Evaluation of constraints in bioremediation of weathered hydrocarbon-contaminated arid soils through microcosm biopile study

This research investigated the factors influencing bioremediation (biopile) of arid soils contaminated by weathered hydrocarbons. Five soils were thoroughly characterised to determine total petroleum hydrocarbons (TPH), their physicochemical properties and microbial diversity. Identified biopile-limiting factors are to be elevated petroleum hydrocarbon concentrations, high electrical conductivity and the magnitude of the recalcitrant hydrocarbon fraction. To optimise the biopile parameters, microcosm study was conducted which showed significant TPH reduction in three of five soils (BP-1, BP- 2 and BP-4) but not in other two (BP-3 and BP-5), where BP-3 had a very high hydrocarbon concentration (123,757 mg kg^-1) and BP-5 had a high proportion of recalcitrant hydrocarbons (>70 % of C₂₉). Highest TPH removal (68 %) occurred in soil BP-2 and the lowest (5 %) in soil BP-3 over 56 days. Surfactant (Triton) addition, nutrient amendment or the soil dilution did not improve TPH degradation in soils BP-3 and BP-5. Phylogenetic analysis conducted during the remediation process found that hydrocarbon concentration and hydrocarbon fraction exerted the main effect on bacterial abundance, diversity and assemblage composition. At lower concentrations (~1000–4000 mg kg^-1), bacterial diversity and abundance increased significantly, whilst decreased in higher concentrations. Although high TPH content and detection of TPH degraders, TPH biodegradation is limited in soil (BP-5) due to the presence of less soluble hydrocarbon fraction which indicated low TPH bioavailability (~7 %). Biopile could be applied as a technology to remediate three soils (BP-1, BP-2 and BP- 4) but further modification of the biopile treatments required for other two soils BP-3 and BP-5.

Keywords
Bioremediation; Biopile; Weathered hydrocarbons; Microbial diversity; Pyrosequencing; TPH