

Validating ultraviolet (UV) reactor performance and UV monitoring strategies through empirical bioassay testing is becoming a common requirement in waste water, water reuse and drinking water disinfection applications. Attesting to this trend is the recent release of UV disinfection validation protocols by NWRI/AWWARF and the USEPA. These protocols are progressive in that they allow for control based not only on intensity sensor set points, but also for control based on dose set points using dose calculation and monitoring strategies. In a dose set point control strategy, RED is quantified during bioassay validation over a range of operating variables (flow, UVT, power setting), providing increased system flexibility. The dose set point approach allows an operator to know the performance being achieved over a range of operating conditions. With this knowledge, the system can be operated to meet different targets (higher or lower RED values) if regulatory objectives change, and system operators can optimize electrical power consumption by changing lamp power levels to maintain required doses in the face of changing flow rates or water UVT (flow rate commonly undergoes a wide daily variation in many treatment plants). In essence, the dose set point approach is a multiple sensor set point approach, and an approach that accommodates multiple targets.The ability to accurately quantify performance as a function of operating variables is key to providing the flexibility offered by the dose set point approach. For testing efforts with variation in parameter values and multiple variables, we describe the application of a technique that accurately describes reactor performance using a multiple linear regression (MLR) approach. The resulting validated performance equation can be used to ensure that UV reactor design and system operation will meet water quality objectives that are not specifically measured by present bacteriological water quality standards.