IWA Specialist Group Directory - Nieuwe Sanitatie - Stowa

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properties and performance. These membranes have higher fl uxes, resist breakage to a much greater extent, and/or exhibit reduced biofouling. Membrane processes based on even more advanced nanoscale control of membrane architecture may ultimately allow for multi-functional membranes that not only separate water from contaminants, but also actively clean themselves and check for damage, detect contaminants, or combine detection, reaction and separation. Several nanomaterials are used for the formation of organic–inorganic porous composite membranes such as Al 2 O 3 , TiO 2 , SiO 2 , nAg (silver nanoparticles), CNT (carbon nanotube), chitosan and others. These nanomaterials improve membrane properties, such as (1) increased skin layer thickness, (2) higher surface porosity of the skin, (3) suppressed macrovoid formation, and (4) higher permeability of the membrane (Taurozzi et al. 2008). The very effi cient transport of water through CNT membranes seems promising for energy reduction in seawater desalination. However, the road to useful industrial applications of CNT membranes may be yet a long and arduous one owing to the selectivity and cost requirements (Verweij 2007). Maximous et al. (2009) prepared PES ultrafi ltration membrane with entrapping Al 2 O 3 nanoparticles and used this membrane at the activated sludge fi ltration. Al 2 O 3 nanoparticles decreased the adhesion or the adsorption of the EPS on the membrane surface and increased the fi ltration performance of membrane. In particular, incorporation of quorum quenching nanomaterials makes the membranes ‘reactive’ instead of a simple physical barrier. Kim et al. (2011) prepared an acylaseimmobilized nanofi ltration membrane with quorum quenching activity. This membrane prohibited biofouling, namely the formation of mature biofi lm on the membrane surface owing to the reduced secretion of EPS. Overall, these nanomaterials could contribute to the development of specifi c membranes in many desired ways. One challenge in the future will be to use these developments to tailor membranes for processes that rely on driving forces other than pressure, such as forward osmosis or membrane distillation. Forward Osmosis (FO) and Membrane Distillation (MD) In the context of climate change, the environmental and energy issues become essential and must be taken into account in the design of membrane systems and in their mode of operation, so that membrane processes remain or become competitive. The relatively high energy demand to operate conventional pressure driven membrane processes (MF, UF, NF, RO) still remains a challenge to be managed. As alternatives to reverse osmosis (RO), membrane distillation (MD) and forward osmosis (FO) are being considered for low-energy seawater desalination and wastewater reuse Forward Osmosis (FO) FO, a novel low-energy and natural process, has been signifi cantly developed in the past few years as an alternative membrane technology for desalination. Many studies IWA Specialist Groups on the use of FO for industrial and domestic applications can be found in literature. During the past decade, FO has been studied in wastewater treatment, seawater desalination, the food industry for stream concentration, as well as for purifying water in emergency situations. New and high performance FO membranes are being researched (Chou et al. 2010; Wang et al. 2010). In September 2008, Modern Water (Guildford, UK) built the world’s fi rst FO desalination plant in Gibraltar on the Mediterranean Sea. This local plant successfully completed testing procedures of the product water and, since May 2009, water has been supplied to the local community. A year later, in September 2009, a larger desalination plant was commissioned in the Sultanate of Oman at Al Khaluf. This new plant shares pre-treatment facilities with an existing RO desalination plant, providing a good opportunity to compare both technologies. Results were better than expectations, especially on resistance to fouling and product water quality. Moreover, despite the very bad quality of the source seawater, the FO membranes have not been cleaned or replaced over the year of operation. In contrast, RO membranes from the other desalination plant had to be cleaned every two to four weeks and had been replaced over the one year operation time. This clearly demonstrates the low fouling propensity of the FO process compared with the RO membrane process. Other key advantages of the FO desalination process are (1) the energy consumption is lower by more than 30% compared with conventional RO, (2) chlorine tolerance and compatibility with a variety of biocides with FO membranes, (3) inherently low product boron levels, and (4) higher availability than conventional RO plant owing to low fouling and simple cleaning when required. The success of the FO process at the industrial level depends on how to prepare an effi cient FO membrane having minimal internal and external concentration polarizations as well as how to separate salt free water effectively from the draw solution (Ng et al. 2006). Membrane Distillation (MD) MD uses hydrophobic porous membranes as supports for a liquid/vapour interface and the vapour is transported in the membrane pores by diffusion. Indeed MD is particularly interesting because the principle itself of the transfer and selectivity of these membranes does not depend on the osmotic pressure of the solution as for the RO or the FO. Recent work has shown the use of the MD process for the over-concentration of brines up to very high salt concentrations and thus for improving the recovery of RO plants (Méricq et al. 2010), for the crystallization of salts for their valorization (Ji 2010). Another interesting application is when coupling the MD process with solar energies (Méricq et al. 2011; Guillén-Burrieza et al. 2011) or the recovery of heat, which can make MD become a sustainable process. The work in progress on this topic throughout the world relates to the design and development of new membrane modules (Winter et al. 2011) and integrated systems, and on the characterization and long-term control of membrane fouling and its properties (Krivorot et al. 2011). Some platforms with long-term testing of the MD system coupled with solar energy or waste heat recovery 47
48 IWA Specialist Groups are under operation in many countries such as the Netherlands, Spain, Tunisia and Singapore. Conclusions and outlook Membrane fouling and energy consumption when operating membrane processes are still important challenges that need to be optimized and improved using innovative tools and technologies, as well as best operational practices. Nevertheless, for a wide range of applications in several areas, membrane treatment is becoming a competitive and economically viable option. The main factors infl uencing the rapid growth of membrane technology are the following: (1) multiple global challenges such as energy/resource shortage, climate change and rapid population growth; (2) improvement in membrane materials and modules; and (3) operational stability such as better antifouling, integrity testing of membrane processes. The key drawbacks of membrane technologies are high energy consumption and relatively high cost. In addition, questions still remain about the durability and lifespan of the membranes: the 20-year lifespan claimed by manufacturers in continuous MBRs has yet to be proved through operational experience. Owing to its aforementioned intrinsic properties, membrane technology will be the centre of one of the core technologies for us to face multiple challenges in the future. Membrane technology will provide great help to meet fi ve of the fi fteen Global Challenges (TMP 2011) for Humanity, namely sustainable development and climate change, water scarcity and water quality, balance population and resources, health issues and reduction of diseases and immune microbes, renewable energy and energy conversion. References Chou S., Shi L., Wang R., Tang C.Y, Qiu C. and Fane A.G. (2010) Characteristics and potential applications of a novel forward osmosis hollow fi ber membrane. Desalination 261(3), 365–372. Drews A. (2010), Membrane fouling in membrane bioreactorscharacterisation, contradictions, cause and cures. Journal of Membrane Science 363, 1–28. Frenkel, V. (2010) Membrane technologies for water and wastewater treatment. International Water Association Conference IWA-2010, June 2–4, 2010, Moscow, Russia. Guillén-Burrieza E. et al. (2011) Experimental analysis of an air gap membrane distillation solar desalination pilot system. Journal of Membrane Science 379(1–2), 386–396. Ji X., Curcio E., Obaidani S.A., Profi o G.D., Fontananova E. and Drioli E. (2010) Membrane distillation-crystallization of seawater reverse osmosis brines. Separation and Purifi cation Technology 71(1), 76–82. Judd, S., the MBR site, http://www.thembrsite.com/features. php. Kim J.H., Choi D.C., Yeon K.M., Kim S.R. and Lee, C.H. (2011) Enzyme-immobilized nanofi ltration membrane to mitigate biofouling based on quorum quenching. Environmental Science and Technology 45, 1601–1607. .Krivorot M., Kushmaro A., Oren Y. and Gilron J. (2011) Factors affecting biofi lm formation and biofouling in membrane distillation of seawater. Journal of Membrane Science 376 (1–2), 15-24. Kwok S.C., Lang H. and O’Callaghan P. (2010) Water Technology Markets 2010: key opportunities and emerging trends. Global Water Intelligence. Kurihara M. (2011) International Conference on Seawater Desalination & Wastewater Reuse, Quingdao, China, June 21. Lesjean B., Tazi-Pain A., Thaure D., Moeslang H. and Buisson H., (2011) Ten persistent myths and the realities of membrane bioreactor technology for municipal applications. Water Science and Technology 63(1), 32–39. Maximous, N., Nakhla, G., Wan, W. and Wong, K. (2009) Preparation, characterization and performance of Al 2 O 3 /PES membrane for wastewater fi ltration. Journal of Membrane Science 341, 67–75. Méricq, J.P., Laborie, S. and Cabassud, C., (2010) Vacuum membrane distillation of seawater reverse osmosis brines. Water Research 44(18), 5260–5273. Méricq JP., Laborie S. and Cabassud C., (2011) Evaluation of systems coupling vacuum membrane distillation and solar energy for seawater desalination. Chemical Engineering Journal 166(2), 596–606. Ng, H.Y., Tang, W. and Wong, W.S. (2006) Performance of forward (direct) osmosis process: membrane structure and transport phenomenon. Environmental Science and Technology 40, 2408–2413. Taurozzi, J.S., Arul, H., Bosak, V. Z., Burban, A.F., Voice, T.C., Bruening, M.L. and Tarabara, V.V. (2008) Effect of fi ller incorporation route on the properties of polysulfone–silver nanocomposite membranes of different porosities. Journal of Membrane Science 325, 58–68. TMP (The Millennium Project) (2001) Global challenges for humanity, Available at (assessed July, 2011). Verweij, H., Schillo M. and Li J. (2007) Fast mass transport through carbon nanotube membranes. Small 3, 1996– 2004. Wang, R., Shi, L., Tang, C.Y., Chou, S., Qiu, C. and Fane, A.G. (2010) Characterization of novel forward osmosis hollow fi ber membranes. Journal of Membrane Science 355(1–2), 158–167. Winter, D., Koschikowski, J. and Wieghaus, M., (2011) Desalination using membrane desalination; experimental studies on full scale spiral wound modules. Journal of Membrane Science 375(1–2), 104–112. Xiong, Y. and Liu, Y. (2010) Biological control of microbial attachment: a promising alternative for mitigating membrane biofouling. Applied Microbiology and Bio technology 86, 825–837. Yeon, K.M., Lee, C.H. and Kim J. (2009) Magnetic enzyme carrier for effective biofouling control in the membrane bioreactor based on enzymatic quorum quenching. Environmental Science and Technology 43, 7403–7409.
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