Method and assembly for water filtration using a tube manifold to minimize backwash

A method of filtering a feed liquid in a membrane filtration assembly is provided comprising introducing feed liquid to be treated into a filtration chamber of a membrane filtration system including a membrane module having one or more permeable hollow membranes, the module being located in the filtration chamber, and the filtration chamber having an open upper end located above an upper header of the membrane module and a closed lower end, and feed tank surrounding the filtration chamber. The feed tank may be configured to provide the feed liquid through the open upper end of the filtration chamber, and the feed liquid may be applied to the surface of the membranes within the membrane module and withdrawn from the lumens of the membranes as filtrate.

TECHNICAL FIELD

The present invention relates to membrane filtration systems and methods and, more particularly, to a system and method that allows for filtration under gravity, under pressure or using a high feed head while minimizing 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 minimize 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chamber associated with said header and in fluid communication with lumens of said membranes for collecting filtrate withdrawn through said membrane lumens;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.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIG. 1, the membrane filtration module5according to one preferred embodiment consists of a bundle of hollow fiber membranes6potted at the top and bottom in upper and lower headers7and8respectively to expose the fiber membrane lumens to collect filtrate. It will be appreciated the fiber bundle may be potted at either or both ends, and further that the fiber 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 carrier9(typically a pipe or tube) extends between the upper and lower headers7and8to allow filtrate to be collected from either or both ends of the fiber membrane lumens. The carrier9may be of any shape in cross section and, though shown in this embodiment in the centre of the module5, it may be located anywhere in the pot and in some embodiments the filtrate carrier9need not be located in the module5but can be connected through external connections as described below.

Referring toFIGS. 2 to 4, the filtration assembly10, according to a preferred embodiment of the invention, consists of a filtration chamber11higher than the module5. If used in the high head filtration mode, as shown inFIG. 4, the filtration chamber11may be significantly higher than the module5. The cross section of the filtration chamber UK preferably resembles the cross section of the module5, however, when spacer fillers12are used, any cross section of the module may be accommodated. The filtration chamber11may be integrally formed as one piece or comprise multiple elements. The filtration chamber11preferably 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 filler12with an exterior cross section closely resembling the cross section of the filtration chamber11and an internal cross section closely resembling the cross section of the module5is provided between the module5and the filtration chamber11. The spacer filler12is not essential to the operation of the filtration assembly10but in the preferred embodiments is used to further reduce backwash and cleaning solution volumes. The spacer filler12may be formed from a single or multiple components.

A cap13is fitted to one end14of the module5to allow filtrate flow15from the end of the module5into the filtrate carrier9.

A module mounting piece16is sealingly attached to lower end of the filtration chamber11. The mounting piece16includes an aeration backwash device17and a filtrate collection chamber18.

As indicated above, the filtrate carrier9need not be located within the module5. Instead, external connections between the cap13and the filtrate collection chamber18or downstream thereof may be provided to allow for the collection of filtrate from the capped end of the module5.

The aeration/backwash device17, at least in part, surrounds a portion of the membrane module5above the lower header8. The aeration/backwash to device17includes a communication chamber19having upper and lower through-openings20and21in fluid communication with the communication chamber19and the membrane module5. 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 chamber19is connected via a pipe22to a feed, aeration, backwash and draindown header23. The communication chamber19in this embodiment is in the form of annulus24which provides for the selective aeration, feed and backwash with through-openings20and21in the inner wall25of the annulus24to allow the flow of gas, feed liquid, backwash liquid into the module5and draindown of waste liquid from the module5. The annulus24may fully or partially surround the membrane module5.

It will be appreciated that the functions of the module mounting piece16may provided by a single component or by multiple components.

A filtrate header26connects the filtrate collection chamber18from multiple modules together to a common outlet (not shown).

The aeration, feed, backwash and draindown header23connects 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 toFIGS. 2 to 4of the drawings, respectively,

Gravity Suction Mode Operation

This mode of operation is illustrated inFIG. 2of the drawings which shows the filtration assembly10located in a feed tank28. Although, the assembly33is shown located in a tank28, it will be appreciated that the tank28is merely one means of providing feed liquid to the filtration chamber11and other means such as pumping, flowing liquid from above and the like are equally applicable.

Filtration

The feed liquid level29in the surrounding feed tank28is raised higher than the filtration chamber11allowing feed liquid30to flow into the filtration chamber11. Feed liquid may also be pumped through the aeration, feed, drain down and backwash header23and suction may be applied to the filtrate header26. Significant pressure can be introduced by high feed levels in the feed tank28.

The feed liquid flows down the filtration chamber11and is diverted into the module5by the spacer filler12. The feed liquid is then filtered through the membranes6located in the module5and filtrate is recovered from the ends of the module5. Filtrate from the capped end31of the module5flows through the filtrate carrier9to the bottom end32of the module5and into the filtrate header26.

During the aeration step, the feed liquid level29is lowered in the surrounding tank28to lower than the top of the filtration chamber11. Gas, typically air, is then introduced through the aeration, feed, drain down and backwash header23to aerate the membrane module5. The gas flows into the communication chamber19and is directed into the membrane module5through the aeration holes20in the module mounting piece16. The gas forms bubbles which scrub the membrane surfaces as they rise through the module5. The feed liquid level in the filtration chamber11is arranged such that, during aeration, no feed liquid is able to escape from the filtration chamber11into the feed liquid in the surrounding tank28.

Feed Backwash

During the feed backwash process, the feed liquid level29is lowered in the surrounding tank28to lower than the top of the filtration chamber Backwash liquid is then introduced through the aeration, feed, drain down and backwash header23. The backwash liquid flows into the communication chamber19and is directed into the membrane module5through the feed backwash holes21in the module mounting piece16. The backwash liquid then scrubs the membrane surfaces as it rises through the module5. The feed liquid level29in the filtration chamber11is arranged such that, during backwash, no feed liquid is able to escape from the filtration chamber11into the feed liquid in the surrounding tank28.

In an alternative feed backwash process, backwash feed liquid is introduced into the filtration chamber by raising the feed level29in the tank28such that it overflows into the filtration chamber. The backwash liquid flows through the module5and out through the aeration, feed, drain down and backwash header23. Suction may be applied to the backwash header.

During the permeate backwash process, the feed liquid level29is lowered in the surrounding tank to lower than the top of the filtration chamber11. Feed is drained from inside the filtration chamber11and permeate is introduced through pressurizing the filtrate header26with permeate. The permeate backwash liquid flows through into lumens and out through the walls of the fibers removing solids from the surfaces of the fibers. During this step, permeate backwash liquid and solids may be drained through the communication chamber19and 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 chamber11into the feed liquid surrounding the tank28.

Drain Down

After either or both of aeration and backwash the liquid and solids in the filtration chamber11are drained out through the holes20and21in the module mounting piece16into the aeration, feed, drain down and backwash header23.

Pressurized Mode Operation

As shown inFIG. 3, for operation in pressurized mode, an assembly33is provided on the top end of the filtration chamber11that allows liquid to flow only into the filtration chamber11but not out thereof and allows gas to flow in both directions. In this embodiment, the assembly33consists of a sealing cone34which seals onto the open end35of the filtration chamber11with an opening36therein which is smaller than a sealing ball37. The sealing ball37, which has an effective density less than the feed liquid, is located and moves freely within the filtration chamber11.

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 assembly33is shown located in a tank28, it will be appreciated that the tank28is merely one means of providing feed liquid to the filtration chamber11and 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 chamber11through the aeration, drain down and backwash header23, and suction may be is applied to the filtrate header26. As the level of the feed liquid in the filtration chamber11is raised the sealing ball37floats up to seal against the sealing cone34and closing opening36, thereby allowing the filtration chamber11to be pressurized.

The feed liquid is then filtered through the membranes6in the module5and filtrate is recovered from the ends of the module5. Filtrate from the capped end31of the module5flows through the filtrate carrier9to the bottom end32of the module5and into the filtrate header26.

During the aeration step, the feed liquid level29is lowered in the filtration chamber11, so that the sealing ball37is no longer in contact with the sealing cone34and the filtration chamber11is depressurized. Gas is then introduced through the aeration, feed, drain down and backwash header23. The gas flows into the communication chamber19and is directed into the module5through the aeration holes20in the module mounting piece16. The gas forms bubbles which scour the membrane surfaces as they rise through the module5. The feed liquid level in the filtration chamber11is arranged such that, during aeration, no feed liquid is able to escape from the filtration chamber11into the feed liquid in the surrounding tank28.

Feed Backwash

During the backwash process, the feed liquid level is lowered in the filtration chamber11, so that the sealing ball37is no longer in contact with the sealing cone34and the filtration chamber11is depressurized. The feed liquid level in the surrounding tank28is 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 fibers. The backwash liquid drains through the aeration, feed, drain down and backwash header23. Suction may be applied to the backwash header.

During the permeate backwash process, feed is drained from inside the filtration chamber11and permeate is introduced through pressurizing the filtrate header26with permeate. The permeate backwash liquid flows through into lumens and out through the walls of the fibers removing solids from the surfaces of the fibers. During this step, permeate backwash liquid and solids may be drained through the communication chamber19and 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 chamber11into the feed liquid surrounding the tank28.

Drain Down

After either or both of aeration and backwash the liquid and solids in the filtration chamber11are drained out through the holes20and21in the module mounting piece16into the aeration, feed, drain down and backwash header23.

High Head Mode Operation

As shown inFIG. 4, for high head mode operation the filtration chamber11is extended significantly beyond the height of the module5such that, when the filtration chamber11is 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 chamber11, via the module5, through the aeration, feed, drain down and backwash header23, or directly into the filtration chamber until the feed liquid level fills the filtration chamber11. Suction may also be applied to the filtrate header26.

The feed liquid is then filtered through the membranes6located in the module5and filtrate is recovered from the ends of the module5. Filtrate from the capped end31of the module5flows through the filtrate carrier9to the bottom end32of the module5and into the filtrate header26. The feed liquid is introduced at such a rate that the level in the filtration chamber11stays within controlled limits maintaining sufficient pressure for filtration.

Gas is introduced through the aeration, feed, drain down and backwash header23. The aeration gas flows into the communication chamber19and is directed into the module through the aeration holes20in the module mounting piece16. The gas forms bubbles which scour the surfaces of the membranes6as they rise though the module5.

Feed Backwash

Backwash liquid is introduced through the aeration, feed, drain down and backwash header23. The backwash liquid flows into the communication chamber19and is directed into the module5through the feed/backwash holes21in the module mounting piece16. The backwash liquid scrubs the surfaces of the membranes as it rises though the module5.

During the permeate backwash process, the feed liquid level29is lowered in the surrounding tank28to lower than the top of the filtration chamber11. Feed is drained from inside the filtration chamber11and permeate is introduced through pressurizing the filtrate header26with permeate. The permeate backwash liquid flows through into the lumens of the fibers6and out through the walls of the fibers removing solids from the surfaces of the fibers. During this step, permeate backwash liquid and solids may be drained through the communication chamber19and 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 chamber11are drained out through the holes20and21in the module mounting piece16into the aeration, feed, drain down and backwash header23.

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.