Detection Technology And System Optimization Of Chemical Oxygen Demand In Seawater

The important indicator of organic matter content in seawater is chemical oxygen demand(COD).The COD of normal seawater is relatively low,generally measured in laboratory by alkaline Potassium Permanganate method,which is one of national standard methods for measuring COD.This method can not be used for real-time monitoring due to its poor timeliness and causing secondary pollution to water.Domestic COD measurement systems are rare.Some detection systems will produce secondary pollution.Some detection systems with better performance still can not use for in-situ detection duo to their high power consumption and large volume and other reasons.Foreign equipment cannot be widely used because of its high price.The purpose of this paper is to realize an immersed in situ optical COD sensor,which is suitable for marine applications.The main research contents and methods are as follows:Firstly,a quantitative analysis model was established by collecting the Ultraviolet absorption spectrum of COD standard solution and using Interval partial least squares(iPLS)to Screening spectral regions.The influence of turbidity,temperature and nitrate nitrogen on the UV absorption spectrum of COD standard solution was analyzed,and the compensation models were proposed.Secondly,the sensor package structure was improved to provide waterproof performance and the sensor can be extended to multi-wavelength work mode in order to meet the need of multi-parameter measurements in the future.The packaging structure of the sensor with low manufacturing cost is easy to process,and the model is convenient for mass production.Thirdly,after a thorough analysis to the characteristics,performances and regularities of UV-LED luminescence,a COD detection optical path system based on the UV-LED was proposed to improve the COD detection accuracy and reduce the minimum detection threshold.Finally,In this paper,COD standard solution was used to calibrate the sensor.The repeatability and stability of the COD standard solution measured by the sensor were tested.According to the different effects of turbidity,temperature and nitrate nitrogen on sensor,different compensation models were proposed.At present,the immersion in situ COD sensor designed in this paper has been tested in the sea.