Efficiency of a new covering system for the environmental control of biopiles used for the treatment of contaminated soils

The objectives of the study were to first characterize a new covering syste m that allows the temperature inside the biopiles to be maintained at a lev el where biodegradation can fake place despite unfavorable climatic conditi ons, and then second to develop a mathematical simulation of the biopile te mperature profile knowing local meteorological conditions and the covering system used. A field study was undertaken with four 60 m(3) biopiles of con taminated soil. The performance of conventional semipermeable black geotext ile was compared with that of two sealed double polyethylene membrane syste ms (a white/white and a black/translucid polyethylene membrane). Heat trans fer was favored or restricted by choosing the color of the polyethylene mem branes and by the presence of an insulating air layer between the two polye thylene membranes. Results showed that the air layer allowed to increase sa il temperature up to a range that could enhance biodegradation. For example , the biopile temperature was maintained above 10 degrees C during fall con ditions using the double membrane system, while it remained between of 5 to 10 degrees C when using the conventional black geotextile. The white/white polyethylene membrane was considered to be the covering system offering th e best performance because if allowed not only the temperature level to inc rease curing fall conditions but also to reduce the temperature gradient wi thin the biopile. A mathematical model describing the temperature profile w ithin a biopile was developed, taking into account sail thermal properties, covering material properties, and local meteorological conditions. Close a greements between simulation results and actual measurements were found wit h maximum deviation within 2 degrees C. This validated model can now be use d to predict thermal profiles within biopiles without costly tests on site.