Patent Publication Number: US-2013228227-A1

Title: Siphon actuated filtration process

Description:
This application claims priority to Canadian Patent Application No. ______, filed on Jan. 25, 2012, entitled SIPHON ACTUATED FILTRATION PROCESS, invented by Jeff J. Kempson and Jason R. Downey. 
     FIELD 
     The present invention relates to the field of water treatment, and more particularly to a method and system for actuating a filtration process using a vacuum assisted siphon. 
     BACKGROUND 
     In wastewater treatment the final step typically comprises a membrane filtration process where the water is filtered by drawing the same through a membrane filter such as, for example, an ultra-filtration membrane. In membrane filtration processes one or more membrane filter modules are typically disposed in a tank facility and submerged in the water that is to be filtered. The water is then drawn through the membrane filters at a controlled flow rate. 
     Present day systems typically employ a positive displacement water pump which is controlled using a pressure sensor and a variable frequency drive to provide a predetermined flow rate of water drawn through the membrane filters. Unfortunately, positive displacement water pumps are expensive and maintenance intensive. Furthermore, variable frequency drives tend to fail over time when operated using low quality electrical power such as, for example, generator power. 
     Alternatively, the water is drawn through the membrane filters by gravity with a shutoff valve to start and stop the flow of the water. However, this system does not enable to control the flow rate of the water drawn through the membrane filters in an automated fashion and does not enable provision of a reverse flow to clean the membrane filters. Furthermore, air bubbles present in the filtrate can cause the flow to stop prematurely requiring operator intervention. 
     Further alternatively, an air vacuum pump is employed to evacuate a large chamber for drawing the water through the membrane filters into the same. Once the chamber is full, the system is vented and the water in the chamber is discharged by gravity or using a water pump. Unfortunately, a variable flow rate of the water flow through the membrane filters is difficult if not impossible to achieve and it is expensive to build such a large vacuum chamber to achieve the desired filtration intervals. Furthermore, for optimum membrane use it may be desired to provide a reverse flow for relaxation of the membrane filters in regular time intervals. For example, the water is drawn through the membrane filters for approximately 9 minutes followed by a reverse flow for approximately 5 seconds and membrane relaxation for approximately 55 seconds or water is drawn through the membrane filters for approximately 9 minutes followed by a reverse flow for approximately 60 seconds. In order to enable such a cycle a large size chamber has to be employed requiring a substantial amount of time for evacuating the same. 
     It is desirable to provide a membrane filtration process having a mechanism for maintaining a constant flow rate of the filtrate. 
     It is also desirable to provide a membrane filtration process that is simple and compact. 
     It is also desirable to provide a membrane filtration process that requires substantially less maintenance and operator intervention. 
     It is also desirable to provide a membrane filtration process that enables implementation of predetermined cycles of filtration and membrane relaxation in an automated fashion. 
     It is also desirable to provide a membrane filtration process that enables implementation of pressurized reverse flow cleaning cycles. 
     SUMMARY 
     Accordingly, one object of the present invention is to provide a membrane filtration process having a mechanism for maintaining a constant flow rate of the filtrate. 
     Another object of the present invention is to provide a membrane filtration process that is simple and compact. 
     Another object of the present invention is to provide a membrane filtration process that requires substantially less maintenance and operator intervention. 
     Another object of the present invention is to provide a membrane filtration process that enables implementation of predetermined cycles of filtration and membrane relaxation in an automated fashion. 
     Another object of the present invention is to provide a membrane filtration process that enables implementation of pressurized reverse flow cleaning cycles. 
     According to one aspect of the present invention, there is provided a system for actuating a water flow through a filter is provided. The system comprises a filtrate withdrawal conduit for being connected to the filter in a water sealing fashion for receiving filtrate therefrom. A filtrate collector is in fluid communication with the filtrate withdrawal conduit for collecting the filtrate. A filtrate siphon is interposed between the filtrate withdrawal conduit and the filtrate collector. A suction mechanism connected to a top portion of the filtrate siphon via an air conduit. The suction mechanism provides suction to the filtrate siphon which is sufficient for drawing the filtrate to the top portion of the filtrate siphon for actuating the water flow through the filter and the flow of filtrate from the filter to the filtrate collector. 
     According to another aspect of the present invention, there is further provided a method for actuating a water flow through a filter. A filtrate withdrawal conduit is connected to the filter in a water sealing fashion for receiving filtrate therefrom. A filtrate collector in fluid communication with the filtrate withdrawal conduit is provided. A filtrate siphon is interposed between the filtrate withdrawal conduit and the filtrate collector such that in operation a predetermined length of the end portion of the filtrate siphon is immersed in the collected filtrate. Suction is provided to the filtrate siphon sufficient for drawing the filtrate to the top portion of the filtrate siphon for actuating the water flow through the filter and the flow of filtrate from the filter to the filtrate collector. 
     One advantage of the present invention is that it provides a membrane filtration process having a mechanism for maintaining a constant flow rate of the filtrate. 
     A further advantage of the present invention is that it provides a membrane filtration process that is simple and compact. 
     A further advantage of the present invention is that it provides a membrane filtration process that requires substantially less maintenance and operator intervention. 
     A further advantage of the present invention is that it provides a membrane filtration process that enables implementation of predetermined cycles of filtration and membrane relaxation in an automated fashion. 
     A further advantage of the present invention is that it provides a membrane filtration process that enables implementation of pressurized reverse flow cleaning cycles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One embodiment of the present invention is described below with reference to the accompanying drawings, in which: 
         FIG. 1   a  is a simplified block diagram illustrating a system for actuating a water flow through a filter according to an embodiment of the invention; 
         FIGS. 1   b  to  1   e  are simplified block diagrams illustrating the system for actuating a water flow through a filter shown in  FIG. 1   a  in various stages of operation; 
         FIG. 1   f  is a simplified block diagram illustrating a detail of the system for actuating a water flow through a filter shown in  FIG. 1   a;    
         FIG. 2   a  is a simplified block diagram illustrating a system for actuating a water flow through a filter according to another embodiment of the invention; 
         FIGS. 2   b  and  2   c  are simplified block diagrams illustrating the system for actuating a water flow through a filter shown in  FIG. 2   a  in different modes of operation; 
         FIG. 3   a  is a simplified block diagram illustrating a system for actuating a water flow through a filter according to yet another embodiment of the invention; 
         FIGS. 3   b  and  3   c  are simplified block diagrams illustrating the system for actuating a water flow through a filter shown in  FIG. 3   a  in different modes of operation; and, 
         FIG. 4  is a simplified block diagram illustrating a control unit for controlling operation of the system for actuating a water flow through a filter shown in  FIG. 3   a.    
     
    
    
     DETAILED DESCRIPTION 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, certain methods and materials are now described. 
     While embodiments of the invention will be described for drawing water through an ultra-filtration membrane in a wastewater treatment process, it will become evident to those skilled in the art that the embodiments of the invention are not limited thereto, but are applicable for use with other submerged filtration media. 
     Referring to  FIGS. 1   a  to  1   f , a system  100  for actuating a water flow through a filter according to a first embodiment of the invention is provided. Filtrate withdrawal conduits  102  are connected to filter module  12  in a water sealing fashion for receiving filtrate therefrom. The filter module  12 —comprising, for example, ultra-filtration membranes—is disposed in tank facility  10  and submerged in water  18  that is to be filtered. Typically, space  14  above the water surface  16  is exposed to ambient air pressure and the tank is filled with the water such that the water surface  16  is kept at an approximately constant level. Filtrate siphon  108  is connected to the filtrate withdrawal conduits  102  in a water sealing fashion. The filtrate siphon  108  actuates the flow through the filter  12  and the filtrate withdrawal conduit  102  into filtrate collector  110 , as will be described herein below. 
     Filtrate siphon end portion  108 B is disposed in the filtrate collector  110  such that in operation a predetermined length L of the end portion  108 B is immersed in the collected filtrate  22 , as illustrated in  FIG. 1   b . For example, filtrate gravity drain  112  is placed such that level  20  of the filtrate is the length L above the end of the siphon  108 . Air conduit  114  is connected to filtrate siphon top portion  108 A. Suction side  116 A of air pump  116  is connected to the air conduit  114  for providing variable suction to the filtrate siphon  108 . Pressure side  116 B of the air pump  116  is vented to ambient air via vent  122 . Furthermore, vent valve  118 —for example, a solenoid valve—is connected to the air conduit  114  for venting the siphon  108 . Pressure in the filtrate siphon top portion  108 A is monitored using vacuum transmitter  120  such as, for example, a pressure sensor. As is evident to one of skill in the art, the technical term “vacuum” used herein is to be understood as referring to a vacuum in the range of “low vacuum”. A reverse flow storage tank  106  can be disposed in proximity to the top portion  108 A of the siphon  108  for storing filtrate therein. Optionally, filtrate shut-off valves  104  are disposed in the filtrate withdrawal conduits  102 , typically, for manual operation during maintenance or to shut off a membrane module that has experienced a membrane failure. The air pump  116  is implemented using, for example, a suitable off-the-shelf air pump. Optionally, the air pump  116  is omitted if there is another vacuum source available for being connected to the air conduit  114 . 
     Referring to  FIGS. 1   b  to  1   f , various stages of operation of the system  100  are illustrated.  FIG. 1   b  illustrates the system  100  in a shut-off stage, for example, after the vent valve  118  has been opened for “venting” the siphon  108  by providing ambient air thereto. At this stage the siphon  108  is filled with ambient air between the filtrate level  16  in the reverse flow storage tank  106 —which is equivalent to the water level  16  in the tank  10  when the space  14  is exposed to ambient air—and the level  20  of the collected filtrate  22 . 
     To initiate the flow through the filter  12  and to the filtrate collector  110 , the vent valve  118  is closed and the air pump  116  is activated for providing suction to the siphon  108  via the air conduit  114 . As illustrated in  FIG. 1   c , the suction provided by the air pump  116  generates a vacuum in the space  108 C in the filtrate siphon  108 , consequently raising the filtrate levels  17 A and  17 B until the filtrate level  17 A reaches the top portion  108 A of the filtrate siphon  108 B and the filtrate flows down the siphon  108 , as illustrated in  FIGS. 1   d  and  1   f.    
     The pressure in the filtrate siphon top portion  108 A above the filtrate level  17 A is monitored using vacuum transmitter  120  connected thereto via the air conduit  114  and the siphon extension  108 D. The siphon extension  108 D is provided to prevent water droplets from being drawn into the air pump  116  during evacuation of the siphon  108 . Provision of a variable vacuum in a controlled fashion enables control of the flow rate of filtrate through the membranes. For example, provision of a higher vacuum raises the height H of the filtrate level  17 A in the filtrate siphon top portion  108 A enabling a variation of the height H between heights H 1  and H 2  corresponding to a low flow rate and a high flow rate, respectively. When a predetermined flow rate has been reached, the air pump  116  is shut off. 
     Furthermore, the air pump  116  and the vacuum transmitter  120  enable controlled provision of the vacuum in order to control provision of a constant flow rate of the filtrate as the membranes plug up. As the membranes plug up during the filtration process, a higher vacuum is needed to draw the water therethrough at a same flow rate. The vacuum is increased, for example, when a decrease in the flow rate is sensed—for example, by sensing the level of the filtrate surface  20  in the filtrate collector  110  or by measuring a flow rate of the discharged filtrate using a flow meter disposed in a discharge conduit such as, for example, discharge conduit  204  illustrated in  FIG. 2   a —or the vacuum is increased in a predetermined fashion depending on the time the filtration process has been performed since the last relaxation. 
     Automated control of the flow rate is enabled, for example, by sensing the flow rate and providing the vacuum in dependence upon the sensed flow rate. Alternatively, correlations between the flow rate, the time the filtration process has been performed since the last relaxation, and the corresponding vacuum, have been previously determined—for example, in an empirical fashion—and operation of the vacuum pump is controlled in dependence upon the signal provided by the vacuum transmitter  120  and the previously determined correlations. 
     To stop the flow through the filter  12  to the filtrate collector  110 , the vent valve  118  is opened and ambient air vents the siphon  108  as indicated by the dashed arrows in  FIG. 1   e , thus breaking the flow of the filtrate through the siphon top portion  108 A and causing a reverse flow through the filtrate withdrawal conduits  102  and the filter  12  as indicated by the solid arrows in  FIG. 1   e . The reverse flow storage tank  106  can be designed to be of sufficient size to provide a sufficient water to fully relax the filter  12 . 
     The operation of the system  100  as described herein above enables implementation of various operating cycles of membrane filters such as, for example, drawing water through the membrane filters for approximately 9 minutes followed by a reverse flow for relaxing the membranes for approximately 5 seconds, with each cycle being implemented as a succession of the stages shown in  FIGS. 1   b  to  1   f.    
     Referring to  FIGS. 2   a  to  2   c , a system  200  for actuating a water flow through a filter according to another embodiment of the invention is provided. The system  200  comprises the same basic components as the system  100  with same reference numerals referring to same components. Here, the filtrate  22  is discharged using filtrate pump  202  connected to discharge conduit  204 . The filtrate pump  202  is, for example, a suitable off-the-shelf water pump mounted to the outside of the filtrate collector  110  or disposed therein. Employment of the filtrate pump  202  enables discharge operation of the filtrate in dependence upon a fill level in the filtrate collector  110 . The fill levels are measured using, for example, off-the-shelf electromechanical ball float level switches  206  and  208 . For example, the filtrate pump  202  is activated when the fill level has reached the level to activate switch  208  and is stopped when the fill level has dropped low enough to deactivate switch  206 , thus ensuring that overflow of the filtrate collector  110  is prevented as well as that the siphon end portion  108 B is immersed in the filtrate. 
     Employment of the filtrate pump  202  enables implementing a cleaning system for cleaning the filter  12 . The cleaning system comprises cleaning conduit  212  connected to the discharge conduit  204  at  210  and to one of: the siphon top portion  108 A; the reverse flow storage tank  106 ; and the filtrate withdrawal conduits  102 , as well as discharge shut-off valve  214  and cleaning valve  216 . The discharge shut-off valve  214  and cleaning valve  216  are implemented using, for example, off-the-shelf electromechanical or manually operated valves. 
     In a first mode of operation, the discharge shut-off valve  214  is opened while the cleaning valve  216  is closed, enabling discharge of the filtrate  22 —collected in the filtrate collector  110  during normal filtering operation—through the discharge conduit  204 , as indicated by the arrows illustrated in  FIG. 2   b . For cleaning the filter  12 , the discharge shut-off valve  214  is closed while the cleaning valve  216  is opened for re-circulating the filtrate into the one of: the siphon top portion  108 A; the reverse flow storage tank  106 ; and the filtrate withdrawal conduits  102 , as indicated by the arrows illustrated in  FIG. 2   c , with excess filtrate flowing back through the siphon into the filtrate collector  110 . The cleaning process is implemented, for example, for being performed in an automated fashion in predetermined time intervals by controlling the filtrate pump  202 , the discharge shut-off valve  214  and the cleaning valve  216  for switching between the filtering operation and the cleaning operation. Alternatively, the cleaning process is implemented as a manual process allowing an operator to add chemicals to the filtrate  22  prior recirculation of the filtrate  22 . 
     Referring to  FIGS. 3   a  to  3   c , a system  300  for actuating a water flow through a filter according to yet another embodiment of the invention is provided. The system  300  comprises the same basic components as the system  200  with same reference numerals referring to same components. The system  300  comprises a pressurizing mechanism for enabling pressurized recirculation of the filtrate  22 . The pressurizing mechanism comprises: a suction air valve  302  interposed between the suction side  116 A of the air pump  116  and the air conduit  114 ; and a pressure air valve  304  interposed between the pressure side  116 B of the air pump  116  and the air conduit  114 . 
     In a first mode of operation, illustrated in  FIG. 3   b , the suction air valve  302  connects the suction side  116 A of the air pump  116  to the air conduit  114  for evacuating the siphon  108 —corresponding to  FIG. 1   c —while the pressure air valve  304  connects the pressure side  116 B of the air pump  116  to the outside ambient air, as illustrated by the dashed arrows in  FIG. 3   b.    
     In a second mode of operation, illustrated in  FIG. 3   c , the pressure air valve  304  connects the pressure side  116 B of the air pump  116  to the air conduit  114  for providing pressurized air to the siphon  108  and, therefore, to the filtrate for cleaning the filter  12 —corresponding to  FIG. 2   c —while the suction air valve  302  connects the suction side  116 A of the air pump  116  to the outside ambient air, as illustrated by the dashed arrows in  FIG. 3   c . During this operation, it may be desired to keep a high fill level in the filtrate collector  110  to ensure sufficient pressurization of the filtrate siphon  108  by controlling pump  202  on level switch  208  rather than level switch  206 . The pressurized air is provided in a controlled fashion, for example, by enabling an operator to adjust an air pressure setpoint. 
     In one case the suction air valve  302  and the pressure air valve  304  are in a closed position when the air pump  116  is shut off. The pressurizing mechanism is implemented, for example, for being performed in an automated fashion by controlling the air pump  116 , the suction air valve  302  and the pressure air valve  304  for switching between the filtering operation and the cleaning operation. The suction air valve  302  and the pressure air valve  304  are implemented using, for example, off-the-shelf 3-way solenoid valves. 
     The pressuring mechanism enables installation of a filtration system, for example, for wastewater treatment, without having to install additional tanks and equipment on the roof of the container for the filter cleaning process. 
     Operation of the above systems for actuating a water flow through a filter can be performed in an automated fashion. Referring to  FIG. 4 , a control unit  402  is provided for controlling the operation of the various components. Operation of the control unit  402  is enabled using an off-the-shelf Programmable Logic Controller (PLC)  404  for executing executable commands which can be stored in non-volatile memory  406  on board the PLC. The PLC  404  is connected to the sensors  120 ,  206 , and  208  for receiving sensor data therefrom, as well as to the valves  118 ,  214 ,  216 ,  302 , and  304 ; and, to the air pump  116  and the filtrate pump  202  for controlling operation of the same in dependence upon the executed commands and the sensor data. A user interface  408  is disposed in the control unit  402  and connected to the processor  404  for displaying display data to the operator  408 A in a human comprehensible fashion and for receiving operator commands  408 B. For example, the operator is enabled to provide user input data relating to the operation of the system such as duration of the various operating cycles, the flow rate, etc. The user interface  408  is provided using, for example, an off-the-shelf touch screen or a combination of a display and push buttons. The control unit  402  may be provided in a rugged fashion for outdoor use and to withstand substantial vibrations generated during transport and operation of the filtration system. 
     The above systems for actuating a water flow through a filter are manufactured depending on the application—for example, wastewater treatment or potable water filtration—using: standard materials such as, for example, steel, stainless steel, or suitable plastic materials; standard manufacturing processes such as, for example, welding, use of screw fittings, or use of adhesives; and off-the-shelf components such as, for example, off-the-shelf piping and off-the-shelf fittings. The design of the above systems is performed using standard engineering technologies for water treatment systems. 
     In an example, implementation an MBR wastewater treatment system was built for processing wastewater from a 50 man mining camp. The water treatment flow rate is 12,500 liters/day. The whole treatment system was assembled in a 8′×40′ pre-fabricated portable building. The membrane tank is 40″ long×49″ wide and 97″ tall. There were 6 membrane packs installed in this tank, each capable of processing 2,450 liters/day at full capacity. The tank water level in the membrane tank is at 7′ 10″ high and activated sludge is re-circulated through the membrane tank from the aeration tank and back to the aeration tank via an overflow pipe. This water is recirculated at 72,000 liters/day. Water is then drawn through the membranes with the siphon actuated filtration process at a maximum flow rate of 12,500 liters/day. 
     The lines  102  are 1″ diameter lines and feed  106  which is a 4″ diameter×16″ long clear PVC pipe. The height from the midpoint of  108 A to the static water level in the membrane tank  16  is 7.8″. The extension  108   d  is 4″ above the midpoint of  108 A. The main body of  108 A is 8′4″ tall and sits  2 ″ above the bottom of tank  110 . The air tubing  114  is 1″ diameter and is connected to a ½″ solenoid valve and to an air vacuum pump that will draw 5 cfm at maximum vacuum of 120″ wc. The discharge tank is 22″ diameter and 48″ tall. LS  206  is located 8″ above the bottom of the tank and LS  208  is located 36″ above the base of the tank. 
     The water discharge line from pump  202  may be designed for maximum water flow 50,000 liters/day. Cleaning loop  212  is all 1″ diameter. 
     The variable vacuum drawn by the vacuum pump will vary when operating between 20″ wc vacuum and 82″ wc vacuum depending on the degree of plugging of the filter. 
     The present invention has been described herein with regard to certain embodiments. However, it will be obvious to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.