Ultrafiltration operating conditions

Crozes G., Jacangelo J., Anselme C., Laine, J.M. (1995a), Impact of ultrafiltration operating conditions on membrane irreversible fouling, Proc. AWWA Membrane Technology Conf., Reno, Nevada, Aug 95,... 

Ultrafiltration equipment suppHers derive K empirically for their equipment on specific process fluids. Flux J is plotted versus log for a set of operation conditions in Figure 6 K is the slope, and is found by extrapolating to zero flux. Operating at different hydrodynamic conditions yields differently sloped curves through C. ... 

Fouling is controlled by selection of proper membrane materials, pretreatment of feed and membrane, and operating conditions. Control and removal of fouling films is essential for industrial ultrafiltration processes. 

Beolchini, F., Pagnanelli, F., De Michelis, I. and Veglib, F. (2006) Micellar enhanced ultrafiltration for arsenic(V) removal effect of main operating conditions and dynamic modeling. Environmental Science and Technology, 40(8), 2746-52. 

The formation of a gel layer of colloidal material at the ultrafiltration membrane surface produces a limiting or plateau flux that cannot be exceeded at any particular operating condition. Once a gel layer has formed, increasing the applied... 

Methodological artefacts may arise for a number of reasons, most notably as a result of specific interactions of species with the filter membrane. Therefore the choice of the ultrafiltration system, the properties and influence of the membrane and the operating conditions must be carefully considered before the ultrafiltration technique is applied for the separation of different radionuclide species in environmental samples. 

A comprehensive mathematical analysis of batch ultrafiltration coupled with diafiltration is presented. The time cycle of the ultrafiltration-diafiltration has been correlated with the volume initially charged, percent of solute recovered, membrane area and flux. The optimum diafiltration volumes which result in the minimum cycle time or the minimum membrane area were solved for in terms of the operating conditions. 

In this paper, complete mathematical formulations for correlating the time cycles with other operating conditions are presented. The optimum diafiltration cycle (in terms of volume fraction), and the total cycle time are solved as functions of membrane area, flux, initial volume and recovery. Convenient charts, which can be used as a guide in designing or modifying an ultrafiltration process, are provided. 

The optimum time cycle and the relative diafiltration volume in the ultrafiltration-diafiltration process can be expressed as a function of three variables, P, Q, and R. P and Q are simple functions of the initial volume, membrane area, and flux (P = mA/Vo, Q = bA/Vo), and R is the solute recovery. From these, the time cycle and relative diafiltration volume (Vd/Vo) can be solved at various values of m, b, Vo, A, and R (m and b are respectively the slope and intercept of the flux, J = m In Vo/V + b). At a fixed recovery, the optimum time cycle and the relative diafiltration volume become functions of only two variables P and Q. Thus, the optimum operating condition can be simply plotted as function of P and Q. These plots, providing convenient and sufficient information, can be used as a guide in the design and operation of the ultrafiltration process. 

Ole Jentoft Olsen (DSS Danish Separation Systems) presented a large-scale industrial example on using ultrafiltration for the production of antibiotics. Within 15 hr, a volume of 100 metric tons of biomass was processed. The design of membrane module, operational conditions, and the overall plant were presented, along with detailed cost considerations for this process. 

The most widely used nominal pore size for ultrafiltration is 1 nm, which is estimated to retain compounds with MWs >1000 Da. The 1 nm pore-sized membrane isolates 20% of the total DOC in surface and deep ocean waters and up to 55% of the DOC in coastal and estuarine environments (Benner et ai, 1997 Carlson et ah, 1985 Guo and Santschi, 1996). Ultrafiltration membranes with a smaller pore size are rare and do not show reproducible retention characteristics filters with a larger pore size retain only a small fraction of total DOC and they are not widely used. In general, the actual MW retained and the isolation of reproducible quantities of DOC by ultrafiltration depends strongly on the membrane (e.g. construction material, manufacturer), sample type (e.g. river, coastal, open ocean), total DOC concentration, concentration factor, extent of desalting and operating conditions (Buesseler et al, 1996 Guo and Santschi, 1996 Guo et ai, 2000). Losses to the ultrafiltration membrane can also be significant (Guo et al., 2000) and depend primarily on the physiochemical characteristics of the particular molecule. 

Membrane materials for reverse osmosis and ultrafiltration applications range from polysulfone and polyethersulfone, to cellulose acetate and cellulose diacetate [12,18-23]. Commercially available polyamide composite membranes for desalination of seawater, for example, are available from a variety of companies in the United States, Europe, and Japan [24]. The specific choice of membrane material to use depends on the process (e.g., type of liquid to be treated and operating conditions) and economic factors (e.g., cost of replacement membranes and cost of cleaning chemicals). The exact chemical composition and physical morphology of the membranes may vary from manufacturer to manufaemrer. Since the liquids to be treated and... 

Several researchers have investigated the possibilities of membranes for the removal of dispersed water-based ink pigments from wash effluent [121-126]. Generally, membranes, in particular ultrafiltration membranes, have been found to completely remove ink pigments from effluent streams. It has also been observed that the permeate flux and the fouling tendency depend on operational conditions and effluent composition. For instance, coagulation pretreatment [125], feed water acidification [121], and surfactant addition [123] have been found to improve the flux and decrease fouhng. 

Typical UF performance for pyrogen removal with a polymeric and ceramic membrane is shown in Table 13. It can be seen that both types of UF membranes can adequately remove pyrogens. The choice of UF membrane (ceramic or polymeric) will depend on operating conditions or other special process requirements. Ceramic membrane ultrafiltration can achieve a 5 log reduction in pyrogen level. These UF membranes have been validated for the production of water meeting the requirements of pyrogen-free water for injection (WFI) standards.f ... 

The removal of MTBE by membrane micro- or ultrafiltration is highly ineffective due to the molecule s small size. Only nanofiltration showed removal potential. However, the process is very elaborate and expensive in terms of equipment and operating conditions (low transmembrane flux, high membrane area). Moreover, the resulting water needs further treatment in order to comply with drinking water standards, and the concentrate has to be treated before discharged. 

Different operating conditions may require some modification of the performed analysis. Ultrafiltration and/or osmosis can promote convective solute or water flux through the membrane wall. Should it happen, radial convection could compete with diffusion as the main substrate and product transport mechanism. The relative importance of the two transport mechanisms can be evaluated by comparing the radial convective velocity to the diffusive velocity, that is the ratio of the diffusion coefficient to the wall thickness. When the first one is negligible relative to the latter, the model applies without modification. The second possible effect of the radial flux is to remove enzymes from the fiber wall, resulting in the reduction of reactor efficiency. 

Diffusion and ultrafiltration fluxes due to pressure drop along the length of fibers play the most important role in substrate and product mass transfer when systems are operated as previously described. However, an ultrafiltration flux can be promoted from the lumen of the fibers outwards and/or from the shell inwards.44 Better reactor performances should result from such operating conditions. 

S. viridosporus LiP has been concentrated by ultrafiltration (UF) for further studies on the enzyme purification and the determination of its chemical and biochemical properties [10, 11, 13, 14]. However, there is no report on the UF operational conditions and on the enzyme activity recovery. 

Operative conditions can be adjusted so that only metals with rate of dissociation of their complexes, within a desired range, are included in the electroactive fraction. Conditions that can be adjusted to achieve selectivity are deposition potential, electrode rotation rate, solution stirring, pulse frequency, potential scan rate, temperature, pH, etc. As electrochemical techniques require much less sample handling than other speciation methods, such as solvent extraction, dialysis or ultrafiltration, the potential sources of contamination are highly reduced. An in depth discussion of the pro and cons of electrochemical speciation is far beyond this article. Theoretical aspects and applications have been covered in great detail by Niirnberg, Florence et al., cf. ° and references therein. 

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