Nano filtration is a pressure driven filtration process where mixture water passes through a membrane by the application of a gravity or pressure. High removal of divalent ions (calcium, magnesium, arsenic, iron, sulphate) and low removal of monovalent ions (sodium, potassium, chloride) can be achieved in Nano filtration process. Nano filtration membranes can be used in desalination, organic matter and iron removal from surface water (Bartels et. al., 2007).
A number of problems such as membrane fouling, corrosion and scaling are caused by suspended solids, organic and inorganic materials in the feed water. Membrane fouling due to high levels of organic compounds in water can change permeability of Nano filtration membrane affecting water quality and operating cost (Bartels, et. al., 2007). Membrane bio fouling, growth of micro-organisms on a membrane, is a serious challenge causing technical problems (Ivnitsky et. al., 2005). According to Ivnitsky et. al. (2005) microbes such as Flavobacterium species, Pseudomonas, Ralstonia and Cytophaga grow rapidly and colonize the membrane even they are present in small numbers if the nutrient is available.
Water treatment procedures such as coagulation, sedimentation, water disinfection with chlorine, addition of scale inhibitor, pH adjustment and microfiltration are carried out before passing the feed into Nano filtration (Hydronautics, 2001). Pre-treatment of water before filtration is one the current water filtration issues (Eltron, 2009). Pre-treatment enables to improve the quality of feed water to pass through the Nano filtration membranes (Hydranautics, 2001).Good quality of feed water can be measured by a number of indicators. Silt Density Index (SDI) is the indicator of suspended solids and Langelier Saturation Index (LSI) is the indicator of saturation level of Calcium Carbonate (Hydranautics, 2001).
Management of concentrate is important aspect of the Nano filtration process. Silica rich concentrate can be effectively treated with lime treatment system (Tarquin et. al., 2004). Treatment of concentrate can be carried out if cost-benefit analysis suggests the worthiness of recovering water than wasting it.
Bartels, C., Lai, K., Wilf, M. (2007) New Generation of Low Fouling Nano Filtration Membranes. Desalination. Vol. 221, Issue 1-3. Pages 158-167.
Eltron Research (2009) High Stability Membranes for Nano filtration and Reverse Osmosis. [Online] Available at http://www.eltronresearch.com [Accessed on 26 February 2013].
Hydronautics (2001) Pre Treatment. [Online] Available at membranes.com/docs/trc/pretreat.pdf [Accessed on 26 February 2013].
Ivnitsky, H., Katz, I., Minz, D., Shimoni, E., Chen, Y., Tarchitzky, J., Semiat, R., Dosoretz, C.Z. (2005) Characterization of Membrane Bio Fouling in Nano Filtration Processes of Wastewater Treatment. Desalination. 185, 255-268.
Tarquin, A. J., Patwardhan, D., Kolluri, B. (2004) The Science of Concentrate Management. [Online] Available at www.wrri.nmsu.edu/publish/watcon/proc49/tarquin.pdf [Accessed on 26 February 2013].