Device for real-time monitoring of oil-in-water and suspended solids based on thermal lens spectrometry and light scattering

A novel system suitable for simultaneous monitoring of both oil-in-water and suspended solids based on thermal lens spectroscopy and forward light scattering is presented. The technique measures the concentration of dissolved hydrocarbons and simultaneously detects single oil droplets and suspended particles separately. The device was tested with injection water samples from an on-field water treatment plant, and hydrocarbon concentrations were measured with a precision better than 5% in the range of up to 100 ppm, reaching resolutions as low as 0.03 ppm. Particle detection was tested with model samples of dyed and undyed polystyrene spheres acting as absorption and scattering centers, which simulated oil droplets and suspended solids, respectively. We show that particles of different sizes are distinguished by the magnitude of the perturbations introduced in the signals, and their concentrations can be measured independently of dissolved components.