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In the coastal water quality monitoring, turbidity has vital effect on the optical method for the measurement of the concentration of the chemical oxygen demand (COD) using UV-Vis spectrum. The mixture absorption spectrum of turbidity and COD was studied using a 10mm optical path in this paper. The COD calculation band is from 200 to 300nm which is contained in the turbidity absorption spectrum (200-720nm), the intensity of absorption spectrum was enhanced with the increase of turbidity, The result shows that the absorption spectrum of COD increases with the increasing of concentration. The absorbance between 300nm and 720nm is almost unchanged, which is mainly caused by turbidity, turbidity compensation can be carried out by eliminating the absorbance between 300-720nm. In order to verify the feasibility of this method, the spectrum of COD and turbidity mixed solution with different concentration was measured. Error analysis is made between calculation results and laboratory measurements. The results show that mean absolute error, variance and standard deviation are 0.83, 0.92 and 0.96 respectively, which can be used for the on-line monitoring.
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