Errors in Ultraviolet Fluence Calculations Due to Particles in Wastewater Samples

Abstract

Abstract Conventional spectrophotometers that do not include an integrating sphere assembly do not account for scattered ultraviolet (UV) light in a water sample containing particles and can therefore overpredict absorbance. Water samples from the secondary effluent of a municipal wastewater treatment plant were monitored over the course of 1 year to determine whether the error introduced in UV absorbance measurements when neglecting scatter was significant. The error was interpreted in terms of UV fluence that would be calculated for varying path lengths of solution. The error ranged from 10% to over 90% and increased independently with total suspended solids and path length. Combination of increasing path length and total suspended solids, together, amplified the error. This study demonstrates that, in some situations, integrating sphere absorbance measurements may be warranted to minimize significant errors in estimated UV fluences; however, in other situations (e.g., short path lengths), conventional ...