Abstract:
An anaerobic water purification system including an anaerobic water purification unit receiving water to be treated and providing an anaerobic-treated water output and biomass carriers for supporting anaerobic microorganisms in the anaerobic water purification unit.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to U.S. Provisional Patent Application Ser. No. 61/252,265, filed Oct. 16, 2009 and entitled “DYNAMIC ANAEROBIC AEROBIC (DANA) REACTOR” and U.S. Provisional Patent Application Ser. No. 61/366,576, filed Jul. 22, 2010 and entitled “UTILIZATION OF BIOMASS CARRIERS IN ANAEROBIC REACTORS”, the disclosures of which are hereby incorporated by reference and priority of which are hereby claimed pursuant to 37 CFR 1.78(a) (4) and (5) (i). 
     
    
       [0002]    Reference is also made to the following patents and patent applications, owned by assignee, the disclosures of which are hereby incorporated by reference: 
         [0003]    U.S. Published Patent Application No. 2009/0211972; 
         [0004]    European Published Patent Application Nos. 1401775 and 2049443; and 
         [0005]    PCT Published Patent Application No. WO 2009/10718. 
       FIELD OF THE INVENTION 
       [0006]    The present invention relates to water treatment generally and more particularly to waste water treatment. 
       BACKGROUND OF THE INVENTION 
       [0007]    The following publications are believed to represent the current state of the art: 
         [0008]    U.S. Pat. Nos.: 3,168,465; 4,632,758; 4,780,198; 4,919,815; 5,196,111; 5,578,214; 5,788,838; 5,855,785; 6,063,273; 6,623,640; 6,758,886 and 7,022,226; 
         [0009]    European Patent No.: 0 382 340; 
         [0010]    http://www.paques.nl/?pid=245&amp;parentid=41, which describes the Paques BIOPAQ® UASB+ system; and 
         [0011]    http://www.paques.nl/?pid=44&amp;parentid=41, which describes the Paques BIOPAQ® UBOX system. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention seeks to provide improved systems and methodologies for water treatment. 
         [0013]    There is thus provided in accordance with a preferred embodiment of the present invention an anaerobic water purification system including an anaerobic water purification unit receiving water to be treated and providing an anaerobic-treated water output and biomass carriers for supporting anaerobic microorganisms in the anaerobic water purification unit. Preferably, the system also includes a gas collection volume located above the anaerobic water purification unit for collecting gas produced by the anaerobic water purification unit. 
         [0014]    In accordance with a preferred embodiment of the present invention, the gas collection volume is located in a headspace above the anaerobic water purification unit. Additionally, the system also includes gas supply functionality for supplying gas to the anaerobic water purification unit for causing relative movement of the biomass carriers. Preferably, the gas supply functionality supplies gas received from the gas collection volume. 
         [0015]    Preferably, the anaerobic water purification unit receives water to be treated at a location near the bottom thereof. Alternatively, the anaerobic water purification unit receives water to be treated at a location near the top thereof 
         [0016]    There is also provided in accordance with another preferred embodiment of the present invention an anaerobic/aerobic water purification system including an anaerobic water purification subsystem receiving water to be treated and providing an anaerobic-treated water output, and an aerobic water purification subsystem, integrated with the anaerobic water purification subsystem, receiving the anaerobic-treated water output and providing an anaerobic- and aerobic-treated water output. 
         [0017]    Preferably, the aerobic water purification subsystem is located physically above the anaerobic water purification subsystem. Additionally, the anaerobic water purification subsystem includes biomass carriers for supporting anaerobic microorganisms. 
         [0018]    In accordance with a preferred embodiment of the present invention, the system also includes a gas collection volume located above the anaerobic water purification subsystem and below the aerobic water purification subsystem for collecting gas produced by the anaerobic water purification subsystem. Preferably, the gas collection volume is located in a headspace above the anaerobic water purification subsystem. 
         [0019]    Preferably, pressure created by the accumulation of the gas produced by the anaerobic water purification subsystem is operative to pump the anaerobic-treated water output from the anaerobic water purification subsystem to the aerobic water purification subsystem. Additionally, the system also includes gas supply functionality for supplying gas to the anaerobic water purification subsystem for causing relative movement of the biomass carriers. Preferably, the gas supply functionality supplies gas received from the gas collection volume. 
         [0020]    In accordance with a preferred embodiment of the present invention, the aerobic water purification subsystem includes moving bed biofilm reactor functionality. Preferably, the anaerobic water purification subsystem receives water to be treated at a location near the bottom thereof. 
         [0021]    There is further provided in accordance with yet another preferred embodiment of the present invention an anaerobic/aerobic water purification system including an anaerobic water purification subsystem receiving water to be treated, including biomass carriers for supporting anaerobic microorganisms, and providing an anaerobic-treated water output, and an aerobic water purification subsystem, receiving the anaerobic-treated water output and providing an anaerobic- and aerobic-treated water output. Preferably, the aerobic water purification subsystem is located physically above the anaerobic water purification subsystem. 
         [0022]    In accordance with a preferred embodiment of the present invention, the system also includes a gas collection volume located above the anaerobic water purification subsystem and below the aerobic water purification subsystem for collecting gas produced by the anaerobic water purification subsystem. Preferably, the gas collection volume is located in a headspace above the anaerobic water purification subsystem. 
         [0023]    Preferably, pressure created by the accumulation of the gas produced by the anaerobic water purification subsystem is operative to pump the anaerobic-treated water output from the anaerobic water purification subsystem to the aerobic water purification subsystem. Additionally, the system also includes gas supply functionality for supplying gas to the anaerobic water purification subsystem for causing relative movement of the biomass carriers. Preferably, the gas supply functionality supplies gas received from the gas collection volume. 
         [0024]    In accordance with a preferred embodiment of the present invention, the aerobic water purification subsystem includes moving bed biofilm reactor functionality. Additionally or alternatively, the aerobic water purification subsystem includes moving bed clarifying reactor functionality. 
         [0025]    Preferably, the anaerobic water purification subsystem receives water to be treated at a location near the bottom thereof. Alternatively, the anaerobic water purification subsystem receives water to be treated at a location near the top thereof 
         [0026]    There is yet further provided in accordance with still another preferred embodiment of the present invention an anaerobic/aerobic water purification system including an anaerobic water purification subsystem receiving water to be treated and providing an anaerobic-treated water output, an aerobic water purification subsystem, located physically above the anaerobic water purification subsystem, receiving the anaerobic-treated water output and providing an anaerobic- and aerobic-treated water output, and a gas collection volume located above the anaerobic water purification subsystem and below the aerobic water purification subsystem for collecting gas produced by the anaerobic water purification subsystem. 
         [0027]    Preferably, the gas collection volume is located in a headspace above the anaerobic water purification subsystem. Additionally, pressure created by the accumulation of the gas produced by the anaerobic water purification subsystem is operative to pump the anaerobic-treated water output from the anaerobic water purification subsystem to the aerobic water purification subsystem. 
         [0028]    In accordance with a preferred embodiment of the present invention, the system also includes gas supply functionality for supplying gas to the anaerobic water purification subsystem for causing relative movement of the biomass carriers. Preferably, the gas supply functionality supplies gas received from the gas collection volume. 
         [0029]    Preferably, the aerobic water purification subsystem includes moving bed biofilm reactor functionality. Additionally, the aerobic water purification subsystem includes moving bed clarifying reactor functionality. Preferably, the anaerobic water purification subsystem receives water to be treated at a location near the bottom thereof 
         [0030]    There is also provided in accordance with another preferred embodiment of the present invention an anaerobic/aerobic water purification method including anaerobic water purification providing an anaerobic-treated water output, and aerobic water purification, integrated with the anaerobic water purification, receiving the anaerobic-treated water output and providing an anaerobic- and aerobic-treated water output. Preferably, the anaerobic water purification utilizes biomass carriers for supporting anaerobic microorganisms. 
         [0031]    Preferably, the method also includes collecting gas produced by the anaerobic water purification in a headspace. Additionally, the aerobic water purification includes moving bed biofilm reactor functionality. Additionally or alternatively, the aerobic water purification includes moving bed clarifying reactor functionality. 
         [0032]    There is further provided in accordance with yet another preferred embodiment of the present invention an anaerobic/aerobic water purification method including anaerobic water purification utilizing biomass carriers for supporting anaerobic microorganisms and providing an anaerobic-treated water output, and aerobic water purification receiving the anaerobic-treated water output and providing an anaerobic- and aerobic-treated water output. 
         [0033]    In accordance with a preferred embodiment of the present invention, pressure created by the accumulation of the gas produced by the anaerobic water purification is operative to pump the anaerobic-treated water output from the anaerobic water purification to the aerobic water purification. Preferably, the method also includes collecting gas produced by the anaerobic water purification in a headspace. 
         [0034]    Preferably, the method also includes supplying gas to the anaerobic water purification subsystem for causing relative movement of the biomass carriers. Preferably, the supplying gas utilizes gas received from the headspace. 
         [0035]    In accordance with a preferred embodiment of the present invention, the aerobic water purification includes moving bed biofilm reactor functionality. Additionally or alternatively, the aerobic water purification includes moving bed clarifying reactor functionality. 
         [0036]    There is also provided in accordance with another preferred embodiment of the present invention an anaerobic/aerobic liquid purification system including an anaerobic liquid purification subsystem including an inlet for receiving liquid to be treated and an outlet providing an anaerobic-treated liquid output, and an aerobic liquid purification subsystem including an inlet for receiving the anaerobic-treated liquid output and an outlet for providing an anaerobic- and aerobic-treated liquid output, and wherein the inlet of the aerobic liquid purification subsystem is connected to the outlet of the anaerobic liquid purification subsystem. 
         [0037]    In accordance with a preferred embodiment of the present invention, pressure in the anaerobic liquid purification subsystem is operative to pump the anaerobic-treated liquid output from the anaerobic liquid purification subsystem to the aerobic liquid purification subsystem. Preferably, the system also includes a gas collection volume located in a headspace above the anaerobic liquid purification subsystem for collecting gas produced by the anaerobic liquid purification system. 
         [0038]    Preferably, the aerobic liquid purification subsystem is located above the anaerobic liquid purification subsystem. Additionally, the anaerobic liquid purification subsystem includes biomass carriers for supporting anaerobic microorganisms. 
         [0039]    Preferably, the system also includes a gas supply mechanism for supplying gas to the anaerobic liquid purification subsystem. Preferably, the gas supply mechanism is connected to the gas collection volume. 
         [0040]    In accordance with a preferred embodiment of the present invention, the aerobic liquid purification subsystem further includes moving bed biofilm reactor functionality. Additionally, the system also includes liquid recirculation functionality. 
         [0041]    There is further provided in accordance with yet another preferred embodiment of the present invention an anaerobic/aerobic liquid purification method including anaerobic purifying of liquid in an anaerobic liquid purification subsystem provided with an anaerobic-treated liquid outlet, aerobic purifying of liquid in an aerobic liquid purification subsystem provided with an inlet for receiving the anaerobic-treated liquid, and integrating the subsystems by connecting the outlet of the anaerobic subsystem to the inlet of the aerobic subsystem. 
         [0042]    In accordance with a preferred embodiment of the present invention, pressure in the anaerobic liquid purification subsystem is operative to pump anaerobic-treated liquid output from the anaerobic liquid purification subsystem to the aerobic liquid purification subsystem. Preferably, at least one of the anaerobic purifying and the aerobic purifying utilizes biomass carriers for supporting microorganisms. 
         [0043]    Preferably, at least one of the aerobic liquid purification subsystem and the anaerobic liquid purification subsystem includes moving bed biofilm reactor functionality. Additionally, the method also includes supplying gas to the anaerobic liquid purification subsystem for causing relative movement of the biomass carriers. Preferably, the supplying gas utilizes gas produced in the anaerobic liquid purification subsystem. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
           [0045]      FIG. 1  is a simplified, partially pictorial, partially schematic, illustration of a synergetic anaerobic/aerobic water purification system constructed and operative in accordance with a preferred embodiment of the present invention; 
           [0046]      FIG. 2  is a simplified illustration of one embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 ; 
           [0047]      FIG. 3  is a simplified illustration of another embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 ; 
           [0048]      FIG. 4  is a simplified illustration of yet another embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 ; 
           [0049]      FIG. 5  is a simplified illustration of still another embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 ; and 
           [0050]      FIGS. 6 &amp; 7  show experimental results of use of the system in accordance with the embodiment of  FIG. 1  of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0051]    Reference is now made to  FIG. 1 , which is a simplified, partially pictorial, partially schematic, illustration of a synergetic anaerobic/aerobic water purification system constructed and operative in accordance with a preferred embodiment of the present invention. As seen in  FIG. 1 , there is provided an integrated reactor, designated generally by reference numeral  10 , which includes an anaerobic water purification subsystem  12  and an aerobic water purification subsystem  14 . 
         [0052]    Anaerobic water purification subsystem  12  comprises an upper zone  16  which includes a plurality of biomass carriers  18 , and a lower zone  20  located below upper zone  16 . 
         [0053]    In the embodiment of  FIG. 1 , anaerobic water purification subsystem  12  may be configured to operate as a Moving Bed Biofilm Reactor (MBBR) wherein biomass carriers  18  are continuously circulated. Alternatively, biomass carriers  18  are periodically circulated or vibrated. Preferably, biomass carriers  18  have a density which is lower than the density of water. Alternatively, biomass carriers have a density which is equal to or greater than the density of water. 
         [0054]    Reactor  10  also includes a pre-acidification tank  30  wherein untreated wastewater is initially pre-acidified. This enables diluting concentrated untreated wastewater while producing influent to be introduced into reactor  10  with a constant feed load. Additionally, nitrogen, phosphorus, pH, temperature and anti-foam can be regulated in pre-acidification tank  30  if necessary. 
         [0055]    After being pre-acidified in pre-acidification tank  30 , wastewater is pumped out of tank  30  by pump  32 , and is introduced into anaerobic water purification subsystem  12  from above by means of a plurality of nozzles  34 , positioned at the top of a gas head space  36  of anaerobic water purification subsystem  12 . Alternatively, wastewater is introduced into anaerobic water purification subsystem  12  from below, through wastewater inlet conduit  38 . 
         [0056]    Influent is sprayed onto upper zone  16  which consists of anaerobic biomass attached to floating biomass carriers  18 . The influent flows from the top of upper zone  16  to the bottom of upper zone  16  through biomass carriers  18 . The organic matter of the influent is converted by the anaerobic biomass into biogas which remains entrapped in between biomass carriers  18  and in cavities of biomass carriers  18 . 
         [0057]    Preferably, the release of the biogas is achieved by Mixing Gas (MG) injection. Gas is injected into lower zone  20  of anaerobic water purification subsystem  12  through gas injectors  40 . Gas bubbles then rise towards gas head space  36  above upper zone  16 . The rising bubbles disturb the consistency of biomass carriers  18 , thereby releasing biogas entrapped therein. Additionally, channeling is prevented. The released biogas rises towards gas head space  36  above upper zone  16 . 
         [0058]    Alternatively, jets  50  can be placed in the wall of upper zone  16 , which are operative to circulate the anaerobic effluent in upper zone  16 . The circulation of the anaerobic effluent causes movement of biomass carriers  18  thereby releasing biogas entrapped therein. Additionally, channeling is prevented. 
         [0059]    To ensure a constant level of gas in gas head space  36 , the pressure of gas collected in head space  20  is controlled by a reducing valve  52  or by a water column (not shown) at a height equal to or greater than the level of anaerobic wastewater in upper zone  16 . 
         [0060]    The biogas produced in anaerobic water purification subsystem  12  consists primarily of methane (CH 4 ) and carbon-dioxide (CO 2 ). Due to recirculation, part of the produced CO 2  is removed, which causes an increase of the pH level of the anaerobic effluent. This reduces the reagents consumption dramatically. 
         [0061]    Biological conversion of up to 90% of mostly organic matter is performed by the anaerobic biomass attached to floating biomass carriers  18 . To ensure efficient conversion of up to 90% of the organic matter in anaerobic water purification subsystem  12  and to facilitate attachment of anaerobic biomass to biomass carriers  18 , the flow-through rate and the hydraulic retention time (refresh rate) of the wastewater must be sufficiently high. 
         [0062]    The immobilization of anaerobic biomass on biomass carriers  18  prevents anaerobic biomass from leaving anaerobic water purification subsystem  12  and reaching aerobic water purification subsystem  14 . 
         [0063]    It is a particular feature of the present invention that the use of biomass carriers in anaerobic water purification subsystem  12  allows obviating the conventional three-phase separation, before biogas collection. 
         [0064]    Preferably, circulation of wastewater within anaerobic water purification subsystem  12  is achieved by pumping wastewater from the bottom of anaerobic water purification subsystem  12  to the top of anaerobic water purification subsystem using a pump  54 , and then dispersing the circulated wastewater by diffusers or jets  50 . Alternatively, circulation of wastewater is achieved by a mechanical mixer (not shown). 
         [0065]    Preferably, anaerobic sludge  56  (S) which accumulates at the bottom of anaerobic water purification subsystem  12  is circulated by a mechanical mixer, a circulation pump or any other circulation device. Additionally or alternatively, the anaerobic sludge  56  is drained from anaerobic water purification subsystem  12  by means of a drain valve  60 . 
         [0066]    Anaerobic effluent produced by anaerobic water purification subsystem  12  flows to aerobic water purification subsystem  14  via an internal conduit  62  for further treatment of organic matter. Alternatively, the transition of wastewater from the anaerobic water purification subsystem  12  to aerobic water purification subsystem  14  is achieved by an external conduit  64 . Additionally or alternatively, anaerobic and/or aerobic effluent is returned to pre-acidification tank  30  from anaerobic water purification subsystem  12  through recirculation pipe  66 , and/or from aerobic water purification subsystem  14  through recirculation pipe  68 . 
         [0067]    Aerobic water purification subsystem  14  comprises gas diffusers  70  that can be installed on the bottom of aerobic water purification subsystem  14  or above the bottom of aerobic water purification subsystem  14 , consistent with the Moving Bed Biofilm reactor (MBBR) configuration or with the Moving Bed Clarifying Reactor (MBCR) configuration as shown in PCT/IL 2009/000825, respectively. 
         [0068]    When the MBCR configuration is applied, gas diffuser outlets  70  are arranged generally between an upper biological treatment turbulence region  72  and a lower solids settling region  74 , and provide gas bubbles which move upwardly through wastewater in aerobic water purification subsystem  14  and through a plurality of biomass carriers  18  disposed within upper biological treatment turbulence region  72 , and create turbulent motion of wastewater in upper biological treatment turbulence region  72 . The gas bubbles, typically of pressurized air, are supplied to outlets  70  via a gas inlet  76 . The outlets  70  may include one or more coarse or fine bubble diffusers and jets. 
         [0069]    Sludge  77  (S) produced in aerobic water purification subsystem  14  is drained by valve  78 . Treated effluent  80  (E) leaves aerobic water purification subsystem  14  and reactor  10  via a wedge wire screen  82  coupled to a wastewater outlet in order to prevent carriers  18  from leaving aerobic water purification subsystem  14 . 
         [0070]    It is a particular feature of the present invention that most of the organic matter conversion is performed in the anaerobic water purification subsystem  12  of reactor  10 . It is another particular feature of the present invention that the aerobic water purification subsystem  14  is filled with biomass carriers  18  which increase the effective surface area of subsystem  14  and immobilize bacteria, thereby preventing wash out and conversion. These two features significantly reduce the amount of energy required for aeration in aerobic water purification subsystem  14  compared to conventional systems. 
         [0071]    Reference is now made to  FIG. 2 , which is a simplified illustration of one embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 . As seen in  FIG. 2 , there is provided an integrated reactor, designated generally by reference numeral  100 , which includes an anaerobic water purification subsystem  102 , receiving water to be treated, such as waste water, at an inlet  104 . Preferably the waste water is supplied from above by means of a plurality of nozzles  106 , which are coupled to inlet  104 . The water level in anaerobic water purification subsystem  102  is typically as designated by reference numeral  107 . 
         [0072]    The anaerobic water purification subsystem  102  provides an anaerobic-treated water output via an outlet  108  to an aerobic water purification subsystem  110 , integrated with the anaerobic water purification subsystem  102  and preferably physically located thereabove, which receives the anaerobic-treated water output at an inlet  112  and provides an anaerobic- and aerobic-treated water output as an effluent at an outlet  114 . If appropriate, the effluent from outlet  114  may be further treated by any suitable technique. 
         [0073]    In accordance with a preferred embodiment of the present invention, the anaerobic water purification subsystem  102  includes a multiplicity of biomass carriers  120  which are disposed in water to be treated. Biomass carriers  120  are operative to support anaerobic microorganisms. The structure and operation of a preferred embodiment of biomass carriers is described in applicant/assignee&#39;s European Published Patent Application No. 1401775 and PCT Published Patent Application No. WO 2009/10718, the disclosures of which are hereby incorporated by reference. Any other suitable biomass carriers may be employed. 
         [0074]    Optionally, an inert gas, such as nitrogen may be periodically introduced into the water to be treated via a gas supply inlet  122  in order to produce limited relative movement of the biomass carriers  120  in order to prevent clogging. Alternatively, this can be accomplished by a circulation pump disposed within the subsystem  102  and/or by a biogas compressor injecting biogas into subsystem  102 . 
         [0075]    Biogas, principally methane and carbon dioxide, generated by the anaerobic water purification in subsystem  102  rises to a gas collection volume  124  in a headspace above the water being treated in anaerobic water purification subsystem  102  and is preferably released for use via a generated gas outlet  126 . Optionally, some of the generated gas may be supplied via gas supply inlet  122  in addition to or in place of the inert gas. 
         [0076]    Biogas pressure in gas collection volume  124  causes the anaerobically treated water to rise from anaerobic subsystem  102  through outlet  108  to inlet  112  in aerobic water treatment subsystem  110 . Inlet  112  is preferably located in a lower portion of the aerobic subsystem  110 . Disposed above inlet  112  there are preferably provided a plurality of air diffusers  130  which are coupled to a source of pressurized air  132 , such as a compressor, via a pressurized air conduit  134 . 
         [0077]    The water level in aerobic water purification subsystem  110  is typically as designated by reference numeral  137 . A multiplicity of biomass carriers  140  are disposed in water to be treated in aerobic water purification subsystem  100  and are operative to support anaerobic microorganisms. Any other suitable biomass carriers may be employed. Biomass carriers  140  are generally confined to the volume above diffusers  130 , by the movement of air bubbles of the diffusers. 
         [0078]    At the bottom of the aerobic water purification subsystem  110 , below diffusers  130  there is preferably provided a sludge settlement volume  142 , which is equipped with a sludge outlet  144 . 
         [0079]    Preferably, the structure and operation of the aerobic water purification subsystem  110  is in accordance with the teachings of applicant/assignee&#39;s European Published Patent Application Nos. 1401775 and 2049443, and U.S. Published Patent Application No. 2009/0211972, the disclosure of which is hereby incorporated by reference. 
         [0080]    Reference is now made to  FIG. 3 , which is a simplified illustration of another embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 . As seen in  FIG. 3 , there is provided an integrated reactor, designated generally by reference numeral  200 , which includes an anaerobic water purification subsystem  202 , receiving water to be treated, such as waste water, at an inlet  204 . Preferably the waste water is supplied from above by means of a plurality of nozzles  206 , which are coupled to inlet  204 . The water level in anaerobic water purification subsystem  202  is typically as designated by reference numeral  207 . 
         [0081]    The anaerobic water purification subsystem  202  provides an anaerobic-treated water output via an outlet  208  to an aerobic water purification subsystem  210 , integrated with the anaerobic water purification subsystem  202  and preferably physically located thereabove, which receives the anaerobic-treated water output at an inlet  212  and provides an anaerobic- and aerobic-treated water output as an effluent at an outlet  214 . If appropriate, the effluent from outlet  214  may be further treated by any suitable technique. 
         [0082]    In accordance with a preferred embodiment of the present invention, the anaerobic water purification subsystem  202  includes a multiplicity of biomass carriers  220  which are disposed in water to be treated. Biomass carriers  220  are operative to support anaerobic microorganisms. The structure and operation of a preferred embodiment of biomass carriers is described in applicant/assignee&#39;s European Published Patent Application No. 1401775 and PCT Published Patent Application No. WO 2009/10718, the disclosures of which are hereby incorporated by reference. Any other suitable biomass carriers may be employed. 
         [0083]    Optionally, an inert gas, such as nitrogen may be periodically introduced into the water to be treated via a gas supply inlet  222  in order to produce limited relative movement of the biomass carriers  220  in order to prevent clogging. Alternatively, this can be accomplished by a circulation pump disposed within the subsystem  202 . 
         [0084]    Biogas, principally methane and carbon dioxide, generated by the anaerobic water purification in subsystem  202  rises to a gas collection volume  224  in a headspace above the water being treated in anaerobic water purification subsystem  202  and is preferably released for use via a generated gas outlet  226 . Optionally, some of the generated gas may be supplied via gas supply inlet  222  in addition to or in place of the inert gas. 
         [0085]    Biogas pressure in gas collection volume  224  causes the anaerobically treated water to rise from anaerobic subsystem  202  through outlet  208  to inlet  212  in aerobic water treatment subsystem  210 . Inlet  212  is preferably located in a lower portion of the aerobic subsystem  210 . Disposed above inlet  212  there are preferably provided a plurality of air diffusers  230  which are coupled to a source of pressurized air  232 , such as a compressor, via a pressurized air conduit  234 . 
         [0086]    The water level in aerobic water purification subsystem  210  is typically as designated by reference numeral  237 . A multiplicity of biomass carriers  240  are disposed in water to be treated in aerobic water purification subsystem  200  and are operative to support anaerobic microorganisms. Any other suitable biomass carriers may be employed. Biomass carriers  240  are generally confined to the volume above diffusers  230 , by the movement of air bubbles of the diffusers. 
         [0087]    Preferably the structure and operation of the aerobic water purification subsystem  210  is in accordance with the teachings of applicant/assignee&#39;s European Published Patent Application Nos. 1401775 and 2049443, and U.S. Published Patent Application No. 2009/0211972, the disclosure of which is hereby incorporated by reference. 
         [0088]    Reference is now made to  FIG. 4 , which is a simplified illustration of yet another embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 . As seen in  FIG. 4 , there is provided an integrated reactor, designated generally by reference numeral  300 , which includes an anaerobic water purification subsystem  302 , receiving water to be treated, such as waste water, at an inlet  304 . Preferably the waste water is supplied from below by means of a plurality of nozzles  306 , which are coupled to inlet  304 . The water level in anaerobic water purification subsystem  302  is typically as designated by reference numeral  307 . 
         [0089]    The anaerobic water purification subsystem  302  provides an anaerobic-treated water output via an outlet  308  to an aerobic water purification subsystem  310 , integrated with the anaerobic water purification subsystem  302  and preferably physically located thereabove, which receives the anaerobic-treated water output at an inlet  312  and provides an anaerobic- and aerobic-treated water output as an effluent at an outlet  314 . If appropriate, the effluent from outlet  314  may be further treated by any suitable technique. 
         [0090]    In accordance with a preferred embodiment of the present invention, the anaerobic water purification subsystem  302  includes a multiplicity of biomass carriers  320  which are disposed in water to be treated. Biomass carriers  320  are operative to support anaerobic microorganisms. The structure and operation of a preferred embodiment of biomass carriers is described in applicant/assignee&#39;s European Published Patent Application No. 1401775 and PCT Published Patent Application No. WO 2009/10718, the disclosures of which are hereby incorporated by reference. Any other suitable biomass carriers may be employed. 
         [0091]    Optionally, an inert gas, such as nitrogen may be periodically introduced into the water to be treated via a gas supply inlet  322  in order to produce limited relative movement of the biomass carriers  320  in order to prevent clogging. Alternatively, this can be accomplished by a circulation pump disposed within the subsystem  302 . 
         [0092]    Biogas, principally methane and carbon dioxide, generated by the anaerobic water purification in subsystem  302  rises to a gas collection volume  324  in a headspace above the water being treated in anaerobic water purification subsystem  302  and is preferably released for use via a generated gas outlet  326 . Optionally, some of the generated gas may be supplied via gas supply inlet  322  in addition to or in place of the inert gas. 
         [0093]    Biogas pressure in gas collection volume  324  causes the anaerobically treated water to rise from anaerobic subsystem  302  through outlet  308  to inlet  312  in aerobic water treatment subsystem  310 . Inlet  312  is preferably located in a lower portion of the aerobic subsystem  310 . Disposed above inlet  312  there are preferably provided a plurality of air diffusers  330  which are coupled to a source of pressurized air  332 , such as a compressor, via a pressurized air conduit  334 . 
         [0094]    The water level in aerobic water purification subsystem  310  is typically as designated by reference numeral  337 . A multiplicity of biomass carriers  340  are disposed in water to be treated in aerobic water purification subsystem  300  and are operative to support anaerobic microorganisms. Any other suitable biomass carriers may be employed. Biomass carriers  340  are generally confined to the volume above diffusers  330 , by the movement of air bubbles of the diffusers. 
         [0095]    At the bottom of the aerobic water purification subsystem  310 , below diffusers  330  there is preferably provided a sludge settlement volume  342 , which is equipped with a sludge outlet  344 . 
         [0096]    Preferably the structure and operation of the aerobic water purification subsystem  310  is in accordance with the teachings of applicant/assignee&#39;s European Published Patent Application Nos. 1401775 and 2049443, and U.S. Published Patent Application No. 2009/0211972, the disclosure of which is hereby incorporated by reference. 
         [0097]    Reference is now made to  FIG. 5 , which is a simplified illustration of still another embodiment of the synergetic anaerobic/aerobic water purification system of  FIG. 1 . As seen in  FIG. 5 , there is provided an integrated reactor, designated generally by reference numeral  400 , which includes an anaerobic water purification subsystem  402 , receiving water to be treated, such as waste water, at an inlet  404 . Preferably the waste water is supplied from below by means of a plurality of nozzles  406 , which are coupled to inlet  404 . The water level in anaerobic water purification subsystem  402  is typically as designated by reference numeral  407 . 
         [0098]    The anaerobic water purification subsystem  402  provides an anaerobic-treated water output via an outlet  408  to an aerobic water purification subsystem  410 , integrated with the anaerobic water purification subsystem  402  and preferably physically located thereabove, which receives the anaerobic-treated water output at an inlet  412  and provides an anaerobic- and aerobic-treated water output as an effluent at an outlet  414 . If appropriate, the effluent from outlet  414  may be further treated by any suitable technique. 
         [0099]    In accordance with a preferred embodiment of the present invention, the anaerobic water purification subsystem  402  includes a multiplicity of biomass carriers  420  which are disposed in water to be treated. Biomass carriers  420  are operative to support anaerobic microorganisms. Any other suitable biomass carriers may be employed. 
         [0100]    Optionally, an inert gas, such as nitrogen may be periodically introduced into the water to be treated via a gas supply inlet  422  in order to produce limited relative movement of the biomass carriers  420  in order to prevent clogging. Alternatively, this can be accomplished by a circulation pump disposed within the subsystem  402 . 
         [0101]    Biogas, principally methane and carbon dioxide, generated by the anaerobic water purification in subsystem  402  rises to a gas collection volume  424  in a headspace above the water being treated in anaerobic water purification subsystem  402  and is preferably released for use via a generated gas outlet  426 . Optionally, some of the generated gas may be supplied via gas supply inlet  422  in addition to or in place of the inert gas. 
         [0102]    Biogas pressure in gas collection volume  424  causes the anaerobically treated water to rise from anaerobic subsystem  402  through outlet  408  to inlet  412  in aerobic water treatment subsystem  410 . Inlet  412  is preferably located in a lower portion of the aerobic subsystem  410 . Disposed above inlet  412  there are preferably provided a plurality of air diffusers  430  which are coupled to a source of pressurized air  432 , such as a compressor, via a pressurized air conduit  434 . 
         [0103]    The water level in aerobic water purification subsystem  410  is typically as designated by reference numeral  437 . A multiplicity of biomass carriers  440  are disposed in water to be treated in aerobic water purification subsystem  400  and are operative to support anaerobic microorganisms. Any other suitable biomass carriers may be employed. Biomass carriers  440  are generally confined to the volume above diffusers  430 , by the movement of air bubbles of the diffusers. 
         [0104]    Preferably the structure and operation of the aerobic water purification subsystem  410  is in accordance with the teachings of applicant/assignee&#39;s European Published Patent Application Nos. 1401775 and 2049443, and U.S. Published Patent Application No. 2009/0211972, the disclosure of which is hereby incorporated by reference. 
         [0105]    Reference is now made to  FIGS. 6 &amp; 7 , which show experimental results of use of the system in accordance with the embodiment of  FIG. 1  of the present invention. 
         [0106]    In an experiment shown in  FIG. 6 , a lab scale anaerobic reactor having a volume of 19 liters, a height of 2 meters and a diameter of 11 cm, was used for a first experiment illustrating the principle of immobilizing anaerobic biomass onto biomass carrier material. A fermented molasses product was fed to the reactor. The volumetric loading rate (VLR) was controlled by adjustments of the COD concentration and feed flow. The reactor was operated in a downflow configuration. The fluid velocity ranged from 0.25 m/h to 0.67 m/h. The pH level was adjusted to pH 7 with NaOH, and the temperature was a constant 35° C. 
         [0107]      FIG. 6  shows the relation between the applied VLR (in kg/m 3 /d) and the conversion (in %) of COD and VFA (with COD conversion shown as a solid line, VFA conversion shown as a dashed line and VLR shown as a dashed-dotted line). During the experiment, an increase in biomass development upon the carrier material was observed, which allowed for a higher VLR. The system showed a stable conversion of VFA and COD up to a VLR of 22 kg/m 3 /d. 
         [0108]    In an experiment shown in  FIG. 7 , a dynamic anaerobic aerobic (DANA) reactor with an anaerobic part having a volume of 2.35 cubic meters, a height of 3 meters, a diameter of 1 meter, a carrier bed height of 1.3 meter, a surface area of 0.78 square meters, and an aerobic part having a height of 3.5 meters, a carrier bed having a height of 1.3 meters, and a diameter of 1 meter, was used to treat waste water from a starch factory. Waste water with an average COD concentration of 5 g/l was treated. The anaerobic reactor was operated in a downflow mode. At a maximum of 200 l/h of waste water fed, combined with a recirculation flow of 400 l/h, the downflow velocity reached was 0.76 m/h. The dissolved oxygen level in the aerobic tank was maintained at 2 mg/l. Temperature of the influent was 35° C.-37° C., and the pH was maintained at 6.8 with NaOH. 
         [0109]    Inoculation of the anaerobic tank was achieved using 10% inoculated carrier material at the top part of the carrier bed. Within one month a volumetric loading rate (VLR) of 10 kg/m 3 /d was reached.  FIG. 7  shows COD and VFA conversion (in %) of the total DANA reactor plotted against the VLR (in kg/m 3 /d). The average conversion of the anaerobic part was 80% and the remaining COD/VFA was 90% converted by the aerobic reactor. The total average conversion for the DANA reactor was 95%. 
         [0110]    It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather, the scope of the invention includes both combinations and subcombinations of various features described hereinabove as well as modifications and variations thereof which would occur to persons skilled in the art upon reading the foregoing and which are not in the prior art.