Membrane Quality
The inner layer of the capillaries has the very thin active filtration surface. The foam structure between capillaries has a permeability that is more than 1000 times higher that the filtration surface so an equal distribution of liquid/water throughout the whole cross section of the fiber can be guaranteed.
The Molecular Weight Cutoff (MWCO) of the membrane is ca 100.000 g/mol which correlates to an average pores size of 10 nm. With this low pore size still the permeatibility of the membrane in clean water (RO water) will exceed the 1000 l/m2/barh.
The membrane material is Polyethersulfone (PES) with high resistance against cleaning chemicals, such as acids, bases or oxidation agents, e.g. hydrogen peroxide and active chlorine
Inside – out filtration
The active layer of the membrane is inside the capillary and therefor a inside – out filtration method is to be followed. This procedure assures that an ongoing equal overflow on the side of the membrane is generated. As the filter cake will also be equally spread over the membrane the cleaning can be excuted in efficient manner. The volume of the feed water in one element (50m2 of membrane is ca 12 liter) and with a backwash cleaning only a limited amount of filtered water has to be used. Depending on the feed water a high recovery of the feed water will be possible. Alternative systems with outside – in membrane will have lower recovery rates in comperable situations.
An inside –out membrane can easily be cleaned in situ with a chemical enhanced backwash. Outside – in systems should on on regular basis being cleaned separately from the filtration tank or vessel.
Advantages of 0.9 mm capillary membrane diameter
Most of the comperable membranes have a diameter of 0.8 mm. With this 0.9 mm membrane a more flexible operation is possible:
- The pressure loss of the overflow is reduced by 40% towards the 0.8 mm diameter membrane fibers
- During backwash the higher diameter is very essential The backwash is excuted with a higher flux and will be effective when an equal flux can be generated throughout the whole length of the capillary.
- With an effective cleaning of the membrane an alternating feed of the membrane via top and bottom mode is not strictly neceassary for most types of water. In these cases this will make the system construction and control system a lot simpler and lower in costs. This process design is being adviced to have pilot period up front the definitive design of the process.
Characteristics of the IMT element
Construction
The high performance of the membrane has been secured with a proven design of the module. Both in filtration mode and the bakwash mode an optimal flow distrubution will be reached. For efficient backwash cleaning only a marginal pressure drop is required, resulting that each capillary will have the same transmembrane pressure (TMP). This requirement is nessecary to be able to carry out an efficient backwashing that reaches every location in a element.
A shorter backwash period can be expected and therefor the recovery of the filtration process will be increased.
No centralized permeate collection tube
Using an inner tube in the element, which constructs a gap between the outer tube and the capillaries an optimal distrubution of the water in both the filtration mode as well as the backwash mode can be reached. Elements with centralized permeate collection tubes will have a substantial pressure drop and decrease of velocity will occur within the capillaries located in the centre of the module. A equal distribution of the water throughout the element is not possible.
Element construction without use of sealings
In many element constructions is a sealing required between feed and permeate connection of the membrane. This may in some cases lead to a contamination of the permeate due to e.g. careless installation or a stress caused by temperature changes. This risk is completely avoided by using only the epoxy raisin as separation between feed and permeate water in this element design.
Main charateristics of membrane system design
Vertical Installation of membrane elements
The vertical installation of elements enables a complete dearation of the element on both the permeate and the feed side. Water types that includes air can alo be easily and reliably treated.
When changing a filter element complete dewatering of the element can be realised and therefor dismounting is much simpler than in horizontal configuration. Additional pressure vessels are not required
The elements are manufactured with PVC tubes which are alos used for the construction of drinking water plants. These elements already forms a unit which is ready for connection without requiring a pressure vessel. No additional mounting is necessary.Parallel operation of elements
In contrast to the concept of using pressure vessels, the elements are not operated in sequences but parallel. When backwashing the dirt rinsed off the system has to pass other modules. Also the parallel configuration enable an operation with overflow (cross flow filtration) which leads to more effective and intense cleaning of the membranes in some cases.
