NAWI has funded a number of pilot projects that are intended to demonstrate the scaling of new technologies from bench scale or laboratory prototypes to large—and often mobile—field-deployed systems on relevant waters at or near their source. One such pilot project, led by Purdue University, is looking at batch reverse osmosis (BRO).
BRO has been proposed as a more energy-efficient alternative to conventional reverse osmosis (RO), primarily due to the former’s ability to operate closer to the brine’s osmotic pressure during permeate production. In this work, David Warsinger and his team designed, constructed, and tested a pilot-scale conventional RO, closed-circuit RO (CCRO), double-acting reciprocating piston BRO, and bladder-based BRO configurations within the combined system. By using the same pilot system across all tests, the influence of variables such as feed water composition, membrane type, piping, and pump selection is minimized. The pilot system is fully operational and can automatically run using a LabView VI.
The system is designed to handle high-salinity water and is comprised of several components (e.g., check valves, 3-way valves, and 2-way valves). A 5-micron cartridge filter was installed to protect the RO membrane and remove small particles. A feed tank provides the necessary feed water to the system, while separate tanks are used to store the brine and permeate flows. Additionally, different sensors and transducers are used to monitor the main operational variables in the system such as flow rates, pressure, conductivity, pH and temperature.
Experimental results obtained with the pilot system were used to parameterize and validate a predictive model. This model discretizes the membrane module’s feed channel in both the axial and transverse directions to capture the effects of concentration polarization and pressure losses on system performance. By simulating the pressure evolution over time, this model can calculate the system’s specific energy consumption (SEC).
The system has operated continuously for over 900 hours, with seamless switching between configurations. To date, more than 800 million data points have been collected.
The pilot has been operated with different feed salinities (brackish and seawater) and a range of water fluxes and recovery ratios. Preliminary results support previous predictions, showing that CCRO and Batch RO outperform Conventional RO in energy efficiency and achievable recovery.
The results also show that the selected performance indicators are being met with minimal to no leaks observed at operating pressures of up to 1000 psi. Both SEC and the recovery ratio remained within 5% of initial values throughout testing, even after consecutive operating cycles.
For more information, access the project research brief.