Research On COD Rapid Detection System For Ship Domestic Sewage

Ship domestic sewage has gradually become the main source of marine environmental pollution,which has attracted the close attention of more and more countries.At the same time,the International Maritime Organization has put forward clear requirements for the emission limits of ship domestic sewage pollutants,of which chemical oxygen demand(COD)is one of the test items of the emission standards.COD is a parameter that reflects the organic matter content in sewage,and the higher the organic matter content,the more severe the pollution level.The traditional chemical detection method requires the addition of multiple chemical reagents,which can easily cause secondary pollution to the environment.The operation process is complex,and the waiting time is long,which cannot meet the rapid detection needs of COD in ship domestic sewage.With the application of optical measurement technology in the field of water quality detection,the shortcomings of traditional methods such as complex operation and long measurement cycle have been overcome.This article designs a rapid COD detection system for ship domestic sewage based on ultraviolet absorption spectroscopy,which has broad application prospects.Firstly,based on the theory of molecular absorption spectroscopy and Lambert Beer’s law,the principle of ultraviolet absorption spectroscopy for detecting COD was explored.Three measurement techniques of ultraviolet absorption spectroscopy were explored.The full spectrum detection method can comprehensively reflect the pollution of organic matter in wastewater and improve the accuracy of COD measurement by scanning the ultraviolet absorption spectrum of water samples.On this basis,the optical structure of the COD detection system was designed,and performance analysis and selection were carried out around optical devices.The focus of the research was on the spectroscopic system.By comparing the structural characteristics of Czerny Turner grating and flat field concave grating,a spectroscopic system based on flat field holographic concave grating was designed.The design parameters of the grating were optimized and 3D simulation analysis was carried out to eliminate the influence of aberration on the imaging spectral line and ensure the quality of ultraviolet absorption spectrum analysis.Then,a design scheme for a spectral acquisition system based on Field Programmable Gate Array(FPGA)was proposed.Select hardware equipment and design hardware circuits for each module based on the functions to be implemented by the system.The linear array CCD(TCD1304AP)is driven by FPGA to complete the photoelectric conversion function.The analog signal is converted into a digital signal through A/D conversion.Finally,the communication module transmits the collected digital signal to the upper computer for processing,completing basic functions such as UV absorption spectrum data visualization display,spectral image storage,and spectral data storage.Finally,considering issues such as high computational complexity and long processing time when modeling full spectrum data.Based on the UV absorption spectra of COD standard solutions with different concentrations,a particle swarm optimization algorithm is used to select the characteristic wavelength.Based on the absorbance values at the characteristic wavelength,a partial least squares method is used to establish a prediction model for absorbance and COD concentration.The model has r=0.9998 and RMSE=0.1311.Based on the established COD concentration prediction model,the performance indicators of the system were tested,and the measurement range of the equipment was determined to be 4.9～500mg/L,with an error range of within 5%.