Treatment of Petroleum Refinery Wastewater in a Constructed Wetland with the Use of Water Lettuce

Abstract

The constructed wetland at the laboratory scale was established at the Faculty of Engineering, Federal University of Petroleum Resources, Effurun, Nigeria, to illustrate the effectiveness of a sand-based constructed wetland utilizing Water Lettuce as the macrophyte. This experiment aimed to showcase the efficiency of Water Lettuce in a constructed wetland for the treatment of petroleum refinery wastewater sourced from the Warri Refinery and Petrochemical Company, Warri (WRPC). The study evaluated the effluent removal and performance of the constructed wetland in treating refinery wastewater over a retention period of five days. Throughout this 5-day retention period, the sand-based constructed wetland, equipped with Water Lettuce, significantly enhanced the quality of the wastewater. The physiochemical analysis of samples taken after 1, 2, 3, 4, and 5 days of detention indicated that by the end of the 5-day period, there was a 100% reduction in turbidity, a 94.61% reduction in BOD5, a 72.815% decrease in nitrate, a 91.41% reduction in sulphate, a 57.72% decrease in chloride, an 89.28% reduction in magnesium, an 80.23% decrease in COD, and over a 99.86% reduction in total hydrocarbon compounds (oil and grease), along with a 77.88% reduction in conductivity. The pH and temperature were reduced by 17.30% and 2.74%, respectively. Dissolved oxygen levels increased by 52.38%, while the initially offensive odor of the untreated water was diminished, albeit with a slight residual trace. The color of the water improved to a colorless state. Kinetic studies on BOD, COD, and THC removal indicated that BOD removal followed zero-order kinetics, whereas COD and THC removal adhered to first-order kinetics. The final effluent was determined to be suitable for non-potable applications, including reuse within the refinery and discharge into aquatic environments. The treatment system has been identified as cost-effective, given that both construction and maintenance expenses are minimal in comparison to alternative methods, while also being environmentally sustainable. It is advisable to utilize the prototype scale for the treatment of wastewater from petroleum refineries.