Low-pressure membrane

Nearly a decade ago, the use of low-pressure membranes such as MF and UF for disinfection and particle removal was only a concept being studied or was used only on a limited basis. The water community foresaw the possibility of providing... 

Tertiary treatment is required often to meet the industry or irrigation standards, especially when disinfection is needed. This step is known as water regeneration. Typical tertiary treatment proposed in the literature [23] is composed of the following stages low pressure membrane filtration (e.g., MF) followed by disinfection stage and finally high pressure membrane filtration (e.g., RO). Industrial... 

As noted in Section 6.1.2, in most applications the control of CP, and fouling, dictates the use of crossflow. However, for dilute feeds and low-pressure membranes it has been accepted that batch cycles of deadend operation with solids accumulation removed by periodic backwash requires potentially lower energy. Usually, deadend is at FF and the TM P cycles from a minimum to maximum or over a specified cycle time during the batch. If fouling occurs it is evident through a steady rise in TM Pmin or Rm. Occasional chemical cleaning may restore Rm. 

Examples of particles to be filtered through low-pressure membranes include casein micelles from milk, lattices from paint, biomass floes from activated sludge, bacteria... 

UF is typically used to retain macromolecules, colloids, solutes with molecular weight higher than a few thousand Daltons. M F is a low-pressure membrane process for separating colloidal and suspended micrometer-size particles [6]. 

Low-pressure membranes have also been developed. These membranes offer high flux at low temperatures and pressure albeit with some reduction in rejection (the permeability of polyamide membranes is a function of temperature, with lower water temperatures generally requiring higher operating pressures to maintain productivity—see Chapter 9.2). These low-pressure membranes allow for operation at low temperature at lower pressure than non low-pressure membranes. 

Bodzek, M. and K. Konieczny (1998). Comparison of various membrane types and module configurations in the treatment of natural water by means of low-pressure membrane methods. Separation Purification Technol, 14, 1-3, 69-78. 

At the second RO treatment stage, the retention index to Cs in the low-pressure membranes was always higher than 98%, and above 99.5% in most cases. 

Pervov, A. et ah, A new solution for Caspian seawater desalination Low pressure membrane, Desalination, 157, 377, 2003. 

Separation of Hazardous Organics by Low Pressure Membranes Treatment of Soil-Wash Rinse-Water Leachates... 

Fu P., Ruiz H., Lozier J., Thompson K., Spangenberg C. (1995), A pilot study on groundwater natural organics removal by low-pressure membranes. Desalination, 102, 47-56. 

Jacangelo J.G., Patania N.L., Laine J.-M., Montgomery J.M., Booe W., Mallevialle J. (1992), Low pressure membrane filtration for particle removal, AWWA Research Foundation and American Water W orks Association. 

Pickering K.D., Wiesner M.R. (1993), Cost model for low-pressure membrane filtration, Journal of... 

Transient uptake rate measurements are subject to intrusion of heat transfer hmitations, especially in batch measurements at low pressures. Membrane permeation, frequency response, and ZLC measurements should not be subject to serious heat transfer limitations but, especially in frequency response and ZLC, there is always a danger of intrusion of extracrystalline resistances to mass transfer, although in principle these can be eliminated by reducing the sample size and ensuring that the crystals within the sample are dis-... 

Figure 7. Desalination performance of Tbray low pressure membranes.

It is the objective of this article to present recent developments and applications of low-pressure membranes which have been developed in the past few years. Improvements and optimization of casting conditions of asymmetric membranes as well as composite membranes are discussed. Comparisons are made where applicable. Some data obtained in our laboratory for the effect of casting conditions on the performance of asymmetric cellulose acetate membranes are also presented and compared with the data from literature. 

Brackish Water Desalination Low-pressure membranes were used by Glueckstern et al. (1986) for brackish water desalination. With a feed water of 6000-6500 mg/1, recovery of 65%, and applied pressure of 14 bars (net driving pressure of 7 bars), a salt rejection of 95% was obtained. An energy saving of 33% was achieved. 

Huang H, Schwab K, and Jacangelo JG. Pretreatment for low pressure membranes in water treatment A review. Environ Sci. Technol. 2009 43 3011-3019. 

Huang et al. [19] explains that based on the operating transmembrane pressure, membranes for water treatment use can be broadly classified as high pressure and low pressure. The latter are operated at relatively low transmembrane pressures (less than 1-2 bar, typically) and include microfiltration (MF) membranes and UF membranes. With pore sizes ranging from 10 to 100 nm, low-pressure membranes are effective in removing suspended solids and particulates to reduce turbidity and pathogens, but they are not effective for substances such as organic micropollutants. 

Significantly improves low pressure membrane (LPM) performance (less fouUng and greater rejection) (1) Requires proper dose that can be difficult to meet if feedwater quality varies rapidly/significantly,... 

Guo, H., Wyart, Y, Perot, J., Nauleau, R, and Moulin, P. 2010. Low-pressure membrane integrity tests for drinking water treatment A review. Water Res. 44 41-57. 

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