The core desalination technology of the platform: a semi-permeable membrane driven by pressure, with recovery, salt rejection, energy and concentrate all derived by real engines.
- Active
- Available
Two-Pass Reverse Osmosis 2P-RO / TPRO
A second RO pass on the first permeate, optionally with interstage recycle, to reach a permeate quality a single pass cannot deliver economically.
Overview
A second RO pass on the first permeate, optionally with interstage recycle, to reach a permeate quality a single pass cannot deliver economically.
How it works
Separation mechanism and feed window. Feed is the first-pass permeate, which is already very low in salt — so the second pass operates at low osmotic pressure but must reject the remaining monovalents.
What the process produces. Permeate substantially below the first-pass TDS; blending with first-pass permeate is common.
Energy. Lower per cubic metre of final product than a single pass at very low product TDS, but the second pass adds capital.
Process sequence
Where this technology normally sits in a treatment train. The steps either side of it are documented in the Library as separate entries.
- First-pass RO
- Interstage recycle (optional)
- Second-pass RO
- Product blending or storage
Typical applications
- Very low-TDS permeate for industrial reuse
- Bolt-on second pass on an existing single-pass plant
- High-purity water where RO alone is not enough
Main equipment
- Second-pass elements and pressure vessels
- Second-pass pump
- Interstage recycle pump and control
- Permeate blending manifold
Key design parameters
The parameters an engineer actually sets, and why each one drives the design. EngiMetric does not assume any of them.
| Parameter | Why it matters |
|---|---|
| First-pass permeate TDS | Sets the second-pass feed, which sets its rejection and energy. |
| Second-pass recovery | Drives both permeate quality and concentrate volume. |
| Interstage recycle ratio | Improves overall recovery at the cost of complexity and TDS. |
| Blend ratio | Often the cheapest way to hit a target product TDS. |
Advantages
- Reaches product quality that would need a third RO stage in one pass.
- Retrofit-friendly on existing plants.
Limitations
- More equipment and a more complex control scheme.
- Interstage recycle raises the second-pass feed TDS and must be modelled correctly.
- Blending re-dilutes quality, so the design target is a system target, not a stage target.
Engineering considerations
- A recycle configuration that is refused for engineering reasons must be reported as refused, not silently applied.
- Overall recovery is a system property; it cannot be read off either stage alone.
Status and EngiMetric support
Industry maturity and commercial status describe the technology itself. EngiMetric support and quantitative modeling describe what this platform does with it — and those two are read from the engineering registry at build time, so they cannot drift from the code.
- Engineering maturity
- Established How established the technology is in the industry. Not an EngiMetric claim.
- Commercial status
- Commercial Where the technology sits in the market. Not an EngiMetric claim.
- EngiMetric support
- Active Derived from the execution registry: ro is registered as supported.
- Design engine
- Yes Whether the Plant Designer can carry this as a configured process step.
- Quantitative modeling
- Available Derived: 10 of 12 registered capabilities run a deterministic engine.
What EngiMetric computes
These capabilities are registered in the EngiMetric execution registry. Each one runs a deterministic engine, so every result is reproducible from the inputs you supply.
- RO permeate TDS calculatePermeateTds
- RO salt rejection calculateSaltRejection
- RO salt passage calculateSaltPassage
- RO water balance verifyFlowBalance
- RO concentrate flow calculateConcentrateFlow
- RO osmotic pressure calculateRoOsmoticPressure
- RO energy and specific power calculateRoEnergy
- RO concentration factor calculateConcentrationFactor
- RO scaling risk analyzeScalingRisk
- RO recovery calculateRoRecovery
Related tools
Every tool below exists and is live. EngiMetric does not duplicate a formula here — the calculation lives in the tool, and this page links to it.
- RO Recovery Calculator Per-pass product and concentrate split.
- RO Mass Balance Calculator Whole-train balance across both passes.
Design this as a plant
The EngiMetric multi-pass engine handles two-pass and concentrate-recycle configurations, and reports whether a recycle is applied or refused for a stated reason.
Verified against the authoritative treatment model, which configures:
ro-stage