Product Overview

A High-Purity Double Pass RO System utilizes two consecutive reverse osmosis stages to process industrial feed water, where the permeate from the first pass feeds directly into the second pass to achieve exceptional ionic and organic rejection, consistently delivering product water below 0.5 µS/cm for critical industrial applications.

Technical Specifications

Parameter	Specification Range
Product Conductivity	< 0.5 µS/cm (at 25°C)
Salt Rejection	≥ 99.5% overall
System Recovery	65% – 75% adjustable
Operating Pressure	1.0 – 1.4 MPa (Max 1.6 MPa)
Power Supply	380V/460V, 50/60Hz, 3-Phase

Performance Rationale

Double Barrier Rejection: A second pass halves residual ion concentration, mitigating raw water fluctuations.

Downstream Protection: Substantially lowers ionic loads on EDI modules or mixed-bed resins, reducing regeneration frequency.

Microbial Control: Combines tight spiral-wound membrane barriers in series to suppress bacteria breakthrough.

Typical Applications

Pharmaceutical Pretreatment: Supplying purified water feed for distillation units and loop systems.

Electronics & Semiconductor: Feeding pure water loops for printed circuit board wet processing.

Laboratory Central Supply: Providing central ultrapure water to analytical instruments like HPLC and ICP-MS.

Fine Chemical Synthesis: Generating high-purity solvent dilution water for specialty chemical manufacturing.

Operational Workflow

First-Pass Filtration: Pre-treated water pressurizes through polyamide composite membranes.

Intermediate Boosting: First-pass permeate enters an intermediate tank or feeds directly via booster pump to the second stage.

Second-Pass Polishing: Water undergoes secondary high-pressure filtration with inter-stage caustic addition to enhance silica rejection.

Reject Management: First-pass concentrate discharges or recycles; second-pass concentrate returns to feed to maximize recovery.

System Configuration

Pumping Units: Multi-stage vertical centrifugal pumps in corrosion-resistant stainless steel.

Membrane Assemblies: Low-fouling elements housed in 304 or 316L stainless steel vessels.

Pretreatment Integration: Automated multimedia, activated carbon adsorption, and 5-micron security filtration.

Instrumentation: PLC automation panel with touchscreen HMI, conductivity meters, and pH transmitters.

Feed Water Requirements

Silt Density Index (SDI)	< 3.0 via upstream filtration.
Free Chlorine	< 0.1 mg/L to prevent oxidation.
Turbidity	< 1.0 NTU.
Permeate Target	First-pass conductivity typically < 10 µS/cm.

Output Water Quality

Conductivity	< 0.5 µS/cm stable performance.
Silica ($SiO_2$)	< 10 ppb.
TOC	< 50 ppb.
Microorganisms	Complete retention via 0.2 µm final microfiltration.

Selection Guide

Capacity Sizing: Base flow rate on peak demand plus a 20% margin for cleaning and standby.

Water Chemistry: Submit full raw water profiles to size membrane surface area and chemical dosing.

Physical Footprint: Verify skid dimensions, ceiling clearance, and utility stub-ins.

Metallurgy: Specify sanitary 316L piping and orbital welding for pharmaceutical compliance.

Customization Options

Structural Skids: Full 304 or 316L stainless steel framing.

Sanitary Connections: Tri-Clamp fittings with internal finish Ra $\le$ 0.4 µm and passivation.

Chemical Dosing: Integrated anti-scalant, sodium bisulfite, and caustic soda dosing modules.

Automated CIP: On-board clean-in-place tank, heater, and recirculation pump assembly.

Communication Protocols: Plant SCADA or DCS integration via Modbus TCP, Profinet, or Ethernet/IP.

Quality Assurance

Pressure Testing: Pneumatic and hydro-testing of pressure vessels and piping at 1.5 times design pressure.

Weld Verification: Boroscopic inspection and weld logs for sanitary networks.

Factory Acceptance Testing: Complete dry/wet electrical checks, instrument calibration, and interlock verification.

Material Traceability: Mill test reports provided for all wetted stainless steel components.

Frequently Asked Questions

Q: What is the typical system recovery rate?

A: Recovery ranges from 65% to 75%, balancing water conservation with scale prevention.

Q: Why implement inter-stage pH adjustment?

A: Raising pH converts weakly ionized elements like silica and boron into charged ions, boosting second-stage rejection.

Q: What is the average membrane lifespan?

A: Membranes typically operate for 3 to 5 years, depending on feed quality and cleaning frequency.

Q: What utility connections are required?

A: Three-phase industrial power, instrument air, a chemical drain, and stable pre-treated feed water.

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