Research on Portable Noncontact COD Measurement Instrument Based on Laser Spectroscopy.

In this paper, a field-portable water quality detection instrument for non-contact Chemical Oxygen Demand (COD) measurement was presented based on laser spectroscopy. In this instrument, a semi-conductor laser at 405 nm was selected as the excitation source. The COD value can be obtained by analyzing the received spectrum based on the fluorescence integral-Raman ratio (FIRR) method when the laser emits into water at a certain distance. For facilitating COD measurements in Lab, the sodium humate and glucose mixed solution at a certain proportion were chosen to simulate natural water. The maximum relative error of COD value measured by our designed instrument at the distance 1-10m is 7.44% with the laser output power of 50mw. At the output laser range of 10-100mw and the distance of 5 m, the maximum relative error is 7.96%. In addition, using the instrument, we measured the field water in Weihai city, China, and the COD results are consistent with those tested by laboratory chemical method. In the experimental process, the instrument was less influenced by the variation of detection distance, laser output power and testing environment. It has advantages of high stability and anti-interference ability, which can be applied in non-contact COD measurement for many water areas.