Desalination of geothermal wastewaters by membrane processes: Strategies for environmentally friendly use of retentate streams

Abstract The paper presents the results of research on the desalination of geothermal wastewater for further environmentally friendly use of the concentrate streams obtained. Three geothermal waters previously used for heating purposes were desalinated. They are 1) lightly mineralised geothermal water (LM-GT), 2) moderately mineralised geothermal water (MM-GT) and 3) heavily-mineralised (HM-GT) geothermal water. The analysis is based on six technical experiments. The results indicated that geothermal wastewater desalination system can provide satisfactory fresh water which can be used for drinking or economic purposes. At the same time high-quality concentrate was obtained which can potentially be used for: 1) balneotherapy treatment – all concentrates; 2) drinking and inhalations – LM-GT; 3) therapeutic purposes – MM-GT. The raw MM-GT product can, for instance, also be considered as medicinal solution, like silica water, due to the high metasilicic acid content. Other concentrates analysed can also be recommended for the treatment of various diseases or cosmetic purposes based on their specific composition. The high boron concentration and elevated chromium content in MM-GT and HM-GT concentrates require additional treatment due to the requirements of some therapeutic instructions and this may limit the possibility of their use as base substance for cosmetic or therapeutic product.