With the rapid development of petrochemical and related industries, oil pollution incidents occur frequently. Aromatic hydrocarbons, benzene series, and polycyclic aromatic hydrocarbons are the main components of petroleum, which have effects of teratogenicity, carcinogenicity, and gene mutation. Once they enter the soil, they will accumulate in the soil for a long time and ultimately affect human health through the food chain. The traditional detection techniques of organic pollutants mainly include gas chromatography, gas chromatography-mass spectrometry, liquid chromatography, etc. Although these methods are standard methods with high sensitivity and excellent accuracy, they have the disadvantages of complex sample pretreatment and slow test speed and are not suitable for rapid on-site detection. At present, the existing optical detection techniques mainly detect the components of organic matter, and the measured components have large errors. In addition, the total amount of organic matter cannot be simply summed. Imaging technology provides an alternative way to realize the total detection of soil organic pollutants. In this paper, an ultraviolet-induced fluorescence imaging system is built, and the direct detection method of the total amount of aromatic hydrocarbons in standard soil is studied, which provides feasibility for the rapid determination of the total amount of aromatic hydrocarbons in soil.
The experimental system is built using a light emitting diode (LED) excitation light source, plano-convex lens, filter, CCD camera, sample holder, control circuit board, and personal computer. After the excitation light from the LED light source is collimated and converged by the lens group, it is irradiated on the surface of the soil sample with a certain size of the light spot, and the aromatic hydrocarbons in the soil are excited to generate fluorescence. After the CCD camera captures the fluorescent image signals, the signals are transmitted to the computer for analysis and processing. A standard soil (GBW07494) is selected to prepare the experimental samples of motor oil (15W-40). The original image captured by the camera is obtained by using the maximum inter-class variance method to obtain the image threshold and converted into a binary image, and the binary image is dot multiplied with original gray image to obtain the gray value data.
Aiming at the problem of rapid detection of the total amount of aromatic hydrocarbons in soil, methods such as the acquisition of aromatic hydrocarbon fluorescence signals in soil, feature extraction, and total concentration inversion based on fluorescence imaging technology are studied. On the basis of an LED ultraviolet excitation light source, area-scanning CCD camera, lens, and other devices, an experimental system is built. The parameters such as the optimal excitation energy and excitation angle of the light source are obtained, and the detection capability of the experimental system is analyzed. Through this experimental system, a series of fluorescence images of petroleum in standard soil with mass fraction ranging from 0 to 25000×10-6 are obtained. Based on the Gaussian noise reduction and maximum inter-class variance method, the image noise suppression and fluorescence signal extraction methods are studied, and an inversion model of the total amount of aromatic hydrocarbons in standard soil is established. Furthermore, the total amount of aromatic hydrocarbons in the sample to be tested is predicted by using the inversion model. The results show that the coefficient of determination (R2) of the total inversion model reaches 0.9889 (Fig. 10), and the detection limit is 82.18. For 20 samples, the errors are basically within 12%.
Fluorescence imaging technology breaks through the shortcomings of traditional organic detection methods such as complex sample preprocessing and slow testing speed, and has the characteristics of fast and convenient detection. In this paper, a fluorescence imaging detection experimental system is built, and a rapid and direct measurement method of the total amount of aromatic hydrocarbons in soil is studied. Its precision and accuracy have met the needs of rapid field detection. In the process of system construction, the influence of the excitation energy of the light source and the receiving parameters of the CCD camera on the fluorescence imaging results is analyzed, and the optimal parameters are selected, with the experimental system optimized. Based on the experimental system, a series of aromatic hydrocarbon fluorescence images for petroleum in standard soil are obtained. The image signal processing method is studied, and a calibration model is established. The coefficient of determination between the fluorescence image signal and the mass concentration is 0.9889, and the detection limit is 82.18. This study provides a method basis for the application of fluorescence imaging in situ monitoring technology to the rapid monitoring of organic pollution of aromatic hydrocarbons in soil. In addition, the effects of physical and chemical parameters such as soil moisture, temperature, pH, and organic matter on the fluorescence image signals of aromatic hydrocarbons in soil are being studied in depth.
