Research On The Online Monitoring Devices For Chemical Oxygen Demand In Water

With the development of industrialization, fresh water resources is suffering serious pollution. In which organic pollution is one of the fastest growing and most serious pollution. Chemical Oxygen Demand is a reflection of comprehensive index of water body polluted by organic reducing substances, and it is necessary for real-time online monitoring of water quality of COD. At present, COD analyzer methods at home and abroad mainly have potassium dichromate oxidation method, potassium permanganate index method, UV spectrophotometry, microwave digestion using nitric acid and electromagnetic induction heating method, etc. They exist complicated operation, high equipment cost, needing to add chemical reagents and other shortcomings. It is necessary to develop a water COD online monitoring device which has advantages of simple structure, fast, efficient, high measurement precision, no secondary pollution. In this paper, the main research results are as follows:1. Based on the COD online monitoring device of ozone cooperating with UV, determining the COD value with oxygen consumption. The results show that there are large deviation with the theoretical value. Through further study and found that the into-ozone and temperature have greater impact on the decomposition and dissolution of ozone. These two variables are used to establish nonlinear compensation model of COD. Experimental results show that the improved measurements is close to the theoretical value.2. Experiments found that the reaction conditions such as the temperature, digestion time, the ozone and pH have a great influence on the digestion efficiency of organic matter. Orthogonal test is used to determine the optimum digestion conditions of the water quality online monitoring device for determining COD, and got the optimum temperature, digestion time, the ozone and p H. The water is oxidated completed, and the detection accuracy is greatly improved.3. Aimed at the problem of the unstable of the measured value, found that the temperature, pH value and COD have an impact on the amount of dissolved oxygen. The three variables and dissolved oxygen were used to establish the estimation model based on support vector machine(SVM), and the determination results was validated by national standard method showing that the compensation effect of the model is good.4. Do some optimized designs with the COD water quality online automatic monitoring device. By optimizing the detection process of device, PLC control module and PC interface device, the COD remote online monitoring device and measurement precision are improved, and the service life of the device is prolonged.