Research of a portable rapid in situ monitoring system for the determination of COD in waters

A portable rapid monitoring system for in situ measuring chemical oxygen demand (COD) of environmental water samples is described. Integrating with the on line sample chemical pretreatment of ultrasound-assisted Fenton reagents digestion of organic compound at normal temperature and normal pressure, system adopts the method of competition for hydroxyl radical between organic compounds and the chromogenic reagent for determination of COD content in water samples. The microspectrometer with the function of continuous spectrum analysis is the core of the system, and the multifunction miniature sample reacting and detecting chamber is the key technology. The system prototype machine can in situ measure the COD content in water samples, and it has a throughput of 3 measurements per hour, a LOD (limit of detection) of 3.5mg/L, a linear response over the calibration range of 0-30mg/L (R-2 = 0.9976), and a precision of 4.3% RSD at 15mg/L (n = 7). Field evaluation of the system prototype machine and detection method had been performed in Chongqing water environment monitoring center and a sewage treatment plant in Chongqing city, where a lot of different environment water samples had been measured over two months by contrast with China's national standard lab analysis method for determination of COD. Good agreement was observed between the samples' determination data from China's national standard lab analysis method and those in situ measured by the system prototype machine. Moreover, the system prototype machine has quite a few technical advantages, such as small volume, low cost, lower power and much shorter measuring time (1/6 of the average). Therefore, it meets the practical demands of modern water quality monitoring and forecasting net.