Impacts of selected leguminous tree species and kaolinite pre-amendment on oil-contaminated soil for bioremediation in the oil-bearing region of Nigeria

Abstract

iii ABSTRACT This study investigates the impacts of selected Leguminous Tree Species (LTS) and kaolinite pre-amendment on oil-contaminated soil. It covered assessment of different levels of contamination (0, 25, 50, 75 and 100 ml in 4000 g soil; which represents the degree of light crude oil spillage concentration as 0.0, 0.63, 1.25, 1.88 and 2.5 %v/w) on the growth performance of Albizia adianthifolia, Albizia odoratissima, Bauhinia monandra, Delonix regia, Peltophorum pterocarpum and Tetrapleura tetraptera LTS investigated. Percentage germination, seedling height, seedling girth, number of leaves and number of nodules decreased as the concentrations of crude oil in soil samples increased. LTS affected soil physicochemical properties. Soil acidity decreased; soil organic matter, carbon content and exchangeable ions increased. N, P and K were altered in the LTS planted soil as compared to controls, but there were no significant (P >0.05) differences. There were increased microbial counts in the crude oil-contaminated soil planted with LTS as compared with non-LTS planted soils. Hydrocarbon removal was significantly higher (P <0.05, n = 3) in LTS planted soil than in non-planted soil. D. regia planted soils had most hydrocarbon removal and had significantly more growth in terms of plant height, girth and leaf production in the field. Kaolinite (10 and 20 g samples) applications were suitable and effective sorbent agents for oil-contamination at the different oil concentrations. The sorption potential of kaolinite increased with the increase in kaolinite to 20 g. The potential re-usability of kaolinite after the initial use for oil sorption was analysed and 10 g of burnt kaolinite sorbed 43.62%, while 20 g sorbed 58.90%. The rate of oil sorption by fresh kaolinite was significantly higher than burnt kaolinite. Results show the considerable potential of phytoremediation protocols with LTS and kaolinite as combined remediating agents for oil spill remediation in the humid tropics.