Low pressure ultrafiltration (UF) membranes are increasingly used for the pre-treatment of raw seawater. However, membrane fouling remains a major issue for this process, particularly during algal blooms, resulting in high operating, maintenance, and cleaning costs. Algae secrete extracellular polymer substances, which are comprised mainly of polysaccharides and proteins, and these combined with humic acids, which are a major compound in seawater, cause significant irreversible fouling.
Develop advanced characterisation techniques for examining seawater organic matter and fouling layers on the membrane surface. Compare the performance of standalone and hybridized UF systems (in-line coagulation and dissolved air flotation – DAF) for the removal of marine microalgae and released organic matter. Assess the efficiency of physical and chemical membrane cleaning methods.
Fluorescence Emission Excitation Matrix (FEEM) and Liquid Chromatography–Organic Carbon Detector (LC-OCD) provided reproducible results for the characterisation of organic fractions in seawater. Using these methods, DAF was shown to more effectively remove biopolymers and humic substances from seawater compared to UF, dual media filtration and bio-filters.
High salt concentration contributed significantly to the fouling potential of humic acid and alginates in seawater. Replacing permeate water backwash with deionised water was effective at removing alginate from the membrane surface; however the remaining foulants i.e. humic acids became increasingly difficult to remove. It is proposed that the alginate layer acts as a dynamic membrane, pre-filtering the smaller humic acid molecules and reducing their absorption on the membrane surface. Once this layer is removed, the humic acid molecules move to block the membrane pores, leading to irreversible fouling. Deionised water backwash is therefore not recommended during algal blooms in seawater feeds due to the high concentration of humic acids.
Through extensive testing and experimental studies, the advantages and disadvantages of various UF fouling mitigation methods such as deionised water backwash, in-line coagulation, and DAF have been outlined. However, there are still several additional options available for enhancing the performance of UF pre-treatment systems. By conducting further studies on these methods and comparing them to the processes already tested, further advances can be made to at least cover all commercially feasible methods.
Further studies on hybridised pre-treatment systems during marine algal blooms are needed. The first step will be to examine the effect of adding powdered activated carbon (PAC) to UF pre-treatment. As PAC can be added to both the standalone and hybridised UF systems and any changes in membrane performance, particularly if an optimum ratio of PAC-coagulant can be established, would maximise fouling mitigation/organic removal effectiveness.
Total Value: $1.24 million (cash and in-kind contributions)
Principal Investigator: Associate Professor Pierre Le-Clech
Title: Optimising low-pressure membrane pretreatment for desalination
Length: 55 months
Personnel: 16 collaborators contributing 9.35 FTE
- 2016. Shutova, Y., et al. Enhancing organic matter removal in desalination pretreatment systems by application of dissolved air flotation. Desalination 383:12-21.
- 2015. Resosudarmo, A. Optimisation of ultrafiltration membranes for the pretreatment of seawater organic matter. PhD thesis, University of New South Wales.
- 2015. Umpong, W. C. Comparison of coagulation, submerged hollow fibre membrane filtration and dissolved air flotation for the removal of organic matters in seawaters. Honours thesis, University of New South Wales.
- 2015. Advances in Pre-Treatment for Desalination. Sydney, Australia.
- 2014. Karna, B. Advanced characterisation techniques to assess seawater organic matter removal dissolved air flotation. Masters thesis, University of New South Wales.
- 2014. Harmful Algal Blooms and Desalination Conference. Muscat, Oman.
- 2013. Resosudarmo, A., et al. Analysis of UF membrane fouling mechanisms caused by organic interactions in seawater. Water Research 47 (2):911-921.
- 2013. 5th International Water Association Specialist Conference on Natural Organic Matter Research. Perth, Australia.
- 2013. Vu, K. Assess of periodical cleaning strategies in coagulation. Honours thesis, University of New South Wales.
- 2013. Anwar, W. Dissolved air flotation as a pretreatment system for seawater. University of New South Wales.
- 2013. 1st International conference on desalination using membrane technology. Sitges, Spain.
- 2013. International Desalination Association World Congress. Tianjin, China.
- 2013. 8th International Membrane Science and Technology Conference. Melbourne, Australia.
- 2012. Nappa, L. Impact of physical and chemical stress on the release of algal organic materials in desalination pre-treatment processes. Honours thesis, University of New South Wales.
- 2012. Vayro, A. On the opportunities of dissolved air flotation as pre-treatment to seawater desalination. Honours thesis, University of New South Wales.
- 2012. 2nd Early Career Researcher Membrane Society of Australasia Symposium. Brisbane, Australia.
- 2011. 2nd Early Career Researcher Membrane Society of Australasia Symposium. Glenelg, Australia.