Membranes

Membranes - ENV 6015 PHYSICAL CHEMICAL TREATMENT Reverse...

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1 ENV 6015 PHYSICAL CHEMICAL TREATMENT Reverse Osmosis And Nanofiltration Notes This material is taken from Chapter 9 in the text “Membrane Processes” published by McGraw- Hill, 1996. The subsections are fouling indices, pretreatment, array configuration, design options, post treatment, instrumentation and concentrate disposal. A conventional RO/NF treatment system includes pretreatment, membrane filtration and post treatment and is shown in Figure 9.6. Common terminology for membrane processes is shown in Table 9.2. Table 9.2 Membrane Terminology Raw Input stream to the membrane process Conventional RO/NF Process A treatment system consisting of acid or antiscalent addition for scaling control (pretreatment), RO/NF membrane filtration and aeration, chlorination and corrosion control for post treatment. Feed Input stream to the membrane array Concentrate, Reject, Retentate, Residual stream The membrane output stream that contains higher TDS than the feed stream Brine Concentrate stream containing total dissolved solids greater than 36,000 mg/L. Permeate or Product The membrane output stream that contains lower TDS than the feed stream Membrane element A single membrane unit containing a bound group of spiral wound or hollow fine fiber membranes to provide a nominal surface area Pressure vessel A single tube that contains several membrane elements in series Stage or Bank Parallel pressure vessels Array or Train Multiple interconnected stages in series High Recovery Array Arrays where concentrate stream from succeeding array is feed to succeeding array to increase recovery System Arrays Several arrays that produce the required plant flow Rejection Percent solute concentration reduction of permeate stream relative to feed stream Solute Dissolved solids in raw, feed, permeate and concentrate streams Solvent Liquid containing dissolved solids usually water Flux Mass (mL -2 t -1 ) or volume (Lt -1 ) rate of transfer through membrane surface Scaling Precipitation of solids in the element due to solute concentration on the feed stream of the membrane Fouling Deposition of existing solid material in the element on the feed stream of the membrane Mass Transfer Coefficient (MTC) Mass or volume unit transfer through membrane based on driving force Any raw water stream used as a feed stream to a membrane process must undergo either conventional or advanced pretreatment. Conventional pretreatment includes acid or antiscalent addition to prevent precipitation of salts during membrane filtration. Advanced pretreatment occurs before conventional pretreatment and is necessary when the raw water contains excessive fouling materials. Membrane filtration is passage of the pretreated water through an active RO/NF membrane surface with a pore size 0.001-0.0001 micron. Post treatment includes many unit operations common to drinking water treatment such as aeration, disinfection and corrosion
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2 control. In all potable water membrane processes there will be one feed stream entering the process and two exit streams leaving the process.
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Membranes - ENV 6015 PHYSICAL CHEMICAL TREATMENT Reverse...

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