Nature-Based Solutions for Restoring an Agricultural Area Contaminated by an Oil Spill

Abstract

A feasibility study is presented for a bioremediation intervention to restore agricultural activity in a field hit by a diesel oil spill from an oil pipeline. The analysis of the real contaminated soil was conducted following two approaches. The first concerned the assessment of the biodegradative capacity of the indigenous microbial community through laboratory-scale experimentation with different treatments (natural attenuation, landfarming, landfarming + bioaugmentation). The second consisted of testing the effectiveness of phytoremediation with three plant species: Zea mays (corn), Lupinus albus (lupine) and Medicago sativa (alfalfa). With the first approach, after 180 days, the different treatments led to biodegradation percentages between 83 and 96% for linear hydrocarbons and between 76 and 83% for branched ones. In case of contamination by petroleum products, the main action of plants is to favor the degradation of hydrocarbons in the soil by stimulating microbial activity thanks to root exudates. The results obtained in this experiment confirm that the presence of plants favors a decrease in the hydrocarbon content, resulting in an improved degradation of up to 18% compared with non-vegetated soils. The addition of plant growth-promoting bacteria (PGPB) isolated from the contaminated soil also promoted the growth of the tested plants. In particular, an increase in biomass of over 50% was found for lupine. Finally, the metagenomic analysis of the contaminated soil allowed for evaluating the evolution of the composition of the microbial communities during the experimentation, with a focus on hydrocarbon- oxidizing bacteria.

Keywords: ecosystem restoration; farming area; hydrocarbon biodegradation; next-generation sequencing; phytoremediation; plant growth promoting bacteria.

Figure 1

Map of the area under study with the indication of the sampling points, the trace of the oil pipeline and the break-in point (black cross).

Figure 2

List of the 20 isolated strains. Biological safety levels (according to three different database: “Classification of Prokaryotes—Bacteria and Archaea—into Risk Groups”, TRBA 466; www.baua.de/abas, accessed on 20 February 2022; Leibniz Institute DSMZ, German Collection of Microorganisms and Cell Cultures GmbH https://www.dsmz.de/, accessed on 20 February 2022; BCCM: Belgian Coordinated Collections of Micro-organisms https://bccm.belspo.be/, accessed on 20 February 2022)) are also shown.

Figure 3

Evaluation of the residual content C9–C18 (a), C19–C36 (b), linear (c) and branched (d) fractions) after the different treatments (NA, L, LB) at the time of collection (30, 60, 90, 120, 180 days) in comparison to the initial content (t0). NA = natural attenuation, L = Landfarming, LB = landfarming + bioaugmentation.

Figure 4

NGS Ion Torrent analysis of all the samples from the three treatments (NA, L, LB) at 30, 90 and 180 days. NA = natural attenuation, L = landfarming, LB = landfarming + bioaugmentation.

Figure 5

Description of the growth-promoting properties shown by the two strains CG13 and CG16 chosen as inoculum for the phytoremediation tests.

Figure 6

Comparative growth of the aerial part of Lupine (a), Alfalfa (b) and Corn (c) on the contaminated soils without (orange bars) and with (light blue bars) the inoculation of the two isolated and characterized PGPB strains with respect to control soil not contaminated (grey bar).

Figure 7

Concentration of the residual hydrocarbons in the four soils, B1, B2, B3 and B4, with the comparison between the starting soil (Ss, light blue bars), the non-vegetated soils (Snv, orange bars) and the vegetated ones (Sv, dark green bars) with Z. mays.