Ultrafiltration experiments

Previous workers have recognised this problem and, for example, achieved equilibration by conditioning membranes with an aliquot of the experimental sample prior to running experiments (Salbu, 1984). The results of such work not only confirm the necessity for such equilibration but also emphasise the fact that other artefacts such as clogging may occur and must be taken into account by monitoring adsorption effects. This is most easily achieved by establishing a mass balance for each radionuclide throughout the ultrafiltration experiment. 

An approach such as that suggested for the re-examination of the molecular weight distribution of dissolved organic carbon in seawater (Carlson et al., 1985) has been successfully adapted to evaluate the performance of ultrafiltration in the study of radionuclide speciation  

Ultrafiltration system Without humic acid With humic acid  

The type of approach described here is obviously more important for systems where the solution chemistry of the nuclide (charge, oxidation state and degree of complexation) is more complicated. Without supporting laboratory data, it is possible that significant retention values may be incorrectly interpreted as being due to radionuclide association with material in a particular size fraction. The components of the environmental sample might contribute to the separation process and retain species which on a size basis should readily pass through the filter membrane. 

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FTIR can be used to screen membranes for fouling tendencies prior to the first ultrafiltration experiment. Screening can be done by means of a simple static adsorption test. Membranes showing greater static adsorption are expected to foul more during ultrafiltration and are disfavored. Figure 8 illustrates the FTIR results... 

Influence of U colloidal transport in organic-poor surface waters has been far less studied. Riotte et al. (2003) reported U losses from 0 to 70% during ultrafiltration experiments for surface waters of Mount Cameroon without nearly any DOC. Even in the low concentration waters, U can be significantly fractionated from other soluble elements by the occurrence of a colloidal phase, probably inorganic in origin. However, such fractionations are not systematic because of the occurrence of various colloidal phases, characterised by different physical and chemical properties, and hence different sorption and/or complexation capacities (Section 2.1). 

Presently, the precise determination of the true dissolved Th fraction in water samples remains a challenge. Results from ultrafiltration experiments on organic-rich water samples from the Mengong river tend to demonstrate that Th concentration is less than 15 ng/L in absence of DOC (Table 2 and Viers et al. 1997), and that Th is still controlled by organic carbon in the final filtrate of the ultrafiltration experiments. The latter conclusion is also supported by the results obtained for the Kalix river (Porcelli et al. 2001). These results therefore not only raised the question of the determination of the amount of dissolved Th in water but also of the nature of Th chemical speciation. 

In Smolders ultrafiltration experiments, 4,000,000 mw polyethylene glycol was used as the solute (500ppm), Small particles (0.5mm) in the fluidized bed failed to augment the flux to any significant degree. Larger particles (2.0mm) resulted in a twofold increase in flux. Smolders concluded that the momentum of the 0.5mm particles was insufficient to remove the gel-layer. 

In the current work, we employed a modified approach, with predeposition of a secondary membrane of yeast (SMY) before starting the filtration of protein. Backflushing was employed periodically to remove the deposited secondary membrane to recover the flux, and a new secondary membrane was deposited subsequently with the start of each new cycle, prior to restarting the filtration of protein. Microfiltration experiments were performed with yeast as the secondary membrane and BSA-only solutions and yeast-BSA mixtures as the feed. Ultrafiltration experiments were performed with yeast as the secondary membrane deposition medium and cellulase enzyme solutions, used in the conversion of biomass into ethanol, as the feed. In this article, we also present direct visual observation images (19) of the formation of the secondary membrane and its subsequent removal. 

Ultrafiltration experiments were carried using the same setup, except the flat-sheet membrane module had a filtration area 38 mm long, 29 mm wide, and 1.6 mm high, with a surface area of 11 cm2. The permeate side had 11 grooved channels that supported the membrane, leaving an effective filtration area of 6.4 cm2. However, the total membrane area including the supports was used in calculating the fluxes. The feed consisted of cellulase enzyme solution (5.0 g/L of supplied cellulase, unless noted otherwise). 

The goal of ultrafiltration, in contrast to microfiltration, is to retain protein molecules by the membrane while passing smaller solutes through the membrane with the permeate. Ultrafiltration experiments were performed with polysulfone membranes (30,000-Dalton mol wt cutoff). Figure 9 shows a comparison of the permeate flux vs time obtained during ultrafiltration of cellulase in the presence and absence of SMY that was periodically removed by backflushing and then replaced with a new SMY. 

South America. Due to its importance in terms of water discharge and to generally high trace-element levels, the Amazon river system has been well documented for a number of elements, including their seasonal variations. In Table 1, we have reported different analyses of the Amazon River and its major tributaries to show their temporal variability at a given location. Results of ultrafiltration experiments for the Amazon and Orinoco rivers demonstrate that the concentration of a number of elements in waters depends on filtration pore size. Finally, data for... 

The comparison of REE concentrations for the <0.2 pm fraction with the lower-filter-size fraction shows that there is no unique pattern of colloidal material when rivers of different pH and different environments are compared. Ultrafiltration experiments conducted by Deberdt et al. (2002) on rivers from the Amazon and Orinoco basins as well as on Cameroon Rivers show slightly depleted LREE patterns to flat REE patterns when the colloidal fraction is normalized to the bulk solution. The results obtained by Sholkovitz (1995) and Ingri et al. (2000) for rivers... 

Ultrafiltration experiments were performed with an Amicon 8050 cell at 25 0 using a stirrer speed of approximately 700 rpm. Water fluxes (hydraulic conductivities) were measured at Ap = 1 psi dextran rejection was measured for feed solutions containing 0.2% T40, 0.2% TIO and 0.1% T500 (see Materials) under conditions of low concentration polarization. Transmembrane fluxes of dextran solutions were of the order of 0.2 x 10 cm/s at Ap = 1 psi. Feeds and permeates were analyzed by size-exclusion chromatography as described in Reference 9, and the chromatographs were used to calculate the rejection curves (Figure 1). 

Ultrafiltration Experiments. There is no boundary layer theory for ultrafiltration of proteins in tubes for the general case of applied pressures comparable to reverse osmotic pressures. The process involves complete rejection of protein, and most... 

Rejection Coefficients for Protein Ultrafiltration Experiments. Since the data for ultrafiltration rates seem to imply the condition of uniform wall flux, the calculation procedure for finding R for these experiments was identical with that used for saline solutions. No doubt the dlffusivity of the small solutes within... 

Protein Ultrafiltration Experiments. In Table IV and in Figures 16 through 19, typical data obtained in ultraf ltration experiments with serum and BSA are shown. Values for ir in Table IV were calculated by using a rearrangement of Equation 5,... 

After we started to analyse the data of ultrafiltration experiment, we came to conclusion that this assuo tlon is not correct. So we decided to measure directly Cg at each experiment by scratching out the gel layer from membrane after measuring steady state flux. Solutes used were polyvinyl alcohol(PVA) and ovalbumin. It was found that Cg is not constant, but was dependent on the experimental condition as shown in Fig. 2, where a case of PVA is plotted. 

When the assumption of constant wall concentration is justified, data for the unstirred batch cell and thin channel systems may be interpreted using models presented in Trettln and Doshi (1980a, 1980b). Such an analysis is performed where agreement is shown to be very good between theory and osmotic pressure limited ultrafiltration experiments. 

Typical results of an ultrafiltration experiment also reflect the presence of concentration polarization. This phenomenon, l.e. accumulation of solute in front of the membrane, was described in great detail by others (Refs. 3, 4). A consequence of concentration polarization is a strong dependence of measured rejection coefficients on transmembrane fluxes. An illustration of the effect is presented in Figure 9, which shows the measured "apparent" rejection coefficients (Rg) as a function of transmembrane flux for two water-soluble polymers (Tetronic 707 and Carbowax 4000). It is clear from Figure 9 that if we want to minimize the effects of concentration polarization, we have to conduct experiments at very low values of transmembrane flux. 

Rowe (Rl) was able to prove that purified albumin prepared from nephrotic serum and urine had the same molecular weight as that from normal serum he concludes that the increased excretion of albumin by nephrotic patients is not the result of a reduction of its molecular dimensions, but rather that the abnormality resides in the kidney. Ultrafiltration experiments showed (Fig. 23) that a selective molecular filtration may be reproduced by a suitable membrane in vitro. Rowe concludes that it is not necessary to invoke tubular activity to account for the composition of the uroproteins. 

The ultrafiltration experiments confirmed the rapid, complete binding of lanthanides to humate. The ion exchange experiments indicate that initially most of the Eu(III) is very weakly bound as the cation exchange resin removed most of the Eu(III) from the humate. After 2 days of... 

Even though enzymatic conversion is not too effective, it is possible to prepare semipermeable membranes whose ultrafiltration yields are higher than those of passive membranes.74 75 Ultrafiltration experiments of cheese whey through cellulosic membranes to which papain was covalently bound, show that flux decay curves of enzymatic membranes are even less sensitive to pH changes.74... 

Ultrafiltration. Millipore 90-mm high-flux ultrafiltration cells and membranes listed in Table I were used for all ultrafiltration experiments. A Prince-... 

Storage procedures are also important in ultrafiltration experiments. Unacidified field samples should be filtered as soon as possible to avoid sorptive losses to LPE bottle walls (52), especially when low levels of cadmium, lead, and copper are present initially. 

The same system as described in the MF section and shown in Figure 4.1 was used for all rejection, fouling, and fractionation ultrafiltration experiments. The balance was connected to a PC for flux data collection. 

We would like to thank the S.E.R.C. and Unilever Research for support for one of us (DNS) Unilever Research also provided access to Si NMR and laser Raman spectrometers. We thank EKA AB, Surte, Sweden, for financial support for another of us (KRA) and for help with the ultrafiltration experiments. We are also very grateful to Mr. Kenneth Rosenquist of the Swedish Institute for Surface Chemistry, Stockholm, for his assistarce in applying the dynamic light scattering technique. Finally we are grateful to the PQ Corporation for making it possible for this paper to be presented at New York. 

Papain is a proteolytic enzyme. It exhibits a proteolytic activity towards various ester and amide finks, as they occur in proteins, or peptides. The performance has been tested with ultrafiltration experiments of casein solutions. The modified membranes show a self-cleaning effect. Whereas the nonenz5miatic membranes are completely blocked during ultrafiltration, the enzyme-functionalized membranes do not clog. 

Barzin et al. characterized poly(ether sulfone) (PES) hollow fibers for hemodialysis by both ultrafiltration experiments and AFM [66]. Hollow fibers were fabricated from poly(ether sulfone) (Ultrason E6020 58 000 flakes from BASE Co.) by the... 

FIGURE 1.1 Setup for ultrafiltration experiments. 1 Membrane module 2 feed tank 3 permeate tank 4 permeate flow meter 5 feed flow meter 6 pump 7 feedback valve 8 control valve and 9 thermometer. 

In practice the ultrafiltration experiment is set up as shown in figure 1. A pump recycles the retentate through the membrane module at a temperature T. controlled by a heat exchanger. The inlet and outlet to the UF module are equipped with a valves which allow the inlet pressure P. and the outlet pressure P to be controlled. A membrane bypass allows the flow from the pump to be divided. The ultrafiltrate which comes through the membrane may be recycled to the retentate tank to achieve steady state conditions and then diverted for collection in the fractionation process. The level in the retentate tank is held constant by a stream of make up supplied by an auxiliary tank and pump. 

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