Remediation of a Model Petroleum Hydrocarbon-polluted Soil after Amendment with Nutrient-rich Sludge Obtained from a Beverage Effluent Treatment Plant in Benin City, Nigeria

The present study investigated the bioremediation of a petroleum hydrocarbon-polluted soil after substrate amendment with nutrient-rich sludge (NRS). Sun-dried top soil was measured into buckets and thoroughly mixed with waste engine oil (WEO) on a weight basis to obtain 5% w/w oil-in-soil. The oil-polluted soil in the buckets were divided into 4 sets of separate treatments including polluted soil only (unamended), polluted soil + 10 g NPK fertilizer, polluted soil + 5%w/w NRS in soil, and polluted soil + 25%w/w NRS in soil. The fifth set of treatments was oil-polluted NRS only (5%w/w). The control was unpolluted soil, unamended. Decrease in heavy metal components of soil was highest in the 25% NRS-amended soil. Total PAH (TPAH) in NPK-amended soils was higher (923.90 mg/kg) when compared to the unamended polluted soil (458.58 mg/kg); this indicated a lower bioremediation efficiency of 38.66% in the former, compared to 69.55% in the latter. Remediation efficiency in the 25% NRS-amended soil (TPAH=260.12 mg/kg) was 82.73%. Phenathrene was totally remediated in the oil-polluted NRS. Micrococcus varians was the most prevalent bacteria species obtained in the present study, followed by Bacillius subtilis, both being hydrocarbon degraders. The fungi species present were Aspergillus niger, Penicillium sp. Fusarium solani, Mucor sp. and Trichoderma sp. Phytoassessment of the study using Vigna unguiculata, showed improved plant growth response in the NRS-amended oil-polluted soils.