Investigating the simultaneous removal of hydrocarbons and heavy metals by highly adapted Bacillus and Pseudomonas strains

Abstract

The status, content and availability of heavy metals and hydrocarbons are highly affected by weathering processes – particularly – in areas characterized by harsh conditions. Their concomitant removal by highly adapted strains of Bacillus and Pseudomonas to weathered oil components was investigated. Indeed, weathered soil collected from Dukhan dumpsite was shown to contain 14 heavy metals with concentrations exceeding the US-EPA limits. Their distribution in such soil was not affected by the soil organics, which is important for the remediation processes. Most of them were strongly bonded to the iron–manganese oxide and the residual fractions, justifying their bioremediation. This study used 18 adapted bacterial strains isolated from extremely weathered oily soils, including the studied soil, all shown tolerant up to 5 mM and above of heavy metals. 4 Bacillus and 3 Pseudomonas strains exhibited the capability to remove 70%–80% of the heavy metals. Concomitantly, they removed up to 73% of the diesel-range organics. Using the PCA methodology with multivariate (bacterial type and adaptation and heavy metals properties), the efficiency of heavy metals removal was shown not related to the adapted bacteria, but to the heavy metal status. This means that the adaptation of these bacterial strains was at the level of the cells’ structure and/or their exopolymeric substances which immobilize the heavy metals and reduce their toxicity allowing their growth and removing hydrocarbons. It is then, a double-adaptation route, leading to concomitant removal of organics and heavy metals, which is of high importance from the practical point of view.