Fig. 1. Structural block diagram of COD sensor

Fig. 2. Multiple water sample data measured by spectrometer

Fig. 3. Scattered light intensity and spatial distribution under different d/λ

Fig. 4. Absorbance-turbidity fitting results. (a) Linear fitting result of absorbance-turbidity for 860-nm light source; (b) linear fitting result of absorbance-turbidity for 254-nm light source

Fig. 5. Other fitting results. (a) Linear fitting result of scattered light measurement value-turbidity for 860-nm light source; (b) linear fitting result of absorbance-COD concentration for 254-nm light source

Fig. 6. Comparison of measurement values of potassium dichromate method and self-made sensor