Abstract:
A wastewater trickle tower has a support structure containing biomedia and a wastewater discharge arrangement for discharging wastewater onto the biomedia. A receptacle below the biomedia receives wastewater falling from the biomedia. The biomedia is surrounded by a flexible curtain suspended from the support structure and extending down to the receptacle. The curtain may have a vertically-extending, releasably-closable opening.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the priority of U.S. Provisional Application Serial No. 60/360,376 filed Feb. 28, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to the treatment of wastewater with biomedia, and more particularly to the arrangement of biomedia in an apparatus for treating wastewater.  
         BACKGROUND OF THE INVENTION  
         [0003]    With greater demands being placed on the treatment of wastewater by regulatory authorities, there has become a growing need for systems that will treat wastewater to a higher level of purity. This has also brought an increasing need for systems that are more versatile in design and can more readily be adapted to handle differing wastewater treatment requirements.  
           [0004]    I have found that a trickle tower system employing strands of looped cord biomedia is more suited to handling today&#39;s increasing demands in wastewater treatment than the conventional systems currently in use. The initial approach of a looped cord biomedia trickle tower system is disclosed in my U.S. Pat. No. 6,241,889 published Jun. 5, 2001. While this tower system has been promising, and the general approach employed appears correct, further improvements and modifications are now desirable for more widespread adoption by industry and civil authorities.  
         SUMMARY OF THE INVENTION  
         [0005]    This invention is concerned with improving and modifying the wastewater treatment process and apparatus disclosed in the above U.S. Pat. No. 6,241,889 the whole disclosure of which is hereby incorporated herein by reference.  
           [0006]    This invention is also concerned with developing further approaches to trickle tower treating of wastewater. Some of these approaches are particularly advantageous with looped cord biomedia, and others are advantageous with other biomedia and other systems in addition to being applicable with looped cord biomedia.  
           [0007]    This invention is particularly concerned with improving the ease, flexibility, and cost of constructing wastewater trickle towers. In this respect, it is particularly concerned with providing more flexibility with the cross-sectional shape and general construction of the trickle tower. At the same time, the invention is concerned with improving the efficiency and effectiveness of these trickle towers.  
           [0008]    According to an aspect of the present invention, there is provided a wastewater treatment apparatus having a support structure with biomedia supported by said support structure. The biomedia preferably comprises a plurality of strands extending downwardly and which may be strips of plastic material, fabric, etc., but are preferably strands of looped cord biomedia. A wastewater discharge arrangement is supported by the support structure for discharging wastewater onto the biomedia. A receptacle is located below the biomedia for receiving wastewater falling from the biomedia. A sleeve forms a wall surrounding the biomedia, the sleeve comprising a flexible curtain suspended from the support structure and extending downwardly to the receptacle.  
           [0009]    Such a flexible curtain enables trickle towers of any cross-sectional shape to be readily accommodated, for example, rectangular, polygonal, elliptical, as well as circular cross-sectional shapes.  
           [0010]    The curtain may be sealed at an upper end to the support structure and at a lower end to the receptacle. The curtain may have an opening located between the upper end and the lower ends, this opening being closed by a releasable fastener. The releasable fastener may comprise cooperative hook and looped strips, a zipper, or other type of fastener, and facilitates access through the curtain to the biomedia. The curtain may comprise at least two sections releasably connected together by at least two releasable fasteners.  
           [0011]    The curtain may have a plurality of holes at its upper end engaged over members extending from the support structure, the holes enabling the curtain to be supported by the support structure while the curtain is being installed around the biomedia.  
           [0012]    The support structure may include a hood extending over the wastewater discharge arrangement, and the curtain may be attached to and around this hood.  
           [0013]    There may be a series of interconnected treatment cells, each cell having its own biomedia suspended from the support structure over an associated receptacle with the cells being spaced apart. Each cell is preferably individually surrounded by a separate flexible curtain. However, two or more cells may be jointly surrounded by the same flexible curtain.  
           [0014]    The support structure is preferably part of a weatherproof building in which the treatment apparatus is housed.  
           [0015]    The biomedia strands are preferably arranged under tension and extending spaced apart, vertically and parallel to each other.  
           [0016]    When a tower of non-circular cross-section is chosen, the wastewater discharge arrangement preferably comprises a rotatable spray arm which in use defines a circular spray pattern, and a plurality of stationary spray nozzles providing a spray pattern of wastewater outside of this circular spray pattern. The stationary nozzles preferably provide pulsing spray jets.  
           [0017]    According to another approach, the wastewater discharge arrangement comprises a manifold extending along and oscillatable about a transverse, preferably horizontal, axis, the manifold having a transversely extending nozzle opening through which a sheet of wastewater is discharged onto the biomedia, this sheet of wastewater passing from one side of the biomedia to an opposite side and then from that opposite side back to said one side as the manifold oscillates.  
           [0018]    According to another aspect of the invention, there is provided a wastewater trickle tower apparatus comprising a support structure housing biomedia. A wastewater discharge arrangement is supported by the support structure above the biomedia for discharging wastewater onto the biomedia. A receptacle below the biomedia receives wastewater falling from the biomedia. The biomedia occupies a block-like space. A flexible curtain is suspended from the support structure and extends down to the receptacle, this curtain surrounding the block-like space.  
           [0019]    The curtain may have at least one slit having a releasable fastener, the fastener including a sealing strip secured to the curtain on one side of the slit and slideable over the curtain on the opposite side of the slit.  
           [0020]    Other objects, features, and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims, and the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    In the accompanying drawings, in which like reference characters in the same or different Figures indicate like parts:  
         [0022]    [0022]FIG. 1 is a schematic vertical section of a trickle tower wastewater treatment apparatus embodying the present invention;  
         [0023]    [0023]FIG. 2 is an elevational side view, with parts removed for clarity, of a single cell unit of the apparatus of FIG. 1;  
         [0024]    [0024]FIG. 3 is a diagrammatic perspective view of a curtain according to the invention that surrounds one or more treatment cells in the apparatus of FIG. 1;  
         [0025]    [0025]FIG. 4 is a partial vertical section illustrating the connection of the top of the curtain of FIG. 3 to a hood part of the apparatus of FIG. 1;  
         [0026]    [0026]FIG. 5 is a partial schematic elevational view in the direction of the arrow  5  in FIG. 4;  
         [0027]    [0027]FIG. 6 is a partial schematic elevational view of the lower section of a cell of the apparatus of FIG. 1 showing the lower part of the curtain inside a base receptacle;  
         [0028]    [0028]FIG. 7 is a section on the line  7 - 7  of FIG. 8 showing details of sealing the curtain to the inside of the base receptacle;  
         [0029]    [0029]FIG. 8 is a simplified plan view of the base container of FIGS. 6 and 7;  
         [0030]    [0030]FIG. 9 is a diagrammatic plan view of an openable vertical connection in the curtain of FIGS. 3 and 5;  
         [0031]    [0031]FIG. 10 is a schematic elevational view, partly in section, of another version of the apparatus of FIG. 1;  
         [0032]    [0032]FIG. 11 is a schematic elevational view in the direction of the arrow  111  in FIG. 10;  
         [0033]    [0033]FIG. 12 is a diagrammatic perspective view of a base container partitioned for use with two cells to be surrounded by a common curtain;  
         [0034]    [0034]FIG. 13 is a diagrammatic perspective view of a biomedia hanger unit used according to the invention in the apparatuses of FIG. 1 and FIG. 10;  
         [0035]    [0035]FIG. 14 is a diagrammatic simplified perspective view of a biomedia grate, according to the invention, made up of a plurality of the units of FIG. 13  
         [0036]    [0036]FIG. 15 is a plan view of the grate of FIG. 14;  
         [0037]    [0037]FIG. 16 is an end view of the upper structure of the grate in the direction of the arrow  16  in FIG. 15;  
         [0038]    [0038]FIG. 17 is an exploded view of FIG. 16 additionally showing a portion of a strand of biomedia;  
         [0039]    [0039]FIG. 18 is a side view of a modification of the grate of FIG. 15 showing the upper portions of the biomedia strands extending downwardly from the upper structure of the grate;  
         [0040]    [0040]FIG. 19 is a simplified elevational view of a base receptacle for the apparatus of FIG. 1 showing the lower portions of eight grates anchored to the bottom of the receptacle; and  
         [0041]    [0041]FIG. 20 is simplified vertical section of an upper part of the apparatus of FIG. 1 modified and showing the suspension of the upper ends of four grates, the left most one in partially exploded view. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]    [0042]FIG. 1 shows an exterior, weatherproof, steel building  2  having a support structure  4  erected on a concrete base  6 , with a covered recirculation tank  8  outside the building. Two wastewater treatment cells  10  are shown. Each cell  10  has an upper closure hood  12 , a flexible curtain  14  draped around the hood  12  and extending downwardly into a base receptacle  16  formed on the concrete base  6 . Biomedia  18  is enclosed by the curtain  14 , and a wastewater spraying or discharge system  20  is mounted inside the hood  12  above the biomedia, both as shown through broken away portions of the left cell  10 . Wastewater  22  from the spraying system  20  flows down the biomedia  18  and drips into the base receptacle  16 , illustrated as a base tray from which the partially treated wastewater flows to the recirculation tank  8  for recirculation to the spraying system  20  of the same or another cell. Of course the base tray  16  could be constructed as a recirculation tank, so eliminating the outside recirculation tank  8 . The hoods  12  are suspended by structural members  24 ,  26  supported by and forming part of the building structure  4 , for example the roof rafters. The curtains  14  are attached and sealed to the outside of the hoods  12 , and to the inside of the base receptacles  16 .  
         [0043]    [0043]FIG. 2 shows one of the cells  10  in side view, the curtain  14  surrounding and defining this cell, extending downwards from the outside of the hood  12  to the inside of the base receptacle  16 . Although varies types of biomedia could be used inside the confines of the curtains  14 , looped cord biomedia having looped continuous filaments is preferred, and preferably the looped cord biomedia is tensioned vertically. To show such a preferred arrangement, the side of the base receptacle  16  has been omitted to expose lower ends of four grates  28  (described in detail later) attached by adjustable tensioning bolts  29  to an anchor bar  30  extending horizontally across the base receptacle  16 . These tensioning bolts  29  are a slip fit through holes in the anchor bar  30 , to allow the bolts  29  to slip downwardly through the anchor bar  30 , if any grate  28  lengthens and drops down a little in use due to the weight of the biomass forming on the biomedia strands of the grate. This prevents such strands from sagging in use.  
         [0044]    [0044]FIG. 3 illustrates in perspective view one of the curtains  14 . It forms a tube-like casing, preferably made of flexible plastic sheeting, for example polyvinylchloride, polypropylene, etc. Due to the flexibility and deformability of the sheeting, the tube-like casing can have any required cross-sectional shape. As shown, it has a square cross-section  32 ; however, the cross-section may be rectangular, elliptical, circular, etc. In this way, the curtain  14  can be adapted to closely surround and define any shaped block of biomedia, whether solid biomedia, suspended strips, or looped cord. Around the top of the curtain is a series of small holes  34  reinforced by metal (preferably stainless steel) grommets  36 . These holes are hooked over pegs extending from the hood (shown in FIGS. 4 and 5); this serves as an aid when mounting the curtain  14  around the hood  12 , and it also provides physical support for the curtain  14  once mounted. Extending the full vertical length of the curtain  14  is at least one releasable fastener  38  closing an opening or slit in the curtain. Preferably, there are two, three, four or more such releasable fasteners  38 , two being shown. These fasteners may comprise a standard type releasable zipper, preferably of plastic material, as used with outer coats such as Parkas, or may comprise any other type of releasable connection suitable around wastewater. Preferably, this fastener comprises inter-engaging looped and hook strips as sold under the trademark VELCRO. One function of the releasable fastener(s) is to facilitate assembly and mounting of the curtain  14  around the biomedia; this enables the biomedia to be assembled in place and then the curtain hung around the biomedia. Another function is to provide ready access to the biomedia, particularly for inspecting the condition of the biomedia in use, and for repairing or replacing the biomedia. Although the releasable fastener  38  preferably runs the full length of the curtain, one or more of these fasteners may extend only for a portion of the length of the curtain  14 .  
         [0045]    [0045]FIG. 4 shows the attachment of the top of the curtain  14  to the hood  12 . One of the grommets  36  at the top curtain edge is engaged over an L-shaped peg or hook  40  mounted on the outside of the hood&#39;s downwardly extending sidewall  42 . Below the peg  40  are two spaced-apart releasable hook and looped connections  44 ,  46  (i.e. two pairs of VELCRO connections). These connections extend all the way around the hood  12 , and sealingly reinforce attachment of the top of the curtain  14  to the hood. Mounted on the hood between the two releasable connections  44 ,  46  is a sealing strip  48  of rubber or other gasket material, which also extends all around the hood  12 . This sealing strip  48  is resiliently compressible, and presses against the inside of the curtain to ensure both a watertight and an airtight joint between the curtain  14  and the hood  12 .  
         [0046]    [0046]FIG. 5 further illustrates the sealed connection of the upper portion of the curtain  14  to the hood  12 . As can be seen, there is a series of L-shape pegs  40  spaced apart around the hood. The vertically spaced-apart VELCRO strip connections  44 ,  46  can be seen above and below the continuous horizontal sealing strip  48 ; however, these strip connections and sealing strip are covered and concealed by the curtain  14 , but are shown through the curtain in FIG. 5 for the purpose of illustration.  
         [0047]    [0047]FIG. 6 illustrates the base receptacle  16  with a transparent sidewall  50 , to show the bottom of the curtain  14  extending down inside the base receptacle.  
         [0048]    [0048]FIG. 7 is a fragmentary section illustrating the sealing of the bottom of the curtain  14  to the inside of the base receptacle  16 . FIG. 8 is a plan view of the top of the base receptacle showing a flange around the outside of the base receptacle  16 . FIG. 7 is a section on the line  7 - 7  of FIG. 8 showing the outside flange  52  formed by two right angle steel bars  54 ,  56  bolted together at  57 . The lower bar  56  is welded to an outside upper lip  58  of the base receptacle  16 , and the upper bar  54  is bolted to a flat bar  60  on the inside of the curtain  14 , the curtain being sealingly clamped therebetween. In this way, a both water and air tight joint  62  is formed between the bottom of the curtain and the inside of the base receptacle. Adhesive may be used between all mating surfaces and, in addition, a gasket may be sandwiched between the two right angle bars  54 ,  56  to further ensure the tightness of joint.  
         [0049]    [0049]FIG. 9 illustrates in plan view an arrangement to make each releasable vertical connection  38  watertight and substantially air tight. At each connection  38 , the adjacent edges of the curtain  14  have right angle flanges  64 ,  66 . The facing sides of these flanges  64 ,  66  each carry a complementary strip  68  of VELCRO or the like, these flanges and strips extending the full vertical length of each curtain edge. On the inside of one curtain edge is welded at  69  a vertical sealing strip  70  of plastic material, e.g. PVC, this strip overlapping the other vertical curtain edge in a sliding and sealing relationship. When the two right angle flanges  64 ,  66  are physically brought together, the complimentary VELCRO strips  68  sealingly and securely engage, and the flap formed by the internal sealing strip  70  slides over and against the inner surface of the adjacent curtain portion  14  to seal the vertical releasable connection  38 .  
         [0050]    To assemble the curtain  14  around the biomedia  18 , the curtain is first supported by placing the grommets  36  over the hooks  40 , next the pair of VELCRO strips  46  are pushed together, then the pair of VELCRO strips  44  are connected so squeezing the gasket  48 . The bottom of the curtain is next connected and sealed to the base receptacle  16 . Finally, the releasable connection  38  is “zippered up” by pressing its VELCRO strips  68  together.  
         [0051]    [0051]FIG. 10 illustrates in side view a variant of the apparatus of FIG. 1 and shows an elongate treatment cell  10  surrounded by a curtain  14 . At the top of this cell  10  are five wastewater spray units  20  fed by a common supply pipe  72 . An elongate base receptacle  16 , with a downwardly inclined floor  74 , communicates with an external free-standing recirculation tank  76  and the spraying system  20  via pipes  78  and a pump system  80 , which effects recirculation of the wastewater through the cell  10 .  
         [0052]    [0052]FIG. 11 is an end view of the apparatus of FIG. 10, and shows four similar treatment cells  10  side by side. Each of these cells  10 , and the biomedia therein, is surrounded and contained by a separate curtain  14 . By viewing FIG. 11 in conjunction with FIG. 10, it will be realized that each cell  10  has an elongated rectangular horizontal cross-section.  
         [0053]    When the horizontal cross-section of a cell is circular, a rotating spray arm, such as shown and described in previously referenced U.S. Pat. No. 6,241,889, would be satisfactory. However, with non-circular horizontal cross-sections, for instance square, oval, and rectangular cross-sections, a circular spray pattern may leave corner and/or end sections starved of sprayed wastewater. To overcome this, stationary spray nozzles may additionally be placed in the corners, or any other area missed by the circular spray pattern. These stationary nozzles preferably should be given a pulsing action to provide the sprayed biomedia with an opportunity to receive alternately wastewater and air. Alternately, an oscillating spray system could be employed, preferably oscillating about a horizontal axis extending along the longer dimension of the cross-section, to spray the wastewater on the biomedia.  
         [0054]    [0054]FIG. 12 illustrates a base receptacle  16  for use with two treatment cells contained in a common surrounding curtain  14 . A partition  82  in the base receptacle  16  divides it into two separate drip trays  84 , each with its own set of outlet ports  86 . Each cell would be of square cross-section, whereas the single curtain wall would be of elongate rectangular cross-section.  
         [0055]    The above illustrates how the flexible curtain can be used to accommodate a variety of different shapes and arrangements. It does so in a way that is easy and inexpensive to install, relatively inexpensive to manufacture, may facilitate inspection of and access to the biomedia, and offers flexibility for different installation configurations. Further, these curtains are virtually maintenance free.  
         [0056]    [0056]FIG. 13 illustrates a frame or hanger  90  of looped cord biomedia. The hanger  90  has a plurality of discrete lengths  92  of looped cord biomedia extending between upper and lower pairs  94 ,  96  of hanger bars. The ends of the looped cord  92  are clamped between the respective pairs of bars. The pairs of bars are secured together by gluing, although this could be done by spot welding, the bars preferably being made of plastic material, for example ABS. Each end of each pair of bars has a pair of vertically spaced apart holes  98  for assembling a plurality of hangers together. When the pairs  94 ,  96  of bars are stretched apart, the lengths  92  of looped cord are spaced apart parallel to each other. The ends of the lengths of looped cord may be cut off flush with the adjacent pair of clamping bars, or may extend just beyond the bars. In the latter case, these extending ends may be heat-treated to cause them to fuse and form enlarged ends to more securely retain the ends from pulling through between the pair of clamping bars.  
         [0057]    These hangers are preferably manufactured as a series of links connected together and rolled up into a somewhat cylindrical roll. This is done by forming a warp of strands of looped cord biomedia and clamping a pair of hanger bars across this warp. The warp is then advanced the desired length for the hanger, and another pair of hanger bars clamped across the warp. Thereafter, the warp is advanced a short distance (e.g. 1 to 4 inches) and another pair of hanger bars clamped across the warp. This process continues with the hangers being reeled onto a spool as further hangers are formed. Individual hangers can be then cut from the spool as required. If the cutting is performed by a hot-air knife, the cut ends of the looped cord biomedia fuse as mentioned above.  
         [0058]    The looped cord biomedia is preferably made from knitted polyester or PVDC yarns. If the knitted structure enables the loops to be orientated in one axial direction, then in the grate, all such loops should be orientated in the same direction. This is enabled by having discrete cut lengths of biomedia formed from a warp. When assembled in a trickle tower, preferably all these loops would be orientated upwards.  
         [0059]    [0059]FIG. 14 shows a plurality of hangers  90  connected together to form a grate  28 . The upper pairs of hanger clamping bars  94  are rigidly bolted together by a pair of bolts  100  at each end through the holes previously mentioned. The lower pairs of hanger clamping bars  96  are similarly rigidly bolted together by bolts  102 . Spacers keep the pairs of bars correctly spaced apart.  
         [0060]    [0060]FIG. 15 shows in plan view the top of the grate  28 , although the pairs  94  of hanger bars are relatively longer than in FIG. 14. Eleven pairs of hanger bars are equally space apart by spacers  104  cut from square aluminum tubing. With this longer grate  28 , five pairs  100  of equally spaced-apart bolts pass through the bars and the spacers. In this way, the upper pairs  94  of bars are rigidly secured together; the lower pairs of bars of this grate are similarly rigidly secured together.  
         [0061]    [0061]FIG. 16 is an end view of the upper hanger bars of the grate in the direction of the arrow  16  in FIG. 15 (the lower hanger bars would look the same). The connecting and securing bolts  100  are tightened by their nuts  106  at the right end in FIG. 16. The hollow spacer tubes  104  extend vertically between the pairs of clamping bars for the full height thereof. FIG. 17 is an exploded view of FIG. 16, but also showing a strand  18  of looped cord biomedia clamped between the right outermost pair of clamping bars and extending downwardly therefrom; the upper cut end  108  of the strand  18  can be seen extending slightly above the hanger bars. Although the strands of biomedia are clamped between the pairs of clamping bars before these are assembled into a grate, the subsequent tightening of the grate bolts  100  further aids the securing of the biomedia ends. This improves the integrity of the grate  28 , and helps the biomedia strands to be able to carry heavier weights of biomass during operation when purifying wastewater.  
         [0062]    [0062]FIG. 18 shows an elevational side view of the grate of FIG. 15 with the beginning of the strands of biomedia  18  extending down from the upper bars  94 . A modification is also shown in the form of reinforcing anchor strips  110  between the nuts  106  and the outer plastic hanger bar.  
         [0063]    [0063]FIG. 19 is a view similar to the bottom portion of FIG. 2, but showing the lower anchoring and tensioning bolts  29  for the multiple grates  28  passing through the bottom  112  of the tank  16 . Also, this base tank  16  is of double width to function as a common tank for two side-by-side treatment cells, each cell having four grates  28 . When the through bolts  29  are tensioned by adjusting their nuts  114  underneath the raised bottom  112  of the tank, the lengths of looped cord biomedia (or any other biomedia strands employed) are tensioned and kept in spaced-apart parallel vertical alignment. The bolts  29  slidingly pass through tubes extending through and sealed to the bottom  112  of the base tank  16 . These tubes extend upwardly above the level of the wastewater in the base tank  16  as shown. This enables the lower ends of the grates to move downwardly slightly, should the biomedia stretch under the weight of the biomass forming on it during processing of the wastewater.  
         [0064]    [0064]FIG. 20 shows in greater detail the mounting of the upper ends of the grates  28  to the hood  12  at the top of each cell. Round headed suspension bolts  116 , extending upwardly between adjacent pairs  94  of hanger bars, are locked in place by clamping nuts  118 , and then pass upwardly through a cross beam  120  attached to the hood structure  12 . Individual lengths of angle bars  122  are disposed under the upper pairs  94  of clamping bars between the round bolt heads  124  and the lower edges of the clamping bars. Individual lengths of flat stock  126  are disposed between the upper edges of the clamping bars and the clamping nuts  118 . By adjusting uppermost tensioning nuts  128  of the suspension bolts  116 , the elevation of the grates  28 , and so the tension of the biomedia strips, can be adjusted. The leftmost grate is shown just before mounting to the hood. Another way of mounting the upper end of the curtain  14  on the hood is shown. The curtain  14  extends the full height of the hood  12 , with the upper edge  130  of the curtain being hooked-shaped and hooked over the top of the hood. This hooked upper curtain edge  130  slidingly engages a rail running around the top of the hood.  
         [0065]    It will be appreciated, that not only does the curtain arrangement of the present invention enable flexibility and economy in designing and building wastewater trickle towers, but the biomedia grate of the present invention adds further flexibility and economy. The new grates can readily be collapsed and packed in a shipping box for shipping and storage. When needed for service, they are simply lifted out of the box and their upper ends readily secured to the hoods; thereafter, the lower ends can readily be installed in the base tanks. Any needed separation of the biomedia strands can easily be accomplished through the openable accesses in the curtains. Thereafter, the lengths of biomedia strands can readily be correctly tensioned.  
         [0066]    It will also be realized, that the sealing of the curtain at the top and bottom of the cells enables the air or other gas content in the cells to be more accurately controlled, thereby improving operating conditions.  
         [0067]    The above described embodiments, of course, are not to be construed as limiting the breadth of the present invention. Modifications, and other alternative constructions, will be apparent which are within the spirit and scope of the invention as defined in the appended claims.  
         [0068]    For example, instead of using one or more releasable fasteners, the edges of the curtain may be more permanently attached together during or after installation. This could be done by welding, sewing, stapling, etc. Although this would hamper subsequent access to the biomedia, it would still enable the advantages of flexibility of shape and cost saving to be obtained.