Patent Description:
The growth of saltwater (e.g., seawater) desalination has been limited by the relatively high cost of desalinated water. This high cost is due in part to energy and capital expenses associated with current desalination systems. Such systems typically employ an onshore facility containing reverse osmosis (RO) desalination membranes contained in highpressure corrosion-resistant housings and supplied with seawater from a submerged offshore intake system. Very high pressures typically are required to drive water through the RO membranes. For example, the widely-used FILMTEC™ SW30 family of reverse osmosis membrane elements (from DuPont Water Solutions) require about an <NUM> psi (<NUM> bar) pressure differential across the membrane to meet design requirements. In addition to such high pressures, onshore RO units suffer from high power demands, primarily for pressurizing the feedwater to membrane operating pressures, and for an onshore RO unit these power demands typically average about <NUM> kWh per thousand gallons of produced fresh water. The seawater and the concentrated brine stream produced by a typical onshore RO unit have high corrosion potential and consequently require expensive components and equipment, including pressure vessels and conduits made from specialized alloys. The highly-pressurized water flow also increases maintenance expenses. Onshore RO units typically also require significant amounts of expensive seaside real estate. Shore-based desalination has in addition been criticized for various environmental impacts, including entrainment of marine life in the intake water, greenhouse gas production associated with producing the energy required, discharge of a strong brine stream with the potential to harm marine life, the use of treatment chemicals that may enter the ocean, and onshore land use that is often expensive and may harm local ecosystems. RO units include those described in <CIT>), <CIT>), <CIT>), <CIT> '<NUM>), <CIT> '<NUM>), <CIT> '<NUM>) and <CIT>).

In the <NUM> years since the invention of semi-permeable RO membranes, various concepts for submerging such membranes and employing natural hydrostatic water pressure to help desalinate seawater have been proposed. Representative examples include the systems shown in <CIT>), <CIT>), <CIT>), <CIT>), <CIT>), <CIT>, <CIT>, <CIT>, <CIT>, <CIT>) and <CIT>); US Patent Application Publication Nos. <CIT>), <CIT>), <CIT>) and <CIT>); <CIT>); International Application Nos. <CIT>), <CIT>, <CIT>), <CIT>), <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <NPL>).

Other water desalination technologies have also been proposed, including systems employing microfiltration, nanofiltration, ultrafiltration and aquaporins. These likewise have various drawbacks. In general, submerged water desalination systems do not appear to have been placed in widespread use, due in part to factors such as the energy cost of pumping the desalinated water to the surface from great depth and the difficulty of maintaining component parts at depth.

In onshore RO systems, RO membrane cartridges are normally arranged in series, using a plug to seal the inlet end of the first permeate tube in the series, tubular interconnectors to join the permeate collector tubes of successive individual cartridges, and an end connector to join the last permeate tube in the series to a product water connection manifold. The plug, interconnectors and end connector normally are equipped with one or more O-rings. These and other exemplary plugs, interconnectors and end connectors are shown in <CIT>), <CIT>), <CIT>) and <CIT>).

From the foregoing, it will be appreciated that what remains needed in the art is an improved system for water desalination featuring one or more of lower energy cost, lower capital cost, lower operating or maintenance cost or reduced environmental impact. Such systems are disclosed and claimed herein.

Compared to land-based water separation, a submerged water separation system can provide several important advantages. For example, submerged operation can significantly reduce pump power requirements, since hydrostatic pressure can provide much or all of the driving force required for desalination, and only desalinated water will need to be pumped onshore. However, repair or replacement of component parts can be difficult, especially when the system is submerged at significant depths, and may require shutting down an entire submerged system or in some cases bringing it to the surface so that repair or replacement can be carried out. Accordingly, it is important to minimize or eliminate potential points of system failure.

In a submerged system employing RO cartridges, parallel rather than serial cartridge arrangements may be employed, as discussed for example in the above-mentioned Johnson et al. and Bergstrom et al applications. In a purely parallel arrangement, interconnectors are not needed, but end plugs and end connectors normally will be required. O-rings may be employed for such plugs and end connectors, but may also lead to system leakage and failure. Such failure may arise for example due to "compression set" (loss of resiliency) that may be experienced by O-rings and other rubber-based seals following prolonged exposure to low temperatures while in a compressed state.

In addition, a parallel RO cartridge arrangement can employ a perforated divider plate for mounting the cartridges and separating the high pressure inlet side of the submerged system from the lower pressure product water side of the system. O-rings may be used to seal the cartridges to the divider plate, but again may lead to system leakage and failure.

The disclosed invention provides in one aspect a submersible water separation membrane module comprising:.

wherein a) the manifold is adhesively bonded to a plurality of the collection tubes, or b) the divider plate is adhesively bonded to a plurality of the cartridge walls or ends, or both a) and b).

The disclosed invention provides in another aspect a method for assembling a submersible water desalination apparatus, the method comprising the steps of:.

wherein a) the manifold is adhesively bonded to a plurality of the collection tubes, b) the divider plate is adhesively bonded to a plurality of the cartridge walls or ends, or both a) and b).

The disclosed apparatus provides a submerged "Natural Ocean Well" that can provide desalinated water at reduced cost and with improved reliability compared to land-based RO systems, and with improved RO membrane maintenance and replacement compared to existing submerged reverse osmosis (SRO) systems, and especially when replacement is accomplished using a remotely operated vehicle (ROV).

Like reference symbols in the various figures of the drawings indicate like elements. The elements in the drawings are not to scale.

The recitation of a numerical range using endpoints includes all numbers subsumed within that range (e.g., <NUM> to <NUM> includes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc.).

The terms "a," "an," "the," "at least one," and "one or more" are used interchangeably. Thus, for example, an apparatus that contains "a" reverse osmosis membrane includes "one or more" such membranes.

The term "brine" refers to an aqueous solution containing a materially greater sodium chloride concentration than that found in typical saltwater, viz. , salinity corresponding to greater than about <NUM>% sodium chloride. It should be noted that different jurisdictions may apply differing definitions for the term "brine" or may set different limitations on saline discharges. For example, under current California regulations, discharges should not exceed a daily maximum of <NUM> parts per thousand (ppt) above natural background salinity measured no further than <NUM> meters horizontally from the discharge point. In other jurisdictions, salinity limits may for example be set at levels such as <NUM> ppt above ambient, <NUM>% above ambient, or <NUM> ppt absolute.

The term "concentrate" refers to an RO apparatus discharge stream having an elevated salinity level compared to ambient surrounding seawater, but not necessarily containing sufficient salinity to qualify as brine in the applicable jurisdiction where such stream is produced.

The term "conduit" refers to a pipe or other hollow structure (e.g., a bore, channel, duct, hose, line, opening, passage, riser, tube or wellbore) through which a liquid flows during operation of an apparatus employing such conduit. A conduit may be but need not be circular in cross-section, and may for example have other cross-sectional shapes including oval or other round or rounded shapes, triangular, square, rectangular or other regular or irregular shapes. A conduit also may be but need not be linear or uniform along its length, and may for example have other shapes including tapered, coiled or branched (e.g., branches radiating outwardly from a central hub).

The term "depth" when used with respect to a submerged water desalination apparatus or a component thereof refers to the vertical distance, viz. , to the height of a water column, from the free surface of a body of water in which the apparatus or component is submerged to the point of seawater introduction into the apparatus or to the location of the component.

The terms "desalinated water", "fresh water" and "product water" refer to water containing less than <NUM> parts per million (ppm), and more preferably less than <NUM> ppm, dissolved inorganic salts by weight. Exemplary such salts include sodium chloride, magnesium sulfate, potassium nitrate, and sodium bicarbonate.

The term "recovery ratio" when used with respect to an SRO system or SRO apparatus means the volumetric ratio of product water (permeate) produced by the system or apparatus to feedwater introduced to the system or apparatus.

The terms "remotely operated vehicle" and "ROV" refer to unoccupied submersible vehicles capable of underwater maneuvering and manipulation of submerged objects.

The terms "saltwater" and "seawater" refer to water containing more than <NUM> ppt dissolved inorganic salts by weight, and thus encompassing both brackish water (water containing <NUM> to <NUM> ppt dissolved organic salts by weight) as well as water containing more than <NUM> ppt dissolved organic salts by weight. In oceans, dissolved inorganic salts typically are measured based on Total Dissolved Solids (TDS), and typically average about <NUM>,<NUM> parts per million (ppm) TDS, though local conditions may result in higher or lower levels of salinity.

The term "submersible" means suitable for use and primarily used while submerged.

In the discussion that follows, emphasis will be placed on the use of RO membranes in a submerged RO (SRO) apparatus for carrying out water separation, it being understood that persons having ordinary skill in the art will after reading this disclosure be able to replace the disclosed RO membranes with other types of water separation membranes. Exemplary such other water separation membranes include those based on microfiltration, nanofiltration and ultrafiltration; aquaporins; and other water separation technologies that are now known or hereafter developed and which will be familiar to persons having ordinary skill in the art.

Referring first to <FIG> and <FIG>, SRO apparatus <NUM> is shown in schematic side view. Raw seawater <NUM> enters apparatus <NUM> via prefilter screens <NUM>, and is separated by RO membrane modules <NUM> into product water permeate stream <NUM> and concentrate or brine discharge stream <NUM>. Permeate stream <NUM> passes into permeate collector <NUM> and thence through permeate conduit <NUM>, submerged pump <NUM> and delivery conduit <NUM> to a ship-borne or onshore collection point (not shown in <FIG> or <FIG>) for post-treatment, conveyance or storage for later use. Such uses may include municipal, private or industrial purposes including potable water, bathing water, irrigation water, process water, water storage, water table replenishment, cooling or heat exchange, and a variety of other purposes that will be apparent to persons having ordinary skill in the art. For example, potential cooling or heat exchange applications for such product water include providing or improving the efficiency of air conditioning systems including Sea Water Air Conditioning (SWAC) systems; operating or improving the efficiency of Ocean Thermal Energy Conversion (OTEC) systems (in addition to those discussed herein); and operating or improving the efficiency of Rankine Cycle heat engines (again, in addition to those discussed herein).

<FIG> shows a conventional plug <NUM>, interconnector <NUM>, end connector <NUM> and O-rings <NUM> for use with permeate collector tubes in conventional RO water separation cartridges. Components <NUM>, <NUM> and <NUM> are typically made from a moldable thermoplastic such as NORYL™ resin or acrylonitrile-butadiene-styrene (ABS) copolymer, O-Rings <NUM> are typically made from ethyl propyl rubber (EPR) or a fluoroelastomer. O-rings <NUM> normally reside in the grooves <NUM>, <NUM> and <NUM> in components <NUM>, <NUM> and <NUM>.

<FIG> shows an end plug <NUM> and end connector <NUM> that can be attached to RO cartridge <NUM> for use in the present invention. Cartridge <NUM> is shown in partial cutaway view to depict the manner in which spiral-wound membrane <NUM> surrounds permeate tube <NUM>. Salinated water enters cartridge <NUM> at its left-hand end (as depicted in <FIG>) via inlet orifices <NUM>. Product water exits cartridge <NUM> at its right-hand end (as depicted in <FIG>) via permeate tube <NUM>, and concentrate or brine exits cartridge <NUM> via openings (not shown in Fig. <NUM>) at the same right-hand end of cartridge <NUM>. End plug <NUM> and end connector <NUM> each include one or more beads of uncured adhesive <NUM>, respectively arranged along the length of reduced diameter tubular portions <NUM> and <NUM>. In one embodiment, adhesive <NUM> includes a fillet (not visible in <FIG>) positioned at the junction between reduced diameter portion <NUM> and increased diameter portion <NUM> of end plug <NUM>. In another embodiment, adhesive <NUM> includes a fillet 406a positioned at the junction between reduced diameter portion <NUM> and increased diameter portion <NUM> of end connector <NUM>. Adhesive <NUM> may also be disposed as a bead of adhesive such as beads 406b and 406c on reduced diameter portions <NUM> and <NUM>. In one embodiment, beads 406b or 406c may be disposed in one or more suitable adhesive recesses (e.g., grooves) in portions <NUM> and <NUM>. In another embodiment (not shown in <FIG>), adhesive <NUM> is disposed as a thin film on reduced diameter portions <NUM> or <NUM>. Prior to the cure of adhesive <NUM>, end plug <NUM> and end connector <NUM> are respectively inserted into inlet end <NUM> and outlet end <NUM> of permeate tube <NUM> and adhesive <NUM> is allowed or caused to cure or otherwise harden. In an additional embodiment, one or both of end plug <NUM> and end connector <NUM> may be enlarged and reshaped to fit over rather than inside the ends of tube <NUM>, and the adhesive beads (and recesses, if used) or adhesive thin films may be relocated as needed to fit in the gap between end plug <NUM> and end connector <NUM> and their corresponding mating surfaces on permeate tube <NUM>. Following the cure of adhesive <NUM>, end plug <NUM> and end connector <NUM> desirably provide a leakproof seal at each end of permeate tube <NUM>. Although adhesives have previously been used to assemble other parts of RO membrane cartridges, for example to fasten separation membranes to permeate collection tubes, adhesives do not appear to have been used to interconnect cartridges or to connect water collection manifolds to cartridges. Doing so could make it much more difficult to replace used cartridges in conventional serially-arranged cartridge arrays.

<FIG> shows an end plug <NUM> and end connector <NUM> which are similar to plug <NUM> and connector <NUM>, but which each employ two beads of uncured adhesive <NUM> and also employ O-ring grooves <NUM> and <NUM> which house O-rings <NUM>. As is the case for adhesive <NUM> on plug <NUM> and connector <NUM>, adhesive <NUM> on plug <NUM> and connector <NUM> may be in the form of a fillet positioned at the junction between reduced diameter portion <NUM> and increased diameter portion <NUM> or at the junction between reduced diameter portion <NUM> and increased diameter portion <NUM> of end connector <NUM>, or may be disposed in one or more suitable adhesive recesses (e.g., grooves) in portions <NUM> and <NUM>, or may be disposed as a thin film on reduced diameter portions <NUM> or <NUM>. Prior to the cure of adhesive <NUM>, O-rings <NUM> are installed in grooves <NUM> and <NUM>, and end plug <NUM> and end connector <NUM> are respectively inserted into inlet end <NUM> and outlet end <NUM> of permeate tube <NUM>. In an alternative embodiment, one or both of end plug <NUM> and end connector <NUM> may be enlarged and reshaped to fit over rather than inside the ends of tube <NUM>, and the adhesive beads (and recesses, if used) or adhesive thin films and the O-rings are relocated as need be to fit in the gap between end plug <NUM> and end connector <NUM> and their corresponding mating surfaces on permeate tube <NUM>. Adhesive <NUM> and O-rings <NUM> desirably provide a leakproof seal at each end of permeate tube <NUM> in RO membrane cartridge <NUM>. Seal durability can be facilitated by using O-rings <NUM> made from cold temperature resistant elastomeric materials such as silicone rubber or ethylene propylene diene monomer (EPDM). When applying adhesive <NUM> to components (such as components <NUM> and <NUM>) that will contact one or more O-rings <NUM>, it is important that the adhesive not contact any O-rings or O-ring grooves before or after component assembly, as the hardened adhesive might prevent the O-ring from functioning correctly. Accordingly, it is preferred to locate adhesive <NUM> and any associated adhesive recesses on end plug <NUM> so that the O-rings <NUM> will slide into tube <NUM> before adhesive <NUM> contacts tube <NUM>. For similar reasons it is preferred to locate adhesive <NUM> and any associated adhesive recesses on end connector <NUM> so that the O-rings <NUM> will slide into tube <NUM> before adhesive <NUM> contacts tube <NUM>. For embodiments in which plug <NUM> or connector <NUM> fit over rather than inside the ends of tube <NUM>, similar care may be needed when locating and placing adhesive <NUM> to avoid contact with and contamination of the O-rings <NUM> or grooves <NUM> and <NUM> during assembly. In any event, the adhesive and O-rings should be sufficiently spatially separated from one another so as to discourage such contamination.

If desired, the disclosed adhesive may be used with other sealing or fastening technologies to fasten the product water collection tubes to the manifolds. Such other technologies include threaded connections, bayonet connections and GRALOC™ connectors from Oceaneering. By combining the adhesive with such other technologies, overall connection reliability may be improved and the likelihood of a connection failure may be reduced. In such instances it may not be necessary to spatially separate the adhesive from such other sealing or fastening technology. For example, an adhesive may readily be used in a threaded or bayonet connection and if desired later be debonded using mechanisms discussed in more detail below.

In the disclosed apparatus, raw seawater, product water and concentrate or brine may each flow in a variety of directions, e.g., upwardly, downwardly, horizontally, obliquely or any combination thereof. In the embodiment shown in <FIG>, reverse osmosis membranes within membrane modules <NUM> are oriented so that concentrate or brine <NUM>-- is discharged generally upwardly from the modules <NUM> and is captured and collected by hood <NUM>. Further details regarding such modules may be found in copending International Application No. (Attorney Docket No. <NUM>. 04WO01) filed even date herewith and entitled SUBMERGED WATER DESALINATION SYSTEM WITH REPLACEABLE DOCKABLE MEMBRANE MODULES. Axial pump <NUM> located at the lower end of riser <NUM> sends captured concentrate or brine <NUM> through riser <NUM> toward surface <NUM>, for further use or dispersal.

In the embodiment shown in <FIG>, concentrate or brine <NUM> exits riser <NUM>, whereupon dispersion and dilution takes place in the surrounding seawater. In an additional embodiment (not shown in <FIG>), concentrate or brine <NUM> is transported through a further conduit to undergo dispersal (and preferably wide area dispersal) at a significant distance (e.g., at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM> or at least <NUM> meters) away from apparatus <NUM>, or into a sustained underwater current <NUM>, to be swept away from apparatus <NUM>. In a further embodiment (also not shown in <FIG>), concentrate or brine <NUM> is transported through a further conduit for an even greater distance (e.g., all the way to or nearly to surface <NUM>) for further use or dispersal. If desired, the concentrate or brine may instead be discharged in another direction such as downwardly or horizontally, while preferably still undergoing wide area dispersal well away from apparatus <NUM>.

The concentrate or brine may be used for a variety of purposes prior to discharge. In one embodiment, the concentrate or brine has desirable volumetric and thermal utility that may be used to operate an OTEC system and provide operating or surplus power, as discussed in copending International Application No. (Attorney Docket No. <NUM>. 03US01P2) filed even date herewith and entitled OCEAN THERMAL ENERGY CONVERSION SUBMERGED REVERSE OSMOSIS DESALINATION SYSTEM.

In the embodiment shown in <FIG>, buoyancy provided by a ring float <NUM> and a foam layer, e.g., an engineered syntactic foam layer (not shown in <FIG>) located beneath the surface of hood <NUM>, help maintain apparatus <NUM> at an appropriate depth D below surface <NUM>. Catenary mooring lines <NUM> affixed to anchors <NUM> in seabed <NUM> help maintain apparatus <NUM> at an appropriate depth D below surface <NUM>, an appropriate height H above seabed <NUM>, and an appropriate height H' above the inlet to pump <NUM>. Depth D preferably is such that the hydrostatic pressure of seawater at depth D is sufficient to drive seawater <NUM> through membrane modules <NUM> and produce product water <NUM> and concentrate or brine <NUM> at a desired overall volume and recovery ratio without the need for additional pumps or other measures to pressurize seawater <NUM> on the inlet side of membrane modules <NUM>.

The depth of the disclosed apparatus <NUM>, height H' and the diameter of the inlet to pump <NUM> are desirably sized to provide at least the net positive suction head (NPSH) or greater pressure (viz. , the pressure caused by the height of the standing column of product water <NUM> in permeate conduit <NUM> and permeate collector <NUM> between membrane modules <NUM> and the inlet side of pump <NUM>) sufficient to avoid inlet side cavitation upon startup and operation of pump <NUM>. Further details regarding such cavitation avoidance during startup and operation may be found in copending International Application No. (Attorney Docket No. <NUM>. 07WO01) filed even date herewith and entitled SUBMERGED WATER DESALINATION SYSTEM WITH REMOTE PUMP.

In some embodiments, pump <NUM> includes one or more sensors, controls or a torque limiting coupling (e.g., a magnetic clutch, hydraulic torque converter, combination thereof or other such device) between the electrical motor powering the pump and the pump impeller so as to limit or avoid inlet side cavitation and accompanying stress or other disturbance of the RO membranes during pump operation. Further details regarding cavitation avoidance during such operation are discussed in copending International Application No. (Attorney Docket No. <NUM>. 05WO01) filed even date herewith and entitled SUBMERGED WATER DESALINATION SYSTEM WITH PRODUCT WATER PUMP CAVITATION PROTECTION.

In one embodiment, pump <NUM> diverts at least a portion of the product water <NUM> for use as a lubricating or cooling fluid directed through one or more of the pump, pump motor or the coupling between the motor and pump. Doing so can improve the pump longevity, while avoiding the need to use seawater, hydraulic fluid or other potentially corrosive or toxic fluids for lubrication or cooling. Further details regarding the use of product water for such lubrication and cooling are discussed in copending International Application No. (Attorney Docket No. <NUM>. 06WO01) filed even date herewith and entitled SUBMERGED WATER DESALINATION SYSTEM PUMP LUBRICATED WITH PRODUCT WATER.

Electrical power and appropriate control signals <NUM> may be supplied to pump <NUM> and other components of apparatus <NUM> through multi-conductor cable <NUM>. The supplied electrical power operates pumps <NUM> and <NUM> and as needed other components in apparatus <NUM>, such as a prefilter cleaning brush system. Further details regarding a desirable prefilter cleaning brush embodiment are discussed in more detail in the above-mentioned copending International Application No. (Attorney Docket No. <NUM>.

When operated at sufficient depth, the RO membranes in apparatus <NUM> will not need to be encased in pressure vessels, and may instead be mounted in a perforated divider plate made from relatively inexpensive and suitably corrosion-resistant materials such as a corrosion-resistant metal, a suitable plastic, a fiber-reinforced (e.g., glass fiber- or carbon fiber-reinforced) plastic or other composite, or a variety of other unreinforced or engineered plastics the selection of which will be understood by persons having ordinary skill in the art. The disclosed adhesive bonding of the water separation cartridges to the divider plate can significantly strengthen the rigidity and overall strength of the disclosed modules <NUM>. Also, avoiding the need for a pressure vessel greatly reduces the required capital expenditure (CAPEX) for constructing apparatus <NUM> compared to the costs for constructing a shore-based RO unit. If the RO membranes are individual units (for example, cartridges containing spiral-wound membranes), then avoidance of a pressure vessel also enables modules <NUM> to be economically designed using a parallel array containing a significantly larger number of cartridges than might normally be employed in a shore-based RO unit, and operating the individual cartridges at a lower than normal individual throughput. For example, the number of cartridges may be at least <NUM> % more, at least <NUM>% more, at least <NUM>% more or at least <NUM>% more than might normally be employed in an onshore RO unit. Doing so can help extend the life of individual membrane cartridges while still providing a desired daily amount of product water. In the embodiment shown in <FIG> and <FIG>, and as discussed in more detail below, modules <NUM> preferably contain a large array of parallel cylindrical RO cartridges operated not only at such low individual throughput, but also with a reduced recovery rate. Doing so can also provide reduced concentrate salinity, reduced fouling potential, and in preferred embodiments will result in a large volume of concentrate that does not qualify as brine in the applicable jurisdiction, and which has substantial cold thermal energy potential for cooling an OTEC system. For example, permeate stream <NUM> is depicted in <FIG> as having a substantially smaller volume than brine discharge stream <NUM>, corresponding to a low recovery ratio. Exemplary recovery ratios may for example be no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>% or no greater than <NUM>%, and may for example be less than <NUM>%, at least <NUM>%, at least <NUM>% or at least <NUM>%. The chosen recovery ratio will depend upon factors including the selected RO membranes, and the depth and applicable jurisdiction in which the SRO apparatus operates. The chosen recovery ratio also influences pump sizing and energy costs. By way of example, for an SRO embodiment employing Dow FILMTEC membrane cartridges to treat seawater with an average <NUM>,<NUM> ppm salinity at an <NUM>% recovery ratio, about <NUM>% of the seawater inlet stream will be converted to product water having less than <NUM> ppm salinity, and about <NUM>% of the seawater inlet stream will be converted to a low pressure or unpressurized brine stream having about <NUM>,<NUM> ppm salinity. By way of a further example, an SRO apparatus employing Nitto Hydranautics membrane cartridges operated at a depth of about <NUM> and a <NUM>% recovery ratio may be used to produce concentrate that does not qualify as brine under the current version of the California Water Quality Control Plan.

In one preferred embodiment, the disclosed SRO apparatus operates at a depth of at least about <NUM>, does not employ seawater pumps on the RO membrane inlet side, and employs a product (fresh) water pump on the outlet side of the RO membranes to maintain at least a <NUM> Bar pressure drop across the membranes and pull product water through such membranes. Advantages for such a configuration include a pump requiring much less energy when operated at the membrane outlet rather than at the inlet, and the avoidance of, or much lower requirements for, any pressure vessels housing the membranes. Use of membranes with a low required pressure differential will enable operation at lesser depths or using smaller pumps. Currently preferred such membranes include Nitto Hydranautics SWC6-LD membranes (<NUM> bar differential pressure) and LG Chem LG-SW-<NUM>-ES membranes (<NUM> bar differential pressure).

Referring to <FIG>, a "water farm" containing an array of portable offshore desalination systems ("pods") <NUM> is shown in perspective view. Product water flows downwardly from the modules <NUM> through conduits <NUM> and horizontally through pumps <NUM> to a centrally located hub <NUM>, and is then pumped towards the surface through delivery conduit <NUM>. Concentrate or brine is pumped upwardly through conduits <NUM> into ocean currents for dispersal away from the pods <NUM> or for use in an OTEC system like that discussed above. The conduits <NUM> may if desired be kept separate from one another, bundled together, or connected to a single larger diameter conduit, and may if desired by equipped with hot-swap water connectors (not shown in <FIG>) to facilitate disconnection, maintenance or replacement of individual pods <NUM>.

As depicted in <FIG>, four pods <NUM> are employed. However, lesser or greater numbers of pods can be used if desired, for example <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or more pods. Using a plurality of connected pods provides redundancy and enables ready scaleup of the disclosed SRO apparatus to meet initial or growing water needs. Operation and maintenance of the disclosed apparatus can be facilitated by providing a plurality of hot-swap water connectors (not shown in <FIG>) between each conduit <NUM> and its associated pump <NUM>, or between each pump <NUM> and hub <NUM>, or at both the inlet and outlet ends of each pump <NUM>. Scaleup of the disclosed apparatus can be facilitated by providing one or more additional hot-swap water connectors (not shown in <FIG>) on hub <NUM> or at another convenient location to enable connection of additional pods or water farm arrays to delivery conduit <NUM> at a later date. If for example the individual pods <NUM> shown in <FIG> each have a <NUM> million gallons per day product water capacity, and if five additional hot-swap connectors are included in hub <NUM>, then the <FIG> water farm could provide <NUM> million gallons of product water per day as initially installed, and up to five additional similarly-sized pods <NUM> could be added in <NUM> million gallons per day increments to provide up to <NUM> million total gallons of product water per day. In another embodiment, a plurality of such arrays may be installed near one another to provide multiple instances of the <NUM> million gallon per day array shown in <FIG>, thereby providing increased capacity, redundancy and multiplicity of scale for the individual components. In yet another embodiment, the pods are not grouped together as depicted in <FIG>, and instead are spaced apart across the seafloor, for example to accommodate topographical changes in the seafloor landscape, mooring line locations or other subsea features.

<FIG> shows a perspective underside view of a polygonal array <NUM> of the disclosed submerged RO membrane modules <NUM> mounted beneath hood <NUM>, with prefilter system <NUM> being removed and with four of the twelve modules <NUM> in the polygonal (viz. , dodecagonal) array <NUM> being numbered in <FIG> (as modules 106A, 106B, <NUM> and <NUM>) and the remaining eight modules being unnumbered. Modules <NUM> have generally tapered module sides that converge towards centrally-located product water (viz. , permeate) collector <NUM> and product water collection conduit <NUM>. Modules <NUM> are in fluid communication with collector <NUM> and conduit <NUM> via hot-swap product water valves <NUM> mounted on collector <NUM>, with three of the twelve valves connected to array <NUM> and conduit <NUM> being numbered in <FIG> (as valves 706A, 706B and <NUM>) and the remaining nine valves being unnumbered. Converging sides (two of which are numbered as side 702C and side 704C) on each module <NUM> assist in underwater docking and reattachment of a detached module <NUM> to a hot-swap product water valve <NUM>. Central rails on modules <NUM> (one of which is numbered as rail 703C) provide further support for the modules <NUM>. When the modules <NUM> are in operation, product water flows downwardly through permeate collector <NUM> and permeate conduit <NUM> and is carried away by a pump such as pump <NUM> in <FIG>.

The disclosed hot-swap product water valves and associated components may utilize a variety of designs, including so-called "hot stab" check valves and receptacles like those used in undersea oil and gas equipment for handling hydraulic fluids. Suitable such valves and receptacles are available from a variety of suppliers including Blue Logic, FES Subsea Engineering Products, James Fisher Offshore, Oceaneering and Total Marine Technology and Unitech. By way of example, the M5 ROV Flyable Full Bore Connector from Oceaneering represents one useful such hot stab valve and receptacle combination. Because hot stab devices are typically designed for use in the undersea oil and gas industries and must tolerate the handling of hydrogen sulfide and other corrosive ingredients at significant pressures, they can be derated and their designs can be simplified and made less expensive when used to handle the noncorrosive or less corrosive fluids and much lower pressures present in the disclosed SRO apparatus.

<FIG> shows a perspective underside view of the disclosed SRO apparatus of <FIG> without array <NUM> and its modules <NUM>. Hood <NUM> includes a supporting framework formed by inclined struts <NUM>, crossbars 710A, 710B and 710C, lower circumferential rim supports <NUM>, lower radial rails <NUM>, lower inner anchoring ring <NUM> and an upper inner anchoring ring located (but not shown in <FIG>) at the junction of hood <NUM> and riser <NUM>. The disclosed framework preferably also receives, captures and supports the disclosed modules and array. Each circumferential rim support <NUM> includes a slotted receiving aperture <NUM> that captures hangers atop each module <NUM>, and which are discussed in more detail below. The disclosed framework supports an overlying hood cover <NUM> that may for example be made from an insulated or uninsulated seawater-resistant textile, plastic or metal covering material. In a preferred embodiment, the inner side <NUM> of hood cover <NUM> is made for example from a buoyancy-imparting material such as an engineered syntactic foam. Hood cover <NUM> preferably provides a protective cover that helps maintain a slight pressure differential (e.g., up to <NUM> psi or thereabouts) between the internal concentrate or brine collected by the hood and the external environment, while isolating the interior of the hood from penetrants. Indentations <NUM> and product water valve couplings <NUM> may be seen near the top of conduit <NUM>, just below ring <NUM>. Rails <NUM>, apertures <NUM> and indentations <NUM> help guide, support and locate modules <NUM> when array <NUM> is installed, and couplings <NUM> assist in the hot-swap attachment and detachment of modules <NUM>. If desired, corrosion resistant magnets or electromagnets may be used to guide, retain or both guide and retain modules <NUM> in place within array <NUM> and apparatus <NUM>.

<FIG> shows a perspective underside view of the disclosed SRO apparatus of <FIG> with prefilters <NUM> installed. In the embodiment shown in <FIG>, each prefilter <NUM> has a generally triangular shape, and is periodically swept clean of debris by oscillating brush arms <NUM> mounted on pivot points <NUM> near lower mounting ring <NUM>. Brush arms <NUM> repeatedly (e.g., intermittently, periodically or continuously, and based on predetermined times, signals from one or more sensors, or an externally-supplied control signal) sweep across the inlet face of each prefilter <NUM> toward central struts <NUM> and then stop, return to the positions shown in <FIG>, or initiate another sweep movement. Crossbars <NUM> help reinforce and support each prefilter <NUM> and can serve as guide rails supporting brush arms <NUM>. In another embodiment, the assembled prefilters may have curved surfaces, a generally conical overall shape, and brush arms configured to sweep over or to revolve around the prefilters.

<FIG> and <FIG> are perspective topside views of a module <NUM> showing a plurality of RO membrane cartridges <NUM> suspended and sealed in apertures <NUM> in perforated, generally triangular divider plate <NUM>. As depicted, cartridges <NUM> are generally cylindrical but may have other shapes if desired. As also depicted, module <NUM> contains <NUM> cartridges, but other greater or lesser numbers of cartridges may be employed in each module as desired, for example at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM> or at least <NUM> cartridges, and up to <NUM>, up to <NUM>, up to <NUM>, up to <NUM>, up to <NUM> or up to <NUM> cartridges. Also, as depicted all the cartridges are generally parallel and in a single layer occupying a single plane, as doing so promotes efficient flow through the disclosed apparatus. However, if desired the cartridges in a module need not be generally parallel to one another, and also if desired multiple layers of cartridges could be employed in a module.

Using <NUM> of the above-mentioned Hydranautics cartridges in each module, the disclosed SRO apparatus may produce about <NUM> million gallons per day from a twelve such modules operated at a <NUM>% recovery rate. Other RO membrane suppliers whose cartridges may be used will be apparent to persons having ordinary skill in the art, and include Aquatech International, Axeon Water Technologies, DuPont Water Solutions (makers of the above-mentioned DOW FILMTEC cartridges), Evoqua Water Technologies, GE Water and Process Technologies, Koch Membrane Systems, Inc. and LG Chem. Customized cartridges having altered features (for example, wider gaps between layers, modified spacers, a looser membrane roll, a modified housing or modified ends) may be employed if desired.

As depicted, the cartridges <NUM> are substantially vertically aligned when module <NUM> is installed in array <NUM> and in use, with the concentrate or brine end outlets <NUM> in each cartridge <NUM> facing upwardly towards hood <NUM> and with the product water outlets (discussed below in connection with <FIG>) facing downwardly. However, other orientations and accompanying flow directions may be employed, for example with the outlets <NUM> facing downwardly, horizontally or obliquely, and with the product water outlets facing upwardly, horizontally or obliquely.

The cartridges <NUM> are preferably mounted in the disclosed modules <NUM> by adhesively bonding and sealing the cartridges in holes in perforated divider plate <NUM>. In the embodiment depicted in <FIG> and <FIG>, the adhesive bond may be at the upper end of the cartridges <NUM> near the concentrate or brine outlets <NUM>. However, as depicted in <FIG>, more than one divider plate <NUM> may be employed, and the divider plate(s) and the adhesive <NUM> that bonds and seals the cartridges <NUM> into the perforations <NUM> in divider plate <NUM> may be located at either or both ends or anywhere along the length of the cartridges <NUM>. <FIG> also illustrates the use of adhesive <NUM> to bond manifold <NUM> to permeate outlet <NUM> as discussed above. To provide greater buoyancy (and desirably neutral buoyancy at the intended operating depth) and as shown in <FIG>, the spaces between cartridges <NUM> are desirably filled or at least partially filled with a suitable buoyant medium <NUM> having a density less than that of seawater. A preferred such medium is engineered syntactic foam, available from suppliers including Engineered Syntactic Systems. Medium <NUM> may be provided in the form of shaped blocks that may be inserted into the modules <NUM> before or after the installation of the cartridges <NUM>, as a premolded perforated slab that is inserted into the modules <NUM> before installation of the cartridges <NUM>, or as an in-situ cured material that may be placed in spaces between the cartridges (e.g., by spraying or other form of injection) after the cartridges have been added to the modules <NUM>. In an embodiment, beads of adhesive <NUM> may be omitted and medium <NUM> can instead serve as the adhesive that bonds and seals the cartridges <NUM> into the perforations <NUM> in divider plate <NUM>. Use of medium <NUM> can significantly assist the underwater removal and installation of the modules <NUM>, by reducing the cantilever effect of the mass of each module <NUM> as it is being removed from or flown into position in the disclosed array, and especially when such removal and installation are conducted using an ROV that grips the outer edge of a module <NUM>. The disclosed adhesive may if desired be used to fasten together any of the other components in the disclosed modules.

Perforated divider plate <NUM> may have a variety of shapes, for example a generally polygonal perimeter such as generally triangular perimeter or a generally trapezoidal perimeter. Plate <NUM> and the remaining components in module <NUM> that support and envelop (viz. , provide a frame for) the cartridges <NUM> may be made from a variety of materials, including corrosion-resistant metals such as stainless steel or titanium, fiber-reinforced polymers or filled composites. Preferably a mixture of such materials is employed, with lower density components being used in appropriate locations to reduce the overall module weight, and higher strength or higher durability materials being used in other appropriate locations within the module where such strength or durability may be required. Divider plate <NUM>, the product water collection tubes and manifold (and if desired any or all of the remaining adhesively-bonded components in module <NUM>) may if desired be surface-treated to increase the associated surface area in locations that may require improved adhesion by the disclosed adhesive, as well as to discourage or resist biofouling.

A variety of adhesives may be used to bond and seal the cartridges in the modules. Exemplary adhesives include the above-mentioned engineered syntactic foams, as well as epoxy, polyurethane, polyester, acrylic, silicone and fluorinated resins. In one preferred embodiment, the adhesive is substantially free or completely free of bisphenol A, bisphenol F and their diglycidyl ethers. In another preferred embodiment, there are no gaskets, O-rings or other preformed seals between the cartridges and the divider plate and the adhesive is primarily or exclusively relied upon to hold the cartridges <NUM> in the modules <NUM>. Suitable adhesives will include those classified as marine adhesives or sealants suitable for use below the waterline, and are available from a variety of suppliers including Dow Chemical Company, Loctite, Sika and <NUM>. In an especially preferred embodiment, the cartridges are adhesively bonded in the disclosed divider plate but are not encased in a pressure vessel. The disclosed adhesive may also be combined with other sealing or fastening technologies to fasten or seal the cartridges in the disclosed modules, including technologies such as gaskets, O-rings and threaded or bayonet connections.

When a module <NUM> is removed from the disclosed array for replacement of one or more of the cartridges <NUM>, it may in some instances be desirable to remove and replace only certain of the cartridges, and in other instances it will be most economical to remove and replace all of them. Removal typically will require debonding the affected adhesive joints so that the associated cartridges <NUM> may be extracted from divider plate <NUM>. Depending on the chosen adhesive, debonding may be performed using a variety of techniques. Exemplary techniques include mechanical force to break the adhesive bond, grinding or other abrasive techniques to remove bound portions of the module, chemical debonding (e.g., using solvents, hydrolysis, or other measures), cryogenic debonding (e.g., using liquid nitrogen or other cold source to embrittle and facilitate fracture of the adhesive), electrical debonding (e.g., using current from an arc welder or other power supply to heat a conductive filler in the adhesive) or thermal debonding (e.g., using a flame or other heat source) and thereby fracture, remove, dissolve, soften, melt, or otherwise eliminate, weaken or degrade the adhesive or its bond to the cartridges and divider plate. Once the adhesive bond has been sufficiently eliminated, weakened or degraded, the cartridges may be pushed, pulled, twisted or a combination thereof to remove them from the module.

Use of the disclosed adhesive provides a number of advantages. Water separation membrane cartridges are normally sealed to other components in a water desalination apparatus using gaskets or O-rings. Gaskets and O-rings represent a potential array leakage point, especially if the gasket or O-ring undergoes significant compression set upon exposure to cold underwater temperatures. Adhesively bonding the membrane cartridges to a perforated divider plate eliminates this potential leakage point while meanwhile increasing the beam strength and rigidity of the assembled module.

Referring again to <FIG> and <FIG>, the lower edges of hood <NUM> preferably overlap with, have a gasketed connection to, or are otherwise sealingly engaged with the upper edges of the modules <NUM>, thereby isolating the collected concentrate or brine from the salinated water surrounding module <NUM>. Divider plate <NUM> is desirably fastened and sealed about its periphery to converging side plates <NUM> and <NUM>, outer end plate <NUM> and inner end plate <NUM>, thereby further isolating the collected concentrate or brine from the surrounding salinated water.

As depicted in <FIG>, suspending hooks <NUM> and <NUM> are fastened atop and near the outer edge of module <NUM>, and point toward the inner edge of module <NUM>. Hooks <NUM> and <NUM> mate with slotted receiving aperture <NUM> shown in <FIG> and help support and guide module <NUM> into a proper position when module <NUM> is pushed into an available open space in array <NUM>. Guide rails <NUM> and <NUM> engage radial rails <NUM> beneath hood <NUM> during insertion of a module <NUM> into array <NUM>. Generally wedge-shaped projecting tang <NUM> also helps to guide and properly affix module <NUM> into place in array <NUM>, and helps ensure proper connection of hot-swappable product water valve <NUM> to permeate collector <NUM>. Upon the completion of such connection, hot-swap valve <NUM> opens to permit the flow of product water into permeate collector <NUM> and permeate conduit <NUM>.

<FIG>, <FIG> and <FIG> are perspective underside views of a module <NUM>. The circular salinated water inlets <NUM> at the lower end of each cartridge <NUM> permit the entry of salinated water into the cartridges <NUM>. Desalinated product water exits a typically centrally-located outlet <NUM> in each cartridge <NUM> via cartridge manifolds <NUM>, branch manifolds 830A through 830I (for the nine depicted rows in the disclosed cartridge array that contain two or more cartridges each side of the array centerline) and a pair of radially-extending product water collection manifolds <NUM> located each side of the array centerline. Three single cartridges <NUM> located on each side of the array centerline near inner end plate <NUM> are directly connected by individual cartridge manifolds <NUM> to product water collection manifolds <NUM>.

The prefilter screens <NUM> shown in <FIG>, sides <NUM>, <NUM>, <NUM> and <NUM> and the underside of perforated divider plate <NUM> cooperate to isolate the filtered water passing through prefilter screens <NUM> from the salinated water surrounding module <NUM> and ensure that the interior portion of module <NUM> surrounding the cartridges <NUM> will contain only filtered water that has passed through a screen <NUM>.

In the embodiment depicted in <FIG>, the modules <NUM> have an approximately wedge-shaped or trapezoidal-shaped cross-section, with sides <NUM> and <NUM> that taper or converge towards permeate collector <NUM> and the vertical central axis of the disclosed SRO apparatus. The disclosed modules may be any desired size, and in a preferred embodiment may for example be about <NUM> to <NUM> meters long by about <NUM> to <NUM> wide by about <NUM> to <NUM> thick, and have shapes and dimensions that facilitate efficient packing of the modules in standard shipping containers as discussed in more detail below. The disclosed modules preferably have neutral buoyancy at the intended operating depth.

In the embodiment depicted in <FIG>, twelve modules are shown, and in their assembled form the depicted modules provide an array with a dodecagonal perimeter in plan view. Other module shapes, numbers of modules (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>) and array shapes (e.g., triangular, square, pentagonal, hexagonal, hexadecagonal, and other polygons made from the numbers of modules mentioned above, as well as circular or other curved shapes) can be employed if desired.

As illustrated in <FIG>, maintenance of an array <NUM> containing a defective, outdated or otherwise ineffective module may be performed by withdrawing such module from the array, thereby leaving a gap formerly occupied by the withdrawn module, and replacing the withdrawn module with a new or rebuilt module <NUM>. Because such replacement will be carried out while the SRO apparatus is submerged, it is desirable that both the module removal and module replacement procedures proceed quickly and efficiently, with minimal disruption in product water output despite potential adverse conditions such as low visibility, underwater currents or difficulties in operating an ROV or other devices that might be used to carry out or assist in module replacement. Module maintenance may for example be scheduled or performed based on signals from one or more sensors that monitor the flow rate or salinity of product water, concentrate or brine flowing through the apparatus, or the flow of water into the apparatus. Such sensors may monitor individual cartridges, individual modules or an entire array. Module maintenance may in addition or instead be based on a preset or adjustable schedule, predictive algorithms, the availability of improved RO membranes or cartridges, and other measures that will be apparent to persons having ordinary skill in the art upon reading this disclosure.

Removal of defective or ineffective modules can be facilitated while continuing to operate the remainder of the disclosed apparatus during module removal, and relying on the portion of the disclosed hot-swap valve <NUM> that remains connected to permeate collector <NUM> to close and seal off permeate collector <NUM> from the surrounding salinated water. Such valve closure may be initiated in a variety of ways, including in response to a suitable electrical command, mechanical switch, or in response to the outward motion of a module <NUM> away from permeate collector <NUM> and separation components in hot-swap valve <NUM>. Hot-swap valve <NUM> accordingly desirably prevents the entry of salinated water into permeate collector <NUM> during module replacement. The portion of hot-swap valve <NUM> remaining on the removed module <NUM> may optionally also be closed upon removal in order to prevent entry of desalinated water into the product water outlet side of the removed module <NUM>. However, doing so generally will not be needed, as the removed module <NUM> will normally be brought to the surface and flushed with fresh water as a part of a repair or rebuilding procedure.

Removal of a module <NUM> may cause unfiltered salinated water to enter the otherwise normally isolated chamber between the prefilters <NUM> and the modules <NUM> in the disclosed array <NUM>. Typically however such unfiltered water entry would take place for a relatively brief time period, until such time as a replacement module or temporary blanking plate can be inserted into the array, and consequently will be unlikely to introduce significant detrimental quantities of debris or other solid matter into such chamber.

During insertion of replacement module <NUM>, converging sides <NUM> and <NUM> and hangers <NUM> and <NUM> assist in underwater docking and attachment of module <NUM> to array <NUM> by helping to align and guide module <NUM> into proper orientation and location in the three-dimensional volume between adjacent modules 906A and <NUM>, and by helping to align and guide hot-swap valve body <NUM> into proper alignment and engagement with the portion of valve body <NUM> that remains attached to permeate collector <NUM>. Hangers <NUM> and <NUM> preferably have inwardly-pointing tapered ends (viz. , ends that point towards the longitudinal central axis of the disclosed array and have a wedge-shaped profile in plan view, side view or both plan and side views). Such tapered ends will significantly assist in docking module <NUM> into the disclosed SRO apparatus. During insertion of module <NUM> into array <NUM>, hangers <NUM> and <NUM> enter the slotted receiving aperture <NUM> shown in <FIG>, and rails like the rails <NUM> and <NUM> shown in <FIG> and <FIG> engage with the radial rails <NUM> shown in <FIG>. Upon reattachment of replacement module <NUM>, the hot-swap valve formed by valve bodies <NUM> and <NUM> can then open to permit resumption of product water collection from the affected portion of the disclosed array. Such valve opening may be initiated in a variety of ways, including in response to a suitable electrical command, mechanical switch, physical manipulation by an ROV, or in response to the inward motion of module <NUM> and joinder of valve bodies <NUM> and <NUM>. In this fashion, removal and inspection or replacement of individual modules <NUM> can be accomplished without having to shut down the disclosed SRO apparatus, thereby enabling continued production of product water and concentrate or brine from the remaining undisturbed modules <NUM>.

In addition to the disclosed tapered sides, rails and hangers, the disclosed module reattachment procedure may be assisted by employing other guidance features or devices. Exemplary such other features or devices will be apparent to persons having ordinary skill in the desalination art upon reading this disclosure, and include appropriately-shaped (e.g., conical or tapered) mating or receiving surfaces, snubbers, guiderails or magnets on the sidewalls of the replacement module or adjacent modules, the upper or lower surfaces of the replacement module, adjacent portions of the framework receiving the replacement modules, or the hot-swap valve bodies <NUM>. Such other guidance features or devices may for example contact the replacement module or adjacent modules during any or all of the start, middle, or end of the disclosed replacement procedure. If desired, one or more gaskets may also be employed on the modules <NUM>, hood <NUM> or assembly of prefilters <NUM> to assist in sealing gaps between the modules <NUM> and the remainder of the disclosed SRO apparatus, and in some embodiments such gaskets may provide guidance features to assist during module insertion.

Claim 1:
A submersible water separation membrane module comprising:
a plurality of water separation membrane cartridges having:
i) a water separation membrane,
ii) an impermeable cartridge wall surrounding the membrane,
iii) a first cartridge end sealed to the wall and through which pressurized salinated water flows into the cartridge and is separated by the membrane into concentrate or brine and at least partially desalinated water,
iv) a second cartridge end from which the concentrate or brine exits the cartridge, and
v) a product water collection tube that collects from inside the cartridge the at least partially desalinated product water passing through the membrane, and through which the at least partially desalinated water exits the cartridge;
a generally parallel array of the cartridges being mounted in a perforated divider plate whose perforations surround the cartridge walls or the first or second cartridge ends, the divider plate separating salinated water flowing into the first cartridge ends from concentrate or brine exiting the cartridges; and
a product water collection manifold in fluid engagement with a plurality of the product water collection tubes and into which the at least partially desalinated water flows;
wherein a) the manifold is adhesively bonded to a plurality of the collection tubes, or b) the divider plate is adhesively bonded to a plurality of the cartridge walls or ends, or both a) and b).