Abstract:
A method and apparatus for treating raw influent water to remove particles, algae and toxic chemicals from the water. Basically, air is dissolved in recirculated water under high pressure in an air contactor unit, the air saturated water is intimately mixed with the raw, particle bearing, water in a particle mixing system, and the water, particle and air mixture is passed through an air bubble separator wherein bubbles formed when the pressure on air saturated water is reduced carry away toxic gases and particulate material. If desired for further cleaning the water can be sent through a second series of air contactor, particle mixer and air bubble separation, but with a gas comprising ozone to further remove suspended particles and non-volatile dissolved organic matter. In order to improve mixing of the particles and the air saturated water passing through tubes, preferably a pattern of dimples is formed on at least part of the interior wall of the tubes. Upon completion of the process the water is ready for use or for further filtration in a conventional filtration plant.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates in general to systems for removing contaminants from liquids and, more specifically to a system for removing volatile gases, pesticides and particles such as algae, other suspended organic solids, dissolved oils and other particles including large and heavy particles and light, fine or buoyant particles from water.  
         BACKGROUND OF THE INVENTION  
         [0002]    Water supplies for domestic drinking water, process water for chemical plants or other liquids are often contaminated with a variety of contaminants, such as toxic chemicals, algae, dissolved oil and various organic and inorganic particles of various sizes. These contaminants must be removed in a reliable, cost effective manner.  
           [0003]    Many older water treatment plants use gravitational separation methods, typically in sedimentation systems or dual-media sand filtration systems that may not be acceptable under the newer water quality standards. In some cases, these systems can meet the standards through the use of properly mixed polymer chemical filter aids. The required expensive and complex polymer chemical mixing equipment requires constant attention, since the amount of the chemicals being added to raw water must be frequently readjusted to match the continually changing chemistry of the water being filtered. Slow sand filters require a considerable investment, but generally can be operate for longer periods without cleaning. Unfortunately, even with pretreatment, both dual-media and slow sand filters fail to meet water quality standards for hours or several days after each backwash cleaning.  
           [0004]    Ordinary chemical flocculation and sedimentation processes do not prevent toxic chemicals, pesticides and algae from passing through the ordinary filter bed. If algae spores are present when chlorine is added, toxic disinfection byproducts are formed, which is highly undesirable and a violation of the USEPA Safe Drinking Water Act. The inability of older municipal filtrations systems to remove algae is apparent in the lack of clarity found when a swimming pool is filled with “clean” tap water. Most pool contractors have to shock tap water with large doses of chlorine chemical pool oxidizer to achieve the desired clear pool water appearance.  
           [0005]    Particulate material has also been removed from liquids by floatation, another gravitational method, in which bubbles of a gas, such as air or oxygen, are introduced into the lower levels of the liquid and float to the top, carrying fine particles with them. Various chemical additives, such as flocculation aids, typically alum polymers, are required with these systems. Flotation is a gravitational method because the rise of bubbles is due to the gravitational acceleration acting on the mass of the liquid in accordance with the basic force equals mass time acceleration relationship. A force balance relative to a pocket of gas phase within liquid (a bubble), where the mass of the bubble is its volume times its density, shows that the bubble must rise to find equilibrium, because the density of a gas is generally less than that of a liquid. Large flotation tanks are required to allow adequate time for air bubbles to reach the surface.  
           [0006]    Failure to remove algae prior to filtration also leads to clogged filters, increases filter operation costs and wastes water required for frequent filter cleaning cycles. The use of flocculation promoting chemicals increases the volume of sludge to be dewatered and removed.  
           [0007]    Thus, there is a continuing need for a separation system that will rapidly and efficiently remove particles and volatile gases from liquids while treating a liquid, will efficiently remove algae and volatile gases such as MTBE during pretreatment prior to filtration and will reduce overall treatment costs and conserves water through less frequent filter cleaning and a smaller sludge volume.  
         SUMMARY OF THE INVENTION  
         [0008]    The above noted problems, and others, are overcome in accordance with this invention by a particle separation system that includes a pretreatment section for economically removing algae and other contaminates prior to filtration. The pretreatment includes injecting millions of extremely small air bubbles per liter into the incoming raw water. This dissolved air flotation technology increases a plants daily capacity and reduces the potential formation of toxic chlorine-chemical and post-treatment byproducts.  
           [0009]    Initially, recirculated plant output water under high pressure and air under high pressure are mixed in a an air contactor element, generally consisting of one tank or two or more tanks in series. Preferably, the tank contains a suitable media that provide a high surface areas that increases adsorption of air into the water. All pressures referred to hereinafter are gauge pressures.  
           [0010]    The air saturated recirculated water enters a particle mixing system where it is mixed with raw influent water. The mixed water passes along a tubular spiral to cause intimate mixing. Preferably, a pattern of dimples is provided on at least part of the inner wall of the spiral tube, to increase flow turbulence and assure optimum mixing.  
           [0011]    The mixed water then passes to an air bubble separator unit where a toroidal flow is induced as the water moves upwardly in the unit, producing a vortex that cause air to move to the center and form an elongated axial air column with the water rotating between the vessel wall and the air column. Heavy solid particles drop to the bottom of the unit. Water largely cleaned of algae and other light particles exits near the top of the unit, with light float particles being removed adjacent to the top of the unit. Air and volatile gases exit at the very top of the unit.  
           [0012]    The cleaned water from this air bubble separation unit may be used for many purposes. However, in some cases further removal of the small amount of remaining contaminates is desirable. In that case cleaned water from the air bubble separator then passes to a second air contactor element at a lower, but above atmospheric, pressure. Oxygen, preferably containing a suitable quantity of ozone, is then absorbed or forced into the air contactor tank under pressure higher than the water pressure. The water now containing a suitable quantity of dissolved oxygen/ozone passes to a second particle mixing system similar to the first particle mixing system as described above. As the process water enters the second particle mixing system, hydroxyl radicals (dissolved ozone) are mixed with the remaining suspended particles and non-volatile dissolved organic matter.  
           [0013]    Water from the second particle mixing system then passes to a second air bubble separator, similar to the first one as described above. Bubbles with microscopic suspended particles coalesce along the unit centerline due to the vortex effect and are extracted at the top of the unit. The process water, now further cleaned of algae and other organic particles, may proceed to any desired conventional filtration system, where any remaining heavy solid particles are removed. Since the pretreatment system removes over 85% of the suspended solids in the original untreated water, filter cycles will be much longer than before, with much lower operating and filter maintenance costs. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]    Details of the invention, and of preferred embodiments thereof, will be further understood upon reference to the drawing, wherein:  
         [0015]    [0015]FIG. 1 is a schematic flow diagram, partially in section, of a first embodiment of the pretreatment particle separation system;  
         [0016]    [0016]FIG. 2 is a perspective view of the particle mixing system;  
         [0017]    [0017]FIG. 3 is a perspective view of the air bubble separator;  
         [0018]    [0018]FIG. 4 is an axial section view of the upper portion of the air bubble separator of FIG. 4;  
         [0019]    [0019]FIG. 5 is an axial section view of the lower portion of the air bubble separator of FIG. 4;  
         [0020]    [0020]FIG. 6 is a schematic flow diagram, partially in section, of a second embodiment of the pretreatment particle separation system;  
         [0021]    [0021]FIG. 7 is a detail elevation view, partially cut away, of an alternate preferred air contractor flow arrangement;  
         [0022]    [0022]FIG. 8 is a detail cross sectional view through a rotationally formed particle mixing system tube in a forming mold;  
         [0023]    [0023]FIG. 9 is a perspective view of an alternative embodiment of an air bubble separator; and  
         [0024]    [0024]FIG. 10 is a side elevation view of the air bubble separator of FIG. 9. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]    A schematic flow diagram for the water treatment system of this invention is provided in FIG. 1. Raw influent water is directed into the particle mixing system  10  (described in detail below) via an inlet pipe  12  as indicated by arrow  14  at any suitable pressure, typically 30 psi. Simultaneously a suitable portion of the product water of the system, passing through system outlet pipe  16 , is recirculated through pipe  18  as indicated by arrows  20  to a pump and flowmeter  22  where pressure is substantially increased, typically to about 100 psi.  
         [0026]    The high pressure recirculated water passes through pipe  23  to an air contactor arrangement  24  typically including two tanks in series. High pressure air (typically at about 100 psi) is passed from a conventional air compressor  26  through a pipe  28 . Air is introduced into the upstream ends of the tanks forming air contactor  24 . The air is dissolved in the high pressure water in air contactor  24 . Any suitable media may be used in the air contactor tanks to aid in fully saturating the air. For optimum operation, hollow membrane fibers of the sort available from the Dainippon Ink and Chemical Corporation under the Separeo EF 04P designation are preferred. While air contactor  24  preferably comprises two tanks in series, a single tank or more than two tanks may be used, if desired.  
         [0027]    Air saturated water passes out of air contactor  24  through a pressure regulator  30  which reduces pressure to a suitable degree. A pressure of 25 to 35 psi is preferred, with about 30 psi being optimum. The air saturated water from air contactor  24  is mixed with the raw water in particle mixing system  10 .  
         [0028]    Particle mixing system  10  as seen in FIG. 2 basically comprises a helical tube  32  within which the raw water and air saturated water mixes. The diameter of tube  32 , the diameter of the helix and the length of tube  32  will depend on the volume of water to be treated. In a typical system, tube  32  will have a diameter of from about 4 to 10 inches, a length of about 70 to 100 feet, with the helical coil having a diameter of from about 2 to 6 feet.  
         [0029]    In order to achieve optimum turbulence to ideally mix the raw water and the air saturated water, I have found that a pattern of dimples  97  (as shown in FIG. 8) should be provided over at least a large portion of the inner wall surface of tube  32 . Also, output pipe  36  from the particle mixing system should have these dimples  97  on the interior wall surface.  
         [0030]    The particle mixing system may be manufactured in any suitable manner. Preferably, the helical tube arrangement will be formed by conventional rotational casting, using an outer mold half  101  outside the helix and an inner helical mold portion  99  within the helix having raised bumps  97 A to create the dimples  97  on the tube, as shown in detail in FIG. 8. Regardless on the manner, the tube  32  may be thus supplied with dimples over almost the entire inner surface. Base  34  that supports helical tube  32  may be formed in any suitable manner, such as vacuum forming.  
         [0031]    Returning to FIG. 1, output from helical tube output  36  passes through pipe  38  to inlet  40  of air bubble separator  42 . Millions of very tiny bubbles will form during mixing in particle mixing system  10  when pressure drops from typically 100 psi in air contactor  24  to typically 30 psi at pressure regulator  30 . These tiny bubbles adhere to small light weight particles and carry the particles upwardly in air bubble separator  42 .  
         [0032]    Air bubble separator  42  consists of a lower section  44  as seen in FIGS. 3 and 5, a central section  46  seen in FIGS. 3 and 4 which is generally tubular and may be formed from a transparent material such as glass or an acrylic resin to permit observation of flow therethrough and an upper section as seen in FIGS. 3 and 5.  
         [0033]    The mixture of water and air enters tangentially through inlet  40 , setting up a spinning vortex of water flowing upwardly though center section  46 , creating a boundary-layer transfer effect much like the laminar flow created as water flows through a pipe. More than one inlet  40  may be used if desired. Inlet  40  may have any suitable end or nozzle configuration. Each “boundary” layer of water molecules moves slower because of the frictional drag created by the slower moving layers closer to the center of the column. Heavier particles settle in the sump at the lower end of the lower section  46  and can be drawn off from time to time through a drain opening  50 . Millions of very tiny bubbles form as the saturated water enters the lower section. The flowing stream of water and tiny bubbles has the appearance of milk.  
         [0034]    Velocity of the spiraling white-water stream accelerates as it flows upwardly through the reducing bell-like chamber  52 , creating a high-pressure zone around the outer parameter of the column and a low-pressure zone in the center of the vortex. Differential pressure between the outer wall and the vortex center increases substantially in center section  46 . Boundary layer friction causes the shape of the microscopic bubbles to flatten. This slower boundary layer frictional drag across the bubble&#39;s high pressure surface side elongates the bubble, which is pulled towards the center vortex. Flattened microscopic air bubbles passing through multiple boundary layers collide with relatively stationary suspended particles in the spiraling stream. Positively charged polymers and flocculents and microscopic air bubbles attach to the particles, forcing them to the center. Millions of these microscopic air bubbles “float” horizontally towards the low-pressure center of the vortex and tend to coalesce there. This moving “screen” of microscopic bubbles cleans the water in the water annulus and outer perimeter areas as the flow spirals upward.  
         [0035]    Velocity of the spiraling water column is reduced as it enters the expansion bell chamber  54 . Laminar friction holds gases and the concentrated buoyant float particles near the center of the vortex until they reach the top of the column.  
         [0036]    Particles and gases stripped from the clean water around the perimeter of upper section  48  form a concentrated slurry in the center of the vortex as it enters the float chamber  56 . Only small microscopic bubbles remain near the outer diameter as the water column flows upwardly. As best seen in FIG. 4, a narrow band of water near weir lip  58  flows over the edge of the weir lip, exiting through the product water discharge port  64 , typically at a rate of about 50 to 200 gpm.  
         [0037]    The spinning slurry of buoyant suspended particles and air bubbles enters the waste float removal chamber  66  and flows over the edge of waste trough  68 , exiting the separator  42  through waste outlet  70 , typically at about 5 to 20 gpm to wasted disposal through pipe  72  (FIG. 1).  
         [0038]    A conventional level controller  74  activates an air relief valve  76  at the top of separator  42 , regulating the surface level of the water-air interface inside the top of the water column. Air relief valve  76  closes as the water level rises and opens when gasses accumulating at the top of the column causes the surface water level inside separator  42  to drop. This maintains the surface level between broken lines  78 , correspondingly between the top and bottom of the waste-float outlet  70 .  
         [0039]    Gases exiting through air relief valve  76  pass through pipe  80  to a conventional volatile gas recovery unit  82  (FIG. 1) for recovery, typically with a carbon filter.  
         [0040]    At this point, the water generally has had nearly all contaminants removed and can be passed to a conventional water plant filtration system via output pipe to remove any remaining large particles. However, in this embodiment a second stage is added as seen in FIG. 1.  
         [0041]    Where the additional cleaning of the water is desired, output pipe  84  is connected to a second contactor unit  86 , basically the same as air contactor  24 . However here air from air compressor  26  is passed to a conventional oxygen concentrator  88 . Oxygen concentrator  88  increases the proportion of oxygen in the gas to about 60 to 90 percent. Next the gas goes to a conventional corona discharge type ozone generator  90  where a suitable percentage of the oxygen is converted to ozone. The resulting high ozone gas is fed to contactor  86  at typically about 35 psi, with the water in the contactor typically at about 30 psi.  
         [0042]    As the mixture of water and ozone containing gas is directed to a second particle mixing system  92 , basically the same as particle mixing system  10  described above, where hydroxyl radicals (dissolved ozone) are mixed with any remaining suspended particles and non-volatile dissolved organic matter.  
         [0043]    The output of second particle mixing system  92  passes through pipe  93  to a second air bubble separator  94  generally the same as air bubble separator  42 , as described above. Preferably, a pattern of dimples is provided over the internal surface of pipe  93  to increase turbulence and the resulting improved mixing, as discussed above. The coalesced partially oxidized suspended buoyant particles and volatile gases are extracted by the vortex in separator  94  and pass to gas recovery unit  82  via pipe  96 . This prefiltration process removes over 85% of the suspended solids from the treatment plant process water flow. Also, substantially all algae is removed. This is sufficient to meet present US EPA Clean Water Act regulations for a minimum 85% removal of suspended solids. Where further removal is desired, the output water from particle mixing system  92  can be passed through pipe  16  to any conventional filtration system.  
         [0044]    As mentioned above, I have found that forming a pattern of dimples on a suitable portion of the interior of tubes  32  in particle mixing systems  10  and  92  and in pipes  38  and  93  will significantly improve turbulence therein and greatly improve mixing of water with the added gases in the two particle mixing systems  10  and  92 .  
         [0045]    [0045]FIG. 6 illustrates an alternative embodiment using a single cleaning stage with the saturated air and eliminates the second, ozone treatment stage shown in FIG. 1.  
         [0046]    As seen in FIG. 2, the air contactor  24 , particle mixing system  10  and air bubble separator  42  are essentially identical to the first stage of FIG. 1. Air from compressor  26  is directed to air contactor  24  together with recirculated water from clean water output line  84  from air bubble separator  42 .  
         [0047]    Saturated water from air contactor  24  passes to particle mixer  10  where bubbles form and pick up buoyant particles. Water and bubbles from air contactor  24  then passes to air bubble separator  42 . There, heavy particles are drained away through drain  50 , waste water with buoyant particles passes out through waste pipe  72  and gasses are passed out through pipe  80  to gas recovery unit  82 . Clean water passes out through pipe  84  to and further filtration treatment, storage or use.  
         [0048]    Water is recirculated through pipe  114  to pump  22  and enters air contactor  24  to continue the process. The clean water from pipe  84  is suitable for many purposes, such as some process water for manufacturing facilities and the like. For higher purity purposes, the system shown in FIG. 1 is preferred.  
         [0049]    [0049]FIG. 7 illustrates an alternate flow path for air and recirculated water through the air contactor unit. Each unit  24  comprises a cartridge having a very large number of thin, porous, tubes  111  connected to a manifold  113  at the top of each unit  24  so that air enters all of tubes  111 . Meanwhile, recirculated water enters the top of one unit  24 , flows between tubes  111 , out the bottom and to the top of the second unit  24  through pipe  29 , thence between tubes the same as tubes  111  and out the bottom of the second unit  24  via pressure regulator  30  to the particle mixing system  10 . Air or oxygen forced, by means of an air compressor  26  (as shown in FIGS. 1 and 6), through the open pores in tubes  111  is adsorbed by the recirculating water flow as it passes over the open pores. Conventional sensors  115  at the bottom of units  24  sense an accumulation of air at the bottom of the unit and open a valve in the sensor to bleed off the air.  
         [0050]    [0050]FIGS. 9 and 10 illustrate an alternative embodiment of an air bubble separator system. Here air bubble separator includes a single piece, unitary housing  120  preferable formed by conventional rotational molding. A base  122  may be formed at the same time housing  120  is formed or may be formed separately and secured to the housing, such as by adhesive bonding. Water from the particle mixing system is injected into the air bubble separator through a tangential inlet  126 . An upper portion  124  of housing  122  has a cylindrical configuration with an outlet  128  through which clean water is released. At the top is a wider top portion  130 , typically 10 to 50% wider than the adjacent upper portion  124 , having an outlet  132 . Two level sensors  134  are provided in top portion  130  to measure the water level.  
         [0051]    Typically, level sensors  134  may be NK ultrasonic level switches from the Kobold company. A gas vent  136  is provided to vent toxic gases and the like. As discussed above, one of sensors  134  will open gas vent  134  when the water level is low to release gas and the other will close the gas vent when water level is high.  
         [0052]    Unit  120  may be formed from any suitable plastic material, such as a polyolefin or an acrylic. This embodiment is easily and rapidly manufactured by rotational molding and is highly resistant to corrosion or other damage from constituents of the water mixture being processed.  
         [0053]    Other applications, variations and ramifications of this invention will occur to those skilled in the art upon reading this disclosure. Those are intended to be included within the scope of this invention, as defined in the appended claims.