Abstract:
The invention provides a waste water treatment system including primary settling tanks. The waste water treatment system includes a trough which causes water to flow in a direction parallel to a bar screen placed in the trough with the base of the bar screen being at a lower elevation than the trough weir. Each primary settling tank has a fine screen box for screening waste water. Each primary settling tank has a scum and floatables trough for collecting scum and floatables which pass through or over a top edge of the bar screen. The scum and floatables troughs are in fluid communication with one. When a scum valve is open, scum, floatables and water in the scum and floatables trough flows from the scum and floatables trough of the first primary setting tank to the scum and floatables trough of the second primary settling tank into a collection container.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a floatables and scum removal apparatus for use with a waste water treatment system. More particularly, the present invention relates to improvements in floatables and scum removal which allow removal of these items at the entrance to the water treatment system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Waste water treatment systems used in the industry generally include, but are not limited to, the following treatment processes: grit removal, fine screening, flow equalization and primary clarification. The typical treatment processes are dependent on the velocity at which the waste water is moving through the system. Waste water, however, is not produced continually by humans, but instead is created in batch type processes, such as showering, flushing a toilet or operating a washing machine. Such water consumptive activities are generally repetitive resulting in daily, weekly, monthly and yearly diurnal flow patterns for a specific waste water treatment system. Accordingly, the volume of waste water produced, and the velocity of that waste water through the treatment system varies significantly throughout the day. 
         [0003]    Grit removal is generally performed in a grit chamber which is velocity sensitive. The most common methods to remove grit are by reducing the velocity of the influent flow so that the grit settles out, or utilizing a circular channel/tank. The circular channel/tank is a hydro-cyclone that causes the grit to settle in a sump, separating the organics from the grit so that they can move forward to the biological processes. The grit is then pumped out of the sump to a grit washer and then discharged to a dumpster for disposal at a landfill. 
         [0004]    Fine screening is typically accomplished by placing a screen in an influent channel. The influent channel must have a minimum velocity of 1.25 feet per second to keep solids from settling out in the channel and a maximum velocity of 3.0 feet per second to keep solids from being forced through the screen. Such a flow is difficult to achieve due to the large variation in diurnal and pumped flow patterns. 
         [0005]    Typical primary clarifiers are also velocity sensitive with the heavy solids going to the base of the clarifier where they are pumped to a digester, the floatable solids, grease and scum are trapped and skimmed off the surface and the neutral buoyant solids/clarified waste water exits the basin via an effluent weir. Primary clarifiers are typically large tanks designed for gravity settling and may include electrical drives, flights and chains, rack arms and paddles or suction tubes and sludge pumps. 
         [0006]    Flow equalization typically occurs in a separate tank. The flow at the waste water plant is subject to travel times in the collection system, collection system design and pump station sizing. In general, larger collection systems use pump stations to lift the waste water to the treatment facility. The pumps are typically placed on variable-frequency drives in an attempt to provide a consistent uniform flow. The system of variable-frequency drives and pumps, however, fails in low and high flow conditions. The pumps must be designed for peak hourly flows and have minimum turn down capabilities. 
         [0007]    Traditional, waste water treatment plants have static bar racks or mechanically cleaned bar screens in channels at the entrance of the waste water into the treatment facility. These influent channels are typically constructed of concrete so as to last the life of the facility and are designed for specific waste water volumes, velocities (1 to 3 feet per second), and the insertion of specific screening and grit removal equipment. 
         [0008]    The social behavior of flushing solids that should go to landfill such as baby wipes, diapers, swizzle sticks, condoms, tampon applicators, etc. creates issues for the operation of the waste water treatment facility. Many of these solids are neutrally buoyant or will float in the waste water. Elongated solids align with the flow and pass or are forced through the bar racks or mechanical screens because of the high flow. The flat sheet solids such as diapers and baby wipes cover the bar racks or screens causing the liquid level in the channel to rise and enter a bypass channel. These solids often end up creating issues in the treatment plant such as fouling pumps, valves, diffusers, and membranes ultimately ending up in the digester or sludge holding tank. 
         [0009]    The increase in frequency and intensity of storm events producing exceptional precipitation combined with leaky sewage collection systems produces greater volumes of waste water delivered to the waste water treatment plant. Changes in societal behavior are not likely to occur. The cost to repair or replace the aged collection systems of developed nations is not fiscally achievable in the time frame needed. Therefore, the limited cross-sectional area of a channel requires an innovative approach to solve the above issues. The solution must be efficient in consideration of the goal to convert energy consumptive waste water treatment plants to sustainable resource recovery facilities where possible. 
         [0010]    To accomplish the above, the influent channels must be replaced with tanks. Waste water design engineers and manufacturers of screening equipment recognize that high velocities and screening are in conflict. Yet the use of channels at the head of the waste water treatment process is still taught to engineering students today. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Recently, a single tank waste water treatment system was developed which eliminates many problems associated with the prior art designs. The system comprises a single primary settling tank that performs grit removal, flow equalization, primary clarification and fine screening. This waste water treatment system is described in U.S. Pat. No. 7,972,505, the disclosure of which is incorporated by reference herein. 
         [0012]    The invention is suitable for use with industrial and municipal waste water treatment. It is also useful for clarifiers, settling tanks or biological processes such as sequencing batch reactors that have changes in liquid elevations in these tanks and for industrial process waste waters containing high or low specific gravity constituents. The present invention increases the surface area of the screen in contact with the liquid by placing the screens in a tank having an influent feed trough, not a channel, to further reduce the velocity at the liquid at the screen interface. The influent feed trough also changes the flow direction at the screen face to prevent elongated items from aligning with the flow. Elongated items align with the flow and pass through the screens. High velocities will push the larger pliable solids through the screen openings. The present invention operates at a reduced water velocity, trapping all solids larger than the screen openings between the tank wall and the screen face. The trapped floatables rise with the liquid in the tank to the top of the screen where a scum trough is in close proximity to the screen. The scum trough is valved to control the liquid flow exiting the tank from the surface. A control system allows the operator to manually open the valve or set the number of tank fill cycles between scum withdrawals. When the liquid is above the trough and the valve is opened, the surface liquid moves towards the trough and then exits the tank. The liquid movement towards the trough moves the scum and floatables to the trough. The liquid transporting the scum and floatables out of the tank discharges into the collection box with an integral basket of fine mesh. A disposable bag may line the interior of the basket. Also, polymers, adsorbents or absorbents may be added to the interior of the disposable bag to capture hydrocarbons or other constituents specific to the waste water being treated. The operator manually disposes of the bag when it is full. The collection box, basket, and bags are volumetrically sized to handle the volume of solids and scum from multiple cycles which allows the captured constituents to be washed with the liquid transporting the scum and floatables. The liquid passing through the scum basket and/or bag returns to the adjacent tank or may be directed to another process for further treatment. 
         [0013]    In the traditional treatment of waste water, tanks are used for flow equalization, clarification, aeration and storage of liquids and or solids. Channels are used as pipes to convey liquids laden with solids from one point to another for treatment. Channels are sized to maintain a velocity of 1 to 3 feet per second to keep solids in suspension. This high velocity pushes solids into and often times through the screen openings. This requires the use of high pressure water, mechanical rakes or scrapers, or brushes to physically remove the solids from the screen openings. It prevents the use of ultrafine screens as the headloss is high and would require a deeper channel upstream of the screen. These ultrafine screens are needed for new waste water process technologies like membranes. It also prevents dietary fibers or soluble biological oxygen demand (SBOD) constituents to settle. The SBOD requires energy to convert to biomass and CO2 where if it could settle, it could be used to generate biogas to power micro-turbines to generate electricity or cleaned to produce compressed natural gas or propane. The dietary fibers cause fouling of hollow fiber membranes, the larger solids plug the flat plate membranes resulting in high energy to scour the membranes. The fouling or plugging of the membranes reduces their life cycle thus increasing operational issues and replacement costs. Unexpected flows from aged collection systems and increased storm intensities cause these traditional systems to cease to function properly. By using tanks instead of channels there is more screen surface area in contact with the waste water liquid so the velocity at the screen/liquid interface is much lower. Tanks can be wider and deeper than channels so the cross-sectional area of the liquid is much larger and the forward velocity is significantly less. The slower the forward and rise velocities, the greater the surface and cross-sectional areas the greater the ability for dense solids, like grit, to settle and for the light solids and liquids to float. This reduces the solids coming in contact with the screen. It allows for screens having smaller openings to be used with less headloss and cleaning required. Static screens may be used as the solids are not being forced into and lodging in the openings. It allows for higher than expected future flows to be handled effectively as there is more screen surface area. 
         [0014]    The invention provides a modular scum and floatables capture system for the retention and directional movement of soluble and solid constituents having a specific gravity of less than 1.0, floatable screenings, removal of retained floatables and scum, and washing of floatables found in waste water (combined sewers, sanitary sewer, petroleum spills, and industrial process waters). The system is installed in a tank or tanks that have liquid elevations that vary between a high and a low liquid level and have an inlet trough or weir. Scum and floatable content may consist of fats, oils, grease, liquid and solids having a specific gravity less than 1.0 such as petroleum products and solids having trapped air to cause objects with a specific gravity greater than 1.0 to float. 
         [0015]    The system consists of stationary or mechanical bar screens, rotational scum troughs, control system to operate actuated valves in manual or automatic modes, actuated valves and slide gates, collection boxes placed inside or outside the tank with each having a removable capture basket that may or may not have a disposable liner bag or just a disposable bag without a basket. An adsorbent may be placed in the disposable bags to capture specific constituents in the waste water such as petroleum products that would separate during the clarification process and rise to the surface of the liquid. 
         [0016]    Stationary or mechanical screens are placed between the interior edge of an influent weir or trough and the tank wall with the waste water entering between the screen and tank wall. The screen may be perpendicular to the liquid surface or vertically inclined and rise to a close proximity (e.g. less than 0.5 inches of the scum trough at the high liquid level in the tank. The screen can be the same dimension or shorter than the horizontal dimension of the scum trough. The screen is set back from the edge of the weir to increase the screen surface area in contact with the liquid (as the weir slopes downward at a 70 degree angle towards the wall) and not to create a disturbance of the liquid at the edge of the weir causing the velocities to be higher and uneven, which might result in a break in cohesion or surface tension to the surface of the weir. Elongated objects will align with the flow so when the liquid turns 90 degree to enter the tank the largest dimension (long dimension) of the solid is perpendicular to the screen. Both the low velocity and causing the elongated side of the solid to be parallel to the screen, prevents solids from being wedged into the open spaces of the screen. This leaves the solids free to move vertically with the liquid level of the tank. 
         [0017]    The collection box may be located inside or outside of the tank depending on the application. If the floating and separated soluble constituents in the surface water are to be adsorbed or reused then the collection box will likely be located outside of the tank so the liquid does not continue to move back and forth between the adjacent tanks creating a concentration loop. The low specific gravity liquids and water will be properly directed to further treatment processes. If there is no adsorption or reuse of the liquid constituents the collection box will likely be placed inside the tank, above the grit box, so the liquid free falls down into the grit box. The exterior walls of the grit box are closed and sealed, and rise to an elevation above the highest liquid level in the tank. Should some floatable solids fall from the basket they remain trapped between the screen and tank wall. The liquid falling into the grit box will then travel into the feed trough and over the weir into the tank. This is efficient because the tank receiving the conveyed liquid along with the floatable solids and scum has a low liquid level and will enter into a fill cycle when the scum cycle in the adjacent tank ends. Current scum cycles require significant amount of transport liquid to move the solids via pumps and piping to the next process. Often the next process is a sludge holding tank or digester and then to a belt press. This surplus liquid from conveying the floatables is then decanted from the surface of the scum holding tank or digester and pumped back to the head of the waste water treatment plant for reprocessing. This increases capital costs, energy consumption, and operation and maintenance costs to keep pipes and pumps free of these solids and FOG (Fats, Oils, Grease) 
         [0018]    When a scum cycle takes place the liquid is at the high level or slightly higher than the scum trough weir the actuated valves open. The scum troughs between adjacent rectangular tanks are common. There are two types of operations possible. In one, the collection box is located inside the tank—one tank has a high liquid level (tank A) and the other tank (tank B) has a low liquid level. A valve at the common wall dividing the adjacent tanks is normally closed until a scum cycle is manually or automatically initiated. When this valve is opened, the liquid in and above the scum trough in tank A moves through the connected scum troughs carrying the scum and floatables to the scum basket or bag located in the collection box of tank B. The scum and floatables are captured in the basket or bag and the liquid returns to the grit chamber and influent feed system of tank B. In the other, the collection box is located outside the tank—one tank has a high liquid level (tank A) and the other tank (tank B) has a low liquid level. A valve at the common wall dividing the adjacent tanks is normally closed until a scum cycle is manually or automatically initiated. When this valve is opened, the liquid in and above the scum trough in tank A moves through the connected scum troughs carrying the scum and floatables to the scum basket or bag located in the collection box located outside of tank B. The scum and floatables are captured in the basket or bag and the liquid is directed to another process. This option is used when the clarified liquid at the surface is to be reused or processed further such as cleanup of fuel spills. 
         [0019]    The system can also be used with two circular tanks adjacent to each other. Each tank can have an internal circular bar screen that extends to the same elevation as the outside wall of the scum trough. The scum trough is circular, located at the top of the tank, has an outer wall higher than the tank wall, the tank wall serves as the inside wall of the scum trough and the bottom of the trough is lower than the top of the tank. Each scum trough has a collection box with a basket or bag located inside to capture the floatables, there is a drain pipe at the bottom of the box that slopes downward and connects to the adjacent circular tank. There is a weighted flap valve at the inlet to the adjacent tank. One tank has a high liquid level (tank A) and the other tank (tank B) has a low liquid level. When tank A is selected to undergo a scum cycle the influent pump continues to add liquid to tank A raising the liquid above the tank wall so the floatable and scum flow over the tank wall and into the trough. The liquid carries the scum and floatables to the opening in the bottom of the trough, falls through the basket onto the bottom of the collection box, down the drain pipe to tank B. The process is the same for a tank B scum cycle. 
         [0020]    The solid scum and floatables are captured in the basket and/or bag as the liquid passes through the basket or bag and returns to the adjacent tank having a low liquid level or to the influent pump station and returned to the tank once again free of scum and floatables or to another treatment process. The basket and or bag are sized for the projected volume of floatables collected over multiple scum cycles. This allows the captured floatables to be washed multiple times with each cycle. 
         [0021]    The rotational scum trough is a pipe cut lengthwise thus forming 2 weirs. A rotational scum trough rests at each end and has a rod running vertically. When the rod is at the 12:00 o&#39;clock position both weirs are at the same elevation. If the rod is rotated to the 11:00 o&#39;clock position then the weir on the left lowers and the weir on the right rises. If the rod is moved to the 1:00 o&#39;clock position, the liquid enters the scum trough from the low side. Typically the rod will be tilted towards the bar screen to pull the trapped floatables and scum into the scum trough. 
         [0022]    Periodically the operator will need to draw off the scum that passes through the screen into the main body of the tank on the opposite side of the screen. 
         [0023]    The invention also includes a bar screen backwash and influent feed trough scour cycle. An actuated slide gate is positioned on an opening in the common dividing wall as close to the high point of the sloped bottom of the influent feed trough. The actuated slide gate controls flow from the full tank to the low liquid level tank. Over time solids are expected to settle in the feed trough and fibers to staple to the bar screen. To address this issue the following operation takes place. On completion of a scum cycle in tank A the grit valve in tank B opens. The solid laden liquid in the influent feed trough drains to the grit box and exits tank B to another treatment process. At a user defined time frame or visual (manual) activation, the actuated slide gate opens and liquid exits tank A to tank B scouring the influent trough of tank B and carrying solids and liquid to the grit box and exits the system. The liquid in tank A flows from the decanter side of the bar screen towards the influent feed system. This reversal of normal flow will dislodge many of the solids and fibers attached to the bar screen as the influent velocity through the bar screen is very low so the solids are not wedged into the screen. This action will minimize the need to physically clean the bar screen. The slide gate will open for a short period of time and only one bar screen will be backwashed at a time to minimize the volume of liquid exiting via the grit box drain. 
         [0024]    In summary, the invention provides a waste water treatment system including at least two primary settling tanks wherein processes of grit removal, sludge removal, primary clarification, and fine screening are carried out. The settling tanks have a waste water level which changes over time between a high level near the top of the primary settling tanks and a low level nearer near the bottom of the primary settling tanks. The waste water treatment system includes an influent feed basin and an influent feed trough which cause water to flow in a direction parallel to the bar screen. Each primary settling tank has a fine screen box which moves in vertical location, between a low level nearer the bottom of the primary settling tank and a high level wherein the screen box is above the high level of the waste water at the start of the scum or decant cycles. The fine screen boxes include a water outlet for removal of screened waste water from within the fine screen boxes. The fine screen boxes have fine screen material with openings of a first size. Each primary settling tank has a bar screen with screen openings of a second size larger than the openings of the first size. The bar screen is located in influent feed trough with a base of the bar screen lower than a weir in the feed trough. This reduces the velocity through the bar screen when the liquid level in the tank is below the influent feed trough weir. The slope of the influent feed trough allows for additional screen surface area. By moving the bar screen away from the weir, the deeper the bar screen goes thus increasing the area of the surface/liquid interface. Another aspect of moving the bar screen back from the weir edge is it improves laminar flow over the weir. If the bars were placed at the weir edge turbulence at the weir edge would be created thus affecting the surface tension and cohesion of the liquid to the exterior face of the trough. Each primary settling tank has a water inlet for introducing waste water to the primary settling tank. The waste water contains scum and floatables. Each primary settling tank has a water inlet area separated from a portion of the primary settling tank by the bar screen. Each primary settling tank has a scum and floatables trough on a side of the bar screen opposite the water inlet for collecting scum and floatables which passes over a top edge of the bar screen. The scum and floatables trough can be rotatably mounted such that it can rotate about its longitudinal axis. The scum and floatables trough of a first primary settling tank, and of a second primary settling tank are in fluid communication with one another and are separated by a scum valve. When the scum valve is open, scum, floatables and water in the scum and floatables trough flow from the scum and floatables trough of the first primary setting tank to the scum and floatables trough of the second primary settling tank. Each scum and floatables trough has a collection container for collecting the scum and floatables that flows through the scum and floatables trough. The collection container could be in the form of a basket or a bag which retain the floatables and allow the water to pass through the basket. The basket or bag is removable such that they may be removed and emptied by an operator of the system. The primary settling tank includes an influent feed basin such that the velocity of the water flowing through the bar screen is decreased. The waste water treatment system includes a weir such that water flowing over the weir flows in a generally laminar flow down the exterior surface of the weir reducing air entrainment that may cause the sludge to float. 
         [0025]    The waste water treatment system includes a backwash valve on the same side of the bar screen as the water inlet such that when the water inlet is closed and the backwash valve is open, water flows from the primary settling tank through the bar screen and through the backwash valve so that water and debris caught in the bar screen on the full tank are removed from the bar screen. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0026]    The foregoing and other objects, features, and advantages of the invention will be apparent from the following drawings and more particular description of the preferred embodiments of the invention. 
           [0027]      FIG. 1  is a perspective view of the present invention; 
           [0028]      FIG. 2  is a partial-cutaway perspective view of the invention of  FIG. 1 ; 
           [0029]      FIG. 3  is a perspective view of the invention of  FIG. 1  including the screen box assembly; 
           [0030]      FIG. 4  is a partial-cutaway perspective view of the invention of  FIG. 1 ; 
           [0031]      FIG. 5  is a partial-cutaway perspective view of the invention of  FIG. 1  showing an alternate embodiment; 
           [0032]      FIG. 6  is a partial-cutaway perspective view of the invention of  FIG. 1 : 
           [0033]      FIG. 7  is a partial-cutaway perspective view of the invention of  FIG. 1 ; 
           [0034]      FIG. 8  is a partial-cutaway perspective view of the invention of  FIG. 1 ; 
           [0035]      FIG. 9  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0036]      FIG. 10  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0037]      FIG. 11  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0038]      FIG. 12  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0039]      FIG. 13  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0040]      FIG. 14  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0041]      FIG. 15  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0042]      FIG. 16  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0043]      FIG. 17  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0044]      FIG. 18  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0045]      FIG. 19  is a partial cut-away front elevation view of the invention of  FIG. 3 ; 
           [0046]      FIG. 20  is a partial cut-away view of the invention of  FIG. 3  illustrating the backwash cycle; 
           [0047]      FIG. 21  is a partial cut-away view of the invention of  FIG. 3  illustrating the backwash cycle; 
           [0048]      FIG. 22  is a perspective view of the invention of  FIG. 3  illustrating the backwash cycle; 
           [0049]      FIG. 23  is a perspective view of the invention of 
           [0050]      FIG. 3  illustrating the backwash cycle; 
           [0051]      FIG. 24  is a partial cut-away front elevation view of an alternative embodiment of the invention of  FIG. 1 ; and 
           [0052]      FIG. 25  is a top plan view of the embodiment of  FIG. 24 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0053]    Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive. It is to be further noted that the drawings are not to scale. 
         [0054]      FIGS. 1 through 25  illustrate the invention. The present invention is a system for the primary treatment of waste water. 
         [0055]      FIGS. 1 and 2  show a primary settling tank  10  which receives waste water from a waste water collection system through an influent pipe  12 . The waste water treatment system may also be used in other applications that benefit from an equalized flow into the waste water treatment processes, such as industrial batch discharges, storm water, and septic receiving at a waste water treatment plant. Waste water reaches the waste water treatment system as a result of gravity, the operation of pumps, or both. The primary setting tank has outer walls  16 . A bar screen  14  is placed in the primary settling tank  10  between the outer wall  16  and the interior  18  of the primary setting tank  10 . The bar screen  14  keeps large inorganic solids from entering the waste water treatment system. 
         [0056]    The primary settling tank  10  is sized based on the daily flow patterns for the collection system using generally known engineering practices. The size of the primary settling tank  10  is large compared to the influent pipe  12  such that the velocity of the incoming flow decreases dramatically upon entrance of the water into the primary settling tank  10 . The first stage of reducing the incoming velocity is to split the flow so there are two influent pipe  12 . 
         [0057]      FIG. 2  shows the primary settling tank  10  with portions cut away to illustrate the interior features. An influent feed trough  20  receives the incoming waste water and directs the flow in the direction of arrow  22 . As the water level rises to the level of the bar screen  14 , scum and sludge (not shown) pass through the bar screen  14 . Floatables  102  (See  FIGS. 9-19 ), such as plastic solids are prevented from passing through the bar screen  14 . Sludge collects in the sludge hopper  30 , and can be removed from the sludge hopper  30  through outlet  32 . A scum and floatables trough  40  is provided to collect scum and floatables, as will be described in greater detail below. A handle  42  is connected to the scum and floatables trough  40  to control the angular position of the scum and floatables trough  40 . A scum and floatables collection box  50  is in fluid communication with the scum and floatables trough  40 . In  FIG. 1 , the scum and floatables collection box  50  is shown on the outside of the primary settling tank  10  but in other embodiments the scum and floatables collection box  50  is inside the primary settling tank  10 . 
         [0058]    Referring to  FIG. 3 , the primary settling tank  10  is shown with the screen box assembly  60 , which includes a screen box  62 , supporting framework  64 , a hydraulic actuator  66  (a winch with pulley and cable may be used as well) and baffle plate  68 . The position of the screen box determines the level of water in the primary settling tank  10 . An overflow outlet  70  prevents water from flowing over the sides of the primary setting tank  10  if the water level rises too high. 
         [0059]      FIG. 4  shows the primary settling tank  10  with some of the outer walls  16  removed to reveal the internal components. The bar screen  14  is shown with the scum and floatables collection box  50  adjacent one side of the bar screen  14 . The bottom of bar screen  14  is lower than the elevation of weir  86  ( FIG. 7 ) thus increasing the bar screen/liquid contact area thus reducing the velocity through bar screen  14 . The scum and floatables collection box includes a flap valve  52  which allows water, scum and floatables to enter the scum and floatables collection box  50  but prevents flow in the opposite direction. A screened basket  54  is provided in the scum and floatables collection box  50 , which allows water to pass through. A valve  56  is provided at the end of the scum and floatables trough  40  to control the flow of water across the scum and floatables trough  40 . Actuator  58  opens and closes the valve  56 . A backwash valve  72  and actuator  74  are provided, the purpose of which will be described below.  FIG. 5  shows the use of a porous bag  154  in place of the screened basket  54 . Porous bag  154  operates in a manner similar to the screened basket  54 . 
         [0060]      FIGS. 6-8  illustrate the fill cycle of the primary settling tank  10 . Waste water  80  enters the primary settling tank through inlet  12 . As it enters the influent feed basin  82  it becomes turbulent as represented by arrows  84 . The water level rises to the influent feed trough  20  as shown in  FIG. 7 . A weir  86  is spaced away from the bar screen  14  and is placed at an angle of preferably 60 to 70 degrees from the horizontal. A bottom directional flow plate  88  slopes toward the sludge hopper  30 . As shown in  FIG. 8 , water passing over the top edge  90  of the weir  86  flows down the exterior surface of weir  86  in generally laminar flow. This slope towards the wall increases the settling volume of the tank. Because the water flows down the surface of the weir  86  in laminar flow, there is no free fall of the liquid thus no air entrainment to improve the settling of sludge. 
         [0061]      FIGS. 9 through 19  illustrate the floatables removal cycle. The floatables  102  are shown at various levels and positions throughout  FIGS. 9 through 19 .  FIGS. 9 through 12  illustrate the floatables  102  removal cycle in a first direction. In  FIG. 9  waste water, scum and floatables  102  enter through the influent pipe  12  into the influent feed basin  82  as represented by arrow  104 . The floatables  102  are shown on the influent feed trough  20 . The floatables  102  are too large to pass through the bar screen  14 .  FIG. 11  shows the floatables  102  which have risen to the top of the bar screen  14  and are in the scum and floatables trough  40 . In  FIG. 12 , the valve  56  has been opened and the floatables  102  have been moved through valve  56  by the liquid above and in the trough across scum and floatables trough  40   a , through flap valve  52   a  and into collection box  50   a.    
         [0062]      FIGS. 13 through 17  illustrate the floatables  102  removal cycle in the opposite direction. Waste water, scum and floatables enter through influent pipe  12   a  as illustrated by arrow  104   a . As shown in  FIG. 13 , the floatables  102  move upward toward the scum and floatables trough  40   a . In  FIG. 15 , the floatables  102  are approaching the scum and floatables trough  40   a  to be flushed through valve  56 .  FIG. 16  shows the floatables  102  ready to be flushed through valve  56 , into scum and floatables trough  40  and into scum and floatables collection box  50 .  FIG. 17  shows the floatables  102  after they have been flushed through the valve  56  and the water represented by arrow  114  has flown through the floatables collection box  50  to exit through valve  116 .  FIGS. 18 and 19  illustrate the floatables  102  removal process starting over again. 
         [0063]      FIGS. 20 through 23  illustrate the bar screen  14  backwash cycle. Referring to  FIGS. 20 and 22 , after the tank  10  has filled, inlet valve  120  is closed and backwash valve  72  is opened. Water, represented by arrows  124  flows through the bar screen  14 , through valve  72 , through valve  122   a  and out through outlet  126   a .  FIGS. 21 and 23  illustrates the backwash cycle for tank  10   a . After tank  10   a  has filled, influent feed stops and backwash valve  72  is opened. Water represented by arrows  124   a  flows through the bar screen  14   a , through valve  122  and through outlet  126 . 
         [0064]      FIGS. 24 and 25  illustrate an alternative embodiment of the present invention. The primary settling tanks  210  and  210   a  are circular. Scum and floatables troughs  240  and  240   a  surround tanks  210  and  210   a . Bar screen cylinders  214  and  214   a  are in the center of the tanks  210  and  210   a . In some applications, depending on the application and solids content of the liquid this bar screen may be omitted. Waste water enters tank  210  through pipe  204  and valve  206 . Similarly, waste water enters tank  210   a  through pipe  204   a  and valve  206   a . Scum and floatables collection boxes  250  and  250   a  are in fluid communication with scum and floatables troughs  240  and  240   a . When valve  256  is opened, scum and floatables exit scum and floatables trough  240  and flow to collection box  250 . In some embodiments, a flex connection is used instead of valve  256 . The flex connection (not shown) would include a check valve on the connecting pipe to allow flow in only one direction. Similarly, when valve  256   a  is opened, scum and floatables  212   a  exit scum and floatables trough  240   a  and flow to collection box  250   a . Sludge collects in sludge hoppers  230  and  230   a  and exits through pipes  232  and  232   a  and valves  234  and  234   a . Screened waste water exits tank  210  through drain pipes  236  and  236   a  and valves  238  and  238   a.    
         [0065]    As will be apparent to those skilled in the art in light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof.