CA2525985A1 - Membrane filtration apparatus and process optionally for sand filter retrofit - Google Patents

Abstract

A filtration apparatus has a horizontally oriented permeate conduit supported on the floor of a tank. A module of filtering membranes may be placed on or over the permeate conduit and communicate with the permeate conduit. The module may be of a variety of configurations including one with vertically oriented hollow fibers. A permeate collector may be connected to the permeate conduit by a second permeate conduit. The connection may be made near the top of the module and may be through an isolation valve. The apparatus is suitable, among other things, for installation in a sand filter tank. Permeation may be by gravity flow.

Description

-'~ -TITLE: MEMBRANE FIL'PRATIQN APPARATUS AND PROCESS OPTIONALLY
FOR SAND FILTER RETROFIT

FIELD
[0001] This document relates to membrane filtration devices or processes.
BACKGROUND

[0002] The following background description does not admit that anything discussed below is citable as prior art or is part of the general knowledge of a person skilled in the art.

[0003] A sand filter, or rapid sand filter may have a tank about 3 m deep. A
set of parallel underdrain pipes may lay horizontally near the bottom of the tank and be connected, for example through a header, to an outlet pipe near the bottom of the tank. The outlet pipe may be connected to a T-fitting such that filtrate can be removed from the tank through the underdrain pipes or wash water can flow into the underdrain pipes. A layer of gravel, for example about 45 cm thick, covers the underdrain pipes. A layer of sand or sand and anthracite covers the gravel, for example in a layer about 75 cm thick. Generaliy horizontal wash water troughs span across the tank between the top of the sand or anthracite and the top of the tank and connect to a backwash outiet_ A raw water inlet allows feed into the tank from near the top of the tank, During filtration, water Is fed into the tank to maintain a water level near the top of the tank to provide a head relative to the outlet to drive water through the anthracite, if any, sand, gravel and underdrain pipes to the outlet. During a backwash, the water surface Is lowered to just over the edges of the wash water troughs and wash water is fed into the outlet to provide an upward flow through the gravel, sand and anthracite, if any. A
gas may also be supplied from below, This upward flow carries filtered solids to the wash water troughs and out the backwash outlet.

[0004] In U.S. Patent No. 8,893,568 issued May 17, 2005 to Janson et al., modules of ultrafiltration or microfiltration membranes are arranged in a tank open to the atmosphere to substantially cover the cross sectionai area of the tank. A filtration oycle has permeation steps and deconcentration steps.
During permeation, supply of feed substantially equals feed removed and little if any aeration is used. During deconcentration, aeration with scouring bubbles is provided with one or both of backwashing and feed flushing. In feed flushing, feed water is supplied to the tank from below the modules. Excess tank water created during deconcentration flows generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.
INTRODUCTION

[0005] This document describes, among other things, one or more membrane filtration apparatuses, processes or systems; methods of converting a sand filter into a membrane filtration system and operating such a system;
and, a kit of items to integrate Immersed membranes into an existing sand filter. One or more inventions may be disclosed but the following introduction is intended to introduce the reader to the contents of this document rather than to define any particular invention. One or more Inventions may reside in combinations or sub-combinations of one or more apparatus elements or process steps described in this or other parts of this documents, for example the detailed description or claims.

[0006] A membrane filtration apparatus, system or process that may be used, for example, in a newly built plant or to retrofit, or provide a method or kit or parts to retrofit, a sand filter and operate the retrofit system. The module may have a plurality of membranes held in a mass of potting material with ends open to a permeate collector. The membranes may be hollow fiber membranes oriented vertically and the permeate collector may communicate with upper ends of the membranes. A permeate pipe may carry collected permeate from one or more modules upwards or down towards the bottom of the module. A releasable connection between the permeate pipe and the permeate collector may be made near or above an upper potting head or the top of the module. An isolation valve may be placed in the permeate pipe or between the permeate collector and the permeate pipe, The releasable connector or isolation vaive or both may be configured such that the module can be removed from the permeate pipe by moving the module or permeate pipe vertically. Further optionally, the bottom of the module may have a gas distributor which may comprise holes through a mass of potting material holding lower ends of the membranes and a skirt or chamber. A system may have permeate or gas pipes or both placed horizontally across or near the bottom of a tank, optionally supported by the bottom of the tank. The pipes may optionally be made in segments attached end to end. The pipes may rest on or be integral with a pedestal. One or more modules may rest on the pedestal, optionally without being connected to the pedestal. The pedestal may comprise a tray which may assist in locating a bottom part of the module and may have openings to allow air to flow from gas pipes to the modules.
Optionally, wash water troughs may be located in the tank above the modules to remove retentate from the tank. If the modules or system are optionally being used to retrofit a send filter tank, one or more of the permeate pipe, gas pipes or troughs may be connected to preexisting fittrate, gas supply and backwash water removal systems of the sand filter respectively. The system may optionally be operated with transmembrane pressure for pemieation provided by head differenr,e or between the feed in the tank and a permeate outlet, suction or siphon. Deconcentration or retentate removal may optionally be by overflow to the troughs. A kit to integrate immer$Qd membranes into a sand filter may comprise one or more of the parts mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is an isometric view of a module pedestal for a horizontal fiber module.

[000$] Figure 2 is an isometric view of a module pedestal for a vertical fiber module.

[0009] Figure 3a is a plan view of a filtration tank partially covered with module pedestals.

[0010] Figure 3b is an elevation section of a filtration tank with modules of vertical hollow fibers.

[0011] Figure 4 is an elevational section view of a module of horizontal hollow fibers on the pedestal of Figure 1.

[0012] Flgure 5 is an elevational section view of a module of vertical hollow fibers on the pedestal of Figure 2.

[0013] Figure 6 is a schematio representation of part of an optional air extraction system.

[0014] Figure 7 is an isometric view of another pedestal with an array of eight of another module on the pedestal.

[0015] Figure 8 is a top, side and bottom view of a module of the array of Figure 7.

[0016] Figure 9 is a cross section of the array of Figure 7 cut through the modules.

[0017] Figure 10 is a cross section of the array of Figure 7 cut through a permeate pipe between modules.

(0018] Figure 11 is an exploded view of a module of Figure 7.
[0019] Figure 12 is an isometric view of the pedestal of Figure 7.

[0020] Figure 13 is a section of a valve from Figure 7 in a closed position.
[0021] Figures 14 shows plan views of alterrmate upper header surrounds of the module of Figure 7.

DETAILED DESCRIPTION
[0022] Various apparatuses or processes will be described below including an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that are not described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses or processes described below. It is possible that an apparatus or proc:ess described below is not an embodiment of any claimed invention. All rights are reserved in any invention disctosed in an apparatus or process that is not claimed in this document. Any one or more features of any one or more embodiments can be combined with any one or more features of any one or more other embodiments.

[0023] Referring to Figures 1-6, the bottom 8 of a filtration tank 10, which may have been formerly used as a sand filter, is prepared to install an immersed membrane retrofit kit by removing the existing underdrain system, for example pipes, and optionally pouring a level layer of concrete into which tracks (not shown) are optionally inserted to secure the module pedestals 12.

[0024] The retrofit kit includes a module pedestal 12 which may be adapted for use with a variety of modules. Each pedestal 12 may be a block or assembly, made for example of plastic, that can be fixed or rest at the bottom of the tank 10 and may contain or form, alone or in combination with other pedestals 12, one or more of: a section of permeate conduit 14; a section of gas or aeration conduit 16; a section of air removal conduit 18; connectors for permeate 20, scouring air 22 and permeate air removal 24; and, a feed-and-drain channel 26 and aeration pipes 28. The pedestal 12 may be made, for example, by a process comprising injection molding or extrusion optionally with further operations such as drilling, milling, gluing or welding to create various passageways or assemblies.

[0025] Pedestals 12 are laid at the bottom 26 of the tank 10 and connected longitudinally to form permeate 30 and aeration headers 32 and air removal headers 33 as shown in Figures 3a and 3b. Each pedestal 12 has intercorinecting male 34 and female 36 ends that may be seaied together by, for example, o-rings, gluing or welding. The bottom 8 of the tank 10 may be completely or generally covered by module pedestals 12 optionally except for the end(s) where room may be left for connecting permeate 30 and air 32 headers into manifolds 38, 40 that tie to the existing sand filter piping network 42, 44. For sand filters without a gas backwash system, gas pipe network 42 a blower and related ancillary equipment and controls may be added, Optionally, air removal headers 33 may Qonnect to air removal manifold 39 which connect to an air extraction system 62 shown in Figure B. Feed may enter the tank 10 from an inlet near the top of the tank 10.

[0026] A horizontal module 52 may resemble a standard ZW-1000 module made by Zenon Environmental Inc. Such a module is described in U.S. Patent No. 6,325,928 issued December 4, 2001, which is incorporated in its entirety herein by this reference to it. The horizontal module 52 may have a permeate header 46 as shown in Figure 4 with a permeate port 48 at the bottom of the header 46, instead of at the back as in a zW 1000 module, to connect to the permeate conduit 14 in the pedestal 12. Alternateiy module 52 may have a permeate header with a permeate port at the top. In this case, groups of modules 52, for example 2#o 6, may be fit#ed with a permeate manifold near the top of the modules and connected to a vertical permeate pipe in a manner analogous to Figures 7 to 14. A fine tube 50, for example less than 10 mm inside diameter or between 3-5 mm, may be inserted Into the top portion of the header 46 and connected to an optional air removal oonduit 18. Hollow fiber membranes may be bOtween 0,1% and 5%, for example about 2%, longer than the distance between the header 46 and an opposed potting head.

[0027] Figure 5 shpws a section view of a verticai moduie 54 with vertical fibres 56 on a pedestal 12. The module shown Is cylindrical, with radially and circumferentiaiiy distributed air holes through the pottirtg material of the lower header, optionally called a potting head, although rectangular or other shaped headers may also be used. The vertical module 54 has an interior, optionally centrai, permeate tube 58 to bring the filtered water to the bottom permeate conduit 14 in the pedestal 12. The vertical module 54 also has an air distribution chamber 59 or skirt which may be used to release air through air passages 61, [002$] Figures 4 and 5 show an optional continuous flexible air removal tube 50 connecting the top of the module permeate cavity 60 to the air removal conduit. Further optionally, two sections of this tube 60 may be integrated into the header 46 and the pedestal 12, respectively, and connected together via a quick-connect mechanism (not shown) when the module 52, 54 is inserted into position.

[0029] For both moduie 52, 54 configurations, air may be removed from the permeate header 46, for example air from degassing or after a membrane integrity test, through the fine air removal tube 50, the air removal conduit 18 and an air extraction system 62 as shown in Figure 6. The air extraction system 82 may be common to all membrane rows in the tank 10 although individual rows may be isofated by air removal isoiation valves 77, for example when a row Is taken out of service. The air extraction system may run throughout permeation, but only has to handle a very small fraction of the permeate flow because head loss through the fine tubes 50 causes very low flow rates even though the pressure in the air extraction system is lower (i.e., the air extraction system 62 has a stronger vacuum) than the permeate withdrawn system. The air extraction system 62 reoeives air or permeate or both through the air removal manifold 39.
Vacuum pump 66 is operated to draw air from the air removal manifold 39. When all air has been drawn out, an amount of permeate may atso be drawn into air extraotion charnber 65. This permeate is removed by liquid pump 68, which may also be a drain. Liquid pump 68 turns on whenever a sensor indicates that extraction chamber 64 has a certain level of liquid in it. In this way, when air is present in the header 46, it is sucked through this network; when not, permeate is extracted. The vacuum applied through this system can by higher than that applied through the permeate extraction network since the amount of permeate flow will be limited by pressure loss through the fine tube 50 section which allows the air extraction system 62 to run during permeation to remove incidental air. On plant or row startup, or after an integrity test, the air extraction system 62 may be run for a period of time before starting permeation to remove air and fully or partially prime the permeate system.

5[0030] The top of the module 52, 54 may have a plastic cover 70 that forms a walk-on platform 72 when all modules 52, 54 are installed into the tank, Each module 52, 54 may have built-in screens 74, for example plastiC mesh with about a 5 mm opening size, at the bottom and at the top for a horizontal fiber module 52 or around the periphery for a vertical fibre module 54.

[0031] The membrane system may allow for an increase in filtration rate over a sand filter. Optionally, for a simpler retrofit of existing sand fiiters, the filtration process may have filtration rates comparable to sand filters. Table shows that only 1 layer of ZW 1000 like modules being for example about 50 to 100 cm high and having 200 to 700 mZ of membrane surface area to cubic meter of voiume, at a flux of 30 Umz/h will allow a filtration rate of 15 m/h, higher than most existing sand filters. For vertical moduies. for example of 50 cm or more in height, a filtration rate of 15 m/h could be obtained with a larger diameter and shorter fibre than what is currently used in ZW-1000.

Table I Comparison of filtration rates Filtration Process Filtration Rate mlh gpm!
Conventional sand filter 5-10 2-4 High rate sand filter 20 8 ZW-1000 - 3 module high (80% coverage) 100 40 60 UmZ/h ZW-1000 - 1 module high (80% coverage) 15 6 ~ 30 Um2/h [0032] The different functions of a membrane filter are reviewed below.

[0033] Filtration may be by gravity using the existing control mechanism at a sand filter plant. Assuming an available head of 2m (0.2 bar or 20 kPa), a fouled membrane permeability of 150 Um2/h/bar would allow the membranes to run at a flux of 30 Llmz/h. This is possible with modern microfiltration or ultrafiltration membranes, some of which have a clean water module permeability of about 400 Um2lhlbar or more.

[0034] Membrane backpulse may be done using existing sand filter backwash pumps. Sand fliters are typically backwashed once per day, using 4 8% of the water filtered. Membrane filters can use roughly the same total amount of water, but with shorter more frequent backwashes, [0035] An existing blower system, or an added blower for older sand filters that do not have air/water backwash, may be used to air scour the membranes.
Isolation valves may be added between the air manifold 38 and the individual aeration headers 32 to allow non-operating rows to be isvlated, [0036] Air may be removed from each module using the optional air extraction system 62. Alternately, air may be entrained in the permeate flow and removed in a permeate air collector or allowed to leave the permeate in an open holding tank.

[0037] Tank water deconcentration may be by overflow using existing backwash or wash water troughs 76. Total or partial tank drains may also be possible if a connection can be made from the bottom of the tank to the backwash water tank.

[003$] For chemical cleaning, if desired, an existing sand filter may be modified by coating surfaces, adding a clean in place network and neutralization equipment. Lowering the membrane packing density (as compared to current ZV1/-1000 designs), if desired, to approach the fiitration rate of existing filters negatively impacts the volume of cleaning solutions. This is offset by reduced fouling rates from operation at lower fluxes. The cleaning procedure may include daily (or less frequent) chlorine maintenance cleaning (acid / base can be used as an alternative) by soaking, using the scouring aeration network or the air removal network for distribution of the cleaning solution, and in-line neutralization on a drain line. Manual recovery cleaning may also be done once or twice per year.

[0039] Membrane integrity tests may be done continuously on a rotation basis on module groups such as a full row using connections (not shown) to the permeate headers 30.

[0040] A full row of modules may be isolated from the permeate manifold 40 upon failure with a valve 78 at the end of a row that can be accessed from the top of the tank 10 as shown in Figure 3b. Other isolation valves similarly isolate a row from the other manifolds 38, 39. Optionally, a new filtration system may be built using the pedestals and modules either in the manner of a retrofit sand filter or with permeation by suction or deconcentration by removing retentate from a drain at the bottom of a tank.

[0041] Figures 7 to 14 show altemate modules and pedestals that may be used in a new filtration system or process, such as a process with permeation by suction and deconcentration by periodic tank drain or in a retrofit sand filter as described above. The alternate components may be used instead of modules 52, 54 and pedestal 12 in the apparatuses and processes described above.

[0042] Figures 7 to 14 show an apparatus 100 having eight alternate vertical modules 102 forming two module arrays 106 resting on a mufti component pedestal 104. The pedestal 104 may be made of a pair of Injection molded supports 108, each of which has a first part and a second part which may be separated to accept a pipe between the parts. A permeate pipe segment 110 and two gas scouring pipe segments 112 may be held inside or on the supports 108. The pipe segments 110, 112 may be generally the same length as the pedestal 104, may be a multiple of the length of the pedestal, or may be of a iength that provides manifolds 38, 40 in one piece spanning multiple pedest0is 104. Segments 110, 112 may have male and female ends and be connected together by o-rings as shown or by giuing, welding or other means. A hole 114 in the gas pipe segments 112 below each module 102 allows gas to travel from the gas pipe segment 112 to an area surrounded by a skirt 110 at the bottom of the module 102. A generally vertical permeate pipe 118, is glued, or otherwise sealed, into a hole in the permeate pipe segment 110 and extends upwarda. A
vertical permeate pipe 118 can be sized such that the expected permeate flow will cause enough permeate velocity to draw bubbles on the permeate side down to permeate pipe 110. Aitemateiy, an air removal system as described above may be used.

(0043] The modules 102 are constructed as shown particularly in Figure 11.
Starting from the bottom, skirt 116 holds a lower mass of structural urethane 120 and a lower mass of soft urethane 122. Lower urethane 120, 122 may have a number of srnafi holes for gas to pass through them. For example, module 102 may be roughly 20 cm square and have 100 to 150 holes of 4 to 8 mm diameter.
Skirt 116 may be sized to accommodate an air pocket of sufficient depth to create a flow of 0.4 to 0.05 scfm per hole. Lower ends of a bundle 126 of hollow fiber membranes may be sealed in lower structural urethane 120 and dispersed about the holes. A screen 124, for example a plastic mesh with about 5 mm openings, may be potted into skirt 116 at one end and an upper header surround 128 at the other end. As shown in Figure 14, alternate upper header surrounds 128 a, b, c, may have ribs 130 a, b, c. Ribs 130 strengthen upper header surround 128 and also separate the membranes into sub-bundles near the top of module 102 to provide passages for bubbles or water to flow horizontally out of the module 102. Upper header surround 128 hokis upper structural urethane 134 and upper soft urethane 132. The upper end of the membranes of bundle 126 are potted in upper urethane 134, 132 with their ends open to the upper face of upper structural urethane 134. Upper header surround 134 is sealed by o-rings -12..

130 into array manifold 138 and held in place by tabs 139 and retainer rings 136.
Retainer rings 136 may be elastomeric rings as shown, ring clamps or other structures with a variable diameter. Array manifold 138 has a manifold cap 140 sealed to the rest of array manifold 138 with o-rings 130.

[0044] The tops of the four modules 102 of an array 106 are sealed to a common permeate collector comprised of the array manifold 138 and cap 140.
The array manifold 138 and cap 140 each have a central opening and fit over the generally vertical permeate pipe 118, and are sealed to pipe 118 by o-rings 130, so the module array 106 can be installed or removed by moving it vertically.
Permeate flows from the tops of the modules, to the space enclosed by array manifold 138 and cap 140 and through holes in the generally vertical permeate pipe 118. As shown in Figures 10 and 13, a valve plug 150 may be lowered to close the holes to the generally vertical pemneate pipe 118 to isolate an array 106 or allow an array 106 to be removed while permeation continues with other arrays 106. Valve plug 150 may be movable directly in the main body of permeate pipe 118 acting as a valve body or as a separate valve body 152 attached to permeate pipe 118 which may serve as an upper part of permeate pipe 118.

[0045] Referring particularly to Figure 12, pedestal 104 comprises a tray 160 which rests on supports 108 directly or through gas pipes 112 or both.
Tray 160 has module openings 162 which allow gas to flow from holes 114 to skirts 116 and also assist in holding modules 102 horizontally in place or guiding modules 102 into place as they are lowered onto tray 160. Tray 160 also has permeate pipe holes 164 with sides extending downwards from the main horizontal surface of tray 160. Side 166 and end 168 walis of tray 160 complete a plenum under the main horizontal surface of tray 160. This plenum may provide additional depth to allow a deeper air pocket to form under the modules 102 but also allows gas to escape under its edges if gas is accidentally supplied at an excessive flow rate. Pedestal 104 may optionally be of different lengths, for example to accommodate 1 or 3 arrays 106, Tray 160 may have tabs, not shown, to positively position lower ends of modules 102 or lower ends of modules 102 or an array 106 may be held to each other by a frame (not shown). Optionally, pedestal 104 may be used to hold air pipes 112 without also holding permeate pipe 110. In this case, a pemneate pipe can be provided above modules 102 with vertical permeate pipe 118 extending upwards from manifold 138 rather thari downwards.

Claims (26)

1. A filtration apparatus comprising:
a) a lower potting head having a plurality of air passages;
b) an upper potting head;
c) a plurality of hollow fiber membranes extending between the potting headers, the membranes each having a membrane wall and a lumen, the membrane walls sealed to the potting heads, the lumen in communication with an upper surface of the upper potting head;
d) a permeate collector sealed to the upper header and defining a permeate collection zone over the upper potting head and in communication with the lumens of the membranes;
e) a first permeate conduit in communication with and extending generally vertically downwards from the permeate collection zone and, f) a releasable connection between the permeate collector and the first permeate conduit located near or above the upper potting head.

2. The apparatus of claim 1 having a gas distribution chamber below the lower potting head.

3. The apparatus of claim 1 or 2 having a second permeate conduit oriented generally horizontally below the lower potting head and connected to the first permeate conduit.

4. The apparatus of any of claims 1 to 3 wherein the bottom ends of the membranes are closed in the lower potting head.

5. The filtration apparatus of any preceding claim further comprising a tank wherein the second permeate conduit rests on a pedestal on the floor of the tank.

6. The filtration apparatus of any preceding claim wherein the lower potting head rests a pedestal.

7. The filtration apparatus of any preceding claim wherein the pedestal further comprises a tray.

8. The filtration apparatus of any preceding claim wherein the module is removable from the tank by moving the module vertically.

9. The filtration apparatus of any preceding claim wherein the first permeate conduit extends downward into an opening in the second permeate conduit.

10. The filtration apparatus of any preceding claim having a gas conduit parallel to the permeate conduit with an opening positioned so as to allow gas to flow from the gas conduit to the gas distribution chamber.

11. The filtration apparatus of any preceding claim having a generally horizontally oriented retentate trough above the module.

12. The filtration apparatus of any preceding claim wherein the permeate pipe is connected to an outlet near the bottom of the tank.

13. The filtration apparatus of any preceding claim wherein the permeate conduit is comprised of a plurality of segments.

14. The filtration apparatus of any preceding claim further comprising an air removal vacuum line connected to the permeate collection zone.

15. A filtration apparatus comprising, a pedestal further comprising a lower surface adapted to rest on a tank floor and an upper surface adapted to support a membrane assembly; a second permeate pipe held by the pedestal; and, a first permeate pipe extending upwards from the second permeate pipe.

16.The filtration apparatus of claim 15 further comprising a gas pipe held by the pedestal.

17. The filtration apparatus of claim 15 or 16 wherein the pedestal further comprises a tray.

18. The filtration apparatus of claim 17 wherein the tray has openings to permit gas to flow through the tray,

19. The filtration apparatus of any of claims 15 to 18 having an isolation valve at the top of the first permeate pipe.

20. The filtration apparatus of any of claims 15 to 19 having a module resting on the pedestal in communication with the first permeate pipe.

21. A permeate isolation valve having a cylindrical body, with ports through the body, a first end adapted to be connected to a permeate pipe and a plunger with a seal inside of the body and movable between a first position in which the seal is between the ports and the first end and a second position in which the seal is on the other side of the ports from the first end.

22. A membrane module having a permeate collector adapted to seal to the outside of the valve body of claim 21.

23. The module of claim 22 wherein the permeate collector is slidable over the valve body.

24.A membrane module having a first potting head, a plurality of gas passages through the potting head, a bundle of hollow fiber membranes having first ends potted in and dispersed about the first potting head, a second potting head, a spacer between the potting heads, and second ends of the membranes potted into the second potting head in two or more sub bundles.

25. The module of claim 24 wherein the first ends of the membranes are sealed in the first potting head and the second ends of the membranes are open.

26. Any combination of one or more apparatus elements or process steps selected from the set of all apparatus elements and process steps described in this document.