Water Quality COD Detection And Sensor Equipment Development Based On Absorption Spectroscopy

Water is a necessary condition for the existence of life and economic development.With the progress of society,the problem of water pollution has become increasingly prominent,which seriously threatens the sustainable development of society and the survival of human beings.In water quality monitoring,Chemical Oxygen Demand is an important environmental monitoring index to evaluate the pollution of water by organic matters.It is also an important parameter to study the water quality of rivers and industrial wastewater and evaluate the treatment effect of sewage treatment plants.Traditional chemical method for COD detection can not meet the needs of modern real-time online measurement.Absorption spectrum technology used to detect COD has the advantages of fast detection speed,no secondary pollution and in-situ measurement.It can realize in-situ detection of water such as oceans,lakes,rivers and reservoirs,and provide real-time and effective detection data for national environmental protection departments.In this thesis,the Partial Least Square algorithm combined with Particle Swarm Optimization algorithm is proposed to quickly select characteristic wavelengths and establish prediction model.A water quality monitor equipment was developed,which can make COD online measurement come ture.The equipment has the functions of acquisition and display of absorption spectrum data,establishment of COD calibration model and display of COD measurement results.The main contents in this thesis are as follows:(1)Aiming at the problems of overlapping spectral information and low prediction accuracy in all-optical spectral data modeling.The PSO-PLS hybrid algorithm was proposed to select the characteristic wavelengths for modeling,the subjects of the experiment is COD standard solution,in this experiment,the PLS,i PLS,SVR and PSO-PLS algorithm prediction model of the standard solution was established,and the modeling effects of the four algorithms was compared and analyzed.The results shows that the model based on PSO-PLS is the best,the correlation coefficient r=0.99998,RMSE=0.1551.It shows that PSO-PLS algorithm can effectively filter characteristic wavelengths,simplify the number of characteristic wavelengths used for modeling,and improve the accuracy of prediction model.(2)The influence of water temperature and turbidity on COD measurement was studied.Firstly,the influence of temperature and turbidity on COD detection of water quality was introduced from the perspective of analytical chemistry;secondly,the Chemical Oxygen Demand standard solution and turbidity standard solution are used as experimental water samples to explore the relevant characteristics of absorption spectrum data when temperature and turbidity changed;finally,the corresponding compensation function was established at the characteristic wavelength selected by PSO-PLS algorithm.(3)A water COD sensor based on absorption spectrum technology was developed.With the micro optical fiber spectrometer as the core measurement unit and the optical fiber probe with variable optical path,a complete set of COD measurement system is designed.At the same time,based on the Lab VIEW programming environment,the software interface of the system is designed to realize the acquisition and display of absorption spectrum,the implantation of chemometrics algorithm,and the real-time measurement of COD parameters.Finally,according to the relevant national standards,the performance of the developed equipment is tested.The test results show that the COD detection accuracy of the equipment is less than 5%,and the detection range is 4.9?500 mg/L,which meets the relevant standards and specifications of China.