Abstract

The reduction in the total petroleum hydrocarbon (TPH) content of a polluted soil is not indicative of reduction in toxicity and soil recovery. However, it is expedient to design methods that will not only remediate the soil but restore it to support agricultural and biological activities. This study involved a bench-scale bioremediation experiment conducted to compare two treatment regimens, NPK and a combined NPK and cow dung (NPK + CD) to enhance petroleum hydrocarbon degradation and eco-restoration. The treatment was conducted in three microcosms representing each treatment and a control (unamended soil). Each pot contained 4kg of soil spiked with Escravos crude oil to a final concentration of 8695.77mg/kg and monitored for a 35 day period using gas chromatography-flame ionization detector. At the end of the monitoring period, 32.56% removal of TPH occurred in control while NPK treatment enhanced TPH removal with 64.62% and NPK+CD had a further biostimulatory effect on TPH with 67.56% attenuation, respectively. Phytotoxicity assay was conducted to determine the extent of soil recovery after the experimental monitoring period. Corn seeds (Zea mays) were planted in all experimental pots and a pristine soil (CTRL-UP) served as control. After the 8th day, root length, shoot length and plant height were measured as 23.3, 6, 10.2cm; 10.2, 5.5, 15.4cm and 4.8, 4.5, 14.2cm for CTRL-UP, NPK+CD and NPK, respectively and the corn plant in NPK treatment died before the 35th day. The results confirmed that bioremediation was nutrient-limited. The presence of requisite hydrocarbonoclastic bacterial community with optimal nutrient availability enhanced the rate of crude oil degradation. The combination of inorganic and organic nutrient amendment is a better treatment option as it improves soil structure, water holding capacity and generally possess a rich microbial population with hydrocarbon utilizing capabilities.

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