Online Monitoring of Oils in Wastewater Using Combined Ultraviolet Fluorescence and Light Scattering with an Artificial Neural Network

摘要

Ultraviolet (UV) fluorescence and light scattering are two analytical methods commonly used in instrumentation for online measurement of oils in water. UV fluorescence-based instruments detect both dissolved and emulsified aromatic constituents of oils. Light-scattering-based sensors measure optical scattering induced by emulsified oil droplets. A major technical challenge for each of these methods is to maintain quantitative accuracy in the presence of chemical and physical interferences, including fluorescent organic compounds (e. g., detergents and natural organic matter), suspended solid particles, dissolved salts, etc. To address this issue, we have been developing a new monitoring system that simultaneously combines both UV fluorescence and light scattering spectroscopy. Four major types of oils (lube oil 2190 and 9250, diesel fuel marine, and WS), each of which had a dozen subtypes of oil samples, were examined to obtain the intensity of both fluorescence and scattering as a function of oil, detergent (Mil-D and Tide), and seawater concentrations. Both fluorescence and light scattering intensities varied significantly with oil types and subtypes. Both Mil-D and Tide greatly influenced the fluorescence and scattering of oil samples. The tremendous variations in fluorescence and scattering intensity with oil types and subtypes, detergents, and seawater make it difficult to calibrate the analytical instrument using traditional methods; hence we have implemented a multi variate, nonlinear calibration of instrumental response through an artificial neural network. We have demonstrated that the simultaneous, combined use of fluorescence and scattering data significantly improves quantitative prediction accuracy. The newly developed technique permits the online monitoring of oil spills, the accurate determination of oil concentrations in wastewater discharged from ships and the oil refinery industry, and oil detection in oil drilling fields.