Global desalination capacity has surpassed 110 million cubic meters per day from over 21,000 operational plants across 183 countries, providing freshwater security to approximately 400 million people in water-scarce regions. However, desalination’s rapid expansion has generated a parallel environmental challenge: brine concentrate discharge. For every cubic meter of freshwater produced, conventional reverse osmosis (RO) desalination generates 1.5–2.0 cubic meters of hypersaline brine reject—containing salts, antiscalants, heavy metals, and biocides—at concentrations 2–4 times seawater salinity. Global brine production has reached approximately 142 million m³/day, posing significant marine ecosystem risks from hypersalinity, dissolved oxygen depletion, and chemical contamination in coastal discharge zones.
Brine Composition and Environmental Impacts
Desalination brine contains elevated concentrations of the feed water’s natural mineral composition—sodium, chloride, magnesium, sulfate, calcium, potassium—plus chemical additives introduced during the treatment process: antiscalants (polyphosphates, polycarboxylates), coagulants (ferric chloride, alum), biocides (chlorine, DBNPA), and antifoaming agents. Thermal desalination brines (MSF, MED) additionally contain corrosion products (copper, nickel) from heat exchanger materials and elevated temperatures (40–80°C at discharge).
Brine Management Technologies
The brine management technology hierarchy prioritizes volume minimization through high-recovery desalination systems before addressing residual concentrate disposal. High-recovery systems—including brackish water RO with concentrate recycling, membrane brine concentrators (MBC), and crystallizers—increase freshwater recovery from conventional 50% to 85–95%, dramatically reducing brine volumes at higher unit treatment costs. Zero Liquid Discharge (ZLD) systems combine RO high-recovery, MBC (achieving 80–90°C thermal evaporation), and crystallization to eliminate liquid brine discharge entirely, recovering dry salt or mineral crystals as saleable byproducts.
Eutectic freeze crystallization (EFC) offers a low-temperature alternative to thermal evaporation MBC, cooling brine to its eutectic temperature (-20°C to -40°C for seawater brine), simultaneously crystallizing ice (freshwater) and salts for separate recovery. EFC has a significantly lower energy footprint than thermal ZLD (3–5 kWh/m³ versus 15–25 kWh/m³ for thermal evaporation) and is particularly suited for cold-climate inland desalination of mining process water and industrial effluents.
Mineral Extraction from Brine: The Resource Recovery Opportunity
Desalination brine contains economically significant concentrations of minerals, creating an opportunity for resource recovery that partially offsets treatment costs. Seawater brine contains approximately 25–35 g/L sodium chloride, 3–4 g/L magnesium (as MgCl₂ and MgSO₄), 2–3 g/L sulfate, and trace concentrations of lithium (0.1–0.2 mg/L), potassium, bromine, rubidium, and uranium. At global brine production volumes of 142 million m³/day, the lithium extraction potential is approximately 14,000 tonnes/day—comparable to current global lithium mine production.
Selective ion exchange resins and electrodialysis systems developed by companies including Sumitomo Metal Mining, Evoqua Water Technologies, and MIT spinoff Lilac Solutions achieve lithium extraction efficiencies of 90%+ from seawater brine at energy costs of 10–15 kWh/kg Li. At lithium carbonate equivalent (LCE) prices of $13,000–20,000/tonne (2024), brine lithium extraction can generate substantial revenue streams that partially offset ZLD capital and operational costs.
Advanced brine management—combining ZLD with selective mineral extraction—is transitioning from a compliance obligation to a competitive advantage for desalination operators. Track water scarcity and climate-driven water stress trends affecting desalination demand at our US Climate Extremes Tracker, and explore water technology investment opportunities at the Sustainability Opportunities Hub.
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