After pretreatment and UF, the raw water enters the primary RO unit (brackish water membrane). A portion of the permeate is directly reused, while the primary RO concentrate serves as the feed water for the SWRO unit. The SWRO membrane withstands higher operating pressures and achieves over 99% rejection of both monovalent and divalent ions, further concentrating the salts. The SWRO concentrate then enters the STRO membrane unit. STRO utilizes open-channel flow paths and high-pressure-resistant membrane elements, with an operating pressure capable of reaching 9 MPa or higher, maintaining stable flux even when treating high-salinity brine.
Through this multi-stage concentration process, the total system recovery rate can be increased to over 85% (depending on raw water quality), significantly reducing the final concentrate volume. Each membrane stage independently controls pressure and recovery. Optional inter-stage energy recovery devices can be added to reduce system operating energy consumption while further increasing the volume of reused water.
The equipment consists of pretreatment filters, a UF (Ultrafiltration) unit, primary RO membrane modules, SWRO high-pressure membrane modules, STRO high-pressure membrane modules, inter-stage booster pumps, an optional energy recovery device, and a comprehensive control cabinet. The SWRO membrane elements are high-rejection seawater desalination membranes. The STRO uses wide-channel spiral-wound membranes that are fouling-resistant and amenable to chemical cleaning. The system is equipped with online conductivity meters, flow meters, and pressure sensors to achieve flow balance across stages and provide fault warnings. Additionally, anti-scalant dosing, pH adjustment, and dedicated cleaning systems are included.
The equipment is primarily used in desulfurization wastewater, circulating cooling system blowdown, and high-salinity process wastewater from industries such as electric power, petrochemicals, and coal chemicals. It is also suitable for centralized wastewater treatment plants in industrial parks, reducing the volume of discharged concentrate by increasing the raw water reuse rate, thereby meeting near-zero discharge policy requirements. The process can effectively concentrate leachate, reducing the load on downstream evaporation systems.