Research On Water Quality Detector Based On Ultraviolet-Visible Spectroscopy Technology

Water is a precious natural resource and one of the essential resources for human survival.However,increasingly serious water pollution not only makes it impossible to meet the increasing demand for water,but also seriously threatens the health of residents.In order to solve the problem of water pollution,water quality parameters need to be tested.Therefore,it is necessary to develop a more convenient and fast water quality detector.This work was supported by Jilin Province Science and Technology Development Plan Project(20190303008SF),according to the ultraviolet-visible absorption spectroscopy,designing a water quality detection system.The detection system has the advantages of fast and accurate,no need to add chemical reagents,and real-time display of detection results.It can detect COD concentration and turbidity value,and can automatically compensate the impact of turbidity on COD detection,which is suitable for detecting COD in surface water.The research of this paper is divided into the following aspects:1.Based on ultraviolet-visible absorption spectroscopy,the spectral data processing algorithm for detecting COD has been studied.A novel hybrid strategy called FDPE_PLS for detecting COD was proposed.We first proposed to combine the first derivative method with the permutation entropy method(FDPE)to determine the characteristic wavelengths.Then we used partial least square(PLS)to establish a COD prediction model.The turbidity value was predicted by the slope of the line of absorbance at 400 nm and 600 nm.In the first derivative spectra,establishing a turbidity compensation model,which can compensate the interference caused by turbidity in COD detection.Finally,actual water samples were used to verify the accuracy of the proposed detection method.2.The structure of the water quality detection system was designed,which mainly includes the optical structure and the circuit structure.The optical structure mainly includes light source,spectroscopic system,sample cell and photodetector.The optical signal was converted into a weak electrical signal by the photodetector.In the circuit structure,the weak electrical signal was first amplified by an amplifier circuit,and then was converted into a digital signal by the AD conversion circuit and sent to the STM32 system control board.The measured concentration value is obtained by calculating the data,and the result is displayed on the LCD display.3.We realized the software design part of the water quality detection system.This part includes controlling the stepping motor to rotate at a uniform speed to realize the uniform scanning of the wavelength,the realization of data collection and conversion,establishing a model to calculate the concentration value,and controlling the display screen to display the calculated concentration values.4.We used the detection system to conduct water quality detection experiments.Based on the processing method of the spectra data,the standard solutions were used to experiment.Combined with the wavelength-voltage diagram obtained by scanning,establishing the prediction model for the detection system.Finally,the actual water samples were tested to verify the performance of the detection system in terms of error,stability and repeatability of the display.