Impact of Organic Mulching on the Enhanced Natural Attenuation of a Petroleum Hydrocarbon Polluted Soil

Abstract

The remediation of oil polluted soil has been a major problem in oil producing countries and investigations on the use of mulch and various soil amendments has been on. In order to identify the organic material that would enhance remediation of crude oil-contaminated soil, the present study was undertaken. Waste engine oil-polluted soils (5% w/w) were made into beds of 120cm × 60cm × 15cm dimension, and then mulched with saw dust, dried cow dung, wood ash, dried ruderal weeds, and dried crushed Chromolaena odorata plants. The set up was left for 3 months on an open field. The result revealed that there were over 88% reductions of polyaromatic hydrocarbon contents in soil 3 months after mulching, from 833.62mg/kg to 103.88mg/kg in the oil-polluted soil. Significant reductions from the original concentrations of Fe, Mn, Zn, Cu, Cr, Cd, Pb, Ni and V were also achieved. Achromobacter spp., Bacillus  pumilis, Sarcina spp. and Micrococcus spp. were prevalent bacteria species found in the polluted soils, while prevalent fungi species included Aspergillus niger, Penicillium, spp. and Fusarium spp. Contamination factor, probable efficient concentration and hazard quotient were generally higher in unmulched soil, compared to the mulched ones. Results of phytoassessment, using seedling development at 3 weeks for yardstick for adjudging the success of remediations, showed improved seedling development in the sawdust-mulched soil (87.62% survival), compared to unmulched oil-polluted soils (25.98%  survival).