AWWA WQTC60557

The spectral ultraviolet (UV) absorbance of the chemical additives used during UV validation to adjust the UVT is an important consideration when validating medium pressure UV systems. The spectral UV absorbance should mimic that of the water that will be treated by the UV system at the water treatment plant. Current UV absorbers used are coffee and lignin sulphonic acid. For a given UV transmittance at 254 nm, the UV absorbance at higher wavelengths tends to be greater than that of water treatment plant waters. This impacts both dose delivery and monitoring by the UV reactor. For a given flow, UVT 254, and lamp output, dose delivery during reactor validation will be lower than at the WTP. For a given flow, UVT 254, and UV sensor reading, dose delivery indicated by the UV reactor's monitoring system during validation will be higher during validation than at the WTP if the UV sensor is located relatively close to the lamps and lower if the UV sensor is located relatively far from the lamps. With the latter case, the US Environmental Protection Agency UVDGM recommends application of a safety factor to account for the underestimation of dose by the monitoring system. All of these outcomes impact the capital and O&M costs of medium pressure systems. In this study, concentrates from reverse osmosis (RO), nanofiltration (NF), and ion exchange (IX), an agricultural growth-enhancement product, and lignin sulphonic acid were compared as UV absorbers for validating MP UV systems. Includes 5 references, tables, figures.