Ultrafiltration membrane cleaning

Zirconia membranes on carbon supports were originally developed by Union Carbide. Ultrafiltration membranes are commercially available now under trade names like Ucarsep and Carbosep. Their outstanding quality is their high chemical resistance which allows steam sterilization and cleaning procedures in the pH range 0-14 at temperatures up to 80°C. These systems consist of a sintered carbon tube with an ultrafiltration layer of a metallic oxide, usually zirconia. Typical tube dimensions are 10 mm (outer diameter) with a wall thickness of 2 mm (Gerster and Veyre 1985). 

Parkin, M.F. and Marshall, K.R., "The Cleaning of Tubular Cellulose Acetate Ultrafiltration Membranes", N.Z. Journ. 

Membranes are made from different materials. Cellulose nitrate ultrafiltration membranes are of limited chemical and thermal compatibility and with imprecise cut-off. The membranes from polyvinylidene fluoride, polyaciyloiutrile or polysulphone possess good chemical compatibility are more stable over a very wide pH range and ate easy to clean. Problems with membrane fouling can usually be overcome by trcatment of the membranes with detergents, proteases or with acid or alkaline solutions. 

Among the numerous approaches studied so far to minimize such phenomena in ED, it is worth citing pretreatment of the feed solution by coagulation (De Korosy et al., 1970) or microfiltration (MF) or ultrafiltration membrane processing (Ferrarini, 2001 Lewandowski et al., 1999 Pinacci et al., 2004), turbulence in the compartments, optimization of the process conditions, as well as modification of the membrane properties (Grebenyuk et al., 1998). However, all these methods are partially effective and hydraulic or chemical cleaning-in-place (CIP) is still needed today, thus... 

Regular cleaning is required to maintain the performance of all ultrafiltration membranes. The period of the cleaning cycle can vary from daily for food applications, such as ultrafiltration of whey, to once a month or more for ultrafiltration membranes used as polishing units in ultrapure water systems. A typical cleaning cycle is as follows ... 

Because of the challenging environment in which ultrafiltration membranes are operated and the regular cleaning cycles, membrane lifetime is significantly shorter than that of reverse osmosis membranes. Ultrafiltration module lifetimes are rarely more than 2-3 years, and modules may be replaced annually in cheese whey or electrocoat paint applications. In contrast, reverse osmosis membranes are normally not cleaned more than once or twice per year and can last 4-5 years. 

During reverse osmosis and ultrafiltration membrane concentration, polarization and fouling are the phenomena responsible for limiting the permeate flux during a cyclic operation (i.e., permeation followed by cleaning). That is, membrane lifetimes and permeate (i.e., pure water) fluxes are primarily affected by the phenomena of concentration polarization (i.e., solute build up) and fouling (e.g., microbial adhesion, gel layer formation, and solute adhesion) at the membrane surface [11]. 

A comparison of the previous resuits with the cleaning effect of ultrasound irradiation at the frequencies in the kHz range, which decreases the fouling conditions of filtration and ultrafiltration membranes (see Section 2.6.1), clearly reveals that this effect does not apply to high-frequenoy US [95]. 

A variety of liquids have been treated with reverse osmosis and ultrafiltration membranes ranging from seawater, to wastewater, to milk and yeast suspensions. Each liquid varies in composition and in the type and fraction of the solute(s) to be retained by the membrane. Complicating factors include the presence of substances such as oil in seawater and wastewater [12-15]. The presence of the oil normally necessitates an additional pretreatment step further complicating the fouling process. The presence of humic acids in surface water and wastewater also needs special attention [16,17]. The fouling phenomena, the preventive means (i.e., pretreatment), and the frequency and type of membrane cleaning cycle are all dependent on the type of liquid being treated. 

Lindau J. and Jonsson A.-S., Cleaning of ultrafiltration membranes after treatment of oily wastewater. Journal of Membrane Science 87 1994 71-78. 

Munoz-Aguado, M.J., Wiley, D.E., and Fane, A.G., Enzymatic and detergent cleaning of a polysulfone ultrafiltration membrane fouled with BSA and whey, J. Membr. Sci., 117, 175, 1996. 

Bohner, H.F. and Bradley, R.L., Effective cleaning and sanitizing of polysulfone ultrafiltration membrane systems, J. Dairy Sci., 73, 2309, 1992. 

Microfiltration and ultrafiltration membranes allow flow capacities of 150 to 500 liters/m per hour when operating on water. This is expressed as water flux for each membrane type. Naturally the flow capacity for juices is lower. After cleaning of a membrane the water flux should reach its original capacity and it serves as an indication whether the membrane was properly cleaned. It is also an indication for when a membrane needs replacement once it plugs over longer periods. 

Polyamide-6 (Nylon-6, Perlon) and polyamide-6.6 (Nylon-6.6) are the most well known polyamides. Polyamide-based filaments find wide spread applications as yarns for textile or industrial and carpet materials [70], However, nylon-based textiles are uncomfortable to wear and difficult to finish due to their hydrophobic character. This characteristic also leads to fouling of PA-based ultrafiltration membranes by proteins and other biomolecules which increases the energy demand for filtration and requires cleaning with aggressive chemicals or replacement [71-73], Consequently the enhancement of the hydrophilicity of nylon is a key requirement for many applications and can be achieved by using plasma treatment [74-76], As a promising alternative, enzymatic hydrophilization of PA requires less energy and is not restricted to planar surfaces. 

Equipment used to produce biotech products should be qualified for design, installation, operation, and performance [15]. The aging and continued performance of re-used process materials such as column resins is an important consideration during the validation of a biotech process. Demonstration of microbial control during processing is also a critical component of process validation, particularly in difficult to clean equipment such as alBnity columns or ultrafiltration membranes. Finally, consistent and reasonable step yield of individual unit operations can be verified during consistency and commercial product manufacturing. 

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