Abstract
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.
Highlights
The rising water demand and the steady decline in conventional water resources are urging the use of non-conventional ones, as desalinated, re-used or reclaimed water [1,2]
The specific energy consumption (SEC)—the energy consumed per cubic meter of water desalted—of current state-of-the-art seawater reverse osmosis (SWRO) plants ranges from 2.5–6.0 kWh m−3 depending on several site-specific factors such as seawater composition and temperature, permeate quality standards, brine management, production capacity and reverse osmosis (RO) configuration [6,7]
The site-specific factors affecting the reverse electrodialysis (RED) system’s technical performance are (i) the properties—i.e., ionic composition, concentration and temperature—and (ii) availability of the feed streams that, alongside (iii) the energy needed to power desalination—SEC, in kWh per m3 of desalted water produced—and (iv) the energy source of the SWRO desalination plant—i.e., the local electricity mix—will bound the energy and emissions RED could save to desalination plants
Summary
The rising water demand and the steady decline in conventional water resources are urging the use of non-conventional ones, as desalinated, re-used or reclaimed water [1,2]. Even though membrane technology’s advances, installation of energy recovery devices and use of more efficient pumps have well declined the energy to drive desalination over the last four decades [4,5,6], seawater reverse osmosis (SWRO) desalination remains an energy-intensive source of. The specific energy consumption (SEC)—the energy consumed per cubic meter of water desalted—of current state-of-the-art SWRO plants ranges from 2.5–6.0 kWh m−3 depending on several site-specific factors such as seawater composition and temperature, permeate quality standards, brine management, production capacity and reverse osmosis (RO) configuration [6,7]. Given that global desalination capacity is projected to increase at a steep pace in the coming years [1,3], and fossil fuels dwarf the current electricity portfolio [8], the shift to low-emissions decentralized renewable power sources with little water needs is decisive in moving forward the gradual decarbonization of the desalination industry
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