Membrane filtration is a treatment process based on the physical separation of the compounds from the water phase with the use of semi permeable membranes. The quality of the permeate water of a membrane installations is excellent and in the recent years the membrane filtration techniques have recognized a rapid development and the costs have strongly decreased due to the decreased costs of membrane elements.



Ultrafiltration is a low- pressure driven membrane separation process that separates particulate matter from soluble components in the carrier fluid (such as water) at transmembrane pressures of, typically, 0.5 to 5 bars. UF membranes typically have pore sizes in the range of 0.01 - 0.10 µm and have a high removal capability for bacteria and most viruses, colloids and silt. The smaller the nominal pore size, the higher the removal capability.
UF membranes can be fabricated essentially in one of two forms: tubular or flat sheet. Membranes of these designs are normally produced on a porous substrate material. The single operational unit into which membranes are engineered for use is referred to as a module. This operational unit consists of the membranes, pressure support structures, feed inlet, concentrate outlet ports, and permeate draw-off points. Two major types of UF modules can be found in the market, i.e., hollow fibers (capillary), and spiral wound.
Most materials that are used in UF are polymeric and are naturally hydrophobic. Common polymeric materials used in UF include: Polysulfone (PS), Polyethersulfone (PES), Polypropylene (PP), or Polyvinylidenefluoride (PVDF).
Operation of UF membrane can be performed in two different service modes, i.e., dead-end flow and cross-flow. The dead-end flow mode of operation is similar to that of a cartridge filter where there is only a feed flow and filtrate flow. The dead-end flow approach typically allows optimal recovery of feed water on the 95 to 98% range, but is typically limited to feed streams of low suspended solids (<1 NTU). The cross-flow mode different with dead-end mode in which there is an additional flow aside from feed flow and filtrate flow (permeate), i.e., the concentrate.
The cross-flow mode of operation typically results in lower recovery of feed water, i.e., 90 to 95% range.
The UF modules contain several small (0.6 to 2 mm diameter) tubes or fibers. As the feed solution flows through the open cores of the fibers, the permeate is collected in the cartridge area surrounding the fibers. It can carry out the filtration in two ways, either “inside-out” or “outside-in”.
Ultrafiltration systems designed nowadays use an IN - OUT flow configuration which allows for less plugging, higher solids loading, higher flow area and easy cleaning.
The design of Spiral wound Ultrafiltration UF membranes, consisting of consecutive layers of large membrane and support material sheet rolled up around a perforated plastic tube maximizes surface area in a minimum amount of space. It is the less expensive but more sensitive to pollution due to its manufacturing process and configuration design.
Compared to conventional water treatment processes, ultrafiltration technology offers various advantages:
  •  Ultrafiltration provides a full barrier against microorganisms and particles
  •  The quality of the filtrate is not depending on the feed water quality
  •  Ultrafiltration is able to eliminate chlorine - resistant pathogens.
  •  Concentrate originated by the ultrafiltration process is only consisting of the water contaminants. The amount of created and to be disposed sludge is significantly lower than with conventional treatments.
  • Compact construction of systems provides lower investment for buildings and space than with conventional treatment.
  • Ultrafiltration can be automated easily.
  • Downstream treatment steps will have higher productivity due to the fact that nearly all foulants have been already removed by ultrafiltration.
  • Investment and operation costs for downstream nanofiltration or reverse osmosis systems are will decrease substantially, since the systems can be operated at higher flux rates and with less cleaning efforts.
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