Comparison of Spectrophotometric and Digital Photometric Methods for Determining Chemical Oxygen Demand

Visible spectrophotometry (VS) and digital photometry (DP) for determining chemical oxygen demand (COD) were compared; the latter method involved image processing of digital photographs of analyte solutions using RGB-AIC software. Statistical analysis showed that COD values of untreated and treated (trickling filter) wastewater samples from a hog slaughterhouse were not significantly different using VS and DP methods. The COD values were not significantly different among the treated samples as well using a* and L* plots. Tests for accuracy and repeatability of the DP method showed acceptable results. The calculated limit of detection (LOD) for DP was 0.73 mg L-1 while the LOD for VS was 0.33 mg L-1. The accuracy of the DP method was validated using glucose solutions of known COD values; t-tests performed at 95% confidence level showed no significant differences in COD values between (1) theory and experiment, (2) VS and DP and (3) a* and L* plots. These findings suggest that digital photometry is accurate and can be used as an equally accurate alternative to conventional spectrophotometry.