In petroleum refineries, cooling towers, steam engines, and vacuum distillation all require a large volume of water. Before being dumped into the water bodies, it is then transported to an industrial water treatment facility. One of the study's objectives is to verify how well different processing units in the industrial wastewater treatment plant at the cycle refinery remove concentrations of chemical and biological oxygen demand (COD) and BOD. Five samples of industrial wastewater were collected before and after each treatment unit and one sample of wastewater was drained as a final product to the Tigris River. Over the summer, the BOD5 values after each processing unit were 180.8, 175.2, 111, 43, and 37 ppm. Winter readings were 106.8, 99.6, 81.2, 33.8, and 31 ppm, with summer and winter complete elimination rates of 79% and 71%, respectively. The reason for higher BOD5 concentrations in summer than in winter is due to higher temperatures that lead to evaporation and increased concentrations of BOD5 and COD pollutants. While COD concentrations were during the summer after each processing unit 399.6, 383.2, 187.2, 72.8, and 55.4 ppm, in winter they were 324.4, 310.2, 115, 46, and 42.6 ppm with a total removal rate of 86% in summer and 87% in winter. It was found that the refinery's water-drained treatment method, which includes a high proportion of BOD5 and COD concentrations in the main treatment plant, is effective. The water that flowed from the treatment plant into the river was within the national standard of the river water.
