Non-contact, scattering-independent water absorption measurement using a falling stream and integrating sphere

Abstract

We have applied an integrating sphere to the measurement of optical absorption in process waters containing high levels of scattering particles. The sphere greatly reduces the effects of scattering, which appear in a conventional transmission measurement as an apparent absorption. Additionally, the water sample flows through the sphere in the form of an unconstrained falling stream, allowing non-contact measurement and removing the fouling suffered by wetted cuvette windows. Using a 430 nm LED, silicon detector and 100 mm sphere, an absorbance resolution of approximately 0.01 has been demonstrated. Errors caused in a spectrometer measurement by levels of scattering contributing an apparent unit absorbance to a 0.2 absorbance dye solution are reduced by a factor of 30 in the sphere configuration. Measurements on streams in drinking water processes are also shown. This combination of two well known techniques offers the potential for highly reliable industrial process measurements, which would otherwise require pre-treatment using sub-micron filtration.