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Membrane Technologies for Water Purification
Published in P.K. Tewari, Advanced Water Technologies, 2020
A number of materials are used to make ultrafiltration membranes, primarily polyacrylonitrile, poly(vinyl chloride)–polyacrylonitrile copolymers, polysulfone, poly(ether sulfone), poly(vinylidene fluoride) . Aromatic polyamides and cellulose acetate are also used. In general, hydrophilic membranes are more fouling resistant than those made from hydrophobic materials. For this reason, water-soluble polymers such as poly(vinyl pyrrolidone) or poly(vinyl methyl ether) are often added to membrane casting solutions used for hydrophobic polymers such as polysulfone or poly(vinylidene fluoride). During the membrane precipitation step, water-soluble polymer leaches out from the membrane; however, enough remains to make the membrane surface hydrophilic. The charge on the membrane surface is important. If the membrane surface has a slight negative charge, adhesion of the colloidal gel layer to the membrane is reduced, which helps to maintain a high flux and inhibit membrane fouling. The effect of a slight positive charge on the membrane is the opposite. Charge and hydrophilic character can be the result of the chemical structure of the membrane material or can be applied to the membrane surface by chemical grafting or surface treatment. Choice of treatment depends on the application and the feed characteristics.
Theoretical Approach behind Membrane Processing Techniques
Published in M. Selvamuthukumaran, Applications of Membrane Technology for Food Processing Industries, 2020
Ultrafiltration is the process of membrane filtration that acts as a barrier and separates high molecular weight materials, organic and inorganic polymer molecules, suspended solids, colloidal matter, bacteria, viruses, and other unwanted harmful foreign materials from the solvent. The pore size of the membrane used in an ultrafiltration process ranges from 0.1 to 0.001 micron. The membrane is not efficient for removing low molecular weight organics and ion species such as sodium, calcium, magnesium and sulfates. The principle associated with the filtration process by ultrafiltration membrane technology involves low hydrostatic pressure applied across the membrane during filtration. Early ultrafiltration methods involve passing the water sample under pressure through aluminium/lanthanum alginate filters (Poynter et al. 1975). These have the specific advantage of being solubilized in isotonic sodium citrate solution. Advanced techniques involve passing the sample through capillaries, hollow fibers, or membranes with a permissible pore size that allows the water and low molecular weight substances to permeate but reject the macromolecules.
Water and Wastewater: Filters
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Water Resources and Hydrological Systems, 2020
Ultrafiltration is a low-pressure system operating at transmembrane pressures of 0.5–5 bars. A UF system comprises series/parallel modules operating according to various modes, ranging from an intermittent single-stage system to a continuous multistage system.[15] Ultrafiltration membranes can be fabricated essentially in tubular or flat sheet forms. Two major types of UF modules can be used, i.e., hollow fibers (capillary) and spiral wound. Other modules are plate and frame, tubular, rotary modules, vibrating modules, and Dean vortices. Operation of a UF membrane can be performed in two different service modes, viz., dead-end flow and cross-flow. The dead-end flow approach allows optimal recovery of feed water in about a 95%–98% range, but is generally limited to feed streams of low suspended solids (<1 NTU). The cross-flow mode differs from the dead-end mode in that there is an additional flow—the concentrate. The cross-flow mode of operation typically results in lower recovery of feed water, about 90%–95%.[16]
Novel Zinc ferrite composite with starch and carboxy methyl starch from biowaste precursor for the removal of Ni (II) ion from aqueous solutions
Published in Journal of Dispersion Science and Technology, 2023
Dimple Sharma, Rimzim Jasrotia, Jandeep Singh, Sunil Mittal, Harminder Singh
Various methods are available for the treatment of wastewater like ion exchange, coagulation, reverse osmosis, solvent extraction, ultrafiltration, membrane extraction, remediation, adsorption, etc.[2] These methods have various advantages and disadvantages. Coagulation is simple and it includes physiochemical process but it has disposal problems and produces sludge in large quantity. The technology behind ion exchange method is simple and various products are available from various manufacturers. Ion exchange method is not suitable because it requires large columns. Ultrafiltration method involves rapid technology and is efficient even at low concentrations. But here in this method rapid membrane clogging is the problem. Solvent extraction method is preferred over recycling of waste water but it is very costly. Among all the methods, adsorption seems to be better because of certain properties like simple, efficient, economical, etc.[7]. There are various types of adsorbents available, however the recent trend is toward the use of environment friendly materials.
Carbon nanotubes: a review on green synthesis, growth mechanism and application as a membrane filter for fluoride remediation
Published in Green Chemistry Letters and Reviews, 2021
Bayisa Meka Chufa, H. C. Ananda Murthy, Bedasa Abdisa Gonfa, Teketel Yohannes Anshebo
In most membrane separation technologies, the major problem is the cost allocated for the operations with high pressure needed to remove dissolved contaminants (e.g. monovalent ions and small organic molecules). The use of CNT in water purification is totally non-toxins yet desalinate water to the highest degree (60). The dissolved ions and organic solutes are effectively removed by reverse osmosis and nano filtrations. However, high pressures up to 100–1000 psi are required to operate reverse osmosis and nanofiltration membranes. On the other hand, ultrafiltration and microfiltration membranes require much lower pressure up to 5–60 psi. Therefore, those membrane filtrations which use high pressure for their operations such as reverse osmosis and nanofiltration are effectively applied for desalination, water purification, electrodialysis (ED) in chlorine caustic cell and hemodialysis for artificial kidneys. Ultrafiltration is used commonly in the food industry for protein separation from milk and apple juice concentration pervaporation (PV) for dehydration of ethanol, controlled release of drugs, genetic engineering, etc.
The removal of antibiotic resistance genes in secondary effluent by the combined process of PAC-UF
Published in Journal of Environmental Science and Health, Part A, 2019
Lihua Sun, Cheng Gao, Ning He, Bingbing Yang, Xi Duan, Tao Chen
In this experiment, a flat membrane ultrafiltration cup system was used to evaluate the contamination of UF using hydraulic reversible resistance and hydraulic irreversibility. Each group was tested with a new PES membrane. The membrane was immersed in pure water for 24 h before use, with the water changed at least 3 times. Then, at least 2 L of pure water was filtered to completely remove the glycerin protective layer on the membrane surface. The ultrafiltration membrane filtration pressure was 96.5 kPa (14.0 psi) and the backwash pressure was 41.4 kPa (6.0 psi). Before filtering the water sample, the self-resistance of the ultrafiltration membrane was tested, by filtering 200 mL of pure water to ultrafiltration water flux J0. The calculation method is as shown in Eq. (1):