Patent Publication Number: US-2012040821-A1

Title: Process for in-situ cleaning of drinking water filtration media

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. application Ser. No. 10/926,272, filed Aug. 24, 2004, the entire contents of which are included herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally directed toward a cleaning process. More specifically, the present invention is directed toward a process for cleaning granular water filtration media, such as various types of sand, anthracite coal or activated carbon. 
     BACKGROUND OF THE INVENTION 
     Filtration is an essential step in the treatment of drinking and industrial water supplies. Filtration is carried out to remove contaminants which are either introduced with the source water or are produced during the treatment process and which can affect water quality. Most commonly large-scale filtration involves passing the water either through granular filter media, such as various types of sand, anthracite coal, granular activated carbon or combinations thereof arranged in layers in a filter media bed. 
     Contaminants removed during filtration accumulate within a granular filter media bed. Over time, this accumulation leads to increased filter backpressure (measured by increased head loss), increased turbidity of the flow-through or in the worst case scenario, to breakthrough of contaminants. Regular backwashing is used to remove accumulated filtrate in an effort to maintain filter performance and capacity. 
     However, like every surface in contact with water, filter media particles will over time accumulate deposits of biological and non-biological material which cannot be removed by backwashing and can significantly interfere with the filter&#39;s function. Thus, it is important to clean the filter bed not only of the loose particles removable by backwashing but also of these surface deposits. 
     Depending on the water source and environmental conditions, these surface deposits on the filter particles, can consist predominantly of organic matter (biofilm), metal oxides, or calcium carbonate scale. Heavy fouling or scaling will eventually reduce filter performance. The consequences can be higher backwash frequency, reduced flow-rates, increased water turbidity, breakthrough of contaminants or a combination of these effects. If the deposits are not removed, the filter performance will decline below tolerable levels and filter media exchange becomes necessary. 
     However, an exchange of the filtration media is very expensive in terms of filtration media and downtime cost and may not be a practical maintenance solution for water treatment installations which are exclusive to a number of consumers and have only a single filtration bed. Thus, maintenance procedures allowing for the cleaning of the filtration media as an alternative replacement are required. 
     Mechanical methods of filtration media cleaning include filter bed aeration during backwash and spraying water on top of the filter bed to disperse soft aggregates. This does not remove persistent surface deposits such as biofilm and scale. Chemical treatments include washing the media in strong acids and bases, sometimes in combination with surfactants. These chemical treatments can be satisfactory for certain types of contamination, such as calcium carbonate scale. However, mixed deposits, which include metal oxides and biological films, are either not removed efficiently or require highly corrosive and hazardous cleaning agents which are difficult to use and may leave residue not acceptable in drinking water processing installations. This generates a need for alternative cleaning procedures, and products, which are sufficiently efficient and convenient to present an alternative to media replacement. 
     Prior art filtration media cleaning methods of the chemical treatment type generally include the steps of applying an aqueous solution of a strong acid or base to the filtration media. However, the treatment liquid flows through the filtration media too quickly for the cleaning reaction to be completed. Therefore, the treatment liquid must be applied repeatedly, requiring vast amounts of treatment liquid, or the treatment liquid must be circulated through the filtration media until the clearing reaction is completed, requiring specialized and expensive circulation equipment. These approaches, although an alternative to extended plant shut-down for filter media replacement, do not offer an economical alternative to filter media replacement. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an efficient and economical alternative to the prior art filtration media cleaning methods and products. The present invention provides a product and process for the removal of surface deposits from granular filter media. More particularly, the invention provides a product and process for the in-situ cleaning of filter media used in drinking water treatment systems, especially a product and process which is NSF certified for such use. 
     In a preferred embodiment, the invention is directed toward a cleaning process for the cleaning of all types of granular water filtration media, such as sand, gravel, manganese greensand, anthracite coal, granular activated carbon (GAC), and ion exchange media or ceramic beads. 
     The invention preferably provides a process for the in-situ cleaning of water filtration media contained within a filtration bed. The preferred process includes the steps of applying a granular cleaner onto the filtration media while the media is located within the filtration bed and applying an activator compound thereafter for activation of the cleaning composition. The granular cleaner reacts in conjunction with the activator resulting in the cleaning of the media. After the cleaning has occurred, the residual cleaner and activator are washed away in a rinsing step along with any suspended and dissolved contamination which was removed from the filtration media. The granular cleaner is preferably wetted after application to dissolve the cleaner and initiate the cleaning reaction. 
     The activator can be applied in granular or liquid form. Preferably, the activator is applied as an aqueous solution. In a variant of the preferred embodiment of the process, the steps of applying the activator and wetting the cleaner are combined by applying the activator in aqueous solution. 
     In another preferred embodiment, the process includes the further steps of draining the water filtration bed prior to applying the granular cleaner. Preferably, the step of wetting the granular cleaner is carried out by spraying water onto the cleaner or by filling the filtration bed with water until the cleaner is submerged. The step of rinsing the water filtration bed is preferably conducted through backwashing said filtration bed. The process preferably includes the further step of allowing the chemical reaction to proceed for at least 1 hour prior to rinsing the filtration bed. The rinsing step is preferably delayed until the dissolved cleaner has reached a bottom of the filtration bed. 
     In a further preferred embodiment, the process includes the additional steps of determining the degree of surface contamination of the filtration media and calculating the amount of granular cleaner to be applied for insuring removal of the surface contaminants. The determination of the degree of contamination preferably includes the steps of taking a representative core sample from the filtration media, the sample having a known volume, and the step of calculating the amount of cleaner includes the steps of measuring the amount of cleaner required for removal of the surface contaminants from the filtration media in the sample and extrapolating to the whole filtration bed by multiplying the measured amount of cleaner by the ratio of filtration bed volume/sample volume. 
     In a preferred embodiment of the process of the invention, the granular cleaner includes an acid component for dissolving scale and metal oxides on and removing biodeposits from the filtration media and optionally at least one component selected from the group of a free flow additive for preventing clumping of the cleaner, a surfactant for enhancing contact of the cleaner with the filtration media, an inhibitor for protecting exposed metal surfaces from corrosion by the acid component, and a dye. The cleaner is preferably in the form of a free-flowing powder with a particle size of ≦0.5 mm for easy spreading of the cleaner on the filtration media. 
     In a preferred embodiment of the cleaner, the acid component is sulfamic acid. In another preferred embodiment, the granular cleaner includes at least one additional component selected from the group of citric acid, phosphoric acid, corrosion inhibitor, free-flow additive and surfactant. Preferably the granular cleaner includes the following components: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Component 
                 Volume (w/w) 
               
               
                   
                   
               
             
            
               
                   
                 sulfamic acid; 
                 50-99%  
               
               
                   
                 citric acid; 
                 0-10% 
               
               
                   
                 phosphoric acid; 
                 0-10% 
               
               
                   
                 corrosion inhibitor; 
                 0-10% 
               
               
                   
                 Free-flow additive; 
                 0-10% 
               
               
                   
                 surfactant; and 
                 0-10% 
               
               
                   
                 sodium bicarbonate 
                 Balance 
               
               
                   
                   
               
            
           
         
       
     
     In the process above, the activator used is an activated oxygen donor. For the purpose of this disclosure, the term activated oxygen donor defines compounds which in aqueous solution decompose to generate oxygen radicals. Numerous activated oxygen donors of this type are known and need not be listed in detail. The activated oxygen donor is preferably selected from peroxides, most preferably hydrogen peroxide, peracetic acid, precursors of peroxides, hydrogen peroxide and peracetic acid and combinations thereof. The activator is most preferably either 5-50% hydrogen peroxide, or 0.2-10% peracetic acid, or a combination of hydrogen peroxide and peracetic acid, with the balance being water. 
     In a preferred embodiment of the process of the invention, the activator can be in a liquid or dry state prior to its introduction into the filtration bed. 
     In a further preferred embodiment, the invention provides a granular cleaner composition, comprising a granular cleaner as defined above and an activated oxygen donor as defined above. 
     In another preferred embodiment of the process of the invention, the rinsing step is preferably carried out by a backwashing procedure. 
     Further objects and features of the present invention will be apparent to those skilled in the art upon reference to the accompanying drawings and upon reading the following description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention will now be further described by way of example only and with reference to the attached drawings, wherein 
         FIG. 1  is a schematic flow diagram of a preferred process in accordance with the present invention; 
         FIG. 2  is a schematic flow diagram of a variant of the process of  FIG. 1 ; 
         FIG. 3  is a schematic illustration of a filter bed being cleaned with the process of the invention and at commencement of the process of  FIG. 1 ; 
         FIG. 4  is a schematic illustration of the filter bed of  FIG. 3  at a later stage in the cleaning process; and 
         FIG. 5  illustrates an alternative method of applying the granular cleaner. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before explaining the present invention in detail, it is to be understood that the invention is not limited to the preferred embodiments contained herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein are for the purpose of description and not of limitation. 
       FIG. 1  is a schematic flow diagram of a preferred embodiment of a process in accordance with the invention for the cleaning of water filtration media  110  contained within a filtration bed  114  (see  FIG. 4 ). In this embodiment, the process includes a first application step  20  in which a granular cleaner is applied to the water filtration media while the media is located within the filtration bed. In a wetting step  22 , the granular cleaner is wetted with an aqueous medium to dissolve the cleaner and promote its vertical spread through the filtration media during the ensuing cleaning reaction. Thereafter, an activator is applied onto the granular cleaner in a third application step  30 . In a reaction step  40 , the cleaner chemically reacts in conjunction with the activator resulting in the cleaning of the media. The duration of reaction step  40  varies depending on the degree of contamination of the media. However, the reaction step  40  is preferably carried out for at least one hour, preferably the reaction step is conducted over night. Most preferably, the reaction step  40  is carried out until the dissolved cleaner has reached a bottom of the filtration bed and the filtration media is completely cleaned. The point in time at which the filtration media is completely cleaned can be determined by visual inspection to check for any foaming which would indicate an ongoing cleaning reaction and/or by measuring the supernatant pH or metal content. 
     The inventors of the present process surprisingly discovered that the automatic gradual advancement of the dissolved cleaner through the filtration media in combination with the even spreading of the cleaner on the top surface of the filtration bed completely obviates the need for circulation or re-circulation of the dissolved cleaner to ensure an even distribution of the dissolved cleaner during the reaction step. Agitation of the filtration bed during cleaning is also neither necessary nor desirable with the process in accordance with the invention. This provides the process of the current invention with significant economical and practical advantages. 
     After the cleaning step  40 , any residual granular cleaner and activator are washed away along with the suspended and dissolved contamination which was removed from the water filtration media by rinsing the filtration media with water in a rinsing step  50 . The rinsing step can be carried out by spraying water onto the filtration media or by backwashing the filter bed. Backwashing is the preferred method of rinsing the filtration media. The rinsing step  50  is best carried out until all residual cleaner and activator and all dissolved and suspended contaminants such as scale, metal oxides and bio-contaminants have been removed. Completion of the rinsing step  50  can be determined by monitoring the turbidity, pH and dissolved metal content of the backwash water, for example. Since the filtration bed is not disturbed during the cleaning step, no settling period is required and the filtration bed can be returned to production after the rinsing step, the same as after a regular backwash cycle, providing the process of the invention with yet another advantage over prior art processes involving agitation of the filtration media during cleaning. 
     In the first application step  20 , the granular cleaner is preferably evenly spread on the top layer of the filtration media to promote an even distribution and concentration of the dissolved cleaner during the reaction step  40 . In the wetting step  30 , the filtration bed is filled with water until all the filter material is submerged. This can be done by initiating a slow backwash flow until the desired water level is reached. The backwash flow should be maintained sufficiently low to avoid agitation of the filter bed and mixing of the granular cleaner with the filter material. For filters with very light filter material which may be easily agitated by backwashing, the wetting step is preferably carried out by spraying water onto the cleaner. 
     An even wetting of the cleaner over the whole area of the filtration media top surface is desirable in order to achieve an even dissolution and concentration of the cleaner throughout. The same applies for the activator, which is preferably evenly spread on the granular cleaner to ensure the same ratio of cleaner to activator throughout the filtration bed during the reaction step  40 . The activator can be applied in granular or liquid form. When the activator is applied in granular form, the cleaner and activator may be mixed prior to application to produce a granular cleaner composition, which allows for the combination of the first and third application steps  20  and  30  into a single application step for the application of the cleaner composition. However, in the most preferred embodiment of the process, the activator is applied as an aqueous solution, which allows the compression of the steps of applying the activator and wetting the cleaner into a single second application step. In another preferred embodiment of the process of the invention the filtration bed is completely drained prior to the granular cleaner application step  20 . 
     The rinsing step  50  is preferably conducted through backwashing of the filtration bed. 
     A further preferred embodiment of the process of the invention as illustrated in  FIG. 2  includes an analysis step  10  for determining the degree of surface contamination of the filtration media and a calibration step  12  for calculating the amount of granular cleaner to be applied for ensuring that the whole filtration media are exposed to unreacted cleaner during the cleaning step  40 . The analysis step  10  preferably includes the step of taking a representative core sample from the filtration media, the sample having a known volume, while the calibration step  12  preferably includes the steps of first measuring the amount of cleaner required for substantially complete removal of the surface contaminants from the filtration media in the sample and then extrapolating to the amount required for the whole filter bed by multiplying the measured amount of cleaner by the ratio of filtration bed volume/sample volume. Preferably, the core sample is taken in an area of maximum or at least average contamination and represents a cylindrical sample extending from the top to the bottom of the filtration bed. Adjusting the amount of cleaner used to the respective contamination conditions provides the process of the invention with a significant economical advantage, since substantially no excess cleaner will be used, reducing the cost of the cleaning materials as well as the cost of disposing any unreacted cleaner and activator. Furthermore, less backwashing is required, reducing the time required for the rinsing step  50  and, thus, the overall cleaning process. This is very important to the operator of drinking water treatment facilities who is desirous to achieve the shortest down times possible. 
     The granular cleaner of a preferred embodiment of the invention includes an acid component for dissolving scale and metal oxides on and removing biodeposits from the filtration media; and at least one additional component selected from the group of a free flow additive for preventing clumping of the cleaner, a surfactant for reducing surface tension and enhancing contact of the cleaner with the filtration media, an inhibitor for protecting exposed metal surfaces from corrosion by the acid component, and a coloring agent. 
     The acid component of the preferred granular cleaner is either sulfamic acid or a combination of a major amount of sulfamic acid with a minor amount of a granular acid, such as phosphoric acid, sodium bisulfate, or citric acid. The acid component is preferably substantially free of hydrochloric acid. In the preferred embodiment, the additional components are at least one of citric acid, phosphoric acid, corrosion inhibitor, free-flow additive and surfactant. 
     Numerous free flow additives applicable for use in the granular cleaner of the present invention are commercially available. However, it is preferable to use inert free flow additives. Free flow additives preferred for use in a granular cleaner of the invention are fumed silicas which adsorb to the cleaner particles to inhibit clumping and are NSF certifiable for use in drinking water processing installations. 
     Surfactants useful for inclusion in a granular cleaner in accordance with the invention can be selected for the group of anionic, cationic, non-ionic and amphoteric surfactants in granular form. Useful anionic surfactants include, by way of non-limiting example, alkali metal salts, ammonium salts, amine salts, aminoalcohol salts, fatty acid salts. Particularly preferred surfactants are isopropanol and isobutanol. Surfactants which are NSF certifiable for use in drinking water processing installations are preferred. 
     Corrosion inhibitors useful for inclusion in a granular cleaner in accordance with the invention can be selected from the group of nitrogen containing organic compounds, such as amines, quaternary ammonium compounds, heterocyclic nitrogen compounds, urea, thiourea, amide, or mixtures thereof. The most preferred inhibitors are Inhibitor 60S, commercially available from Thoma, Inc. and Rodine 102, from Parker Amchem. 
     Numerous coloring agents useful for inclusion in the granular cleaner of the invention are commercially available. The preferred coloring agent is a dye commercially available under the name Phylam Acid Red LX-6515 from Phylam Chemicals. 
     In the process above, the activator used is an activated oxygen donor, preferably selected from hydrogen peroxide, peracetic acid, precursors of hydrogen peroxide and peracetic acid and combinations thereof. Examples of granular precursors of activated oxygen donors are sodium percarbonate and BSC 8080, available from Buckman Laboratories. The activator is preferably either 5-50% hydrogen peroxide, or 0.2-10% peracetic acid with the balance being water. The activator can be in a liquid or dry state prior to its introduction into the filtration bed. 
     The cleaner in accordance with the invention preferably includes the following components at the indicated amounts: 
                                             Component   Volume w/w                          sulfamic acid;   50-100%            citric acid;   0-30%           phosphoric acid;   0-10%           sodium bisulfate   0-10%           corrosion inhibitor;   0-10%           free-flow additive;   0-10%           surfactant   0-10%                        
As will be readily understood from the indicated volume ranges, all components having a volume range with a lower value of 0 are optional components.
 
     The mineral or organic acid components of the granular cleaner composition of the invention are present in their respective crystalline form. 
     Although the granular cleaner composition is preferably in the form of a free-flowing powder with a particle size of ≦0.5 mm for ease of spreading of the cleaner on the filtration media, the granular cleaner may also be in the form of compressed pellets or granules, especially for application in the form of a slurry, as will be described in more detail further below. 
     Exemplary formulations illustrating preferred embodiments of the above general cleaner formulation are described in detail in the following: 
     Example 1 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Component 
                 Volume w/w 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 sulfamic acid 
                 85.5% 
               
               
                   
                 citric acid 
                 5.0% 
               
               
                   
                 phosphoric acid 
                 5.0% 
               
               
                   
                 corrosion inhibitor 
                 1.5% 
               
               
                   
                 Free-flow additive 
                 1.0% 
               
               
                   
                 surfactant 
                 2.0% 
               
               
                   
                   
               
            
           
         
       
     
     Example 2 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Component 
                 Volume w/w 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 sulfamic acid 
                 65.5% 
               
               
                   
                 citric acid 
                 25.0% 
               
               
                   
                 phosphoric acid 
                 5.0% 
               
               
                   
                 corrosion inhibitor 
                 1.5% 
               
               
                   
                 Free-flow additive 
                 1.0% 
               
               
                   
                 surfactant 
                 2.0% 
               
               
                   
                   
               
            
           
         
       
     
     Example 3 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Component 
                 Volume w/w 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 sulfamic acid 
                 65.5% 
               
               
                   
                 citric acid 
                 25.0% 
               
               
                   
                 sodium bisulfate 
                 5.0% 
               
               
                   
                 corrosion inhibitor 
                 1.5% 
               
               
                   
                 Free-flow additive 
                 1.0% 
               
               
                   
                 surfactant 
                 2.0% 
               
               
                   
                   
               
            
           
         
       
     
     The constituents of the granular cleaners described herein are known in the art and are commercially available from various sources including those described in  McCutcheon&#39;s Functional Materials  (Vol. 2), North American Edition, 1991; and in Kirk-Othmer, Encyclopedia of Chemical Technology, 3 rd  edition, Vol. 22, the contents of which are herein incorporated by reference. For any particular cleaner, the optional components used should be compatible with all other ingredients included in the cleaner. 
     As shown in  FIG. 4 , the granular cleaner  100  in a preferred embodiment of the process of the invention is spread evenly on the top surface  112  of the filtration media  110  in the filtration bed  114  during the first application step  10  (see  FIG. 1 ). The cleaner  100  is wetted to achieve dissolution of the cleaner. The activator  116  is then evenly spread on top of the cleaner  100  either in granular or liquid form. The dissolved cleaner and the activator together move downward through the filtration bed  114 . This generates a moving cleaning front  120  of concentrated acid and activator as shown in  FIG. 5  which illustrates the filtration bed  114  during the reaction step  40  (see  FIG. 1 ). The cleaning front  120  is the front edge of the dissolved cleaner/activator mixture. The cleaning front  120  normally advances through the filtration bed  114  at a constant speed which is dependent on the type and particle size of the filtration media  110 , the degree of media contamination and the cleaning chemical dosage. In stratified filter beds including several strata of different filtration media, the speed of advance of the cleaning front  120  may change from one stratum to the next, again depending on the properties of the filtration media in the adjacent strata. Not only will the cleaning front  120  and, thus, the dissolved cleaner  100  and the activator  116 , automatically move through the filtration bed  114 , the even application of both together with the movement of the mixture around the filtration media particles ensures an even concentration and admixture of both components. Furthermore, the advancement of the cleaning front  120  is slowed sufficiently by the friction created during movement of the mixture though the filtration bed  114  to achieve more than sufficient residence time of the mixture on the filtration media particles to ensure a full cleaning thereof. Moreover, any unreacted mixture will continue to move downward until it comes in contact with a contaminated filtration media surface or the filtration bed  114  is completely cleaned. This provides several significant advantages over the prior art. The circulation equipment required with the prior art cleaning processes using liquid cleaning compositions to ensure complete spread of the cleaner and sufficient residence time is obviated with the process of the present invention, resulting in a significant economical advantage. Significant overdosing of the cleaning compounds as required in the prior art cleaning processes to ensure all contamination is removed is not necessary with the process of the invention, since all of the cleaning mixture will ‘drain’ from the filtration bed, which means it will automatically move through the whole bed and can get used up completely. Additional advantages of the present method over the prior art are a minimized corrosion of metal parts and minimized formation of hazardous fumes. 
     For large filtration beds, where it may be difficult to reach all locations of the bed&#39;s top surface, it may be challenging to spread the granular cleaner or granular cleaner composition in a dry form as described above. In those situations, the granular cleaner can be applied to the filtration media in the form of a slurry. The slurry is prepared by mixing the dry granular cleaner or cleaner composition with approximately the same volume of water at a mixing station  200  (see  FIG. 5 ) and then spread on the top surface of the filtration bed by way of a pressure pump  210  connected to the mixing station  200 , delivery hoses  220  emanating from the pump  210  and an optional spreader nozzle  230 . The granular cleaner shipping containers can be used as the mixing station  220  by filling the containers with water to the top. Various types of slurry mixing and pumping equipment are commercially available and need not be described in more detail herein. 
     While the invention has been described with a certain degree of particularity, it is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claims or including the full range of equivalency to which each element thereof is entitled. 
     The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.