Remediation of soils contaminated with total petroleum hydrocarbons through soil washing with surfactant solutions

Soil fulfils vital functions for life on Earth and so, just like water and air, its protection from all sources of contamination is a major concern. However, the extensive use of petroleum derived products, either as energy sources or as commodities, leads to important environmental liabilities. Ex situ soil washing is a technology to concentrate contaminants, allowing soil cleaning and the reuse of extracted petroleum derived products. This work focuses on the optimization of ex situ soil washing process using surfactants, introducing an evaluation of the washing solution recycling and its after use safe disposal, promoting the reduction of raw materials, energy and water resources costs. Two surfactants, sodium dodecyl sulphate (SDS) and polyoxyethylene sorbitan monooleate (Tween 80), were tested in the decontamination of an artificially contaminated soil with engine lubricant oil waste. The optimization of the washing conditions, such as stirring speed, liquid-solid ratio, number of washing stages, and surfactant concentration, was carried out using a design of experiments (DOE) software, so that the maximum extraction efficiency of total petroleum hydrocarbons (TPHs) was achieved. A TPH removal efficiency of (80.7 +/- 3.2)% was obtained with Tween 80 after 5 h of washing and (90.7 +/- 2.8)% with SDS after 2 h at 200 rpm on an orbital shaker with a liquid to solid ratio (L/S) of 15. The potential for reuse of the washing solutions was evaluated. Finally, the discharge of the washing solution was considered using activated carbon to remove the surfactants and ensure its safe disposal.

Automated summary

Soil plays a vital role in supporting life on Earth, and its protection from contamination is of great importance. This study focuses on optimizing the ex situ soil washing process using surfactants, aiming to reduce the costs of raw materials, energy, and water resources. Two surfactants, SDS and Tween 80, were tested for decontaminating oil-contaminated soil, and the washing conditions were optimized using a design of experiments software. The results showed that Tween 80 achieved a TPH removal efficiency of (80.7 +/- 3.2)% after 5 hours of washing, while SDS achieved (90.7 +/- 2.8)% after 2 hours at 200 rpm. The potential for reusing the washing solutions was evaluated, and the safe disposal of the washing solution was ensured by using activated carbon to remove the surfactants.