Novel method of turbidity compensation for chemical oxygen demand measurements by using UV-vis spectrometry

In recent years, ultraviolet-visible spectroscopy has been widely used for chemical oxygen demand (COD) measurements of water. However, turbidity in water can cause measurement deviations, so it is very important to compensate for the impact of turbidity. In this study, a novel method of turbidity compensation is proposed. The absorption spectra of standard solutions and their mixture were sampled in the wavelength range from 220 to 750 nm. We used a normalization technique to estimate the turbidity and dynamically simulate the absorption spectra of the turbidity. In addition, hydrogen bonds made the absorption peak blue shift in the mixture solutions. We established a numerical fitting curve to describe the relation between the blue shift and turbidity, and then we corrected the peak position. Furthermore, turbidity particles decreased the absorption peak of organic molecules. We introduced an impact index kN(λ) to describe the peak height reduction, and experiments demonstrated that kN is negatively associated with the absorbance of the standard COD solution. After the process of turbidity compensation, the root mean square errors (RMSEs) of the predictions were very small, which highlights the potential of this method for improving the accuracy of COD measurements based on ultraviolet-visible spectrum.