Membrane systems, modules continuous

Nanofiltration will continue to be a rapidly growing segment of the membrane industry. To sustain this growth, a better understanding of transport is needed, in particular the differences between aqueous and organic systems. Additionally, tremendous opportunities exist in membrane and module development for separations that fall in the gap between reverse osmosis and ultrafiltration. 

Since installed membrane systems for natural gas treatment are continuing to increase in scale, strategies that reduce the number of required modules and therefore total system cost continue to be of interest. 

The membrane system used for the MBR is ZENON s ZeeWeed 500d (Crossley et al., 2003). Membrane cassettes containing 48 modules of 31.6 m each (Fig. 7.4a) were arranged into separate membrane tanks, shown in Figure 7.4c (2, 6, 8, and 12 tanks for the four flow rates simulated). The continuous mixed liquor recirculation flow rate between the membrane tanks and the main bioreactor was set at 5 x (2ave to deconcentrate... 

The intrinsic rejection and maximum obtainable water flux of different membranes can be easily evaluated in a stirred batch system. A typical batch unit (42) is shown in Figure 5. A continuous system is needed for full-scale system design and to determine the effects of hydrodynamic variables and fouling in different module configurations. A typical laboratory/pilot-scale continuous unit using computer control and on-line data acquisition is shown in Figure 6. 

Membrane modules can be configured in various ways to produce a plant of the required separation capability. A simple batch recirculation system has already been described in cross-flow filtration. Such an arrangement is most suitable for small-scale batch operation, but larger scale plants will operate as feed and bleed or continuous single pass operation (Figure 16.20). 

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. 

Labor and operating costs are low. The system is highly automated allowing for minimal operator intervention. The two major operating costs are power and membrane maintenance. Allied-Signal s commitment and continued research and development of the AQUATECH membranes and stack design ensures longer lifetime on the membrane and even more power efficient units. Membrane replacements are facilitated by cell modules pre-assembled for easy installation. 

Figure 13.18 Continuous recycle fermentor membrane reactor. An ultrafiltration module removes the liquid products of fermentation as a clean product. This system is being developed for production of ethanol, acetone and butanol by fermentation of food processing waste streams...

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