Salinity gradient energy capture by reverse electrodialysis (SGE-RED) can play a part in the shift away from fossil fuels towards a carbon-neutral renewable energy supply; however, like other renewable power technologies, SGE-RED environmental soundness hinges on its whole life-cycle environmental loads. This study surveys the Life Cycle Assessment of SGE-RED technology. We quantified (i) the environmental loads per 1.0 kW h generated by a stand-alone RED unit and then, (ii) the environmental burdens related to the energy provision from an up-scaled RED system to a seawater reverse osmosis (SWRO) desalination plant per 1.0 m³ of desalted water. The RED unit's assessment results show that SGE-RED is environmentally competitive with other renewable sources such as photovoltaics or wind. Regarding the component's contribution analysis, the spacer's fabric material drives the RED environmental burden as the number of cell pairs is increased. The scaling-up of the RED unit, however, improves its full environmental profile. Preliminary results of SGE-RED combination with a SWRO plant suggest that the energy harnessed from SWRO's concentrate streams by RED could enhance the environmental performance of the desalination industry. Further research is required to identify SWRO-RED design alternatives that minimize the life cycle burden while still yielding good technical and economic performance.

Salinity gradient energy harvesting by reverse electrodialysis (RED) is a promising renewable source to decarbonize desalination. This work surveys the potential reduction in energy consumption and carbon emissions gained from RED integration in 20 medium-to-large-sized seawater reverse osmosis (SWRO) desalination plants spread worldwide. Using the validated RED system’s model from our research group, we quantified the grid mix share of the SWRO plant’s total energy demand and total emissions RED would abate (i) in its current state of development and (ii) if captured all salinity gradient exergy (SGE). Results indicate that more saline and warmer SWRO brines enhance RED’s net power density, yet source availability may restrain specific energy supply. If all SGE were harnessed, RED could supply ~40% of total desalination plants’ energy demand almost in all locations, yet energy conversion irreversibility and untapped SGE decline it to ~10%. RED integration in the most emission-intensive SWRO plants could relieve up to 1.95 kg CO₂-eq m⁻³. Findings reveal that RED energy recovery from SWRO concentrate effluents could bring desalination sector sizeable energy and emissions savings provided future advancements bring RED technology closer to its thermodynamic limit.

The chemical potential difference at the discharge points of coastal Wastewater Treatment Plants (WWTPs) uncovers the opportunity to harness renewable salinity gradient energy (SGE). This work performs an upscaling assessment of reverse electrodialysis (RED) for SGE harvesting of two selected WWTPs located in Europe, quantified in terms of net present value (NPV). For that purpose, a design tool based on an optimization model formulated as a Generalized Disjunctive Program previously developed by the research group has been applied. The industrial scale-up of SGE-RED has already proven to be technically and economically feasible in the Ierapetra medium-sized plant (Greece), mainly due to a greater volumetric flow and a warmer temperature. At the current price of electricity in Greece and the up-to-date market cost of membranes of 10 EUR/m², the NPV of an optimized RED plant in Ierapetra would amount to EUR117 thousand operating with 30 RUs in winter and EUR 157 thousand for 32 RUs in summer, harnessing 10.43 kW and 11.96 kW of SGE for the winter and summer seasons, respectively. However, in the Comillas facility (Spain), this could be cost-competitive with conventional alternatives, namely coal or nuclear power, under certain conditions such as lower capital expenses due to affordable membrane commercialization (4 EUR/m²). Bringing the membrane price down to 4 EUR/m² would place the SGE-RED’s Levelized Cost of Energy in the range of 83 EUR/MWh to 106 EUR/MWh, similar to renewable sources such as solar PV residential rooftops.