(176a) Membrane Technology– POTENTIAL for A LOWER CARBON Future

Following a brief retrospective of membrane technology, this presentation considers a major challenge and opportunity for the industry. It is now evident that membrane technology has a major future in water and wastewater processing, including low pressure membranes (MF and UF) for water treatment, membrane bioreactors (MBRs) and as pretreatment, and high pressure RO is the preferred technology for desalination and water reclamation. However membrane technology has an image of being ?energy expensive' and this poses a major challenge with the need to curb green house gases. This presentation examines the role of membranes in the water industry and the possible responses to climate change. It is based on assessments of global technology trends as well as examples of research findings from the speaker's laboratories in Singapore and Sydney.

Seawater desalination by reverse osmosis (RO) is growing by at least 15% per year, and a ?business as usual' approach could see SWRO becoming a major GHG emitter by 2050. Reduced energy will come from developments in membranes, modules and operation. The prospects for very high permeability RO membranes requires redesign of the RO cascade with energy savings of 30 to 40% possible but at a capital cost penalty. The spiral wound RO element is amenable to further improvement as shown by CFD analysis. Significant energy savings, with GHG reduction, can be achieved by improved control of fouling in RO desalination and reclamation processes.

Membrane alternatives to RO include membrane distillation (MD) and forward osmosis (FO). Both offer lower GHG strategies. MD is a thermal process but uses available waste heat or solar energy and little electrical energy. It can operate effectively at very high recovery (product/feed) and can be coupled with a crystallizer to produce salt solids, and may be viable as a ?concentrate' treatment process. Water production from waste water by a dual membrane process (MF/UF + RO) comes at about half the energy cost of RO desalination. However the pretreatment energy now becomes significant and increases with flux. LCA shows that to minimize energy requires a much lower flux than the economic minimum; again a capital cost penalty to reduce GHG.

The MBR shows dramatic growth in application. Energy savings are being achieved by optimization of air-scour, and research into complex membrane fouling. Anaerobic MBRs are being developed and could also achieve energy savings. Membrane contactors could upgrade biogas. Novel MBRs incorporating MD and/or FO and driven by waste or solar heat could become alternatives to the conventional MBR + RO reclamation process , with a smaller GHG footprint.

Finally, membranes provide an opportunity for generation of renewable power based on the controlled mixing of salt water and fresh water. One approach uses pressure retarded osmosis, which has a long history but has been revived as a possible answer to reducing GHG emissions. This process promises a source of renewable energy, but also presents formidable challenges to the membrane community in terms of membrane and module design, pretreatment and fouling control.