COD, TOC determination using UV spectrophotometry and its application to monitor the potassium hydrogen phthalate degradation by H2O2-HCO3– oxidation system

In this study, the COD and TOC in H2O2-HCO3– oxidation system containing potassium hydrogen phthalate were determined by UV spectrophotometry (260-310 nm). The pH and H2O2 concentrations were investigated as factors influencing the absorbance measurements. The obtained standard curves were Abs = (3.10±0.04)x103xCOD - (0.015±0.003) (R2=0.9996) with LOD of 5.1 mg O2/l and LOQ of 13.6 mg O2/l, and Abs = (0.008±0.0001)xTOC - (0.015±0.003) (R2=0.9996) with LOD of 1.6 mg/l and LOQ of 5.4 mg/l. The method was applied to monitor the degradation of potassium hydrogen phthalate by the H2O2-HCO3– oxidation system. The results revealed that the COD and TOC removal efficiencies reached ~85% after 90 minutes of UVC irradiation. The UV spectra and HPLC chromatographs showed that no aromatic compounds were obtained in the degradation products.

Implications of COD analysis use in the peracetic acid-based wastewater treatment

Peracetic acid (PAA) stands out as a safe and environmental-friendly oxidant and disinfectant which has been effectively used in wastewater treatment. Chemical oxygen demand (COD) is a very popular analysis in wastewater treatment, however the interference of residual PAA on the COD measurement is still unknown. In this context, this study investigated the implications of applying the COD analysis in PAA-based treatment. Each 1 mg·L−1 of PAA increased the COD concentration around 13.5 mg O2·L−1. Residual PAA and hydrogen peroxide (H2O2) were efficiently neutralized by sodium metabisulfite (SMBS) at the optimal SMBS/PAA ratio of 10.2:1 in a wide pH range (5 to 9). The effect of PAA addition in the COD concentration was evaluated in different water matrices (potassium hydrogen phthalate and wastewater solutions). The COD results with the SMBS addition at optimal SMBS/PAA ratio were lower than the ones without it. It may happen due to the neutralization of residual H2O2/PAA and the complexity of the water matrices which can interfere in the COD results. This study discussed the impact of the residual H2O2/PAA neutralization before the COD analysis and this investigation can be used as a practical guideline for the correct COD measurement in PAA-based treatment.