Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F3/00—Biological treatment of water, waste water, or sewage
  • C02F3/02—Aerobic processes
  • C02F3/12—Activated sludge processes
  • C02F3/1236—Particular type of activated sludge installations
  • C02F3/1257—Oxidation ditches
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/0018—Separation of suspended solid particles from liquids by sedimentation provided with a pump mounted in or on a settling tank
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/0024—Inlets or outlets provided with regulating devices, e.g. valves, flaps
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/0039—Settling tanks provided with contact surfaces, e.g. baffles, particles
  • B01D21/0042—Baffles or guide plates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/02—Settling tanks with single outlets for the separated liquid
  • B01D21/04—Settling tanks with single outlets for the separated liquid with moving scrapers
  • B01D21/06—Settling tanks with single outlets for the separated liquid with moving scrapers with rotating scrapers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/24—Feed or discharge mechanisms for settling tanks
  • B01D21/2405—Feed mechanisms for settling tanks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/24—Feed or discharge mechanisms for settling tanks
  • B01D21/2427—The feed or discharge opening located at a distant position from the side walls
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/24—Feed or discharge mechanisms for settling tanks
  • B01D21/2444—Discharge mechanisms for the classified liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/24—Feed or discharge mechanisms for settling tanks
  • B01D21/245—Discharge mechanisms for the sediments
  • B01D21/2461—Positive-displacement pumps; Screw feeders; Trough conveyors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/30—Control equipment
  • B01D21/32—Density control of clear liquid or sediment, e.g. optical control ; Control of physical properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D21/00—Separation of suspended solid particles from liquids by sedimentation
  • B01D21/30—Control equipment
  • B01D21/34—Controlling the feed distribution; Controlling the liquid level ; Control of process parameters
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F3/00—Biological treatment of water, waste water, or sewage
  • C02F3/006—Regulation methods for biological treatment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/11—Turbidity
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/42—Liquid level
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2209/00—Controlling or monitoring parameters in water treatment
  • C02F2209/44—Time
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W10/00—Technologies for wastewater treatment
  • Y02W10/10—Biological treatment of water, waste water, or sewage
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S210/00—Liquid purification or separation
  • Y10S210/918—Miscellaneous specific techniques
  • Y10S210/926—Miscellaneous specific techniques using oxidation ditch, e.g. carousel

Definitions

• This invention relates generally to aerobic wastewater treatment systems and methods and, more particularly, to aerobic wastewater treatment systems and methods which utilize a moving stream of mixed liquor in a retention basin, such as an oxidation ditch.
• a retention basin such as an oxidation ditch
• a continuous channel contains the flowing mixed liquor, which is aerated as it flows around the channel to provide oxygen for microorganisms which decompose the waste in the channel.
• Clarifiers are used to clarify the mixed liquor by settling the suspended solids and removing clarified wastewater from the system.
• Intrachannel clarifiers may be employed for this purpose. Examples of intrachannel clarifiers may be seen in Harold J. Beard's U.S. Patent Nos. 4,362,625; 4,383,922; and 4,457,844. Maintenance of the proper biological balance in the basin is essential for proper operation of the system.
• sludge age For a given concentration of waste entering the basin and a given concentration of waste within the basin, the sludge age can be calculated. Thus, the number of pounds of waste within the basin divided by the number of pounds of waste per day entering the basin will yield a sludge age in days. It has been found empirically that a sludge age of 23- 25 days will yield excellent biological activity within the basin.
• a mixed liquor wasting system comprising a thickener tank, having a sidewall and a bottom; a waste line having a first end and a second end, the first end fluidly connected to the retention basin, and the second end fluidly connected to the thickener tank; a first flow control device, such as a pump, for continuously removing a portion of the mixed liquor from the basin at a desired constant flow rate through the waste line, positioned in the waste line; a sludge removal line having a first end and a second end, the first end fluidly connected to the bottom of the thickener tank, and the second end fluidly connected to a sludge disposal system; a second flow control device, such as a pump, for removing a concentrated portion of the mixed liquor from the thickener tank, positioned in the sludge removal line; and a return line having a first end and a second end,
• a method for wasting the mixed liquor comprising the step of continuously removing a portion of the mixed liquor from the basin at a desired constant flow rate.
• DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic depiction of an embodiment of the system of the invention.
• Figure 2 is a schematic depiction of another embodiment of the system of the invention.
• Figure 3 is a perspective view of an embodiment of the thickener tank of the invention.
• Figure 4 is a curve showing the relationship of solids concentration versus retention time for mixed liquor in the thickener tank having a sludge volume index of 67-100.
• Figure 5 is a curve showing the relationship of solids concentration versus retention time for mixed liquor in the thickener tank having a sludge volume index of 130-155.
• Figure 6 is a curve showing the relationship of retention basin sludge age versus pumping rate to the thickener tank.
• a mixed liquor wasting system 1 is attached to an extended aeration wastewater treatment system 16.
• Treatment system 16 includes a retention basin 2, shown in the form of an oxidation ditch 3.
• Oxidation ditch 3 is formed by a continuous outer wall 7 and a partition wall 8.
• Untreated wastewater enters the basin 2 through wastewater inlet 9 and is retained in the basin 2, where it is aerated by aerators 5.
• Collected wastewater in ditch 3 forms a mixed liquor 4, which is retained and circulated in the ditch 3 for a desired period of time, allowing microorganisms to decompose the waste in the water.
• Many different types of extended aeration systems 16 are used in the art. Most employ some sort of retention basin 2, to which the invention 1 may be attached.
• the invention 1 will be discussed herein in conjunction with systems 16 utilizing oxidation ditches 3.
• decomposed waste in the form of suspended solids must be removed through settlement, filtration or both.
• Separation between sludge (settled suspended solids) and clarified wastewater can be accomplished inside of oxidation ditch 3 through the use of an intrachannel clarifier 6, as shown in Figure 1.
• Intrachannel clarifier outlet line 60 removes clarified wastewater from the ditch 3, and sludge is returned to the ditch 3.
• An external clarifier 57 shown in Figure 2, may also be employed to accomplish the same task.
• Mixed liquor 4 flows into external clarifier 57 from ditch 3 through external clarifier inlet line 58.
• one major problem associated with extended aeration wastewater treatment systems 16 is the maintenance of proper biological conditions. It is accepted that maintaining a constant sludge age is effective in maintaining proper basin biology. The inventor has discovered that the continuous removal of a portion of the mixed liquor 4 from the basin 2, through waste line 10, at a constant flow rate will result in a constant sludge age within the basin 2. This is true on an average basis regardless of the concentration (BOD) of the incoming waste or the flow rate of the incoming waste.
• BOD concentration
• waste line 10 While maintaining a constant flow rate through waste line 10 maintains a constant sludge age, stabilizing basin conditions, something must be done with the suspended solids being removed from the basin 2 through waste line 10. Because of the large water content in the mixed liquor, it is desirable to thicken the sludge prior to further processing in order to reduce handling costs and disposal volumes. In order to accomplish this goal a thickener tank 13 was designed to concentrate suspended solids for disposal while returning clarified wastewater to the basin 2 or to a clarifier outlet line 59,60. As discussed above, waste line 10 has a first end 11 fluidly connected to basin 2 and a second end fluidly connected to thickener tank 13.
• a first flow control means 18 for continuously removing a portion of mixed liquor 4 from basin 2 at a desired constant flow rate, fluidly connected to basin 2.
• first flow control means 18 comprises a first pump 19, although gravity flow control could be utilized where feasible.
• a gravity flow device could be a flow control weir (not shown) connected to return line 28, thus establishing a substantially constant flow through waste line 10 and thickener tank 13.
• First pump 19 may be set at a desired constant flow rate in order to accomplish the method of the invention.
• thickener tank 13 is has a sidewall 14 (circular in the embodiment shown) and a bottom 15.
• bottom 15 has a sloped portion 17 (preferably at an angle no less than thirty-five degrees with horizontal) , sloping inward from sidewall 14 to encourage sludge concentration at bottom 15.
• a sludge removal line 20 has a first end 21 fluidly connected to bottom 15 and a second end 22 fluidly connected to a sludge disposal system 23.
• Sludge disposal system 23 can include such conventional components as a digester 24 having aerators 25 located therein.
• a second flow control means 26 is fluidly connected to thickener tank 13.
• second flow control means 26 includes a second pump 27, positioned in sludge removal line 20. Pump 27 may operate intermittently or continuously at a relatively slow rate to remove accumulated sludge from tank 13.
• a bottom valve 61 is provided in sludge removal line 20 for additional control. If gravity drain to sludge disposal system 23 is possible, means 26 may comprise only bottom valve 61, which may be intermittently or continuously opened (either manually or electronically) to remove accumulated sludge.
• a support structure 62 supporting a mixer 40, including a motor 41, a shaft 42 rotatably attached to motor 41, and a blade 43 fixedly attached to shaft 42 just above bottom 15.
• blade 43 extends to either side of shaft 42 as shown, and is oriented parallel to bottom 15.
• a resilient scraper extension 44 preferably made of pliable material, such as rubber, is fixedly attached to blade 43 and extends downward so as to lightly touch bottom 15 so as to eliminate any dead zones beneath blade 43. It has been found that, by operating mixer 40 so as to turn blade 43 at a tip speed of twenty feet per minute (three revolutions per minute for a 1.208 foot blade radius), gas build-up from denitrification is released preventing sludge floatation from denitrification. It is believed that the tip speed for blade 43 should be designed to be twenty to twenty-five feet per minute so as to achieve proper mixing and yet create minimum turbulence.
• baffle 46 is provided just above the entry point of waste line 10 and below collector pipes 51. Although any arrangement which dampens turbulence will suffice, the X-shaped arrangement of baffles 46 shown in Figure 3 appears to be effective.
• Diffuser 47 includes a top plate 48 and bottom plate 31.
• Baffles 50 are contained between and around the periphery of plates 48,31 and serve to dampen inlet flow and allow sludge to begin to settle immediately upon entry into tank 13.
• Baffles 50 and holes 49 in bottom plate 31 allow mixed liquor to flow both horizontally outward from between plates 48,31 and downward through holes 49 in bottom plate 31.
• Diffuser 47 is supported by support angle 67, connected to waste line 10 and recycle line 39.
• recycle line 39 When recycle line 39 is employed, it should enter tank 13 through diffuser 47 opposite waste line 10, as shown in Figure 3, allowing the opposing flows to dampen each other. If recycle line 39 is not employed an additional plate (not shown) should be added to diffuser 47 in place of the termination of recycle line 39 to dampen flow from waste line 10.
• Tank 13 should therefore be sized such that the height of concentrated portion 55 does not approach collector pipes 51 during periods of high solids concentration.
• Figures 4 and 5 depict the relationship of retention time in tank 13 versus the concentration of solids at the bottom 15. As shown, the concentration reaches a substantially constant value as the retention time in tank 13 increases, for a given sludge volume index (SVI) . As shown in Figure 4, for a mixed liquor 4 having an SVI of 67- 100, an optimum concentration is safely reached at a retention time greater than 100 minutes. As shown in Figure 5, for a mixed liquor 4 having an SVI of 130-155, an optimum concentration is safely reached at a retention time greater than 225 minutes. The volume of concentrated portion 55 in cubic feet divided by the pumping rate of second pump 27 in cubic feet per minute will give a value for sludge retention time in minutes.
• SVI sludge volume index
• a means 53 may be provided for maintaining a desired level of concentrated portion 55 within tank 13.
• Means 53 may take any form known in the art, such as a level controller 54 having sensors 64,65 which sense when the level of concentrated portion 55 exceeds or falls below a desired level. For example, when the level of concentrated portion 55 rises above upper sensor 64, controller 54 (such as a BTG Model SMS-3000 Solids Monitoring System) will activate second pump 27. When the level of concentrated portion 55 falls below lower sensor 65, controller 54 will deactivate second pump 27.
• flow through return line 28 may be diverted through a clarified fluid line 32, utilizing a flow selection means 33, such as return valve 34 and clarified fluid valve 35.
• Flow selection means 33 may be controlled by a means 36 for determining clarity of fluid and a control means 37, such as a combination turbidity meter and automatic valve control 38, which will select a flow path dependent upon the clarity of fluid in return line 28.
• sludge removal line 20 may be connected to a digester 24.
• the digester 24 may be connected to a decant tank 66.
• decant tank 66 In decant tank 66, sludge is settled for removal, and clarified fluid is decanted and sent through recycle line 39 back to thickener tank 13 for further thickening, thus further minimizing the amount of water in digester 24.
• the system 1 is extremely versatile. When used with an intrachannel clarifier 6 (shown in Figure 1) , waste line 10 may be connected to intrachannel clarifier 6 so as to remove more concentrated mixed liquor 45 from within the clarifier 6. However, the system 1 may just as easily be used as shown in Figure 2, removing mixed liquor 4 directly from the basin 2.
• the system 1 and method described herein allows treatment plants to maintain a constant sludge age, stabilizing plant biology, while decreasing the water content of sludge removed from the plant.
• Other embodiments of the invention will occur to those skilled in the art, and are intended to be included within the scope and spirit of the following claims.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Life Sciences & Earth Sciences (AREA)
• Microbiology (AREA)
• Biodiversity & Conservation Biology (AREA)
• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Molecular Biology (AREA)
• Health & Medical Sciences (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Treatment Of Sludge (AREA)
• Activated Sludge Processes (AREA)

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Publications (2)

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• 1993
  • 1993-09-16 AU AU52906/93A patent/AU687759B2/en not_active Ceased
  • 1993-09-16 EP EP93923113A patent/EP0719239A4/de not_active Withdrawn

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