Development Of The Technology For Online Monitoring Of Chemical Oxygen Demand In Water

In all kinds of pollution, organic pollution is one of the fastest growing and most serious pollution. Chemical Oxygen Demand(COD) is an important indicator of evaluating organic content in water, thus it is very important to take real-time monitoring COD in water. At present, the commonly used measurement methods are chemical method, electrochemical method, optical method, etc. Chemical method is accurate, but it is cumbersome to operate and easy to cause secondary pollution; electrochemical method has little secondary pollution, but the high cost instrument makes it difficult to spread; optical method does not need to consume chemical reagents and it takes short testing time, but it doesn’t have universality and the turbidity, p H value of water could also affect the measurement accuracy. Thus developing a simple, accurate technology with green environmental protection and real-time operation is particularly important. In the thesis, the main research results are as follows:1. Based on a built set of COD online monitoring system with ozone ultraviolet oxidation and multi- sensors integration, several experiments are done to get the sensor data which will be analyzed. Firstly, a preliminary COD model is established and tested whose results show that there is a big deviation between the measurement value and actual value. After a deep analysis on the oxidation-degradation reaction of the sample, a new COD model is proposed. Experimental results show that the improved method can get more accurate value than the preliminary one.2. Multiple measurements COD values of the same concentration samples using the improved detection methods show unstable results. The different ozone dissolution and decomposition law in different solutions may cause the instability. In addition, the temperature and the amount of ozone are proved to be two main factors on the law of ozone dissolution and decomposition in different solutions. After analysing these two factors quantitatively, two methods of the nonlinear regression method and support vector machine are used for the compensation of measured value of COD during 0~100mg/L. The simulation results show that support vector machine is better.3. A monitoring interface with WEI LUN TONG MT6100iv2 wv HMI is developed. It has the same function as the monitoring interface developed by Labview on computer platform, enabling automatic process control and online monitoring, enhancing system integration, being easier to carry.