Abstract:
A system for backflushing materials from the upstream side of a bar screen in a primary waste water treatment installation having a reservoir of influent material disposed within a primary settling tank on the downstream side of the bar screen, wherein the system comprises a drain pipe in communication with the interior of the primary settling tank, a drain valve disposed in the drain pipe, and a programmable controller controllably connected to the drain valve and to an influent supply valve disposed in an influent supply pipe connected to an entry port in the primary settling tank. Preferably the system includes a first sensor disposed within the settling tank and a second sensor and flowmeter disposed within the drain pipe. Backflushing is provided by reverse flow of influent from the reservoir when the influent supply valve is closed and the drain valve is opened.

Description:
RELATIONSHIP TO OTHER PATENTS AND APPLICATIONS 
       [0001]    The present application is a Continuation-In-Part of a pending US Patent Application, Ser. No. 14/142,099, filed Dec. 27, 2013, which is incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE APPLICATION 
       [0002]    The present invention relates to a floatables and scum removal system (method and apparatus) for use with a primary waste water treatment system. More particularly, the present invention relates to improvements in floatables removal which allow removal of these items from the upstream side of the bar rack screening apparatus of the waste water treatment system. 
       BACKGROUND 
       [0003]    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, vary significantly throughout the day. 
         [0004]    In the prior art, grit removal is generally performed in a grit chamber which is velocity sensitive. The most common method to remove grit is by reducing the velocity of the influent flow so that the grit settles out, utilizing a rectangular or circular channel/tank. Either tank causes the grit to settle in a sump, separating the organics from the grit so that the organics 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. 
         [0005]    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. 
         [0006]    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 influent 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. 
         [0007]    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. 
         [0008]    Traditionally, 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. 
         [0009]    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. Flat sheet solids such as diapers and baby wipes can 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 of pumps, valves, diffusers, and membranes, and ultimately ending up in the digester or sludge holding tank. 
         [0010]    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. The cost to repair or replace the aged collection systems of developed nations is not fiscally feasible or achievable in the time frame needed. Therefore, the limited cross-sectional area of an existing 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. 
         [0011]    To accomplish the above, the influent channels must be replaced with tanks, as disclosed in U.S. patent application Ser. No. 14/142,099 (“the parent application”). 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. 
         [0012]    An additional problem is the removal of solids from the bar racks or screens. As used herein, the interchangeable terms “bar rack” and “bar screen” should be taken to mean any primary screening device in the influent flow path ahead of a settling tank. 
       BRIEF SUMMARY 
       [0013]    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 &#39;505 patent), the disclosure of which is incorporated by reference in its entirety for al purposes herein. 
         [0014]    The parent application discloses an improvement 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. 
         [0015]    In conventional systems, bar racks are cleaned by mechanically scraping and spraying with a wash which may be water or a combination of water and a cleaning agent such as citric acid. In one aspect of the current application, 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. 
         [0016]    In another aspect of the present application, backflushing of the bar rack is performed by causing already-screened influent in the settling tank to flow backwards in a timely way through the bar rack to a drain, thereby removing floatables and large solids trapped against the upstream side of the bar rack. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0017]    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, wherein: 
           [0018]      FIG. 1  is a partial-cutway perspective view of a single tank waste water treatment installation, substantially identical to that disclosed in  FIG. 2  of the parent application; 
           [0019]      FIG. 2  is a schematic elevational view of a first embodiment of a portion of a wastewater treatment system in accordance with the present application; 
           [0020]      FIG. 3  is a schematic elevational view of a second embodiment of a portion of a wastewater treatment system in accordance with the present application; 
           [0021]      FIG. 4   a  is a schematic elevational view of a third embodiment of a portion of a wastewater treatment system in accordance with the present application; 
           [0022]      FIG. 4   b  is a schematic plan view of a portion of a wastewater treatment system shown in  FIG. 4   a;    
           [0023]      FIG. 5   a  is a schematic plan view of a portion of a wastewater treatment system in accordance with the present application, showing a first drainage arrangement; 
           [0024]      FIG. 5   b  is a schematic plan view of a portion of a wastewater treatment system in accordance with the present application, showing a second drainage arrangement; 
           [0025]      FIG. 5   c  is a schematic plan view of a portion of a wastewater treatment system in accordance with the present application, showing a third drainage arrangement; and 
           [0026]      FIG. 6  is a schematic elevational view of a fourth embodiment of a portion of a wastewater treatment system in accordance with the present application. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    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. 
         [0028]      FIGS. 1 through 6  illustrate the invention. The present invention is a system (method and apparatus) for backflushing materials from the upstream side of a bar screen in a primary waste water treatment system. 
         [0029]      FIG. 1  shows a rectangular primary settling tank disclosed in the parent application. Primary settling tank  10  receives waste water from a waste water collection system through an influent pipe  12  controlled by a control valve (not shown). 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 rack  14  is placed in the primary settling tank  10  between the outer wall  16  and the interior  18  of the primary settling tank  10 . Bar rack  14  keeps large solids and floatables from entering the waste water treatment system. 
         [0030]    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 diameter of influent pipe  12  such that the velocity of the incoming flow decreases dramatically upon entrance of the water into primary settling tank  10 . Preferably, the incoming velocity is further reduced by splitting the flow so there are two influent pipes  12  at opposite ends of tank  10  (second influent pipe  12  is not visible in cutaway  FIG. 1 ). 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 , over a fixed weir  15 , and into the interior  31  of tank  10 . Large floatables (not shown), such as plastic solids, are prevented from passing through the bar screen  14 . Sludge collects by gravity 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 that passes through bar screen  14 . 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 (not shown) is in fluid communication with the scum and floatables trough  40 . 
         [0031]    Primary settling tank  10  is shown with a screen box  62  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. 
         [0032]    A As disclosed fully in the parent application, the primary settling tank may be circular, and the backflushing system of the present invention may be readily adapted thereto by one of ordinary skill in the art. 
         [0033]    In operation, the prior art primary treatment system performs primary separation of large floatables, grease, and scum from smaller floatables, grease and scum via bar screen  14 . The smaller floatables, grease, and scum that pass through bar screen  14  are separated from the liquid influent in two ways: a) by overflowing into trough  40  and b) via screen box  62  and baffle plate  68 . Screen box  62  provides a second and fine screening, allowing finely-screen liquid influent to pass through a central drain  69  and attached hose to an additional drain for secondary treatment in known fashion (hose and drain not shown). Flow into tank  10  preferably is intermittent, allowing gravitational separation of grit and heavy particles into grit hopper  30  and fostering a relatively clear supernatant layer at the top of the liquid. Further, because inflow velocities over weir  15  are low and the tank is replenished from relatively near the bottom, the mass of liquid in the tank experiences a general upwelling with small horizontal flow components near screen box  62 . 
         [0034]    Referring now to  FIGS. 1 and 2 , in a first embodiment  100  of a system in accordance with the present application for backflushing a bar screen, an exemplary primary settling tank  110  is substantially the same as tank  10  in  FIG. 1 , and comprises first and second bar screens  114  topped by respective first and second scum and floatables troughs  140 . (As used herein, the terms “backflush” and “backwash” are interchangeable.) Influent flows  104  through first and second influent feed pipes  112  are controlled by first and second control valves  113  and programmable controller  900 , optionally a dedicated computer. Each of influent feed pipes  112  is provided with a sidearm drain pipe  117  extending to a drain  119 , and includes a drain valve  121  and optionally a flow meter  123  and optional sensor  125  connected to programmable controller  900 . Further, an optional sensor  127  connected to programmable controller  900  may be positioned within tank  110  for immersion in a reservoir of screened influent  133 . 
         [0035]    System  100  may be operated manually without the assistance of programmable controller  900 , but the preferred embodiment includes programmable controller  900  to allow various modes of automation. 
         [0036]    In operation, influent  104  flows through valves  113  and feed pipes  112  into first and second chambers  129  upstream of bar screens  114 . A first portion of influent  104  passes through bar screens  114 , over weirs  115 , and into the interior  131  of tank  110 , defining primary screened influent  133 . A second portion  135 , typically comprising grease, scum, solids, fibrous materials, and floatables, is retained against the upstream side of bar screens  114 . At equilibrium upward flow, the level  137  of screened influent  133  reaches scum and floatables troughs  140  where grease, scum, and floatables are removed as described in the parent application. 
         [0037]    Over time, significant quantities of second portion  135  accumulate and must be removed from the upstream sides of bar screens  114 . 
         [0038]    When tank  110  is near full, screened influent  133  has been in tank  110  long enough that suspended materials have settled from screened influent  133 , as described above, leaving a relatively clear supernatant liquid  139  near the top of tank  110 . 
         [0039]    In a first step, programmable controller  900  closes inlet valves  113  and opens drain valves  121 , allowing influent in chambers  129  to flow under gravity to drains  119 . The concomitant drop in hydrostatic pressure against the upstream sides of bar racks  114  causes liquid  139  to flow outward through bar racks  114  into chambers  129  and then to drains  119 . A sufficiently vigorous backflow flushes accumulated grease, scum, solids, fibrous materials, and floatables  135  from the bar racks and down drains  119 . When bar racks  114  have been suitably cleaned, drain valves  121  are closed and inlet valves  113  are re-opened. 
         [0040]    In one embodiment, scum and floatables may be removed from influent  133  and  139  manually or via troughs  140  prior to starting a bar rack cleaning cycle. 
         [0041]    In another embodiment, the bar rack cleaning, cycle is performed after a predetermined number of cycles of filling and emptying the tank in standard influent treatment cycles. 
         [0042]    In another embodiment, inlet valves  113  are closed and drain valves  121  opened in response to a signal from sensor  127  to programmable controller  900 , which signal may indicate that the upper portion  139  of screened influent  133  has a BOD level above an acceptable threshold as measured by a UV absorption sensor in known fashion. 
         [0043]    In another embodiment, the bar rack cleaning cycle is performed after sensor  127  indicates that upper portion  139  has a turbidity level below an acceptable threshold. In such instance, sensor  127  typically comprises a turbidimeter or particle counter. 
         [0044]    Closing of drain valves  121  may be performed after a predetermined amount of fluid has been backwashed through the bar racks as observed and manually activated by an operator. 
         [0045]    In one embodiment, the amount of fluid backwashed through the bar racks is measured via flow meters  123 . 
         [0046]    In another embodiment, the amount of fluid backwashed through the bar racks is governed by mode signals of UV absorption, turbidity, or particles from sensors  125  to programmable controller  900 . 
         [0047]    In another embodiment, cessation of backflushing may be governed by measured increase in BOD or turbidity in tank  110  by sensor  127 . 
         [0048]    The screened influent  139  that is passed through drains  119 , along with all the backflushed materials formerly retained by bar racks  114 , must be treated, typically in one or a combination of ways (not shown). In one embodiment, the solids and fluid in the backwash are separated using a dewatering press or a hydrocyclone. The solids are sent to a landfill or otherwise disposed of. The fluid may be returned to the primary settling tank  10  for treatment, or further treated via secondary treatment processes such as a dewatering press or an anaerobic digester. 
         [0049]    Referring now to  FIG. 3 , in a second embodiment  200  of a system in accordance with the present invention for backflushing a bar screen, an exemplary primary settling tank  210  is substantially the same as tank  110  in  FIG. 2  except as noted below. 
         [0050]    The influent fill pipe and ports  112 , and valves  113 , are positioned essentially as shown in  FIG. 2  at or near the bottom of tank  210 . However, separate drain pipe and ports  217  and valves  221  are provided, preferably at about the elevation at which bar racks  114  come into contact with the walls of weirs  115 . This is the region associated with highest fluid velocities passing through the bar rack during filling and during backwash. The higher velocities make this region of the bar racks more prone to trapping larger materials against the bars. 
         [0051]    Referring now to  FIGS. 4   a  (elevational view) and  4   b  (plan view), in a currently preferred third embodiment  300  of a system in accordance with the present invention for backflushing a bar screen, an exemplary primary settling tank  310  is substantially the same as tank  210  in  FIG. 3  except as noted below. 
         [0052]    An internal sluice  320  is mounted to inner wall  316  of tank  310  and includes an inner sluice lip  322  that defines a weir for the backflush flow  324  from bar rack  114 . Internal sluice lip  322  modulates any variations in the amount of backflush flow  324  over the width of bar rack  114 , creating a single flow  326  to a single outlet port  328 , permitting the outlet port to be located asymmetrically at the end of the sluice as shown. 
         [0053]    Referring to  FIG. 5   a , without a sluice, flows  324  being directed to a single outlet port  428  may not flow uniformly from all parts of bar rack  114  and may tend to stagnate in the ends  430  of chamber  429 . 
         [0054]    Referring to  FIG. 5   b , such stagnation may be prevented to some degree by providing a manifold of a plurality of outlet ports  528 . 
         [0055]    Referring to  FIG. 5   c , the ultimate manifold is simply an external sluice  620  disposed on the outer wall of tank  310  and connected through the tank wall with chamber  629  via a sluice gate  622 . 
         [0056]    Referring now to  FIG. 6 , in a fourth embodiment  400  of a system in accordance with the present invention for backflushing a bar screen, an exemplary primary settling tank  410  is substantially the same as tank  210  in  FIG. 3  except as noted below. 
         [0057]    The influent fill pipe and ports  112 , and valves  113 , are positioned essentially as shown in  FIG. 4  at or near the bottom of tank  410 . However, separate drain pipes and ports  417 ,  418 ,  419  and valves  421 ,  422 ,  423  are provided. The elevation of the drain pipes and ports  417 ,  418 ,  419  are arranged to provide control of fluid velocities at the corresponding elevation of the bar rack during the backwash process. Selectively partial or complete opening of valves  417 ,  418 ,  419  provides the ability to selectively control the relative fluid velocities at each corresponding elevation during the backwash process. 
         [0058]    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.