Abstract:
A phosphorus removal system is operable to remove phosphorus from an influent. The system includes a first section receiving the influent and discharging a first flow. A first coagulant inlet is positioned upstream of the first section and is in fluid communication with the influent to introduce a first coagulant selected to precipitate phosphorus. A second section receives the first flow and discharges a second flow, and a third section receives the second flow and discharges an effluent. A second coagulant inlet is positioned downstream of the first section and upstream of the third section to introduce a second coagulant selected to precipitate phosphorus.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority to co-pending U.S. Provisional Patent Application Ser. No. 60/696,846 filed on Jul. 6, 2005 and incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a system and method for removing phosphorus from an influent. More particularly, the invention relates to a system and method for removing phosphorus from an influent using a multi-stage treatment system. 
         [0003]    Influent, such as contaminated water, is often treated using a multi-stage process to allow for the removal of various contaminates. The treatment processes may include coagulation, absorption, adsorption, filtration, biological treatment, and/or chemical treatment. However, phosphorus can be difficult to remove because it may be present in different forms such as soluble phosphorus, polyphosphate, and phosphorus tied to bacteria or other organic material. In addition, some particulate phosphorus is too small for filtration or coagulation to be effective. 
         [0004]    Present systems generally cannot reduce the level of phosphorus in an influent below about 50 parts per billion (ppb). 
       SUMMARY 
       [0005]    In one embodiment, the invention provides a phosphorus removal system that is operable to remove phosphorus from an influent. The system includes a first section receiving the influent and discharging a first flow. A first coagulant inlet is positioned upstream of the first section and is in fluid communication with the influent to introduce a first coagulant selected to precipitate phosphorus. A second section receives the first flow and discharges a second flow, and a third section receives the second flow and discharges an effluent. A second coagulant inlet is positioned downstream of the first section and upstream of the third section to introduce a second coagulant selected to precipitate phosphorus. 
         [0006]    In another embodiment, the invention provides a method of reducing the quantity of phosphorus in a flow that passes through a multi-section treatment process. The method includes selecting a first coagulant that precipitates phosphorus, mixing the first coagulant with the flow to define a first flow, and directing the first flow to a first section. The method also includes drawing a second flow from the first section, introducing the second flow to a second section, and drawing a third flow from the second section. The method further includes introducing the third flow to a third section, discharging an effluent from the third section, selecting a second coagulant that precipitates phosphorus, and introducing the second coagulant into one of the second flow and the third flow. 
         [0007]    In another embodiment, the invention provides a method of reducing the quantity of phosphorus in a flow. The method includes selecting a first coagulant that precipitates phosphorus, adding a quantity of the first coagulant to the flow to produce a first flow, and directing the first flow to a first section that is operable to remove a portion of the first coagulant and a portion of the phosphorus in the first flow, and to discharge a second flow. The method also includes directing the second flow to a filter that is operable to filter the second flow and to discharge an effluent, backwashing the filter, and adding a quantity of a second coagulant to the filter during the backwashing step. The method further includes collecting a portion of particles from the filter during the backwash and adding at least a portion of the collected particles to the first flow. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a schematic illustration of a multi-stage treatment system during normal operation; and 
           [0010]      FIG. 2  is a schematic illustration of the multi-stage treatment system of  FIG. 1  during a rinse of a second stage and a backwash of a third stage. 
       
    
    
       [0011]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION  
       [0012]      FIG. 1  is a schematic illustration of a multi-stage treatment system  10  that is capable of treating an influent  15  to produce an effluent  20  having desired properties (e.g., desired contaminant levels, turbidity, etc.). Systems similar to the one illustrated are sold by USFILTER as TRIDENT water treatment systems. The illustrated treatment system  10  includes three stages of treatment, with other systems including more or fewer stages. For example, many systems  10  employ a settling stage in which the influent  15  is allowed to settle for a predetermined period of time before it is directed into the three illustrated stages. Other systems may include ozone treatment or still other treatments, in addition to those discussed herein. As such, the invention should net be limited to three-stage systems, nor should the invention be limited to the three particular stages described herein. 
         [0013]    Influent  15  enters the illustrated three-stage system  10  via a pipe, conduit, or other flow path. Chemicals  25  can be added to the influent  15  to adjust the pH and the alkalinity of the flow before further treatment. In addition, a first coagulant  30  and a first polymer  35  are added to the influent  15  to define a first flow  40  that then enters the three stage system  10 . 
         [0014]    The first flow  40  enters a first stage  45  of the multi-stage treatment system  10 . In the illustrated construction, the first stage  45  includes a lamella, or tube section that functions to separate the first flow  40  into a second flow  50  and a sludge  55 . The tube section  45  includes a bottom portion  60 , a top portion  65 , and a plurality of substantially vertically oriented tubes  70  that extend between the bottom portion  60  and the top portion  65 . The first flow  40  enters the tube section  45  at the bottom portion  60  and the second flow  50  exits the tube section  45  from the top portion  65 . 
         [0015]    The first polymer  35  acts as a flocculent to collect contaminates within the first flow  40  and form larger heavier particles of contaminates (floc). Similarly, the first coagulant  30  collects contaminates and forms larger, heavier particles. The first coagulant  30  is preferably selected from a number of available metal salts, with aluminum-based salts (e.g., alum, etc.) and iron-based salts (e.g., ferric chloride, ferric sulfate, ferrous sulfate, etc.) being preferred. The metal salts aid in precipitating phosphorus from the first flow  40 . Thus, the first coagulant  30  reduces the amount of phosphorus in the first flow  40  as it passes through the tube section  45 . 
         [0016]    In the tube section  45 , the larger, heavier particles do not flow upward through the tubes  70  with the second flow  50 , but rather fall downward and collect on the bottom to form the sludge  55 . One or more pumps  75  are positioned to draw sludge  55  from the tube section  45  and pump the sludge  55  to waste  80  as required. In some constructions, the pumps  75  operate continuously to draw the sludge  55  from the tube section  45 , with other constructions employing intermittent pump operation. In preferred constructions, a portion of the sludge  85  is pumped into the influent  15  or first flow  40 , via a first return line, before the first flow  40  enters the tube section  45 . This allows any of the first coagulant  30  or first polymer  35  that remains active within the sludge  85  to collect additional contaminates, thus reducing the quantity of first coagulant  30  and first polymer  35  required. 
         [0017]    In some constructions, a second coagulant  90  is added to the flow of sludge  85  before it enters the influent  15  or first flow  40 . The additional coagulant  90  further improves the reduction of contaminates in the second flow  50 . Generally, the same metal salt is employed as the second coagulant  90  as was employed as the first coagulant  30 . However, other systems may employ a different coagulant, or multiple coagulants (e.g., alum in combination with ferric chloride) if desired. 
         [0018]    The second flow  50  exits the tube section  45  and flows into a second section  95  of the multi-stage treatment system  10 . In some constructions, a third coagulant  100  is added to the second flow  50  before it enters the second section  95 . In preferred constructions, the third coagulant  100  includes the same metal salt as was used as the first coagulant  30  and/or the second coagulant  90 , with other coagulants also being suitable for use. Additional polymer  105  can also be added before the second flow  50  enters the second stage  95  if desired. Like the coagulant  100 , preferred constructions employ the same polymer  105  that was used as the first polymer  35 . However, other polymers may be employed as desired. 
         [0019]    The second section  95  of the illustrated multi-stage treatment system  10  includes an adsorption clarifier  107  having a bottom portion  110  and a top portion  115 . The second flow  50  enters the adsorption clarifier  107  near the bottom  110  and flows upward to the top portion  115 . A third flow  120  exits the adsorption clarifier  107  from the top portion  115 . 
         [0020]    In a preferred arrangement of the adsorption clarifier  107 , a media retainer  125  such as a screen holds a buoyant adsorption media  130  in place. The second flow  50  flows upward through the adsorption media  130 , which adsorbs unwanted contaminates as the flow passes. 
         [0021]    Periodically, the adsorption clarifier  107  must be flushed (see  FIG. 2 ) to collect the unwanted contaminates that have been adsorbed by the adsorption media  130 . The collected contaminates are directed to waste  80 , with a portion of the collected contaminates  135  being directed to the influent  15  or first flow  40  via a second return line. In some constructions, a fourth coagulant  140  is added to the flow  135  within the second return line before the flow  135  enters the influent  15  or the first flow  40 . As with the other coagulants, the fourth coagulant  140  is preferably a metal salt, and more preferably, the same metal salt as is used as the first coagulant  30 , the second coagulant  90 , and/or the third coagulant  100 . 
         [0022]    The third flow  120  passes out of the adsorption clarifier  107  near the top portion  115  and enters a third section  145  of the multi-stage treatment system  10 . In some constructions, a fifth coagulant  150  is added to the third flow  120  before the third flow  120  enters the third section  145 . As with prior coagulants, preferred constructions employ the same coagulant for the fifth coagulant  150  as is employed as the first coagulant  30 , the second coagulant  90 , the third coagulant  100 , and/or the fourth coagulant  140 , with other coagulants also being possible. 
         [0023]    In the illustrated construction, the third section  145  includes a mixed media filter  155  that receives the third flow  120 , including the fifth coagulant  150  if added, near a top portion  160  of the filter  155 . The mixed media filter  155  includes the top portion  160  and a bottom portion  165  that supports an underdrain structure  170 . Mixed media  175  (e.g., gravel, sand, fine heavy density material, and the like) is arranged above the underdrain structure  170  such that the particle size becomes smaller from the top portion  160  to the bottom portion  165 . This course-to-fine arrangement contributes to the filter&#39;s ability to capture unwanted contaminate particles to produce a high-quality (low contaminant) effluent  20  (e.g., drinking water). 
         [0024]    As the third flow  120  passes through the filter media  175 , additional contaminates are removed. The flow eventually reaches the underdrain structure  170  which collects the fluid and discharges it from the multi-stage treatment system  10  as the effluent  20 . 
         [0025]    Periodically, the mixed media filter  155  is backwashed, as illustrated in  FIG. 2 , to remove the contaminates captured by the filter media  175 . During the backwash, water and/or air  178  are introduced into the underdrain system  170  under pressure such that the water and air flows in reverse (i.e., bottom to top) through the filter media  175 . The contaminates and water are drawn from the top of the mixed media filter  155  and are directed to waste  80 . A portion of the collected contaminates and water  180  is directed to the influent  15  or the first flow  40  via a third return line. In addition, a sixth coagulant  185  can be added to the flow  180  within the third return line before the flow  180  enters the first flow  40 . As with prior coagulants, the sixth coagulant  185  is preferably the same coagulant as the first coagulant  30 , the second coagulant  90 , the third coagulant  100 , the fourth coagulant  140 , and/or the fifth coagulant  150 , with other coagulants also being possible. 
         [0026]    In operation, the multi-stage treatment system  10  receives the flow of influent  15  containing phosphorus. The flow of influent  15  is treated to achieve a desired pH and alkalinity. In addition, a quantity of polymer  25  and coagulant  30  is added to produce a first flow  40 . The first flow  40  enters the first section  45  of the multi-stage treatment system  10  where the polymer  25  functions to produce large clumps of contaminates or floc, and the coagulant  30  precipitates a portion of the phosphorus. The precipitate and floe collect to form the sludge  55  which is pumped to waste  80 . In one arrangement, a portion of the sludge  55  is pumped to the influent  15  or first flow  40  before the first flow  40  enters the first section  45 . In preferred arrangements, one to five percent of the sludge  55  is recirculated with other quantities being possible. As discussed, coagulant  90  may be added to the recirculated flow of sludge  55  if desired, to further reduce the phosphorus content of the fluid in the system  10 . 
         [0027]    The flow exits the first section  45  as the second flow  50  and passes to the second section  95  of the multi-stage treatment system  10 . During the transit between the first section  45  and the second section  95 , additional coagulant  100  and polymer  105  may be added, as desired. 
         [0028]    The second flow  50  passes through the second section  95  where additional contaminates, including additional phosphorus is removed from the flow  50 . The third flow  120  leaves the second section  95  and enters the third section  145  of the multi-stage treatment system  10 . During the transit from the second section  95  to the third section  145 , additional coagulant  150  may be added to the third flow  120  to further reduce the quantity of phosphorus within the flow  120 . 
         [0029]    The third flow  120  passes through the third section  145  of the multi-stage treatment system  10  and exits the multi-stage treatment system  10  as the effluent  20 . 
         [0030]    As illustrated in  FIG. 2 , the second section  95  is periodically rinsed and the third section  145  is periodically backwashed to remove a significant portion of the contaminates collected by the two sections  95 ,  145  of the multi-stage treatment system  10 . The contaminates are collected from the respective sections  95 ,  145  and are directed to waste  80 . A portion of the contaminates  135 ,  180  from each of the respective stages can be redirected to the influent  15  or the first flow  40  prior to the first flow&#39;s entry into the first section  45 . In addition, additional coagulant  140 ,  185  can be added to one or both of the redirected flow of contaminates  135 ,  180  as desired. 
         [0031]    In a preferred arrangement, additional coagulant is added only between the first stage and second stage ( 100 ), or to the sludge  85  being pumped back to the influent  15  of the first flow  40  ( 90 ). 
         [0032]    In one construction, a control system monitors the level of phosphorus, as well as other contaminate levels, throughout the treatment process to determine where to add additional coagulant and in what quantity that must be added to achieve the desired level of phosphorus in the effluent  20 , while using the least amount of coagulant possible. In one arrangement, the multi-stage treatment system  10  reduces the level of phosphorus below about 10 ppb. 
         [0033]    Thus, the invention provides, among other things, a new and useful multi-stage treatment system  10 . More specifically, the invention provides a multi-stage treatment system  10  that reduces the quantity of phosphorus in the treated fluid.