The present invention relates to membrane filtration systems, and more particularly, to a simple, low cost filtration system which may be used in remote, underdeveloped regions of the world or in locations where normal infrastructure has been damaged or destroyed by a natural or man-made disaster.
In many areas of developing countries, clean drinking water is a scarcity. Also for the more remote regions electricity is not available. In such regions the use of expensive, energy intensive water filtration systems is impractical. Filtration systems employing porous membranes have been in use for many years, however, these systems require expensive equipment and complex pumping, valve and cleaning systems. The expense is usually justified where a large-scale system is employed servicing a large community.
In poorer developing countries and/or in remote locations where economies of scale are not possible and ready access to electricity is limited or non-existent, there is a need for a simple, low cost filtration system which can deliver high quality drinking water on a small or limited scale such as a single farm house or a small rural village.
The present invention seeks to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
According to one aspect, the present invention provides a method of cleaning a permeable, hollow membrane in an arrangement of the type wherein a pressure differential is applied across the wall of the permeable, hollow membrane immersed in a liquid suspension, said liquid suspension being applied to the outer surface of the permeable hollow membrane to induce and sustain filtration through the membrane wall wherein:
Preferably, the method includes removing, at least partially, liquid from the feed side of the membrane before and/or during the step of producing the mechanical agitation.
According to another aspect, the present invention provides a method of cleaning retained solids from the surface of the permeable hollow membrane used in a membrane filtration system including the step of producing mechanical agitation between the membrane and liquid in which the membrane is immersed to dislodge at least some of the retained solids.
For preference, the mechanical agitation is produced by moving the membrane relative to the liquid or vice versa. The liquid is typically held in a vessel which may be open or closed to atmosphere. In such arrangements, the agitation may be produced by moving the vessel and the liquid therein relative to the membrane/s or vice versa. Such movement includes inter alia, rotation, lateral movement along an axis of the vessel and/or rocking movement. The movement is preferably oscillatory.
The cleaning method may be supplemented by use of a liquid backwash and/or chemical cleaning of the membranes using appropriate cleaning agents.
According to another aspect of the present invention there is provided a method of treating a liquid suspension to remove particulate material using one or more permeable, hollow membranes, the method including:
(a) applying a pressure differential across the walls of the permeable, hollow membranes immersed in a liquid suspension, said liquid suspension being applied to the outer surface of the permeable hollow membranes to induce and sustain filtration through the membrane walls wherein:
In one form of this method, the liquid suspension may be contained in a closed vessel and the liquid suspension fed into the vessel under force of gravity such that pressure is applied on the feed side of the membranes by gravity feed of liquid into the vessel and/or suction is applied to the membrane lumens by gravity flow therefrom.
According to another aspect of the present invention there is provided a method of treating a liquid suspension to remove particulate material using one or more permeable, hollow membranes, the method including:
(a) applying a pressure differential across the walls of the permeable, hollow membranes immersed in a liquid suspension, said liquid suspension being applied to the outer surface of the permeable hollow membranes to induce and sustain filtration through the membrane walls wherein:
According to another aspect of the present invention there is provided a method of treating a liquid suspension to remove particulate material using one or more permeable, hollow membranes, the method including:
(a) applying a pressure differential across the walls of the permeable, hollow membranes immersed in a liquid suspension, said liquid suspension being applied to the outer surface of the permeable hollow membranes to induce and sustain filtration through the membrane walls wherein:
In one embodiment the method includes the step of removing, at least partially, liquid from the feed side of the membrane before and/or during the step of producing the mechanical agitation.
The invention includes, in other aspects, apparatus for performing the various methods described.
Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Referring to
The filtration module is of the type described in our International Patent Application No. WO 98/28066, however, it will be appreciated that any suitable membrane filtration device may be used. In this module, however, no gas scouring is used and the openings within the lower pot are used for removing feed liquid from the module.
When operating in the filtration mode, a pressure differential is produced across the membrane by a siphoning action applied to the membrane lumens through the filtrate cup 8. Filtrate is drawn from the cup 8 and out through hose 10 into the external container 11 under atmospheric pressure. Additional suction pressure can be applied to the membrane by adding a suction device to the filtrate line. The advantage is that the differential pressure across the membrane is limited to the atmospheric pressure and hence excessive fouling of the membrane can be avoided.
The membrane at the bottom of the module is blocked off from the feed such that the filtrate and feed liquid remain physically separated. The openings (not shown) in the bottom pot 12 facilitate cleaning of the module 7.
Over time, the filtration flow rate reduces due to fouling of the membrane. Due to the low-pressure operation of the filtration process, the foulant formed on the filtrate side of the membrane is easily removed through mechanical agitation.
The mechanical agitation used for cleaning the membranes can take a number of forms which will be described later.
In the present embodiment, which uses an open vessel 6, agitation to the membrane is applied by plunging the membrane module 7 up and down inside the tubular vessel 6 and/or oscillating the module 7 about its longitudinal axis. To help remove solids from the inner membranes, holes in the lower pot 12 assist in providing agitation through hydraulic motion during the plunging operation.
Another form of agitation may be to apply gas pressure to produce bubbles to agitate the membrane through the holes in the lower pot 12. Alternatively, if the membrane module 7 is lying horizontally, then the gas can be applied along the length of the module.
After agitation, the tube vessel 6 is emptied of concentrated liquid containing the dislodged impurities and refilled. Emptying of the liquid may be done by pouring the liquid from the vessel 6, draining liquid through the base of the vessel, and/or pumping or siphoning liquid from the vessel. Depending on the feed liquid, it may require successive agitation, emptying and fill cycles to recover the filtration flow rate. On completion of cleaning the membrane module 7, filtrate cup 8 and hose 10 are primed with water to reinitiate filtration.
The advantage of the closed vessel is that additional pressure using a header tank or any other pressure-boosting device can be placed across the membrane to provide a higher filtration flow.
Similar to embodiment of
After agitation the vessel 6 is again emptied of concentrated liquid containing dislodged impurities and refilled. Depending on the feed water, it may require successive agitation, drain and fill cycles to recover the filtration flowrate. It is advantageous to continue mechanical agitation during the emptying of the vessel 6. On completion of cleaning, the tubular vessel 6 and module 7 are primed with liquid to reinitiate filtration.
FIGS. 3 to 6 illustrate various embodiments of how the module may be mechanically agitated. It will be appreciated the methods illustrated are not exhaustive and a variety of mechanical agitation methods can be employed without departing from the scope of the invention described.
Referring to
In
In use, the arrangement operates in a similar manner to the embodiment illustrated in
It will be apparent to those in the art that the mechanical agitation steps of the method can be performed manually and/or be automated by the addition of an appropriate form of mechanical drive.
It will be appreciated that further embodiments and exemplifications of the invention are possible without departing from the spirit or scope of the invention described.
Number | Date | Country | Kind |
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2005900156 | Jan 2005 | AU | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/AU06/00039 | 1/13/2006 | WO | 7/13/2007 |