Study On Fiber Optic Spectroscopy Detecting Method For Petroleum Pollutants In Water

Pollution of the water environment is worsening with the rapid growth of the nationaleconomy. Petroleum pollutant is one of the major sources of pollution in water. Accurate,rapid, and convenient detection method of petroleum pollutants in water has veryimportant theoretical value and practical significance in grasping the changes in waterquality, effectively controling water pollution accidents and the protection of waterresources.This paper summarizes relevant literature of the various testing methods forpetroleum pollutants in water and proposes a new method to detect petroleum pollutants inwater based on fiber-optic evanescent wave absorption spectroscopy in combination withNIR analysis technology. The fiber-optic NIR-evanescent wave absorption spectroscopydetection unit structure is proposed. Theoretical and experimental researches are done forthe detection unit; suitable NIR chemometrics algorithms for qualitative identification ofsingle petroleum pollutants and quantitative analysis of multi-component complexpetroleum contaminants are discussed. The major contents of the paper are as follows:First, the paper introduces the basic principle of the NIR spectroscopy and commonlyused chemical metrology algorithm in detail; The analysis of three typical oil pollutantsNIR spectra of gasoline, diesel and kerosene are conducted to demonstrate the feasibilityof using fiber-optic NIR spectroscopy to detect petroleum pollutants in water.Second, the paper proposes the optic fiber NIR-evanescent wave absorption detectionunit structure with hydrophobic oleophilic film, numerically calculating the relationshipbetween the evanescent wave energy with the main parameters including the radius of thefiber core, the remaining thickness of the cladding layer, hydrophobic film thickness, filmrefractive index and the length of the detection unit, providing theoretical basis for theoptimal design of the detection unit.Third, after discussing the characteristic of the hydrophobic oleophilic materials, theidea of coating the polystyrene polymer solution on the surface of the corrosion singlemode fiber is studied. The hydrophobic oleophilic coating not only avoids the watermolecules’ strong absorption interference in the near-infrared region, but also plays the role of adsorption of oils in water; the corrosion and coating process of detection unit isdescribed in detail and the gasoline, diesel and kerosene oil-water mixed solution is made,and the detection unit performance test system is set up based on the fourier transformnear-infrared spectrometer; then the paper compares the near-infrared spectra of theoil-water mixed solution gained by the detection unit with the NIR spectra of pure oil,pure water and oil-water mixed solution gained by the probe measurements of thespectrometer.Fourth, traditional NIR methods do not take full account of the absorbance datanon-negative characteristics, resulting in the analysis lack of reasonable explanation. Forthis problem, the qualitative discriminate method of single species petroleumcontaminants based on non-negative matrix factorization feature extraction combined withsupport vector machine classification algorithm is studied. Non-negative matrixfactorization algorithm and support vector machine classifier parameters on classificationaccuracy are discussed in depth to optimize NIR qualitative classification model.Last, for the problem of quantitative analysis of the complex multi-componentmixing petroleum pollutants, the quantitative analysis model of gasoline, diesel andkerosene, a three-component mixed pollutant solution is established based on partial leastsquares regression algorithm and partial least squares support vector machine regressionalgorithm respectively. The optimal parameters of quantitative model are given based onparticle swarm optimization. The paper uses the three-component model to predict theconcentration of the validation set, and compares the predicted results with two regressionmethods.This paper conducted in-depth theoretical studies and experimental work of usingfiber-optic NIR evanescent wave absorption spectroscopy to detect petroleum pollutants inwater. The research can provide a valuable reference for the use of fiber evanescent waveabsorption spectroscopy detection and NIR spectroscopy technology in the field ofenvironmental monitoring applications.