Bioremediation of clayey soil contaminated with crude oil: comparison of dynamic and static biopiles in lab-scale

Abstract

Bioremediation of aged and newly clayey soil contaminated with crude oil was investigated in lab-scale using two different strategies (biostimulation-BIOS and bioaugmentation-BIOA), also simulating two different technological options: dynamic biopile (M) and static biopile with forced aeration (B). The inoculum used for bioaugmentation was obtained from the aged contaminated soil. The treatments were performed in triplicates and included one control (original contaminated soil-CONT). The treatments were monitored with soil sampling obtained after 0, 24, 59 and 121 days when the populations of total heterotrophic microorganism (THM), total fungi (TF), and oil-degrading microorganism (ODM) as well as the extracted total petroleum hydrocarbons (TPH) and the 16 polycyclic aromatic hydrocarbons (PAH) prioritized by U.S. EPA were analyzed by gas chromatography. It was observed a trend for reduction of the microbial population density from 0 to 121 days. As expected, the population densities of THM and ODM were much higher in bio-augmented soils in both technologies (BIOA-m and BIOA-b) at day 0. However, after 121 days, the superiority in THM density was observed only in the bioreactor simulating static biopile with forced aeration (BIOA-b). Regarding treatment efficiency, the static biopile with forced aeration performed better in the removal of TPH when associated with bioaugmentation (BIOA-b), being equivalent to the microcosms (simulating dynamic biopile) for the other treatments (CONT and BIOS). For PAH, the superiority of the bioreactor was less conspicuous but observed in both bioremediation strategies (biostimulation BIOS-b and bioaugmentation BIOA-b). The results suggested that regarding TPH, the strategy of bioaugmentation was superior to biostimulation and that the bioreactor (simulating static biopile with forced aeration) reached better contaminant reductions than the microcosm (simulating dynamic biopile). Clayey soil contaminated with crude oil poses big challenges for the bioremediation, due to the texture of the soil favouring adsorption of organic contaminants and due to the complex crude oil composition. The bioprocesses are slow, cleavage of larger molecules are likely to generate smaller hydrocarbons and therefore the elimination of the toxicity is very slow, which may require longer periods and auxiliary tools, such as surfactants.