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7_61X-FLOW The XIGAT"° Concept and Operation Manual The XIGATm Philosophy Filtration The XIGATm element is a PVC cartridge with a central permeate tube, containing membrane capillaries made from a blend of polyethersulphone and polyvinylpyrrolidone. The membrane capillaries fixated in the PVC-housing with only 2-3 cm epoxy resin, are fed to the inside with feed water. Particles bigger then the membrane poresize will be rejected from the membrane surface, keeping it within the capillaries. The liquid containing only ions and particles smaller than the membrane pore size will pass through the membrane (permeate) and will be collected in the central permeate tube. This process mode is called filtration. Filtration is enabled by a pressure difference between the feed side (in the capillaries) and the permeate side (out of the capillaries), also called trans membrane pressure or TMP. The TMP in a module according to the XIGATM -Concept is very low, most of the time < 0.5 bar. It is important to keep this TMP level low although it will increase during operation. The maximum TMP during the filtration mode is 1 bar. A TMP above 1 bar will cause an irreversible fouling on the membrane surface. Depending on the feed water quality and the membrane type used, the typical flux rate during filtration is 70-100 I/M2h. and the duration of this mode is 10-60 minutes. Backwash If not removed, the particles that remain within the capillaries will -in time-block the membranes, increasing the TMP. Therefore a periodical backwash is required. During the backwash the water flow will be reversed. Clean permeate water will be forced from the outside of the capillaries to the inside, and will transport the foulant out of the capillaries. Also during the backwash mode it is important to keep monitor the TMP. The maximum TMP during backwash is 3 bar. During the backwash the TMP is not the only important factor. The speed within the capillaries to transport the dirt out of the capillaries is also important. Therefore it is recommended to perform a backwash with a flux rate of 250-300 I/mzh. Furthermore it is important that the duration of the backwash is sufficient to remove all dirt-, not only out of the membrane element but also out of the membrane system (pressure vessel). In general the actual duration of a backwash is approximately 30-40 seconds. Feed Feed Permeate Permeate Feed Feed �— ermeate Permeate Feed dui Retentate :. ; • Permeate Permeate Filtration mode Backwash mode Schematic view on waterflow in XIGATM —Concept Chemically Enhanced Backwash If a backwash is insufficient to remove all foulants, the backwash efficiency can be enhanced by adding chemicals into the backwash (Chemically Enhanced Backwash). When using disinfectants, the system can also be disinfected by the CEB. The CEB mode consists of a normal backwash procedure, a backwash with chemicals (these can be dosed after the backwash pump with a dosing unit), a soaking period and a backwash to flush out the chemicals. CAPF-XIGA-0143