Chlorine tolerance

Chemical attack is often a result either of fouling prevention or cleaning in response to fouling. Chlorine and hypochlorite damage most RO and NF membranes, as do oxidants generally (see discussion of chlorine tolerance below). 

Chlorine Tolerance Most of the best RO membranes are attacked by oxidants, and they are particularly susceptible to chlorine. A particularly sensitive locus for attack is the amidic hydrogen. Cellu-losic membranes are generally less sensitive, and pass the chlorine into the permeate giving downstream biocidal activity, veiy useful for under-the-sink RO. These factors are largely responsible for CA s survival in RO membranes. Chlorine, whatever its vices, has the virtue of being a known, effective, residual bactericide and a good inhibitor of... 

Membranes are commonly rated for their chlorine tolerance in ppm-hours, simply the product of the concentration and the contact time. Tolerance is temperature dependent. 

The process is fairly robust. As for one of the main problematic inputs, chlorine from PVC, the plant was able to handle MPW with the regularly occurring PVC content of 4%-5%. This implies a chlorine tolerance of some 2.5%. As for the emissions and resource use, Heyde and Kremer (a.6) have carried out an extensive study. All emissions will comply with local regulations. 

For a few years after the development of the first interfacial composite membranes, it was believed that the amine portion of the reaction chemistry had to be polymeric to obtain good membranes. This is not the case, and the monomeric amines, piperazine and phenylenediamine, have been used to form membranes with very good properties. Interfacial composite membranes based on urea or amide bonds are subject to degradation by chlorine attack, but the rate of degradation of the membrane is slowed significantly if tertiary aromatic amines are used and the membranes are highly crosslinked. Chemistries based on all-aromatic or piperazine structures are moderately chlorine tolerant and can withstand very low level exposure to chlorine for prolonged periods or exposure to ppm levels... 

Williams, M.L., Palmer, C.G. and Gordon, A.K. (2003) Riverine macroinvertebrate responses to chlorine and chlorinated sewage effluents - Acute chlorine tolerances of Baetis harrisoni (Ephemeroptera) from two rivers in KwaZulu-Natal, South Africa, Water SA 29 (4), 483-488. 

Since the late 1970 s, researchers in the US, Japan, Korea, and other locations have been making an effort to develop chlorine-tolerant RO membranes that exhibit high flux and high rejection. Most work, such as that by Riley and Ridgway et.al., focuses on modifications in the preparation of polyamide composite membranes (see Chapter 4.2.2).11 Other work by Freeman (University of Texas at Austin) and others involves the development of chlorine-tolerant membrane materials other than polyamide. To date, no chlorine-resistant polyamide composite membranes are commercially available for large-scale application. 

Membrane material. During the early days, membranes were usually made of cellulose acetate. At present, membranes can also be made from aromatic polyamide and thin-filmed polymer composites. Different membrane materials have their own distinctive characteristics, such as hydraulic resistance, pH range, temperature range, chlorine tolerance, and biodegradation tolerance. 

Agent Water Threat Stable in Water Chlorine Tolerance... 

This section intends to provide a review on the advanced materials used in the recent development of TFC-NF membranes and the effects of the advanced materials on the improvement of composite membrane properties with respect to permeability/selectivity, chlorine tolerance, solvent stability, fouling resistance, etc. The advanced materials that are used in composite membrane fabrication to improve either the top active layer properties or substrate properties can be generally categorized into (a) active monomer, (b) surfactant/ additive, (c) nanoflller, and (d) polymeric substrate. 

Development of Membranes for Boron Removal, Chlorine Tolerance, and Antibiofouling.38... 

Park HB, Freeman BD, Zhang ZB, Sankir M, and McGrath JM, Highly chlorine-tolerant polymers for desalination, Angewandte Chemie 2008, 120, 6108-6113. 

High performance thin-film composite membranes for reverse osmosis applications were fabricated by coating solutions of a highly chlorine-tolerant disulfonated PAES [92,93]. As base monomers, 4,4 -dichlorodiphenyl sulfone and 4,4 -biphenol are used. 4,4 -dichlorodiphenyl sulfone is then directly sulfonated to get a disulfonated monomer, 3,3 -disutfonate-4,4 -dichlorodiphenyl sulfone. These monomers can be directly copolymerized on a commercially available porous polysulfone support. 

R2A agar NWRI agar (HPCA) 35°C for more that 48 h 20°C or 28°C for 5-7 days Low-nutrient medium relatively high bacteria count suitable for culturing stressed and chlorine tolerant bacteria from drinking water [2,114,115]... 

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