Use of natural sorbents for accelerated bioremediation of grey forest soil contaminated with crude oil

Due to the extensive oil extraction and transportation that occurs in oil-producing countries, many lands remain contam-inated because of accidental leakages. Despite its low cost and environmentally safe nature, bioremediation technology is not always successful, mainly because of the soil toxicity to the degrading microbial populations and plants. Here we re-port a three-year microfield experiment on the influence of natural sorbents of mineral (zeolite, kaolinite, vermiculite, di-atomite), organic (peat), carbonaceous (biochar) origin, and a mixed sorbent ACD (composed of granular activated carbon and diatomite) on the bioremediation of grey forest soil contaminated with weathered crude oil (40.1 g total petroleum hydrocarbons (TPH) kg-1). Optimal doses of the sorbents significantly accelerated bioremediation of petroleum -contaminated soil through bioaugmentation followed by phytoremediation. The main reason for the influence of the sor-bent amendments relied upon the creation of optimal conditions for the activation of hydrocarbon-utilizing bacteria and plant growth due to the reduction of soil toxicity, as well as maintaining an optimal pH and water-air regime in the soil. That happened because of reducing the soil hydrophobicity, increasing porosity and water holding capacity. The content of the TPH in the best samples (2 % biochar or ACD) reduced to their local permissible concentration accepted for remediated soils in the Russian Federation (<= 5 g kg-1) after two warm seasons compared to that after three warm sea-sons in the other samples. Although some sorbents decelerated biodegradation of highly condensed polycyclic aromatic hydrocarbons (PAHs, including benzo(a)pyrene) in the soil, the overall risk from the residual contaminants present in the remediated soil and plants was minimized. The final total content of the main PAHs in the sorbent-amended soils did not exceed the maximal permissible levels that are accepted in most EU countries (1000-40,000 mu g kg-1), and they did not accumulate in the aboveground phytomass of grasses in dangerous concentrations.

Automated summary

This study investigates the influence of different natural sorbents on the bioremediation of contaminated soil. The optimal doses of sorbents significantly accelerate the bioremediation of petroleum-contaminated soil, reducing the toxicity and residual contaminants in the soil and plants.