Research on COD parameter in water based on the combination of UV absorption photometry and laser spectroscopy

Chemical Oxygen Demand (COD) is widely utilized as a representative and required measurement indicator of water pollution as well as water quality monitoring. The spectral technology is an important development direction in water quality detection. In this paper, a novel COD monitoring instrument is designed based on ultraviolet (UV) absorption photometry and laser spectroscopy. The instrument consists of CODcr and CODmn detection modules. The CODcr module is based on the Lambert-Beer law to measure UV absorption of organic matter in water, which can be used to measure the COD parameter in high concentration organic pollution in water. The CODmn module is based on the ratio method of fluorescence and Raman to analyze the spectral signals generated by the laser-excited water body, which can determine the COD parameter in low contaminated water. By analyzing the CODcr and CODmn parameters together, the comprehensive evaluation of organic pollutants in water can be realized. In the experiment, the CODcr and CODmn modules are respectively calibrated with the potassium hydrogen phthalate (KHP) solution as well as the mixed solution of humic acid sodium and glucose. Then the stabilities of the two detection modules are tested, and the detected result drifts are stable within six days. In addition, to verify the reliability of measuring results in complex environments, we test the instruments at 10 monitoring sites of the Sow River in Weihai city. The results of on-site monitoring are highly consistent with those of national standard method. The study result shows that the instrument developed in this paper can measure both CODcr and CODmn simultaneously, which can expand the COD detection range, and provide a new method for the comprehensive detection of organic pollutants in water.