Efficiency of a New Covering System for the Environmental Control of Biopiles Used for the Treatment of Contaminated Soils

Abstract

The objectives of the study were to first characterize a new covering system that allows the temperature inside the biopiles to be maintained at a level where biodeg-radation can take place despite unfavorable climatic conditions, and then second to develop a mathematical simulation of the biopile temperature profile knowing local meteorological conditions and the covering system used. A field study was undertaken with four 60 m3 biopiles of contaminated soil. The performance of conventional semipermeable black geotextile was compared with that of two sealed double polyethylene membrane systems (a white/white and a black/translucid polyethylene membrane). Heat transfer was favored or restricted by choosing the color of the polyethylene membranes and by the presence of an insulating air layer between the two polyethylene membranes. Results showed that the air layer allowed to increase soil temperature up to a range that could enhance biodegradation. For example, the biopile temperature was maintained above 10°C during fall conditions using the double membrane system, while it remained between of 5 to 10°C when using the conventional black geotextile. The white/white polyethylene membrane was considered to be the covering system offering the best performance because it allowed not only the temperature level to increase during fall conditions but also to reduce the temperature gradient within the biopile. A mathematical model describing the temperature profile within a biopile was developed, taking into account soil thermal properties, covering material properties, and local meteorological conditions. Close agreements between simulation results and actual measurements were found with maximum deviation within 2°C. This validated model can now be used to predict thermal profiles within biopiles without costly tests on site.