Consistency Testing of an Integrated SWRO–Brine Valorization Architecture: Alkalinity as the Binding Constraint
- 1Independent Researcher
Abstract
Integrated seawater reverse osmosis (SWRO) with brine valorization is widely proposed as a route to lower energy and near-zero liquid discharge, but such architectures are rarely tested against the physical bounds their stages must obey. Here a consistency-testing framework is applied to an architecture combining subsurface intake, isobaric energy recovery, membrane brine concentration, selective Ca/Mg precipitation and mechanical-vapor-compression crystallization. Each subsystem is checked against a thermodynamic or stoichiometric constraint rather than an assumed value. The concentrator duty commonly assumed in this class of study, 0.5–1.0 kWh m−3 of brine, lies at or below the least work of separation for that feed, 0.94 kWh m−3. A bounded estimate from that minimum and a 25–55% second-law efficiency gives 1.7–3.8 kWh m−3, raising the modeled total specific energy consumption to a median of 13.1 kWh m−3. Magnesium recovery is limited by alkalinity rather than by magnesium. The base required carries 10.0 kg CO2 per cubic meter of permeate in embodied carbon, roughly double the plant's grid emissions, or 27 kWh m−3 if generated electrochemically. Lime dosing releases 5.3 times more calcium than the carbonate step removes, so the train does not close. Costing those reagents explicitly is decisive: at $1.70 m−3 they exceed the $1.25 m−3 mineral credit, and Monte Carlo propagation (300,000 samples) gives a net levelized cost of $2.20 m−3 against $0.76 m−3 for conventional SWRO. Closing the calcium balance costs $0.44 m−3; above $0.069 kWh−1 no on-site base can close the loop, because the reversible limit of water dissociation binds.
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BibTeX
@misc{sandler2026consistency,
title = {{Consistency Testing of an Integrated SWRO–Brine Valorization Architecture: Alkalinity as the Binding Constraint}},
author = {Leon Sandler},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15011006/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15011006/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Consistency Testing of an Integrated SWRO–Brine Valorization Architecture: Alkalinity as the Binding Constraint
AU - Leon Sandler
PY - 2026
DA - 2026/10/25
PB - ChemRxiv
DO - 10.26434/chemrxiv.15011006/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15011006/v1
AB - Integrated seawater reverse osmosis (SWRO) with brine valorization is widely proposed as a route to lower energy and near-zero liquid discharge, but such architectures are rarely tested against the physical bounds their stages must obey. Here a consistency-testing framework is applied to an architecture combining subsurface intake, isobaric energy recovery, membrane brine concentration, selective Ca/Mg precipitation and mechanical-vapor-compression crystallization. Each subsystem is checked against a thermodynamic or stoichiometric constraint rather than an assumed value. The concentrator duty commonly assumed in this class of study, 0.5–1.0 kWh m−3 of brine, lies at or below the least work of separation for that feed, 0.94 kWh m−3. A bounded estimate from that minimum and a 25–55% second-law efficiency gives 1.7–3.8 kWh m−3, raising the modeled total specific energy consumption to a median of 13.1 kWh m−3. Magnesium recovery is limited by alkalinity rather than by magnesium. The base required carries 10.0 kg CO2 per cubic meter of permeate in embodied carbon, roughly double the plant's grid emissions, or 27 kWh m−3 if generated electrochemically. Lime dosing releases 5.3 times more calcium than the carbonate step removes, so the train does not close. Costing those reagents explicitly is decisive: at $1.70 m−3 they exceed the $1.25 m−3 mineral credit, and Monte Carlo propagation (300,000 samples) gives a net levelized cost of $2.20 m−3 against $0.76 m−3 for conventional SWRO. Closing the calcium balance costs $0.44 m−3; above $0.069 kWh−1 no on-site base can close the loop, because the reversible limit of water dissociation binds.
ER -