Bioremediation Potential of Duckweed (Lemna paucicostata) on Wastewater from a Mechanic Workshop, Port Harcourt, Nigeria

Abstract

Wastewater pollution and its bioremediation remain a major challenge in urban areas. Lemna paucicostata were exposed to wastewater containing some amount of used engine oil in a four-week relative static bioassay. The physicochemical characteristics of the wastewater were determined using standard methods. The results obtained from the experiment showed that L. paucicostata was able to purify and concentrate nutrients from the wastewater. The efficacy of purification was manifested in the results where the total hydrocarbon content reduced from 8.15% - 4.00% over the period. Turbidity also reduced from 66.7% - 23.08%; biochemical oxygen demand reduced from 70.00% - 14.29%. Phosphate and nitrate also reduced from 34.59% - 12.09% and 39.74% - 11.92%, respectively. Chemical oxygen demand and total suspended solids increased from 22.92% - 73.16% and 2.90% - 14.39% respectively, over the periods. The temperature slightly changed from 29.3oC to 29.5oC. The pH also changed slightly from 7.00 – 7.50, making the wastewater slightly alkaline. Slightly alkaline conditions enhance overall hydrocarbon biodegradation in wastewater. However, prolonged exposure of L. paucicostata led to its mortality especially in the higher concentrations of hydrocarbons. Percentage mortality increased with concentrations and period of exposure, from 10% to 60% at the 3rd week and from 20% to 80% at the 4th week. Lethal concentration (LC50) of 14.60ppm was noticed at the 3rd week, while LC50 of 12.60ppm was noticed at the 4th week. The effectiveness of this algae, L. paucicostata, on the bioremediation of wastewater is not only of scientific but also of economic and social importance.