Research On COD Green Detection Method Based On O₃/UV

As a comprehensive indicator to reflect the severity of the water being contaminated by organic matters,the determination of chemical oxygen demand?COD?is of great significance for water environmental protection and water pollution prevention.In order to solve the shortcomings of COD online detection technology,such as consuming chemical reagents and taking long time to degrade,the ozone combined with ultraviolet radiation?O₃/UV?advanced oxidation process is introduced,and the COD online monitoring device based on multi-sensor information fusion is developed.Based on the existing research results of the laboratory,this paper has carried out the following researches around this detection method:?1?In order to improve degradation efficiency of organic compounds and reduce energy consumption for the reaction system by using the ozone combined with ultra violet radiation?O₃/UV?technique,based on the SHB mechanism of ozone?O₃?decomposition and photolysis mechanism of O₃ and organic compounds under ultra violet?UV?radiation,a kinetic model of O₃/UV reaction system is established by studying the 3 possible degradation pathways of organic compounds and the concentration change of gas phase O₃.The model was applied to study the change rules of digestion rate for organic compounds during the degradation process and further to optimize the degradation conditions.Taking Phenol and acetic acid as the target organic compounds to conduct the simulation the sensitivity of the kinetic model to different reaction conditions and the synergy between O₃ and UV were verified theoretically.The superiority and accuracy of the proposed model was confirmed via comparison with other kinetic models and actual measurements in digestion experiments.The simulation results for the respective contribution rate of three degradation pathways under different pH values demonstrate the importance of pH value in this reaction system.This study illustrates that a synergy between the UV radiation intensity and the added O₃concentration is existed in the O₃/UV system,better digestion rate can be obtained when they are adjusted together;organic compounds are directly degradated by O₃ under acidic conditions,and by radicals under alkaline conditions.?2?Aiming at the problem that the solubility of dissolved gas affects the measurement accuracy when COD is detected by O₃/UV,a method for estimating the amount of dissolved gas in COD detection process is proposed,which is used to compensate the COD detection model.The measurement data and experimental analysis data of different concentrations of COD standard water samples in the digestion process were collected.Based on PLS-LSSVMs,an estimation model of dissolved oxygen and dissolved carbon dioxide was established.The output of the model was used as the compensation term for the COD detection model.The experimental results show that the model established based on PLS-LSSVMs has higher estimation accuracy than the model established by PLS or LSSVMs.The relative errors between the measured COD by O₃/UV method and the national standard method are less than5%after the dissolved gas is compensated.?3?In order to improve the detection efficiency and detection accuracy of COD on-line monitoring device based on O₃/UV method,a relationship between the change rate of carbon dioxide generation concentration and the organic matter digestion rate in different digestion processes was studied.The detection method can automatically determine by the termination of digestion.By collecting the data of each sensor in the digestion process,the digestion end time is automatically determined based on the standard deviation of the carbon dioxide gas concentration change rate calculated using the sliding standard deviation method.Digestion experiments were carried out on different types and concentrations of organic matter.It was found that when the standard deviation of the real-time concentration of carbon dioxide was less than 0.003,the organic matter was completely digested completely,and it was considered that the reaction end point was reached.The method can be used not only for online monitoring of COD to improve detection efficiency and detection accuracy,but also for guiding wastewater treatment based on O₃/UV method.