Transmembrane Pressure-Assisted Forward Osmosis: Impacts and Implications

Globally, water resources are overburdened due to increased water consumption and climate change, straining regional economic and ecological systems. Consequently, there is a growing shift towards water reclamation and reuse. Forward osmosis (FO) is a rapidly growing membrane treatment technology that can facilitate sustainable water reclamation and reuse, thus generating new sources of water.

In FO, a concentrated draw solution induces an osmotic pressure difference across a semipermeable membrane to extract water from impaired streams, thereby concentrating it and reducing residual management costs. Engineered osmosis systems are attractive because they require minimal hydraulic pressure, membrane fouling is reduced compared to pressure-driven membrane processes, and they provide high rejection of dissolved and suspended contaminants. Research in academia in the last decade has established the viability of FO and together with the industry they have established standard methods for evaluating membrane performance. The testing methods are an important tool to compare new and rapidly developing membranes; however, we now must bridge the gap between academic research and the true conditions under which these membranes operate in industrial applications in the real world. Though FO systems successfully recover water from domestic wastewater, oil and gas drilling wastes, and even landfill leachates, hydraulic conditions not captured by standard testing methods may affect membrane performance when operated at these larger scales.

In this study we investigated the performance of FO membranes under elevated transmembrane hydraulic pressure typical in industrial-scale FO membrane modules. A novel bench-scale system and a range of hydraulic pressures were explored to mimic the conditions inside commercial FO membrane modules and systems. Experiments with cellulose triacetate (CTA) and polyamide thin-film composite (TFC) FO membranes demonstrated that transmembrane hydraulic pressure, common in industrial operation of FO membrane elements, could affect membrane performance. Results will be presented that demonstrate the effects of transmembrane hydraulic pressure on water flux, salt rejection and leakage, and rejection of trace organic contaminants.