Collaborative Learning Supported by a Brownfield Remediation Case Study

Abstract

Industrial activity of the past has created several contaminated brownfields, which, particularly in remote areas, are difficult to remedy from an economic point of view. In this project, a novel approach for in-situ removal of mineral hydrocarbons from soil was investigated. The underlying concept was to flush contaminated soil with emulsions of plant oil in water, to suck off the contaminant-laden emulsion from the ground water level and to separate oil and water using oil-binding non-wovens. The process development was carried out in a research project, where students from a university of applied sciences and from a technical college were involved. Based on the specific case of brownfield remediation, a collaborative learning experience for the students was created. Environmental protection and safeguarding is a topic of high interest to students, and there was a high motivation to obtain results. Due to the COVID19 pandemic, most collaboration was handled remotely via virtual teams.

The chosen brownfield for this case study was a former petroleum refinery site in Lower Austria, were up to 40 g/kg of mineral hydrocarbons were found in the soil in the non-saturated zone. Mineral hydrocarbons show good solubility in plant oils. Emulsions of 5–10% of rapeseed oil in water were prepared and chosen, to have better wettability of the ground materials and lower viscosity. The goal was to develop a process that can extract 80–90% of mineral hydrocarbons in the soil, and which leaves only a minor fraction of the plant oil in the soil.

When the trials, which were carried out in the lab and in the field, showed that the permeability of soil is very low, it was decided to develop a prototype for on-site soil washing. The soil of the chosen brownfield is partly made from gravel and sand, where an in-situ flushing process is possible. However, there is also clay, and that material hardly lets water or emulsion penetrate. For the on-site washing process, a laboratory-scale prototype was developed. It was built by the Linzer Technikum (LITEC) and tested with different soils at the university of applied sciences.

The prototype could be built by LITEC, with an extraction vessel made of steel and a mixer. Trials were done to determine the degree of extraction of mineral oil and the fraction of plant oil that is not recaptured. 500 g of soil were mixed intensely with 500 g of solvent (water and emulsions). Table 1 presents the results for sand and clay.

The process of washing out mineral hydrocarbon contamination from soil was found to show a good potential. The ground material should be sieved to remove coarse material (>10 mm), and the finer fraction can be subjected to the washing of plant oil in water, where the plant oil fraction can be between 5 and 50%, depending on degree of contamination. To reduce the amount of non-recaptured plant oil, a second and third washing cycle with a lower oil fraction, or with pure water, can be applied.