Abstract:
The use of a sulfur-impregnated organoclay provides a mercury or arsenic removal media having increased reactivity, stability, and mercury removal ability. The Hg/As removal media described herein is prepared by impregnating an organophilic clay with elemental (free state) sulfur. Alternatively, the clay can be made organophilic by onium ion reaction prior to or simultaneously with impregnating the organoclay with sulfur.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to compositions; methods of manufacturing the compositions; and methods of using the compositions for removing mercury (organic mercury, Hg, Hg + ; and/or Hg +2 ) and/or arsenic (As −3  and/or As +5 ) from water. The compositions, also identified herein as “media”, or “mercury removal media”, or “arsenic removal media”, or “Hg/As removal media”, can be used to remove mercury and/or arsenic from any water source and is particularly useful for removal of mercury and/or arsenic from drinking water; industrial wastewater; contaminated groundwater; contaminated sediment; offshore produced water, so that the produced water can be returned to the ocean; and for removal of mercury and/or arsenic from aqueous mining wastes. The Hg/As removal media comprises a homogeneous, preferably extruded composition comprising a layered phyllosilicate, elemental sulfur (free state sulfur), and an organic phyllosilicate surface treating agent, preferably an onium cation, resulting in an organoclay containing sulfur. The sulfur is bonded to the phyllosilicate covalently, ionically, physically, or by a combination of mechanisms. 
     BACKGROUND AND PRIOR ART 
     The technologies available for mercury and arsenic removal, such as precipitation, coagulation/co-precipitation, activated carbon adsorption, ion-exchange and the like, are not sufficiently effective for mercury and arsenic (arsenite and arsenate compounds) removal. This assignee&#39;s organoclay has been proven effective on a variety of organic contaminants in the last decade. See, for example, this assignee&#39;s U.S. Pat. Nos. 6,398,951; 6,398,966; 6,409,924; and 6,749,757, incorporated herein by reference. A new Hg/As filtration media, described herein, can be operated in a similar fashion, or together with the organoclay media, but is much more effective for mercury or arsenic removal. 
     The Hg/As removal media described herein has a similar physical form to the organoclays used for organic contaminant removal and can be similarly packed in a canister or cartridge, as described in the above-listed patents. In addition, the Hg/As removal media described herein can be deployed in single layer or multi-layer water-permeable mats, as described in this assignee&#39;s published applications, Ser. Nos. 10/718,128, filed Nov. 19, 2003 (Publication No. 2005-01013707 A1), Ser. No. 11/221,019, filed Sep. 7, 2005 (Publication No. 2006/0000767 A1), [Ser. No. 11/489,383, filed Jul. 19, 2006, (Publication No. 2006-0286888 A1)], Ser. No. 11/599,080, filed Nov. 14, 2006 (Publication No. 2007-0059542 A1); and Ser. No. 11/741,376, filed Apr. 27, 2007, all of which are hereby incorporated by reference. Fundamentally, the Hg/As removal media is based on organoclay technology but it has been substantially modified using several unique chemistries to enhance adsorption of mercury and arsenic-containing compounds. The mechanism of mercury adsorption is based upon chemical bonding, ionic bonding, mechanical bonding, or a combination thereof. The mercury and/or arsenic will be bonded to the media&#39;s external and internal surfaces and the bonding process is non-reversible. 
     The Hg/As removal media described herein is effective on all sources of mercury and arsenic including organic types of mercury and arsenic, including organic mercury and arsenic compounds, mercury metal (zero valent); arsenite and arsenate compounds; arsenic ions (both III and V valent); and mercury ions (both I and II valent). When the organic-based mercury and/or arsenic is involved, the adsorption mechanism of partition could be involved in addition to chemical bonding. In addition, the Hg/As removal media described herein also is effective to remove oil, grease and other organic contaminant molecules. The media will be spent eventually when all of the adsorption sites are saturated. The actual media life will depend on the contaminated water compositions and the field operation conditions. 
     Greco U.S. Pat. No. 5,512,526 describes a clay-based heavy metal removal media prepared by reacting a fatty mercaptan, e.g., dodecylmercaptan, with a fatty alkyl-containing quaternary ammonium compound. As described, the mercaptan&#39;s hydrophobic fatty alkyl group associates in some manner with the fatty alkyl group of the quaternary ammonium compound. 
     SUMMARY 
     It has been found in accordance with the present invention that the use of a sulfur-impregnated organoclay provides a mercury and arsenic removal media having increased reactivity, stability, and mercury and arsenic removal ability. The Hg/As removal media described herein is prepared by impregnating an organophilic clay with elemental (free state) sulfur. Alternatively, a clay can be made organophilic by treating the clay with a surface-treating agent, such as a polymer capable of increasing the d-spacing of the clay platelets, or preferably, with onium ions prior to or simultaneously with impregnating the resulting organoclay with sulfur. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         FIGS. 1 and 2  are graphs showing the mercury removal efficacy of the Hg/As removal media described in the examples; 
         FIG. 3  is a graph showing the arsenic removal results for the Hg/As removal media of Example 6; 
         FIG. 4  is a side view of an offshore oil well drilling platform generally showing the Hg/As removal media held within a canister attached to an offshore oil well drilling platform support structure with an alternative placement of a sump tank; 
         FIG. 5  is a sectional view of an embodiment of a vessel containing a plurality of Hg/As removal media-containing cartridges or canisters for efficient removal of mercury and arsenic contained in water; 
         FIG. 6  is an elevational view of a preferred embodiment of a vessel containing a plurality of Hg/As removal media-containing cartridges or canisters; 
         FIG. 7  is a top plan view of the header of the vessel shown in  FIG. 6  and openings within the header for receiving permeable conduits each of which can extend through a stack of cartridges or canisters as shown in  FIGS. 5 and 6 ; 
         FIG. 8  is a partially broken-away side view of an embodiment of a Hg/As removal media-containing vessel, containing multiple, stacked cartridges ( FIGS. 5 and 6 ); and 
         FIG. 9  is an elevational view of a preferred embodiment of a mercury removal media-containing cartridge shown in  FIGS. 5 and 6 . 
     
    
    
     It should be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It should be understood that while the following description of the preferred embodiment of the invention is directed to the use of the methods, apparatus and mercury/arsenic removal media on an offshore drilling platform, the invention is also useful for mercury and arsenic removal from any contaminated water, including drinking water; industrial wastewaters; contaminated ground water supplies; aqueous mining wastes; and contaminated underwater and soil sediments, particularly when contained in a reactive mat, as described in the applications identified in paragraph [0003], or when used in bulk form. 
     The Hg/As removal media described herein is a sulfur-containing layered organophilic phyllosilicate that is (or has been) made organophilic by reaction with an organic phyllosilicate surface-treating agent, preferably an onium ion-liberating compound, and has been made mercury-reactive and arsenic reactive by impregnation with elemental sulfur. 
     Phyllosilicate 
     The phyllosilicate can be a smectite clay, e.g., bentonite, montmorillonite, hectorite, beidellite, saponite, nontronite, volkonskoite, sauconite, stevensite, and/or a synthetic smectite derivative, particularly fluorohectorite and laponite; a mixed layered clay, particularly rectonite and their synthetic derivatives; vermiculite, illite, micaceous minerals, and their synthetic derivatives; layered hydrated crystalline polysilicates, particularly makatite, kanemite, octasilicate (illierite), magadiite and/or kenyaite; attapulgite, palygorskite, sepoilite; or any combination thereof. 
     Clay Surface Modification Agents 
     The surface modification (intercalant) agents used for organoclay formation include but are not limited to primary amine, secondary amine, tertiary amine, and onium ions and/or onium salt compounds, polyquat, polyamine, cationic polymers and their derivatives, nonionic polymers, and mixture of thereof. 
     In the wet process, the surface modification agent, e.g., onium ion, is introduced into the layered material galleries in the form of a solid or liquid composition (neat or aqueous, with or without an organic solvent, e.g., isopropanol and/or ethanol, if necessary to aid in dissolving the onium ion compound) having a surface modification, e.g., onium ion concentration sufficient to provide a concentration of about 5% to about 10% by weight clay (90-95% water) and the surface modification agent, e.g., onium ion compound, is added to the clay slurry water, preferably at a molar ratio of onium ions to exchangeable interlayer cations of at least about 0.5:1, more preferably at least about 1:1. The onium ion-intercalated clay then is separated from the water easily, since the clay is now hydrophobic, and dried in an oven to less than about 5% water, preferably bone dry. The onium ion surface modification agent compound or polymer can be added as a solid with the addition to the layered material surface modification agent blend of preferably about 20% to about 40% water and/or organic solvent, more preferably at least about 30% water or more, based on the dry weight of layered material. Preferably about 30% to about 40% water, more preferably about 25-35% water, based on the dry weight of the layered material, is included in the onium ion intercalating composition, so that less water is sorbed by the intercalate, thereby necessitating less drying energy after onium ion intercalation. 
     In general, a dry process can be described, as follows, for organoclay media preparation or manufacturing. The powder form of clay mineral is fed into a mixer through a major port for solids, typically an extruder. A separate port for the 2 nd  powder form of solid can also be used besides the clay feeding port. The liquid forms of the additives, including water, intercalant agent, and the coupling agent if any, are fed into the mixer through the separate ports. Either multiple forms of the solids or the liquids could be pre-mixed, or both the solids and the liquids can be pre-mixed through a separate mixer, before they are fed into the extender. A preferred liquid weight is from 10% to 50% based on the total mixture weight, more preferably from 20% to 40%, most preferably from 25% to 35%. The intimate mixture from the extruder will be further dried through a dryer, and be ground to the preferred particle size. A screening process could be used to collect the finished product in the desired particle size distribution. 
     The onium ions may generally be represented by the following formula: 
     
       
                 
         
             
             
         
      
     
     The preferred phyllosilicate surface-treating agent is one or more onium salt compounds, generally represented by the following formula: 
                                
wherein Q=N, P, S;
 
wherein A=halide, acetate, methylsulfate, hydroxide, preferably chloride;
 
wherein R 1 , R 2 , R 3  and R 4  are independently organic moieties, or oligomeric moieties or hydrogen. (Ref. U.S. Pat. No. 6,376,591), hereby incorporated by reference. Examples of useful organic moieties include, but not limited to, linear or branched alkyl, benzyl, aryl or aralkyl moieties having 1 to about 24 carbon atoms.
 
     EXAMPLES 
     bis(hydrogenated tallow alkyl)dimethyl ammonium chloride (Arquad® 2HT); benzylbis(hydrogenated tallow alkyl)methyl ammonium chloride (Arquad® M2HTB); benzyl(hydrogenated tallow alkyl)dimethyl ammonium chloride (Arquad® DMHTB); trihexadecylmethyl ammonium chloride (Arquad® 316); tallowalkyl trimethyl ammonium chloride (Arquad® T-27W and Arquad® T-50); hexadecyl trimethyl ammonium chloride (Arquad® 16-29W and Arquad® 16-50); octadecyl trimethyl ammonium chloride (Arquad® 18-50(m)); and dimethylhydrogenated tallow-2-ethylhexyl ammonium methylsulfate. 
     Additional phyllosilicate surface-treating agents include the materials set forth below in paragraphs [0024]-[0030]. 
     Quaternary ammonium ions containing ester linkage: (ref. U.S. Pat. No. 6,787,592, hereby incorporated by reference, see columns 5 and 6) 
     Example 
     di(ethyl tallowalkylate)dimethyl ammonium chloride (Arquad® DE-T). 
     Quaternary ammonium ions containing amide linkage: (ref US patent application 2006/0166840 hereby incorporated by reference, see page 2) 
     The onium ions may be functionalized such as protonated α,ε-amino acid with the general formula (H 3 N—(CH 2 ) n —COOH) + . 
     Alkoxylated quaternary ammonium chloride compounds (ref. U.S. Pat. No. 5,366,647 hereby incorporated by reference) 
     Examples 
     cocoalkylmethylbis(2-hydroxyethyl) ammonium chloride (Ethoquad® C/12); octadecylmethyl[polyoxyethylene(15)] ammonium chloride (Ethoquad® 8/25); and octadecylmethyl (2-hydroxyethyl) ammonium chloride (Ethoquad 18/12). 
     Polyquat (U.S. Pat. No. 6,232,388, hereby incorporated by reference) 
     Example 
     N,N,N′,N′,N′-pentamethyl-N-tallowalkyl-1,3-propane diammonium dichloride (Duaquad® T-50). 
     Polyamine: (ref. US patent application 2004/0102332 hereby incorporated by reference) 
     Examples 
     N-tallow-1,3-diaminopropane (Duomeen® T); N-tallowalkyl dipropylene triamine (Triameen® T); and N-tallowalkyl tripropylene tetramine (Tetrameen® T). 
     Cationic polymers, non-ionic polymers, including homopolymer or copolymer, low molecular weight or high molecular weight 
     Examples 
     Polydiallydimethylammonium chloride; Poly(dimethylamine-co-epichlorohydrin); Polyacrylamide; and Copolymers of acrylamide and acryloyloxylethyltrimethyl ammonium chloride. 
     Hg/As Removal Media 
     In a preferred embodiment, particularly in offshore environments, the Hg/As removal media described herein can be used after the use of an organoclay for removal of organics in order to protect and extend the active life of both the organoclay, in an initial organoclay stage, and the Hg/As removal media, used after organic contaminant removal. An operation procedure using an initial organoclay media followed by contact with the Hg/As removal media, in series, is highly effective. A carbon media can also be used before or after the Hg/As removal media, if necessary. In general, the retention time of contact between Hg-contaminated or AS-contaminated water and the Hg/As removal media should be no less than about 10 seconds, preferably at least about 1 minute, more preferably about 2 minutes or more. 
     The preferred amount of components of the sulfur-containing organoclay media are as follows: 
                                                                   Phyllosilicate   Intercalant Agent   Elemental Sulfur                                    Preferably    1-90   10-50   0.5-50        More Preferably   35-83   15-45    2-20       More Preferably   50-77   20-40    3-10       More Preferably   59-71   25-35   4-6       Most Preferably   65   30   5                    
Laboratory Study
 
     A column study was conducted in order to demonstrate the mercury removal media&#39;s ability to remove mercury. The influent was composed of ˜10 ppm of Hg(NO 3 ) 2  solution with dilute nitric acid matrix. The effluent samples were taken at regular intervals and the mercury content was measured by an ICP analytical test. The flow rate was about 10 bed volumes (BV) per hour, using a 6-minute retention time. A commercial mercury removal media (Hg-A of SME Associates, Houston, Tex.) containing a mixture of 85-90% activated carbon and 10-15% sulfur was also included in this study for comparison purposes. 
     Example 1 
     Sample L1S 
     400.0 g of bentonite clay (particle size&lt;75 μm preferred, and ˜8% moisture content) was dry-mixed with 28.75 g of sulfur in the powder form (purchased from Aldrich) using the Kitchen Aid mixer for one minute. 80.0 g of deionized water was added to this bentonite-sulfur mixture slowly under shearing using the same mixer and mixed for ˜2 minutes. 209.6 g of melt quat (ARQUAD® 2HT from Akzo Nobel, bis(hydrogenated tallow alkyl)dimethyl ammonium chloride, ˜83% active) was added to this clay-sulfur-water mixture under shearing using the same mixer, and mixed for 5 minutes. The mixture was extruded three times using a laboratory-scale extruder with a die-plate, and the final extrudates were oven-dried at 85° C. to a moisture content of less than 5% by weight. The dried extrudates were ground and resulting particles between 18 and 40 mesh (US standard sieves) were collected and tested for their performance. 
     Example 2 
     The media material collected in Example 1 was packed in a column having an inner diameter of 1.5″ and having an empty bed volume (BV) of ˜86 mL. The influent was composed of ˜10 ppm of Hg(II) in the presence of nitric acid. The effluent samples were taken at regular intervals and the mercury content was measured by the Inductively Coupled Plasma (ICP) analytical technique. The flow rate was about 10 BV/hr with a 6-minute retention time. A commercial organoclay media Hg-A (without sulfur) is also included in this study for the comparison purpose. 
     Example 3 
     Production Trial 1 
     Bentonite powder and sulfur powder (from Harwick Standard Distribution Corporation, grade 104) were blended in a ratio of 93.3:6.7 by weight, and then this mixture was fed into a 5″ Readco continuous processor at a feed rate of 900 lb/hr. About 0.25 gallon/minute of water and 1.04 gallon/minute of quat (ARQUAD® 2HT from Akzo Nobel, bis(hydrogenated tallow alkyl)dimethyl ammonium chloride, ˜83% active) were also fed in the Readco processor through two independent ports in sequence. The discharged extrudates from the processor were sent to a dryer, the dried extrudates were further milled and the granular particles between 18 and 40 mesh with moisture content less than 5% by weight were collected as the finished product. 
     Example 4 
     A similar column test as described in Example 2 was conducted on the product sample collected in Example 3. 
     Example 5 
     The media described in Example 2 was tested under offshore platform conditions using actual offshore mercury-contaminated water. A commercial available organoclay product, CrudeSorb™, was also used in front of this Hg/As removal media. The influent had a mercury concentration of 11.4 ppb, and the effluent was 3.4 and 3.9 ppb after the 30 minutes and 90 minutes treatment, respectively. A total mercury removal efficiency of &gt;65% was achieved. 
     Arsenic Removal Example 
     Example 6 
     The media described in Example 3 was examined for its ability to remove arsenic. The media materials were packed in a column with inner diameter of 1.5″ and empty bed volume of ˜86 mL. The influent solution was composed of ˜5 ppm of As(V). The As(V) stock solution was prepared by dissolving Na 2 HAsO 4 .7H 2 O in the de-ionized water. The effluent samples were taken at regular intervals and the arsenic content was measured by the Inductively Coupled Plasma (ICP) analytical technique. The flow rate was around 10 BV/hr with 6-minute retention time. 
     Offshore Field Study Example for Both Hg and As Removal 
     Example 7 
     The media material described in Example 3 was tested under offshore platform conditions using the actual wastewater contaminated by both mercury and arsenic. The contaminated water was pumped through two columns in series. Each column had a diameter of 3″ and held about 1.5 Liter of media (˜1,125 grams). The first column was packed with the commercial available organoclay media, CrudeSorb™, and the second column was packed the media material described in Example 3. The retention time was roughly equal to 5-minute. The influent had mercury and arsenic concentration of 11.4 ppb and 7.55 ppb, respectively. After the 30 minutes and 90 minutes treatment, the effluent had mercury concentrations of 3.4 ppb and 3.9 ppb, arsenic concentrations of 5.18 ppb and 5.16 ppb, respectively. So a total mercury and arsenic removal efficiency of greater than 65% and 30% were achieved, respectively. 
     Turning now to the drawings, and initially to  FIG. 4 , there is shown an offshore drilling platform generally designated by reference numeral  10  including a work deck support structure  12  for supporting a plurality of stacked work decks at a substantial height above an ocean water level  14 . The work decks commonly include a cellar deck  16  at a lowest work deck level, a second deck  18  located directly above the cellar deck  16 , a third deck  20  disposed directly above deck  18 , and a main deck  22  at an uppermost work deck level. In extant offshore drilling platforms, a sump tank  24  has been connected to the drilling platform  10  at the cellar deck level  16  and rainwater, including entrained hydrocarbons, particularly oil, paraffins and surfactants have been directed from all deck levels, which are contained so that rainwater and entrained hydrocarbons do not spill over to the ocean, to drain by gravity into the sump tank  24 . As described in this assignee&#39;s U.S. Pat. Nos. 6,398,951; 6,398,966; 6,409,924; and 6,749,757, hereinafter incorporated by reference, further separation of hydrocarbons from rainwater, in addition to gravity separation, is required for effective elimination of ocean water hydrocarbon contamination by providing a secondary hydrocarbon recovery apparatus containing an organo-clay after the produced water and/or rainwater has been separated by gravity in the sump tank  24  or  24 A. In the preferred embodiment of mercury and/or arsenic removal using the methods and apparatus described herein for mercury and arsenic removal offshore, one or more canisters (not shown) containing an organoclay, for hydrocarbon removal, is used in series with one or more canisters containing the Hg/As removal media (in any order). It is preferred to remove the hydrocarbons with organoclay-containing canister(s) prior to mercury and/or arsenic removal with Hg/As removal media-containing cartridges. 
     In accordance with a preferred embodiment of the methods, apparatus and Hg/As removal media described herein, it has been found that the apparatus and methods described herein function best, in offshore platform use, when the sump tank  24 A is disposed on or near a boat landing deck level  26  ( FIG. 4 ) of the offshore drilling platform  10 . However, the sump tank can also be disposed at an upper level, such as at reference numeral  24  in  FIG. 4 . 
     Mercury and/or arsenic from ocean water that is collected on the production decks  16 ,  18 ,  20  and  22  that may accumulate during dry weather on the inner surfaces of the conduit  28  and inner surfaces of sump tank  24  can be separated from the water that flows from the decks to the Hg/As removal media-containing cartridge  44  for recovery and separation in accordance with the apparatus and methods described herein. 
     Water containing mercury and/or arsenic is conveyed via conduit  28  from the deck areas  16 ,  18 ,  20  and  22  along the platform infrastructure or support leg  12  down to the sump tank  24  or  24 A, preferably sump tank  24 A for convenient servicing and/or Hg/As removal media cartridge replacement. As stated in this assignee&#39;s U.S. Pat. Nos. 6,398,951, 6,398,966 and 6,409,924, it is expedient to dispose the separation apparatus described herein at or near the boat landing deck level  26  (such that at least a portion of the sump tank  24 A is within about 10 feet of ocean level) since contaminants collected on the production decks  16 ,  18 ,  20  and  22  that may accumulate during dry weather on the inner surfaces of the conduit  28  and inner surfaces of sump tank  24 A can be separated from the water that flows from the decks to the sump tank  24 A for recovery and separation in accordance with the apparatus and methods described herein. 
     In accordance with an important feature of the methods, apparatus and mercury removal media described herein, a downwardly extending leg portion  42  of water leg  34  is operatively interconnected to, and in fluid communication with, one or more mercury and/or arsenic media-containing vessels  44 . As shown in  FIG. 5 , the mercury removal media within vessel  44  captures the mercury and thereby separates essentially all mercury from the water (less than about 10 parts per million, preferably less than about 1 part per million mercury remains). The treated water flows through the liquid-permeable covers  76  of the cartridges  55  into the vessel  44 . The treated water then flows by gravity through water exit opening  46  in the water and coalesced hydrocarbon collection vessel  44  and through exit conduit  48  back to the ocean water  14 . 
     As shown in  FIGS. 5 and 8 , vessel  44  includes an outer, fluid-impermeable housing  48  having a water inlet  42  interconnected through the housing  48  so that mercury-contaminated water enters vessel  44  and then flows through the Hg/As removal media-containing cartridges  55 , through a plurality of longitudinal, axial, central inlet conduits  56 ,  56 A,  56 B,  56 C and  56 D that may form part of a header, described in more detail hereinafter. The mercury removal media-containing cartridges  55  are water-permeable by virtue of flow apertures  57 , in the cartridge cover  76 , that are sized sufficiently small such that the mercury removal media does not pass therethrough. Water entering vessel  44  through inlet conduit  42  and cartridge inlet conduits  56 ,  56 A,  56 B,  56 C and  56 D flows radially outwardly through the mercury removal media  45  where the mercury removal media captures, and removes, the mercury from the contaminated water. The purified water flows through the openings  57  in each liquid permeable cartridge cover  76  and collect in vessel  44 . The clean water exits the vessel  44  through exit conduit  69  and through valve  71  and then is returned to the ocean  14  via outlet  73 . 
     Turning to  FIG. 6 , another embodiment of a vessel  100  is shown containing stacks of cartridges, one of which is shown at  102 . Each cartridge stack includes a plurality of annular cartridges  104  through which a porous contaminated liquid inlet conduit  106  extends. The porous inlet conduit  106  is connected to a header  108  which is disposed within a bottom section  110  of the vessel  100 , similar to the contaminated water inlet conduits  56 ,  56 A,  56 B,  56 C and  56 D shown in  FIG. 5 . 
     Turning to  FIGS. 6 and 7 , the header  108  is connected to a mercury-contaminated water inlet  112  which includes a flange  114  which is connected to the flange  116  of the header  108  by a plurality of fasteners, such as bolts (not shown). The header is also supported within the bottom structure  110  (see  FIG. 6 ) of the vessel by a plurality of supports shown at  118 . The header  108  includes a plurality of openings  120 , each of which receives a permeable conduit  106  (see  FIG. 6 ). In the embodiment illustrated in  FIGS. 6 and 7 , the header  108  is connected to  23  permeable conduits and therefore supports  23  stacks  102  of cartridges  104 . By providing the header  108  within the bottom structure  110  of the vessel  100 , a permeable tube sheet  111  shown in  FIG. 5  is not needed for collecting solids and the bottom section  110  of the vessel can be used to collect accumulated solids, or solids which do not pass through the outer covers  76  of the filter cartridges  104 . A drain  122  is provided for purposes of flushing out the accumulated solids which settle in the bottom structure  110  of the vessel  100 , together with the clean water. The clean water can be passed through a solids filter  123  before being directed to the ocean through conduit  125 . In contrast, solids will accumulate on top of the tube sheet  111 . Thus, the solids must be removed from above the tube sheet  108  using one or more nozzle openings shown at  109  in  FIG. 5 . As shown in  FIG. 6 , these additional nozzle openings are not required in the vessel  100  because the accumulated solids are easily flushed down the drain pipe  122  into solids filter  123 . 
     As shown in  FIG. 6 , an extremely dense number of stacks of cartridges  104  is provided by the header  108 . Specifically, the header  108 , as shown in  FIG. 7 , includes  23  openings  120 , and therefore  23  porous conduits  106  and therefore  23  stacks  102  of cartridges  104 . Accordingly, the volumetric flow rate that can be handled by the vessel  100  is substantially greater than the volumetric flow rate that can be handled by the vessel  44 . Of course, smaller vessels with fewer stacks of cartridges and large vessels with more stacks of cartridges are anticipated. 
       FIG. 8  illustrates a single cartridge  55  containing the Hg/As removal media  45  that is loosely packed within the canister  55  between liquid-permeable contaminated water inlet tube ( 56 ,  56 A,  56 B,  56 C and  56 D of  FIG. 3 ) and an outer, liquid-permeable cartridge cover  76 . As shown, the mercury removal media  45  comprises an organoclay containing sulfur.