Membrane modules recovery

Recovery (sometime referred to as "conversion") is a term used to describe what volume percentage of influent water is "recovered" as permeate. Generally, RO system recoveries range from about 50% to 85%, with the majority of systems designed for 75% recovery. (Individual spiral wound membrane module recoveries vary from about 10% to 15%—see Chapter 4.3). A system recovery of 75% means that for every 100 gpm influent, 75 gpm will become permeate and 25 gpm will be retained as concentrate. 

Adherence to recommended concentrate flow rates and membrane module recovery can also minimize Beta and the effects of concentration polarization. 

Figure 9.12 Individual membrane module recovery and rejection as a function of position in a 2-stage RO system with 6 modules per pressure vessel.

The efficiency of a membrane module is characterized by the recovery or conversion ratio CR = permeate flow rate/feed flow rate. Low conversion means that fluid has to be repeatedly cycled past the TFF module to generate permeate. High-efficienCT NFF has CR = 1. 

Membrane Module System Characteristics PES Fibers Continuous Cost, plugging PES Spirals Continuous Cost Cellulose, PES, PVDF Cassette Batch, NFF Recovery PES Fibers Continuous, single-pass Cost PES, PVDF Tubes Batch Plugging, cost... 

Cabral and coworkers [253] have investigated the batch mode synthesis of a dipeptide acetyl phenylalanine leucinamide (AcPhe-Leu-NH2) catalyzed by a-chymotrypsin in a ceramic ultrafiltration membrane reactor using a TTAB/oc-tanol/heptane reverse micellar system. Separation of the dipeptide was achieved by selective precipitation. Later on the same group successfully synthesized the same dipeptide in the same reactor system in a continuous mode [254] with high yields (70-80%) and recovery (75-90%). The volumetric production was as high as 4.3 mmol peptide/l/day with a purity of 92%. The reactor was operated for seven days continuously without any loss of enzyme activity. Hakoda et al. [255] proposed an electro-ultrafiltration bioreactor for separation of RMs containing enzyme from the product stream. A ceramic membrane module was used to separate AOT-RMs containing lipase from isooctane. Application of an electric field enhanced the ultrafiltration efficiency (flux) and it further improved when the anode and cathode were placed in the permeate and the reten-tate side respectively. 

Design of the membrane module system involves selection of the membrane material the module geometry, eg, spiral-wound or hollow-fiber product flow rate and concentration solvent recovery operating pressure and the minimum tolerable flux (9,11). The effects of these variables can be obtained from laboratory or pilot experiments using different membranes and modules. The membrane module as well as the solvent recovery can be chosen to minimize fouling. Spiral-wound modules are widely used because these offer both high surface area as well as a lower fouling potential. 

The current ultrafiltration market is approximately US 200 million/year but because the market is very fragmented, no individual segment is more than about US 10-30 million/year. Also, each of the diverse applications uses membranes, modules, and system designs tailored to the particular industry served. The result is little product standardization, many custom-built systems, and high costs compared to reverse osmosis. The first large successful application was the recovery... 

System design plays a role in determining acceptable recovery by an RO. Flow rates per pressure vessel, recovery per module, and BETA values must all be taken into account when considering acceptable recovery by the RO system (see Chapters 9.4, 9.5, and 9.6). The higher the recovery of the RO system, the closer concentrate flow rates and individual module recoveries come to reaching limits recommended by membrane manufacturers. 

Teramoto M, Matsuyama H, and Ohnishi N. Development of a spiral-type flowing hquid membrane module with high stability and its application to the recovery of chromium and zinc. Sep Sci Technol, 1989 24(12-13) 981-999. 

Teramoto M, Ohnishi N, Kitada S, Matsuyama H, Matsumiya N, and Mano H. Simultaneous recovery and enrichment of C02 by novel capillary membrane module with permeation of carrier solution. Abstracts of Papers, 225th ACS National Meeting, New Orleans, LA. American Chemical Society, Washington, DC 2003 IEC-009. 

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