Abstract:
The present invention relates to a system and a process of running the system that allows for the long term filtration of product without loss of filtration capability due to clogging or fouling. The system is a normal flow filtration system having one or more filter cartridges attached to an outlet of a housing in the system. The filter cartridge(s) are contained within a bowl and depend preferably vertically from the outlet. Liquid enters the bowl of the housing and contacts the outer surfaces of the one or more cartridges. Impurities are trapped on or in the surface of the filter and the filtered liquid flows through the filter and through the outlet. One or more parameters such as flow rate, transmembrane pressure drop and/or time are measured and when the desired parameter(s) are met, the filtration ceases. A backflushing occurs back through the filter cartridges so as to remove the trapped impurities on or in the filter surface. This backwashed material is directed to an outlet of the bowl that is connected to a drain. Additionally a port formed in the side of the housing adjacent an outer surface of the cartridge(s) can be used to provide a lateral washing of the filter surfaces. The system is then recirculated in a downstream manner to reestablish equilibrium and filtration is the restarted.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
       [0001]    This application claims priority to European Patent Application No.: 08382063.9, filed on Nov. 11, 2008 the entire contents of which are incorporated by reference herein. 
         [0002]    The present invention relates to a system and a method for the filtration of liquids. More particularly it relates to a system and method for the filtration of liquids which may have high solids contents such as beer, wine, water and fruit juices, or biological streams such as from bioreactors containing polyclonal, monoclonal or other desired proteins or enzymes. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wines, beers, fruit juices, water and the protein containing streams from bioreactors and other such liquids need to be filtered to remove impurities such as sugar crystals from wine; or cell debris and other cellular components from the bioreactor stream, or yeast from beer, or grape, other fruit skins and other debris found in raw and even partially purified liquids. 
         [0004]    Traditionally, this has been done with loose diatomaceous earth that is added to the liquid and allowed to settle. More advanced technology has become the various lenticular or plate and frame products that are formed of a cellulosic fiber material and various fillers such as diatomaceous earth and various charged polymers. These filters are normal flow devices, meaning that liquid is directed at them and the liquid flows through them to an outlet while impurities remain trapped in the pad(s). These filters are arranged in a housing which may contain one or more, generally several of these filters either I a frame in a plate and frame device or on a central rod that has a series of holes leading to the outlet within the rod in a lenticular pad device. Liquid enters through an inlet generally at the bottom side of the housing and flows around and through the filter(s) to the openings in the rod and out the bottom of the housing through an outlet. The pad filters become easily clogged with impurities that limit their use in production runs. This often requires the use of two or more identical filter systems that are run sequentially during a filtration operation to ensure adequate capacity. 
         [0005]    More recently, users have begun to look at TFF (tangential flow filtration) devices for such filtration applications. The TFF systems utilize the tangential flow across the face of the membrane to constantly sweep the membrane surface clean of materials that could block or plug the membrane leading to a decline in filter efficiency and life time. These devices can be made of flat or hollow fiber ceramic filters or flat, hollow fiber or spiral wound polymeric filters. 
         [0006]    While helpful in increasing the life of the filter system, such TFF systems have drawbacks including cost both of the equipment and to run it as well as high hold-up volumes and potential injury/degradation to the liquid due to numerous recirculations through the pump(s) of the system. 
         [0007]    TFF filter systems are more capital intensive than pad filters and require extensive specialized equipment including special filters, holders, pumps, retentate lines, etc. that are expensive to purchase. Additionally, the process using this type of filter is different and requires special training and dedicated capital equipment to do so. Moreover, the system uses 10 to 20 times the energy of a pad system for the pumping to create adequate recirculation of the fluid to create and maintain the TFF flow. Likewise, due to the extensive plumbing used in such systems, there is a large holdup volume in the system after filtration is completed. The fluid that has not been filtered and is in the tank, retentate lines, pumps, etc. is discarded after the filtration process. Often this is measured in 10 s of gallons of liquid that is lost and can amount up to 10% (depending of the hold up capacity of the system and the length and number of repeat cycles of filtration) of the starting volume leading to lower overall yield of product. Lastly, many liquids are sensitive to shear and other similar forces imposed upon them in TFF devices and can degrade or injure the product especially wine. 
         [0008]    Ceramic filters work but have the additional disadvantage of being susceptible to breakage under a variety of conditions which for the most part can&#39;t identified or quantified. An alternative to TFF ceramic filters is now a plastic or polymeric hollow fiber system with low or limited cross flow so as to reduce the number of cycles that the liquid is recirculated. While stating that the quality of the liquid is improved by reducing the recirculation, there are still the drawbacks of expense and large hold up volume. However and more importantly, the low crossflow is accomplished by increasing the surface area of the membranes used, often by at least 2× that of a traditional TFF system, again increasing cost and holdup volume. Additionally, TFF polymeric membranes are relatively weak in strength and are susceptible to rupture if too much pressure or shear is applied to them. Additionally, cleaning such filters is difficult, costly and time consuming making the cost of such filtration much more expensive 
         [0009]    Besides, TFF is in general very difficult to apply to cold filtration such as may be used with wine, beer, and fruit juice applications as higher viscosity of the liquid due to the lower temperature leads to lower flow rates and therefore bigger systems making them difficult to be economically viable. Another disadvantage in using polymeric TFF filters in cold wine or fruit juice applications which often include the filtration of crystals is that the polymeric membranes are not compatible with the “scratching” effect of the crystals of sugar in cold filtration causing wear on the filters and the production of particles into the fluid. 
         [0010]    What is needed is a system for filtration of high solids systems that is simple to set up, run and is less expensive than the TFF systems to purchase and operate and which increase yields with minimal filtration passes through the system to minimize degradation. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention relates to a system and a process of running the system that allows for the long term filtration of product without loss of filtration capability due to clogging or fouling. The system is a normal flow filtration system having one or more filter cartridges attached to an outlet of one or more housings in the system. The filter cartridge(s) are contained within a bowl and depend preferably vertically from the outlet. Liquid enters the bowl of the housing and contacts the outer surfaces of the one or more cartridges. Impurities are trapped on or in the surface of the filter and the filtered liquid flows through the filter and through the outlet. One or more parameters such as flow rate, transmembrane pressure drop and/or time are measured and when the desired parameter(s) are met, the filtration ceases. A backflushing occurs back through the filter cartridges so as to remove the trapped impurities on or in the filter surface. This backwashed material is directed to an outlet of the bowl that is connected to a drain. The system is then recirculated in a downstream manner to reestablish equilibrium and filtration is the restarted. 
         [0012]    Optionally, there may also be a lateral flushing of the outside of the cartridges through one or more ports formed in the sidewall of the bowl adjacent the outer surface(s) of the one or more cartridges. This may be done in lieu of but preferably in addition to the backflushing step and may occur either before or after the backflushing step but before the recirculation step. Unfiltered liquid is directed against the outer surfaces of the cartridge(s) to dislodge any trapped impurities and to remove any impurities that may have settled in the bowl. The port(s) may be tangential to the vertical surface of the filter cartridge(s); preferably the port(s) are perpendicular to the outer vertical surface(s) of the cartridge(s). 
         [0013]    Additionally, steps for the washing of the filter(s) with water and cleaning of the system can be conducted using the existing system design. 
         [0014]    Moreover, a system with two or more housings may be used so that at least one is on line while the other(s) is being regenerated or cleaned. 
         [0015]    The system can be used in a process that may be manually operated (by a system operator manually operating the valves, pumps, etc) or automatically (through a series of PIDs, a CPU, computer, computer network or other system that controls hardware and/or software). 
         [0016]    The system also includes a process for the filtration of a liquid through one or more filter cartridge(s), backflushing of filter cartridge(s), optionally lateral flushing of the exterior of the cartridge(s) through a port in the housing sidewall and a recirculation step. Optionally, water washing or CIP may also be accomplished in the present system. 
     
    
     
       IN THE DRAWINGS 
         [0017]      FIG. 1  shows a housing useful in a system according to the present invention in cross sectional view. 
           [0018]      FIG. 2  shows a close up of a portion of the housing of  FIG. 1  according to the present invention in cross sectional view. 
           [0019]      FIG. 3  shows the flow path for filtration in a system according to the present invention in cross sectional view. 
           [0020]      FIG. 4  shows the flow path for backflushing in a system according to the present invention in cross sectional view. 
           [0021]      FIG. 5  shows the flow path for recirculation in a system according to the present invention in cross sectional view. 
           [0022]      FIG. 6  shows the flow path lateral flushing in a system according to the present invention in cross sectional view. 
           [0023]      FIG. 7  shows the flow path for water washing or cleaning in place (CIP) in the reverse direction in a system according to the present invention in cross sectional view. 
           [0024]      FIG. 8  shows a system of the present invention using two such housings either in parallel or alternately. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    By “port(s)” it is meant that one or more ports exist or can be used. By “filter cartridge(s)” it is meant that one or more cartridges can exist or be used. 
         [0026]      FIG. 1  shows a filter housing  2  according to the present invention. It is formed of two major components, a head  4  and a bowl  6 . The head contains an inlet  8  and an outlet  10 . The bowl  6  has a drain  12  formed at or near its lowermost point  14 . 
         [0027]    The bowl  6  may have a frustoconical bottom  16  as shown or it may have a rounded, a tapered or even a flat bottom if desired. Preferably, it is a frustoconical, rounded or tapered shape. By having such a shape adjacent and/or at its lowermost point  14 , the drain  12  can work more efficiently to remove debris and impurities from the housing  2  as will be described further in. Often these shapes allow for the concentration of the impurities so that minimal amounts of product are lost from the system when the impurities are removed from the housing. 
         [0028]    As shown the one or more filter cartridges  18  are attached to the outlet  10  of the housing  2 . The cartridge(s)  18  are arranged so that the cartridge(s)  18  hang vertically from the outlet  10  of the head  4  into the bowl  6 . These cartridge(s)  18  are well known in design and have a closed end  19  which in this embodiment is farthest from the outlet  10  and an open outlet end  21  which is attached to the outlet  10  of the housing  2 . The cartridge(s)  18  contain one or more layers of filter material which may be pleated porous plastic membrane, spun or wound fibers such as of plastic, glass and the like and/or non woven materials. If desired various support and protective layers such as an outer porous protective cage, an inner porous core and one or more layers of filter support materials such as porous non-woven scrims and the like. 
         [0029]    Typical plastics for the filter material include but are not limited to polyolefins such as polyethylene and polypropylene, polyvinylidene fluoride (PVDF), polyvinyl alcohols, polyvinyl chlorides, polysulfones, polyarylsulfones, polyethersulfones, polyphenylsulfones, PTFE resins, PFA resins, polyesters, nylons, polyamides, polyimides, and celluloses and modified cellulosic materials such as cellulose acetate. 
         [0030]    The pore size of the filter will vary depending upon the filter type chosen, the impurities to be filtered and the like. They may range from about 0.1 micron average pore size to 10 microns pore size. Typically, a 2.0, 1.0, 0.65, 0.45 or 0.22 micron pore size are used for membrane type filters depending on the application, the impurities to be removed, the amount of impurities present and the like. Preferably filter having a pore size between about 0.65 and 2.0 microns is used. Non-wovens and depth filters such as wound filters and the like are not often rated by pore size but the extent that they are the same pore sizes as for membranes can be used. 
         [0031]    The housing may also contain one or more additional port(s)  20  in the side of the housing  2  adjacent the filters  18  that is used in the cleaning process described further below. The port(s) are tangential to the substantially vertical surface of the filter cartridge(s) and may be at an angle φ formed between the centerline (A-A)  23  of the cartridge(s) and the centerline (B-B)  25  of the port  20  as shown in  FIG. 2 . Preferably the angle φ is from about 15° to about 165°, more preferably from about 30° to about 150° or 45° to 135° and most preferably it is substantially perpendicular or about 90°. The port(s)  20  are in fluid communication with the source  26  of unfiltered fluid by a port conduit  21  which branches off of the conduit  28 . This port conduit  21  is generally closed by a port valve (not shown) and only opened for a lateral flushing step explained below at  FIG. 6 . 
         [0032]      FIG. 3  shows such a housing  2  and the system into which it is incorporated. A pump  22  is connected at its inlet  24  to a source of liquid  26  to be filtered. A conduit  28  connects the outlet  30  of the pump  22  to the inlet  8  of the housing  2 . Liquid enters the bowl  6  and is drawn through the filter  18  and through the outlet  10 . Drain  12  is connected to a waste line  32  and closed off from the waste line by a valve (not shown). 
         [0033]    Optionally a first sensor  36  is located at the inlet  8  and a second sensor  38  is located at the outlet  10 . The two sensors  36 ,  38  in combination can measure the transmembrane pressure in the one or more filter cartridges  18  or the flow rate of the system as will be described below. The sensors may be pressure sensors when determining transmembrane pressure differential or flow meters when determining flow rates. Any pressure sensor may be used, be it dial or analog or digital read out. The pressure sensor may be “dumb” requiring the operator to monitor the gauge or read out to determine if a desired parameter has been met (as will be explained below) or it may be intelligent and provide a signal to the system when the parameter is reached. Likewise any flow sensor may be used, such as a paddle wheel flow sensor that determines flow by counting the revolutions of the wheel or propeller in the sensor. It may be a dial or analog or digital read out. The sensor may be “dumb” requiring the operator to monitor the gauge or read out to determine if the desired parameter (flow rate) has been met (as will be explained below) or it may be intelligent and provide a signal to the system when the parameter is reached. 
         [0034]    Filtrate (liquid that has passed through the filter layer(s) of the cartridge(s)  18 ) exits the housing  2  through outlet  10  to conduit  40  and through valve  44  to a next step or storage tank  42 . Also shown is valve  46  in conduit  48  that selectively allows filtrate to flow to backflushing tank  50  for storage and use as described below. Valve  46  is normally closed off allowing filtrate to flow through valve  44 . 
         [0035]    In operation, liquid to be clarified or filtered is supplied from the source  26  such as a vat, tank or bin to the pump inlet  24 . The pump  22  moves the liquid through conduit  28  to the inlet  8  of the housing  2 . The liquid enters the bowl  6  outside of the filter cartridge(s)  18  and passes through the filter layer(s) of the cartridge(s)  18  to the outlet  10  of the housing  2 . Then through conduit  40  and valve  44  to a downstream component such as a next step or storage tank  42 . 
         [0036]    Impurities either are kept in the bowl  6  or become trapped in the filter layer(s) of the cartridge(s)  18 . After a while the filtration rate will decline and/or the transmembrane pressure differential will increase above the accepted parameter and the filter cartridge(s)  18  will need to be backflushed. When this backflushing is to occur can be determined by a variety of parameters, including but limited to time, transmembrane pressure and flow rates. 
         [0037]    As to the use of a time parameter, one can simply apply a timer to the controls for the pump  22  and/or valves into and out of the housing  2  if any. At a predetermined schedule, the pump  22  is shut off and filtrate is pulled from tank  50  through pump  52  and conduit  54  and valve  56  which is opened and back through the filter(s)  18  to dislodge any impurities that are adjacent or embedded in the filter(s)  18 . The impurities then settle out toward the lowermost portion  14  of the bowl  6 . Valve  58  is also closed at this time. The backflushed liquid is then preferably sent to drain so that all clogging material is removed from the system. This step and its flow path are shown in  FIG. 4 . 
         [0038]    The period of backflushing does not need to be long. It merely needs to provide a pulse of backflow and pressure sufficient to clean the filter cartridge(s)  18  to a degree sufficient to allow further filtration to proceed. In a preferred embodiment, the period of time for backflushing is from about 2 to 20 seconds, more preferably from about 5 to 10 seconds. 
         [0039]    The pressure of the backflushing can be about the same as the filtration pressure differential (generally around 1 bar over the actual downstream pressure). If desired additional pressure may be applied to the backflushing operation. 
         [0040]    Then the pump  22  is turned back on and the remaining fluid from the backflushing step above in  FIG. 4  is moved through conduit  28  into the housing  2  and out through conduit  40  as in the filtration step of  FIG. 3 . Valves  44  and  46  are closed and valve  60  is opened to allow the liquid to recirculate back to the inlet  24  of the pump  22 . Optionally and preferably, new unfiltered liquid is also drawn into the system at the same time from source  26 . This recirculation need only occur for a short period of time so that the liquid is reequilibrated and/or any filtration cake that is needed for filtration to occur is formed. Valve  60  is then closed and valve  44  is reopened and filtration resumes. Additionally, at some point during the filtration process, valve  46  is opened and valve  44  is closed to allow tank  50  to refill for the next flushing cycle. 
         [0041]    The period of recirculation does not need to be long. It merely needs to provide a filtration cake if needed for filtration and/or equalize all the liquid within the system before filtration can begin again. In a preferred embodiment, the period of time for backflushing is from about 20 seconds to 60 seconds, more preferably from about 20 to 40 seconds and most preferably about 30 seconds. 
         [0042]    The pressure of the recirculation should be about the same as the filtration pressure differential (generally around 1 bar over the actual downstream pressure). If desired additional pressure may be applied if desired (for example to generate a filtration cake). 
         [0043]    Preferably, in one embodiment of the present invention where time is used as the parameter, one sets a schedule based upon the load of impurities in the stream, the filter cartridge(s)  18  selected and the volume of material to be filtered. Typically, it has been found that a schedule set between every 10 to every 20 minutes is useful for most applications. For most the preferred time parameter is every 10 minutes. The same process of valve openings/closing and pump movements are used as described above to create the backflushing and recirculation steps. 
         [0044]    The period of backflushing and the pressure used is the same as described above. 
         [0045]    As to the use of a transmembrane pressure parameter, one can simply select a transmembrane pressure upper limit that corresponds to a certain level of clogging of the filters. One can use pressure sensors as sensors  36  and  38  to measure the upstream and downstream pressures of the filter layer(s) and determine when the transmembrane pressure (the difference between the upstream or inlet pressure and the downstream or the outlet pressure) is too great. When that parameter is met or exceeded the same backflushing and recirculation steps occur. 
         [0046]    Preferably, in one embodiment of the present invention where transmembrane pressure is used as the parameter, one sets a limit of from about 0.2 bar (20 KPa) to about 5.0 bar (500 KPa) depending upon the impurities in the stream, the filter(s)  18  selected and the volume of material to be filtered. Typically it is between about 0.2 bar (20 KPa) and 1 bar (100 KPa) difference (but again, the pressure differential chosen is dependant of the quality of impurities, and therefore of the fluid to be filtered). For most applications, the preferred transmembrane pressure differential parameter is 0.2) bar (20 KPa). 
         [0047]    As to the use of the flow rate parameter, one can simply select a sensor to measure flow rate such as flowmeter preferably on the downstream or outlet side of the system. A reduced flow rate that equates to a certain level of clogging of the filter(s) is determined and when that reduced flow rate is reached the backflushing operation described above in relation to the transmembrane pressure differential or time system above is utilized. 
         [0048]    Preferably, in one embodiment of the present invention where flow rate is used as the parameter, one sets a limit of from about 50% to about 80% of the initial flow rate depending upon the impurities in the stream, the filter cartridge(s)  18  selected and the volume of material to be filtered. Typically it has been found that a reduction in flow rate of between 20 and 40% from the initial flow rate is useful for most applications. 
         [0049]    At some point in the process or as an alternative to the backflushing step (although the backflushing step of  FIG. 4  is preferred and this optional step is an additive step that may be used as desired either before or after the backflushing step), one may use a lateral flushing step by introducing liquid through port(s)  20  in the side of the housing  2  rather than through the inlet  8 . Impurities are pushed of off and out of the filter cartridge(s)  18  and then are discarded through the drain  12  in a manner described above. This optional step is shown in  FIG. 6 . Fluid from source  26  flows into conduit  21  through one or more ports  20  and against the outer surface of the cartridges  18 . From there, the fluid and any impurities removed from the cartridges are flowed out of the system to the drain  12 . 
         [0050]    The period of lateral flushing does not need to be long. It merely needs to provide a pulse of liquid at a pressure sufficient to clean the filter cartridge(s)  18  to a degree sufficient to allow further filtration to proceed. In a preferred embodiment, the period of time for lateral flushing is from about 2 to 20 seconds, more preferably from about 5 to 10 seconds. 
         [0051]      FIG. 7  shows a step for cleaning the system after use or flushing the system before use to remove any potential contaminants that may have entered the system during assembly. Water be it cold  70  or hot  72  or optionally steam instead of one or the other waters  70 , 72  is supplied by conduit  74  through tank  50  pump  52  and conduit  54  to conduit  40  and outlet  10  of the housing  2 . Various valves such as  76  are closed to cause the water or steam to flow through the housing  2  and it can be returned to the tank  50  via conduit  80  for recirculation. After the desired time, the water or and/or steam is shut off and valve  78  is shut to close off the water return conduit  80  and the water/steam is drained through conduit  82  to a water/steam drain. Optionally, the conduits used in this step may also be subjected to pressurized air to cause the water/steam to drain out more efficiently as is well known in the art. 
         [0052]      FIG. 8  shows a system having more than one or two or more housings  2 A and B. The operation of the system is similar to that explained in  FIGS. 3-7  and would be obvious to one of ordinary skill in the art the only addition being a dedicated water/steam tank  100 . This allows one to use one housing  2 A while the other is being regenerated through the process described in  FIGS. 4 and 5  and optionally  6  and/or  7 . Alternatively, the two or more housing can be run in parallel at the same time if desired. 
         [0053]    Preferably the temperature of the process in any embodiment is kept at a range between about −6° C. and about 20° C. (minus temperatures may be used for liquids that contain alcohol or salts that depress their freezing point or are formed of materials that have freezing points below 0° C.). For many applications, such as wine filtration, fruit juice filtration, biological filtration, the process takes place in chilled rooms and in chilled systems with temperatures ranging between about 4° C. and about 10° C. In the case of filtration of wine for removing bitartrate crystals (cold stabilization of wines), the temperature of filtration is as a rule of thumb minus half of the alcohol content (otherwise the crystals would redissolve). This means for alcohol of 11% one would conduct the filtration at temperatures of about −4° C., or −5° C. 
         [0054]    The liquid can be prechilled before entering the system. The system may be insulated if desired but generally it is not needed as the time spent in the system is relatively low. Alternatively, the system may be run in a cooled or “cold” room to minimize any shift in temperature within the liquid while being processed. In some extraordinary situations, the system can be affirmatively cooled by cold water circulation systems or chilling blankets as are well known in the art. 
         [0055]    The filter is a normal flow polymeric filter such as a Polygard® CE filter available from Millipore Corporation of Billerica, Mass. which contain a glass fiber/diatomaceous earth/polypropolene fiber blend of materials. However any normal flow filter that can withstand backflushing pressures on repeated cycles can be used in the present invention. 
         [0056]    The system can be used in a process that may be manually operated (by a system operator manually operating the valves, pumps, etc) or automatically (through a series of PIDs, a CPU, computer, computer network or other system that controls hardware and/or software). 
       Example 
       [0057]    A system according to that of  FIG. 8  which had a twin two 3 round  30 ″ Polygard® CE filter cartridges (2-micron pore size) available from Millipore Corporation of Billerica, cartridges in parallel was used and incorporated a housing according to that of  FIG. 1  such that the outlets of the cartridges were attached to the outlet of each housing via the housing round plate as is well known in the art so that liquid leaving the housing outlets first passed through the filter cartridges. 
         [0058]    500 liters of unfiltered white wine with an alcohol content 12% from a stainless steel tank was supplied to the inlet of the pump at a temperature of −2° C. at an upstream pressure of 0.2 bar (20 KPa) as read by the upstream pressure monitor on the inlet to the housing. Filtrate passed through the outlet of the housing at a pressure of 0.2 bar (20 KPa). 
         [0059]    Time was the parameter measured and this was done by a stop watch. 
         [0060]    After 10 minutes, the pump was shut off manually and the backwashing step as taught in  FIG. 4  was run for 6 seconds at a pressure of 0.7 bar (70 KPa) as read on the pressure sensor of the outlet. 
         [0061]    The recirculation step as described in relation to  FIG. 5  was run at 0.7 bar (70 KPa) measured at the upstream sensor on the inlet to the housing for 28 seconds to reequilibrate the systems and create the desired filter cake on the filter surface. 
         [0062]    The above steps were run in sequence 6 times. 
         [0063]    After 5 filtration and backflushing steps were completed a lateral washing step through the side ports) of the housing was conducted for 6 seconds at a pressure of about 0.7 bar (70 KPa), followed by the recirculation step. 
         [0064]    A control system formed of a standard TFF hollow fiber system (Ronfil hollow fiber system, sold by Domnick Hunter Ibérica) was run using the same wine and both systems had flow rates, turbidity of wine and clogging index (filterability index) measured. 
         [0065]    The Clogging Index is a filterability index is widely used in European wineries to gauge the filterability of a wine. Clogging index is the difference in time between how long it takes to filter from 200 ml and 400 ml as compared to the time it takes to filter the first 200 ml on a continuous experiment at a given pressure and membrane. 
         [0066]    The method for calculating it is the following: 
         [0067]    T 0 =initial time of 0 seconds. 
         [0068]    T 2 =time in seconds to filter the first 200 ml (from 0 ml to 200 ml) of wine through a 0.65 membrane at 2 Bar inlet pressure. 
         [0069]    T 4 =time to filter the second 200 ml (from 200 ml to 400 ml) of wine through the same filter and at the same pressure. 
         [0000]        CI =( T 4− T 2)−( T 2− T 0)= T 4−2*( T 2) 
         [0070]    Units are reported in seconds, but it is normally treated as a index with no units assigned. 
         [0071]    The wine filtered according to the control and the present invention had the following characteristics as set forth in Table 1: 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Control 
                   
                   
                   
                   
                   
               
               
                   
                 Flow 
                   
                 Control 
                 Invention 
                 Invention 
                 Invention 
               
               
                   
                 Rate 
                 Control 
                 Clogging 
                 Flow Rate 
                 Turbidiy 
                 Clogging 
               
               
                 Time (min) 
                 (l/h) 
                 Turbidity (NTU) 
                 Index 
                 (l/h) 
                 (NTU) 
                 Index 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 1200 
                 &lt;1 
                 10 
                 600 
                 &lt;1 
                 11 
               
               
                 20 
                 900 
                 &lt;1 
                 12 
                 600 
                 &lt;1 
                 14 
               
               
                 30 
                 650 
                 &lt;1 
                 8 
                 600 
                 &lt;1 
                 12 
               
               
                 40 
                 450 
                 &lt;1 
                 11 
                 600 
                 &lt;1 
                 14 
               
               
                 50 
                 150 
                 &lt;1 
                 10 
                 600 
                 &lt;1 
                 13 
               
               
                   
               
             
          
         
       
     
         [0072]    The holdup and lost volume for backflushing and lateral backflushing for the present invention was 5 liters or 1% of the starting volume and the filtration occurred in 50 minutes. 
         [0073]    The holdup and lost volume for the control was 35 liters or 7% of the starting volume and the filtration required 66 minutes to complete. 
         [0074]    As can be seen for the example the present invention significantly reduced the volume lost to hold up volume of the system and completed the filtration quicker and maintained a high, consistent flow rate through out the entire test. 
         [0075]    While the above example was with wine, this system can be used equally well with other liquids which need clarification such as beer, water, fruit juices, energy drinks that contain impurities such as fruit pulp or skin, solid impurities, clarification aids such as egg albumin or diatomaceous earth and the like. Likewise it is suitable for use with biological streams such as the output from a bioreactor which contains a protein of desire, such as a monoclonal antibody, along with other impurities including but not limited to clarification aids such as diatomaceous earth or flocculants, cell debris, host proteins and other undesirable cell elements and the like.