Relationships between water quality parameters in rivers and lakes: BOD5, COD, NBOPs, and TOC

Biological oxygen demand (BOD₅) or chemical oxygen demand (COD) analysis is widely used to evaluate organic pollutants in water systems as well as the efficiency of wastewater treatment plants. However, both analysis methods have restrictions such as being insensitive, imprecise, time-consuming, and the production of chemical waste. Therefore, total organic carbon (TOC) analysis for organic pollutants has been considered for an alternative analysis instead of BOD₅ or COD. Several studies have investigated the replacement of BOD₅ or COD with TOC in wastewater samples; however, few studies have investigated the relationships between water quality parameters in rivers and lakes. Therefore, this study evaluated the relationships between BOD₅, COD, or NBOPs and TOC by the analysis of national water quality monitoring data of rivers and lakes for 5 years. High correlation coefficients (r) of 0.87 and 0.66 between BOD₅ and TOC (p