Ultrafiltration water treatment membrane applications

By contrast porous ceramic membranes had found application since the 1960s in the field of large-scale gas diffusion processes for uranium isotope separation. It was only in the 1980s that porous ceramic membranes found other non-nuclear industrial applications, mainly oriented towards microfiltration and ultrafiltration water treatment processes. 

Pretreatment For most membrane applications, particularly for RO and NF, pretreatment of the feed is essential. If pretreatment is inadequate, success will be transient. For most applications, pretreatment is location specific. Well water is easier to treat than surface water and that is particularly true for sea wells. A reducing (anaerobic) environment is preferred. If heavy metals are present in the feed even in small amounts, they may catalyze membrane degradation. If surface sources are treated, chlorination followed by thorough dechlorination is required for high-performance membranes [Riley in Baker et al., op. cit., p. 5-29]. It is normal to adjust pH and add antisealants to prevent deposition of carbonates and siillates on the membrane. Iron can be a major problem, and equipment selection to avoid iron contamination is required. Freshly precipitated iron oxide fouls membranes and reqiiires an expensive cleaning procedure to remove. Humic acid is another foulant, and if it is present, conventional flocculation and filtration are normally used to remove it. The same treatment is appropriate for other colloidal materials. Ultrafiltration or microfiltration are excellent pretreatments, but in general they are... 

Ultrafiltration processes (commonly UF or UF/DF) employ pressure driving forces of 0.2 to 1.0 MPa to drive liquid solvents (primarily water) and small solutes through membranes while retaining solutes of 10 to 1000 A diameter (roughly 300 to 1000 kDa). Commercial operation is almost exclusively run as TFF with water treatment applications run as NFF. Virus-retaining filters are on the most open end of UF and can be run as NFF or TFF. Small-scale sample preparation in dilute solutions can be run as NFF in centrifuge tubes. 

Water reclamation, the treatment of wastewater to meet the water quality standards of various applications economically, is becoming increasingly important in view of the increasing world population and scarcity of fresh water sources. The major technology used for water reclamation is membrane technology. This entry gives an overview of the major membrane types used for water reclamation reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and liquid membranes. Applications of these membranes in municipal and industrial wastewater reclamation have been described. 

R.O. systems utilizing externally wound tubular membrane element in modular assemblies have been used in the desalination of brackish and sea waters, the treatment and/or concentration of industrial waste waters, the separation/concentration of fluid food, pharmaceuticals and chemical solutions, and the manufacture of water purifiers for domestic use. Generally, externally wound tubular membrane systems have been found to be highly suitable for ultrafiltration applications in the processing Industry and in water pollution control applications. 

For water treatment applications the flux decline was significant. Rejections may be comparable to those obtained with the use of some ultrafiltration membranes and thus it would be interesting to compare which process is more economic at a similar water quality. 

This book, by Andrea Schafer, deals with the other important requirement in water treatment, the removal of natural organic matter (NOM). For many water sources NOM is a problem and must be removed to avoid the formation of trihalomethanes, by-products in the disinfection process. The Water Industry, wishing to use membranes, has a choice of options for NOM removal. This book provides valuable input to that choice. For applications with moderate to high NOM the choice could be Nanofiltration and for low or intermittent NOM the choice could be Micro- or Ultrafiltration with chemical coagulant as required. However the optimal choice remains a moot point, driven by costs and operational issues. 

Submerged membrane bioreactors are revolutionizing waste water treatment [108]. These units dramatically increase the capacity of waste water treatment ponds while simultaneously producing a higher quality water by using an ultrafiltration membrane to remove treated water from the mixed liquor suspended solids (MLSS) produced by biological treatment. Such process intensification is one of the hallmarks of applications where membrane processes have achieved commercial success (in addition to energy reduction and purification of labile compounds). 

Several physicochemical methods and biological have been used to remove organic compounds in industrial effluents. Application of membrane filtration systems and adsorption processes in water treatment and effluent was used by a group of researchers. They developed a system for removal of phenol from an aqueous solution through a combined process of ultrafiltration and adsorption using kaohnite and montmorillonite. The adsorption experiments were performed in batch with 0.2 g of day and 100 mL of water contaminated in the range of variable concentration of the organic compound from 20 to 1000 mg L l, stirred for 12 h at 25°C. The results showed that the phenol removal efficiency was 80% and a maximum adsorption cap>adty equal to 40 mg (Lin et al., 2005). 

Currently, the pressure-driven membrane processes, reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF), are widely used in water treatment, biotechnology, food industry, medicine, and other fields (Baker 2004). However, one of the main problems arising from the operation of the manbrane units is membrane fouling, which seriously hampers the applications of manbrane technologies (Scot and Hughes 1996). 

Kennedy MD, Kamanyi J, Salinas Rodriguez SG, Lee NH, Schippers JC and Amy G (2008), Water treatment by microfiltration and ultrafiltration in Advanced Membrane Technology and Applications, New York, John Wiley Sons, 131-170. 

By considering forthcoming new environmental regulations, nanofiltration and ultrafiltration using hydrophilic membranes have become even more important for applications in water treatment such as oil-water emulsions. Conventional membranes are effective in the removal of oily microemulsions from water, but they often suffer from low flux due to limited permeability and surface fouling [66, 67]. Membrane surface hydrophilicity is widely accepted as a dominant factor that... 

Ultrafiltration can adequately produce disinfected water directly from strrface water for different applications. MF can also be used for disinfection, although not all viruses are removed. However, direct membrane filtration is limited by fouling, which, during constant-flux filtration, leads to a continuous increase in transmembrane pressure. In addition, UF and MF membrane treatment alone cannot effectively and consistently remove organic material, measured as total organic carbon (TOC), and THM (tri-halo-methane) precursors, measured as chloroform formation potential (Berube et al., 2002). 

Heidenreich S and Scheibner B. Hot gas filtration with ceramic filters Experiences and new developments. Filtr. Sep. 2002 May 22-25. Heidenreich S and Wolters C. Hot gas filter contributes to IGCC power plant s reliable operation. Filtr. Sep. 2004 June 22-25. Larbot A, Bertrand M, Marre S, and Prouzet E. Performances of ceramic filters for air purification. Sep. Purif. Technol. 2003 32 81-85. DeFriend KA and Barron AR. A simple approach to hierarchical ceramic ultrafiltration membranes. J. Membr. Sci. 2003 212 29-38. Endo Y, Chen D-R, and Pui DYH. Collection efficiency of sintered ceramic filters made of submicron spheres. Filtr. Sep. 2002 March 43-47. Sakol D and Konieczny K. Application of coagulation and conventional filtration in raw water pre-treatment before microfiltration membranes. Desalination 2004 162 61-73. 

Some areas of application are the nuclear industry and the treatment of radioactive liquid wastes, with two main purposes reduction in the waste volume for further disposal, and reuse of decontaminated water. Pressure-driven membrane processes (microfiltration, ultrafiltration, nanofiltration, and reverse osmosis [RO]) are widely used for the treatment of radioactive waste. 

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