Use of UV/VIS Spectrometer for Controlling a Tertiary Treatment Process

The use of online monitors for monitoring and control purposes has gained prominence in recent years. Watercare Services Limited operates the largest advanced wastewater treatment plant in New Zealand and has implemented the online instrument for controls purposes at Mangere Wastewater Treatment Plant (WWTP). An in-situ UV/VIS spectrometer was used to measure UV transmittance (UVT) in the UV inlet channel at Mangere WWTP. The measurement is use to control the UV plant dose system by determining a variable offset factor based on the UVT% measured. Addition of UVT% for dose calculation was derived due to the work undertaken by a comprehensive study undertaken by an expert Disinfection Review Group (DRG). The developed algorithm was first implemented to one of the twelve UV channels for testing and the results monitored prior to implementation on all UV channels. Variability in UVT% was monitored against another online UVT% instrument. Stringent maintenance and calibration of the spectrometer were introduced to ensure reliable measurements. The algorithm was rolled out to the other eleven channels once the performance was proven satisfactory by Watercare Services. This paper describes the process of developing and implementing the new dosage control to the UV plant.