Comparative environmental life cycle assessment of alternative osmotic and mixing dilution desalination system configurations

Abstract

An environmental life cycle assessment (LCA) methodology was applied to compare the conventional SWRO desalination process to two contemporary low-pressure membrane desalination processes: an osmotic dilution desalination (ODD) and a mixing dilution desalination (MDD). The ODD process combines a forward osmosis (FO) membrane and a low-pressure RO membrane (LPRO) in a hybrid (FO-RO) configuration. The MDD process couples the ultrafiltration (UF) with LPRO in a hybrid UF-RO configuration. SimaPro™ was used to conduct the LCA study. CML environmental impact assessment method was used to evaluate 11 environmental impact categories. Results from LCIA reveal the strong dependency of environmental impacts on the clean in place (CIP) process in dilution desalination systems while the energy flow in the standalone RO shows almost similar levels of dependency of environmental impacts instead of CIP process. Overall, the ODD process with FO-RO hybrid membrane technology has the highest environmental impact. The normalised comparison LCIA indicates that standalone RO has the lowest total environmental impacts as the fossil fuel is considered as the main source of power generator. Compared to conventional SWRO, the MDD process coupled with hybrid UF-RO technology had a lowest contribution to global warming and ozone layer depletion but had higher impacts to marine and aquatic resource depletion. Scenarios substituting the conventional with renewable energy sources to power the water treatment options favoured the MDD process coupled with hybrid UF-RO technology and prove the hybrid UF-RO process as the most environmentally favourable comparing to the conventional SWRO and hybrid FO-RO.