University of Guilan Caspian Journal of Environmental Sciences 1735-3033 20 1 2022 01 01 An inquiry into the relationships between BOD5, COD, and TOC in Tigris River, Maysan Province, Iraq 37 43 5390 10.22124/cjes.2022.5390 EN Haleem K. Alewi Southern Technical University, Technical Institute of Shatra, Thi -Qar, Iraq Emad A Abood University of Baghdad. Baghdad, Iraq Gaith Ali Ministry of Water Resources, Thi-Qar, Iraq Journal Article 2022 02 10 Despite its universally wide use in water quality indices and evaluating the efficiency of wastewater treatment plants, chemical oxygen demand (COD) or biological oxygen demand (BOD₅) analyses have disadvantages such as being imprecise, time-consuming, insensitive, as well as the production of hazardous wastes. Total organic carbon (TOC) will introduce as an alternative analysis, the relationship between BOD₅, COD, and TOC has been investigated in this study. A total number of 216 samples were taken from three stations (kumait, Al Amara, and Al Majar Al Kabeer) in Tigris River, Maysan Province, Iraq. The sampling was on a monthly basis during a two-year period.  The tests were performed according to ASTM D7573 - 18ae1, ASTM D6238-98, and ASTM D125-06 for TOC, BOD₅, and COD respectively at the Pollution Research Centre of the Al-Shatra Institute, the data were statistically analyzed using the SPSS program to predict a relationship between the COD or BOD₅ and TOC. The analysis showed a good relationship concerning to a value of correlation coefficient, i.e., r = 0.93 or r = 0.94 between TOC and BOD₅ or COD respectively, as well as the coefficient of determination, i.e., R²= 0.91 or R²= 0.92 between TOC and BOD₅ or COD respectively. The validation of the suggested formulas has been tested using data from the Pollutant Centre in Al Shatra Institute for Shat al Gharaf River. The formulas gave reasonably acceptable values. It could be used in monitoring water quality and wastewater plants as a surrogate parameter to have pre-impression of the plant efficiency. https://cjes.guilan.ac.ir/article_5390_75ff439ad8a62bf8b54f416212d4f8fe.pdf