An effective pre-treatment system for reverse osmosis (RO) desalination which alleviates colloidal and organic fouling (the precursors of biofouling) is the key for the success for any RO desalination. Biofouling is caused by the residual organics in inlet raw water and is the major cause of membrane biofouling. Conventional pre-treatment systems cannot reliably remove some pollutants but a small number of studies using micro- and ultra-filtration (MF and UF) membranes have indicated their cost effectiveness in removing colloidal matter. However, the use of MF/UF systems without other processes does lead to organic fouling and unsustainable operation. There is a need to establish an integrated hybrid system incorporating membrane filtration with adsorption and flocculation.
Develop and evaluate novel immersed membrane flocculation hybrid systems as pre-treatment processes to both brackish and seawater RO desalination. Construct a semi-pilot scale system and field test at Chowder Bay, Sydney. Test polymeric inorganic and organic flocculants for their effectiveness at removing colloidal matter and a wide range of organic foulants, which should lead to significant chemical and sludge reduction. Evaluate whether any valuable by-products can also be recovered from the chemical sludge.
The effect of flocculation on the performance of MF was investigated using poly ferric silicate, ferric chloride and titanium tetrachloride. All were effective at removing organic however, poly ferric silicate performed better at reducing turbidity and dissolved organic carbon and titanium tetrachloride was more effective at removing low molecular weight compounds and humics. The titanium tetrachloride sludge was incinerated to produce titanium dioxide nanoparticles.
Two hybrid systems were developed and tested, a submerged membrane flocculation system and submerged membrane flocculation- adsorption system. The latter system performed the best in terms of organic compound removal and critical flux. With doses of ferric chloride and powder activated carbon, the system was able to remove 72% of the dissolved organic carbon and reduced fouling incidence by a factor of five.
The organic compound removal by stainless membranes alone was found not to be effective as a pre-treatment system, which was likely due to the large pore sizes of the membrane. The addition of granular activated carbon as a pre-absorbent or into the membrane reactor however, demonstrated an improvement of up to 56% removal of protein-like compounds.
An energy efficient, compact submerged membrane flocculation hybrid pre-treatment system was developed that is able to reduce the organic fouling. The use of chemical usage and subsequent sludge production was reduced through the use of alternative chemicals and effective additional pre-treatment, such as pre-adsorption. Recovery of titanium dioxide from sludge also reduced the final amount of sludge to be discharged. Alternative polymeric inorganic flocculants with or without pre-adsorption reduced the chemical usage and sludge production while achieving superior organic removal.
A series of experiments with in-line flocculation filtration as pre-treatment to RO are planned to test the organic and biofouling reduction, which will be useful for the modification of flocculant dose in the existing desalination plants. Biosorption experiments are planned to determine if this is a viable alternative to adsorption.
Total Value: $820,000 (cash and in-kind contributions)
Principal Investigator: Professor Saravanamuth Vigneswaran
Title: Membrane flocculation hybrid system as pre-treatment to brackish water reverse osmosis desalination system: Emphasis on chemical use reduction and recovery
Length: 46 months
Personnel: 15 collaborators contributing 1.75 FTE
- 2015. Jeong, S., et al. Removal of natural organic matter at the Gunbower water treatment plant in northern Victoria, Australia. Desalination and Water Treatment:1-9.
- 2014. Nguyen, T. V., et al. Effect of granular activated carbon filter on the subsequent flocculation in seawater treatment. Desalination 354:9-16.
- 2014. Jeong, S., et al. Experimental investigation and modeling of dissolved organic carbon removal by coagulation from seawater. Chemosphere 95 (0):310-316.
- 2013. Jeong, S., et al. Foulant analysis of a reverse osmosis membrane used pretreated seawater. Journal of Membrane Science 428 (0):434-444.
- 2013. Jeong, S., et al. A detailed organic matter characterization of pretreated seawater using low pressure microfiltration hybrid systems. Journal of Membrane Science 428 (0):290-300.
- 2013. Jeong, S., et al. Ti-salt flocculation for dissolved organic matter removal in seawater. Desalination and Water Treatment 51 (16-18):3591-3596.
- 2013. Shrestha, A., et al. Seawater biofiltration pre-treatment system: comparison of filter media performance. Desalination and Water Treatment:1-8.
- 2013. Jeong, S., and S. Vigneswaran. Assessment of biological activity in contact flocculation filtration used as a pretreatment in seawater desalination. Chemical Engineering Journal 228 (0):976-983.
- 2012. Jeong, S., et al. Biofouling Potential Reductions Using a Membrane Hybrid System as a Pre-treatment to Seawater Reverse Osmosis. Applied Biochemistry and Biotechnology 167 (6):1716-1727.
- 2012. Jeong, S., et al. Submerged membrane hybrid systems as pretreatment in seawater reverse osmosis (SWRO): Optimisation and fouling mechanism determination. Journal of Membrane Science 411–412 (0):173-181.
- 2012. 5th International Desalination Workshop. Jeju, China.
- 2011. Jeong, S., et al. Submerged membrane coagulation hybrid system as pretreatment to organic matter removal from seawater. Water Science & Technology: Water Supply 11 (3):352–357.
- 2011. Jeong, S., et al. Pretreatment for seawater desalination by flocculation: Performance of modified poly ferric silicate (PFSi-δ) and ferric chloride as flocculants. Desalination 283 (0):106-110.
- 2011. Khorshed, C., et al. Assessment of Loddon water treatment processes: detailed organic matter characterisation and membrane fouling indices at the Loddon Water Treatment Plant, Victoria, Australia. Water Science & Technology: Water Supply 11 (3):274–280.
- 2011. 4th International Desalination Workshop, Jeju, China.
- 2011. International Conference on New Horizons in Biotechnology. Trivandrum, India.
- 2011. 2nd Biofouling Workshop. Sydney, Australia.