The undertaken study includes investigating the performance and effluent characteristics of the treatment plant of Al-Doura refinery. Influent concentrations for some important contaminants, which are TDS, oil and grease, TSS, COD, BOD, and turbidity were 2595 mg/L, 13934 mg/L, 466.45 mg/L, 2538.9 mg/L, 1739.2 mg/L, and 89.18 NTU, respectively, while the effluent concentrations were 1337.8 mg/L, 0.53mg/L, 21.7mg/L, 25.45 mg/L, 17.81 mg/L, and 7.08 NTU, respectively, giving removal efficiencies of 44.47%, 99.99%, 94.4%, 98.96%, 98.96% and 92.05%, respectively. All these results indicate that Al-Doura wastewater treatment plant was efficient in removing contaminants according to Iraqi and EPA specifications. Hence, the second part of this study concentrated on finding a simple and efficient treatment method to treat the effluent so that it can be reused in the boiler system. A pilot plant was designed and dedicated for this purpose, including three units of granular activated carbon filter, ultra filtration filter, and reverse osmosis filter. Average removal efficiencies of oil and grease, turbidity, COD, and BOD were 85.25%, 100%, 34.92%, and 31.11%, respectively at the granular activated carbon filter, with very low efficiencies for the removal of TDs and conductivity. Ultra filtration showed average removal efficiencies for COD and BOD of 30.81% and 32.31%, respectively. While the average removal efficiencies for TDs and conductivity was very low. The reverse osmosis filter removed TDs and conductivity very efficiently, giving average removal efficiencies of 97.63% and 95.43%, respectively. In addition, it provided good removal percentages for COD and BOD, with values of 61.73% and 64.1%, respectively. A recycling procedure was created and the results were eventually comparable to those conferred by some of the traditional approaches.
