Table of Contents
The Research Breakthrough
In September 2026, a Tsinghua research group published results in Environmental Science & Technology describing a subnano-confined membrane (SCM) — built by modifying a commercially available nanofiltration membrane with an ion exchange polymer — that concentrated brine to near saturation in a single electrodialysis stage and went on to crystallize sodium chloride by the third stage. NaCl saturation sits around 265 g/L at the temperatures ZLD plants actually run at. Conventional ED ion exchange membranes typically stall out with concentrate TDS in the 100,000–150,000 mg/L range, so the gap is significant.
The useful thing about this result is that the base membrane is a commercial product, not a laboratory curiosity, which matters if the technology is ever to be manufactured at scale.
For system engineers the interesting question is not whether the lab result is sound — it is peer-reviewed in one of the field’s main journals — but whether it survives contact with real industrial feed, and what instrumentation is needed to control and validate the process. That second question is where we have a direct interest.
Understanding the Science: Why Subnano-Confinement Works
The Water Transport Problem in Conventional ED
In an electrodialysis stack, an applied electric field drives ions from the dilute compartment through ion exchange membranes into the concentrate compartment. Ions do not travel alone. They take part of their hydration shell with them, and osmotic effects move additional water across. That water dilutes the concentrate, and at some concentration the water flux matches the ion flux — which is where conventional ED stops, typically in the 100,000–150,000 mg/L range.
The Subnano-Confined Membrane Solution
The SCM attacks the problem at the membrane structure. Sub-nanometre channels force a strong dehydration effect: as ions pass through, the confined geometry strips a substantial share of their hydration water, so less water arrives in the concentrate compartment per unit of salt. The result is a much higher achievable concentration in the same single stage.
The paper reports near-saturated brine from a single stage — a concentration that would take two or three conventional ED stages — with salt crystallizing at the third stage of operation. In principle, that removes or shrinks the thermal crystallization step in a ZLD train.
Implications for ZLD System Design
Simplified Treatment Train
If single-stage ED can approach saturation and crystallize salt by the third stage, the train gets shorter. A conventional hybrid train looks like: pretreatment → RO → ED stage 1 → ED stage 2 → MVR evaporation → crystallization. An SCM-ED route could look like: pretreatment → SCM-ED (1–3 stages) → centrifuge/drying. Fewer unit operations means less capital, less energy and less plot space.
Energy Savings
Electrodialysis concentration in general consumes a fraction of what thermal evaporation does, because it is moving ions rather than boiling water. Pushing the membrane stage closer to saturation transfers work from the most energy-intensive step in the train to one of the cheapest, which is the real prize here. Existing ED pilots give a sense of what the technology class can do: a pilot study published in Desalination concentrated seawater RO brine to 245 g/L NaCl using monovalent-selective electrodialysis, so near-saturation operation in ED is not unprecedented — doing it in a single stage with a modified commercial membrane is the new part.
Monitoring Requirements
An SCM-ED process needs conductivity data at four points to be controllable:
- Feed conductivity: baseline TDS for calculating concentration factor and current efficiency
- Diluate conductivity: confirms ion removal and permeate quality
- Concentrate conductivity: the critical reading — it has to track TDS accurately at the top of the range, where the conductivity-to-TDS relationship bends
- Crystallizer slurry conductivity: confirms saturation conditions for crystal growth
Shanghai ChiMay’s 0–500,000 mg/L auto-ranging meters cover that whole trajectory from one instrument model, which is what makes a single-instrument architecture feasible. Accuracy at 150,000 mg/L and above is the part that separates a usable meter from a wide-range one.
Challenges for Commercial Deployment
Membrane Fouling
The paper is explicit that pretreatment discipline is what keeps ED operation stable. SCM membranes may be more fouling-sensitive than conventional membranes, because sub-nanometre channels are easier to block with organics or precipitated scale. Turbidity testers and COD sensors at the feed point catch fouling precursors before they become membrane damage.
Scale-Up Considerations
Lab demonstrations use small membrane areas and clean feed. Commercial SCM-ED has to cope with variable feed composition, membrane quality consistency across large areas, years of continuous operation, and integration with whatever pretreatment and thermal equipment already exists. Real-time conductivity data is how operators see deviation from design performance early enough to act on it.
Validation and Quality Assurance
If you are buying an SCM-ED system, you will want independent measurement to verify performance rather than the vendor’s own numbers. Shanghai ChiMay conductivity meters ship with ISO calibration certificates and NIST-traceable test reports — documentation you can hand to your auditor.
The Path Forward
Since SCM-ED is still on the laboratory-to-commercial path, we cannot sell anyone a control strategy for a plant that does not exist yet. What we can say is that the measurement requirements it creates are already within the range of standard instruments: wide measurement range, stable accuracy at high TDS, corrosion-resistant wetted materials and direct Modbus integration with the ED power supply. If the technology lands, the instrumentation is not the bottleneck.
Buy the sensor, own the outcome.
Laboratory Results vs. Commercial Reality: What ZLD Operators Need to Know
The Laboratory Achievement
The Gao et al. paper (Environmental Science & Technology, September 8, 2026) is worth reading in full. The relevant findings for anyone tracking ZLD costs:
- The SCM was made by modifying a commercially available nanofiltration membrane with an ion exchange polymer, so the base material is accessible
- High brine concentration was achieved in a single ED stage, reducing the number of concentration stages needed
- Crystallized NaCl was obtained at the third stage, showing that solid salt can come out of the membrane train rather than only from a crystallizer
- The membrane’s ultralow water permeance and the reduced hydration number of transported ions are the mechanism behind the improvement
Challenges for Scale-Up
Four things stand between this result and a commercial plant:
Membrane manufacturing at scale: lab-prepared membranes have to become consistent products across large areas without losing channel structure.
Long-term stability: the lab ran for laboratory timescales. Commercial ZLD requires 3–7 years of continuous service, with the channels resisting fouling, chemical attack and mechanical stress.
Feed water variability: lab work uses controlled composition. Industrial feed carries mixed salts, organics and trace contaminants that will not behave like a clean NaCl solution.
System integration: an SCM-ED stage has to be engineered into a train with existing pretreatment upstream and thermal equipment downstream.
The Monitoring Infrastructure That SCM-ED Requires
Whatever the timeline, the monitoring requirement is consistent with what standard instrumentation already provides:
Wide-range conductivity: the process moves from roughly 30,000 mg/L feed to near-saturated concentrate. Shanghai ChiMay’s 0–500,000 mg/L auto-ranging covers it in one model.
Resolution for optimization: optimisation platforms need conductivity data with enough resolution and update frequency to see trends. Modbus output delivers sub-second updates at ±1 percent accuracy.
Corrosion-resistant materials: concentrated mixed-salt brine attacks wetted parts. Titanium bodies with PEEK insulators are built for it.
Digital integration: SCM-ED needs tight coupling between conductivity measurement and ED stack power control. Modbus RTU/TCP handles that without gateway hardware.
Timeline and Market Implications
Technology transitions of this kind usually run 3–5 years from laboratory demonstration to full commercial deployment: pilot-scale validation first, then commercial pilot with an industrial partner, then wide deployment. Operators planning ZLD investments today should assume conventional hybrid trains for the current project and treat SCM-ED as a reason to specify instruments that will still be adequate if the membrane stage absorbs more of the concentration duty later.
That is a low-risk position to take, because the instruments required for near-saturated brine are the ones you would want at the membrane-thermal interface anyway.
Sources
- Gao, T. et al., “Subnano-Confined Membrane Enables Efficient Brine Concentration and Salt Crystallization in Electrodialysis,” Environmental Science & Technology, September 8, 2026. https://doi.org/10.1021/acs.est.6c06151
- Reig, M. et al., “Concentration of NaCl from seawater reverse osmosis brines for the chlor-alkali industry by electrodialysis,” Desalination 342 (2014) 107–117.
- Mordor Intelligence, “Zero Liquid Discharge (ZLD) Systems Market (2026–2031),” September 2026. https://www.mordorintelligence.com/industry-reports/zero-liquid-discharge-zld-systems-market
- Aquatech, “Aquatech Acquires FTS H2O to Advance Energy-Efficient Lithium Processing, Zero Liquid Discharge, and Brine Mining,” May 2026. https://www.aquatech.com/blog/aquatech-acquires-fts-h2o-to-advance-energy-efficient-lithium-processing-zero-liquid-discharge-and-brine-mining
- Stratview Research, “Zero Liquid Discharge Systems Market Analysis 2025–2032.” https://www.stratviewresearch.com/market-reports/zero-liquid-discharge-systems-market.html
About the Author: Prepared by the Shanghai ChiMay application engineering team, which works on monitoring architecture for membrane brine concentration and crystallisation stages.
