Hybrid forward osmosis/ultrafiltration membrane bag for water purification

In this work, a novel forward osmosis (FO)-ultrafiltration (UF) hybrid membrane is designed, constructed and its performance tested. The membrane consists of FO and UF membrane bilayer, between which highly concentrated sodium polyacrylate (SPAA) solution is sandwiched as a draw solution. When the FO side of the hybrid membrane is brought into contact with waste water, seawater or brackish water, clean water is drawn into the SPAA solution through FO membrane. The clean water is then squeezed out of the SPAA solution through the UF membrane by applying pressure, which can be either hydraulic or mechanical. Experiments were carried out to prove the validity of the design concept. Some model equations were derived to simulate the performance of the hybrid membrane and the experimental data were analyzed based on the model equations. The novel hybrid membrane is believed to allow the production of RO quality water at the UF pressure that is much lower than the pressure for RO, thus leading to significant reduction of energy consumption for water production.