2. DESCRIPTION OF THE PRIOR ART Filtration is the separation of two phases, typically, a solid from a liquid.

Filtration is often referred to as mechanical separation because the separation is accomplished by physical means. However, chemical and thermal pretreatment can be used to enhance filtration. Filtration systems typically include a porous filtration medium contained in a housing. A driving force, usually in the form of a static pressure difference, must be applied to achieve flow through the filter medium. It is immaterial how the pressure difference is generated but there are four main types of driving force: gravity; vacuum; pressure; and, centrifugal.

Mechanical filters (e. g., horizontal wire mesh filters and vertical leaf filters) are used in the filtration process to assist in separating insoluble particles from a liquid.

Typically however, mechanical filters alone are insufficient to effect a desired filtration of a liquid containing fine, insoluble particles. In addition, mechanical filters tend to quickly accumulate contaminates, which can often inhibit or completely stop the filtration process. Accordingly, it is well known in the art to use cake, or surface, filtration.

Where the unfiltered liquid is a malt beverage, it is known in the art that the filter media can include the following naturally occurring materials: cellulose, silica gel, diatomaceous earth ("DE"), perlite, charcoal, wood dust, and similar materials.

Synthetic materials e. g. plastic particles of the appropriate size distribution and similar regeneration properties as perlite can also be used. DE is the most widely used of these materials. In the filtration of malt beverages, the fine, solid particles which are contained in the unfiltered malt beverage include remnants of the brewing process. These particles include yeast cells, barley fragments, proteins complexed with polyphenols and other fine solid particles.

It is also known in the art to use chill-proofing agents to aid in the coagulation and removal of particles from the malt beverage. It is desirable to remove small particles because they will cause the malt beverage to have an undesirable cloudy appearance, known as"chill haze", when it is chilled. Moreover, these particles tend to settle out of the malt beverage when it is chilled.

The term"chill-proofing"refers to the addition of chill-proofing agents to effect the removal of these particles. Typically, these chill-proofing agents are dispersed within the unfiltered malt beverage. The chill-proofing agents, e. g., gallotannin, combine with chill haze producing components to form larger particles which are then more effectively filtered out of the beverage. Silica gel is another chill-proofing agent which removes chill haze by adsorbing proteins on solid silica gel particles. The silica gel particles then are filtered out of the beer into the filter media.

Another material used in the chill-proofing process is polyvinyl polypyrolidone ("PVPP"). PVPP acts as a stabilizer by adsorbing polyphenols which combine with proteins to form chill haze. PVPP is an expensive material and can be regenerated with caustic washing and specialized equipment, either before or after normal filtration, to dissolve out the polyphenols adsorbed to the PVPP from the beer.

In cake filtration, the mechanical filter provides a support for a filter medium such as perlite or diatomaceous earth. Typically, a pre-coat of the filter media is applied to a mechanical filter to form an initial layer of filter media on the mechanical filter. As the filtration continues, the initial layer of filter media or"pre-coat layer"becomes "spent", i. e., the filter media becomes less effective at removing contaminants from the liquid. To extend the length of the filtration, fresh filter media is added to the filter bed by dispersing fresh filter media in the unfiltered liquid. This is known as"bodyfeed".

The bodyfeed accumulates as additional filter media on the mechanical filter. This

dispersion of additional filter media increases the effective filter bed depth, creating new pores and voids for incoming solid particles to be filtered out, thus extending the length of the filter run. As a result, the filter bed of filtered solids and filter media are deposited onto the mechanical filter resulting in the formation of a cake-hence, the name"cake filtration."The terms"cake"or"filter cake"refer to a packed layer of filtered matter which is produced adjacent the mechanical filter by the progressive deposition of filtered matter and filter media thereon.

Eventually, the cake becomes thick enough so that an unacceptable pressure drop occurs between the cake input and output side. The filtration process must then be discontinued to remove the spent cake from the mechanical filter. The remaining fluid can be removed with carbon dioxide pressure. The filter media remaining on the mechanical filters can be removed by spraying with water. This process is known as "sluicing".

In current systems, the spent filter media is not reused and is disposed of after one use. The cost of disposal of spent filter media and the cost for a continuous supply of new filter media are high. Thus, there have been attempts to regenerate spent filter media. However, in known regeneration processes, an undesirable amount of performance deterioration of the spent filter media occurs. Moreover, these traditional regeneration processes have not provided a desirable degree of regeneration of the spent filter media. Consequently, only modest cost savings can be achieved with such systems.

Some of these traditional regeneration processes have involved the use of DE, as the filter media. However, these traditional processes which sought to regenerate DE have not proven commercially feasible within the brewery environment. The natural three-dimensional structure of DE hinders a complete regeneration because some of the filtered particles remain in the interior of the three dimensional DE structure.

Polysaccharide concentration in the regenerated DE builds up over successive regenerations limiting the number of regenerations before filtration performance is unacceptable. Typically, DE can only be regenerated 3 to 5 times before it must be disposed of. Also, continuous regeneration and re-use of DE will break down its three dimensional structure and contribute to decreasing filtration effectiveness. Accordingly,

these traditional regeneration methods involving the regeneration of DE have not proven to be economically advantageous. In addition to being difficult to regenerate, DE purchase and disposal costs are high.

Thus, there is a need in the art for an improved process that successfully provides for a practical regeneration of spent filter media that is cost effective, practical and compatible within a brewery operation.

SUMMARY OF THE INVENTION The present invention provides an improved process that provides for continuous in-brewery regeneration of filter media that is external to the mechanical filter.

Continuous beer filtration is not slowed down by the regeneration process. The present invention also provides an improved process for the cost effective regeneration of a filter media which produces a desirable regeneration and which allows for the same filter media to be regenerated many times. The regeneration process of the present invention provides for the regeneration of a filter media without significant deterioration of the filter media in each successive regeneration step.

The process of the present invention includes combining collected spent filter cake that includes filter media, chill-proofing agent and filtered particles in mild caustic and at mild temperatures (33 °-110°F); and, mixing said combination in a regeneration tank for at least 6 hours. No external heat is applied to the regeneration tanks.

Regeneration occurs at ambient temperature. To complete the regeneration, the perlite is washed with a separate caustic solution followed by a dilute acid and then water. The filter media is preferably perlite. The chill-proofing agent can be silica gel. PVPP may also be used. Constant stirring is required to avoid settling of filter media and to ensure efficient regeneration action by the caustic.

Background Perlite is a generic term for naturally occurring siliceous rock. Since perlite is a form of natural glass, it is chemically, and in terms of flavor, inert.

Perlite mines are located throughout the world. In the United States, perlite mines are located in Colorado, New Mexico, Oregon, Utah, and Nevada. In addition, large quantities of perlite ores are imported, particularly from Greece.

In its natural state, perlite occurs as a gray to brown glassy volcanic rock consisting of fused sodium potassium aluminum silicate plus 3% to 5% water. When fractured and heated to high temperatures, it pops like popcorn because of the presence of occluded water, expanding 20 times or more of its original volume. The expanded material is crushed to yield a white powder. The expanded perlite is then milled and

sized to produce graded materials with particle size distribution ranges defined by the specific application.

Graded perlites are used for many non-food applications, e. g., in the horticulture, construction, and agriculture industries. These applications use products that are milled to comparatively coarse particle size distributions.

Filtration grades require particle size distributions that are finer than for other applications, particularly if yeast levels in beer are low. Filtration grades are used in the food industry, e. g., for filtering wine, vegetable oils, sugar, pharmaceuticals, fruit juices, and beer. These filtration grades are produced in the United States by Grefco, Silbrico, Renaissance, and World Minerals.

Although perlite filtration has had limited use in some breweries, DE remains the filter media of choice to-date for malt beverages. One reason perlite is not used more widely is that the perlite particle size distribution has not been optimized for filtration of malt beverages.

Another reason that perlite has not been widely utilized is that in its natural form it has unacceptably high beer soluble iron ("BSI") levels. Commercially available DE and perlites contain about the same amount of native iron, but the DE used for beer filtration includes a process step that modifies the state of the surface iron. This causes the surface iron to become less extractable by beer, therefore lowering BSI.

Commercially available perlite has not been treated to reduce BSI. This problem is compounded by the small particle size necessary for perlite to have adequate filtration characteristics. Generally, the smaller the particle size, the more surface iron is exposed to the malt beverage, thus producing higher BSI values.

Perlite Regeneration Process DE particles are fossilized diatoms and as such, they have two features that are not found in perlite particles. The fossilized DE particles come in a complex variety of shapes with hollow spaces inside the particles. For instance, up to 10% of a DE filter bed's voids are composed of hollow spaces inside the particles that are not attributed to spaces between the particles. During filtration, tiny particles from the beer become tightly embedded within these hollow spaces and they cannot readily be cleaned out.

These embedded organics can only be removed by heating in strong acid or destruction by intense heat. Neither of these techniques are conducive to a simple regeneration system that is suitable for installation in a brewery.

Another difference between DE particles and perlite particles is that some of the DE particles have become fused together during processing, creating larger particles.

Both of the above features help to filter out tiny particles from beer because of the interlocking, hollow nature of the DE particles.

Because DE's three dimensional structure is composed of brittle fossilized crystalline silicate, it is susceptible to degradation by pumping and other steps in the regeneration process. The crystalline silicate present in DE has been recently identified as a potential carcinogen..

However, perlite contains less than 0.1% crystalline silicate making it less brittle than DE and consequently is it rated as a non-carcinogenic natural mineral. After expansion and milling of perlite, the resulting irregularly shaped tiny particles are essentially two dimensional solid flakes which contain no hollow spaces to embed organic materials. Because perlite is not crystalline and does not have as complex a three dimensional structure, it is less likely to be degraded further by pumping and other regeneration steps.

Filtration with perlite occurs on the bed surface and between the perlite particles since the perlite particles are not hollow. Filtration with DE occurs similarly, but also by trapping particles from beer within the hollow particles. As a result of this difference in mode of filtration and because some of the three dimensional structure of DE will continually fracture by reuse and regeneration, perlite is a much better material for regeneration using a mild, cyclical process that is compatible within a brewery operation.

The regeneration operation is carried out in a batch mode external to the mechanical filter as described below. The initial step of regeneration is to dissolve, degrade or soften the trapped materials contained in spent filter media sluices using a caustic solution. Clean up of the perlite can then be accomplished using basket centrifugation or pressure filtration and the remains of the organic materials will readily slide between the solid perlite particles and out into the waste steam. Similar mild

treatment of DE would continually leave organic materials inside the DE particles, rapidly reducing permeation, filterability and run length.

If chill-proofing with silica gel is used with beers along with filter media, most of these silica gel particles also wind up in the spent filter media so that they have to be removed during regeneration. This is accomplished by the same mild regeneration technique used for removing particles from the spent filter media. Chill-proofing silica gels are very susceptible to caustic and as such are dissolved in the mild caustic regeneration step. The dissolved silica gel can be washed out of the spent filter media.

However, perlite is essentially not affected by the mild conditions utilized for regeneration. Chill-proofing with tannin would also produce particles that are readily degraded by caustic. If PVPP is used for chill-proofing, the extended caustic treatment would dissolve away bound polyphenols, thus regenerating PVPP. It would not be affecte by caustic and be reused within the regenerated perlite.

Details of Regeneration Recovery of Spent Perlite Spent filter media is sluiced out of the K-filters into regeneration/collection tanks. Optionally, the spent filter media may be transported first to a holding tank and then to a regeneration tank. Sluice volumes go into these tanks except for possibly the last tailings which contain only a very small amount of perlite. When a regeneration tank is full, further sluice volume will be directed to the next empty regeneration tank.

The last tailings can be diverted to the sewer if desired.

Regeneration Sluice water temperature from the K-filters to the regeneration tanks is not critical but they should be maintained above 32 °F. Optimally, the regeneration tank should have a temperature between about 50°F to about 110°F environment. The tanks should be continually stirred with agitators to prevent settling of the filter media.

Regeneration is initiated with the addition of caustic. If silica gel is used for chill-proofing, the weight of added caustic to a regeneration tank must be sufficient to dissolve all of the silica gel contained within a given regeneration tank. However, a significant amount of excess caustic can be avoided by pH control. Operationally, final

caustic concentration in a regeneration tank will be approximately 0.5-3 weight percent based on silica gel concentration. If PVPP or tannin is used for chill-proofing, the added caustic can be less than with silica gel. Regeneration is then carried out with continual mixing, mild temperature, and low caustic concentration. Caustic degradation or modification of yeast and other particles in beer occurs while completely dissolving the silica gel. The time for regeneration is determined primarily by the time required to dissolve all of the silica gel. Under these mild conditions, approximately 6 hours are required to dissolve all of the silica gel. At this point, it is considered"ready"for final clean-up. Final clean up is achieved by completely washing these contaminants out of the perlite cake by forces developed in a basket centrifuge.

Basket Centrifuge Clean Up The action of the centrifuge is analogous to that of the bowl in a conventional washing machine. The centrifuge bowl has a series of openings covered by a removable semi-permeable polypropylene filter cloth covering the holes in the bowl. A spray nozzle is situated in the bowl and is used to spray incoming slurry onto the sides of the spinning bowl. Clean up is carried out in batched sequences as follows.

The first step is to spray"ready"regeneration slurry onto the sides of the spinning bowl creating a perlite cake. The solubilized and degraded organic materials permeate through the cake and out the plastic filter media. After the cake reaches a preset depth (controlled by a centrifuge PLC program), incoming regenerate slurry is stopped and washing of the established cake is started.

Three washing steps are used for final clean up.

Step 1: Dilute, cool caustic is sprayed onto the spinning cake for several minutes. The purpose of this wash is to wash out any remaining dissolved silica gel and degraded organics.

Step 2: Dilute, cool acid, e. g., sulfuric or phosphoric acid is sprayed onto the spinning cake for several minutes. The purpose of this wash is to neutralize the caustic, remove acid soluble impurities produced by beer filtration and to reduce beer soluble iron levels. Each regeneration will require BSI reduction by acidic rinses as the surface iron is modified by the action of caustic to a more beer extractable form. Washing with acid reduces BSI levels to low levels by dissolving surface iron.

Step 3: Hot water, approximately 140°F-180°F is sprayed onto the spinning cake several minutes. The purpose of this wash is to remove remaining acid, as an added sterilization step and to remove remaining extractable iron solubilized by the acid wash.

Step 4: After the hot water wash, while the perlite is still moist, the centrifuge gently scrapes the perlite offthe walls. The regenerated perlite drops into a centrifuge slurry tank containing sterilized water. A final spray with sterilized water is used to clean the plastic filter media.

Reuse of Perlite from Centrifuge Slurry Tank The concentration of the perlite in the centrifuge slurry tank can optionally be controlled by an insertion densitometer and appropriate addition of sterile water. The tank itself can be open to the atmosphere as the regenerated perlite from each batch will be gravity fed into the tank while the tank is continually stirred with an agitator.

On demand from the finishing control room, regenerated slurry is then pumped to a filter media silo slurry tank where a known weight is added to adjust the concentration required for both precoat and bodyfeed tanks. The weight of perlite used for filtration will be somewhat less than DE since perlite is less dense, but the total volume will be approximately the same. If PVPP is used as chill-proofing agent, it will be incorporated at a preset level within the requested perlite and will have been regenerated along with the perlite.

Make-up with Fresh Perlite Operationally, it is planned to add fresh perlite (and PVPP if used as a chill- proofing agent) periodically into the filter media slurry tank as required because of attrition from incomplete sluicing and as necessary to maintain filtering (and PVPP chill- proofing) efficiency.

Pilot filtrations have been carried out over 20 times using the same perlite without significant loss of filterability, without increasing pressure drop and without detectable build-up of organic material. Small amounts of fresh perlite can be added at regular intervals as needed to make up for handling attrition. Fresh perlite make up will constitute a small percentage of perlite going to the filters and will then be washed in the

next regeneration cycle so that filtration will be carried out with primarily regenerated material. Embodiments of the invention are now described with reference to the accompanying drawing. These embodiments are described by way of example only and are not intended to limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram depicting a filtration process in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 depicts a flow diagram of a process for the regeneration of filter media used in the filtration of fine particles from a liquid (e. g., a malt beverage such as beer) in accordance with the present invention. The following detailed description of the preferred embodiment involves the filtration of a malt beverage using a filter media composed of perlite. The preferred filter media is primarily composed of perlite. The use of small amounts of PVPP in addition to the perlite is preferred. The PVPP aids in removing chill haze producing components and can eliminate or permit the use of less silica gel in the chill producing step. Advantageously, the PVPP can be regenerated using the same process that regenerates the perlite. The preferred particle size range for the perlite is determined by custom produced ranges that achieve the best beer clarity and longest filtration run times determined for the types of beers to be filtered.

Generally, the perlite should have a maximum particle size less than 250 microns and a Darcy permeability of 0.20 or less. The particle size ranges required are very small and need to be tailored to the malt beverages being filtered.

Initially, a slurry of fresh filter media contained in a pre coat tank 10 is transported through lines 41,42 and 43 and deposited as a pre coat onto mechanical filters contained in filter tanks 12. The number and size of the filter tanks are not critical.

The filter tank 12 typically contains a plurality of mechanical filters such as vertical leaf filters and other mechanical filter elements as known to those skilled in the art, e. g., candle filters. A flow path is defined within the filter tank 12 and the mechanical filter is interposed perpendicular or horizontally to the direction of the flow path. The preferred mechanical filters in the filter tank 12 are vertical leaf filters which are wire mesh filters or wire mound candle filters. As shown in FIG. 1, it is preferred to have a plurality of filter tanks 12 connected in parallel to allow for alternating between filling with spent sluice, regenerating with caustic and feed ready slurry to a basket centrifuge or pressure filter so as to produce a continuous filtration of the unfiltered liquid. The use of several filtration tanks 12 connected in parallel allows for the continuous processing of the spent filter media even though each individual tank 12 provides for batch filtration. Thus, the term"filtration cycle"refers to a batch filtration

process which includes those steps which occur from one shutdown to another of an individual tank 12.

The precoat suspension of filter media is typically applied directly to the mechanical filter in the filter tank 12 as a slurry. A slurry of the filter media can be prepared by mixing the filter media with a liquid and then recirculated through the filter to form a filter bed. Preferably, the suspension of filter media in the precoat tank 10 is a slurry of perlite wherein the liquid is water or a fermented liquid (e. g., beer). It has been found that perlite provides for the desired filtration as well as requiring only infrequent replacement. Other filter media that have a low occurrence of hollows or voids that can bind with the filtered particles are also expected to work well with the invention. PVPP may also be used in conjunction with filter media other than perlite. The preferred concentration of the slurry of perlite in the pre coat tank 10 is typically in the 5 to 25 weight percent range.

After the precoat suspension of filter media is applied to the mechanical filter in the filter tank 12, an unfiltered malt beverage is then passed into the filter tanks 12 from a feed tank 14 through lines 44 and 45. The unfiltered malt beverage from the feed tank 14 includes the fine, solid particles that are to be filtered. These particles are remnants of the fermentation process and include particles such as yeast and parts of barley.

Chill-proofing agents can be to the unfiltered malt beverage in the feed tank 14. Chill- proofing agents can be organic compounds (e. g., tannin) or inorganic compounds (e. g., silica gel). A turbity meter (not shown) at the filter outlet is used to determine whether the malt beverage has been adequately filtered.

As the filtration process continues, the precoat of filter media becomes spent and additional filter media is required for adequate filtration. Accordingly, additional filter media from a body feed tank 16 is continually added to the filter via lines 46,42 and 43 to maintain an acceptable quantity of fresh filter media in the filter tank 12. An additional body feed tank 16 is used to supply filter media to filter tank 12 via lines 47, 42 and 43. The dispersion of additional filter media in the unfiltered malt beverage not only serves to provide additional unspent filter media to the mechanical filters in the filter tank 12, but it also serves to maintain the permeability of the developing filter cake.

During the deposition of filter media and chill-proofing agents on the mechanical filter,

numerous capillaries are formed in the filter cake that are small enough to retain the particulate contaminants, but are also numerous enough to ensure adequate permeability.

For this invention, the precoat tank 10 and the body feed tank 16 both contain a slurry of filter media substantially composed of perlite wherein the liquid is water or beer.

The unfiltered malt beverage is pumped through the layer of filter media deposited on the mechanical filter in the filter tank 12. As the unfiltered malt beverage passes through the filter media, the fine, insoluble particulate contaminants are retained within the filter media and the malt beverage passes through the mechanical filter and is collected in a collection tank 18. Thus, the filtration of fine, insoluble particulate contaminants from the unfiltered malt beverage is accomplished by the use of filter media through which the unfiltered malt beverage is passed. The filtered particles are retained within the filter media because the size of the particles is greater than the size of the passageways through the filter media including chill-proofing particles, e. g., silica gel; whereas, the malt beverage passes through the filter media because it is liquid, not particulate. In addition, there is somewhat of a chemical attraction between the particles and the filter media such that the filter media serves to retain the particles chemically as well as physically.

This filtration stage continues until the build up of filtered matter and filter media on the mechanical filter is such that the thickness of the filter cake becomes undesirable.

Alternatively, the filtration stage can be halted at a pre-set time period which has been identified as desirable.

The liquid which passes through the filter media exits from the filter tank 12 and flows to the collection tank 18 via lines 48 and 49. The flow of filtered liquid from tank 12 to tank 18 through lines 48 and 49 is regulated with valves and other means familiar to those skilled in the art. While the filter media and chill-proofing agents of the present invention are used to effect filtration of a malt beverage, they do not substantially affect the chemical composition of the filtered liquid which is collected in the collection tank 18.

After pressurizing the liquid contents out of the filter tank, the filter cake is then removed from the mechanical filter in the filter tank 12. The preferred method for removing the filter cake from the mechanical filter is to wash the filter cake from the mechanical filter using pressurized non-carbonated water. This process is referred to as "sluicing."The resulting solution of filter cake and water is then transferred to a holding tank or to one of the multiple use collection/regeneration/feed tanks.

Regeneration of the Spent Filter Media The solution of spent filter cake and water that is contained within the holding tank 20 (not shown) are pretreated with dilute caustic (e. g., sodium hydroxide) at about 70°F. The preferred solution has a sodium hydroxide concentration between about 0.25 and about 3.0 weight percent. Preferably, the preferred caustic has a concentration from about 0.25 to about 1.0 weight percent caustic at the end of the regeneration process if silica gel is not used; if silica gel is used sufficient caustic must be added to totally dissolve the silica gel. An approximate pH of about 12.0 to 13.0 is maintained within the holding tank 20. The addition of dilute caustic to the holding tank 20 also serves to form sodium silicates when silica gel has been used as a chill-proofing agent. Thus, in the preferred embodiment, the holding tank 20 contains a mixture substantially composed of perlite, caustic, chill-proofing agents and beer organics.

A mixer within the holding tank 20 stirs the contents thereof to maintain the solid particles in slurry form in order to complete regeneration action. A mixer with blades that do not substantially degrade the media should be used. Optionally, the holding tank 2G may be omitted and the spent filter media sent directly from the K-filters to one or more regeneration tanks 22 via lines 50,51,52,53,54 and 55.

As shown in FIG. 1, a plurality of regeneration tanks 22 are used in parallel so as to allow for the continuous regeneration and clean up of filter media in accordance with the process of the present invention.

Preferably, a pH of about 12.0 to 13.0 is maintained within the regeneration tanks 22.

It is preferable to maintain the temperature below 90°F. Surprisingly, these mild conditions provide for the adequate regeneration of the filter media. When the preferred filter media (perlite and PVPP) is regenerated under these conditions, neither perlite nor

PVPP degrades significantly. It has been found that when the spent filter media is regenerated at pH greater than 13.0 and at temperatures greater than about 120°F perlite will be slightly deteriorated. Thus, those harsher conditions are avoided. It has also been found that the treatment of spent filter media which is substantially composed of perlite and PVPP or silica gel at temperatures below 50°F increases the time to regenerate perlite and PVPP or dissolve silica gel. Likewise, it has been found that the treatment of spent filter media which is substantially composed of perlite and PVPP or silica gel at a pH of greater than 13.0 and at a temperature greater than 120°F causes an increase in the rate of deterioration of the perlite.

Preferably, the filter cake is combined with the caustic in a weight ratio of about 2 to 1 of silica gel to caustic. Thus, it is preferred that the filter cake is combined with the sodium hydroxide such that there is a weight ratio of about 2 to 1 of silica gel to sodium hydroxide.

In the proportions, it has been found that silica gel dissolves in about 6 hours in a 0.5 weight percent caustic solution with a temperature of about 70°F. Moreover, the process of the present invention regenerates spent perlite so that only about 0.02% of the original weight of perlite is lost per hour of regeneration.

Washing of the Regenerated Media After the filter media has been treated in the regeneration tank 22, the resulting solution is itself passed from regeneration tanks 22 by lines 56,57 and 68 to line 59 and through a filter 24. The filter 24 can be a pressure plate filter or a basket centrifuge.

The preferred filter 24 is a basket centrifuge which is lined with an appropriate plastic filter membrane. This filtration process produces a solids cake comprising primarily regenerated perlite (and PVPP if used).

As regenerated filter media from the regeneration tank 22 exits line 59, it is sprayed into the spinning centrifuge. A cake is built up on the wall of the spinning basket, while most of the caustic liquid passes through the plastic membrane and is discarded. The discarded waste material contains the bulk of the added caustic, dissolved silica gel and degraded organic materials.

The semi-dry filtrate which is caked on the walls of the spinning centrifuge basket is then washed with fluid entering from line 1 that contains about 0.1 to about 0.5

weight percent sodium hydroxide at about 70°F. This rinse is brief in time and in volume. Preferably, about 0.3 weight percent of sodium hydroxide is used at about an ambient temperature, not to exceed about 90°F. This rinsing step is performed to insure complete removal of the remaining caustic soluble material and the silica gel in the form of soluble sodium silicate. This rinsing step can be repeated if necessary.

The cake is then rinsed with a dilute acid (e. g., about 0.2 to 0.5% sulfuric acid or phosphoric acid) at about 70°F. This rinsing step is performed to neutralize any remaining caustic and to wash out acid soluble materials. This wash is brief in time and in volume. This rinsing step can be repeated if necessary.

The cake is then rinsed with water at about 140°F to about 180°F. This rinsing step is performed to remove any residual acid and any remaining degraded materials and to help sterilize the perlite and PVPP. This step, in connection with the acid wash step, extracts surface iron made available by the caustic and lowers the remaining surface iron to a form that has a low BSI level.

The cake is then removed from the walls of the basket by scraping and spraying with sterile water.

Next, the regenerated filter media is transferred to a holding tank 30 via line 61.

Sterile water is added to the holding tank 30 and the resulting slurry is stirred. Holding tank 30 serves to hold the regenerated filter media until it is needed.

As needed, the regenerated filter media is transferred to a tank 32 through line 63 and is de-aerated using carbon dioxide dissolved in sterile water. Tank 32 is agitated to maintain the regenerated filter media in a slurry. The slurry of regenerated filter media is then available for addition to either the precoat tank 10 through lines 64 and 65 or the body feed tank 16 through lines 64,66 and 67 as needed. Fresh filtration media is maintained in tank 34 and can be added to tank 32 via line 69 as needed.

The process of the present invention allows the filter media to be regenerated and reused many more times than known regeneration processes because the process does not significantly alter the filtration characteristics of the filter media and perlite can be more completely regenerated than can DE. In one example, the same perlite has been regenerated and reused twenty-three (23) times. This process allows for the continual maintenance of a consistent particle size product which eliminates the problems

associated with using a new batch of filter media each time which can vary in particle size. Moreover, this process allows for the strict control of the BSI level, which can vary considerably between fresh DE and perlite batches. The process also allows for reductions in the amount of filter media needed and therefore the cost without sacrificing filterability. This process also does not regenerate inside the mechanical filter which would reduce filtration utilization. This process also does not require additional heat energy for regeneration since it occurs at ambient temperature.