Inland desalination is a growing practice due to the increasing water demand by both inland based communities and commercial operations. Although reverse osmosis technologies are useful for these applications, there are still many challenges that result in major reductions in the total cost of product water. For instance, there are ongoing concerns relating to high electricity consumption, management of brine waste and a lack of material development to counter significant problems encountered with membrane fouling. There is a real need to develop novel enabling technologies that address these problems and also deliver value to inland communities and companies.
The application of ceramic membranes is a promising concept because of the stability, life time and low maintenance requirements. There is an opportunity to develop robust membranes that will enable the desalination of water at high temperatures with chemically or physically aggressive feeds, using a thermally driven process. This combination offers the potential for lower cost desalination by using waste heat instead of electricity to operate the process and the treatment of liquids with a high salt concentration (>50 000 mg/L). Indeed, the thermally driven ceramic membrane desalination system is well suited for such conditions and could present a more economical alternative compared to other thermal systems like brine concentrators.
Develop an optimised manufacturing protocol for ceramic membranes using the robust and versatile sol-gel method. Successfully demonstrate the desalination of coal seam gas (CSG) waters using the manufactured membranes and develop a proof of concept test for a scaled−up multi−tube module of 530cm2 total membrane surface area over several cycles of temperature, for a minimum of 2200 hours.
A number of silica based membranes were synthesised in order to further optimise the effect of manufacturing parameters on the membrane formation and performance. All membranes were produced as ultra−thin films on high or medium quality ceramic supports obtained from either the Netherlands or Melbourne. This structure made the membranes asymmetric and thus more mechanically robust. In order to improve the quality of the membrane i.e. reduce surface roughness, the membranes were coated several times and heat treated at —600°C to produce the final silica membrane. Testing with CSG water however, revealed poor performance due to the alkaline waters damaging the membranes and further investigations were abandoned.
New ceramic membranes based on titania were developed in order to overcome the degradation issue. A major benefit of using the TiO2 anatase membrane is that they cost significantly less to produce, with cheaper supports decreasing substrate cost by 93%. Fabrication time was also quicker and water flux and stability were improved. The best water fluxes were measured at 75°C and an improvement of 80% compared to the silica membranes. This is primarily attributed to both the minimisation of the water transport resistance due to the absence of interlayers in tandem with the specific textural property of the TiO2 material. Salt rejection was measured between 99.9% and 90%, depending of the operating conditions (feed pH, temperature and salt concentration), delivering potable drinking water even from brine feed waters. The best cleaning strategy was a simple procedure consisting of backwashing with a limited amount of pure water at 50°C.
The TiO2 membranes were scaled up to a multitube membrane module for a long-term test processing CSG water. The module was successfully designed and assembled and contained four permeate lines assembled in parallel, exhibiting a total membrane surface area of 533cm2. Prior to testing of the full module, each individual line was tested in pure water in order to ensure and validate comparable performance across the entire system. The long-term tests lasted more than 2200 hours and demonstrated a remarkably stable water flux of 4.1 kg/m−2/h-1 on average at room temperature. After 600 hours of operation, a minor decline of the flux was observed, possibly due to the minor scaling on the ceramic membrane surface. However, the integrity of the TiO2 matrix was not affected as excellent salt rejection of >98% was maintained for length of the test. Complete recovery of the water flux of these membranes was possible with the appropriate cleaning strategies employed as previously discussed indicating scaling and/or salt blockage was not detrimental. The results for long-term operation suggest that use of the TiO2 membranes is best suited to processing CSG waters in opposition of the previous silica membranes.
Economic modelling was used to predict realistic membrane cost and flux targets for the process to become commercially attractive as a brine treatment option. To have treated water cost 20% lower than existing brine concentrators, the membrane cost would have to reduce to $346m2 from $550m2 or the flux would have to increase to 14.5kg/m−2/h−2. Both of these values are reasonable and and could see the process become economically viable for brine waste management.
The technology requires further flux improvements of one order of magnitude for further consideration. One future direction would be to use this technology for brine processing, which is beyond the capabilities of reverse osmosis membranes.
Total Value: $764,027 (cash and in-kind contributions)
Principal Investigator: Professor Joe da Costa
Title: High water recovery inland desalination using membrane distillation with ceramic membranes
Length: 37 months
Personnel: 8 collaborators contributing 2.7 FTE
- 2015. Yacou, C., et al. Mesoporous TiO2 based membranes for water desalination and brine processing. Separation and Purification Technology 147:166-171.
- 2014. 13th International Conference on Inorganic Membranes. Brisbane, Australia.
- 2014. Wong, C. CAPEX and OPEX analysis. Honours thesis, University of Queensland.
- 2013. de Carvalho, B. A. Development of titania-based membranes for water desalination. Undergraduate project, University of Queensland.
- 2013. NCEDA Project Review Meeting. Perth, Australia.
- 2013. 8th International Membrane Science and Technology Conference. Melbourne, Australia.
- 2010. 7th International Membrane and Science Technology Conference. Sydney, Australia.