Fouling:
Ultrafiltration systems kept on working under a fixed pressure of range 3-4 bar. The permeate flux was measured over time while keeping the feed solution circulating at a fixed pressure across the surface of the membrane. Fouling is the existence of colloidal and macromolecular substances on the membrane surface which is an important factor in determining the performance of the ultrafiltration membranes (Baker, 2012).
The flux of pure water is normally very high reaching to about 500l/m2.h. But when adding a membrane, this flux drops dramatically 10 times lower reaching to values of 50l/m2.h. the formation of a gel that adds u solutes is the main reason behind this drop. This layer of gel adds resistance by forming a barrier to the flow. As illustrated in figure 2.3 (Baker, 2012).
Figure 2.3 fouling on an ultrafiltration membrane
The composition and the fluid dynamics also dictate the flux and its initial decline. Depending on the feed solution sometimes the flux might keep at its declined flux for weeks, and pure water is used to retest the membrane to return the flux to its normal rate. The precipitation of the gel layer and the formation of this barrier also known as membrane fouling is sometimes hard to control. Several techniques can be applied to control this problem like: regular membrane cleaning, back flushing, or using membranes with surface characteristics that minimize adhesion. Also a new technique is being used which called air is scrubbing. Also reducing the pressure helps reduce and delay the formation of the gel layer.
A representation of the slow decrease in flux that can result from consolidation of the fouled layer is presented in figure 2.4.
Figure 2.4 ultrafiltration fluxes as a function of tim...
... middle of paper ...
... across the membrane reached 0.3 the system was taken of-line and cleaned. It is clear that by decreasing the flux the cleaning cycle expands over a longer period of time.
Figure 2.6 the constant flux effect on the transmembrane pressure
The trans-membrane pressure versus time curves has a unique form. The pressure increases gradually overtime until it reaches a certain high value. After which the pressure rises sharply, after which the system needs to be taken off-line and cleaned.
This curve is due to the fact that during the process the pores are not all clogged uniformly. Some are clogged while others are still open for the flux. The left pores which are still open exhibit high flux which leads to their clogging and fouling faster than the initial ones this symbolizes the sharp increase in the curve over time, leading to the complete closing of the membrane.
Dead end filtration is flow applied perpendicular to the membrane surface. Particles smaller than the effective pore size pass through as filtrate, and particles that are
Set Parameters- FiO2 40%; Tidal Volume 70 ml; Peak Flow Auto-flow; RR 30/min; PEEP 5 cmH2O; Pressure Support 10 cmH2O; Minute Ventilation 2.1 L/min; Slope
Dialysis tubing is made from regenerated cellulose or cellophane, and is used in clinical circumstances to ensure that molecule have a filtered flow, and that larger solute molecules do not enter the dialysis tubing (Alberts, 2002). Like a cell membrane, dialysis tubing has a semi-permeable membrane, which allows small molecule to permeate through the membrane. Thus, the dialysis tubing mimics the diffusion and osmosis processes of the cell membrane (Alberts, 2002). Although the dialysis tubing has a semi-permeable membrane, which mimics a cell, its structure is different. The me...
The interactive force between the fluid and the porous medium is due to the frictional forces only and this force proportional to the flow velocity which represents by the term , where is the Darcy's coefficient, is the fluid viscosity and is the permeability of the porous medium.
... NaCl solutions and opening the dialysis tubes. Apparatus needed to be manipulated skillfully to attain more precise results for comparisons and observations. The apparatus also needed to be handled with care to prevent any breakages, especially because a lot of equipment was made of glass. Skills were required when understanding the ratios to determine the range of concentrations and creating the various NaCl solutions. This was a critical skill because the concentration of NaCl in the solution was the independent variable and a fault would have greatly influenced the results. Splitting, opening and tying the dialysis tubes needed to be completed with care and competence because it was an imperative part of adequately representing the cell. Any mistake or inconsistency in this process would have negatively affected the results when observing the process of osmosis.
Comment on class result with respect to differences in filter types, differences in filter assemblies, and overall on the confidence you would have in using this type of sterilisation process in preparation of pharmaceutical products. List the factors that may cause contamination during filtration. (20 marks)
This occurs as in the process of osmosis, the water moves from a dilute solution to a more concentrated solution through a protein pore or semi-permeable membrane, without the expenditure
Chemicals: Ultrapure water with an electrical conductivity of 18.2 MΩ cm-1 produced from nano-filter (EMD Millipore Corporation, UK) was used for cleaning, making solutions, and doing electrochemical measurements. Cleaning solvents such as ethanol was purposed from Decon Laboratories (USA), acetone was purposed from Fisher Chemicals, USA, and isopropanol was purchased from Macron Fine Chemicals, USA. Chloroauric acid, hydrogen chloride, nitric acid, sodium phosphate monobasic, and sodium phosphate bibasic were purchased from Sigma-Aldrich, USA. L-ascorbic acid were purchased from Sigma-Aldrich, USA
The process of osmosis has a few limiting factors. Osmosis can only occur through a semipermeable membrane, meaning there are proteins on the phospholipid bilayer that regulate what can come in and out of the cell. It also takes longer for the two sides to become equal if the solvent particles are bigger on one side, and if the particles are less crowded. If the particles are bigger, it is harder to get them through the membrane. If the two sides are almost at an equal state of water and solute concentration, it will take longer for the water to diffuse to the other side of the
The bacteria and wastewater is mixed in an aeration tank and therefore the contaminants are removed by action of sorption and series of breakdown by the bacteria.
Water desalination is the process of removing salts and minerals from water that has a high concentration of salt dissolved in it, and can therefore not be consumed as drinking water. Desalination of saline water can be achieved by a technique known as reverse osmosis. In osmosis the net movement of solvent molecules occurs from an area of low solute concentration to a more concentrated one through a semi-permeable membrane to balance the concentration of solute on either side of the membrane. However, in reverse osmosis the net flow of solvent is in the opposite direction this can be achieved by applying an external pressure that is great enough to stop osmosis from occurring, this is known as the osmotic pressure. If a pressure greater than
the result of the distribution of tension on the thin film of soap, is another
The next factor is the time. In cleaning the equipment sometimes a long time does not guarantee a cleaner environment because some equipment only needs a flash rinsing. Even different vessels require different time for cleaning. Most fermenter tanks required more time as they leave more residue in the tank depending on the type of yeast used. A
The most common type of membrane separation is called reverse osmosis. Seawater is forced through a semipermeable membrane that separates salt from water. Because the technology typically requires less energy than thermal distillation, most new plants, like Tampa's, now use reverse osmosis.
Turbidity and algae are removed from raw waters by screens, gravel filters and slow sand or rapid gravity filters. The difference between slow and rapid sand filtration is not the speed of filtration, but in the underlying concept of the treatment process. Slow sand filtration is essentially a biological process whereas rapid sand filtration is a physical treatment process.