Membrane systems design

The design of an integrated or hybrid membrane water system entails a comprehensive design of the feed water treatment system, the design of the membrane array based on 

The RO and NF membrane processes are discussed in detail in Chapter 1. RO membranes are weU-suited to rejecting dissolved ions and most organics (some organics such as ethanol and acetone have very low rejections of 45-55%). The rate of water transport through a membrane depends on membrane properties (polymeric, chemical, morphological), water temperature, and the difierence in applied pressure across the membrane, less the difference in osmotic pressure between the concentrated and dilute solutions. Osmotic pressure is proportional to the solution concentration and temperature, and depends on the type of ionic species present. For solutions of predominandy sodium chloride at 25°C, a mle of thumb is that the osmotic pressure is 0.7 bar per 1000 mg/1 concentration (see Table 6.11 for osmotic pressures of various solutions). 

Standard SW modules are 20 cm diameter x 100 cm long with a membrane surface area of 41 rc (see Table 2.10). Larger SW modules (40 X 100 cm and 45 x 150 cm) have been developed for seawater and brackish water desahnation. These larger modules are more efficient and result in lower system costs. The surface area of 40 cm diameter x 104 cm long (nominal) modules is 158 vc . The world s largest SWRO desahnation plant (540,000 m /day) in Sorek, Israel (commissioned in 2013) is the first large desalination plant using 40 cm diameter SW modules. 

Spiral-wound loose wrap or full-fit modules (FFM) are used in many pharmaceutical systems because there are no brine seals to prevent the by-pass of feed water. When a brine seal is utilised, a large pocket of water remains stagnant around the RO membrane. Since the water is not chlorinated in the case of PA membrane elements, stagnant water is 

Membrane type Thin-fikn Thin-film Homogenous S, Thin-film 

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Membrane System Design Features For the rate process of permeation to occur, there must be a driving force. For gas separations, that force is partial pressure (or fugacity). Since the ratio of the component fluxes determines the separation, the partial pressure of each component at each point is important. There are three ways of driving the process Either high partial pressure on the feed side (achieved by high total pressure), or low partial pressure on the permeate side, which may be achieved either by vacuum or by introduc-... 

Another factor that affects membrane system design is the degree of separation required. The usual target of a gas separation system is to produce a residue stream essentially stripped of the permeable component and a small, highly concentrated permeate stream. These two requirements cannot be met simultaneously a tradeoff must be made between removal from the feed gas and enrichment in the permeate. The system attribute that characterizes this trade-off is called the stage-cut. The effect of stage-cut on system performance is illustrated in Figure 8.15. 

Wastewater reclamation is a logical extension of desalination technology. Much of the membrane system design is common to both applications, and the membranes available for wastewater treatment are those originally developed for desalination. The first major project designed for... 

Four parameters related to the membrane, feed stream and operating conditions determine the technical as well as economic performance of an inorganic membrane system. They are the transmembrane flux, permselectivity, maintenance of the permeating flux and permselectivity over time and stability toward the applications environment These parameters are the primary considerations for all aspects of the membrane system design, ai lication, and operation. 

Consider the effect of the distribution equilibrium (9.8.32) for an ion-exchanging membrane system designed to detect cation M" ". The total activity of M" " in the test solution is... 

The study focuses on the behavior of the ULP RO membranes in the full-scale system [62]. The ULP membranes have salt rejections comparable to conventional RO membranes, but the hydraulic characteristics are significantly different. Hence, modifications to conventional membrane system design mnst be considered to optimize the use of the ULP RO membrane. Several design options are evaluated for function, effectiveness, and cost impact. 

The SEC of SWRO has dropped from 10 kWh/m to typically <4.0 kWh/m in the last 30 years [3,5,9,12-14] as a result of improvements in membranes, systems design and hardware. The process, however, is still energy intensive. Additional reductions of 10—20% may be achievable when operating with modified staged des ps of membrane arrays [5,6,14] and/or operating in a combined heat and power mode [13]. 

The emphasis taken here to achieve these desired tissue microenvironments is through use of novel membrane systems designed to possess unique features for the specific apphcation of interest, and in many cases to exhibit stimulant/response characteristics. These so-called intelligent or smart membranes are the result of biomimicry, that is, they have biomimetic features. Through functionalized membranes, typically in concerted assembhes, these systems respond to external stresses (chemical and physical in nature) to eliminate the threat either by altering stress characteristics or by modifying and protecting the ceU/tissue microenvironment. An example (discussed further later in this chapter), is a microencapsulation motif for beta ceU islet clusters to perform as an artificial pancreas. This system uses multiple membrane materials. 

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