Abstract:
A drum filter assembly comprising a hollow drum filter having a longitudinal axis and an outer filter screen or mesh material, the drum filter being supported on external rollers for rotation about its longitudinal axis and an inlet for introducing liquid to be filtered into the interior of the drum filter. Rotation of the drum filter is effected by the liquid flowing into the drum filter. Alternatively, the drum filter may be driven by an external motor.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
   This application is a division of U.S. application Ser. No. 10/478,210, filed Nov. 28, 2003, which matured into U.S. Pat. No. 7,029,577, on Apr. 18, 2006. 

   BACKGROUND OF THE INVENTION  
   This invention relates to a drum filter assembly which is suitable for use in aquaculture systems but which may be used in any other water treatment application. 
   Aquaculture has commonly been conducted by growing fish, prawns and other marine invertebrates in outdoor ponds. The ponds however eventually become polluted because faeces, uneaten food and algae work their way to the bottom of the ponds. This makes the ponds almost impossible to clean. In addition large quantities of valuable water are required to keep these systems functional. Other disadvantages are also associated with outdoor aquaculture systems. For example pests can eat stock, adverse weather conditions such as floods can cause stock loss by washing the stock away and very hot weather can cause growth of algal blooms which can kill the stock. In addition in very hot or very cold weather, the stock will stop growing. Muddy waters or disturbed water can also cause the stock to have an unpalatable taste. 
   In order to overcome the above disadvantages, indoor commercial aquaculture systems were introduced where fish or other marine invertebrates are grown in tanks placed in large buildings or sheds. 
   A disadvantage of the known systems is that the buildings or sheds housing the aquaculture system resemble a maze of pipes and plumbing as water is pumped between the system components such as tanks, filters, biological filters, foam fractionators, ultraviolet water treatment units and other water treatment components. These components are individual components which have to be set up in different parts of the building. 
   Drum filters have been a part of the aquaculture systems for filtering the water of fine waste particles created from waste food, faeces, and other extraneous matter. The majority of filters are electric motor driven off central drive shafts with bearings on which the drum filter is supported for rotation. In most cases the cleaning takes place through a centre mounted vertical disc through which the water must pass. The drum filters are separate units and include an outer housing which is specifically designed to hold the filter and its supporting components and to also hold the water. Water inlets and outlets must also be provided along with special float switches to activate a cleaning process when the water level rises. 
   As a general rule, during cleaning the water flow is stopped or bypassed which allows uncleaned water back into the fish tanks. If the water is stopped for any length of time, it can be very detrimental to the fish stock as in times of heavy stock loading, the fish can only stay alive for around six minutes before fatalities begin to occur. Another major drawback is that if a bearing or another major mechanical failure happens, removal the drum filter and all of the fittings is extremely time consuming and in many cases can lead to total stock losses. Cleaning of the current drum filters in any event is difficult as easy access cannot be had to the interior of the drum. 
   SUMMARY OF THE INVENTION  
   The present invention aims to provide an improved drum filter particularly suited for use in aquaculture systems but which may also be used in other water treatment apparatus. Other objects and advantages of the invention will become apparent from the following description. 
   The present invention thus provides in a first preferred aspect a drum filter assembly comprising a hollow drum filter, said drum filter having a longitudinal axis and an outer filter screen or mesh material, means externally of said drum filter for supporting said drum filter for rotation about its longitudinal axis, an inlet for introducing liquid to be filtered into the interior of said drum filter, and means for rotating said drum filter about said longitudinal axis. 
   Preferably cleaning means are provided externally of the drum filter for cleaning the filter screen or mesh material. The cleaning means may comprise means above the drum filter for spraying water against the screen or mesh material. The means for spraying water may comprises an elongated feed tube extending longitudinally of the drum filter, the feed tube having one or more water spray outlets. The cleaning means may additionally or alternatively comprises means for applying pressurized air against the screen or mesh material. The means for applying pressurized air may comprises an elongated air tube extending longitudinally of the drum filter, the air tube having one or more pressurized air outlets. 
   Means are preferably provided internally of the drum filter for catching and collecting materials dislodged from the filter screen or mesh material by the cleaning means. The means for catching dislodged materials comprises a hopper internally of and extending longitudinally of the drum filter. The hopper may communicate with a waste line for directing those materials to waste. The hopper may extend beyond one or opposite ends of the drum to ensure that substantially all material dislodged from the drum is collected. 
   The inlet suitably also comprises a supply duct having one or more liquid outlets. The supply duct may extend longitudinally of the drum filter. In one form, the liquid outlets are preferably provided within the drum filter. The liquid outlets may be defined by radially extending duct members. The supply duct may have a baffle beyond the duct members to prevent liquid passing out of the drum filter. The hopper may communicate with an extending portion of the supply duct beyond the baffle which is connected to or communicates with a waste. 
   The external support means for the drum filter may comprise rotatable rollers which support the drum filter such that its longitudinal axis is substantially horizontal. 
   Preferably the drum filter includes a pair of end members having a circular periphery supported on the rollers for rotation about the longitudinal axis. At least one of the end members may comprise an annular member having a central opening comprising the inlet. Alternatively the end members may comprise a circular member. 
   Preferably the drum filter has a plurality of rotation members adapted to cooperate with a flowing liquid to effect rotation of the drum filter. The rotation members may be provided internally of the drum filter. Preferably the rotation members comprise circumferentially spaced members. 
   In another form the rotation members are provided on the exterior of the drum filter. 
   The flowing liquid suitably comprises liquid flowing from the one or more liquid outlets. 
   In another driving arrangement, means may be provided for rotatably driving at least one said roller to effect rotation of said drum filter. Alternatively means coupled to the drum filter may be provided for directly rotating the drum filter. The means for rotating the drum filter may comprise a motor coupled to the drum filter. 
   The drum filter suitably includes a plurality of circumferentially spaced members extending longitudinally between the end members, said filter screen or mesh material being supported by the circumferentially spaced members. The screen or mesh material thus extends around the periphery of the drum filter. The circumferentially spaced members may comprise ribs which extend between and are fixed to the end members of the drum filter. Where the drum filter is driven by liquid flowing from the liquid outlets, the liquid outlets are preferably positioned adjacent to the ribs. The outlets are suitably spaced along the supply duct. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     In order that the invention may be more readily understood and put into practical effect reference will now be may to the company drawings which illustrate the preferred embodiments of the invention and wherein: 
       FIG. 1  illustrates in perspective view, a building module defining an aquaculture system incorporating a drum filter according to a first embodiment of the present invention; 
       FIG. 2  is a sectional elevational view of the building of  FIG. 1 ; 
       FIG. 3  is a sectional plan view of the building of  FIG. 1 ; 
       FIG. 4  illustrates the building of  FIG. 1  with the end flaps open; 
       FIG. 5  illustrates the layout of the plumbing pipes of the system incorporated in the base or foundation of the building module; 
       FIG. 6  is a perspective view of the drum filter for use in the system and its manner of support; 
       FIG. 7  is a side view showing the drum filter and associated feed, discharge and cleaning components; 
       FIG. 8  is an end view in the direction A of  FIG. 7 ; 
       FIGS. 9 and 10  illustrate in side and end views a further embodiment of drum filter for use in the aquaculture system of the invention; and 
       FIGS. 11 and 12  illustrate alternative drive systems for the drum filter. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
   Referring to the drawings and firstly to  FIGS. 1 to 4 , there is illustrated an aquaculture system  10  in accordance with an embodiment of the invention in the form of a modular building  11  comprising and defining a main chamber  12  for holding fish or marine invertebrates, a swirl chamber  13  which serves as a primary filter and a biological filter-drum or screen filter chamber  14  of a secondary filter. The chambers  12 ,  13  and  14  have their bases at substantially at the same level however the water level in each chamber is controlled such that the level in chamber  14  is less than the level in chamber  13  and the level in chamber  13  is less than the level in chamber  12 . This then allows flow of water from the main chamber to the swirl chamber  13  and then to the chamber  14  under the influence of gravity without pumping. The building module  11  also defines a biological filter tank  15  which is elevated and located above the main chamber  12 . Opposite end integral hip roof and wall sections  16  and  17  extend from opposite sides of the tank  15  and over the main chamber  12  and swirl chamber  13  and filter chamber  13  respectively to define enclosed air spaces over the main chamber  12  and chambers  13  and  14 . The building  11  may be constructed of any suitable materials such as steel, timber, fiberglass or any other mouldable materials, or any other materials however the preferred material of construction is concrete suitably a concrete which is waterproof and provides sufficient strength to the building  11  and additionally has high insulation properties such that no additional insulation is required and further facilitates moulding of the tank  12  and chambers  13 , 14  and  15 . The main chamber  12  and chambers  13  and  14  may be formed as one moulding indicated generally at  18 , and the tank  15 , and roof and wall sections  16  and  17  as separate mouldings which are then assembled and jointed to the lower moulding  18 . Opposite end walls of the tank  15  and roof and wall sections  16  and  17  are thus aligned with the opposite side walls of the moulding  18  and the outer ends walls of the roof and wall sections  16  and  17  are aligned with opposite end walls of the moulding  18 . The opposite end walls of the roof and wall sections  16  and  17  are closed by hinged panels  19  which may be pivoted upwardly as shown in  FIG. 4  to provide access at one end to the chamber  12  or at the other end to the chambers  13  and  14 . The biological filter tank  15  is also closed by upper lid panels  20  which are hingedly mounted by central hinges  21  to enable them to be lifted to provide access to the interior of the chamber  15 . It will be apparent that when they panels  19  are closed, the building  11  defines a fully enclosed air space over the chambers which facilitates control of air and water temperature as described further below. 
   The main chamber  12  is of a generally rectangular or square configuration with the corners thereof being truncated as at  22 . A spillway  23  is provided on one side of the chamber  12  and at an elevated location to convey water in the chamber  12  above the level of the spillway  23  into the swirl chamber  13 . This acts as a skimmer to remove any floating scum or other materials from the surface of the water in the chamber  12 . A screen  24  of mesh-like form is provided across the spillway  23  to prevent fish from escaping from the main chamber  12  into the swirl chamber  13 . The main chamber  12  also includes a central drain outlet  25  which communicates through a passage  26  with the periphery of the base of the swirl chamber  13  at  27  which directs water from the chamber  12  into the chamber  13  in a generally circumferential direction such as to effect anti-clockwise swirling motion of water in the chamber  13 . The passage  26  carries fish and food waste from the main chamber  12  into the swirl chamber  13  without the use of pumping equipment which may breakup particles within the chamber  12 . The passage  26  may also have a branch line  28  through which water may be drained from the chamber  12  under the control of a valve  29  externally of the building module  10  (see  FIG. 5 ). 
   The main chamber  12  also includes in the outer pair of truncated corners  22 , a pair of foam fractionators  30  for oxygenating and cleaning the water in the main chamber  12 . Associated with each foam fractionator  30  is an ultraviolet unit  31  for killing pathogens in the water and optionally one or more ozone reactor or generator units  32  for introducing ozone into the water in the fractionator  30  for sterilizing the water. 
   The foam fractionator  30  communicates with the main chamber  12  via the ultraviolet unit  31  which houses an elongated ultraviolet light generator whereby water before passing into the foam fractionator  30  is exposed to ultraviolet light. 
   The ozone generator unit  32  houses an ozone reactor or generator o inject ozone into the water in the foam fractionator  30  for passage as bubbles upwardly through water in the foam fractionator  30  to expose the water therein to ozone. 
   Thus water for treatment in the foam fractionator  30  initially passes through the ultraviolet unit  31  where it is exposed to ultraviolet light which will destroy pathogens in the water. Air supplied to the foam fractionator  30  exits as bubbles in the water which pass upwardly through the fractionator  30  to carry dirt and fat particles or other impurities in the water to the surface. In addition, the ozone reactor or generator unit  32  creates bubbles of ozone which also pass upwardly through the fractionator  31  to sterilize and clean the water. 
   The swirl chamber  13  is of a generally hexagonal shape to assist in the swirling of water flow and receives water through the spillway  23  from the main chamber  12  which carries floating wastes into the chamber  13 . The spillway  23  enters the chamber  13  at the periphery thereof and at a generally tangential orientation to induce into the chamber  13  a circulating or swirling flow. The outlet  27  which communicates with the base of the chamber  12  also is directed generally circumferentially or tangentially to induce swirling of flow of water in the chamber. As the water level in the chamber  13  is below that in the chamber  12 , water will flow from the chamber  12  into the chamber  13  from the top and bottom thus carrying wastes into the chamber  13 . The swirling flow of water will cause heavy particles fish and foot waste to collect centrally at the base of the chamber  13 . 
   A water outlet  33  extends through a side wall  34  of the chamber  13  to direct water from the chamber  13  into the filter chamber  14 , the wall  34  being common to both chamber  13  and chamber  14 . The outlet  33  is below the level of the spillway  23  and thus sets the normal level of water in the chamber  13  below the level in the main chamber  12 . A feed pipe  35  is releasably coupled to the outlet  33  through a male/female connection and extends centrally and coaxially through a drum filter  36  for the fine filtering of the water flowing in from the swirl chamber  13 . The drum filter  36  as more clearly shown in  FIG. 6  includes a pair of annular end members  37  joined by a plurality of longitudinally extending ribs  38  which are spaced around a circumferential line arranged midway between the inner and outer diameters of the annular members  37 . The ribs  38  which comprise flat strip-like members have their major dimension lying in substantially radially extending planes as is apparent in  FIG. 8  and support a fine filtering screen or mesh  39  which is wrapped circumferentially around the ribs  38  and which is secured to the ribs  38  such as by stapling. Each annular end member  37  is supported by and runs in a pair of free running grooved guide wheels or rollers  40  which are rotatably mounted to a cradle or baffles  41  in the chamber  14  to support the drum filter  36  for rotation about a substantially horizontally axis which extends longitudinally of the drum filter  36 . As illustrated in  FIGS. 6 to 10 , each guide wheel or roller  40  is provided with an annular groove extending around its periphery in which the peripheral portion of an end member  37  of the drum filter  36  locates. 
   The incoming water through the feed pipe  35  as well as being fed to the drum filter  36  for filtering is also used to rotatably drive the drum filter  36 . For this purpose, a series of spaced apart radial ducts  42  extend from the feed pipe  35  and open adjacent the ribs  38 . A baffle  43  in the feed pipe  35  prevents water passing straight through the pipe  35 . When water flows into the feed pipe  35  and out through the ducts  42  as at  44 , it applies a force to the respective ribs  38  to thereby cause rotation of the drum filter  36 . In addition, water flowing out of the ducts  42  is filtered by passage through the filter screen  39  as at  45 . The end members  37  define through their annular configuration an inner annular lip  46  spaced radially inwardly of the filter screen  36 . The lip  46  prevents any water from running out of the open ends of the drum filter  36  before passing through the screen material  39 . In the extreme case of the water level rising within the drum filter  36 , it cannot jam up the drum filter  36  by over filling as it will simply cascade over the end lips  46  and thus will not prevent the drum filter  36  from rotating. 
   For cleaning of the filter screen  39 , a pair of ducts  47  and  48  are provided above the drum filter  36  to extend longitudinally thereof. One duct  47  is connected to a water pump  49  submerged in an end section  50  of the chamber  14  and has a plurality of spaced nozzles  51  through which water can be directed towards the screen  39  to wash the screen  39 . The other duct  48  is also provided with a plurality of spaced nozzles  52  and is connected to an air pump  53 . Timers are associated with the water pump  49  and air pump  53  to operate the pumps at regular intervals to force pressurised water and air through the nozzles  51  and  52  and impact against the screen  39  to clean materials gathering on the screen  39 . Materials displaced from the screen  39  are collected in a waste collecting trough  54  which is of a hopper-like V-shaped cross section and which is arranged to extend within the drum filter  36  and centrally thereof beneath the cleaning water and air ducts  47  and  48 . The waste collector trough  54  receives materials displaced from the filter screen  39  along with the water forced through the screen  39 . The waste collector trough  54  sits within a longitudinally extending slot  55  in the feed pipe  35  and projects out of each end of the filter drum  36 . The opposite ends  56  of the trough  54  are flared outwardly in a funnel-like configuration to catch all materials washed from the drum filter  36 . The end  56  adjacent the section  50  of the chamber  13  extends beyond the baffle  43  and has an opening  57  therein which allows water and fine materials to be discharged into an extended portion  58  of the feed pipe  35  beyond the baffle  43 . The end of the extending portion  58  of the feed pipe  35  directs the collected waste into a drainpipe  59 , which also serves as an overflow drain if the level of water in the chamber  13  exceeds a predetermined level. 
   The cleaning ducts  47  and  48  provide the advantage of enabling cleaning of the filter screen  39  while the drum filter  36  it is running at full capacity without stopping of water flow, or for any need to bypass the system. As the drum filter  36  rotates, air or water or both dislodges any fine material clogging the screen  36  and blows or forces it into the V section collector trough  54  for passage into the feed pipe section  58  and then to the drain pipe  59 . Water flowing into the drainpipe  59  may be simply discharged to waste. Optionally, a filter bag  60  may be connected to the pipe section  58  via a valve for collecting fines and filtering the collected waste water. The bag  60  may be removed and cleaned or replaced at regular intervals or when clogged or filled with waste. Alternatively or additionally a filter device may be provided in the drainpipe  59  so as to enable waste water to be recycled. 
   The drum filter  36  may be easily removed by detaching the feed pipe  35  from the outlet  33  and when the pipe  35  is detached, the V-shaped waste collector trough  54  is also detached being supported by the pipe  35 . The cleaning water ducts  47  and air ducts  48  can be simply folded down to opposite sides of the filter drum  36 . After removal of the feed pipe  35  and trough  54 , the entire drum filter  56  can be removed. This means that one drum filter  56  can be removed and another complete drum filter  56  installed quickly if desired. 
   Water filtered by the drum filter  56  and flowing through the filter screen  59  as at  45  passes to the lower portion of the chamber  14  which contains a bio-filter medium  61  to provide a surface for bacteria to live on. The chamber  14  is also provided with drains  62  being connected to waste via a common duct  63  and valve  64  which can be opened as and when required for draining or cleaning the chamber  14  (see  FIG. 5 ). 
   One or more submergible pumps  65  are provided in the end section  50  of the chamber  14  to pump water from the chamber  14  to the main biological tank  15  via a duct  66 . The pumps  65  operate continuously and cause the circulating flow of water through the whole system  10  and further ensure that the water pumped out of the chamber  14  is the same or greater than water entering the chamber  14  through the feed pipe  35  to thereby maintain the level of water in the chamber  14 . The pumps  65  may also be used to augment the cleaning of the screen  39  of the drum filter  36  through a branch line which can be opened to connect the pump or pumps  65  to the spraying duct  47 . 
   The base of the tank  15  also includes an inclined section through which one or more water outlets  67  pass from through which water from the tank  15  is returned or recirculated to the main chamber  12  (see  FIG. 3 ). 
   To control the temperature of air within the building module  11 , a reverse cycle air conditioner  68  is provided through a wall in the section  16  of the building  11  over the main chamber  12  to enable temperature within the building module to be controlled by heating or cooling. The conditioned air as well as circulating above the chamber  12  also passes through the air ducts  112  into the region above the swirl chamber  13  and drum filter chamber  14 . This maintains a substantially constant temperature within the sections of the building module  11 . The air conditioner  68  as well as controlling the air temperature within the building module  11  also controls the temperature of the water circulating through the system  10  as the air pumped by air pump/s through the water in the foam fractionator  30  and bacterial filter tank  15  is derived from the air within the building module  11 . 
   Referring now to  FIGS. 9 and 10 , there is illustrated a further form of drum filter arrangement for use in the aquaculture system of the invention. The drum filter  69  is of similar construction to the filter  36  of  FIG. 6  in that it includes annular end walls  70  joined by longitudinally extending ribs  71  around which a filter fabric or material  72  is wrapped and secured. The filter  69  is also supported for rotation on spaced wheels  73  mounted to baffles  74  and the drum filter  69  is supplied with water from the swirl chamber in by a feed tube  75  in a similar manner to that described with reference to  FIG. 7  except that openings  76  in the tube  75  permit water to pass downwardly from the tube  75  through the filtering fabric  72  of the filter  69 . To effect rotation of the drum filter  69 , one or both ends walls  70  are provided with a number of circumferentially spaced members  77  which may comprise extension of the ends of the ribs  71  and be shaped to cooperate with water supplied through a feed tube  78 . This action effects rotation of the drum filter  69  to continuously present a new section of filter fabric  72  to the water exiting the openings  76 . As with the embodiment of  FIG. 6 , air and water cleaning tubes  79  and  80  are provided for spraying at timed intervals water or air through the fabric  72  for collection in the trough  81  for direction to the waste pipe  59 . 
   As an alternative driving arrangement shown in  FIG. 11 , one or more of the guide wheels  73  may be driven by an electric or hydraulic motor  82  via an endless belt or chain  83  to cause rotation of the driven wheel  73  and thus the drum filter  69  to continuously present a new filtering surface to incoming water. In yet an alternative arrangement shown in  FIG. 12 , the drum filter  69  may be directly driven by being coupled through a wheel or pulley  84  coaxial with the drum filter  69  and a drive belt or chain  85  to a drive motor  86 . 
   The drum filters described in the above embodiments do not need or use a vertical screen which reduces the area of mesh for the water to strain through, have no centre shaft or bearings, and do not need a special outer housing. The drum filters can be mounted on a simple cradle and suspended over the fish tank if required, and can clean themselves whilst continuing to operate at full capacity. As the drum filters do not have a shaft, components can easily fitted within the interior of the filter. By incorporating the use of compressed air as well as water, the drum filter can clean continually or spasmodically which ever is required. The water and air bars can be set side-by-side for individual use or incorporated into one. Other gases may be used for cleaning provided they are non-toxic or polluting. 
   The drum filter systems described above may of course be used in aquaculture systems other than those described or in any other filtering application.