Bioremediation of soil contaminated by hydrocarbons with the combination of three technologies: bioaugmentation, phytoremediation, and vermiremediation

Abstract

The aim of this study was to evaluate the removal of total petroleum hydrocarbons (TPH), alkanes and polycyclic aromatic hydrocarbons (PAH). Using phytoremediation (Panicum maximum) (G), vermiremediation (Pontoscolex corethrurus) (E), and bioaugmentation (encapsulated bacterial consortium) (B), individually and in combination, in contaminated soil by oil (PS) with sterilized (St) and non-sterilized treatments. Grass and earthworm biomass and the number of cocoons were determined after 112 days. The biomass of the P. maximum increased significantly from 1.7 to 2.6-folds overtime when it was cultivated in contaminated soil, either alone, in combination with earthworms, or with the bacterial consortium. After 112 days, the earthworm biomass significantly increased 2.0–2.6-folds with the highest increase in combination with the bacterial (PS+E+B), and its population increased from 4.9 to 8.5 times. P. corethrurus was not affected by the contamination so that deposition and hatch of cocoons (12–20) were observed. In sterilized treatments, no earthworms were detected after 112 days, which indicated that soil microorganisms are necessary for the earthworm’s survival and colonization. Most alkane and PAH removal occurred within 28 days; at 112 days, the alkane was 78.5–94.5% and the PAH 54.5–77.2% in non-sterilized soil. Panicum maximum treatment (SP+G) removed 74–99% of alkanes from C10 to C38 and also removed PAHs in 43–50% (2–3 rings), 46–90% (4 rings), 73% (5 rings), and 59% (6 rings) after 112 days. The combination of the grass with P. corethrurus and the bacterial increased the PAHs removal of 2 and 3 rings (54–62%), 4 rings (56–92%), 5 rings (80%), and 6 rings (70%) after 112 days. In non-sterilized treatments, the highest TPH removal was with earthworms plus bacterial (E+B) (86.4%), followed by E+G+B (82.7%) and B (82.6%). The use of endogeic earthworms and plants species from the same contaminated field can be an efficient alternative for increasing hydrocarbon removal.