Potential Use of Mushrooms and Spent Substrate in Decontamination and Cleanup of Oil Contaminated Soil: A Mini Field Climate Resilient Practical Approach

Abstract

Oil spills from petroleum exploration constitutes a serious environmental damage and injury to climate that remains unresolved despite so much reports on bioremediation studies.Preliminary studies on the enhancement of biodegradation of used lubricating oil, a petroleum bye product, in soil amended with dried powdered Pleurotus tuberregium (PT) and Pleurotus ostreatus fruits (PO), Powdered sclerotium of Pleurotus tuberregium (SCPT) and spent substrate of Pleurotus ostreatus (SPO) was carried out in randomized pots of 400g of oil contaminated soil. The objective was to study the effect of mushroom and spent substrate as a biocatalyst in the cleanup of soil contaminated with petroleum products in the tropics. An absorption spectrophotometer with a wavelength of 640nm was used to analyze the oil content of the contaminated soil after defatting 50grams of it with a non-polar solvent-hexane. After seven weeks, the amount of lubricating oil in the untreated soil (not amended with the mushroom fruits, sclerotium and spent substrate) dropped from 960mg/g to 282mg/g. On application of varying quantities up to 60g each of PT, PO, SCPT, SPO, into the lubricating oil contaminated soil and left for seven weeks, the residual lube oil concentration dropped drastically from 960mg/g to 0.05mg/g, 0.5mg/g, 1mg/g and 27mg/g respectively. Pleurotus tuberregium supported faster break down of the oil than PO, SCPT and SPO. Corroboration between the crude protein and biodegradation efficiency was noted. PT (42.2%) protein while the least SCPO (9.8%) protein with least biodegradation. The PH of untreated soil (lubricating oil contaminated soil unamended) slowly dropped from 8.15 at the start of the experiment to 7.77 by the 7th week while PH of lubricating oil contaminated soil treated with PT, PO, SCPT, and SPO tend toward neutral (7.0) for the same period. Total aerobic mesophilic bacterial counts increased in the treated soil specimens from 1.5 x 104 CFu/g to too numerous to count (TNTC) in the 7th week. However, nutrient agar cultures of soil amended with mushroom fruits suggest luxuriant colonies/confluent and profuse growth than with sclerotium, spent substrate and control (unamended soil). More bacterial isolates and in higher counts were recovered from the amended soil including Pseudomonas spp, Bacillus spp, Enterobacter spp, Citrobacter, and E coli than with the control. The study suggests strongly that the biodegradation of the oil increased with increasing time, quantity and quality of biocatalyst added. The findings further suggest that mushroom and spent substrate of pleurotus ostreatus could be employed as cheap clean up agents of lubricating oil contaminated soil in the tropics and probably elsewhere.