Abstract:
In one embodiment, a method for treating waste water includes passing ozonized waste water through a bed of moving sand.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims subject matter disclosed in provisional patent application Ser. No. 60/583,979 filed Jun. 30, 2004 now abandoned, entitled Reactive Filtration. This application is a continuation-in-part of co-pending patent application Ser. No. 10/727,963 filed Dec. 2. 2003, entitled Reactive Filtration. 
    
    
     BACKGROUND 
     Chlorine has historically been the chemical of choice in the treatment of water. More recent developments in the cost-effective generation of ozone and in the knowledge of undesirable environmental impacts of trihalomethanes and other chlorinated compounds have made ozone based water treatment an increasingly preferred treatment method. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a moving bed particle filtration system that may be used to implement various embodiments of the invention. 
         FIG. 2  illustrates a moving bed filtration system in which the waste water is pre-treated with a metal salt reagent before ozone is added to the waste water. 
     
    
    
     DESCRIPTION 
     “Waste water” as used in this document means any water to be treated. Waste water is not necessarily highly contaminated water and may contain only trace amounts of phosphorus, arsenic, or other contaminants such as pesticides or pharmaceuticals (organic or inorganic compounds and in single or mixed solution) or disease causing organisms or molecules. 
       FIG. 1  illustrates a moving-bed particle radial filtration system  10  that may be used to implement embodiments of the invention. Referring to  FIG. 1 , waste water flows into a vertically oriented cylindrical treatment vessel  12  through an inlet pipe  14 . Vessel  12  includes a filter chamber  16 , a stem  18  and an expansion gravity settling chamber  20 . Filter chamber  16  contains a bed of sand  22 , iron oxide coated sand, sand and iron granules or another suitable filter media. Inlet pipe  14  extends down into filter chamber  16 . Waste water is discharged into sand  22  along the perforated lower part  24  of inlet pipe  14 . Treated water flows out of filter chamber  16  through a perforated outer perimeter  26  into a sleeve  28  and is removed from vessel  12  through an outlet pipe  30 . The perforations in the lower part  24  of inlet pipe  14  and the outer perimeter  26  of filter chamber  16  are screened as necessary to prevent sand from passing through the perforations. 
     The comparatively narrow stem  18  of vessel  12  connects filter chamber  16  with expansion chamber  20 . A sludge removal port  32  is positioned near the bottom of expansion chamber  20 . A recirculation pipe  34  extends from the bottom of filter chamber  16  to the top of expansion chamber  20 . An air compressor  36  pumps air into recirculation pipe  34  at the bottom of filter chamber  16  causing a counterclockwise motion of air, water, sand and filtered particulates through vessel  12 . A back flow preventer  38 , such as a flapper valve, prevents materials in recirculation pipe  34  from flowing back into compressor  36 . A flow control valve  39 , sampling tube  40 , sampling valve  42  and clean-out  43  on recirculation pipe  34 , and a sight glass  44  in stem  18 , may be provided if necessary or desirable. 
     In operation, waste water pumped into filter chamber  16  through inlet pipe  14  passes radially through sand  22  into sleeve  28  and flows out outlet pipe  30  as treated water. Sand  22  moves continuously down through vessel  12  under the influence of gravity. An aerated mixture of used sand and water flows from the bottom of filter chamber  16  back up to expansion chamber  20  through recirculation pipe  34  along with contaminants removed from the waste water. Air is vented to the atmosphere at the top of expansion chamber  20  to prevent pressurization of the system. The pressure head of water in sand  22  is kept such that some of the treated water flows from filter chamber  16  up through stem  18  into expansion chamber  20  to rinse contaminants from the used sand particles returning to expansion chamber  20 . This rinse water, now carrying a high concentration of contaminants less dense than sand, is removed from chamber  22  and flows out through sludge removal port  32 . In a preferred operation, the top of the sand bed for filtration is three fourths the height of filter chamber  16 . Expansion chamber  20  and narrow stem  18  contain a dilute sand and water mixture that contains filtered particles that have been moved first to the bottom of sand  22  and circulated via pipe  34  into the water residing in expansion chamber  20 . Water flow at inlet pipe  14 , outlets  30  and  32  and recirculation pipe  34  can be balanced so that a preferred rate of 5-10% of the inlet water carrying contaminants is discharged through sludge removal port  32 . 
     The system of  FIG. 1  may be used to implement embodiments of a new oxidation process for treating waste water. Ozone gas (O 3 ) is mixed with the waste water before the water passes through sand  22  at an ozone inlet port  46 . Since ozone solubility in water is limited, mineral surfaces on the sand  22  adsorb ozone from the passing ozonized waste water. As used in this document, “ozonized” water means any mixture or other combination of water and ozone. The adsorption of ozone on the surface of sand  22  enhances reaction with oxidizible substances in the water. Since any oxidant will have preferred chemical reactivity, such as ozone attacking double bonded carbon, it is desirable to enhance the destructive pathways available to oxidizible contaminants by introducing or creating multiple oxidation pathways. The silica in typical sand acts as a reversible ozone sorption site and activated surface. Mineral oxides in the sand or adsorbed to the sand, such as iron oxide or manganese oxide, act as catalysts to convert ozone to reactive hydroperoxides. As water passes through sand  22 , the surface reaction with sorbed ozone, hydroperoxides and other oxidative byproducts and hydroperoxides enhances the reactive solution chemistry of the dissolved ozone. This allows for surface reactions for oxidation of dissolved chemical compounds, enhanced disinfection via oxidative attack on microbial cell walls and cell constituents and the conservation of total oxidant loading via solid surface storage. 
     Embodiments of the process create and utilize a renewable, catalytic, oxidizing filter media that removes contaminants by filtering and by oxidation. Maximum oxidation of contaminants is combined with the particulate removal filtration properties of the moving sand  22 . Ozone levels in the waste (port  32 ), treated water (port  30 ) and recirculation water (pipe  34 ) may be monitored to help optimize the amount of ozone introduced into the incoming waste water. Ozone is mixed with the waste water using any suitable gas-liquid mixing techniques, for example, contactors, diffusers or venturi effect mixers with headspace vented or vacuum pumped to prevent undesirable gas bubbles from entering the sand filter bed. 
     Deploying the sand or other suitable filter media in a moving bed assists in continuously renewing the ozone sorption sites as well as catalytic and activated surfaces. Movement may be accomplished, for example, by fluidizing or moving the bed using the fluid flow, by mechanical action such as augers or mixing bars, by acoustic action such as the application of ultrasonic waves or by physical transport using compressed air. 
     The application to the ozone containing water of ultrasonic energy for acoustic cavitation or pressure jets or diffusers for hydrodynamic cavitation may be desirable in some applications to form high energy, reactive oxidants including superoxide, hydroxyl radicals and peroxide. A reagent capable of creating a reactive surface on the filter media may be added to the incoming flow of waste water as necessary or desirable to assist in the removal of reactive contaminants such as dissolved organic matter and phosphorus. While it is expected that soluble forms of manganese, aluminum or other metals such as zinc and copper will provide suitable reagents, iron will typically be used as the reagent due to its proven reactivity with a variety of contaminants and its current widespread use in water treatment. Ferric chloride, for example, is a preferred reagent when phosphorus or arsenic is the target contaminant. Suspended iron-oxy-hydroxide particulates in the wastewater following the addition of ferric chloride also become catalytic surfaces for hydroperoxide formation from ozone. It is expected that the addition of ferric chloride or other fully oxidized metal salts will have minimal effect on the direct consumption of or competition for ozone. 
       FIG. 2  illustrates a moving bed filtration system  50  in which the waste water is pre-treated with a metal salt reagent before ozone is added to the waste water. Referring to  FIG. 2 , filtration system  50  includes a pre-reactor system  52  and a reactive filter system  54 . Waste water is pumped into the serpentine piping  56  of pre-reactor  52  through an inlet pipe  58  and flow control valve  60 . A metal salt or other suitable reagent is introduced into serpentine piping  56  through a reagent inlet port  62  immediately downstream from inlet pipe  58 . Preferably, serpentine piping  56  is substantially larger than inlet pipe  58  to slow the flow through piping  56  compared to inlet pipe  58 . A slower flow increases the time available for the reagent to mix with the waste water and react with contaminants in the waste water. The waste water flow will be more turbulent near the transition from the smaller inlet pipe  58  to the larger serpentine piping  56 . Introducing the reagent into this turbulent flow also helps mixing. 
     The waste water/reagent mix flows through straight-aways  64  and gentle bends  66  of serpentine piping  56 . The waste water/reagent mix exits serpentine piping  56  into an outlet pipe  68  that takes the mix into reactive filter system  54 . Prescribed dosing for the allotted reaction time introduces the reagent in sufficient quantities and concentrations to (1) allow for the co-precipitation and flocculation reactions between the reagent and the dissolved contaminants in pre-reactor system  52  to go to near completion to dilute levels as opposed to equilibrium and diffusion limited processes which limit further reaction, (2) saturate competing reactive pathways with natural waters with reagent, and (3) leave enough excess reagent in the mix to activate the filter media in reactive filter system  54 . The amount of excess reagent is determined by the reactive capacity of the influent solution and the desire to deliver excess reagent to the sand filtration bed for the continuous formation of iron oxide coated sand that can catalytically react with ozone or be available for direct surface sorption or mineralization reactions with contaminants. 
     The comparatively slow flow through serpentine piping  56  allows for better coagulation of precipitates. The straight-aways  64  allow for less turbulent flow to enhance coagulation. Periodic gentle bends  66  introduce and maintain additional turbulent flow and introduce flow vortices to periodically mix the flowing solution. Preferably, the serpentine mixing array allows for a decrease in flow velocity for 2-8 minutes allowing for sufficient pre-reaction time. Design of the array needs to consider maintaining sufficient flow to prevent deposition of precipitation solids in the pre-reactor assembly. The actual length and diameter of serpentine piping  56  for most applications will result for an optimization of the required reaction time (usually 1-5 minutes), the desired flow rate, the space available at the site of deployment, and the presence of competing reactions in the treatment water. 
     Ozone is mixed with the pre-treated waste water at ozone inlet port  69  or alternately at the beginning of serpentine piping  56 . This can be followed by venting or vacuum treatment of any headspace formed by excess gas from the ozonation process as large quantities of gas bubbles entering the sand filter are not desirable. The pre-treated ozonated waste water flows into the vertically oriented cylindrical treatment vessel  70  of reactive filtration system  54  through an inlet pipe  72 . Inlet pipe  72  is positioned at the center of vessel  70 . Vessel  70  includes a filter chamber  74  that contains a bed of sand  76  or another suitable filter media. Inlet pipe  72  extends down into filter chamber  74  to discharge the waste water into the lower portion of sand bed  76  through a perforated manifold  78 . Waste water pumped into filter chamber  74  passes up through sand  76 , over a baffle  80  near the top of filter chamber  74  as fully treated water, into a basin  82  and is removed from vessel  70  through an outlet pipe  84 . 
     A recirculation tube  86  extends from the bottom to the top of filter chamber  74  at the center of vessel  70 . Inlet pipe  72  extends down the center of recirculation tube  86 . Inlet flow discharge manifold  78  extends out through openings in recirculation tube  86 . An air compressor  88  pumps air into used sand and water at the bottom of vessel  70  through an air inlet pipe  89 . The aerated mixture of used sand and water rises through recirculation tube  86  along with contaminants removed from the waste water up to a sand and particulate/water separator  90 . Separator  90  represents generally any suitable separation device that may use, for example, physical separation, gravity separation, particle size separation, magnetic separation, membrane separation, or cyclonic separation. The sand removed from the mix by separator  90  is recycled back to filter chamber  74 . The now highly contaminated waste water is removed through a sludge removal port  94 . Sand  76  moves continuously down through vessel  70  under the influence of gravity. 
     Phosphorus exists in waters and waste waters as dissolved ortho-phosphate, polyphosphate and complex organic-phosphorus compounds. In typical phosphorus containing waste waters, such as the secondary or tertiary effluents of municipal waste water treatment plants, there is a dissolved fraction, primarily as ortho-phosphate (PO 4   3− ) and poly-phosphates and as a micro-particulate or suspended fraction of phosphoros containing solids. Trace levels of arsenic are sometimes found in some sources of drinking water and in higher concentrations in some waste waters. Arsenic can occur in natural waters in the reduced arsenite, As(III) or oxidized arsenate, As(V) forms. Arsenate reacts with iron and aluminum salts to form insoluble compounds. Waters with arsenite contamination can be treated with an oxidizer such as chlorine to allow for further reaction with reactive metal salts. Ferric chloride or sulfate is typically used as a metal salt reagent to remove phosphorus and arsenic from water, although other salts and ferrous compounds can be used. These metal salts can react with other contaminants in solution either by physical means (coagulation, flocculation) or by direct or indirect chemical reaction. 
     In the system described above, excess ferric iron enters sand bed  76  along with the particulate Fe—As or Fe—P solids and residual As or P in solution in the waste water. Ferric ions react with sand surfaces to form iron oxide coated sand (IOCS). IOCS sorbs residual solution As/P out of solution. The physical action of the moving sand abrades the surface of the sand granules, refreshing active sites for additional IOCS formation and Fe—As or Fe—P reactions. Hence, fresh reactive sites for As/P binding are continually presented to the flowing water via microscopic erosion of the sand surface. The ozone will oxidize any reduced As(III) to As(IV) making it more reactive with iron compounds. Ozone and the related solution oxidants will also destroy organic contaminants and lead to disinfection. 
     Chemical and microbial contamination enters water through natural and anthropogenic means and removing such contamination makes water suitable for a variety of uses including drinking water and return of wastewater to natural water bodies. Oxidation can convert contaminating chemical compounds to their mineralized forms such as the products of carbon dioxide and water from hydrocarbon chemicals. Applying simultaneous multiple oxidation modes such as ozonation, metal oxide catalytic ozonation, surface adsorbed ozonation and ultrasonic or hydrodynamic cavitation with ozone can increase the total number and chemical diversity of the oxidants available thus increasing the likelihood of complete mineralization, even for recalcitrant or refractory compounds. This has direct application reducing the concentration of highly toxic or highly bioactive substances in water via enhanced oxidation. Examples of highly bioactive substance in wastewater are pharmaceuticals and hormonally active compounds. Concomitantly, the enhanced oxidation has the desirable effect of enhancing the completeness of disinfection of water contaminated with infectious disease agents such as bacteria and viruses. 
     U.S. patent application Ser. No. 10/727,963 filed Dec. 3, 2003 describes reactive filtration materials and processes that can be used with the ozone treatment described above. The disclosure in application Ser. No. 10/727,963 is, therefore, incorporated herein by reference in its entirety. 
     The present invention has been shown and described with reference to the foregoing exemplary embodiments. It is to be understood, however, that other forms, details, and embodiments may be made without departing from the spirit and scope of the invention which is defined in the following claims.