A comparative life cycle assessment of eutectic freeze crystallisation and evaporative crystallisation for the treatment of saline wastewater

Two processes are compared by means of Life Cycle Assessment (LCA) to determine which one causes less environmental impact for the treatment of saline mining wastewater: Eutectic Freeze Crystallisation (EFC) or Evaporative Crystallisation (EC). EC is a well established technology whereas EFC is a new promising technology that has the potential to compete with EC but so far has not been built at industrial scale. As the processes yield by-product water in different states, system expansion was used to effect a fair comparison. The study considers three different geographical areas: South Africa, France and Europe, in order to identify the effect the source of energy has on the comparison. The energy efficiency of the chilling technology is studied parametrically. The LCA results show that for the modelled 4wt.% sodium sulphate solution, the EFC process is strongly preferred to EC regardless of the country energy mix, requiring 6–7 times less energy resources, but also that process energy integration and chiller energy efficiency can further reduce its environmental impacts significantly. ► Two desalination techniques, EFC and EC, were compared by Life Cycle Assessment (LCA). ► EFC process is strongly preferred to EC for the modelled 4wt.% Na2SO4 solution. ► EFC performs better for “global warming” and “non-renewable energy” impact categories. ► The environmental performance of EFC can be significantly reduced by heat integration.