The article discusses the comparison between chemical oxygen demand (COD) and total organic carbon (TOC) measurements in wastewater. The traditional COD method requires long processing times, expensive chemicals, and toxic reagents, limiting its use. In recent years, TOC has increasingly replaced COD due to its faster analysis and reduced environmental impact. However, the relationship between COD and TOC is not consistent across all compounds, and the ratio varies depending on the molecular structure. For example, the COD/TOC ratio ranges from 2 to 3, with higher values for certain compounds like macrolides and lower values for fluoroquinolones and tetracyclines. The study analyzed 70 contaminants, including pharmaceuticals and pesticides, and found that COD values generally agree with theoretical calculations within 10%, though some compounds showed discrepancies. The ratio changes during degradation in advanced oxidation processes (AOPs), making TOC less reliable as a substitute for COD in these contexts. The study emphasizes that the COD/TOC ratio must be determined individually for each compound, as it depends on molecular structure and oxidation state. In AOPs, COD decreases more rapidly than TOC, indicating that COD reflects oxidation progress while TOC indicates the final step of carbon transformation to CO₂. Therefore, the replacement of COD with TOC is not recommended in AOP studies, as the two parameters have different meanings and implications. The findings highlight the importance of understanding the relationship between COD and TOC for accurate wastewater characterization and treatment.The article discusses the comparison between chemical oxygen demand (COD) and total organic carbon (TOC) measurements in wastewater. The traditional COD method requires long processing times, expensive chemicals, and toxic reagents, limiting its use. In recent years, TOC has increasingly replaced COD due to its faster analysis and reduced environmental impact. However, the relationship between COD and TOC is not consistent across all compounds, and the ratio varies depending on the molecular structure. For example, the COD/TOC ratio ranges from 2 to 3, with higher values for certain compounds like macrolides and lower values for fluoroquinolones and tetracyclines. The study analyzed 70 contaminants, including pharmaceuticals and pesticides, and found that COD values generally agree with theoretical calculations within 10%, though some compounds showed discrepancies. The ratio changes during degradation in advanced oxidation processes (AOPs), making TOC less reliable as a substitute for COD in these contexts. The study emphasizes that the COD/TOC ratio must be determined individually for each compound, as it depends on molecular structure and oxidation state. In AOPs, COD decreases more rapidly than TOC, indicating that COD reflects oxidation progress while TOC indicates the final step of carbon transformation to CO₂. Therefore, the replacement of COD with TOC is not recommended in AOP studies, as the two parameters have different meanings and implications. The findings highlight the importance of understanding the relationship between COD and TOC for accurate wastewater characterization and treatment.