I. Technical Definition and Core Features

• Open Flow Channel Design: It employs a trapezoidal or 45° diamond double-layer grid structure with a flow channel spacing of 1.2-4 mm. This significantly reduces flow resistance and concentration polarization effects while enhancing the scouring force on the membrane surface to minimize pollutant deposition. Compared to the diamond grid structure of traditional spiral-wound membranes, its flow channel is closer to that of tubular membranes, reducing resistance by more than 60%.
• High-Pressure Resistance: The membrane components are available in pressure ratings of 7.5 MPa, 9.0 MPa, and 12 MPa, with the ability to withstand up to 80 bar pressure. This allows for the concentration of brine TDS to 80-120 g/L, making it suitable for treating wastewater with high osmotic pressure.
• Anti-fouling Performance: The combination of trapezoidal grids and transverse reinforcement ribs increases the turbulence of the feed solution, reducing concentration polarization. The independent membrane shell structure for each membrane component facilitates cleaning and maintenance after fouling, making it particularly suitable for treating wastewater with high COD (such as landfill leachate with COD up to 16,350 mg/L) and high suspended solids.

II. Technical Principle and Process Flow

• Working Principle: STRO is based on the principle of reverse osmosis. A high-pressure pump (with pressure reaching 6.0-6.5 MPa) drives the water through the membrane components. Water molecules pass through the semi-permeable membrane to form permeate, while salts and pollutants are retained on the concentrate side. Its unique design includes:
• Membrane Component Structure: Anti-fouling polyamide composite membrane sheets are wound around a high-pressure-resistant central tube, combined with trapezoidal grids to form a spiral flow channel.
• Operation Mode: It uses high-flow, high-pressure circulation. The recovery rate is dynamically adjusted based on feed water TDS, flux, and pressure. For example, a 7.5 MPa membrane can concentrate wastewater to three times its original volume (with a recovery rate of 66%).
• Typical Process Flow:
• Pre-treatment: Softening, tubular microfiltration, or ultrafiltration is used to remove suspended solids and hardness.
• Multi-stage Concentration: First-stage reverse osmosis (TDS 3,500→14,000 mg/L) → Concentrate reverse osmosis (TDS 30,000→80,000 mg/L) → STRO ultra-concentration (TDS 80,000→120,000 mg/L).
• Post-treatment: The concentrate is fed into an evaporation crystallization system, while the permeate is reused or discharged.

III. Application Scenarios and Case Studies

• Landfill Leachate Treatment:
• Case: The Shanghai Laogang Landfill used a two-stage STRO system to treat leachate, achieving a COD removal rate of >99.5%, an ammonia nitrogen removal rate of 99.2-99.5%, and a TDS rejection rate of 92-95%, with no membrane scaling or pollution.
• Advantages: It can tolerate feed water COD up to 300 mg/L and maintain a stable flux of 15-17 L/(m²·h) for continuous operation over 14 days.
• Zero Liquid Discharge (ZLD) for Industrial Wastewater:
• Case: The Yangquan Coal Industry's ethylene glycol project used STRO to concentrate high-salinity wastewater (TDS 30,000→80,000 mg/L), reducing the electrical energy consumption per ton of water by 0.72 kW compared to evaporation crystallization and lowering operating costs by 60%.
• Applicable Industries: Chemical (desulfurization wastewater, coal chemical wastewater), electroplating, pharmaceutical, and other high-salinity wastewater fields.
• Seawater Desalination and Resource Recovery:
• Potential: Although RO technology is the mainstay, STRO can be coupled for specific high-salinity seawater pre-treatment or concentrate re-concentration, thereby increasing the overall recovery rate.

IV. Technical Advantages and Economic Benefits

• Performance Advantages:
• High Desalination Rate: The desalination rate is ≥98%, with permeate TDS potentially reduced to below 100 mg/L.
• Energy Conservation and Consumption Reduction: By utilizing energy recovery devices to reuse the pressure of the concentrate, the electrical energy consumption per ton of water is reduced by 50% compared to evaporation crystallization.
• Convenient Maintenance: The modular design supports rapid disassembly and cleaning, extending the membrane life to 3-5 years.
• Economic Comparison:
• Investment Cost: Each membrane component has an area of up to 25 m² (8 inches × 1 m), resulting in compact equipment and a 30% reduction in land area.
• Operating Cost: When treating high-salinity wastewater, the cost per ton of water for STRO is 1/3 to 1/2 of that for evaporation crystallization.

V. Challenges and Future Development Trends

• Current Limitations:
• High-Pressure Energy Consumption: A 12 MPa membrane system requires high-cost pumps and valves, and there are no application cases in China yet.
• Pre-treatment Requirements: It is necessary to strictly control the feed water SDI<5. When suspended solids exceed 50 mg/L, enhanced pre-treatment is required.
• Technical Development Directions:
• Material Innovation: Develop chlorine-resistant and high-temperature (>45℃) membrane materials to expand application scenarios.
• Intelligent Integration: Combine AI to optimize operating parameters and monitor membrane fouling status in real-time.
• Green Processes: Reduce the frequency of chemical cleaning and promote the use of biodegradable membrane materials.