This long-term, pilot-scale investigation used a dual-barrier, hybrid forward osmosis–reverse osmosis (FO–RO) system for treatment of reclaimed water to produce potable water.
Researchers at the Colorado School of Mines and at CH2M Hill in Texas have evaluated the performance of forward osmosis (FO) with osmotic dilution (ODN) to achieve simultaneous seawater desalination and wastewater reclamation at the pilot scale.
The investigation was performed with a commercial spiral-wound FO membrane element for approximately 1300 h of continuous operation, processing 900 000 L of wastewater effluent and producing 10 000 L of purified water through a hybrid forward osmosis–reverse osmosis (FO–RO) process.
Water and solute fluxes were monitored during the study, and both reversible and irreversible membrane fouling were observed. However, water flux was maintained at a relatively constant rate with membrane bioreactor (MBR) permeate feed and seawater draw solution.
A subsequent increase of total suspended solids (TSS) concentration in the FO feed (secondary treated effluent) resulted in incremental flux decline. However, the membrane typically achieved stable water flux after initial exposure to foulants.
Additional analysis focused on bidirectional transport of inorganic species, and a detailed evaluation of dissolved organic matter permeation through the membranes in the hybrid process.
Evaluation of sample fluorescence revealed that the FO membrane and the hybrid process provide a strong barrier to protein-like fluorophores associated with wastewater effluent.
The results also demonstrated the robust nature of dual-barrier membrane systems to achieve >99.9% removal of orthophosphate and dissolved organic carbon, and >96% rejection of nitrate.
On completion of the study, a comprehensive membrane autopsy was performed on the FO and RO membranes. Organic fouling on the FO membrane was observed to have low adhesion to the membrane surface, but did result in some modification to membrane active layer properties.
