Abstract:
A membrane filtration assembly ( 10 ) including having a filtrate carrier ( 9 ) for minimizing backwash. The membrane filtration assembly includes a membrane module ( 5 ) having one or more permeable hollow membranes ( 6 ) supported therein by an upper header ( 7 ) and a lower header ( 8 ). The filtrate carrier ( 9 ) extends between the upper ( 7 ) and lower ( 8 ) headers to allow filtrate to be collected from either or both ends of membranes ( 6 ). A filtrate collection chamber ( 18 ) is associated with the upper ( 7 ) and lower headers ( 9 ) and in fluid communication with lumens of the membranes ( 6 ) for collecting filtrate withdrawn through said membrane lumens. A filtration chamber ( 11 ) is provided for receiving feed liquid to be applied to the surface of membranes ( 6 ) within the module ( 5 ). The filtration chamber ( 11 ) includes an open end for receiving the feed liquid. The open end is located beyond the height of the module ( 5 ) to enable gravity feed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application and claims the benefit under 35 U.S.C. §371 of International Application No. PCT/AU2006/001215 filed on Aug. 22, 2006, entitled AN ASSEMBLY FOR WATER FILTRATION USING A TUBE MANIFOLD TO MINIMISE BACKWASH, which is based on Australian Patent Application No. 2005904552 filed on Aug. 22, 2005, entitled AN ASSEMBLY FOR WATER FILTRATION USING A TUBE MANIFOLD TO MINIMISE BACKWASH, each of which is entirely incorporated herein by reference for all purposes, and to which this application claims the benefit of priority. 
     TECHNICAL FIELD 
     The present invention relates to membrane filtration systems and, more particularly, to a system that allows for filtration under gravity, under pressure or using a high feed head while minimising the backwash and cleaning solution volume. 
     BACKGROUND OF THE INVENTION 
     In a membrane filtration operation, periodically cleaning the membrane by liquid or gas backwash is essential to keep a longer membrane operation time without the need for a chemical cleaning stage. However, during each backwash, a certain amount of liquid waste is produced, which reduces the feed liquid recovery and increases the requirements on post treatment of backwash is waste. The liquid or gas backwash is also supplemented by periodic cleaning of the membranes using a chemical cleaning agent. This process again produces liquid waste which must be further treated or disposed of in an environmentally safe manner. It is thus desirable in any filtration operation to minimise the volume of waste liquid produced during the backwash and chemical cleaning phases of operation in order to reduce costs of operation and any environmental impact. 
     SUMMARY OF THE INVENTION 
     According one aspect the present invention provides a membrane filtration assembly including:
         a membrane module having one or more permeable hollow membranes supported therein by at least one header, a filtrate collection chamber associated with said header and in fluid communication with lumens of said membranes for collecting filtrate withdrawn through said membrane lumens;   a filtration chamber for receiving feed liquid to be applied to the surface of membranes within said module, said filtration chamber enclosing said module and extending beyond the height of said module.       

     Preferably, the membranes extend between a pair of spaced, opposed headers. For preference, a filtrate collection chamber is associated with one or both of said headers. Preferably, said membranes are positioned vertically within said module and said headers are respective upper and lower headers. For preference, a filtrate carrier is provided between and in fluid communication with said filtrate collection chambers. Preferably, said filtrate carrier extends through said module between said headers. For preference, an opening or openings are provided in the upper header to allow the flow of fluid therethrough. 
     In one embodiment, said filtration chamber is closed at one end and open the other. In another embodiment, the open end of the filtration chamber is provided with a valve which allows gas flow therethrough while only allowing liquid flow into the filtration chamber. 
     Preferably, the region defined between the filtration chamber and the module is filled with one or more filler elements. For preference an aeration backwash device is provided in fluid communication with said filtration chamber for selectively communicating gas and/or liquid to and/or from said filtration chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  shows a schematic sectional elevation view of a filtration module according to one embodiment of the invention; 
         FIG. 2  shows a schematic sectional elevation view of the filtration assembly according to one embodiment of the invention operating in a gravity suction mode; 
         FIG. 3  shows a schematic sectional elevation view of the filtration assembly according to one embodiment of the invention operating in a pressurised mode; and 
         FIG. 4  shows a schematic sectional elevation view of the filtration assembly according to one embodiment of the invention operating in a high head mode. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , the membrane filtration module  5  according to one preferred embodiment consists of a bundle of hollow fibre membranes  6  potted at the top and bottom in upper and lower headers  7  and  8  respectively to expose the fibre membrane lumens to collect filtrate. It will be appreciated the fibre bundle may be potted at either or both ends, and further that the fibre lumens may be open at either or both ends. An opening or openings may be provided in the upper header to allow the flow of fluid therethrough. 
     A filtrate carrier  9  (typically a pipe or tube) extends between the upper and lower headers  7  and  8  to allow filtrate to be collected from either or both ends of the fibre membrane lumens. The carrier  9  may be of any shape in cross section and, though shown in this embodiment in the centre of the module  5 , it may be located anywhere in the pot and in some embodiments the filtrate carrier  9  need not be located in the module  5  but can be connected through external connections as described below. 
     Referring to  FIGS. 2 to 4 , the filtration assembly  10 , according to a preferred embodiment of the invention, consists of a filtration chamber  11  higher than the module  5 . If used in the high head filtration mode, as shown in  FIG. 4 , the filtration chamber  11  may be significantly higher than the module  5 . The cross section of the filtration chamber  11  preferably resembles the cross section of the module  5 , however, when spacer fillers  12  are used, any cross section of the module may be accommodated. The filtration chamber  11  may be integrally formed as one piece or comprise multiple elements. The filtration chamber  11  preferably has a constant cross-section along its length, however, it may consist of multiple sections with a thicker cross section towards its base. 
     A spacer filler  12  with an exterior cross section closely resembling the cross section of the filtration chamber  11  and an internal cross section closely resembling the cross section of the module  5  is provided between the module  5  and the filtration chamber  11 . The spacer filler  12  is not essential to the operation of the filtration assembly  10  but in the preferred embodiments is used to further reduce backwash and cleaning solution volumes. The spacer filler  12  may be formed from a single or multiple components. 
     A cap  13  is fitted to one end  14  of the module  5  to allow filtrate flow  15  from the end of the module  5  into the filtrate carrier  9 . 
     A module mounting piece  16  is sealingly attached to lower end of the filtration chamber  11 . The mounting piece  16  includes an aeration backwash device  17  and a filtrate collection chamber  18 . 
     As indicated above, the filtrate carrier  9  need not be located within the module  5 . Instead, external connections between the cap  13  and the filtrate collection chamber  18  or downstream thereof may be provided to allow for the collection of filtrate from the capped end of the module  5 . 
     The aeration/backwash device  17 , at least in part, surrounds a portion of the membrane module  5  above the lower header  8 . The aeration/backwash device  17  includes a communication chamber  19  having upper and lower through-openings  20  and  21  in fluid communication with the communication chamber  19  and the membrane module  5 . It will be appreciated however that the function of the upper and lower through-openings may be performed by one or more elongate openings which are, preferably, varying in width and, more is preferably, are wider at the lower end than at the upper end. The communication chamber  19  is connected via a pipe  22  to a feed, aeration, backwash and draindown header  23 . The communication chamber  19  in this embodiment is in the form of annulus  24  which provides for the selective aeration, feed and backwash with through-openings  20  and  21  in the inner wall  25  of the annulus  24  to allow the flow of gas, feed liquid, backwash liquid into the module  5  and draindown of waste liquid from the module  5 . The annulus  24  may fully or partially surround the membrane module  5 . 
     It will be appreciated that the functions of the module mounting piece  16  may provided by a single component or by multiple components. 
     A filtrate header  26  connects the filtrate collection chamber  18  from multiple modules together to a common outlet (not shown). 
     The aeration, feed, backwash and draindown header  23  connects the aeration gas, feed liquid, backwash and draindown liquids from multiple modules together to a common inlet/outlet (not shown). 
     Various modes of operation of this embodiment of the invention will now be described, by way of example only, with reference to  FIGS. 2 to 4  of the drawings, respectively. 
     Gravity Suction Mode Operation 
     This mode of operation is illustrated in  FIG. 2  of the drawings which shows the filtration assembly  10  located in a feed tank  28 . Although, the assembly  33  is shown located in a tank  28 , it will be appreciated that the tank  28  is merely one means of providing feed liquid to the filtration chamber  11  and other means such as pumping, flowing liquid from above and the like are equally applicable. 
     Filtration 
     The feed liquid level  29  in the surrounding feed tank  28  is raised higher than the filtration chamber  11  allowing feed liquid  30  to flow into the filtration chamber  11 . Feed liquid may also be pumped through the aeration, feed, drain down and backwash header  23  and suction may be applied to the filtrate header  26 . Significant pressure can be introduced by high feed levels in the feed tank  28 . 
     The feed liquid flows down the filtration chamber  11  and is diverted into the module  5  by the spacer filler  12 . The feed liquid is then filtered through the membranes  6  located in the module  5  and filtrate is recovered from the ends of the module  5 . Filtrate from the capped end  31  of the module  5  flows through the filtrate carrier  9  to the bottom end  32  of the module  5  and into the filtrate header  26 . 
     Aeration 
     During the aeration step, the feed liquid level  29  is lowered in the surrounding tank  28  to lower than the top of the filtration chamber  11 . Gas, typically air, is then introduced through the aeration, feed, drain down and backwash header  23  to aerate the membrane module  5 . The gas flows into the communication chamber  19  and is directed into the membrane module  5  through the aeration holes  20  in the module mounting piece  16 . The gas forms bubbles which scrub the membrane surfaces as they rise through the module  5 . The feed liquid level in the filtration chamber  11  is arranged such that, during aeration, no feed liquid is able to escape from the filtration chamber  11  into the feed liquid in the surrounding tank  28 . 
     Feed Backwash 
     During the feed backwash process, the feed liquid level  29  is lowered in the surrounding tank  28  to lower than the top of the filtration chamber  11 . Backwash liquid is then introduced through the aeration, feed, drain down and backwash header  23 . The backwash liquid flows into the communication chamber  19  and is directed into the membrane module  5  through the feed backwash holes  21  in the module mounting piece  16 . The backwash liquid then scrubs the membrane surfaces as it rises through the module  5 . The feed liquid level  29  in the filtration chamber  11  is arranged such that, during backwash, no feed liquid is able to escape from the filtration chamber  11  into the feed liquid in the surrounding tank  28 . 
     In an alternative feed backwash process, backwash feed liquid is introduced into the filtration chamber by raising the feed level  29  in the tank  28  such that it overflows into the filtration chamber. The backwash liquid flows through the module  5  and out through the aeration, feed, drain down and backwash header  23 . Suction may be applied to the backwash header. 
     Permeate Backwash 
     During the permeate backwash process, the feed liquid level  29  is lowered in the surrounding tank to lower than the top of the filtration chamber  11 . Feed is drained from inside the filtration chamber  11  and permeate is introduced through pressurising the filtrate header  26  with permeate. The permeate backwash liquid flows through into lumens and out through the walls of the fibres removing solids from the surfaces of the fibres. During this step, permeate backwash liquid and solids may be drained through the communication chamber  19  and into the aeration, feed, drain down and backwash header. The rate of introduction of the permeate backwash liquid is arranged such that, during permeate backwash, no permeate backwash liquid is able to escape from the filtration chamber  11  into the feed liquid surrounding the tank  28 . 
     Drain Down 
     After either or both of aeration and backwash the liquid and solids in the filtration chamber  11  are drained out through the holes  20  and  21  in the module mounting piece  16  into the aeration, feed, drain down and backwash header  23 . 
     Pressurised Mode Operation 
     As shown in  FIG. 3 , for operation in pressurised mode, an assembly  33  is provided on the top end of the filtration chamber  11  that allows liquid to flow only into the filtration chamber  11  but not out thereof and allows gas to flow in both directions. In this embodiment, the assembly  33  consists of a sealing cone  34  which seals onto the open end  35  of the filtration chamber  11  with an opening  36  therein which is smaller than a sealing ball  37 . The sealing ball  37 , which has an effective density less than the feed liquid, is located and moves freely within the filtration chamber  11 . 
     It will be appreciated by those in the art that a variety of valve arrangements can be used to achieve the required function. 
     Although, the assembly  33  is shown located in a tank  28 , it will be appreciated that the tank  28  is merely one means of providing feed liquid to the filtration chamber  11  and other means such as pumping, flowing liquid from above and the like are equally applicable. 
     Filtration 
     During filtration, the feed liquid is introduced to the filtration chamber  11  through the aeration, drain down and backwash header  23 , and suction may be is applied to the filtrate header  26 . As the level of the feed liquid in the filtration chamber  11  is raised the sealing ball  37  floats up to seal against the sealing cone  34  and closing opening  36 , thereby allowing the filtration chamber  11  to be pressurised. 
     The feed liquid is then filtered through the membranes  6  in the module  5  and filtrate is recovered from the ends of the module  5 . Filtrate from the capped end  31  of the module  5  flows through the filtrate carrier  9  to the bottom end  32  of the module  5  and into the filtrate header  26 . 
     Aeration 
     During the aeration step, the feed liquid level  29  is lowered in the filtration chamber  11 , so that the sealing ball  37  is no longer in contact with the sealing cone  34  and the filtration chamber  11  is depressurised. Gas is then introduced through the aeration, feed, drain down and backwash header  23 . The gas flows into the communication chamber  19  and is directed into the module  5  through the aeration holes  20  in the module mounting piece  16 . The gas forms bubbles which scour the membrane surfaces as they rise through the module  5 . The feed liquid level in the filtration chamber  11  is arranged such that, during aeration, no feed liquid is able to escape from the filtration chamber  11  into the feed liquid in the surrounding tank  28 . 
     Feed Backwash 
     During the backwash process, the feed liquid level is lowered in the filtration chamber  11 , so that the sealing ball  37  is no longer in contact with the sealing cone  34  and the filtration chamber  11  is depressurised. The feed liquid level in the surrounding tank  28  is arranged such that feed liquid overflows into the filtration chamber to backwash the module. The backwash feed liquid flows is through the module removing solids from the surfaces of the fibres. The backwash liquid drains through the aeration, feed, drain down and backwash header  23 . Suction may be applied to the backwash header. 
     Permeate Backwash 
     During the permeate backwash process, feed is drained from inside the filtration chamber  11  and permeate is introduced through pressurising the filtrate header  26  with permeate. The permeate backwash liquid flows through into lumens and out through the walls of the fibres removing solids from the surfaces of the fibres. During this step, permeate backwash liquid and solids may be drained through the communication chamber  19  and into the aeration, feed, drain down and backwash header. The rate of introduction of the permeate backwash liquid is arranged such that, during permeate backwash, no permeate backwash liquid is able to escape from the filtration chamber  11  into the feed liquid surrounding the tank  28 . 
     Drain Down 
     After either or both of aeration and backwash the liquid and solids in the filtration chamber  11  are drained out through the holes  20  and  21  in the module mounting piece  16  into the aeration, feed, drain down and backwash header  23 . 
     High Head Mode Operation 
     As shown in  FIG. 4 , for high head mode operation the filtration chamber  11  is extended significantly beyond the height of the module  5  such that, when the filtration chamber  11  is filled, a significant pressure is generated across the filtration surfaces of the membranes. 
     Filtration 
     During the filtration step, the feed liquid is introduced to the filtration chamber  11 , via the module  5 , through the aeration, feed, drain down and backwash header  23 , or directly into the filtration chamber until the feed liquid level fills the filtration chamber  11 . Suction may also be applied to the filtrate header  26 . 
     The feed liquid is then filtered through the membranes  6  located in the module  5  and filtrate is recovered from the ends of the module  5 . Filtrate from the capped end  31  of the module  5  flows through the filtrate carrier  9  to the bottom end  32  of the module  5  and into the filtrate header  26 . The feed liquid is introduced at such a rate that the level in the filtration chamber  11  stays within controlled limits maintaining sufficient pressure for filtration. 
     Aeration 
     Gas is introduced through the aeration, feed, drain down and backwash header  23 . The aeration gas flows into the communication chamber  19  and is directed into the module through the aeration holes  20  in the module mounting piece  16 . The gas forms bubbles which scour the surfaces of the membranes  6  as they rise though the module  5 . 
     Feed Backwash 
     Backwash liquid is introduced through the aeration, feed, drain down and backwash header  23 . The backwash liquid flows into the communication chamber  19  and is directed into the module  5  through the feed/backwash holes  21  in the module mounting piece  16 . The backwash liquid scrubs the surfaces of the membranes as it rises though the module  5 . 
     Permeate Backwash 
     During the permeate backwash process, the feed liquid level  29  is lowered in the surrounding tank  28  to lower than the top of the filtration chamber  11 . Feed is drained from inside the filtration chamber  11  and permeate is introduced through pressurising the filtrate header  26  with permeate. The permeate backwash liquid flows through into the lumens of the fibres  6  and out through the walls of the fibres removing solids from the surfaces of the fibres. During this step, permeate backwash liquid and solids may be drained through the communication chamber  19  and into the aeration, feed, drain down and backwash header. 
     Drain Down 
     After either or both of aeration and backwash the liquid and solids in the filtration chamber  11  are drained out through the holes  20  and  21  in the module mounting piece  16  into the aeration, feed, drain down and backwash header  23 . 
     It will be appreciated that the various backwashing processes and steps described above may be performed in a variety of combinations and sequences depending on the operating outcomes desired by the user. 
     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.