Fouling Experiments

Two filtration protocols were used for fouling experiments, one for the 10 kDa membrane and another for the 100 kDa membrane. The different fluxes did not allow the filtration of similar volumes. 

All experiments were stirred at 270 rpm unless otherwise indicated. A feed reservoir of 1.5 L was connected to the stirred cell to provide extended filtration volume. Pure water flux was measured after the filtration of 1 L of MilliQ water for both membranes. 

For the 10 kDa membrane, 225 mL of feed solution were introduced into the reservoir. Pressure was adjusted to 300 kPa. A total of 150mL were filtered (three permeate samples of 50mL each were taken), leaving 75mL of retentate. 

For the 100 kDa membrane, 450 mL of feed solution were introduced into the reserv oit. Pressure was adjusted to 100 kPa and the filtradon cell was fiUed up. The permeate was sampled once (sample volume 50 mL) and then recycled into the reservoir together with the retentate and filtration was repeated. This was repeated a third rime. This recycling experiment enabled the separation of concentration polarisation effects from fouling effects. The 110 mL of retentate was then also sampled. Pure water flux was measured again after each experiment with approximately 300 mL and 1000 mL of MilliQ filtered for the lOkDa and lOOkDa membranes, respectively. Membrane samples were kept in a Petri dish for deposit analysis. 

The amount M of solute or colloid deposited (in m on the membranes was calculated by using mass balance (see equation (6.1)), where Vf, Vr, and Vpi, are the volumes of feed, retentate and permeate (sample i), respectively, and cf, cr, and cpi the concentrations of feed, retentate and permeate. 

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Delplace, F., Leuliet, J.C. and Tissier, J.P., 1994, Fouling experiments of a plate heat exchanger by whey proteins solutions. Trans. I.Chem.E., Vol. 72, Part C, 163- 169. 

Separation of charge and size effects for organics and ion separation and the effect of speciation Effect of pretreatment on membrane processes for rejection enhancemenr and fouling control. Colloidal fouling experiments with model colloidal systems and known aggregation behaviour... 

The masses of about 5 pg adsorbed correspond to only 0.2% of organic carbon in a fouling experiment, where the membrane (surface of 21.2 lO m ) is brought in contact with a feed that contains a total of 2.5 mg organic carbon (12.5 mgL" DOC). 

Stirring had a large effect on the mass transfer coefficient with the mass transfer coefficients var)hng from 0.14 lO ms at 0 rpm (unstirred) to 2.18 10 ms at 560 rpm. This indicates that unstirred filtration will cause significandy higher wall concentrations, which explains the differences observed in rejection and fouling experiments. 

Fouling experiments confirmed the hypothesis of precipitation. Large compounds, which are slower in their diffusion away from the membrane, did foul more readily, especially in the presence of calcium. The effect was stronger in the absence of stirring when the boundary concentration is even higher. 

Vrijenhoek et al. [38] studied the surface morphology, permeability, rejection, and colloidal fouling behavior with respect to two commercial RO and two commercial NF membranes. The RO membranes were Hydranautics LFC-1 (Oceanside, CA) and Trisep X-20 (Goleta, CA). The NF membranes were Dow-FilmTec NF-70 (Minneapolis, MN) and Osmonics HL (Minnetonka, MN). Table 8.8 shows the performance properties and the AFM parameters of the membranes. It is obvious from the data that the authors made RO and fouling experiments at different pressures for different membranes to adjust the initial flux to the same value. 

Alginate, a major component of the effluent organic matter in wastewater, was selected as the model foulant to conduct the FO membrane fouling experiments. Each FO fouling experiment... 

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