Research On The Spectroscopy Measurement Method Of Water COD And Sensor Development

Due to excessive use of chemical fertilizers and pesticides, chemical byproducts and sewage discharge and other abuse, these organic pollutants have caused serious damage to the resources and environment of water. Chemical Oxygen Demand(COD) as the characterization parameters of organic matter, fast and accurate monitoring of water COD became the urgent needs of environmental protection, and has brought a greater challenge to monitoring and analysis technology of water's COD. Traditional chemical analysis techniques have many disadvantages, such as high cost of detection, measurement for a long time, no secondary pollution, etc. Environmental protection technology as a real-time method for rapid detection and analysis technology, has many advantages like high-efficiency analysis, in-situ detection, easy to carry, higher detection accuracy and so on, can overcome the bottleneck of chemical methods well and meet the development requirements of modern environmental testing.This topic researched the status of COD detection methods at home and abroad, and developed a portable water COD sensor based on the ultraviolet spectrum. When measuring the concentration of the organic pollutants in water, fiber-optic probes into the water to complete the collection of the organic matter absorption spectrum. The regression model has established between the absorbance and COD through training experiment, and implanted it into the spectral processing software sensor, further to calculate COD of the body. Research contents of this paper are:1. The study analyzed the situation of water testing technology currently, focused on the basic theory of spectrometry COD in water, included: detecting mechanism spectroscopy, the spectrum acquisition method, the algorithm of pretreatment spectrum and modeling, evaluation parameters,etc, which built a theoretical foundation for follow-up study.2. This study carried out specific experiments, verified the feasibility of detecting COD by spectroscopy method, compared the prediction effect of ultraviolet and near infrared method, and selected the absorption characteristics band of organic pollutants in water, won a detection model based on ultraviolet. Comparative analysis on the effects of various algorithms modeling. First, this project obtained Ultra Violet(UV) absorption spectroscopy and infrared spectroscopy from municipal wastewater respectively, by using different bands spectral modeling, compared with the modeling results and selected the feature bands with distinct spectral pretreatment methods combined with Partial Least Squares(PLS) and Multiple Linear Regression(MLR) modeling. The results revealed that the UV absorption spectrum after Savitzky Golay Moving Average(S-G) smoothing could better enhance the modeling results. Baseline correction and S-G smoothing method can improve the accuracy of prediction by near infrared spectroscopy model. Comparative analyzed the near infrared and ultraviolet spectral method using PLS, MLR model to predict the effect. PLS modeling based on UV absorption spectra had highest correlation coefficient(R2) with prediction set, R2 is 0.9921, Root Mean Square Error of Prediction(RMSEP) is 10.4386; R2 of MLR modeling prediction set is 0.9280, RMSEP is 19.0746. PLS modeling based on near infrared spectroscopy of prediction set has best R2 of 0.9877, RMSEP of 5.9760; The MLR modeling of prediction set of 0.9573, RMSEP is 11.2962.3. This study designed a portable water COD measuring sensor based on USB2000+ spectrometer. The sensor includes two parts, physical hardware and software for processing spectral. Hardware includes the chassis housing, Y type optical fiber, fiber probe, voltage converter module, lamp source, electronic control modules, power modules and touch screen and driven circuit. The software part includes model load module, spectra collection module, spectra save module, result display module and parameter setting module. Finally, the performance of the sensor has verified by experiments and analysis. Verification results showed that the sensor can be used to the water COD detection applications.