Patent Publication Number: US-2010108617-A1

Title: Stormwater filtration system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from U.S. Provisional Application Ser. No. 61/124,994, filed Apr. 21, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stormwater treatment method, and, more particularly to a storm water treatment method which employs reusable materials to filter stormwater. 
     2. Description of Related Art 
     Generally, treatment of stormwater to remove pollutants dates back only to the early 1990&#39;s with the advent of regulations such as the Chesapeake Bay Preservation Act and the adoption of Stormwater Ordinances by local governments. Because of these new regulatory initiatives, permitting requirements now called for treatment before discharge of stormwater in any new developments, typically utilizing some form of Best Management Practice (“BMP”), usually a stormwater detention pond. Notwithstanding these steps, by far, the bulk of stormwater that fell prior to such regulations and which still falls today in any municipality, flows untreated though the existing stormwater system into rivers, bays, estuaries, and finally to the ocean. This is due to the fact that the majority of our cities already had constructed stormwater collection infrastructure prior to 1990, and there was no regulatory requirement to retrofit existing facilities. 
     Promulgation of the Clean Water Act resulted in permit issuance for virtually every “end-of-pipe” situation, so that the chief source of pollutants flowing into our waters today comes from “non-point” sources, or stormwater runoff from cities, farms, and commercial and industrial sites. Permitting agencies at the national and state level now are focusing very closely on the reduction of non-point source pollution. These mandates will only become more rigorous as the regulatory bar is raised to reduce pollutant levels. 
     The most common prior art device for stormwater treatment typically used in BMPs for new construction is a stormwater pond. Such ponds are not used for infrastructure that was built before the early 1990&#39;s when stormwater ordinances came into effect mandating BMP&#39;s for all new construction. In the case of Virginia Beach, Va., for example, only 17% of the water that falls in the land area that flows to the Lynnhaven River is currently treated before it reaches the Lynnhaven estuary. Obviously, this untreated flow contributes disproportionately to stormwater pollution. 
     There are numerous applications for technology which can treat a much higher portion of stormwater. 
     An object of the present invention is to provide a stormwater treatment method and apparatus. 
     An object of the present invention is to provide a stormwater treatment method and apparatus which can treat a large portion of stormwater. 
     An object of the present invention is to provide a stormwater treatment method and apparatus which can be retrofit into existing facilities. 
     Another object of the present invention is to provide a stormwater treatment method and apparatus which can be used in new facilities. 
     Yet another object of the present invention is to provide a stormwater treatment method and apparatus which benefits from reusable materials. 
     Finally, it is an object of the present invention to accomplish the foregoing objectives in a simple and cost effective manner. 
     SUMMARY OF THE INVENTION 
     The present invention addresses these needs by providing a device for filtering contaminants from stormwater. The device has an insert which has openings to allow flow through of stormwater and contaminants contained therein and an amount of aggregate material placed within the insert such that the aggregate is retained therein while stormwater flows through the aggregate material. The insert is preferably constructed from a rigid water resistant material. The aggregate material is preferably placed in a mesh bag or a mesh pocket which is placed within the insert. In a particularly preferred embodiment, the device includes a water direction element for directing stormwater into the insert and through the aggregate. 
     A method for filtering contaminants from stormwater using this apparatus is also described. The insert described above is placed within a sewer system such that stormwater flows through the aggregate material within the insert and contaminants are collected by the aggregate material from the stormwater. Once the aggregate has collected contaminants from the stormwater, it is removed from the sewer system, and replaced with a second insert containing fresh aggregate material. In a particularly preferred embodiment, upon removal of the insert, debris, such as recyclables, organic matter, dirt and residuals, is removed from the sewer system. Such debris may then be treated by sorting and selling of recyclables, composting vegetative matter, reselling common dirt as fill, and taking the residuals to an appropriate landfill. The aggregate material in the removed insert may be treated to remove the contaminants such that the aggregate material may be reused. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete description of the subject matter of the present invention and the advantages thereof, can be achieved by the reference to the following detailed description by which reference is made to the accompanying drawings in which: 
         FIG. 1  shows a perspective cutaway drawing of an insert box according to the preferred embodiment of the present invention; 
         FIG. 2  shows an installed insert box according to the preferred embodiment of the present invention; 
         FIG. 3   a  shows an alternate embodiment for installing a filtration medium according to the preferred embodiment of the present invention; 
         FIG. 3   b  shows an alternate embodiment for installing a filtration medium according to the preferred embodiment of the present invention; 
         FIG. 4  shows an installed stack of insert boxes according to the preferred embodiment of the present invention; 
         FIG. 5  shows an installed stack of insert boxes according to the preferred embodiment of the present invention; 
         FIG. 6  shows a method for directing stormwater according to the preferred embodiment of the present invention; and 
         FIG. 7  shows a method for directing stormwater according to the preferred embodiment of the present invention. 
     
    
    
     ELEMENT LIST 
     
         
         
           
               12  light weight aggregate 
               14  insert 
               16  top of insert 
               18  hole 
               20  screen mesh 
               22  filtration layer 
               24  porous material 
               26  mesh pocket 
               28  mesh bag 
               30  hose 
               32  water direction device 
               34  exit hole 
           
         
       
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following detailed description is of the best presently contemplated mode of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating general principles of embodiments of the invention. 
     The new technology presented here is centered around a system which can be placed in existing facilities and which can be included in new construction. Generally, an insert or series of inserts includes lightweight aggregate (“LWA”) in a manner such that the aggregate is retained in the insert. The insert includes openings to allow water to flow into the insert and through the aggregate such that contaminants are captured by the aggregate and removed from the water which exits the insert. 
     The typical use of LWA is as a raw material in the manufacturing of lightweight block, lightweight concrete, or as fill material to span an area where poor soils exist and a road is being built over them. Besides being lighter in weight, LWA provides better fire ratings, better sound absorption, and savings from the manufacturer being able to deliver more product on a given vehicle because of the lower weight of the finished product. 
     The lower unit weight of raw material also allows a lesser amount to be used to achieve the same volume of aggregate as compared to normal weight aggregates in formulations of concrete mixes, often resulting in material cost savings as well. Gradation of LWA will vary to meet specific sizing requirements in different product areas. 
     In addition to its valuable properties as a raw material in construction, LWA has a unique ability to physically remove pollutants from stormwater because of its physical structure. Porous openings allow non-dissolved pollutant particles to lodge in the porous cells, remaining there until the LWA is cleaned through various treatment trains. Gradation issues are important in the use of LWA to remove pollutants from stormwater, as residence time for stormwater as it passes through the insert in the storm drain is a vital part of effective pollutant removal. For that reason, specific gradation measures are taken to allow the greatest amount of residence time while enabling reasonable flow rates to be able to fully receive the first flush before bypass occurs. 
     Pollutants commonly found in stormwater are total suspended solids (TSS), nutrients (nitrogen and phosphorous), heavy metals (cadmium, chromium, copper, lead, nickel, zinc), oil and grease and fecal coliform. 
     It is the intent of this invention to utilize loose light weight aggregate (“LWA”)  12  by placing it in an insert  14 , which then is placed into a storm drain as shown in  FIG. 2 . As shown in  FIG. 1 , the preferred embodiment of the present invention is to use LWA  12  in a stacked insert  14  system with an indented top covering  16  which includes holes  18  to allow flow through of storm water. The bottom of the insert  14  also includes holes  18  to allow the stormwater to exit the insert after pollutants have been removed. Within the top covering  16  of the insert  14  is a layer of #8-#100 sized mesh  20  which keeps LWA  12  from floating out of the insert  14  as it is inundated with stormwater. For additional filtration of large debris, a layer of gravel  22  or other similar sized particles may be used. To prevent LWA  12  from exiting with the stormwater, the bottom of the insert  14  is covered with a porous material  24  such as cheesecloth. The insert  14  is formed from a rugged material suitable for use in water. In that there are a variety of storm drains with different configurations, there is no set shape for the insert  14 , other that it contains sufficient LWA  12  to provide adequate treatment of stormwater flow. 
     In alternate embodiments of the present invention, the LWA  12  may be placed into an open top mesh pocket  26  ( FIG. 3   a ) or a closed mesh bag  28  ( FIG. 3   b ). The mesh pocket  26  or mesh bag  28  is made from a material which is porous but which is has a fine enough mesh to retain the LWA  12 . 
     In use, a storm drain is engineered to capture a certain amount of flow from the first flush. This is predicated on the amount of land the drain must service as well as the desired depth of first flow treatment. Thus, the insert  14  must allow flow-through of water and pollutants such that the pollutants are allowed to come in contact with and be collected by the LWA  12  within the insert  14 . The insert  14  may flexible or rigid so long as the first flush of stormwater passes through the insert  14 , which is sized to accommodate this initial flow, and which typically contains the greatest amount of pollutants. As the storm event grows and the flow of stormwater exceeds the first flush, the insert  14  is designed to allow bypass of this cleaner water directly to the exit point of the storm drain. Thus, the LWA  12  in the insert  14  captures and removes the most noxious pollutants. 
       FIGS. 4 and 5  show a preferred structure for use of the present invention. In this exemplary system, mesh bags  28  which are filled with LWA  12  are placed into three inserts  14 . Each insert includes a top  16  having multiple holes  18  to allow stormwater to enter. The inserts  14  are then stacked within the sewer system as shown. The stormwater flows onto the top  16  of the insert  14 , falls through the holes  18 , passes through the mesh bag  28  and then comes in contact with the LWA  12 . Pollutants gather in the LWA  12  allowing filtered water to pass through the bottom of each insert  14 . Allowing the stormwater to flow through the stack of inserts  14  provides optimal filtration. 
     Different methods are available for causing stormwater to flow into the inserts  14 .  FIGS. 4 and 5  show one such method. In this method, stormwater flowing into the sewer opening is directed into a hose  30 . The stormwater flows through the hose  30  and exits the hose at the top of the stack of inserts  14 . 
       FIGS. 6 and 7  show a device for directing stormwater to the top of stacked inserts  14 . The device  32  is placed within the sewer opening at street level. Stormwater enters the device  32  and flows through an exit hole  34  in the bottom of the device  32  which leads into the hose  30 . 
     Once sufficient storm events have taken place for the LWA  12  to reach breakthrough such that it is no longer capable of efficiently removing pollutants from stormwater, the spent inserts  14  are removed and replaced with inserts  14  with fresh LWA  12 . The spent LWA  12  material may then be treated as described below such that it may then be used to replace spent LWA  12  material. 
     The spent inserts  14  are then preferably brought back to a central treatment facility, where various treatment methods are employed to remove captured pollutants from LWA  12  so it can be reused. Pollutants which are removed from the LWA  12  include heavy metals, fecal coliform, oil and grease, non-dissolved nutrients, and organics. A variety of treatments may be utilized: For metals treatment, tanks with mild acid solutions may be used to precipitate metals from the LWA  12 , piles of LWA  12  may be treated with bacteria which consume oil and grease, or a rotary kiln may be employed to destroy organics and oil and grease by exposure to heat. Once the LWA  12  is cleaned to a certain standard, we also can blend some of it with topsoil to sell as a landscaping mix—the porous and water-retaining LWA  12  assures that moisture is maintained in the mix. Landscapers often blend LWA  12  with soil to use as an effective growing medium. Other treatment methods and uses of the treated LWA are possible. Another choice may be to entomb the LWA in concrete block and bypass some or all of the remediation steps. 
     A particularly preferred step in this method is to clean out the curb inlets when they are serviced, removing all debris—sand, cans, bags, etc. This debris may then be brought to a treatment facility, to allow sorting and selling of recyclables, composting vegetative matter, reselling common dirt as fill, and taking the residuals to an appropriate landfill. 
     The current invention is a significant improvement over the prior art allowing treatment of stormwater by servicing the existing environment, from which a significant and constant portion of stormwater pollution will always come unless something like this is done. Prior art does not employ the simplified method of servicing the aggregate once its absorption qualities have been depleted. 
     Furthermore, while we have described use of this invention to treat stormwater, such description is exemplary in nature and is not to be seen as limiting. Use of this invention is not restricted to treatment of stormwater. The LWA containing inserts can be used to treat other water such as drinking water and waste water from sanitary sewers. Additional possible treatment sites include (a) upon entering and/or leaving residences and businesses, (b) sewer lines, (c) upon entering or leaving water treatment plants and waste water treatment plants and/or (d) wells. 
     In an alternate embodiment of the present invention, the nature of this invention relates to removal of pollutants from stormwater during new construction. The physical removal process is the same as with inserts, as is the treatment methodology for spent LWA. What is different is the application, because we are not retrofitting a storm drain in the “built” environment; rather, we are constructing precast concrete box(es) that hold LWA and are sized to receive the “first flush” for the required treatment area. 
     As new roads are constructed, at the edge of the roadway a section of curb and gutter is built using ready mixed concrete placed into forms. At its bottom the rounded curb meets a roughly 12″ wide section of concrete gutter extending into the roadway up to the edge of asphalt or concrete pavement. This “gutter pan” is angled slightly towards the edge of the street, away from the center of the roadway. This slight inclination and the crowning of the street towards the outside, forces stormwater to flow towards the curb and be carried down the gutter pan to the storm drain. The curb and gutter also has a slight fall to move water to the storm drain over however many linear feet of roadway the storm drain is designed to receive stormwater flow. 
     Our invention allows modular insertion of sections of precast concrete boxes, in the place of the gutter pan, with open steel grates on the top, to receive this stormwater flow as it moves towards the storm drain, filtering and removing pollutants and allowing clean water to flow through a tube at the bottom of the box into the storm drain. 
     As the storm event picks up in intensity and the velocity of flow exceeds the first flush, water simply will pass over the grate, as the underlying LWA is saturated with stormwater, and will enter the mouth of the storm drain. This is the bypass mechanism built into the invention. All of the initial flow, or first flush, the box(es) are designed to treat, will flow down the concrete gutter and through the grate into the LWA below (once the stormwater reaches a receiving box), for subsequent pollutant removal. If a larger footprint of area needs to be treated, additional boxes are simply installed end to end, providing more treatment area to receive stormwater flow. Through a pipe flowing from one box into the next, these modular sections allow treated water to flow into the storm drain. 
     When the device needs to be serviced, the grates simply are removed and the LWA insert is lifted out and taken to a treatment facility for treatment, with fresh inserts put in the place of spent material. The device may have a set of baffles at the bottom to enhance sediment deposition, which is cleaned out with a vacuum truck when the inserts are changed. The exit pipe from the storm drain is covered with wire to assure no gross trash or vegetative waste flows down the pipe into our waterways. 
     An important facet of this invention is the fact that no BMP taking valuable land needs to be constructed. The box is the BMP. This saves the municipality land and construction funding and particularly relates to an infill situation in an area of the city where there is insufficient land to build the BMP. As well, as BMP&#39;s are seldom if ever serviced and sediments escape into our waterways as ponds fill up because they are not cleaned out when full, the service component of the invention keeps our waterways as pristine as possible. 
     With respect to the type of LWA which is appropriate for use in this invention, there are various types. 
     Naturally occurring through volcanic explosions, as in pumice, scoria, tuff, lava rock, perlite (which can be expanded by addition of heat). Domestic pumice is found in the western United States and trades under names such as: Hess, Copar, CR Minerals, Glass Mountain, California Lightweight, Cascade and Sierra Cascade. Foreign sources include LWA from Greece, Italy, Turkey, Germany, Canary Islands, Azores, Monserrat, Martinique, and Mexico. 
     Expanded shales, slates, and clays. These aggregates are created through the expansion of the above-referenced type of rock by feeding them through a rotary kiln at temperatures from 1800-2400 degrees F. As the rock moves through the kiln, expanded gases escape from the rock, changing its physical configuration by bloating it and creating porous cells, which results in lower weights and greater porosity to the resulting product. Well-known names of these products and/or their domestic manufacturers include Solite, Stalite, Norlite, Haydite, Kenlite, Livlite, Gravelite, Arkalite, Utelite, Buildex, and Themo Lite. Expanded products manufactured in other countries include Liapor, Leca and Argex. 
     Coal combustion byproducts, as in the bottom ash that is remaining after coal is burned in an industrial utility or power plant setting. Bottom ash is a coarse, granular LWA that typically has the same physical characteristics and low unit weight as naturally occurring LWA and expanded LWA. 
     Manufactured, like “zonolite”, an expanded vermiculite. Perlite is a naturally occurring material that can be expanded through the addition of heat. Fly ash is a coal combustion byproduct that is very fine and can be formed into LWA through some means of agglomeration, like pelletization or extrusion. Typically, there also is added a binding agent like cement, scrubber sludge, or cement kiln dust. The resulting LWA is either cold-bonded or can be cured with the addition of some form of heat. Typical ash-based LWA includes Versalite, Aardelite, PFA, and Lytag. 
     Filtration Test 
     A local river, the Lynnhaven River was selected for testing. Because the Lynnhaven River fails state requirements for contaminants, namely fecals, it was considered a good beta test site. 
     A series of 14 tests were conducted by an independent laboratory to determine the filtering capability of the instant invention. 
     The mixture of contaminants developed to create a controlled artificial stormwater was devised after analyzing stormwater collected behind a shopping mall flowing into a finger of a local creak. In order to standardize the mixture, all of the metals were added at the highest level detected in the creek sample. In doing this, most of the metals in the mixture are 6 to 50 times more concentrated than in the actual stormwater sample. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Creek 
                 Laboratory 
               
               
                   
                 Stormwater Sample 
                 mixture 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Cadmium 
                 non-detect 
                 0.5 mg/L 
               
               
                   
                 Chromium 
                 0.009 mg/L 
                 0.5 mg/L 
               
               
                   
                 Copper 
                 0/084 mg/L 
                 0.5 mg/L 
               
               
                   
                 Lead 
                 0.016 mg/L 
                 0.5 mg/L 
               
               
                   
                 Nickel 
                 0.010 mg/L 
                 0.5 mg/L 
               
               
                   
                 Zinc 
                 0.489 mg/L 
                 0.5 mg/L 
               
               
                   
                 TSS 
                   109 mg/L 
                 100 mg/L  
               
               
                   
                 Oil and Grease 
                 non-detect 
                  50 mg/L 
               
               
                   
                 Fecal Coli form 
                 Sample expired 
                 275 CFU/100 mL 
               
               
                   
                   
               
            
           
         
       
     
     The following is a synopsis of the test results: 
     
       
         
           
               
             
               
                   
               
               
                 Metals 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Cadmium 
                 86.1% average removal 
                 (range 56.9 to 95.6%) 
               
               
                 Chromium 
                 97.4% average removal 
                 (range 92.3 to 100%)* 
               
               
                 Copper 
                 94.2% average removal 
                 (range 80.0 to 100%)* 
               
               
                 Lead 
                 98.0% average removal 
                 (range 93.7 to 100%)* 
               
               
                 Nickel 
                 77.6% average removal 
                 (range 51.0 to 88.3%) 
               
               
                 Zinc 
                 90.0% average removal 
                 (range 71.0 to 97.9%) 
               
               
                 Total Suspended 
                 87.05 average removal 
                 (range 72.0 to 100%)* 
               
               
                 Solids (TSS) 
               
               
                 Fecal Coli form 
                 99.3% average removal 
                 (range 97.8 to 100%)* 
               
               
                 Oil and Grease 
                 100% average removal* 
               
               
                   
               
               
                 *Note: Tests indicating 100% removal mean that any contaminant left after filtration was below the detection ability of the laboratory&#39;s equipment. 
               
            
           
         
       
     
     Obviously, many modifications may be made without departing from the basic spirit of the present invention. Accordingly, it will be appreciated by those skilled in the art that within the scope of the appended claims, the inventions may be practiced other than has been specifically described herein. Many improvements, modifications, and additions will be apparent to the skilled artisan without departing from the spirit and scope of the present invention as described herein and defined in the following claims.