A shift from chemical oxygen demand to total organic carbon for stringent industrial wastewater regulations: Utilization of organic matter characteristics.

From 2022, industrial wastewater discharge regulations in South Korea will replace chemical oxygen demand (COD Mn) with total organic carbon (TOC). A shift from COD Mn to TOC is a pioneering change in protecting water bodies from organic contaminants. However, several industries are struggling to meet these TOC requirements even though their effluents met the COD Mn limits. Effluent COD Mn /TOC ratios (1.28 ± 0.64) found in our study were lower than the COD Mn /TOC coefficients (1.33–1.80) suggested by the Ministry of Environment in South Korea. Aliphatic and particulate organic matter contents in effluents likely influenced the COD Mn /TOC ratio. Regardless of the industrial category, dissolved organic carbon often consists of low molecular weight neutrals, hydrophobic organic carbon, and protein-like substances in raw and treated industrial wastewaters. The present study also revealed that TOC and COD Mn represented different organic matter fractions in the paper mill and oil refinery wastewater, whereas the industrial park wastewater showed similar dissolved organic matter characteristics. Specifically, COD Mn was effective in the determination of humic content in paper mill wastewater but was underestimated in oil refinery wastewater. Additionally, only paper mill effluents exceeded the TOC requirements (4 of 6 samples) and required an additional post-treatment process owing to higher organic loads. [Display omitted] • Hydrophobic and low MW neutral organic carbons were the most abundant in wastewater. • Humic substances in paper mill wastewater were often oxidized via COD Mn method. • Oil refinery wastewaters were biodegradable and COD Mn underestimated organic contents. • Effluent COD Mn /TOC ratio was lower than conversion coefficient and led to higher TOC. [ABSTRACT FROM AUTHOR]