AQUIFER BIOTHERMOREMEDIATION USING HEAT PUMPS: SOUND THEORETICAL BASIS AND RESULTS ON THERMAL, GEOCHEMICAL AND BIOLOGICAL IMPACTS ON AQUIFERS

Geothermal heat pumps have been operated on aquifer over the past thirty years. Currently, these systems constitute a major sector of renewable energy development. However, this development is accompanied by several difficulties at scientific, technical and administrative levels, to describe short and long term interactions with aquifers, at both the local and regional scale, especially close to urbanized or industrialized areas. As a typical example, the long-term use of groundwater heat pumps for air conditioning of homes or buildings can induce significant increases in temperature of the aquifer, if, for given groundwater flow direction and rate, there is an imbalance between the demands for cooling and heating. Therefore, the aquifer (groundwater and sediments) can be affected. In fact, it is expected that a wide variety of geochemical reactions and microbiological changes with variable intensity should occur which depends on the sediment characteristics and hydrogeological background. The presence of organic pollutants in the aquifer can amplify these phenomena. The predictable results may progressively be: (i) precipitation, which reduces the porosity of the aquifer and/or the well productivity, (ii) an inappropriate temperature for the use of groundwater heat pumps for air conditioning, but also and especially (iii) pollutant bioremediation, which has a beneficial impact on the aquifer. Under certain conditions, this bio-thermo-remediation can be considered as an attractive option for some contaminated aquifers, taking into account the fact that, administratively in Europea