Research On Online Monitoring System For COD Based On Sensing Technology

Chemical Oxygen Demand?COD?is the main characteristic indicators for the polluted degree of organic matter in water,which has important significance and value for the evaluation of water pollution.Therefore,the importance of accurate measurement and effective monitoring of COD is self-evident.This article describes mainly improvements for a set of self-built COD on-line monitoring system which using advanced oxidation of ozone combined with UV?UV/O₃?to oxidize water samples.Oxygen equivalent can be obtained through calculating the reaction model with several variables measured by sensors.Then the value of COD can be calculated by the oxygen equivalent.The main research results of this article have the following three aspects.?1?The experiments are carried out on the original on-line monitoring device for COD.The experimental results indicate that the measurement results by COD calculation model for low concentration standard solution is beyond the theoretical value,while the results for high concentration standard solution is below the theoretical value.By means of analyzing the factors caused by water quality COD on-line monitoring system,which may cause the error of the COD determination results.It is found that the influence of the amount of relevant gas dissolved is not taken into consideration during the measurement.Therefore,the amount of dissolved oxygen and carbon dioxide in water samples after digestion are measured by chemical measurement and theoretical estimation.The estimation model of dissolved gases is established by using a support vector machine.The COD calculation model is revised and compensated as well.The measurement results are improved and basically the same as the theoretical values,which have a good consistency with the national standard method.The average relative error is less than 5%and the detection accuracy of the system is obviously improved.?2?After the detection accuracy of COD on-line water quality monitoring system is improved,it is necessary to conduct further research on the detection efficiency of the system.The detection efficiency of the system is closely related to the digestion time of water samples.Therefore,how to grasp the characteristics of organic substances in water samples and determine whether the digestion process is completed has great significance.The appropriate digestion time of water samples is determined by studying the relationship between the concentration of carbon dioxide produced and the digestion rate of organic substances during the digestion process.Based on the research,the standard solution of glucose,potassium hydrogen phthalate and phenol which have different digestion degrees at different concentrations is studied.From their relationship between the content of carbon dioxide produced and the digestion rate of organic substances during the digestion process,the conditions for the termination of digestion are determined.The method helps the system automatically determine and control the digestion time of different water samples,which improves the detection efficiency of the system and saves energy consumption.?3?Based on the above research and analysis,combined with the inadequacies of the original on-line monitoring device for COD,the device is re-optimized in design and layout.And a new set original on-line monitoring device for water quality COD is constructed.The new device mainly upgrade some key sensors and other hardware devices.And the detection process of the original on-line monitoring device for COD is optimized and streamlined,which can be able to realize the on-line monitoring of water quality COD through the industrial touch-control machine.