Membrane technologies nanofiltration

Tony Franken (membrane technologies nanofiltration reverse osmosis membrane distillation). Director, Membrane Application Centre Twente (MACT bv), Enschede... 

Singh, Rajindar (M.A.E. Environmental Technologies). A Review of Membrane Technologies Reverse Osmosis, Nanofiltration and Ultrcfiltration. Ultrapure Water, Tall Oaks Publishing, Inc., USA, March 1997. 

Son, E.J. Choe, E.K. Nanofiltration membrane technology for caustic soda recovery. Text. Chem. Color. Am. D. 2000, 32, 46-52. 

Membrane technology has been performed using either micro-, ultra- or nanofiltration or reverse osmosis in either batch-wise or continuous-flow membrane reactors (CFMR). 

In this chapter, the impact of other membrane technologies on the operation of RO systems is discussed. Technologies considered include microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) as pretreatment to RO, and continuous electrodeionization (CEDI) as post-treatment to RO. This chapter also describes the HERO (high efficiency RO—Debasish Mukhopadhyay patent holder, 1999) process used to generate high purity water from water that is difficult to treat, such as water containing high concentrations of silica. 

Membrane technology is a mature industry and has been successfully applied in various food industries for separation of undesirable fractions from the valuable components of the feed streams. The industrial membranes are classified into various categories such as microfiltration, ultrafiltration, nanofiltration, reverse osmosis, and pervaporation. 

Membrane technology may become essential if zero-discharge mills become a requirement or legislation on water use becomes very restrictive. The type of membrane fractionation required varies according to the use that is to be made of the treated water. This issue is addressed in Chapter 35, which describes the apphcation of membrane processes in the pulp and paper industry for treatment of the effluent generated. Chapter 36 focuses on the apphcation of membrane bioreactors in wastewater treatment. Chapter 37 describes the apphcations of hollow fiber contactors in membrane-assisted solvent extraction for the recovery of metallic pollutants. The apphcations of membrane contactors in the treatment of gaseous waste streams are presented in Chapter 38. Chapter 39 deals with an important development in the strip dispersion technique for actinide recovery/metal separation. Chapter 40 focuses on electrically enhanced membrane separation and catalysis. Chapter 41 contains important case studies on the treatment of effluent in the leather industry. The case studies cover the work carried out at pilot plant level with membrane bioreactors and reverse osmosis. Development in nanofiltration and a case study on the recovery of impurity-free sodium thiocyanate in the acrylic industry are described in Chapter 42. 

Nanofiltration is a rapidly advancing membrane separation technique for concentration/separation of important fine chemicals as well as treatment of effluents in pharmaceutical industry due to its unique charge-based repulsion property [5]. Nanofiltration, also termed as loose reverse osmosis, is capable of solving a wide variety of separation problems associated with bulk drug industry. It is a pressure-driven membrane process and indicates a specific domain of membrane technology that hes between ultrafiltration and reverse osmosis [6]. The process uses a membrane that selectively restricts flow of solutes while permitting flow of the solvent. It is closely related to reverse osmosis and is called loose RO as the pores in NF are more open than those in RO and compounds with molecular weight 150-300 Da are rejected. NF is a kinetic process and not equilibrium driven [7]. 

Therefore, the need of the hour was to develop an economical alternate separation technology capable of replacing the GFC system by providing rejection of all impurities in a single step with permeation of NaSCN and water. The membrane-based nanofiltration technique appeared to be a suitable alternative based on some of the aspects discussed in the scope of the work [180-184]. 

Membrane technology used in water reclamation includes five major membrane types reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and liquid membranes. These five types of membranes are discussed briefly, and examples of their applications in municipal and industrial wastewater reclamation is also described. 

AUgeier S.C., Summers R.S. (1995a), Development of a rapid bench-scale membrane test for the evaluation of nanofiltration performance, Proc. AWWA Membrane Technology Conf, Reno, Nevada, Aug 95, 207-227. 

Bourbigot M.M., Cote P., Agbekodo K. (1993), Nanofiltration An advanced process for the production of high quality drinking water, Proc. of AWWA Membrane Technology Conf., Baltimore, Aug 93, 207-211. 

CheUam S., Jacangelo J.G., Bonacquisti T.P., Long B.W. (1997a), Effect of operating conditions and pretreatment for nanofiltration of surface water, Proc. AWWA Membrane Technology Conference, New Orleans, Feb. 97, 215-231. 

Childress A.E., Elimelech M. (1997), Effects of natural organic matter and surfactants on the surface characteristics of low pressure reverse osmosis and nanofiltration membranes, Proc. A WA Membrane Technology Conference, New Orleans, Feb. 97, 717-725. 

Oily water wastes constitute a major environmental problem in many industries. Stable oil/water emulsions, which cannot be broken by mechanical or chemical means, require more sophisticated treatment to meet the effluent standards. Various physical methods including microfiltration, ultrafiltration, nanofiltration, centrifugation, air flotation, and fiber or packed bed coalescence have been applied in oil-surfactant-water separation [131]. Among these physical methods, membrane technology is by far the most widely used. 

To summarise, the development and remarkable success of commercial membrane processes for Uquid separations — RO, nanofiltration (NF), UF, and MF — would not have been possible without the discovery and subsequent development of high-flux, extremely thin (skinned) CA membranes by Srinivas Sourirajan and Sidney Loeb at UCLA, culminating in the development of TFC PA membranes by John Cadotte. Membrane technologies such as NF, PV and GS got the impetus from the work on RO in the 1950s and 1960s. These successes have led to the development of newer membrane processes such as membrane distillation (MD) and forward osmosis (FO). 

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