Comparison of the Efficacy of Remediation by Enhanced Natural Attenuation with Phytoremediation in the Recovery of Crude-Oil Polluted Soils

The efficacy of remediation by enhanced natural attenuation (RENA) and phytoremediation using the leguminous crop, Vigna unguiculata (PVU) in the recovery of crude oil polluted soils was compared. The potency of both remediation techniques was evaluated by the activities of selected soil enzymes serving as soil quality indicators. The rate and progress of the remediation processes were monitored at two weeks interval for a period of six weeks, beginning from the 7th day of pollution. The crude oil polluted soil experienced a significant (P<0.05) increase in soil acid phosphatase activity with a corresponding decrease in soil alkaline phosphatase and amylase activities respectively. The remediation processes showed that with RENA, the soil’s acid phosphatase activity decreased from 7.23±0.56 to 5.66±0.50 (U/L) but with PVU, its activity increased from 7.60±0.64 to 21.13±7.8 (U/L). Both RENA and PVU showed progressive significant (P<0.05) decreases in alkaline phosphatase activity. However, RENA recorded a marked increased activity from 8.13±5.40 on day 35 to 10.95±5.71 (IU/L) on day 49. Soil amylase showed a decreased activity from 4.71± 0.77 and 4.76± 0.34(U/L) on day 7 to 3.81± 1.03 and 3.65 ±1.15 (U/L) on day 21 for RENA and PVU respectively. The findings of this study strongly suggest that remediation by enhanced natural attenuation and phytoremediation with V.unguiculata are suitable in the recovery of crude oil polluted soils. However, remediation by enhanced natural attenuation showed greater efficiency in the remediation of polluted agricultural lands. Key words: Efficacy, Enhanced Natural Attenuation, Phytoremediation, Enzyme activities