Development Of Seawater Chemical Oxygen Demand Measurement Instrument Based On Ozone Analysis

The ocean covers the earth's 71% surface area, and is an important composing part for supporting the global ecosystem. Along with the ocean development of human beings, the ocean will be bearing more and more environmental pressures. Among various sea pollutions, the organic pollution with quickest spreading speed is the gravest and the most serious pollution to be controlled. The chemical oxygen demand is the important index for monitoring the propagating of ocean organic substance, and is also an important parameter for detecting the quality of seawater. It is essential to detect and control the COD of seawater in time for ocean pollution treatment and protection.Presently,the design principle of COD automatic on-line monitoring instruments are mostly based on the national standard of China, namely, by simulating traditional wet chemical method to achieve online analysis. The analytical period is long for the sample; and many reagents are used in these methods. Moreover, various pipelines and valves are introduced in this system, which are complex and difficult to operate and maintain. Furthermore, eluting waste causes terrible second pollution. Therefore, it is of great significance to develop fast, simple, and convenient water COD monitoring instrument automatically.This paper describes the development of water COD measuring technique and instruments. In order to overcome the drawback of the current COD measuring instrument, we propose an "ozone chemiluminescence" based method to detect the organic content in seawater, and also develop the measuring instrument for chemical oxygen demand based on seawater ozone. The instrument consists of an automatic sampling system, an ozone-generating device, a chemical reaction chamber, a signal acquisition system, and data processing system. It is a new and on-line seawater COD monitoring instrument without any secondary pollution, and is fast, reliable, intelligent. The instrument utilizes the stable and known concentrations ozone as the oxidant solution, which is provided by electrolysis-type ozone generator,and employs the chemiluminescence based detection method. In this paper, we analyze the method that can produce a stabilizing concentration and improve oxidation by electrolysis-type ozone generator, and produce the COD measurement with structured design. In addition, we analyze the measures of chemiluminescence detection, collecting and processing signal of data for elimination of errors. The optimum analytical condition is determined based on the analytical method, and the accuracy of method is tested by contrasted experiments on site. The experimental results show that the proposed method is easy and quick to operate and has high sensitivity. Comparing our method to the standard manual method by using practical water sample, the results indicate that the measuring results are well identical with the national standard method, and the proposed method is suitable to monitor the practical seawater on-line.