Abstract:
Sludge dewatering apparatus includes an inflatable membrane to press solids against a screen and thereby separate liquid therefrom, and nozzles to wash the screen of the separated solids.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a process for wastewater filtration. More particularly, the invention provides a multi-stage press apparatus for automatic sludge dewatering. 
         [0002]    Many innovative sludge dewatering technologies and products have been implemented in order to address issues related to better performance, higher throughput or cost efficiency. Due to concerns about global warming and energy costs, there has been an effort to employ systems which consume less electrical power, chemicals and washing water. 
         [0003]    Any wastewater and sludge process requires dewatering in order to minimize transportation and disposal volumes. Usually sludge is transported after the clarification, inefficiently, due to having a high, 89-90% liquid content. 
         [0004]    As an example, with a daily wastewater volume of 100 cubic meters per day at solids concentration of 1000 parts per million, and when the clarifier used is DAF (dissolved air filtration), then an approximate sludge yield is approximately 2000 kg, or approximately 2 cubic meters per day, which contains approximately 5% dry solids. After pressing, the volume of this sludge that contains 30% Dry solids reaches approximately 330 liters (disposal volume). 
         [0005]    The three major methods of achieving this dryness are plate filter press, belt press, and centrifugal decanter. 
         [0006]    Belt press and centrifugal decanters have proven to be too large and uneconomical for the volume in the example above, besides having other drawbacks, such as high power consumption and being too mechanically complex and therefore costly. 
         [0007]    Filter presses are usually manually operated and, therefore, require close operator attention. These presses quickly become dirty, necessitating periodical filter media cleaning. 
         [0008]    In U.S. Pat. No. 5,614,092 to Di Leo, there is disclosed a filter system for the separation of solids and liquids from industrial muds. The filter in the system includes a deformable membrane and a fluid pump which varies the size of the volume of the membrane, thereby squeezing the filter. 
         [0009]    While alleviating many of the tasks related to dewatering muds, such as squeezing and filtering, the filter disclosed in this patent does not address the need to minimize the down time due to the need to remove and clean the filter between the filtering operations, and, furthermore, does nothing to eliminate the need for man-hour input required for the cleaning. 
       SUMMARY OF THE INVENTION 
       [0010]    It is therefore one of the objects of the present invention to obviate the disadvantages of prior art sludge filter and to provide a sludge filtering device which is capable of continuous operation and minimal or no down time. 
         [0011]    It is a further object of the present invention to provide a sludge filtering device which is capable of high yield and would be easy to manufacture and operate. 
         [0012]    The present invention achieves the above objects by providing a multi-stage press apparatus for automatic, PLC (programmable logic controller) controlled, sludge dewatering and waste water filtration, comprising: 
         [0013]    a substantially cylindrical tank for receiving a mixture of sludge or waste water and coagulant, the cylindrical tank being designed to effectively allow suspended solids to be separated and later dewatered, and being provided with a lower, openable port for discharge of dewatered solids and having a substantially vertical cylindrical double layer mesh wired screen for discharge of cleared liquid; 
         [0014]    a centralized inflatable membrane, positioned to press the solids against the screen, whereby a stream of discharged, cleared liquid, passes through the screen and is discharged to a sewage drain or a further tank, the screen being provided with perforations sized to enable the passage of clear liquid therethrough while retaining fine and coagulated solids on the internal surface thereof; 
         [0015]    a load sensor in contact with the cylindrical tank to determine the combined weight of the apparatus and of solid and liquid internally retained thereon and to control the sequence of operation, and the filling and pressing duration as a function of the weight, whereby a solids cake of about 30 mm thickness of fine and coagulated solids is formed and retained on the internal surface of the fine screen layer, thereby improving the filtering and dewatering capacity of the apparatus, the apparatus further comprising a bottom opening with a second pneumatic inflatable membrane to seal and to open the bottom opening and thereby enabling downward discharge of solids into a sludge collecting bin; 
         [0016]    a set of high pressure nozzles located on the external side of the mesh screen body, to efficiently wash the screen from outside to inside, the nozzles being operationally linked to a drive mechanism which moves the nozzle assembly up and down in response to a PLC command during the cleaning cycle; and 
         [0017]    a PLC provided to manage all cycles of operation along with pneumatic and other electrical control items to activate solenoid valves, pumps and load cells, and to provide for a continuous dewatering and filtration operation. 
         [0018]    In a preferred embodiment of the present invention there is provided a press apparatus as defined above, further comprising a first tank provided with a sludge or waste water inlet pipe to supply sludge or waste water comprising a mixture of solids and liquid to the first tank; a pumping device, and a means for adding a coagulant to the sludge or waste water; and an outlet pipe leading to the cylindrical tank. 
         [0019]    In another preferred embodiment of the present invention there is provided a press apparatus wherein the inflatable membrane is formed of rubber and is pneumatically inflatable. 
         [0020]    In a further preferred embodiment of the present invention there is provided a press apparatus further comprising a pneumatic vibrator to improve the detachment of solids from the internal screen of the double layer mesh wired screen. 
         [0021]    In a further preferred embodiment of the present invention there is provided a press apparatus further comprising a liquid collecting sump pan, which is pneumatically displaceable upon the washing cycle, the liquid collecting sump pan being located below the press bottom to collect the washing liquid into the sewage system or back to the processing tank. 
         [0022]    In yet a further preferred embodiment of the present invention there is provided a press apparatus wherein the screen is coated with a non-stick material. 
         [0023]    In another preferred embodiment of the present invention there is provided a press apparatus wherein the load sensor is also used for determining the rate of weight loss of the combined weight. 
         [0024]    In another preferred embodiment of the present invention there is provided a press apparatus wherein the coagulants are selected from the group consisting of alum, ferric chloride, ferric sulfate, ferrous sulfate, titanium dioxide, lime, polyacrylates, cationic polyamines, cationic resin amines, cationic polyacrylamides and anionic polyacrylamides. 
         [0025]    In another preferred embodiment of the present invention there is provided a press apparatus wherein the set of nozzles is disposed generally surrounding the external side of the screen. 
         [0026]    In a most preferred embodiment of the present invention there is provided a press apparatus wherein the set of nozzles contains about 10 to about 30 nozzles. 
         [0027]    In a most preferred embodiment of the present invention there is provided press apparatus wherein each of the nozzles ejects a jet of liquid. 
         [0028]    In a most preferred embodiment of the present invention there is provided press apparatus wherein each of the nozzles ejects a jet of air. 
         [0029]    Yet further embodiments of the invention will be described hereinafter. 
         [0030]    The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood. 
         [0031]    With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a general diagrammatic view of a preferred embodiment of the apparatus according to the invention; 
           [0033]      FIG. 2  is a sectional view of the apparatus with the internal parts, at filling cycle; 
           [0034]      FIG. 3  is a sectional view of the apparatus with the internal parts, at pressing cycle; 
           [0035]      FIG. 4  is a sectional view of the apparatus with the internal parts, at unloading cycle; 
           [0036]      FIG. 5  is a sectional view of the apparatus with the internal parts, at cleaning cycle; and 
           [0037]      FIG. 6  is a diagramatic description of sludge and wastewater modes. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    There is seen in  FIG. 1  a multi-stage apparatus  10  for continuous sludge dewatering and waste water treatment. 
         [0039]    A first tank  11  is provided with a wastewater inlet pipe  12  arranged to supply thereinto sludge or waste water containing suspended solids. The first tank  12  is further provided with a coagulant inlet  34  to mix coagulant into the wastewater  12  introduced therein. The coagulant is activated while mixed in a tank  33  by a mixer, or circulation pump  35 . Addition of the coagulant enhances the efficiency of operation of the subsequent stages, and further chemical additions may provided through an inlet  15 , wherein activation thereof is performed by the static mixer  24 , and activation duration is provided in a pipe flocculator  16 . 
         [0040]    Coagulant  34  may suitably be selected from the group consisting of alum, ferric chloride, ferric sulfate, ferrous sulfate, TiO 2 , lime, and polyacrylate flocculent  15  such as cationic PAM (polyacrylamide), cationic polyamine, cationic resin amine and anionic PAM (polyacrylamide). 
         [0041]    First tank  12  is provided with a pump  14  for feeding the sludge or wastewater according a command from a PLC  21 . PLC  21  receives signals from a level detector  13  positioned on top of first tank  11 . PLC  21  controls dosage of chemicals  34  and  15 , as long as pump  14  operates. 
         [0042]    During a filling step, multistage press  10  is fed solids and liquid mixture via a conduit  17 . Prior to the filling step, the weight of the empty press is detected by a load cell  20 , and is registered by PLC  21 . 
         [0043]    Press  10  further contains a rubber membrane  39  with an air inlet  19 , a bottom sealing membrane  36 , a double layer screen mesh  37 , a cleaning mechanism  38 , a vibrator  18 , a liquid sump receptacle  22 , a pneumatic rotating cylinder  25 , and a pneumatic controller  26 . 
         [0044]    Filling step is initiated by a signal from level sensor  13 , signaling the PLC that a sufficient amount of sludge or wastewater is present in tank  12 . The end of the filling cycle is determined by counting time or by feedback from load cell  20 , therefore allowing the filling time to vary between cycles, assuring the shortest possible filling, regardless of other process parameters. A control algorithm in PLC  21  analyses the signals from load cell  20  throughout the stages and dynamically adjusts the cycle duration as a function of the weight of solids-liquid mixture inside apparatus  10 . 
         [0045]    Following the filling cycle, there follows the pressing, unloading and subsequent cycles which are be explained hereinafter. 
         [0046]    At the end of the unloading cycle, the unloaded weight of the solids  32  dumped into container  27 , is registered by the PLC for logistic or other purposes. 
         [0047]    Apparatus  10  is firmly mounted on a metal structure  23 , above a solids container  27 . The liquid that is pressed from the sludge or wastewater is discharged onto a sump  22  and then from pipes  29  or  30 , depending on the state of a directional valve  28 , to the sewage, or back to the sludge or to a wastewater storage tank. 
         [0048]    Details of the operation cycle are further illustrated in the following drawings. 
         [0049]    There is seen in  FIG. 2  a sectional view of the apparatus with the internal parts thereof, during a filling cycle. A flocculated and coagulated mixture  42  of solids and liquid, or wastewater is entering via port  53  onto a cylindrical void found between the internal fine mesh screen  41 , preferably of 60-200 mesh, which is supported by an external cylindrical coarse mesh screen  31 , preferably 4-10 mesh, and assembled onto a cylindrical pipe housing  55 , which is further attached by rods  49 , screws, bolts and Bellville® springs, and spring washers  47  to a main supporting structure  23 , and the flexible rubber membrane  39 , of 40-60 Shore hardness, made from natural rubber, EPDM, polyurethane, or other rubber types. 
         [0050]    The clean liquid expressed from mixture  42  is percolated outwardly through a fine screen  41  and a coarse screen  31 , and a flow  48  is drained into sump pan  22 , which can be moved aside by pneumatic cylinder  25 , and further via pipe  30  or  29  depending on the position of valve  28 , while the flocculent solids are retained between fine mesh screen  41  and the squeezing action of a flexible rubber membrane  39 . Low pressure air may be applied through port  19 , at pressures of 0.5-16 bar, to the inside volume of rubber membrane  39 , in order to accelerate the rate of percolation. 
         [0051]    The solids-liquids mixture is prevented from a downward flow, by a second rubber membrane  36  being pressurized from port  56  at a regulated air pressure. Membrane  36  is made of the same material as membrane  39 . 
         [0052]    The net weight of the mixture as measured by load cell  20  varies with time, and the load cell measures the net weight accumulation of solids and liquid retained in the void between membrane  39  and screen  41 . At the start of the filling cycle the net weight changes slowly since most of the liquid  50  percolates over screen  41 , however, when the screen becomes partly clogged the rate of increase of the net weight rises, until the whole void is full, at which point the pressure in the void rises also, at about 0.5-16 bar filling pressure, whereupon an auto air regulator stops supplying air to air diaphragm pump which pumps mixture  42  through port  53 , and no more mixture is fed thereinto. Thereupon load cell  20  detects the occurrence, the PLC sends a command to stop the filling and feeds of chemicals. 
         [0053]    Other parts of the press of the present invention which can be seen in this embodiment are the following: 
         [0054]    the vertical supporting beams  46 , the load cell moment release shaft  44 , and a pneumatic rod less cylinder  40  which moves a set of nozzles  38 , which receive the cleaning medium through a flexible tube  52  and a port  54 . There is also seen a splash protector  51  which is made of metal or plastic; 
         [0055]    a pipe  43 , clamped by a bolt, which connects rubber membrane  36  to another pipe  57  by a screwed connection  58 , and, similarly, an upper bolt  59  which connects membrane  39 , to the top plate  45  with internal air conduits leading from ports  19  and  56 ; and metal pipes  43  and  57  which form air-tight connections with the membranes. 
         [0056]    There is seen in  FIG. 3 , a sectional view of the press with the internal parts thereof, during a pressing cycle. 
         [0057]    The pressing cycle follows the filling cycle wherein the lower bottom remains closed by membrane  36 , which receives air pressure of 4-16 bars from port  56 , while membrane  39  receives compressed air via port  19 , thereby inflating the membrane and pressing the solids-liquid mixture against screen  41 , causing a formation of cake  60 , having a thickness of 5-50 mm, according to the pre-programmed parameters in the PLC, which monitors cake thickness via input from load cell  20 . 
         [0058]    Excess liquid  48  is drained off, through the lower pan  22 , via pipes  29 , or  30 , controlled by manual or automatic valve  28 . 
         [0059]    The end of a cycle is determined either by weight measurement via load cell  20 , by reaching the pre-programmed weight value, or by time count, whichever comes first. 
         [0060]    Another option for stopping the pressing cycle is by the measurement of weight loss rate, in order to determine when the rate of loss is below the end value of the pressing cycle. 
         [0061]    There is seen in  FIG. 4  a sectional view of the apparatus with the internal parts thereof, during an unloading cycle. The bottom opening membrane  36  is opened, by relieving the air, thereby creating a passage to void  61 . 
         [0062]    Upper membrane  39  is contracted as a result of air being released, and, at this point, a vibrator  18  may be activated to apply vertical vibration that causes a dewatered solids layer  60  to detach from a screen  41  surface, with the vibrator being activated continuously or periodically according to a program stored in the PLC. Air may be blown from a ring  38  of nozzles surrounding external screen  31 . Air is delivered to the nozzles via port  54 . Ring  38  is capable of being moved up and down by the action of an air piston  40 . This vertical movement enables a thorough, air backwashing of the whole surface of screen  41 , thereby assuring a successful detachment of solids layer  60 . 
         [0063]    Dry solid layer  60  collapses and accumulates in a solids container  27 . 
         [0064]    There is seen in  FIG. 5  a sectional view of the press with the internal parts thereof, during a screen cleaning cycle. 
         [0065]    Following unloading of the press apparatus, and before starting a new set of cycles, a screen  41  surface must be free and clean of dirt. Screen  41  may be permanently coated with a layer of a non-stick material such as Teflon®, or sprayed with a material of similar properties, to prevent dirt adhesion. Some solids will always be retained on the screen surface, however, and this cycle serves to remove the remaining dirt with minimum amount of backwashing liquids such as water. 
         [0066]    A liquid sump or a receiver  22 , is swung into position by a pneumatic actuator  25 , whereupon the main washing function is being performed by ring  38  of nozzles, preferably composed of about 10-30 nozzles. The nozzles generate a planar stream of liquid or air, the pressure thereof preferably being between 3 to 20 bars, and total backwashing flow rate preferably being between 5 to 20 liters per minute. The pressurized liquid is delivered from a port  10  to the movable ring of nozzles by a flexible pipe  52 . 
         [0067]    The nozzles circumferentially surround screen  31  and generate overlapping spray patterns. The clearance between exhaust tips of the nozzles to the external surface of screen  41  is preferably 10-50 mm. 
         [0068]    The ring of nozzles is moved along the vertical axis upon a command from the PLC to a rodless pneumatic cylinder  40 , whereupon the dirt trapped inside the holes in screen  13  is dislodged by liquid jets from nozzles  38 , and can be seen contained in stream  62  which flows downward, directed by a receiver  22  and ducted exterior to the press apparatus via pipe  29  or  30  as controlled by valve  28 . 
         [0069]    There is seen in  FIG. 6 , is a diagrammatic description of sludge and wastewater modes. 
         [0070]    It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.