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Ultraviolet visible spectroscopy can realize the detection of chemical oxygen demand (COD), especially for low concentration levels due to its high sensitivity, but the issue of insufficient real water sample data has always been a challenge owing to the low probability of occurrence of actual water pollution events. However, in existing methods, generated absorption spectra do not conform to actual situations as the former neglect the actual spectral characteristics. On the other hand, the diversity and complexity are restricted because the information in one-dimensional data is not enough for direct spectral generation. This study proposed a spectral sample generation method based on the variational modal decomposition and generative adversarial network (VMD–GAN). First, the VMD algorithm was utilized to separate principal components and residuals of absorption spectra. Among them, the GAN was used to generate new principal components to ensure that the major spectral characteristics of actual water samples are not lost. The corresponding residuals were then obtained by adjusting the parameters of a three-order Gaussian fitting function, which is more beneficial than the direct use of GAN in the aspect of diversity and complexity. Based on the spectral reconstruction with new principal components and residuals, various absorption spectra were generated more coincident with actual situations. Finally, the effectiveness of this method was evaluated by establishing regression models and predicting COD for actual water samples. In all, the insufficient water sample data can be expanded for a better performance in modeling and analysis of water pollution using the proposed method. [ABSTRACT FROM AUTHOR]

In recent years, absorption spectroscopy is being widely used for water quality monitoring. However, much of the spectral analysis results do not provide any physical meaning and the use of traditional parameters for monitoring water quality, such as chemical oxygen demand (COD), is not a radical research method because of the large diversity of chemical components in water. Here in, we studied the absorption spectra of eight typical contaminants and proposed four integral parameters in different spectral ranges, which were relative to different functional groups. The proposed surrogate parameters can be used to rapidly analyze and predict the categories of contaminants based on their changes without using any modeling. We used a dynamic partitioning algorithm based on the fourth-order derivative spectrum to adapt the movement of absorption bands. The impact of turbidity was eliminated by deducting the turbidity component from surrogate parameters based on the proportion of four parameters in formazine turbid solution. Using this method, we conducted long-term monitoring of the wastewater released by a dyeing and printing plant. The rapid analysis and prediction potential of different categories of water contaminants was demonstrated. The prediction results can provide evidence for more targeted and detailed analysis and water quality monitoring. [ABSTRACT FROM AUTHOR]

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 k N ( λ ) to describe the peak height reduction, and experiments demonstrated that k N 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. [ABSTRACT FROM AUTHOR]

In chemical oxygen demand (COD) measurements based on ultraviolet–visible spectroscopy, turbidity interference represents a difficult technical problem. Common methods need the spectrum of real turbidity particles as the baseline, but it is inconvenient and vain to obtain because it changes with perturbation. Due to lack of theoretical guidance, the direct derivative method with no need of baseline was rarely used. Here in, we studied the absorption spectra of turbidity particles in series of samples and proposed an order determination method in the' direct derivative. In turbidity interference handling, the absorbance derivative of turbidity at each wavelength fell to zero by determining the appropriate derivative order. Two parameters were presented for order determination, which represented the overall size of particles and its scattering type based on the spectral shape and profile. Experiments showed that the formazine solution, as an extreme situation, had the largest parameters, so the derivative order was determined depending on it to ensure effective turbidity correctionin various real water samples. Through comparing the correction effects and COD prediction results of first-to-fourth order derivative spectra, the proposed method was verified to provide theoretical basis of direct derivative method and reduce blindness in the order determination. Image 1 • An order determination method in direct derivative for turbidity correction is proposed. • First, the superiority and feasibility of direct derivative method is analyzed. • Two parameters were presented to evaluate the overall size of turbidity particles. • Turbidity spectra of formazine and real water samples were obtained and analyzed. • Fourth-order derivative was selected to correct turbidity effect for various water samples. [ABSTRACT FROM AUTHOR]