Research On On-line Detection Method Of Water Quality Chromaticity Based On Spectroscopy

Water environment monitoring and evaluation is the basic means to control water pollution and prevent water environment degradation.The waste water discharged by industrial manufacturers such as textile,printing and dyeing,leather making,paper making,pharmaceuticals,food,dyes,pigments,etc.,as well as our domestic sewage,will cause the appearance of the water body,such as the color and transparency of the water,to change in different slender.Therefore,strengthening the monitoring and analysis of water quality and chromaticity is a very necessary work and has important significance for protecting the water environment.According to the current national standards,colorimetric detection methods include visual colorimetric method and dilution multiple method.Both of these methods are greatly affected by subjective factors,and the steps are cumbersome,so it is impossible to achieve high accuracy and high stability of water color.In view of the limitations of current colorimetric detection methods,the paper was jointly funded by the National Natural Science Foundation Youth Fund Project（61805029）and the Chongqing Municipal Social Undertaking and the People’s Livelihood Security Technology Innovation Project（cstc2017shmsA1497）to carry out research on the online detection method of water quality and chromaticity based on spectrometry.In order to obtain higher accuracy and more stable water quality chromaticity detection method,this paper first applies the transmission method to the chromaticity detection,respectively using the absorbance method,tristimulus value and color difference method to characterize the water quality chromaticity,based on this plastic optical fiber evanescent wave sensor replaces the transmission method.At the same time,in order to reduce the influence of physical parameters on the chromaticity measurement results,an optical fiber Bragg grating sensor was developed for temperature and humidity detection.The main research work and results of this article are as follows:（1）Direct spectroscopy is used to detect the chromaticity of water quality.Among the three methods,absorbance method,tristimulus value and color difference method,the 1976（LUV）color difference method is the most accurate representation of chromaticity.First,refer to the national standard to configure platinum-cobalt standard solutions of different concentrations,build a water quality chromatic spectroscopy detection system,directly measure the absorbance curve of the solution,and use a single wavelength to directly express chromaticity.Under the premise of meeting national standards,430 nm can be used as a color Reference wavelength expressed in degrees;when tristimulus values are used to express chromaticity,the results show that the improved Z-value color measurement scheme is more stable;on the basis of tristimulus values,the results of chromaticity represented by three uniform color spaces are compared and analyzed.The results show that the three methods are used for chromaticity analysis,and the relationship between the stability and accuracy of the numerical results is: color difference method> tristimulus value method> absorbance method.Among the three uniform color spaces,the goodness of fit of 1976（LUV）reached 0.98878,and the relative deviation was 3.3%.（2）In order to reduce the impact of environmental changes on the detection results of water quality and chromaticity,an optical fiber Bragg grating sensor for accurately measuring temperature and humidity was prepared for collecting water quality and chromaticity monitoring field environmental parameter changes.A sensor for accurate measurement of temperature and humidity in the environment was constructed using polyimide and FBG.The response characteristics of FBG₁ and FBG₂ to temperature and humidity,and the response characteristics of FBG under variable temperature and humidity environment were experimentally studied.The results show that: FBG₂ can respond to temperature and temperature simultaneously when FBG₂ diameter and grating length are 7.8 μm and 12 mm,and polyimide film thickness is 80 μm in 20 90% RH and 30 70 ℃ variable temperature and humidity test environment.Humidity change information,and the response sensitivities to temperature and humidity are 16.8pm/℃ and 17.1pm/（%RH）respectively;FBG₁ only responds to temperature,and its response sensitivity is 9.9pm/℃;the sensor can accurately measure temperature and humidity The temperature and humidity information in the environment,the relative errors of humidity and temperature measurement are lower than 3.8% and 2.6%,respectively.（3）In order to further improve the accuracy and stability of water quality chromaticity detection results,an online water quality chromaticity monitoring sensor based on evanescent wave of optical fiber is proposed.Through the grinding method,a plastic optical fiber evanescent wave sensor is prepared,and its performance parameters are characterized by methylene blue.The minimum detection limit of the sensor is on the order of 10-7 mol/L.Experimental research results show that the sensor can effectively overcome the influence of subjective factors when used in water quality chromaticity measurement.Combined with a spectrometer,it can realize online in-situ measurement,which can improve the detection accuracy and stability of water quality chromaticity.Compared with the transmission method,the sensitivity is increased by 2.65 times The minimum detection limit is 0.065372/C,the average relative error is 1.6%.