Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Korean Patent Application No. 2014-0017107, filed on Feb. 14. 2014, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety are herein incorporated by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present disclosure relates to an apparatus and method for anaerobic wastewater treatment with membrane distillation, and more particularly, to an apparatus and method for anaerobic wastewater treatment with membrane distillation, which combines membrane distillation and biological treatment to improve treated water quality, and performs anaerobic treatment to the wastewater to generate bio-gas and effectively restrain contamination of a membrane surface. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, a membrane bio-reactor (MBR) is frequently used for treating sewage and wastewater. The membrane bio-reactor combines a biological treatment process, represented by activated sludge, with a membrane to treat wastewater at high efficiency. If the membrane bio-reactor is used, since a microbial concentration in the reactor may be kept in a high level regardless of settleability of sludge, it is possible to allow compact facility and high-load operation, and also excellent treated water quality may be obtained. In particular, due to a compact design and efficient energy, an submerged membrane bio-reactor in which a membrane is directly immersed in an aeration tank to suck treated water is most frequently applied, as disclosed in Korean Patent Registration No. 315968, Korean Unexamined Patent Publication Nos. 2000-0065883, 2000-0003714, 2002-0089255, 2003-0039038 or the like. 
         [0006]    If this submerged membrane bio-reactor is applied, the membrane is inevitably clogged due to contamination of the membrane surface, and thus turbulence may be formed by aeration to prevent the membrane from being clogged. However, in this case, the required amount of aeration is much greater than the amount of air required for biological treatment, which results in excessive energy consumption and great maintenance costs. 
         [0007]    To remedy the above shortcomings, &lt;K. H. Ahn, K. G. Song, I. T. Yeom, K. Y. Park, (2001). “Performance comparison of direct membrane separation and membrane bioreactor for domestic wastewater treatment and water reuse,” Water Science and Technology, 1 (5-6), 315-323&gt; and Korean Unexamined Patent Publication No. 2007-0075947 disclose a technique for restraining clogging of a membrane by using a membrane module to which a rotary disk or propeller is mounted. However, in this technique, in order to effectively form turbulence for restraining clogging of a membrane, it is required to accelerate a rotating speed of the rotary disk or propeller, and the energy consumption for rotating the rotating disk or propeller is still a drawback. 
         [0008]    Meanwhile, in order to perform biological treatment to wastewater, aerobic treatment for supplying oxygen is generally used. However, the aerobic treatment consumes a great amount of energy to supply oxygen. On the contrary, the anaerobic treatment need not supply air and also generates bio-gas to produce available renewable energy. However, for the anaerobic treatment, it is important to maintain anaerobes having a relatively low growth rate at a high concentration in the reactor, and this may be solved if media at which anaerobes may be adhered and grow are supplied and simultaneously a membrane bio-reactor is used. Along with it, an existing membrane bio-reactor generally uses a technique in which a microfilter (MF) is coupled to the bio-reactor, but the microfilter is impossible to treat most dissolved or ionic substances. Therefore, there is needed another technical agony to improve the treated water quality. 
       RELATED LITERATURES 
     Patent Literature 
       [0000]    
       
         Korean Patent Registration No. 315968 
         Korean Unexamined Patent Publication No. 2000-0065883 
         Korean Unexamined Patent Publication No. 2000-0003714 
         Korean Unexamined Patent Publication No. 2002-0089255 
         Korean Unexamined Patent Publication No. 2003-0039038 
         Korean Unexamined Patent Publication No. 2007-0075947 
       
     
       Non-patent Literature 
       [0000]    
       
         &lt;K. H. Ahn, K. G. Song, I. T. Yeom, K. Y. Park, (2001). “Performance comparison of direct membrane separation and membrane bioreactor for domestic wastewater treatment and water reuse,” Water Science and Technology, 1 (5-6), 315-323&gt; 
       
     
       SUMMARY 
       [0016]    The present disclosure is directed to providing an apparatus and method for anaerobic wastewater treatment with membrane distillation, which may improve treated water quality by combining membrane distillation and biological treatment, and generate bio-gas and effectively restrain contamination of a membrane surface by performing anaerobic treatment to the wastewater. 
         [0017]    In one aspect, there is provided an apparatus for anaerobic wastewater treatment with membrane distillation, which comprises: a bio-reactor configured to give a space for filtration and biological treatment of wastewater by submerged membrane modules and operated in an anaerobic condition; submerged membrane modules provided in the bio-reactor to filter the wastewater; and rotary disks provided at both sides of the submerged membrane module to induce turbulence of the wastewater and moving of fluidizable media by means of rotation, wherein a channel is provided in the submerged membrane modules so that a cooling water flows therein, and moisture of the wastewater is evaporated due to a temperature difference of the wastewater and the cooling water and moved to the channel to filter the wastewater. 
         [0018]    The apparatus may further comprise fluidizable media provided in the bio-reactor to fluctuate by flow of the wastewater and rotation of the rotary disk so that contaminants are detached from a surface of the membrane modules and a bio-film is formed at the surface thereof to biologically treat the contaminants. In addition, anaerobes may be adhered to and grow at the surface of the fluidizable media and in the pores thereof. 
         [0019]    The submerged membrane module may comprise: a channel-formed plate having a channel formed therein so that the cooling water flows therethrough; and unit membranes respectively provided at front and rear surfaces of the channel-formed plate to isolate the channel from an external environment and to reject contaminants in the wastewater. In addition, the unit membrane may be composed of a porous hydrophobic membrane, and moisture of the wastewater does not directly pass through the unit membrane but only vapor may pass through pores of the unit membrane. 
         [0020]    The channel-formed plate may comprise a master plate, a rectangular frame and a central frame, the rectangular frame may be provided on a circumference of the master plate to be perpendicular to the master plate, the central frame may be disposed at a center portion of the master plate in parallel to both sides of the rectangular frame, and an inner space of the master plate may form a U-shaped channel by the rectangular frame and the central frame. 
         [0021]    A rectangular frame and a central frame having the same shape may be provided at front and rear surfaces of the master plate, and based on the master plate, a first channel may be provided at a front surface of the channel-formed plate and a second channel is provided at a rear surface thereof. In addition, a cooling water inlet and a cooling water outlet may be provided at one side of the channel-formed plate, and the cooling water introduced through the cooling water inlet may flow through the channel of the channel-formed plate and discharge through the cooling water outlet. 
         [0022]    When a cooling water having a lower temperature than the wastewater is supplied to the channel in the submerged membrane module, a temperature difference may be generated between a first surface of the unit membrane in contact with the wastewater and a second surface of the unit membrane in contact with the cooling water, moisture in contact with the first surface at a relatively higher temperature may be evaporated into vapor due to the temperature difference between the first surface and the second surface of the unit membrane, and the corresponding vapor may move through the unit membrane to the second surface and finally to the submerged membrane module in contact with the second surface to join the cooling water. 
         [0023]    The fluidizable media may be made of an organic polymer material having a porous surface, and the fluidizable media may have a hexahedral or spherical shape made of any one of polyurethane, polypropylene and polyethylene or a spherical shape in which yarns made of any one of polyurethane, polypropylene and polyethylene are bundled. 
         [0024]    A plurality of rotary disks may be provided to be separated from each other, and the membrane module may be provided in each space between the rotary disks. In addition, wherein a bio-gas pipe for extracting bio-gas generated through anaerobic digestion may be further provided at a part of an upper portion of the bio-reactor, and a bio-gas storage tank for storing the extracted bio-gas may be further provided at one side of the bio-reactor. 
         [0025]    In another aspect, there is provided a method for anaerobic wastewater treatment with membrane distillation, which comprises: a wastewater introduction step for introducing wastewater into a bio-reactor having an submerged membrane modules and fluidizable media; a filtration and biological treatment step for filtering the wastewater by the submerged membrane modules and also performing biological treatment to the wastewater in the bio-reactor; and a contaminant removal step for rotating rotary disks provided at both sides of the submerged membrane module to remove contaminants at a surface of the membrane module by means of the wastewater having turbulence and the fluidizable media, wherein in the filtration and biological treatment step, when a cooling water having a lower temperature than the wastewater is supplied to a channel in the submerged membrane module, a temperature difference is generated between a first surface of a unit membrane in contact with the wastewater and a second surface of a unit membrane in contact with the cooling water, moisture in contact with the first surface at a relatively higher temperature is evaporated into vapor due to the temperature difference between the first surface and the second surface of the unit membrane, and the corresponding vapor moves through the unit membrane to the second surface and finally to the submerged membrane module in contact with the second surface to join the cooling water and filter the wastewater. 
         [0026]    The contaminant removal step may be applied simultaneously with the filtration and biological treatment step. 
         [0027]    The apparatus and method for anaerobic wastewater treatment with membrane distillation according to the present disclosure gives the following effects. 
         [0028]    By combining the bio-reactor with a membrane distillation process, the quality of treated water may be improved. In addition, by applying a rotary disk and fluidizable media, contamination at a surface of an submerged membrane module may be effectively reduced by using just small energy. Moreover, by operating the bio-reactor in an anaerobic state, bio-gas may be additionally obtained, which allows great improvement of energy efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a perspective view showing an apparatus for anaerobic wastewater treatment with membrane distillation according to an embodiment of the present disclosure. 
           [0030]      FIG. 2  is a front view showing an apparatus for anaerobic wastewater treatment with membrane distillation according to an embodiment of the present disclosure. 
           [0031]      FIG. 3  is a side view showing an apparatus for anaerobic wastewater treatment with membrane distillation according to an embodiment of the present disclosure. 
           [0032]      FIG. 4  is an exploded perspective view showing an submerged membrane module according to an embodiment of the present disclosure. 
           [0033]      FIG. 5  is a reference view for illustrating a membrane distillation process by using the submerged membrane module according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    The present disclosure proposes a technique in which a membrane distillation process is combined with a bio-reactor. The membrane distillation process induces evaporation of water by endowing a temperature difference to both sides of the membrane and condenses and extracts the evaporated vapor, which gives great improvement of treated water quality. In the present disclosure, the membrane modules are immersed in a bio-reactor, and detailed configurations of the membrane modules and the channel for an optimal membrane distillation process are proposed. 
         [0035]    In addition, the present disclosure proposes a technique for generating bio-gas by operating the bio-reactor in an anaerobic condition, and also proposes a technique for minimizing adhesion of contaminants to a surface of the membrane by providing rotary disks at both sides of the membrane module and also providing a fluidizable media in the bio-reactor to contact the surface of the membrane. 
         [0036]    Hereinafter, an apparatus and method for anaerobic wastewater treatment with membrane distillation according to an embodiment of the present disclosure will be described in detail with reference to the drawings. 
         [0037]    Referring to  FIGS. 1 to 3 , the apparatus for anaerobic wastewater treatment with membrane distillation according to an embodiment of the present disclosure comprises a bio-reactor  100 . 
         [0038]    The bio-reactor  100  performs anaerobic treatment to wastewater to induce generation of bio-gas and also gives a space for mounting submerged membrane modules  10 . In order to maintain the anaerobic state, the bio-reactor  100  is isolated from an external environment, and an air supply device such as an air diffuser provided at an existing MBR is excluded. 
         [0039]    The submerged membrane modules  10  provided in the bio-reactor  100  play a role of filtering off contaminants in the wastewater through a membrane distillation process. The membrane distillation process basically gives a temperature difference at both sides of the membrane to filter contaminated water by evaporating moisture from the contaminated water and retrieving the clean water by condensing evaporating moisture. In the present disclosure, in order to implement the membrane distillation process, the submerged membrane module  10  is configured as follows in detail. 
         [0040]    The submerged membrane module  10  comprises a channel-formed plate  110  and a unit membrane  120  (see  FIG. 4 ). Channels are provided at both surfaces of the channel-formed plate  110 , and the unit membranes  120  are provided on both surfaces of the channel-formed plate  110 . Here, the ‘channel’ means a moving passage of cooling water, and the cooling water includes treated water condensed by means of membrane distillation. 
         [0041]    The channel-formed plate  110  comprises a master plate  111 , a rectangular frame  112  and a central frame  113  in detail. The master plate  111  is a flat plate with a predetermined area, and the rectangular frame  112  is provided on a circumference of the master plate  111  to be perpendicular to the master plate  111 . Accordingly, an inner space of the master plate  111  and an outer space of the master plate  111  are divided by the rectangular frame  112 , and a space corresponding to the height of the rectangular frame  112  is formed in the master plate  111 . 
         [0042]    The central frame  113  is a straight frame having a predetermined height and a predetermined length, and the central frame  113  is disposed at a center portion of the master plate  111  in parallel to both sides of the rectangular frame  112 . The central frame  113  is shorter than the length of the rectangular frame  112  disposed in parallel, and accordingly one end of the central frame  113  is connected to the rectangular frame  112  and the other end of the central frame  113  does not extend to one end of the master plate  111 . In this configuration, the inner space of the master plate  111  forms a ‘U’ shape by the rectangular frame  112  and the central frame  113 , and the ‘U’-shaped space means a channel. 
         [0043]    As described above, the rectangular frame  112  and the central frame  113  forming a U′-shaped channel are provided on one surface of the master plate  111 . In addition, on the other surface of the master plate  111 , a rectangular frame  112  and a central frame  113  having the same shape as above are provided to form a channel. In other words, ‘U’-shaped channels are provided at both surfaces based on the master plate  111 . In other words, based on the master plate  111 , a first channel is provided at a front surface of the channel-formed plate  110  and a second channel is provided at a rear surface thereof. In addition, the rectangular frames  112  at the front and rear surfaces of the master plate  111  may be integrally formed, and the rectangular frame  112  may have various shapes, without being limited to a rectangular shape, as long as it may divide the inner space of the master plate  111  and the outer space thereof. 
         [0044]    Meanwhile, a cooling water inlet  114  and a cooling water outlet  115  are provided at an upper side of the rectangular frame  112 . Cooling water is introduced through the cooling water inlet  114 , and the introduced cooling water passes through the U-shaped channel and discharges through the cooling water outlet  115 . At this time, the cooling water inlet  114  and the cooling water outlet  115  are spatially connected to both the first channel and the second channel of the channel-formed plate  110 , respectively. In other words, the cooling water introduced through the cooling water inlet  114  is distributed to the first channel and the second channel, and both the cooling waters of the first channel and the second channel discharge through the single cooling water outlet  115 . 
         [0045]    The channel-formed plate  110  has been described above. Here, the unit membranes  120  are provided on the rectangular frames  112  at the front and rear surfaces of the channel-formed plate  110 . The unit membrane  120  is closely adhered to the rectangular frame  112 , and accordingly the channels (the first channel and the second channel) of the channel-formed plate  110  are isolated from the external environment. The unit membrane  120  is made of a porous hydrophobic membrane, so that water does not directly pass through the unit membrane  120  but only vapor passes through pores of the unit membrane  120 . 
         [0046]    In a state where the submerged membrane module  10  of the present disclosure is configured as above, a membrane distillation process using the submerged membrane module  10  will be described below (see  FIG. 5 ). 
         [0047]    In a state where wastewater of 35 to 55° C. is provided in the bio-reactor  100 , the cooling water of the cooling tank  40  is supplied through the cooling water inlet  114  of the channel-formed plate  110  to the first channel and the second channel. The cooling water supplied to the first channel and the second channel passes through the U-shaped channel and discharges through the cooling water outlet  115 , and the discharged cooling water is returned to the cooling tank  40 . The cooling water repeatedly circulates in the order of the cooling tank  40 , the cooling water inlet  114 , the first channel and second channel, the cooling water outlet  115  and the cooling tank  40 . 
         [0048]    In the above circulation of cooling water, the first surface  121  of the unit membrane  120  comes into contact with the wastewater, and the second surface  122  of the unit membrane  120  comes into contact with the cooling water which moves along the first channel and the second channel. At this time, since the temperature of the cooling water is lower than the temperature of the wastewater, a temperature difference is generated between the first surface  121  and the second surface  122  of the unit membrane  120 . 
         [0049]    Due to the temperature difference between the first surface  121  and the second surface  122  of the unit membrane  120 , moisture contacting the first surface  121  having a relatively high temperature is evaporated into vapor, and the corresponding vapor passes through the unit membrane  120  to the second surface  122 , and finally to the first channel and the second channel in contact with the second surface  122  to join the cooling water. In other words, contaminants in the wastewater are filtered off on the first surface  121  of the unit membrane  120 , and only moisture is evaporated to move through the pores of the unit membrane  120  and condensed at the second surface  122  of the unit membrane  120  to join the cooling water which moves along the first channel and the second channel. The wastewater is filtered by means of generation of vapor due to the temperature difference, movement of the vapor through the unit membrane  120 , and join to the cooling water, as described above, and this means the membrane distillation process using the submerged membrane module  10  of the present disclosure. 
         [0050]    Heretofore, the submerged membrane module  10  of the present disclosure and the membrane distillation process using the same have been explained. A plurality of submerged membrane modules  10  may be provided, and a cooling water pipe  41  may be provided for a connection between the cooling tank  40  and the cooling water inlet  114  and between the cooling tank  40  and the cooling water outlet  115 . In addition, since the cooling water discharges while containing a condensed vapor, the temperature of the cooling water may rise. This, in order to maintain the temperature of the cooling water constantly, the cooling tank  40  may be controlled by a separate cooling device. Along with it, a treated water tank  50  for storing a predetermined amount of treated water may be provided at one side of the cooling tank  40 . 
         [0051]    Meanwhile, as the membrane distillation process using the submerged membrane module  10  is performed, the surface of the submerged membrane module  10 , namely the first surface  121 , may be clogged by filtered contaminants. In order to prevent this, a rotary disk  20  and a fluidizable media  30  are provided in the bio-reactor  100 . 
         [0052]    In detail, rotary disks  20  are provided at both sides of the submerged membrane module  10 . The rotary disk  20  rotates by a motor  22  connected to one side thereof. The rotation of the rotary disk  20  induces turbulence of the wastewater, which ultimately detaches contaminants adhered to the surface of the membrane module  10  or restrains adhesion of contaminants to the surface of the membrane module  10 . The rotary disk  20  and the surface of the membrane module  10  are spaced apart from each other by a predetermined distance, and two rotary disks  20  provided at both sides of the membrane module  10  are connected to the motor  22  by means of a shaft  21  so that both rotary disks  20  rotate simultaneously by the motor  22 . In another embodiment, it is also possible to connect each rotary disk  20  to a motor  22  separately so that the rotary disk  20  operates independently. Meanwhile, the rotary disks  20  may be installed successively at the shaft  21  depending on the number of installed membrane modules  10  so that each membrane module  10  is interposed between the rotary disks  20 . In other words, a plurality of rotary disks  20  may be provided at intervals, and the membrane module  10  may be provided in each space between the rotary disks  20 . 
         [0053]    By means of the rotation of the rotary disk  20 , contamination of the membrane module  10  may be restrained. Here, the contamination restraining effect of the membrane module  10  may be further improved by adding the fluidizable media  30 . In detail, in a state where a plurality of fluidizable media  30  having a predetermined unit size are provided in the bio-reactor  100 , the fluidizable media  30  may be allowed to fluctuate due to the turbulence caused by the rotation of the rotary disk  20  so that contaminants may be detached due to the fluctuation of the fluidizable media  30  as well as the contact between the fluidizable media  30  and the membrane surface. 
         [0054]    In addition, the fluidizable media  30  is made of porous material, and anaerobes may be attached to and grow at the surface of the fluidizable media  30  and in the pores thereof so as to treat contaminants in the bio-reactor  100  and generate bio-gas such as methane gas. In particular, since anaerobes attached on the surface of the fluidizable media  30  may treat contaminants and the attached anaerobes may be present at a high concentration and take the place of suspended anaerobes to treat contaminants, the concentration of suspended anaerobes could be reduced. Therefore the concentration of floating substances which should be rejected by the submerged membrane module  10  is lowered greatly, and thus the contamination of the submerged membrane module  10  may be greatly reduced in comparison to an existing membrane separation bio-reactor  100  in which suspended microorganisms are used for treatment. 
         [0055]    Along with it, the fluidizable media  30  has a porous form to serve as a habitat of anaerobes and is made of organic polymer material such as polyurethane, polypropylene, polyethylene or the like, which are so soft not to damage the membrane when producing friction with the surface of the membrane. In addition, the media has a hexahedral or spherical shape with a diameter of 1 to 20 mm or a spherical shape in which yarns made of the above materials are bundled. 
         [0056]    A baffle (not shown) is provided at a top portion of the bio-reactor  100  to prevent the fluidizable media  30  from rising over the top of the membrane module  10 . In addition, at one side of the top portion of the bio-reactor  100 , a bio-gas pipe (not shown) for extracting bio-gas such as methane gas generated through anaerobic treatment in the bio-reactor  100  is provided, and the extracted bio-gas passes through the bio-gas pipe and is stored in a bio-gas storage tank  60 . Along with it, a water level sensor for detecting a water level of the bio-reactor  100  is provided at one side of the bio-reactor  100 . 
         [0057]    Heretofore, the configuration of the apparatus for anaerobic wastewater treatment according to an embodiment of the present disclosure has been described. Next, operations of the apparatus for anaerobic wastewater treatment will be described. 
         [0058]    If wastewater is introduced into the bio-reactor  100 , anaerobic treatment is performed to the wastewater by means of anaerobes flowing in the bio-reactor  100  and anaerobes present in the bio-film formed at the surface of the fluidizable media  30  and in the pores thereof. Since the bio-reactor  100  comes to an anaerobic state in which air supply is blocked as described above, if the wastewater stays in the bio-reactor  100  for a predetermined time, an anaerobic digestion process is performed. Bio-gas such as methane gas is generated due to the anaerobic digestion of the wastewater, and the generated bio-gas is carried to the bio-gas storage tank  60 . 
         [0059]    Meanwhile, along with the anaerobic treatment process, a membrane distillation process is performed by the submerged membrane module  10 , and contaminants in the wastewater are filtered off by the submerged membrane module  10  during the membrane distillation process. In detail, if a cooling water having a lower temperature than the wastewater is supplied to the channels (the first channel and the second channel) in the submerged membrane module  10 , a temperature difference is generated between the first surface  121  of the unit membrane  120  in contact with the wastewater and the second surface  122  of the unit membrane  120  in contact with the cooling water, moisture in contact with the first surface  121  having a relatively higher temperature due to the temperature difference between the first surface  121  and the second surface  122  of the unit membranes  120  is evaporated into vapor, and the corresponding vapor passes through the unit membrane  120  and moves to the second surface  122 , finally to the first channel and the second channel in contact with the second surface  122  to join the cooling water. Moisture of the wastewater is evaporated into vapor, finally condensed to join the cooling water, and then discharges to the cooling tank  40 . Also, contaminants in the wastewater are filtered off by the unit membrane  120 . 
         [0060]    Meanwhile, along with the anaerobic treatment process and the membrane distillation process, contaminants at the surface of the submerged membrane module  10  are removed. In a state where the fluidizable media  30  fills the bio-reactor  100 , the rotary disks  20  provided at both sides of the membrane module  10  are rotated to remove contaminants at the surface of the membrane module  10  by means of turbulence of the wastewater, and simultaneously contaminants at the surface of the membrane module  10  are removed by means of the fluidizable media  30 . The rotary disks  20  are rotated while the filtering process is in operation, and the rotary disks  20  may also be operated intermittently. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 Reference Symbols 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10: submerged membrane module 
                 20: rotary disk 
               
               
                 21: shaft 
                 22: motor 
               
               
                 30: fluidizable media 
                 40: cooling tank 
               
               
                 41: cooling water pipe 
                 50: treated water tank 
               
               
                 60: bio-gas storage tank 
                 100: bio-reactor 
               
               
                 110: channel-formed plate 
                 111: master plate 
               
               
                 112: rectangular frame 
                 113: central frame 
               
               
                 114: cooling water inlet 
                 115: cooling water outlet 
               
               
                 120: unit membrane 
                 121: first surface of the 
               
               
                   
                 unit membrane 
               
               
                 122: second surface of the unit membrane

Technology Category: 4