WO2007059240A1

WO2007059240A1 - Synthetic infiltration collection system

Info

Publication number: WO2007059240A1
Application number: PCT/US2006/044398
Authority: WO
Inventors: Anthony Jones; Robert Campbell
Original assignee: Oases Uk, Ltd.
Priority date: 2005-11-15
Filing date: 2006-11-14
Publication date: 2007-05-24
Also published as: WO2007059240A9; US20070108112A1

Abstract

The present invention is a filtered seawater collection system (10) for installation at seaside locations. TMs system filters undesirable elements from seawater including garbage, debris, volatile organics and biologies such as toxic algaes. The resulting filtered seawater is then pumped to a desalination plant for de-salting. This system (10) comprises a subterranean reservoir (12) installed at a sheltered location, such as behind a set of dunes (14). A borehole (32) is created by directional drilling, the borehole (32) breaking through the surf line (30) and into open ocean (24). A pipe (20) is laid extending from the reservoir (12) out to the open ocean (24). The pipe (20) ends in an intake (42), which is overlapped by gravel packets (50) which act as filtration media. The intake (42) receives water filtered through the gravel packets (50), which is transported through the pipe (20) to the reservoir (12).

Description

PCT Patent Application of

Anthony T. Jones and Robert L. Campbell

for

Synthetic Infiltration Collection System

1. Technical Field

This invention relates to the field of desalination of seawater and more specifically to a system and method for filtering seawater to remove suspended solids, debris and biological material prior to subjecting the seawater to desalination. The system and method of filtering seawater described herein also can be applied to cooling water intakes for power plants.

2. Background

Seawater desalination is becoming an attractive source of drinking water in coastal states as the costs for desalination decline. A prime consideration for seawater desalination is a source of feed water that is reliable and consistent to sustain operations and produce potable water effectively and efficiently. The amount and quality of feed water entering a desalination plant is greatly dependent upon the placement of the feed water intake. Up to the present time, feed water intakes have been of two basic types, namely: 1) directly from the sea and 2) indirectly from the sea. Each of these types of intakes has significant benefits and significant drawbacks as will be further explained below.

Open ocean intakes, or direct intakes can be as simple as dredged channels through a nearshore region to draw in seawater. More sophisticated direct intakes involve the construction of pipelines from shore to beyond the nearshore, out to waters deeper than 35 meters. Deeper water is desirable in that the intake is less affected by wave and tidal action, but added pumping costs and pipeline costs limit the depth to which direct intakes can be practically placed. Direct intakes are fairly long lived in that they can have a service life of 30-50 years. They also provide an unlimited supply of seawater to a desalination plant as the seawater is pumped directly to the plant. However, a first drawback of direct intakes is that they are hampered by impingement and entrainment of planktonic organisms that require additional filtration and pretreatment once the seawater arrives at the plant, thereby driving up fresh water production costs. Other common problems associated with direct intakes include biological fouling of intake pipes; trash and other debris in intakes; hydrocarbon products occurring in feed water; and recirculation of discharge to intakes. Additionally, uncertain construction permitting outcomes related to direct intakes in light of modified regulatory practices derived from Section 316(b) of the Clean Water Act plague desalination plant developers. Indirect seawater intakes include vertical beach wells, Ranney wells, and infiltration galleries. Common among these indirect seawater intakes is that they are all dependent upon the nearshore zone geology in which they are placed, to provide a filtered seawater product.

Vertical beach wells are placed near a shoreline, typically very close to the nearshore in order to capture seawater filtering through the local nearshore geology. The beach well is a subterranean reservoir that is sunk with its top portion approximate to sea level, coupled to a pipe that is driven outward from the bottom of the reservoir into the nearshore geology, the pipe having a plurality of through-holes for allowing the flow of seawater into the pipe. The distance that the pipe can be driven into the surrounding nearshore geology limits the length of pipe. As water flows into the reservoir, it fills the reservoir until the level of water in the reservoir is the same as at sea level. The water is then pumped from the reservoir to the desalination plant to be de-salted. Beach wells are advantageous because they avoid issues related to volatile organic spills and lessen potentially harmful algal blooms. Hence, the water quality provided by beach wells is excellent. However a drawback exists in that the water supply produced by a beach well is totally dependent on hydrogeologic conditions at the site. Furthermore, in comparison to the unlimited seawater supply from direct intakes, beach wells typically provide water volumes in the range of only 400-4000 cubic meters per day.

A Ranney well employs a plurality of radially arranged collector wells located horizontally beneath a beach. The collector wells channel filtered seawater to a central sunken reservoir from which the seawater is pumped to a desalination plant for de- salting. Ranney wells typically have higher infiltration rates than vertical beach wells, ia that they can produce filtered seawater volumes in a range of 8,000-20,000 cubic meters per day. However, like beach wells, they are limited by the nearshore geology. Also, Ranney wells can be hampered by silt buildup and may also influence onshore groundwater resources, so careful evaluation of site characteristics must be employed before a Ranney well can be installed.

Indirect seawater intakes also suffer from a shorter life span, usually 15-20 year:; when compared with the 30-50 year life span of direct intakes. Further, the limitation in production capacity limits the use of indirect seawater intakes to only small desalination plants. Also, due to the fact that indirect seawater intakes must be placed in the nearshore region, they are vulnerable to storm damage or damage from beach erosion.

Present seawater intakes for use with desalination plants require choices and compromises between high volume, long life direct intakes and the low volume, shorter life, but higher water quality provided by indirect intakes. Therefore a need exists for n seawater infiltration system that incorporates the high volume and long life of a direct intake while providing the high water quality of an indirect intake without being limited by suiTounding nearshore geology.

The foregoing reflects the state of the art of which the inventor is aware, and is tendered with a view toward discharging the inventor's acknowledged duty of candor, which may be pertinent to the patentability of the present invention. It is respectfully stipulated, however, that the foregoing discussion does not teach or render obvious, singly or when considered in combination, the inventor's claimed invention.

SUMMARY QF THE INVENTION The inventive filtered seawater collection system provides high quality water without being dependent upon local nearshore geology. The system also provides water volumes much higher than systems that depend upon indirect intakes that are dependent on nearshore geology. The inventive system's ability to eliminate dependency on local nearshore geology allows it to be placed in coastal areas of the world where the nearshore geology renders indirect intakes an impossibility. The inventive system is comprised of a subterranean reservoir in communication with the first end of an intake pipe. The reservoir is buried with its top portion at a level seawater collection system shown installed at a coastal location.

FIG. 3 is a top plan view of the inventive system shown without filter media packets installed on the intake portion of the system.

FIG. 4 is a side cutaway view through a filter media packet of the inventive system.

FIG. 5 is a top plan view showing the filter media packets arranged around a seawater intake in accordance with the present invention.

FIG. 6 is a side view of a seawater intake attached to an alternative embodiment seawater filter. FIG. 7 is a top plan view of an alternative embodiment of the seawater intake, which employs multiple intakes.

FIG. 8 is a top plan view of an alternate embodiment fan-shaped intake having multiple pipes for drawing in high volumes of seawater.

FIG. 9 is a top plan view of an alternate embodiment high-volume intake having a branching configuration.

FIG. 1OA is a plan view of an alternate embodiment of a filter media container shown anchored to an intake pipe located upon a sea floor.

FIG. 1OB is a side view of the alternate embodiment of FIG. 1OA.

FIG. 1 IA is a plan view of a further embodiment of a filter media container which inserts over an intake pipe.

FIG. 1 IB is a side view of the alternate embodiment of FIG. 1 IA.

FIG. 12 is an elevated perspective view of a funnel-shaped intake embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a preferred embodiment of the filtered seawater collection system 10 is shown. The system 10 is comprised of a subterranean reservoir 12 that is preferably sunk in the ground at an area that is protected from wind, beach erosion, littoral drift, storm surges and other damaging coastal forces. Here, the reservoir 12 is shown sunk behind a first set of dunes 14 adjacent to a beach 16. The reservoir 12 is connected with a first end 18 of a pipe 20, and the pipe 20 extends outward from the reservoir 12 through the nearshore 22 and out into the open ocean 24. The nearshore 22 as shown is a geologic area below the beach 16 and below sea level. In some coastal regions, the nearshore 22 has a porous geology, which allows seawater 28 to filter down free of biological material and debris. However, in other coastal regions the nearshore 22 has an all but impermeable geology. As noted previously herein, the geology of the nearshore 22 is the limiting factor with regard to whether an indirect intake could be used in a seawater pre-filtration system. The inventive system 10 bypasses the nearshore 22 by extending the pipe 20 out through the surf line 30 and into the open ocean 24.

The pipe 20 is inserted through a bore 32 drilled into the nearshore geology 22 between the bottom of the reservoir 12 and through the surf line 30. Directional drilling techniques that have been used in the petroleum recovery arts are applied here to place the pipe in the manner shown and described. Directional drilling can produce a bore 32 several hundred yards long or even up to a half-mile or more. The use of directional drilling allows the reservoir 12 to be placed significantly far out of harms way such that damage to the reservoir 12 from natural coastal forces would be a limited possibility.

The reservoir 12 is sunk in the ground at a depth where the top portion 34 of the reservoir is approximately at sea level 26 as shown. The top portion 34 of the reservoir 12 is sloped to approximate the slope of the beach 16 which helps prevent sand erosion around the reservoir 12. Filtered seawater 29 flows into the bottom of the reservoir 12 from the pipe 20 and achieves sea level 26. A submersible pump 36 placed into the reservoir 12 transfers the filtered water to the desalination plant (not shown) for de- salting.

The pipe 20 extends past the surf line 30 and out into the open sea 24 a sufficient distance from shore 38 and at a depth to avoid tidal effects. Generally, the placement of pipe 20 is not limited by water depth. The pipe 20 can be mounted 41 to the sea floor 40 as shown in FIG. 1 or else it could placed in a bore 32 which extends beneath the sea floor 40 and only breaks the sea floor 40 at the intake end 42 as shown in FIG. 2. The configuration shown in FIG. 2 is presented as a lower profile design which is meant to minimally disrupt the ecosystem and also presents a lower profile to avoid contact with sea dredges, bottom trawl nets and other man made activity.

Referring also to FIG. 3, the seawater intake end of the pipe can be one opening or a plurality of openings 44 in the pipe terminus. The openings 44 draw in the filtered seawater 29 which travels up the pipe 20 to the subterranean reservoir 12. The intake 42 also preferably has an end cap 46 or other access point to periodically clean out and service the pipe intake. Likewise, the reservoir 12 includes a manhole access 48 for regular servicing, as needed.

FIGS. 4 and 5 demonstrate the filter media portion of the inventive system 10. In the embodiment of these figures, filter media packets 50 surround the intake end 42 of the pipe 20. The packets 50 are comprised of a porous container 52 containing a filter media 54. The filter media 54 must have the characteristics of removing undesired filtration elements including detritus, suspended soil, suspended sediment, planktonic organisms, and biologies such as toxic dinoflagellates and diatoms found in seawater. Additionally, the filter media fosters an environment for microbial communities to effectively remove bioavailable nutrients such as phosphorus and nitrogen compounds. Also, the media 54 must be inexpensive and be able to operate on the intake end 42 in a filtering capacity for a long while before becoming overloaded with undesired filtration elements. Further, it is preferable that upon becoming overloaded the media 54 be able to be cleaned and re- used or else replaced inexpensively. The inventors have found that geologic filtration medias 54 meet these requirements; specific geologic filtration medias 54 include various gravel combinations. As shown in FIG. 4, the porous container 52 is filled with gravel media 54 and the container 52 has a flat, mattress-like quality. The containers 52 are made of porous and durable materials including nylon, geotextile fabrics, geo-membranes or other engineered materials. The interiors of the containers are partitioned 56 so that the gravel is placed in separate compartments 58. This makes the packets 50 easier to handle and less unwieldy. The internal structure provides integrity to the containers. The pliable nature of the media containers allows for encasing the intake end of the pipe. Handling is further eased by the addition of attachment points 60 which can be coupled to a crane cable (not shown) for lowering into the sea and guiding into place over the intake end 42 by a dive crew.

An example of a filtration media 54 which enables this invention is a sequence of 27% filter sand (typically NSF/ANSI Standard A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (1/4 to 1/8, NSF /ANSI Standard A8073), flint 10.8% (1/2 to % NSF/ANSI Standard A8074), anthracite 14.8% (#1, 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet 24.3% (#30 to #40, NSF/ANSI Standard A8037). Site specific factors can augment this recipe.

FIG. 5 illustrates how the packets 50 are arranged around the intake end 42 of the pipe 20 so as to cover all of the pipe openings 44 in a filtering manner. The packets 50 settle around and form to the pipe intake end 42, thereby helping to seal off the pipe intake openings 44 from raw seawater 28. Further, to make sure that the pipe intake openings 44 receive only filtered seawater, the packets 50 can be layered and overlapped to form a sealed geological unit around the pipe intake 42. The filter media packets 50 provide a filtering geology that can be transported to and adapted to any coastal situation in the world. Therefore, the invention allows nearshore regions 22 having less than optimal filtration characteristics to be bypassed and further allows a more effective filter substrate geology to be installed near any coastline in the world.

FIG. 6 is an alternative embodiment of the invention, which, instead of enclosing the filtration media in mattress-like containers, encloses the media in filter canisters 66 which can be coupled to the end of a solid pipe 20. The filter canister 66 shown here would have porous qualities and could be a geologic filter with gravel 54 being the preferred media. The intake end 42 of the pipe would no longer be endowed with a plurality of openings 44. Instead, the pipe 20 would be solid up to the point of its terminus and would have a coupler 68 on the end of the pipe. The coupler 68 would have a sealing quality to prevent the influx of raw seawater 28. The coupler 68 could therefore be a threaded arrangement, a gasket arrangement or other known mechanical means, which could achieve the sealing coupling of the filter canister shown.

FIG. 7 illustrates an alternative embodiment of the intake. This embodiment employs multiple intakes 42, which feed water to the subterranean reservoir 12 in the manner previously described. The multiple intakes 42 feed into corresponding pipes 20. A larger pipe 70 functions as a type of bore lining for containing multiple intake pipes 20. The pipe 70 is preferably sealed with a cover 71 through which penetrate pipes 20. Cover 71 effectively prevents raw seawater from entering pipe 70 and potentially fouling the filtered seawater 29 contained in reservoir 12. The bore 32 created by directional drilling can be made to have a diameter of 30" or greater. As shown in FIG. 7, a 30" or larger bore 32 allows for the placement of the large pipe 70, so that a plurality of intake pipes 20 can be placed inside of the large pipe 70 and connected to the reservoir 12. This allows for the filtration of much higher volumes of seawater from the multiple intakes. Also, as desalination needs grow with population growth, this configuration allows for more intake pipes 20 to be added.

FIG. 8 illustrates a fan-shaped intake 74 having multiple pipes 76 for drawing in high volumes of seawater. This intake 74 would be attached to a pipe 20 having sufficient volumetric capacity to accommodate the large intake of seawater provided by this fan-shaped intake embodiment. The filter media packets 50 (not shown in this view) would be assembled around the multiple pipes 76 in the manner previously described. An impermeable geo-membrane 78 is preferably laid beneath the fan-shaped intake 74 to help prevent the influx of anoxic trace metals, which are especially prevalent in sea floors having high mud or clay compositions. The geo-membrane layer 78 could also be adapted to be laid beneath any of the other pipe intake embodiments described herein. FIG. 9 shows another high-volume intake 80 having a branching configuration. The branches represent pipes 82 which can be added as desalination capacity is increased. This configuration can grow along with growing desalination needs.

FIGS. 1OA and 1OB illustrate an embodiment of a filter media container 84 which relies upon the use of polyurethane foam 86 as a filter media. Instead of multiple gravel packets 50, the container 84 is a large single piece, and bag-like. The length of container 84 would cover intake openings 44 on pipe 20. The container is anchored 88 to the sea floor 40 to keep container 84 tight over the intake openings 44. The container remains porous and its polyurethane foam filling results in a malleable assembly which forms itself to the pipe 20 over intake openings 44.

FIGS. 1 IA and 1 IB show another filter media container 90 which would preferably employ a foam filter media. It has been found that polyurethane foam 96 operates as a filter media in accordance with the invention. The container 90 is bag-like and is intended to insert over intake end 42 of pipe 20. Pipe 20 inserts into an inner cavity 92 of container 90, the inner cavity 92 being lined with porous container material and keeping the intake openings 44 separate from the filter media 96. The polyurethane foam filter media 96 is injected through a valve opening 94. This is to allow easy assembly over the end of the pipe by first inserting the pipe 20 into the empty container 90 and then filling the container with filter media 96 through valve 94. The filter media can be replaced periodically by suctioning it back through the valve and replacing with fresh filter media.

FIG. 12 offers a funnel-shaped intake embodiment 100 wherein the funnel 102 is filled with different layers 104, 106 of gravel filter media. The advantage of a funnel- shaped intake 100 over a pipe intake is that the flow into the intake is significantly slowed while keeping the volume of water entering pipe 20 to a high level. By slowing the water flow rate, biological materials are less likely to be attracted into the funnel.102. Also, because the funnel opening 108 extends upwardly from the sea floor 40, contact with anoxic metal-containing sea muds and clays is significantly reduced. The layers 104, 106 of gravel media can be selected according to site-specific water characteristics. Finally, although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. This invention may be altered and rearranged in numerous ways by one skilled in the ait without departing from the coverage of any patent claims which are supported by this specification.

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Claims

1. A system for treating seawater, comprising: a pipe for drawing seawater through, said pipe having a first end connected to a subterranean reservoir, said pipe further having a second end comprising an intake, said intake being located in raw seawater; a filtration media, said filtration media being contained within a porous container, said container being arranged about said intake to allow raw seawater to be filtered through said filtration media prior to said seawater entering said intake and being drawn through said pipe to said reservoir.

2. A system for treating seawater, comprising: a pipe extending through a nearshore region out into the open ocean, said pipe being connected to a subterranean reservoir at a first end of said pipe, said pipe further comprising a second intake end located in the raw seawater, said pipe acting as a conduit for drawing seawater from said intake end to said reservoir; and a filtration media contained in porous containers, said containers being positioned upon said intake end of said pipe, wherein said system draws raw seawater through said porous containers and wherein the seawater is filtered through said filtration media prior to being drawn through said intake of said pipe.

3. The system for treating seawater as recited in claim 2, wherein said filtration media filters undesirable elements from raw seawater, said undesirable elements comprising detritus, suspended soils, suspended sediment, planktonic organisms, toxic dinofiagellates and diatoms.

4. The system for treating seawater as recited in claim 2, wherein said filtration media further comprises a geologic filtration media.

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5. The system for treating seawater as recited in claim 4, wherein said geologic filtration media further comprises gravel combinations.

6. The system for treating seawater as recited in claim 5, further comprising a gravel combination consisting of 21% filter sand (NSF/ANSI Standard

A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (1/4 to 1/8, NSF /ANSI Standard A8073), flint 10.8% (1/2 to % NSF/ANSI Standard A8074), anthracite 14.8% (#1, 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet 24.3% (#30 to #40, NSF/ANSI Standard A8037).

7. The system for treating seawater as recited in claim 1, further comprising a bore lining for containing said pipe within.

8. The system for treating seawater as recited in claim 7, further comprising a plurality of pipes being contained within said bore lining, said pipes terminating in a corresponding plurality of said intakes, said plurality of pipes being coupled to said reservoir at a first end of each pipe, wherein each of said intakes receives filtered seawater through a said filtration media container.

9. The system for treating seawater as recited in claim 2, further comprising a bore lining for containing said pipe within.

10. The system for treating seawater as recited in claim 9, further comprising a plurality of pipes being contained within said bore lining, said pipes terminating in a corresponding plurality of said intakes, said plurality of pipes being coupled to said reservoir at a first end of each pipe, wherein each of said intakes receives filtered seawater through a said filtration media container.

11. A system for treating seawater, said system for being placed at shoreline locations, said system comprising an underground subterranean reservoir, said reservoir being placed at least behind a first set of dunes at a shoreline

12 location, said reservoir further comprising a sloped top to conform with the approximate slope of a shoreline at which said reservoir is placed; a pipe for drawing seawater there through, said pipe having a first end connected to said reservoir, said pipe extending outward from said reservoir past the shoreline and into open seawater, said pipe terminating in a second end having a plurality of openings for drawing seawater into said pipe; a geologic filtration media enclosed within plurality of porous containers, said filtration media being selectable for optimized filtration characteristics, said plurality of containers being arranged about said second end to allow raw seawater to be first filtered through said filtration media prior to entering said second end openings and being drawn through said pipe to said reservoir.

12. A seawater intake for providing filtered seawater, comprising: an intake opening positioned in raw seawater; at least one porous and formable container, said container containing a seawater filtration media; said container being formably positioned over said intake opening to pul said opening in filtering contact with said container for allowing raw seawater to be drawn through said container and said filtration media prior to entering said intake opening.

13. The seawater intake as recited in claim 12, wherein said intake is a component of a desalination plant.

14. The seawater intake as recited in claim 12, wherein said intake is a component of a power plant.

15. The seawater intake as recited in claim 12, wherein said intake is a component of any industrial plant

16. The seawater intake as recited in claim 12, wherein said seawater filtration

13 media further comprises a geologic filtration media.

17. The seawater intake as recited in claim 16, wherein said geologic filtration media further comprises gravel combinations.

18. The seawater intake as recited in claim 17, further comprising a gravel combination consisting of 27% filter sand (NSF/ANSI Standard A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (1/4 to 1/8, NSF /ANSI Standard A8073), flint 10.8% (1/2 to % NSF/ANSI Standard A8074), anthracite 14.8% (#1 , 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet

24.3% (#30 to #40, NSF/ANSI Standard A8037).

19. The seawater intake as recited in claim 12, wherein said container further comprises a compartmentalized interior, said filter media being distributed with said compartments.

20. The containers as recited in claim 19, further comprising attachment points for attaching a lifting apparatus to said container.

21. The seawater intake as recited in claim 12, wherein said filtration media filters undesirable elements from raw seawater, said undesirable elements comprising detritus, suspended soils, suspended sediment, planktonic organisms, toxic dinoflagellates and diatoms.

22. A filtration media container, comprising: a porous outer cover having a compartmentalized interior; a filtration media contained inside of said compartmentalized interior; and attachment points for attaching a lifting apparatus to said container.

23. The filtration media container as recited in claim 22, wherein said seawater filtration media further comprises a geologic filtration media.

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24. The filtration media container as recited in claim 23, wherein said geologic filtration media further comprises gravel combinations.

25. The filtration media container as recited in claim 24, further comprising a gravel combination consisting of 21% filter sand (NSF/ANSI Standard A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (1/4 Io 1/8, NSF /ANSI Standard A8073), flint 10.8% (1/2 to % NSF/ANSI Standard A8074), anthracite 14.8% (#1, 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet 24.3% (#30 to #40, NSF/ANSI Standard A8037).

26. The filtration media container as recited in claim 22, wherein said filtration media filters undesirable elements from raw seawater, said undesirable elements comprising detritus, suspended soils, suspended sediment, planktonic organisms, toxic dinoflagellates and diatoms.

27. A seawater intake for providing filtered seawater, comprising: A pipe end having an opening; and

A porous filter, said filter containing a geologic filtration media, said filter and said pipe end coupling together in a sealing manner, wherein raw seawater is drawn through said filter prior to entering said opening in said pipe end.

28. The seawater intake as recited hi claim 27, wherein said geologic filtration media further comprises gravel combinations.

29. The seawater intake as recited in claim 28, further comprising a gravel combination consisting of 27% filter sand (NSF/ANSI Standard A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (1/4 to 1/8, NSF /ANSI Standard A8073), flint 10.8% (1/2 to ¹A NSF/ANSI Standard A8074), anthracite 14.8% (#1, 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet

24.3% (#30 to #40, NSF/ANSI Standard A8037).

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0. The seawater intake as recited in claim 27, wherein said filtration media filters undesirable elements from raw seawater, said undesirable elements comprising detritus, suspended soils, suspended sediment, planktonic organisms, toxic dinoflagellates and diatoms.

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