The main process used for treating brackish waters is reverse osmosis (RO) desalination, a proven technology. However only water recoveries of 70-80% are achievable, partly due to the presence of soluble scaling compounds. Subsequent processing of the brine usually requires the construction of evaporation ponds, resulting not only in a valuable water resource being lost to evaporation but also construction of the ponds is expensive. The estimated cost of evaporation ponds is $0.6 million/ha for a single liner, with large double-lined ponds required for the treatment of high volumes of brine, costing tens of millions of dollars. A process, such as vacuum membrane distillation (VMD) that is not as susceptible to scaling and would increase the recovery of water from RO brine, has the potential not only make available a valuable water source but also substantially reduce capital costs for industry.
Investigate VMD as a means to better manage RO brine streams by reducing the volume of brine to be disposed of. Develop a process engineering model and predict single pass performance under various operational conditions. Investigate effective membrane cleaning protocols.
The process engineering model was developed and parameters such as vacuum pressure, membrane type and length, feed temperature and velocity are able to be varied. This model is able to be utilised as a design tool for future VMD modules. Modelling results were subsequently verified by laboratory studies, which were somewhat consistent, and impacted negatively on by the compressibility of the membranes that were used for testing.
At higher feed flow rates and temperatures, it was more efficient to operate the VMD in recirculation mode rather than single pass mode. Thermal energy contributes most to the total energy required for VMD process. To lower the thermal energy requirement, low grade waste heat resource and heat recovery of latent heat from permeate vapour are needed. Process engineering modelling indicated the electrical energy consumption for VMD is comparable or lower than seawater RO; as a result VMD may not be able to compete with RO directly but could be used as a complimentary technology such as in brine concentrate treatment as suggested in this study.
Cleaning experiments were conducted following direct contact MD experiments using either coal seam gas water or seawater RO brine. Inorganic scaling was most prevalent for this water at high water recoveries, and was easily removed with acid cleaning. However, small amounts of organic fouling were also observed and these were not removed by acid cleaning or acid cleaning followed by alkali cleaning. The organic fouling was irreversible in these experiments.
A collaborative project with the University of Wollongong and AGL will conduct a field trial of VMD on a coal seam gas site (see Related Project below).
The researchers would like to hear from parties interested in trialing the model for the potential commercial applications of the process. For more information please contact the Principal Investigator.
Total Value: $631,624 (cash and in-kind contributions)
Principal Investigator: Professor Stephen Gray
Title: Reverse osmosis brine management by membrane distillation crystallisation
Length: 19 months
Personnel: 12 collaborators contributing 3.7 FTE
- 2015. Zhang, P., et al. Scale reduction and cleaning techniques during direct contact membrane distillation of seawater reverse osmosis brine. Desalination 374:20-30.
- 2013. 8th Conference of Aseanian Membrane Society. Xi’an, China.
- 2013. NCEDA International Desalination Workshop. Melbourne, Australia.
- 2013. Zhang, J., et al. “Influence of module design and membrane compressibility on VMD performance.” Journal of Membrane Science 442(0): 31-38.
- 2013. Zhang, J. et al. “Modelling of vacuum membrane distillation.” Journal of Membrane Science 434(0): 1-9.
- 2012. 7th Aseanian Membrane Sociey Conference. Busan, Korea.
- 2011. Zhang, P. Fabrication of direct contact membrane distillation bench scale apparatus. PhD thesis, Victoria University.