Geothermal water and energy are used for various purposes: heating and cooling buildings, drying building materials and agricultural products, rearing livestock, thermophilic fish farming, soil heating, recreation and balneology (Ney, 1997; Lund, 2010; Lund et al., 2005, 2010; Bujakowski, 2005, 2010; Kepmska, 2005). In some cases, after heat recovery, geothermal water is introduced into the water supply network if it satisfies applicable physico-chemical and health requirements (Bujakowski and Tomaszewska, 2007; Tomaszewska, 2009; Bujakowski et al., 2010; Tomaszewska and Pajak, 2010).
A model procedure for the management of geothermal water and energy should involve their comprehensive utilization in order to optimize the operation of geothermal systems. The studies currently underway focus on improving the economic performance of existing facilities and streamlining their operation.
Theoretical research concerning the opportunities for geothermal water desalination, including consideration of variability in the physical properties and chemical composition of the geothermal waters extracted in Poland, started in 2008. A project was developed at that time which included technology that has now gone into the pilot stage. One of the main research topics is the evaluation of the feasibility of using geothermal water resources in order to enhance drinking water management through the use of desalinated water (permeate). Another research field is related to the assessment of whether the water desalination technology can be used in order to reduce corrosion and mineral precipitation in geothermal installations. It appears that the mixing of raw geothermal water cooled in heat exchangers with the permeate in suitable proportions may improve the performance of plant. At the same time the recovery of mineral substances from the concentrate may be of balneological and economic importance (Bujakowski and Tomaszewska, 2007; Tomaszewska, 2009; Bujakowski et al., 2010).
Pilot water desalination tests have been conducted on a semi-industrial scale at two geothermal facilities (first in Podhale Basin and second in Polish Lowlands). In pilot tests the renewable energy (heat) is used for drinking water production:
• the use of geothermal water heat for optimal operation of RO at 30°C, since geothermal water can secure this level of temperature;
• geothermal and solar energy (heat) planned to be used to concentrate retentate obtained from RO, which is a second level recovery of distillate. This does not exclude to gain in this way concentrate for commercial purposes such as medical, therapeutics and cosmetics.
Geothermal energy will be therefore used for production of drinking water in two stages: first – the use of geothermal waters in a membrane system (optimum temperature of geothermal water for desalination processes) and second – concentrate of retentate (using water temperature of 80°C). In the second case geothermal energy (heat) will be supported by solar energy.