Abstract:
A water-handling installation comprises a tank interceptor for receiving liquid and in which oil or suspended solids are separated from the liquid prior to discharge. The water-handling installation further comprises a pH adjustment module in fluid communication with the tank interceptor. The pH adjustment module receives a portion of liquid contained in the tank interceptor and adjusts the pH thereof prior to returning the diverted portion back to the tank interceptor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/289,131, which was filed on Nov. 29, 2005, and entitled “ENHANCED SEPARATION TANK WITH pH CONTROL”, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to separator tanks or interceptors, adapted to receive primarily rainwater from a storm sewer or drain, and additionally to perform the function of separating and entrapping any oil- or gasoline-based materials and suspended solids that may enter, allowing the water fraction to discharge into municipal receiving sewers or water courses. In particular, this invention is related to separator tanks and the ability to adjust the pH of the liquid contained therein, so as to achieve a pre-determined pH set point. 
       BACKGROUND OF THE INVENTION 
       [0003]    Separator tanks are known in the art. An improved tank interceptor construction is the subject of U.S. Pat. No. 4,985,148, issued Jan. 15, 1991, and entitled, “Improved Separator Tank Construction”. This tank interceptor provides two distinct responses to two different operating conditions. 
         [0004]    When the materials entering the interceptor include discharge from a service station, garage, machine shop, factory or the like, or oil that has spilled accidentally, these non-aqueous materials are collected within the interceptor. The aqueous fraction is allowed to leave the interceptor and pass on to a storm sewer or the like, but the liquid fraction made up of oil or fat of animal, vegetable or mineral origin, gasoline and the like remains trapped within the interceptor until the same is pumped out. Further, any heavier-than-water materials sink to the bottom of the interceptor and are confined to a particular location from where they can also be pumped out at intervals. 
         [0005]    The interceptor is also adapted to deal with inflow resulting from heavy rain during a storm. Such inflow would typically be a combination of storm drainage from an adjacent industrial property, garage or the like, as well as inflow from storm drains adapted to catch rainwater. When peak flows during a heavy rain storm arrive at the interceptor, the interceptor automatically diverts most of this peak flow directly to an outlet opening which passes it directly to a storm sewer. Only a portion of the peak flow of the incoming rainwater is allowed through the treatment/storage chamber of the interceptor. 
         [0006]    To accomplish the aforesaid goals, the interceptor includes a passageway extending substantially directly between the interceptor inlet and the outlet. The passageway is essentially sealed from communication with the remainder of the interior of the tank interceptor, except for an opening adjacent the inlet and an opening adjacent the outlet. Each opening communicates the passageway with the remainder of the tank interior, which may be regarded as a treatment chamber. A weir is provided within the passageway, disposed with respect to the first opening such that, under relatively low entry flow rates, all entering materials are contained by the weir and flow through the first opening and into the treatment chamber, whereas under relatively high entry flow rates, part of the entering material overflows the weir and is delivered by the passageway to the outlet. 
         [0007]    Recognizing that it was not necessary for the entire volume inside the interceptor tank (except for the passageway) to be used as a treatment chamber, and in view of the desirability of making the passageway more fully accessible to personnel wishing to inspect the interceptor for damage, improper accumulations of materials, etc., an improved version of the separator tank was developed and is the subject of U.S. Pat. No. 5,498,331, issued Mar. 12, 1996. This interceptor includes a treatment compartment provided in the bottom portion thereof and a by-pass compartment in the top portion thereof (the latter being a convenient area where inspection personnel may stand). 
         [0008]    More particularly, the tank interceptor includes a container having a bottom wall, a side wall and a top wall which together define an internal chamber, a partition dividing the chamber into a by-pass compartment above the partition and a treatment compartment below the partition, the partition having an upper surface. A main inlet is provided in the side wall above the partition and is adapted to permit liquid to flow into the by-pass compartment. An outlet adjacently above the upper surface is spaced away from the inlet, the outlet being adapted to permit liquid to flow out of the by-pass compartment. The upper surface of the partition is configured to include a raised portion which isolates the inlet from the outlet, the raised portion constituting a weir, such that liquid entering at the inlet and seeking to reach the outlet through the by-pass compartment must overflow the weir in order to do so. The partition has first and second openings on opposite sides of the raised portion of the upper surface of the partition, both openings communicating the by-pass compartment with the treatment compartment, and allowing liquid, without having to overflow the raised portion, to travel from the inlet to the outlet by passing through the treatment compartment. Each of the first and second openings communicates with the top of a respective vertical pipe, each pipe having a bottom end communicating with the treatment compartment. 
         [0009]    Because it is necessary to allow personnel to inspect, clear and/or repair portions of the treatment compartment below the partition, the container of the interceptor is provided with an inspection opening in the partition, large enough to allow maintenance personnel to pass through, along with a man-hole cover adapted to close the inspection opening in a liquid-tight manner. 
         [0010]    It was subsequently realized that the inspection opening could be realized by making one of the openings through the partition (the openings connected to the respective pipes) large enough to allow maintenance personnel to pass through and into the treatment compartment, as disclosed in U.S. Pat. No. 5,725,760, issued Mar. 10, 1998. In this interceptor, the access opening at the top of the container (allowing access to the by-pass compartment) is positioned in alignment with the large-diameter partition opening, to allow visual inspection and sampling from outside the container, and to facilitate the entry of a snorkel for the purpose of pumping out the contents of the treatment compartment. 
         [0011]    With increasing awareness of environmental issues, especially that of industrial impacts upon environmental health, there is a continual drive towards ‘green’ technologies. While the above noted technologies are very effective in capturing oils and sediment, they are not geared to address a further important aspect of stormwater runoff, that being pH. In certain industrial environments, for example concrete production facilities, stormwater runoff can be considerably alkaline, due to aggregates stored on the sites. 
         [0012]    Conventional practices to neutralize alkali stormwater include holding ponds or tanks and injecting hazardous hydrochloric acid (HCl) or sulfuric acid (H 2 SO 4 ) into the stormwater prior to discharge. Employing such dangerous treatment methods raises serious concerns such as inconsistent treatment, high equipment maintenance due to the highly corrosive nature of the acids used, chemical storage issues and employee safety. A consistent, effective and safe-solution was required. 
         [0013]    Other patents, only peripherally related to the subject matter of this specification, are as follows: 
         [0014]    U.S. Pat. No. 4,136,010 to Pilie et al, Jan. 23, 1979; 
         [0015]    U.S. Pat. No. 1,844,443 to Schmidt, Feb. 9, 1932; 
         [0016]    U.S. Pat. No. 942,907 to Huff, Dec. 14, 1909; 
         [0017]    U.S. Pat. No. 3,567,024 to McCormick, Mar. 2, 1971; and 
         [0018]    U.S. Pat. No. 3,221,881 to Weiler et al, Dec. 7, 1965. 
       SUMMARY OF THE INVENTION 
       [0019]    Accordingly, in one aspect, there is provided a water-handling installation comprising: 
         [0020]    a tank interceptor for receiving liquid and in which oil or suspended solids are separated from the liquid prior to discharge, and 
         [0021]    a pH adjustment module in fluid communication with the tank interceptor, the pH adjustment module receiving a portion of liquid contained in the tank interceptor and adjusting the pH thereof prior to returning the diverted portion back to said tank interceptor. 
         [0022]    According to another aspect, there is provided a tank interceptor for rainwater and waste-water, comprising: 
         [0023]    a container including a bottom wall, at least one side wall and a top wall, said walls defining an internal chamber, 
         [0024]    a partition dividing the chamber into a by-pass compartment above the partition and a treatment compartment below the partition, the partition having an upper surface, 
         [0025]    an inlet through the side wall adjacently above said upper surface of the partition, the inlet being adapted to permit liquid to flow into the by-pass compartment, 
         [0026]    an outlet through the side wall adjacently above the upper surface of the partition, the outlet being adapted to permit liquid to flow out of said by-pass compartment, 
         [0027]    the upper surface of the partition being configured to include a raised portion which isolates the inlet from the outlet, while being spaced from the top wall of the container, the raised portion requiring that liquid entering through the inlet and seeking to reach the outlet through the by-pass compartment must overflow the raised portion in order to do so, 
         [0028]    first and second openings through the partition on the inlet side and the outlet side, respectively, of the raised portion, 
         [0029]    a first pipe commencing substantially at said first opening, extending downward therefrom, and opening into said treatment compartment at an intermediate vertical location therein, 
         [0030]    a second pipe commencing substantially at said second opening, extending downward therefrom, and opening into said treatment compartment at an intermediate vertical location therein, 
         [0031]    whereby said openings and pipes communicate the by-pass compartment with the treatment compartment, 
         [0032]    the openings and corresponding pipes being such that liquid, without having to overflow said raised portion, can travel from the inlet to the outlet by passing through the first opening into the treatment compartment, thence through the treatment compartment, thence through the second opening into the by-pass compartment, thence to the outlet, 
         [0033]    one of said openings and the corresponding pipe having an internal diameter large enough to allow passage of a maintenance worker from said by-pass compartment into said treatment compartment, 
         [0034]    an access opening through the top wall of the container, positioned such that maintenance personnel can, without having to enter the container, pass a snorkel through the access opening and said one of the openings in the partition, in order to pump out the contents of the treatment compartment, 
         [0035]    a pH measurement device configured to measure pH in the treatment compartment, and 
         [0036]    a liquid suction and discharge pipe in fluid communication with the treatment compartment for diverting a portion of the liquid to a pH adjustment module for pH adjustment of the diverted liquid. 
         [0037]    According to yet another aspect there is provided a water-handling installation, comprising: 
         [0038]    a tank interceptor for rainwater and waste-water, comprising: 
         [0039]    a container including a bottom wall, a side wall and a top wall, said walls defining an internal chamber, 
         [0040]    a partition dividing the chamber into a by-pass compartment above the partition and a treatment compartment below the partition, the partition having an upper surface, 
         [0041]    an inlet through the side wall adjacently above said upper surface of the partition, the inlet being adapted to permit liquid to flow into the by-pass compartment, 
         [0042]    an outlet through the side wall adjacently above the upper surface of the partition, the outlet being adapted to permit liquid to flow out of said by-pass compartment, 
         [0043]    the upper surface of the partition being configured to include a raised portion which isolates the inlet from the outlet, while being spaced from the top wall of the container, the raised portion requiring that liquid entering through the inlet and seeking to reach the outlet through the by-pass compartment must overflow the raised portion in order to do so, 
         [0044]    first and second openings through the partition on the inlet side and the outlet side, respectively, of the raised portion, 
         [0045]    a first pipe commencing substantially at said first opening, extending downward therefrom, and opening into said treatment compartment at an intermediate vertical location therein, 
         [0046]    a second pipe commencing substantially at said second opening, extending downward therefrom, and opening into said treatment compartment at an intermediate vertical location therein, 
         [0047]    whereby said openings and pipes communicate the by-pass compartment with the treatment compartment, 
         [0048]    the openings and corresponding pipes being such that liquid, without having to overflow said raised portion, can travel from the inlet to the outlet by passing through the first opening into the treatment compartment, thence through the treatment compartment, thence through the second opening into the by-pass compartment, thence to the outlet, 
         [0049]    one of said openings and the corresponding pipe having an internal diameter large enough to allow passage of a maintenance worker from said by-pass compartment into said treatment compartment, 
         [0050]    an access opening through the top wall of the container, positioned such that maintenance personnel can, without having to enter the container, pass a snorkel through the access opening and said one of the openings in the partition, in order to pump out the contents of the treatment compartment, 
         [0051]    a pH adjustment module for adjusting the pH of a liquid flow diverted from the treatment compartment of the tank interceptor, wherein the installation is configured with a pH measurement device configured to measure pH in the treatment compartment, and 
         [0052]    a liquid suction and discharge pipe in fluid communication with the treatment compartment for diverting a portion of the liquid to the pH adjustment module for pH adjustment of the diverted liquid. 
         [0053]    According to still yet another aspect, there is provided, for use with handling highly alkaline water runoff, utilizing a water handling installation comprising a tank interceptor and pH adjustment module, the tank interceptor having an outer wall that encloses an internal volume which is divided by a substantially horizontal partition into a treatment compartment below the partition and an overflow compartment above the partition, the pH adjustment module being in fluid communication with the treatment compartment so as to divert a flow of water from the tank interceptor and effect a pH shift by injecting CO 2  into the liquid flow, 
         [0054]    a process comprising the following modes: 
         [0055]    a first mode carried out by the tank interceptor in which arriving water travels through an inlet which opens through the outer wall, passes through a first opening in the partition into the treatment compartment, thence through the treatment compartment, thence upwardly through a second opening in the partition and thence to an outlet in the outer wall for discharge, and 
         [0056]    a second mode carried out by the pH adjustment module in which upon detection of highly alkaline conditions, the pH adjustment module draws a portion of the water and effects a pH correction by injecting CO 2 , thereby shifting the pH below a predetermined pH set point. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0057]    One embodiment is illustrated in the accompanying drawings, in which like numerals denote like parts throughout the several views, and in which: 
           [0058]      FIG. 1  is a vertical, axial sectional view of a tank interceptor and pH adjustment module combination; 
           [0059]      FIG. 2  is a lateral sectional view of  FIG. 1 , taken at the line  2 - 2 ; 
           [0060]      FIG. 3  is a sectional view of the pH adjustment module; and 
           [0061]      FIG. 4  is a sample treatment regimen for alkaline stormwater runoff from a representative concrete production facility. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0062]    Attention is first directed to  FIG. 1 , in which a tank interceptor is shown generally at the numeral  10 . The tank interceptor  10  includes a container  12  which has a circular bottom wall  14 , a cylindrical side wall  16  (made of interlocking sections) and a substantially circular top wall  18 . 
         [0063]    The walls  14 , 16  and  18  define an internal chamber  20  which is divided, by a partition  22 , into a by-pass compartment  24  above the partition  22 , and a treatment compartment  26  below the partition  22 . 
         [0064]    An inlet  28  is provided through the side wall  16  adjacently above the upper surface  30  of the partition  22 , the inlet  28  being adapted to permit liquid to flow into the by-pass compartment  24 . At a peripheral location on the side wall  16  which is spaced away from the inlet  28 , an outlet  32  is provided through the side wall  16  adjacently above the upper surface of the partition  22 , the outlet  32  being adapted to permit liquid to flow out of the by-pass compartment  24 . Typically, the outlet  32  is located slightly lower than the inlet  28 , to provide a gradient that promotes flow through the tank interceptor  10 . 
         [0065]    The upper surface  30  of the partition  22  is configured in such a way as to include a raised portion  34  which isolates the inlet  28  from the outlet  32 , while being spaced below the top wall  18  of the container  12 . The raised portion  34  requires that liquid entering through the inlet  28  and seeking to reach the outlet  32  through the by-pass compartment  24  must overflow the raised portion  34  in order to do so. 
         [0066]    The partition  22  exhibits a first opening  36  on the inlet side of the raised portion  34 , and a second opening  40  on the outlet side of the raised portion  34 . Preferably, the opening  36  is provided by an annular insert  38  which is one of several inserts having different opening sizes, to accommodate different average flow-rates or different interceptor sizes. 
         [0067]    A first pipe  42  beginning at the opening  36 , extends downward therefrom, and opens into the treatment compartment  26  at an intermediate vertical location therein. More specifically, the first pipe  42  terminates at a T-connection  44  set at right angles to the radius of the container  12 , thus promoting circumferential movement of any liquid entering the compartment  26  at the bottom of the pipe  42 . 
         [0068]    A second pipe  48  commences at the second opening  40  and extends downward therefrom, opening into the treatment compartment  26  at an intermediate vertical location therein. 
         [0069]    Thus the openings  36  and  40 , along with the associated pipes  42 ,  48 , respectively, communicate the by-pass compartment  24  with the treatment compartment  26 . 
         [0070]    It will thus be understood that the openings  36 ,  40  and the corresponding pipes  42 ,  48  are arranged such that liquid, without having to overflow the raised portion  34 , can travel from the inlet  28  to the outlet  32  by passing through the first opening  36  and the associated pipe  42 , thence into the treatment compartment  26 , thence through the treatment compartment  26  to the bottom of the pipe  48 , thence upwardly through the pipe  48  and the opening  40 , thence to the outlet  32  for discharge. 
         [0071]    In order to permit continuous monitoring and adjustment of pH in the treatment compartment  26 , an oil/inspection port  50 , which rises from the surface  22 , located underneath an opening  100  on the container and which is adjacent to opening  40  and raised portion  34 , is used to permit passage of a pH probe  52  into this region below the partition  22  (see  FIG. 2  for placement relative to opening  40  and raised portion  34 ). In the preferred embodiment, the pH probe is affixed to a probe extension assembly  56 , so as to facilitate insertion, as well as removal for cleaning and/or replacement and calibration. To maintain the pH probe and extension assembly  56  in a fixed position, any suitable attachment means  58  may be used. In this embodiment, the attachment means  58  is a clip for affixing the pH probe and extension assembly to the sidewall of the oil/inspection port. It will be appreciated, however, that other suitable attachment means may be used, for example, friction fit couplers, threaded couplers, clamps, etc. 
         [0072]    The pH of the liquid in the treatment compartment  26  is adjusted by a separate pH adjustment module, generally represented as  60  (best seen in  FIG. 3 ). This module takes a portion of the liquid from the treatment compartment  26 , subjects the extracted liquid to a pH adjustment if necessary, and returns the liquid to the treatment compartment  26 , thereby effecting a pH adjustment of the liquid contained therein. To deliver liquid to the pH adjustment module, a suction pipe  62  is positioned adjacent the interior sidewall of opening  40 . The open end  64  of the suction pipe preferably resides at least 2 feet under the water level (top of the outlet  32 ). The open end  64  may optionally be fitted with a T-connection set at right angles to the radius, so as to draw liquid from substantially a horizontal plane within the treatment compartment  26 . The suction pipe  62  extends upwards as shown in  FIG. 1 , passes through an opening  66  in the cylindrical side wall  16  and connects to a self-priming pump  68 . 
         [0073]    While the flow of liquid can be maintained in a single conduit, in this embodiment, the liquid is directed into a manifold  70  which splits the flow into at least two streams  72 ,  74 . Each separate flow of liquid in the manifold  70  is then subject to pH adjustment (discussed in greater detail below), after which the liquid is returned to the tank interceptor  10  via a discharge pipe  76 . As shown in  FIG. 1 , the discharge pipe  76  enters the tank interceptor  10  by passing through an opening  78  in the cylindrical side wall  16 . The discharge pipe  76  is attached via a coupler  80  to an access port  82  that extends through the partition  22  on the inlet side of the raised portion  34 . The access port  82  preferably has a pipe extension  84  extending downward therefrom, opening into the treatment compartment  26  at an intermediate vertical location therein. In a preferred embodiment, the pipe extension  84  is fitted with a T-connection  86  set at right angles to the radius of the container  12 , thus promoting circumferential movement of any liquid returning to the treatment compartment  26  from the pH adjustment module  60 , thereby ensuring that captured sediment is not disturbed. It should be noted that in certain applications, the access port  82  and discharge pipe  76  may be of different diameters. In these circumstances, it will be appreciated that the coupler  80  can be configured to effect the necessary diametral transition. It will be further appreciated that while the access port  82  is the preferred route for returning the pH adjusted liquid, the discharge pipe  76  can be configured to return to the treatment compartment  26  via an alternate route, for example through the second opening  40 . 
         [0074]    The pH measurements registered by the pH probe  52  are transmitted to a controller  88  contained within the pH adjustment module  60 . The pH adjustment module  60  continuously monitors the sensed pH and automatically activates pH adjustment relative to a preset pH point. While it will be appreciated that the pH adjustment module  60  can be used to adjust the pH either up or down, in this embodiment, the pH adjustment module  60  is used to lower the pH of basic (alkaline) liquids to below a predetermined pH set point using carbon dioxide (CO 2 ) injection. 
         [0075]    As discussed above, in the pH adjustment module  60 , the liquid directed into manifold  70  is split into two separate flows  72  and  74 . Each separate flow of liquid in the manifold  70  is then subject to pH adjustment. This is accomplished by injecting CO 2  contained within a CO 2  cylinder  92  into each flow of liquid using Venturi injectors  90 . The Venturi injectors  90  ensure high mass transfer between the CO 2  and the liquid. To prevent liquid migration up the CO 2  supply lines, check valves  91  may be fitted in place. With this arrangement, the CO 2  cylinder  92  is fitted with a primary regulator  94  that governs the initial feed pressure of CO 2  in conduit  96 . The CO 2  then feeds first into solenoid valve  98  and then secondary regulator  99 , both being controlled by the controller  88  of the pH adjustment module  60 . Actuation of the solenoid valve  98  permits the CO 2  to flow to the Venturi injectors  90  for injection into each flow of liquid. While the solenoid valve  98  opens and closes the feed of CO 2 , the secondary regulator  99  serves to control the amount of CO 2  that flows into the liquid for a given injection period. As will be readily understood by one skilled in the art, the incorporation of the CO 2  into the liquid serves to lower the pH. In fact, the use of CO 2  to reduce the pH has the added advantage of being self-buffering as the pH approaches neutral pH levels. This inherent inability to overshoot the preset pH set point is especially advantageous as it eliminates the possibility of dangerously acidic runoff being discharged from the tank interceptor  10 . 
         [0076]    In use, low-flow liquid entering at the inlet  28  is constrained by the weir (raised portion  34 ) to pass downwardly through the opening  36  and into the treatment compartment  26 . The liquid gradually accumulates in the compartment  26  until it reaches the bottom of the pipe  48 . Continuing inflow through the opening  36  gradually compresses the air located under the partition  22  (at locations other than the openings  36  and  40 ). Floating contaminants like oil, grease, etc. tend to accumulate under the partition  34 , thus trapping them in this position and not allowing them to rise up along the larger pipe  48  to gain access to the outlet  32 . 
         [0077]    During this operation, the pH adjustment module  60  continuously monitors the pH in the treatment compartment  26  When the controller  88  detects a pH in excess of the predetermined pH set point (i.e. pH of 8.5), the controller  88  activates the self-priming pump  68 , thus drawing liquid from the tank interceptor  10 . Concurrently, the controller activates the solenoid valve  98 , allowing CO 2  from the CO 2  source to be injected into the liquid flowing through the pH adjustment module  60 , The secondary regulator  99 , also controlled by controller  88  serves to control the amount of CO 2  that flows into the liquid for any given injection period. The pH adjusted water then returns to the tank interceptor, thereby imparting a pH adjustment upon the liquid contained therein. When the pH of the liquid in the treatment compartment  26  falls below the predetermined pH set point, the controller closes the solenoid valve  98  and stops the pump  68 . A sample treatment regimen for alkaline stormwater runoff is shown in  FIG. 4 . 
         [0078]    In the embodiment described above, the pH adjustment module  60  is maintained as a separate element from the tank interceptor. While this is a preferred embodiment, it will be appreciated that the pH adjustment module can be integrated into the construction of the tank interceptor  10 . 
         [0079]    It has been mentioned that the pH adjustment module  60  can be automated to continuously monitor and control/adjust the pH of the liquid. The pH adjustment module  60  can be further adapted with additional controls depending on the site specifics, i.e. integrated PLC controls can be used to monitor the system and relay information to a centralized reporting center, for easy operation and maintenance. 
         [0080]    The pH adjustment module may be of the type sold by Green Turtle Technologies of Toronto, Ontario, Canada under the name PHIX™ Basic Series System. It will be appreciated, however, that any suitable CO 2  injection/treatment system could be implemented as a substitute for the above described configuration. 
         [0081]    In the embodiment illustrated, the opening  40  (i.e. the opening on the “outlet” side of the weir constituted by the raised portion  34 ) has an internal diameter large enough to allow passage of a maintenance worker from the by-pass compartment  24  into the treatment compartment  26 . 
         [0082]    In  FIG. 1 , it will be seen that the top wall  18  of the container  12  provides the access opening  100 , which is offset with respect to the axis of the circular top wall  18 , such that it approximately overlies the position of the opening  40  and oil/inspection port  50 . A cover and grate  102  is provided to close the access opening  100 . By generally aligning the opening  100  and the oil/inspection port  50  and opening  40 , it is possible to carry out inspection, sampling and the pumping out of the entire contents of the treatment compartment  26  from a position above the access opening  100 , thus making it unnecessary, at least for a large number of maintenance tasks, for a worker to actually enter the container  12 . 
         [0083]    However, to facilitate the work of personnel that do need to enter the containers for cleaning and other purposes, a standard ladder  104  is anchored into the cylindrical side wall  16  of the container  12 . 
         [0084]    Although the illustrated embodiment shows the disposition of the weir constituted by the raised portion  34  to be around opening  36 , i.e. the raised portion  34  may be around opening  40 , simply by reconfiguring the size and disposition of the weir constituted by the raised portion  34 . 
         [0085]    It is preferred also that the upper surface  30  of the partition  22  lie substantially in a single horizontal plane. 
         [0086]    While  FIG. 1  shows the inlet and outlet to be approximately diametrally opposed, this is not critical. 
         [0087]    While one embodiment has been illustrated in the accompanying drawings and described hereinabove, it will be evident to those skilled in the art that changes and modifications may be made therein, without department from the scope thereof, as set forth in the appended claims.