Disc Tube Reverse Osmosis (DTRO) is a cutting-edge membrane separation technology specially developed for complex, high-salinity and heavily polluted wastewater that conventional spiral-wound reverse osmosis cannot handle stably. The two-stage DTRO system, as an upgraded integrated solution, combines primary rough desalination and secondary deep purification, breaking the limitations of single-stage DTRO on effluent quality and overall water recovery rate. Widely applied in landfill leachate, incineration plant leachate, chemical high-salt wastewater, desulfurization wastewater and zero-liquid-discharge projects, it has become the mainstream standardized equipment for treating refractory industrial and municipal wastewater worldwide.
Core Structural Principle of DTRO Membrane Module
Different from spiral-wound RO with narrow flow channels, the DTRO membrane column adopts stacked disc membrane sheets and open wide flow channels (3–4 mm, 6–10 times wider than spiral RO) separated by diversion trays. Raw water enters the pressure vessel and flows along an S-shaped turbulent path between disc components. The ribbed diversion trays generate strong cross-flow turbulence on the membrane surface, drastically weakening concentration polarization and membrane fouling risk, allowing stable operation even with feed water SDI up to 15.
Under high pressure (70–120 bar), water molecules penetrate the RO membrane to form clean permeate, while organic pollutants, heavy metal ions, ammonia nitrogen and dissolved salts are intercepted to form concentrated liquid. The modular membrane column design enables independent disassembly, inspection and replacement of single membrane sheets, greatly simplifying daily maintenance.
Working Flow of Two-Stage DTRO System
The complete two-stage DTRO unit consists of pretreatment unit, primary DTRO unit, secondary DTRO unit, energy recovery device, automatic CIP cleaning system and PLC intelligent control cabinet. The full process runs automatically as follows:
Pretreatment Stage
Raw wastewater undergoes pH adjustment, sand filtration and security cartridge filtration to remove suspended solids, fiber particles and scale-forming ions, protecting subsequent high-pressure pumps and membrane stacks from abrasion and clogging.
First-Stage DTRO (Primary Separation)
Pretreated water is pressurized by high-pressure plunger pumps and delivered to primary membrane columns. Most clean permeate flows into the secondary DTRO for advanced treatment, while high-salinity concentrate is sent to concentrate storage tank for further reduction or incineration. The water recovery rate of the first stage is controlled at 50%–60%. An energy recovery pressure exchanger recycles residual pressure from concentrate, cutting energy consumption by 30%–40%.
Second-Stage DTRO (Deep Purification)
Permeate from the first stage still contains residual trace salts and organics. After secondary high-pressure filtration, final standard-compliant permeate is produced for discharge or industrial reuse. Concentrate generated in the second stage has low salinity and is recycled back to the inlet of the first stage, lifting the overall system recovery rate to 65%–85%.
Automatic Online Cleaning
The PLC system regularly triggers acid, alkali and special chemical cleaning cycles to eliminate organic fouling and inorganic scaling on membrane surfaces, restoring membrane flux and extending service life over 5 years under stable operation.
Unique Advantages of Two-Stage DTRO Equipment
1. Ultra-Strong Anti-Fouling & High Pressure Resistance
Open turbulent flow channels avoid frequent blockage; the membrane column withstands maximum operating pressure of 120 bar, capable of treating wastewater with TDS up to 80,000–120,000 mg/L and COD of tens of thousands mg/L, a capability traditional RO cannot match.
2. Superior Pollutant Rejection & Stable Effluent
Two-stage serial separation achieves comprehensive rejection rate over 98% for TDS, 99%–99.95% for COD and 98%–99.98% for ammonia nitrogen. Effluent quality is barely affected by fluctuations in raw water quality, consistently meeting strict local discharge and reuse standards.
3. Higher System Water Recovery
Single-stage DTRO generally has limited recovery, while the two-stage design recycles secondary concentrate to the front end, minimizing wastewater volume and lowering concentrate disposal costs, ideal for zero liquid discharge (ZLD) projects.
4. Compact Modular & Containerized Design
All units are factory pre-assembled and debugged, featuring small footprint and movable containerized configuration. No complex civil construction is required; the equipment can reach standard effluent within one week after on-site power and water connection, shortening project cycle significantly.
5. Low Operation & Maintenance Cost
Full-automatic PLC control reduces manual labor; single membrane sheets can be replaced separately without replacing the entire membrane column. The energy recovery device cuts long-term power expenditure, with a typical investment payback period of 2–3 years.
Main Application Scenarios
Municipal solid waste treatment: Landfill leachate, waste incineration leachate, kitchen waste and transfer station leachate treatment
Heavy industrial wastewater: Coal chemical wastewater, power plant desulfurization wastewater, electroplating wastewater, printing & dyeing wastewater, mine high-salinity water
Resource recovery & zero discharge: Reuse of industrial production water, concentration and recovery of high-value liquid raw materials, reduction of reverse osmosis concentrated water
Emergency wastewater disposal: Mobile containerized two-stage DTRO units for sudden pollution and temporary wastewater treatment projects
Conclusion
As a mature and reliable membrane treatment technology, two-stage DTRO equipment solves the core pain points of high-concentration wastewater treatment: severe membrane fouling, unstable effluent and low water recovery. Its robust anti-pollution performance, automated operation and flexible modular layout make it a preferred solution for environmental engineering companies and industrial enterprises worldwide. With increasingly stringent global wastewater discharge regulations, two-stage DTRO will continue to play an irreplaceable role in waste reduction, water resource recycling and sustainable environmental governance.
