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. This abstract is not to be used to construe the claims.

Description:
[0001]     This is an application claiming the benefit under 35 USC 119(e) of U.S. Application Ser. No. 60/740,641 filed Nov. 30, 2005 and claims priority to Canadian Application Serial No. 2,525,985 filed Nov. 8, 2005. U.S. Application Ser. No. 60/740,641 and Canadian Application Serial No. 2,525,985 are incorporated herein, in their entirety, by this reference to them. 
     
    
     FIELD  
       [0002]     This document relates to membrane filtration devices or processes.  
       BACKGROUND  
       [0003]     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.  
         [0004]     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. Generally 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 outlet. 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.  
         [0005]     In U.S. Pat. No. 6,893,568 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 sectional area of the tank. A filtration cycle 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.  
         [0000]     Introduction  
         [0006]     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.  
         [0007]     This document describes a membrane filtration apparatus, a system and a 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 or 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 valve 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 sand filter tank, one or more of the permeate pipe, gas pipes or troughs may be connected to preexisting filtrate, gas supply and backwash water removal systems of the sand filter respectively. The system may optionally be operated with transmembrane pressure for permeation provided by head difference 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 immersed membranes into a sand filter may comprise one or more of the parts mentioned above.  
         [0008]     This document also describes a filtration apparatus comprising a lower potting head having a plurality of air passages, an upper potting head, 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, 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, a first permeate conduit in communication with and extending generally vertically downwards from the permeate collection zone and, a releasable connection between the permeate collector and the first permeate conduit located near or above the upper potting head.  
         [0009]     This document also describes 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.  
         [0010]     This document also describes 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. A membrane module may have a permeate collector adapted to seal to the outside of the valve body. The permeate collector may be slidable over the valve body.  
         [0011]     This document also describes 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.  
         [0012]     This document also describes a kit to integrate an immersed membrane into existing sand filters while minimizing changes to the existing plant. The kit is installed in-situ, optionally from all-plastic components that can be transported by a person, without the use of machinery. Permeate and air headers are built in-situ at the bottom of the sand filter tank. Modules are installed and removed from the top without having to disassemble any piping. Air (from degassing or after a membrane integrity test) is removed via the bottom through a fine tube inserted into the header. Modules can be installed without removing existing backwash channels. The retrofitted plant can be used with the existing feed inlet and filtrate outlets. The membrane modules may produce a similar filtration rate to the existing sand filter to reduce the extent of any changes required to the remainder of the plant. Optionally, fine tubes from the permeate cavity of each module may be connected individually to a pneumatic control system. The pneumatic control system may be used to assist in providing one or more ancillary functions. For example, the pneumatic control system may be used for one or more of extracting air from the permeate side of the modules, performing a membrane integrity test or isolating a module or group of module from the rest of the system.  
         [0013]     This document also describes a module pedestal with interconnected permeate and air headers.  
         [0014]     This document also describes a permeate connection at the bottom of a module.  
         [0015]     This document also describes a cassette-less construction for a plurality of filtering modules.  
         [0016]     This document also describes a walking deck part of a module.  
         [0017]     This document also describes a system and process for air removal within a header of a module using a vacuum tube line.  
         [0018]     This document also describes an air removal conduit independent of a permeate header and situated below an air inlet level and an associated method of operation.  
         [0019]     This document also describes a pressure actuated isolation valve built into a module permeate header or between a module permeate header and a permeate conduit.  
         [0020]     This document also describes a pneumatic control system operable to do one or more of extract air, perform a membrane integrity test (MM or isolate a module or group of modules.  
         [0021]     This document also describes a process for providing a continuous rotating MIT without production interruption.  
         [0022]     This document also describes a system and process for air removal from degassing or after an MIT.  
         [0023]     This document also describes an automatic isolation of modules not meeting an integrity criterion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  is an isometric view of a module pedestal for a horizontal fiber module.  
         [0025]      FIG. 2  is an isometric view of a module pedestal for a vertical fiber module.  
         [0026]      FIG. 3   a  is a plan view of a filtration tank partially covered with module pedestals.  
         [0027]      FIG. 3   b  is an elevation section of a filtration tank with modules of vertical hollow fibers.  
         [0028]      FIG. 4  is an elevational section view of a module of horizontal hollow fibers on the pedestal of  FIG. 1 .  
         [0029]      FIG. 5  is an elevational section view of a module of vertical hollow fibers on the pedestal of  FIG. 2 .  
         [0030]      FIG. 6  is a schematic representation of part of an optional air extraction system.  
         [0031]      FIG. 7  is an isometric view of another pedestal with an array of eight of another module on the pedestal.  
         [0032]      FIG. 8  is a top, side and bottom view of a module of the array of  FIG. 7 .  
         [0033]      FIG. 9  is a cross section of the array of  FIG. 7  cut through the modules.  
         [0034]      FIG. 10  is a cross section of the array of  FIG. 7  cut through a permeate pipe between modules.  
         [0035]      FIG. 11  is an exploded view of a module of  FIG. 7 .  
         [0036]      FIG. 12  is an isometric view of the pedestal of  FIG. 7 .  
         [0037]      FIG. 13  is a section of a valve from  FIG. 7  in a closed position.  
         [0038]     FIGS.  14  shows plan views of alternate upper header surrounds of the module of  FIG. 7 .  
         [0039]      FIG. 15   a  is an elevational view of a second module pedestal for a horizontal fiber module.  
         [0040]      FIG. 15   b  is an elevational view of a second module pedestal for a vertical fiber module.  
         [0041]      FIG. 16  is an elevational section view of a second module of horizontal fibers on the second pedestal of  FIG. 15   a.    
         [0042]      FIG. 17  is a schematic representation of a pneumatic valve.  
         [0043]      FIG. 18  is a schematic representation of a pneumatic control system. 
     
    
     DETAILED DESCRIPTION  
       [0044]     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 process described below is not an embodiment of any claimed invention. All rights are reserved in any invention disclosed 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.  
         [0045]     Referring to  FIGS. 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 .  
         [0046]     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  8  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.  
         [0047]     Pedestals  12  are laid at the bottom  28  of the tank  10  and connected longitudinally to form permeate  30  and aeration headers  32  and air removal headers  33  as shown in  FIGS. 3   a  and  3   b . Each pedestal  12  has interconnecting male  34  and female  36  ends that may be sealed 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 connect to air removal manifold  39  which connect to an air extraction system  62  shown in  FIG. 6 . Feed may enter the tank  10  from an inlet near the top of the tank  10 .  
         [0048]     A horizontal module  52  may resemble a standard ZW-1000 module made by Zenon Environmental Inc. Such a module is described in U.S. Pat. No. 6,325,928 issued Dec. 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  FIG. 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 . Alternately module  52  may have a permeate header with a permeate port at the top. In this case, groups of modules  52 , for example 2 to 6, may be fitted with a permeate manifold near the top of the modules and connected to a vertical permeate pipe in a manner analogous to FIGS.  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 conduit  18 . Hollow fiber membranes may be between 0.1% and 5%, for example about 2%, longer than the distance between the header  46  and an opposed potting head.  
         [0049]      FIG. 5  shows a section view of a vertical module  54  with vertical fibres  56  on a pedestal  12 . The module shown is cylindrical, with radially and circumferentially distributed air holes through the potting 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 central, 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 .  
         [0050]      FIGS. 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  50  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.  
         [0051]     For both module  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  FIG. 6 . The air extraction system  62  may be common to all membrane rows in the tank  10  although individual rows may be isolated by air removal isolation 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  receives 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 also be drawn into air extraction chamber  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.  
         [0052]     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 .  
         [0053]     The membrane system may allow for an increase in filtration rate over a sand filter. Optionally, for a simpler retrofit of existing sand filters, the filtration process may have filtration rates comparable to sand filters. Table 1 shows that only 1 layer of ZW-1000 like modules being for example about 50 to 100 cm high and having 200 to 700 m 2  of membrane surface area to cubic meter of volume, at a flux of 30 L/m 2 /h will allow a filtration rate of 15 m/h, higher than most existing sand filters. For vertical modules, 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 1                           Comparison of filtration rates                Filtration Rate                    Filtration Process   m/h   gpm/ft 2                         Conventional sand filter   5-10   2-4           High rate sand filter   20   8           ZW-1000 - 3 module high   100   40           (80% coverage) @ 60 L/m 2 /h           ZW-1000 - 1 module high   15   6           (80% coverage) @ 30 L/m 2 /h                      
 
         [0054]     The different functions of a membrane filter are reviewed below.  
         [0055]     Filtration may be by gravity using the existing control mechanism at a sand filter plant. Assuming an available head of 2 m (0.2 bar or 20 kPa), a fouled membrane permeability of 150 L/m 2 /h/bar would allow the membranes to run at a flux of 30 L/m 2 /h. This is possible with modern microfiltration or ultrafiltration membranes, some of which have a clean water module permeability of about 400 L/m 2 /h/bar or more.  
         [0056]     Membrane backpulse may be done using existing sand filter backwash pumps. Sand filters are typically backwashed once per day, using 4-6% of the water filtered. Membrane filters can use roughly the same total amount of water, but with shorter more frequent backwashes.  
         [0057]     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 isolated.  
         [0058]     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.  
         [0059]     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.  
         [0060]     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 ZW-1000 designs), if desired, to approach the filtration 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.  
         [0061]     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 .  
         [0062]     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  FIG. 3   b . 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.  
         [0063]     As an option to the design described above, and with reference to  FIGS. 15   a  to  18 , the air removal conduit  18  can be replaced by a cavity  80  in a second module pedestal  82  to house air extraction fine tubes  50  from individual second modules  84  or small groups of second modules  84  (2 to 6) in each row ( FIGS. 15   a  and  15   b ). In this design, the air removal fine tubes  50  shown in  FIGS. 4 and 5  extend all the way to a pneumatic control system  86  situated outside of the membrane tank  10 .  
         [0064]     In this optional design, a float valve  88  is integrated into or in communication with the module permeate header  46  to allow module isolation (single module, or small group of modules) in conjunction with the pneumatic control system  86  (shown in  FIG. 16  for a horizontal fiber second module  84 ; not shown for a vertical fiber module). To group second modules  84 , the fine tubes  50  from the group of modules are joined together to a single fine tube  50  which extends to the pneumatic control system  86 .  
         [0065]     The fine tubes  50  in each second module  84  or group of second modules  84  are connected to small 3-way valve manifolds  90  that are used to perform various functions which may include one or more of extracting air from module permeate headers  46 , performing a membrane integrity test (MIT), isolating a second module  84  (or group of second modules  84 ) that fail the MIT. Some of these functions may also be performed with modules  52 ,  54  not having a float valve  88 . Other valves that respond to pressure fluctuations in a fine tube  50  or module permeate header  46  may be used in place of float valves  88 .  
         [0066]     The 3-way valve manifolds  90  ( FIG. 17 ) are pneumatic valve manifolds as often used in control systems but selected or adapted to handle air and water. As shown in  FIG. 17 , each  3 -way valve manifold  90  has the following positions: 
        Position  1 : pulling a vacuum to extract air (water) from permeate side of module(s)  52 ,  54 ,  84      Position  2 : transmitting pressurized air, for example at 15 psi, to the module(s)  52 ,  54 ,  84      Position  3 : isolating module(s)  84         
 
         [0070]     During normal operation, the valve manifold  90  is in Position  1  and degassed air is extracted form the module permeate header  46 . Air may be removed with a continuous stream of water in 2-phase flow. When the 3-way valve manifold  90  is in Position  1 , the header float valve  88 , if any, is in an open position and the module  52 ,  54 ,  84  is in filtration mode.  
         [0071]     To perform a MIT, the pneumatic 3-way valve manifold  90  is switched to Position  2 . 15 psi air is transmitted to the module(s)  52 ,  54 ,  84  and the water is evacuated through the module permeate header  46  and the membranes  56 . The pressurized air also drives the float valve  88  to its closed position and isolates second module(s)  84 . For other modules  52 ,  54 , the permeate isolation valve  78  of the relevant row is closed. Once this purge phase is completed, a pressure decay valve  92 , which may be common to all modules  52 ,  54 ,  84  but connected through a single pneumatic valve manifold  90  to the module(s)  52 ,  54 ,  84  being tested, is closed to perform the pressure decay test (PDT) ( FIG. 18 ). During a PDT, all other valve manifolds  90  in communication with the pressure decay valve  92  are either in Position  1  or  3 .  
         [0072]     After the pressure decay, the pneumatic valve manifold  90  is normally switched back to Position  1  to purge the air and resume filtration. Filtration may resume after the next programmed backwash that will pop the module float  88  open or by opening the permeate isolation valve  78 .  
         [0073]     If the PDT indicates a failure, the pneumatic valve manifold  90  is toggled between positions  1  and  3  to isolate the second module  84  from permeation (Position  2  to pressurize with 15 psi air and Position  3  when a PDT is done on another module) until it can be repaired. Alternately, an entire row of modules  52 ,  54  can be isolated by closing a permeate isolation valve  78 .  
         [0074]     FIGS.  7  to  14  show alternate 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.  
         [0075]     FIGS.  7  to  14  show an apparatus  100  having eight alternate vertical modules  102  forming two module arrays  106  resting on a multi 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 length that provides manifolds  38 ,  40  in one piece spanning multiple pedestals  104 . Segments  110 ,  112  may have male and female ends and be connected together by o-rings as shown or by gluing, 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  116  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 upwards. 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 . Alternately, an air removal system as described above may be used.  
         [0076]     The modules  102  are constructed as shown particularly in  FIG. 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 small 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  FIG. 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  holds 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  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 .  
         [0077]     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  FIGS. 10 and 13 , a valve plug  150  may be lowered to close the holes to the generally vertical permeate 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 .  
         [0078]     Referring particularly to  FIG. 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  walls 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 permeate pipe can be provided above modules  102  with vertical permeate pipe  118  extending upwards from manifold  138  rather than downwards.