The laboratory scale constructed wetland was set up at the Faculty of Engineering; Delta State University, Abraka (Oleh Campus), Nigeria to demonstrate the performance of a sand-based constructed wetland, using Water Lettuce as Macrophyte. The experiment was carried out to demonstrate the efficiency for Water Lettuce with constructed wetland in treating petroleum refinery wastewater, which was gotten from the Warri refinery and Petrochemical Company, Warri. The effluent removal and performance evaluation of the constructed wetland in treatment of the refinery wastewater against retention period of five days was investigated. During the 5-day retention period, the sand- based constructed wetland set up with Water Lettuce had improved the wastewater quality significantly as indicated after a 1, 2, 3, 4, 5-days detention period, physiochemical analysis of the samples showed that on day-5 detention period, it has reduced by 100% for Turbidity, BOD5 by 94.61%, Nitrate by 72.815%, Sulphate by 91.41, Chloride by 57.72%, Magnesium by 89.28%, COD by 80.23%,  Total Hydrocarbon Compound (oil and grease) by over 99.86% and Conductivity by 77.88%. pH and Temperature was reduced by 17.30% and 2.74%, respectively. Dissolve Oxygen had an increment of 52.38%, while the initial offensive odour of the untreated water was reduced though, still with a little trace. The colour of the water improved to become colourless. Kinetics on BOD, COD and THC removal shows that BOD removal was of zero order while COD and THC removal is of first order. The final effluent was found to be suitable for non-drinking purposes which includes reuse in the refinery and discharge into water bodies. The treatment system was found to be economical, as the cost of construction and maintenance is minimal compared to other processes and also environmentally friendly. The prototype scale is recommended for use in treating petroleum refinery waste water.

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