CA1155976A - Apparatus for anoxic-aerobic activated sludge process and treatment of waste waters - Google Patents
Apparatus for anoxic-aerobic activated sludge process and treatment of waste watersInfo
- Publication number
- CA1155976A CA1155976A CA000405406A CA405406A CA1155976A CA 1155976 A CA1155976 A CA 1155976A CA 000405406 A CA000405406 A CA 000405406A CA 405406 A CA405406 A CA 405406A CA 1155976 A CA1155976 A CA 1155976A
- Authority
- CA
- Canada
- Prior art keywords
- zone
- zones
- anoxic
- sludge
- reaction tank
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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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
-
- 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
- C02F3/30—Aerobic and anaerobic processes
- C02F3/308—Biological phosphorus removal
-
- 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
Abstract
A B S T R A C T.
A simplified high rate mixed-fluidized bed Anoxic-Aerobic Activated Sludge System is capable of simultaneous biological removal of carbonaceous, nitrogenous and phosphorous compounds and suspended solids from municipal and industrial waste waters without the use of chemicals and without the use of the seconda-ry clarifiers. The process apparatus is simple, does not require compressors, mixers, piping, pumps, sludge scrapers and clarifiers and provides optimum Anoxic-Aerobic Activated sludge Process con-ditions with reliable maintenance free operation at reduced ca-pital and operational costs. The apparatus meets all process re-quirements at reduced consumption of energy in mixing, aeration and recirculation of the reactor mixed liquor between the anoxic and aerobic stages in a single reaction tank and is suitable for use in designing the standardized waste water treatment packaged plants as well as in designing the large municipal and industrial waste water treatment facilities.
" Apparatus for Anoxic-Aerobic Activated Sludge Process and Treatment of Waste Waters."
A simplified high rate mixed-fluidized bed Anoxic-Aerobic Activated Sludge System is capable of simultaneous biological removal of carbonaceous, nitrogenous and phosphorous compounds and suspended solids from municipal and industrial waste waters without the use of chemicals and without the use of the seconda-ry clarifiers. The process apparatus is simple, does not require compressors, mixers, piping, pumps, sludge scrapers and clarifiers and provides optimum Anoxic-Aerobic Activated sludge Process con-ditions with reliable maintenance free operation at reduced ca-pital and operational costs. The apparatus meets all process re-quirements at reduced consumption of energy in mixing, aeration and recirculation of the reactor mixed liquor between the anoxic and aerobic stages in a single reaction tank and is suitable for use in designing the standardized waste water treatment packaged plants as well as in designing the large municipal and industrial waste water treatment facilities.
" Apparatus for Anoxic-Aerobic Activated Sludge Process and Treatment of Waste Waters."
Description
~ ~5976 SPECIFICATION
FIELD OF INVENTION
This invention relates to a simplified high rate mixed-fluidized bed Anoxic-Aerobic Activated Sludge Treatment System capable of simultaneous biological removal of carbonaceous, ni-trogenous and phosphorous compounds and suspended solids from municipal and industrial waste waters without the use of chemicals and without the use of the traditional secondary clarifiers. It has -for its object a provision of a simplified process apparakus not requiring compressors, mixers, piping, pumps, sludge scrapers and clarifiers and providing optimum Anoxic-Aerobic Activated Sludge Process conditions with reliable maintenance free operation at reduced capital and operating costs. The apparatus of this invention meets all process requirements along with reduced con-sumption of energy in mixing, aeration and recirculation of the reactor mixed liquor between the Anoxic and Aerobic stages in a single reaction tank and is suitable for use in designing the standardized waste water treatment packaged plants as well as in designing the large municipal and industrial waste water treatment facilities.
BACKGROUND TO T~E INVENTION
In a review of the most advanced technology for kreatment of waste waters, Barth, E.H. et al. (International Nutrient Control Technology for Municipal Effluents, Jour. WPCF. V.53, No.12, 1981) outlined the various process flowsheets and process parameters currently used in removing the carbonaceous, nitrogenous and phosphorous compounds from municipal waste waters.
D-~
~ ~L559~
It was reported there that removal of carbonaceous and nit-rogenous compounds and phosphorus has been achieved in large scale commercial plants using a single Activated sludge system comprising an anoxic stage r an aerobic stage and a clarifier in which the sludge age is maintained by withdrawing the excess sludge from the clarifier. Further, i-t was shown by Beer, C.
et al. (Activated Sludge Systems Using Nitrate Respiration -Design Considerations, Jour. WPCF., 5ept. pg. 2120, 1978) that the denitrification rate when using the waste water carbonaceous material as energy source in nitrate respiration is considerably higher than that achieved with endogenous nitrate respiration and that the Activated Sludge System in which an Anoxic stage is followed by an Aerobic stage produces significantly less excess sludge, uses significantly less oxygen and removes sig-nificantly less alkalinity from the processed waste water thanthe Activated Sludge System in which an Aerobic stage is followed by an Anoxic stage.
~ince in an Anoxic-~erobic Activated Sludge Process de-composition of the organic nitrogen and the nitrification of the ~mmonia nitrogen to nitrate takes place in the second -Aerobic stage while denitrification of the nitrate nitrogen to nitrogen gas takes place in the first - Anoxic stage, to achie~e efficient removal of nitrogen the Anoxic - Aero~ic Activated Sludge Process requires an extremely high recircu-lation of the reactor mixed liquor between the two reaction stages. Depending on the concentration of total nitrogen in the incoming waste water and on the required low concentration of the total nitrogen in the effluent, the desired mixed liquor to feed recirculation ratio usually varies in the range j,;~
.... ~
1 ~59716 between 10 to 50. Such high recirculation rates are impossible to achieve in current waste water treatment facili-ties in which recirculation of the mixed liquor and sludge between the two reaction stages is maintained by mechanical pumps. As a result the concentration of nitrogenous compounds in the effluents from current Anoxic-Aerobic Activated Sludge Systems is undesir-ably high.
Further it is known that in an Activated sludge Process the performance of the biochemical reactor, i.e. the reactor volumetric loading rate depends on the concentration of the contaminant and on the concentration of mixed liquor volatile suspended solids (MLVSS) in the reactor. Because of the re-circulation of the mixed liquor between the two reaction stages in the Anoxic-Aerobic Activated Sludge Process the concentration of the contaminant in the two reaction stages is usually very low and because of use of secondary clariiers the concentration of MLVSS in the two reaction stages is limited and usually less than 5,000 mg/lit. As a result the volumetric loading rates in all existing Anoxic ~erobic Activated Sludge Systems designed for removal of nutrients are very low and usually less than 0.4 kg/m3 day~
It has been also demonstrated in large commercial plants that in the Anoxic-~erobic Activated Sludge Pro~ess the removal of phosphorus is being achieved simultaneously with removal of nitrogen due to a biological stress imposed on the mixed micro-bial population while in the Anoxic reaction stage. Since phosphorus is removed from the processed waste water by assim-ilation of phosphorus into the cellular material of the micro-~ 1.55976 organisms the phosphorus removal ef~iciency increases withincreased BOD loadings and with reduced sludge age. The per-missible sludge age howe~er is effected by the growth rate of the nitrifiers and by the required removal of the ammonia nitrogen. Depen~ing on the operating temperature the minimum sludge age to achieve efficient nitrification may vary in the ranye from 4 to 10 days and usually is maintained at 7 - 8 days if simultaneous removal of nitrogen is to be achieved efficiently.
With view to the above discussed Anoxic-Aerobic Activated Sludge Process variables it then follows that to increase the overall nitrogen removal efficiency it is necessary to increase the mixed liquor recirculation rate, to increase the ~erformance it is necessary to increase the concentration of MLVSS in the two reaction stages and to increase the removal of phosphorus it is necessary to operate the system at the minimum permissihle sludge age.
The Anoxic-Aerobic Activated Sludge Process of my invention covered by Can. Pat. No. 1 114 528, and 1 116 323 (U.S.Pat.App.
No. 181 r 136 and 268,725) meets all the above discussed process requirements. Contrary to all current art systems it does not require a separate clarification stage and as schematically shown in Fig. 1 it briefly consists of a) feeding the waste water into the Anoxic stage, recycling the mixed liquor by a new type mixer-aerator from the Aerobic stage into the Anoxic stage at the mixed liquor to feed recir-culation ratio greater than 20, mixing the waste water with the recycled mixed liquor in the Anoxic stage and contacting the waste water with MLVSS in the Anoxic stage in the absence ...
1~L55976 of dissolved oxygen therein and at concentrations of l~LVSS
greater than 15,000 mg/lit. In the Anoxic stage the soluble BOD5 is partially used up as energy source in nitrate respir-ation and in new cell synthesis, NO3--N is gasified and released due to substrate nitrate respiration by the mixed microbial population and NH3-N and PO4 are partially assimilated in new cell synthesis.
b) flowing -the denitrified mixed liquor with the partially treated waste water from the ~noxic stage into the Aerobic stage, the Aerobic stage comprising a downflow Aeration zone and an upflow fluidized bed zone, mixing the anoxic liquor with the sludge withdrawn from the fluidized bed zone and aerating the mixture of liquor and sludge by air while continuously recir-culating the mixture of liquor and sludge in a loop downwardly through the aeration zone and upwardly through the fluidized bed zone. In the Aerobic stage the remaining BOD5 and the TKN
are biooxidized by the activated sludge along with new cell synthesis~ endogenous respiration, assimilation of nitrogen and phosphorus into new cells and nitrification of the ammonia nitrogen to nitrate nitrogen.
In addition the recirculated sludge as it moves upward through the fluidized bed zone flocculates and forms a fluidized bed which efficiently filters out all suspended solids present in the processed waste watert leaving a clear effluent collected above the fluidized bed zone. To maintain the desired sludge age a portion of the recirculated sludge is withdrawn from the -fluidized bed zone.
The major process differences between the described process i ~1559~B
of my invention and the current art can be su~narized as foll~ws:
a) the mixed liquor to feed recirculation ratio in the described process is greater than 20/ while in the current art systems it is only 2 to 4, b) the concentration of the ~VSS in the described process is greater than 15l000 mg/lit, while in the current art systems it is less than 5,000 mg/lit, c) the Aerobic stage in the described process comprises a downflow aeration zone and an upflow fluidized bed zone with the reactor liquor and sludge continuously recirculating in a closed loop through the two zones, while the current art syste~s utilize a completely mixed aeration zone, d) in the described process suspencled solids are removed from the processed waste water by filtration in the fluidized bed within the Aerobic stage, while in the current art systems suspended solids are removed from the treated waste water by gravity settling in an additional clarifying stage with the settled sludge being recirculated from the clarifying stage into the Anoxic stage.
The described Anoxic-~erobic Acti~ated Sludge Process can be used either a~ to achieve complete oxidation of volatile suspended solids associated with less efficient removal of phosphorus, or b~ for efficient removal of BODs, suspended solids and nutrients associated with increased production of excess sludge. Complete oxidation is usuall~ desirable for "on site" treatment applications where maintenance and excess sludge are to be minimlzed and where water flow rates are usually small, while efficient removal of phosphorus with ~.~"
~1559 76 maximized production of excess sludge may be desirable for large waste water flow rates, when the excess sludge may be recovered for reuse either because of its energy content or because of the nutrient values of the excess sludge vola-tile suspended solids. In both situations the Anoxic-Aerobic Activated Sludge Process of my invention when compared with current art systems offers considerable savings in capital and operating costs due to reduction of the required reaction volume, elimination of the secondary clarifier, elimination of piping and pumps, elimination of compressors, mixers and aerators, reduction in consumption of energy used in aerationl mixing and recirculation of the mixed liquor, reduced maintenance and supervision and elimination of chemicals such as methanol and lime required by current art systems in nitrification - denitrification and/or in removal of phosphorus~ For comparison of the Anoxic-Aerobic Activated Sludge Process of my invent:ion with the Completely ~ixed Nitifyin~ Activated Sludge Process the major process char-ac~eristics of the two processes are presented in Table 1.
Durin~ ongoing investigation of ~he above described Anoxic-Aerobic Activated Sludge Process hydraulics I have found that the performance of the process apparatus of my invention covered by the above listed Canadian and U.S. Pat. can be further improve~
by improving the efficiency of mixing of the reactor liquor and sludge solids -MLVSS in the Anoxic stage.
I have also found that such improved mixing can be achie~ed without increasing the consumption of energy and along with simp-lification of the reaction tank r particularly when applied in large waste water treatment plants when capacity of the plant ~559~6 may be increased by joining together and in parallel a number of modular reaction units.
It is therefore the object of the present invention to provide an improved apparatus for use with the above described Anoxic-Aerobic Activated Sludge Process of my invention.
More specifically it is the object of the present invention to provide an apparatus with improved process hydraulics in mix-ing of the reactor liquor with sludge solids in the Anoxic stageand in recirculation of the reactor liquor and sludge solids be-tween the Anoxic and Aerobic stages.
It is another object of this invention to provide a simpli-fied reacticn tank that would be more suitable for use as a modu-lar reaction unit in designing the large waste water treatment plants.
It is another object of this invention to provide an appara-tus with improved hydraulies of the upwardly moving fluidized bedof the floceulated sludge and in withdrawal of the floccula~ed sludge from the fluidized bed zone.
It is also the object of this invention to provide an appara-tus with improv~d energy utilization efficiency in mixin~, recir-cuIating and aerating the reactor mixed liquor and the flocculated sludge.
Other objects and features of the present invention will be understood from the following deseription of the apparatus and claims.
_ 9 _ ~551~76 SUMMARY OF TH~: INVENTIO~
The present invention provldes an improved apparatus for use with the Anoxic-Aerobic Activated Sludge Process of my in-vention covered by the above Canadian Patents and U.S. Patent Applications.
More specifically the improved apparatus provides for more efficient process hydraulics involving mi~ing of -the reactor liquor with sludge solids in the Anoxic stage, more efficient recirculation of the reactor liquor and sludge solids between the two reaction stages and more efficient aeration of the re actor liquor and sludge solids without increased consumption of energ~. It also provides improved recirculation of sludge solids through the aeration zone and fluidized bed zone, provides a more simple reaction tank more suitable for use as a modular unit in large waste water treatment plants.
BRIEF DESCRIPTION QF THE DRAWINGS
The forgoing and other objects and advanta~es of the present invention will becGme apparent from the followin~ detail descrip-tion which proceeds with reference to the accompanying drawings where in Fig. 1 is a simplified schematic diagram of th~ Anoxic~
Aerobic Process of my invention covered by the abo~e listed Cana dian Patents and U.S. Pat. ~pplications which is being used in treatment of waste waters with the apparatus of the present in-vention.
Fig. 2 is a ~ertical view through one prefered embodiment i597~
of the apparatus of this invention.
Fig. 3 is a plan view of the prefered embodiment of the apparatus shown in Fig. 2.
Fig~ 4 is a schematic representation of a large treatment system comprising a number of modular units of the apparatus shown in Fig. 2 and Fig. 3 joined into a single reaction tank of the present invention.
DESCRIPT~ON OF THE PREFERED E~BODIMENTS
Before explaining the present invention in detail it is -to be understood that the invention is not limited in its appli-cation to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of bein~ practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the pur-pose of description and not of limltation.
Reference is made to Fig. 2 and Fig. 3 for an explanation of one prefered modification of the apparatus of the present ; in~ention. ~s is there shown the apparatus comprises a reaction tank 10 equipped with two first solid wall partitions 1, la, two second solid wall partitions 2,2a, inverted funnels 3, 3a, two 25 endless belts 5, 5a, an inlet 7, two outlets 8, 8a equipped with weirs 9, 9a and one excess sludge withdrawal pipe 18.
The two endless belts 5, 5a each comprise a pair of endless chains 5.1 joined wi-th a plurality of horizontal pipes 5O2 of a specific diameter and length dictated by the treatment capacity ~ :~S~7~
of the reaction tank 10. The horizontal pipes 5.2 ha~e their side ends closed and are permanen~ly attached to t~e endless chains 5.1 to prevent rotation and change in position of the plurality of openings 5.3 located on the top and on the bottom sides of pipes 5.2. The two endless belts 5, 5a are positioned within the reaction tank 10 with their top portion extending above the liquid level of the reactor liquor held in reaction tank 10 and are supported at the top by a pair of rotating sprockets 5.4, 5.4a mounted on a shaft 5.5, 5.5a rotated b~ a motor. The hottom portion of endless belts 5, 5a extend near the bottom of the reaction tank 10 where they are kept in posi-tion by a pair of leading sprockets 5.6, 5.6a. The two endless belts may rotate at same or at different speeds, which speed may vary in the range from 5 to 100 c~/sec, and preferably is maintained in the range from 15 to 50 cm/sec.
The two solid wall partitions 1, la are positioned inside the endless ~elts 5, 5a and are attached to the two side walls of the reaction tank 10 thus separating the reaction tank into 20 a single anoxic zone 11 and two aerobic zones 12, 12a located on two opposite sides of the anoxic zone 11 and/or at the two end sides of the reaction tank 10. The anoxic zone 11 is in communication with the two aerobic zones 12, 12a.via openings 1.1, 1.2 and l.la, 1.2a located in the two solid wall partitions 1, la.
The two second solid wall partitions 2, 2a each are posit-ioned in parallel with first solid wall partitions 1, la and alongside the endless ~elts 5, 5a and are attached to the two side walls of the reaction tank 10. The top ends o~ the two 1 ~55976 second solid wall partitions 2, 2a extend above the liquid level of the reaction tank 10 and the bottom ends extend dia-gonally into the aerobic zones 12, 12a to form between partitions 1 and 2 and la and 2a the downflow aeration zones 12.1 and 12.1a and to form between partitions 2 and 2a the end side walls of the reaction tank 10 the upflow fluidized bed zones 12.2 and 12.2a. The fluidized bed zones 12.2, 12.2a are in communication with their respective aeration zones 12.1 and 12.la via a number of inverted funnels 3, 3a located at the top of the fluidized bed zones 12.2, 12.2a and via openings 2.1 and 2.la formed be-tween the bottom of partitions 2 and 2a and the bottom of the aeration tank 10.
Clear well zones 13, 13a are formed in the two aerobic zones 12, 12a above the two fluidized bed zones 12.2, 12.2a for withdrawal of the effluent via weirs 9, ~a and exits 8, ~a.
Openings 2.2, 2.2a located in solid wall partitions 2, 2a are provided for skimming of the floating solids from the clear well zones 13, 13a into the aeration zones 12.1, 12.la and pipe 18 is provided for withdrawal of the excess sludge from the fluidized bed zone 12.2.
::
Referring to the system's hydraulics, when endless belts 5, 5a rotate in the direction shown by arrows ~0 they perform the following functions:
a~ First, the pipes 5.2 act as propellers in maintaining a double loop lla, llb rotation of the reactor liquor in the anoxic zone 11 as shown by arrow 21. Since there are no re-sistances in the path of the rotating reactor liquor, accept the tangentially located side wall of the feed inlet trench 7a 1~5~j~7~
diverting the rotating liquor downwardly in the centre of the anoxic zone 11, the energy used in maintaining the double loop rotation of the reactor li~uor in the anoxic zone 11 is minimal.
Because of the inherent momentum the path of the solid parti-cles is different from the path of the rotating liquid with thesolid particles penitrating from the right rotating loop lla into left rotating loop llb and the solids from the left side rotating loop llb penitrating into the right side rotating loop lla as shown by arrows 22, thus improving the ef~iciency of mixing and contacting the sludge solids with the reactor liquor rotating in two hydraulic loops in the anoxic zone 11 without increasing the consumption of energy above that used in mixing of the content of the anoxic zone in a single rotating hydrau-lic loop of the apparatus of my invention described in my above 5 listed patents.
b) Second, when pipes 5.2 are moving downwardly through throats 19, l9a, each space formed between two neighboring pipes and the chain links of chains 5.1 forms a cavity 5.7 which when moving at the given speed of the belts 5, 5a through 0 the throats 19, l~a pumps out the liquid from the throat down-wardly into the aeration zones 12.1, 12.la. secause of this pumping effect of cavities 5O7 the liquid level in the throats 19, 19a drops below the liquid level maintained in clear wells 13, 13a resulting in a gravity flow of the sludge from the top of the fluidized bed zones 12.2, 12.2a via funnels 3, 3a into the throats 19, 19a and from there down through the aeration zones 12.1 and 12.1a and back into the fluidized bed zones 12.2, 12.2a forming the sludge recirculation loop maintained in the aerobic zones 12, 12a to improve the efficiency of transfer of the air oxygen to microorganisms and to improve floccuIationof sludge solids in the fluidized bed zones and to improve ~ ~ ~i5976 filtration of suspended solids from the processed waste water flowing through the fluidized flocculated sludge into the clear well zones and out of reaction tank 10. In addition a contin-uous small stream of the clari~ied effluent via openings 2.2,
FIELD OF INVENTION
This invention relates to a simplified high rate mixed-fluidized bed Anoxic-Aerobic Activated Sludge Treatment System capable of simultaneous biological removal of carbonaceous, ni-trogenous and phosphorous compounds and suspended solids from municipal and industrial waste waters without the use of chemicals and without the use of the traditional secondary clarifiers. It has -for its object a provision of a simplified process apparakus not requiring compressors, mixers, piping, pumps, sludge scrapers and clarifiers and providing optimum Anoxic-Aerobic Activated Sludge Process conditions with reliable maintenance free operation at reduced capital and operating costs. The apparatus of this invention meets all process requirements along with reduced con-sumption of energy in mixing, aeration and recirculation of the reactor mixed liquor between the Anoxic and Aerobic stages in a single reaction tank and is suitable for use in designing the standardized waste water treatment packaged plants as well as in designing the large municipal and industrial waste water treatment facilities.
BACKGROUND TO T~E INVENTION
In a review of the most advanced technology for kreatment of waste waters, Barth, E.H. et al. (International Nutrient Control Technology for Municipal Effluents, Jour. WPCF. V.53, No.12, 1981) outlined the various process flowsheets and process parameters currently used in removing the carbonaceous, nitrogenous and phosphorous compounds from municipal waste waters.
D-~
~ ~L559~
It was reported there that removal of carbonaceous and nit-rogenous compounds and phosphorus has been achieved in large scale commercial plants using a single Activated sludge system comprising an anoxic stage r an aerobic stage and a clarifier in which the sludge age is maintained by withdrawing the excess sludge from the clarifier. Further, i-t was shown by Beer, C.
et al. (Activated Sludge Systems Using Nitrate Respiration -Design Considerations, Jour. WPCF., 5ept. pg. 2120, 1978) that the denitrification rate when using the waste water carbonaceous material as energy source in nitrate respiration is considerably higher than that achieved with endogenous nitrate respiration and that the Activated Sludge System in which an Anoxic stage is followed by an Aerobic stage produces significantly less excess sludge, uses significantly less oxygen and removes sig-nificantly less alkalinity from the processed waste water thanthe Activated Sludge System in which an Aerobic stage is followed by an Anoxic stage.
~ince in an Anoxic-~erobic Activated Sludge Process de-composition of the organic nitrogen and the nitrification of the ~mmonia nitrogen to nitrate takes place in the second -Aerobic stage while denitrification of the nitrate nitrogen to nitrogen gas takes place in the first - Anoxic stage, to achie~e efficient removal of nitrogen the Anoxic - Aero~ic Activated Sludge Process requires an extremely high recircu-lation of the reactor mixed liquor between the two reaction stages. Depending on the concentration of total nitrogen in the incoming waste water and on the required low concentration of the total nitrogen in the effluent, the desired mixed liquor to feed recirculation ratio usually varies in the range j,;~
.... ~
1 ~59716 between 10 to 50. Such high recirculation rates are impossible to achieve in current waste water treatment facili-ties in which recirculation of the mixed liquor and sludge between the two reaction stages is maintained by mechanical pumps. As a result the concentration of nitrogenous compounds in the effluents from current Anoxic-Aerobic Activated Sludge Systems is undesir-ably high.
Further it is known that in an Activated sludge Process the performance of the biochemical reactor, i.e. the reactor volumetric loading rate depends on the concentration of the contaminant and on the concentration of mixed liquor volatile suspended solids (MLVSS) in the reactor. Because of the re-circulation of the mixed liquor between the two reaction stages in the Anoxic-Aerobic Activated Sludge Process the concentration of the contaminant in the two reaction stages is usually very low and because of use of secondary clariiers the concentration of MLVSS in the two reaction stages is limited and usually less than 5,000 mg/lit. As a result the volumetric loading rates in all existing Anoxic ~erobic Activated Sludge Systems designed for removal of nutrients are very low and usually less than 0.4 kg/m3 day~
It has been also demonstrated in large commercial plants that in the Anoxic-~erobic Activated Sludge Pro~ess the removal of phosphorus is being achieved simultaneously with removal of nitrogen due to a biological stress imposed on the mixed micro-bial population while in the Anoxic reaction stage. Since phosphorus is removed from the processed waste water by assim-ilation of phosphorus into the cellular material of the micro-~ 1.55976 organisms the phosphorus removal ef~iciency increases withincreased BOD loadings and with reduced sludge age. The per-missible sludge age howe~er is effected by the growth rate of the nitrifiers and by the required removal of the ammonia nitrogen. Depen~ing on the operating temperature the minimum sludge age to achieve efficient nitrification may vary in the ranye from 4 to 10 days and usually is maintained at 7 - 8 days if simultaneous removal of nitrogen is to be achieved efficiently.
With view to the above discussed Anoxic-Aerobic Activated Sludge Process variables it then follows that to increase the overall nitrogen removal efficiency it is necessary to increase the mixed liquor recirculation rate, to increase the ~erformance it is necessary to increase the concentration of MLVSS in the two reaction stages and to increase the removal of phosphorus it is necessary to operate the system at the minimum permissihle sludge age.
The Anoxic-Aerobic Activated Sludge Process of my invention covered by Can. Pat. No. 1 114 528, and 1 116 323 (U.S.Pat.App.
No. 181 r 136 and 268,725) meets all the above discussed process requirements. Contrary to all current art systems it does not require a separate clarification stage and as schematically shown in Fig. 1 it briefly consists of a) feeding the waste water into the Anoxic stage, recycling the mixed liquor by a new type mixer-aerator from the Aerobic stage into the Anoxic stage at the mixed liquor to feed recir-culation ratio greater than 20, mixing the waste water with the recycled mixed liquor in the Anoxic stage and contacting the waste water with MLVSS in the Anoxic stage in the absence ...
1~L55976 of dissolved oxygen therein and at concentrations of l~LVSS
greater than 15,000 mg/lit. In the Anoxic stage the soluble BOD5 is partially used up as energy source in nitrate respir-ation and in new cell synthesis, NO3--N is gasified and released due to substrate nitrate respiration by the mixed microbial population and NH3-N and PO4 are partially assimilated in new cell synthesis.
b) flowing -the denitrified mixed liquor with the partially treated waste water from the ~noxic stage into the Aerobic stage, the Aerobic stage comprising a downflow Aeration zone and an upflow fluidized bed zone, mixing the anoxic liquor with the sludge withdrawn from the fluidized bed zone and aerating the mixture of liquor and sludge by air while continuously recir-culating the mixture of liquor and sludge in a loop downwardly through the aeration zone and upwardly through the fluidized bed zone. In the Aerobic stage the remaining BOD5 and the TKN
are biooxidized by the activated sludge along with new cell synthesis~ endogenous respiration, assimilation of nitrogen and phosphorus into new cells and nitrification of the ammonia nitrogen to nitrate nitrogen.
In addition the recirculated sludge as it moves upward through the fluidized bed zone flocculates and forms a fluidized bed which efficiently filters out all suspended solids present in the processed waste watert leaving a clear effluent collected above the fluidized bed zone. To maintain the desired sludge age a portion of the recirculated sludge is withdrawn from the -fluidized bed zone.
The major process differences between the described process i ~1559~B
of my invention and the current art can be su~narized as foll~ws:
a) the mixed liquor to feed recirculation ratio in the described process is greater than 20/ while in the current art systems it is only 2 to 4, b) the concentration of the ~VSS in the described process is greater than 15l000 mg/lit, while in the current art systems it is less than 5,000 mg/lit, c) the Aerobic stage in the described process comprises a downflow aeration zone and an upflow fluidized bed zone with the reactor liquor and sludge continuously recirculating in a closed loop through the two zones, while the current art syste~s utilize a completely mixed aeration zone, d) in the described process suspencled solids are removed from the processed waste water by filtration in the fluidized bed within the Aerobic stage, while in the current art systems suspended solids are removed from the treated waste water by gravity settling in an additional clarifying stage with the settled sludge being recirculated from the clarifying stage into the Anoxic stage.
The described Anoxic-~erobic Acti~ated Sludge Process can be used either a~ to achieve complete oxidation of volatile suspended solids associated with less efficient removal of phosphorus, or b~ for efficient removal of BODs, suspended solids and nutrients associated with increased production of excess sludge. Complete oxidation is usuall~ desirable for "on site" treatment applications where maintenance and excess sludge are to be minimlzed and where water flow rates are usually small, while efficient removal of phosphorus with ~.~"
~1559 76 maximized production of excess sludge may be desirable for large waste water flow rates, when the excess sludge may be recovered for reuse either because of its energy content or because of the nutrient values of the excess sludge vola-tile suspended solids. In both situations the Anoxic-Aerobic Activated Sludge Process of my invention when compared with current art systems offers considerable savings in capital and operating costs due to reduction of the required reaction volume, elimination of the secondary clarifier, elimination of piping and pumps, elimination of compressors, mixers and aerators, reduction in consumption of energy used in aerationl mixing and recirculation of the mixed liquor, reduced maintenance and supervision and elimination of chemicals such as methanol and lime required by current art systems in nitrification - denitrification and/or in removal of phosphorus~ For comparison of the Anoxic-Aerobic Activated Sludge Process of my invent:ion with the Completely ~ixed Nitifyin~ Activated Sludge Process the major process char-ac~eristics of the two processes are presented in Table 1.
Durin~ ongoing investigation of ~he above described Anoxic-Aerobic Activated Sludge Process hydraulics I have found that the performance of the process apparatus of my invention covered by the above listed Canadian and U.S. Pat. can be further improve~
by improving the efficiency of mixing of the reactor liquor and sludge solids -MLVSS in the Anoxic stage.
I have also found that such improved mixing can be achie~ed without increasing the consumption of energy and along with simp-lification of the reaction tank r particularly when applied in large waste water treatment plants when capacity of the plant ~559~6 may be increased by joining together and in parallel a number of modular reaction units.
It is therefore the object of the present invention to provide an improved apparatus for use with the above described Anoxic-Aerobic Activated Sludge Process of my invention.
More specifically it is the object of the present invention to provide an apparatus with improved process hydraulics in mix-ing of the reactor liquor with sludge solids in the Anoxic stageand in recirculation of the reactor liquor and sludge solids be-tween the Anoxic and Aerobic stages.
It is another object of this invention to provide a simpli-fied reacticn tank that would be more suitable for use as a modu-lar reaction unit in designing the large waste water treatment plants.
It is another object of this invention to provide an appara-tus with improved hydraulies of the upwardly moving fluidized bedof the floceulated sludge and in withdrawal of the floccula~ed sludge from the fluidized bed zone.
It is also the object of this invention to provide an appara-tus with improv~d energy utilization efficiency in mixin~, recir-cuIating and aerating the reactor mixed liquor and the flocculated sludge.
Other objects and features of the present invention will be understood from the following deseription of the apparatus and claims.
_ 9 _ ~551~76 SUMMARY OF TH~: INVENTIO~
The present invention provldes an improved apparatus for use with the Anoxic-Aerobic Activated Sludge Process of my in-vention covered by the above Canadian Patents and U.S. Patent Applications.
More specifically the improved apparatus provides for more efficient process hydraulics involving mi~ing of -the reactor liquor with sludge solids in the Anoxic stage, more efficient recirculation of the reactor liquor and sludge solids between the two reaction stages and more efficient aeration of the re actor liquor and sludge solids without increased consumption of energ~. It also provides improved recirculation of sludge solids through the aeration zone and fluidized bed zone, provides a more simple reaction tank more suitable for use as a modular unit in large waste water treatment plants.
BRIEF DESCRIPTION QF THE DRAWINGS
The forgoing and other objects and advanta~es of the present invention will becGme apparent from the followin~ detail descrip-tion which proceeds with reference to the accompanying drawings where in Fig. 1 is a simplified schematic diagram of th~ Anoxic~
Aerobic Process of my invention covered by the abo~e listed Cana dian Patents and U.S. Pat. ~pplications which is being used in treatment of waste waters with the apparatus of the present in-vention.
Fig. 2 is a ~ertical view through one prefered embodiment i597~
of the apparatus of this invention.
Fig. 3 is a plan view of the prefered embodiment of the apparatus shown in Fig. 2.
Fig~ 4 is a schematic representation of a large treatment system comprising a number of modular units of the apparatus shown in Fig. 2 and Fig. 3 joined into a single reaction tank of the present invention.
DESCRIPT~ON OF THE PREFERED E~BODIMENTS
Before explaining the present invention in detail it is -to be understood that the invention is not limited in its appli-cation to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of bein~ practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the pur-pose of description and not of limltation.
Reference is made to Fig. 2 and Fig. 3 for an explanation of one prefered modification of the apparatus of the present ; in~ention. ~s is there shown the apparatus comprises a reaction tank 10 equipped with two first solid wall partitions 1, la, two second solid wall partitions 2,2a, inverted funnels 3, 3a, two 25 endless belts 5, 5a, an inlet 7, two outlets 8, 8a equipped with weirs 9, 9a and one excess sludge withdrawal pipe 18.
The two endless belts 5, 5a each comprise a pair of endless chains 5.1 joined wi-th a plurality of horizontal pipes 5O2 of a specific diameter and length dictated by the treatment capacity ~ :~S~7~
of the reaction tank 10. The horizontal pipes 5.2 ha~e their side ends closed and are permanen~ly attached to t~e endless chains 5.1 to prevent rotation and change in position of the plurality of openings 5.3 located on the top and on the bottom sides of pipes 5.2. The two endless belts 5, 5a are positioned within the reaction tank 10 with their top portion extending above the liquid level of the reactor liquor held in reaction tank 10 and are supported at the top by a pair of rotating sprockets 5.4, 5.4a mounted on a shaft 5.5, 5.5a rotated b~ a motor. The hottom portion of endless belts 5, 5a extend near the bottom of the reaction tank 10 where they are kept in posi-tion by a pair of leading sprockets 5.6, 5.6a. The two endless belts may rotate at same or at different speeds, which speed may vary in the range from 5 to 100 c~/sec, and preferably is maintained in the range from 15 to 50 cm/sec.
The two solid wall partitions 1, la are positioned inside the endless ~elts 5, 5a and are attached to the two side walls of the reaction tank 10 thus separating the reaction tank into 20 a single anoxic zone 11 and two aerobic zones 12, 12a located on two opposite sides of the anoxic zone 11 and/or at the two end sides of the reaction tank 10. The anoxic zone 11 is in communication with the two aerobic zones 12, 12a.via openings 1.1, 1.2 and l.la, 1.2a located in the two solid wall partitions 1, la.
The two second solid wall partitions 2, 2a each are posit-ioned in parallel with first solid wall partitions 1, la and alongside the endless ~elts 5, 5a and are attached to the two side walls of the reaction tank 10. The top ends o~ the two 1 ~55976 second solid wall partitions 2, 2a extend above the liquid level of the reaction tank 10 and the bottom ends extend dia-gonally into the aerobic zones 12, 12a to form between partitions 1 and 2 and la and 2a the downflow aeration zones 12.1 and 12.1a and to form between partitions 2 and 2a the end side walls of the reaction tank 10 the upflow fluidized bed zones 12.2 and 12.2a. The fluidized bed zones 12.2, 12.2a are in communication with their respective aeration zones 12.1 and 12.la via a number of inverted funnels 3, 3a located at the top of the fluidized bed zones 12.2, 12.2a and via openings 2.1 and 2.la formed be-tween the bottom of partitions 2 and 2a and the bottom of the aeration tank 10.
Clear well zones 13, 13a are formed in the two aerobic zones 12, 12a above the two fluidized bed zones 12.2, 12.2a for withdrawal of the effluent via weirs 9, ~a and exits 8, ~a.
Openings 2.2, 2.2a located in solid wall partitions 2, 2a are provided for skimming of the floating solids from the clear well zones 13, 13a into the aeration zones 12.1, 12.la and pipe 18 is provided for withdrawal of the excess sludge from the fluidized bed zone 12.2.
::
Referring to the system's hydraulics, when endless belts 5, 5a rotate in the direction shown by arrows ~0 they perform the following functions:
a~ First, the pipes 5.2 act as propellers in maintaining a double loop lla, llb rotation of the reactor liquor in the anoxic zone 11 as shown by arrow 21. Since there are no re-sistances in the path of the rotating reactor liquor, accept the tangentially located side wall of the feed inlet trench 7a 1~5~j~7~
diverting the rotating liquor downwardly in the centre of the anoxic zone 11, the energy used in maintaining the double loop rotation of the reactor li~uor in the anoxic zone 11 is minimal.
Because of the inherent momentum the path of the solid parti-cles is different from the path of the rotating liquid with thesolid particles penitrating from the right rotating loop lla into left rotating loop llb and the solids from the left side rotating loop llb penitrating into the right side rotating loop lla as shown by arrows 22, thus improving the ef~iciency of mixing and contacting the sludge solids with the reactor liquor rotating in two hydraulic loops in the anoxic zone 11 without increasing the consumption of energy above that used in mixing of the content of the anoxic zone in a single rotating hydrau-lic loop of the apparatus of my invention described in my above 5 listed patents.
b) Second, when pipes 5.2 are moving downwardly through throats 19, l9a, each space formed between two neighboring pipes and the chain links of chains 5.1 forms a cavity 5.7 which when moving at the given speed of the belts 5, 5a through 0 the throats 19, l~a pumps out the liquid from the throat down-wardly into the aeration zones 12.1, 12.la. secause of this pumping effect of cavities 5O7 the liquid level in the throats 19, 19a drops below the liquid level maintained in clear wells 13, 13a resulting in a gravity flow of the sludge from the top of the fluidized bed zones 12.2, 12.2a via funnels 3, 3a into the throats 19, 19a and from there down through the aeration zones 12.1 and 12.1a and back into the fluidized bed zones 12.2, 12.2a forming the sludge recirculation loop maintained in the aerobic zones 12, 12a to improve the efficiency of transfer of the air oxygen to microorganisms and to improve floccuIationof sludge solids in the fluidized bed zones and to improve ~ ~ ~i5976 filtration of suspended solids from the processed waste water flowing through the fluidized flocculated sludge into the clear well zones and out of reaction tank 10. In addition a contin-uous small stream of the clari~ied effluent via openings 2.2,
2.2a from clear well zones 13, 13a into the throats 19, 19a is maintained to assure skimming of the floating solids from the clear well zones 13, 13a into the aeration zones 12.1, 12.la. Several funnels 3, 3a may be used in each fluidized bed zones to achieve more even redistribution and withdrawal of sludge solids from fluidized bed zones 12.2, 12.2a.
c) Third, when belts 5, 5a are moving upwardly in the anoxic zone 11 and when the pipes 5.2 are located above the liquid level of the reaction tank 10 at positions 23, 23a the liquid held in pipes 5.2 is flowing out o~ the pipes into the anoxic zone 11 via the plurality of openings 5.3 located on the bottom side of pipes 5.2 while at the same time atmospheric air is entering into the pipes via the pluxality of openings 5.3 located on the top side of pipes 5.2 until all liquid in pipes 5~2 is replaced with air. When pipes 5.2 are then moving down-ward into the throats 19, l~a and then into the aeration zones12.1j 12.1a they are filled only with air. ~hen pipes are submerged into the recirculated reactor liquor and sludge in the aeration zones 12.1, 12.la the en-trapped air is slowly released from pipes 5.2 via the plurality of openings 5.3 lo-cated on the top side of pipes into the downwardly recirculatedliquor and sludge and simultaneously the air released from pipes 5.2 is being replaced with the recirculated liquor and sludge which liquor and sludge are then transported in pipes 5.2 from the aeration zones 12.1, 12.la into the anoxic zone 11 where the liquor and sludge are released from pipes into the anoxic zone at positions 23, 23a. In this way reactor liquor and ~, .
5~6 sludge are continuously recirculated from aerobic zones 12, 12a into the anoxic zone 11 at a recirculation rate that may be controlled by controlling the speed of the endless belts 5, 5a. The volume of liquor and sludge pumped by pipes 5.2 from aerobic zones 12, 12a into the anoxic zone 11 is replaced by the anoxic mixed liquor continuously flowing by gravity from the anoxic zone 11 into the aerobic zones 12, 12a via openings 1~1, l.la located in first solid wall partitions 1, la. In this way recirculation of the reactor liquor and sludge solids between the aerobic zones 12, 12a and the anoxic zone 11 is achieved at reduced hydraulic resistance and therefore at reduced consumption of energy.
d) Fourth, the air is being released from pipes 5.2 into a downwardly recirculated liquor and sludge via the plurality oF
openings 5.3 in form of coarse bubbles which are then dispersed through out the aeration zones 12.1, 12.la and which bubbles rise in the aeration zones countercurrently to the downwardly recir-culated liquor to the top of the aeration zones. At the top and under the throats 19, l9a the collected air is redispersed and recycled into the recirculated liquor and sludge by the mechanical action of pipes 5.2 acting here as propellers and by the kinetic energy of the recirculated liquor. Since the downflow~velocity of the recircula-ted liquor and sludge drops due to incrased cross-sectional area of the aeration zones 12.1, 12.la at the bottom part of the aeration zones~ the air bubbles are separated from the recirculated slud~e and stay within the aeration zones. Thus the air bubbles are not present and therefore they do not disturb the fluidized bed of the flocculated sludge held in the fluidized bed zones 12.2~ 12.2a in which the floccuIation of the sludge solids takes place as the sludge continuously flows u~wardly ~ ~5~
through the fluidized bed zones back into the aeration zones.
Since sludge is continuously recirculated in a closed loop downwardly through the aeration zone and upwardly through the fluidized bed zone the hydrostatic pressure difference between the aeration zone and the fluidized bed zone is eliminated and the hydraulic resistances are minimized. Since the upward velocity of the rising bubbles in a stationary liquid is within the range from 15 to 45 cm/sec, and because the downward velocity of the recirculated liquor may be controlled within the same range, the velocity of the rising bubbles relative to the aeration zone may be controlled in the range from 0 to about 25 cm/sec.
Consequently the contact time of the air bubbles with the liquor and sludge is extended and the efficiency of transfer of air oxygen to microorganisms significantly increased when compared with completely mixed aeration reactors. As a result the energy used for aeration of the reactor li~uor and for mixing and re-circulation of the liquor and sludge in the reaction tank of this invention is utilized more efficiently than that used in surrent art systems.
e) Fifth, as the reactor liquor and sludge reci~culates downwardly through aeration zones 12.1, 12.la and upwardly through fluidized bed zones 12.2, 12.2a the absorbed oxygen is used up ~y the activated sludge in the fluidized bed in biooxidation of the remaining BODs, T~N and in nitrification of the ammonia nitrogen to nitrate nitrogen. Consequently the concentration of the dis-solved oxygen in the recirculated liquor and sludge entering the aeration zone may be maintained close to zero mg/lit thus in-creasing the oxygen transfer rate in the aeration zones~ Further, with better control of the dissolved oxygen in the fluidized bed zone and with improved withdrawal of the sludge from the top of ~. , ;5~76 the fluidized bed zone into the aeration zone the ~locculati.on of the sludge in the ~luidized bed zones of the apparatus of the present invention is improved and the removal of suspended solids from the processed waste water is more efficient. Since the suspended solids present in the waste water are removed from the treated waste water by the flocculated and fluidized sludge as the treated waste water is filtered through the flo-cculated sludge a separate clarifi.cation stage is not needed.
The filtered and/or clarified effluent is collected above the ~luidized bed of sludge b~ weirs 9, 9a located in clear well zone~ 13, 13a with the effluent continuously flowing out by gravity via exits 8, 8a. The e~cess sludge can be withdrawn continuously or periodically from the fluidized bed zone 12.2 via pipe 18 either for further treatment or disposal.
From the above description of the prefered apparatus and the associated process hydraulics it i.s evident that the ~noxic-Aerobic Activated Sludge System of the presen-t invention does not re~uire the traditional secondary clarifier, does not xequire the traditional compressors and air diffusers and/or surface aerators for aeration of the reactor liquor, does not require the traditional mixers to maintain the biolo~ical activity in the denitrification stages of the treatment in the anoxic zone 11, does not require the traditional pumps and piping for recir-culation of -the reactor liquor and sludge between the Anoxic and Aerobic stages, does not require sludge return pumps/ sludge scrapers and the associated piping as commo~n in all current art systems.
It is also evident that the described apparatus of t~e present invention does not use equipment or parts that wou].d .~
~L ~ 5 ~
require maintenance or parts that can fail.
From the described hydraulics it is also evident that the efficiency in utilization of energy in recirculation of the reactor liquor and sludge between the Anoxic and Aerobic stages, in mixing o~ the reactor liquor and sludge in the Anoxic and Aerobic stages and in aeration of the reactor liquor and sludge in the aeration zones is much better than that in current art systems. It is also evident from the described Anoxic-~erobic Activated Sludge Process used in the apparatus of the present invention that the performance offered by the present apparatus is much higher than that offered by current art systems. It therefore follows that the capital and operating costs for the described system may be expected to be much lower than that of the current art systems.
Reference is now made to Fig. 4 which represents another embodiment of the apparatus of the present invention in which a large Anoxic-Aerobic Activated Sludge System is provided by joining four modular units utilizing the apparatus of the present in~ention shown in Fig. 2 and 3.
; As shown schematically in Fig. 4 a single reaction tank 100 is formed by joining four modular units lO to form a single anoxic zone ll located between eight aerobic zones 12. Each aerobic zone 12 has the same arrangement of parts as those shown in Fig. 2 and Fig. 3 with two endless belts 5 located in each aerobic zone.
Baffles 30 may be pro~ided :in the anoxic zone 11 to utilize a small portion of the kinetic energy of the ro-tating reactor liquor to induce a longitudinal circulation of the rotating liquo~ in the anoxic zone ll shown by arrows 31 to further improve the mixlng ~ ~5$576 of the anoxic zone content. ~aste water inlet 7 may be directed into the waste water distribution channel 7.1 from which waste water is distributed into the anoxic zone via openings 7.2. The clarified effluent flows out from each aerobic stage 12 via in-dividual exits 8 into a common trench 8.1 and the excess sludgemay be withdrawn via pipe 18.
It should be apparent that an efficient apparatus for bio-logical purification of waste waters can be constructed also by other modifications of the anoxic and aerobic stages or by modifi-cation of other parts of the described apparatus. It should be also apparent that the apparatus of the present inventicn can be combined with any current art apparatus designed for pretreatment of the incoming waste water and/or designed for further treatment o:E the effluent to achieve higher effluent quality.
Having described the prefered embodiments of the present in-vention it should be apparent to those skilled in the art that the sa~e permits modification in arrangement and details. I
therefore claim as my invention all such modifications as come within the -true spirit and scope of the following claims.
.
~5~7~
ABLE 1 - Comparison of the Anoxic-Aerobic Systems (A-A-S) vs Complete Mix Nitrifying Activated Sludge System (N.A.S.S.) Design Base: Flow = 454 m3/d Domestic Waste Water;
T = 15C; BODs - 300 mg/l; TSS = 250 mg/l;
USS = 200 mg/l; TKN = 50 mg/1, PO4P = 10 mg/l; Alkalinity = 200 mg/l COMPLETE COMPLETE COMPLETE
OXIDATION TREATMENT MIX
PROCESS PARAMETER A-A-S A-A-S N.A.S.S.
1. Sludge Age -Areation Days 16 8.8 8.8 2. Sludge Age -Denitrification Days 9 6.2
c) Third, when belts 5, 5a are moving upwardly in the anoxic zone 11 and when the pipes 5.2 are located above the liquid level of the reaction tank 10 at positions 23, 23a the liquid held in pipes 5.2 is flowing out o~ the pipes into the anoxic zone 11 via the plurality of openings 5.3 located on the bottom side of pipes 5.2 while at the same time atmospheric air is entering into the pipes via the pluxality of openings 5.3 located on the top side of pipes 5.2 until all liquid in pipes 5~2 is replaced with air. When pipes 5.2 are then moving down-ward into the throats 19, l~a and then into the aeration zones12.1j 12.1a they are filled only with air. ~hen pipes are submerged into the recirculated reactor liquor and sludge in the aeration zones 12.1, 12.la the en-trapped air is slowly released from pipes 5.2 via the plurality of openings 5.3 lo-cated on the top side of pipes into the downwardly recirculatedliquor and sludge and simultaneously the air released from pipes 5.2 is being replaced with the recirculated liquor and sludge which liquor and sludge are then transported in pipes 5.2 from the aeration zones 12.1, 12.la into the anoxic zone 11 where the liquor and sludge are released from pipes into the anoxic zone at positions 23, 23a. In this way reactor liquor and ~, .
5~6 sludge are continuously recirculated from aerobic zones 12, 12a into the anoxic zone 11 at a recirculation rate that may be controlled by controlling the speed of the endless belts 5, 5a. The volume of liquor and sludge pumped by pipes 5.2 from aerobic zones 12, 12a into the anoxic zone 11 is replaced by the anoxic mixed liquor continuously flowing by gravity from the anoxic zone 11 into the aerobic zones 12, 12a via openings 1~1, l.la located in first solid wall partitions 1, la. In this way recirculation of the reactor liquor and sludge solids between the aerobic zones 12, 12a and the anoxic zone 11 is achieved at reduced hydraulic resistance and therefore at reduced consumption of energy.
d) Fourth, the air is being released from pipes 5.2 into a downwardly recirculated liquor and sludge via the plurality oF
openings 5.3 in form of coarse bubbles which are then dispersed through out the aeration zones 12.1, 12.la and which bubbles rise in the aeration zones countercurrently to the downwardly recir-culated liquor to the top of the aeration zones. At the top and under the throats 19, l9a the collected air is redispersed and recycled into the recirculated liquor and sludge by the mechanical action of pipes 5.2 acting here as propellers and by the kinetic energy of the recirculated liquor. Since the downflow~velocity of the recircula-ted liquor and sludge drops due to incrased cross-sectional area of the aeration zones 12.1, 12.la at the bottom part of the aeration zones~ the air bubbles are separated from the recirculated slud~e and stay within the aeration zones. Thus the air bubbles are not present and therefore they do not disturb the fluidized bed of the flocculated sludge held in the fluidized bed zones 12.2~ 12.2a in which the floccuIation of the sludge solids takes place as the sludge continuously flows u~wardly ~ ~5~
through the fluidized bed zones back into the aeration zones.
Since sludge is continuously recirculated in a closed loop downwardly through the aeration zone and upwardly through the fluidized bed zone the hydrostatic pressure difference between the aeration zone and the fluidized bed zone is eliminated and the hydraulic resistances are minimized. Since the upward velocity of the rising bubbles in a stationary liquid is within the range from 15 to 45 cm/sec, and because the downward velocity of the recirculated liquor may be controlled within the same range, the velocity of the rising bubbles relative to the aeration zone may be controlled in the range from 0 to about 25 cm/sec.
Consequently the contact time of the air bubbles with the liquor and sludge is extended and the efficiency of transfer of air oxygen to microorganisms significantly increased when compared with completely mixed aeration reactors. As a result the energy used for aeration of the reactor li~uor and for mixing and re-circulation of the liquor and sludge in the reaction tank of this invention is utilized more efficiently than that used in surrent art systems.
e) Fifth, as the reactor liquor and sludge reci~culates downwardly through aeration zones 12.1, 12.la and upwardly through fluidized bed zones 12.2, 12.2a the absorbed oxygen is used up ~y the activated sludge in the fluidized bed in biooxidation of the remaining BODs, T~N and in nitrification of the ammonia nitrogen to nitrate nitrogen. Consequently the concentration of the dis-solved oxygen in the recirculated liquor and sludge entering the aeration zone may be maintained close to zero mg/lit thus in-creasing the oxygen transfer rate in the aeration zones~ Further, with better control of the dissolved oxygen in the fluidized bed zone and with improved withdrawal of the sludge from the top of ~. , ;5~76 the fluidized bed zone into the aeration zone the ~locculati.on of the sludge in the ~luidized bed zones of the apparatus of the present invention is improved and the removal of suspended solids from the processed waste water is more efficient. Since the suspended solids present in the waste water are removed from the treated waste water by the flocculated and fluidized sludge as the treated waste water is filtered through the flo-cculated sludge a separate clarifi.cation stage is not needed.
The filtered and/or clarified effluent is collected above the ~luidized bed of sludge b~ weirs 9, 9a located in clear well zone~ 13, 13a with the effluent continuously flowing out by gravity via exits 8, 8a. The e~cess sludge can be withdrawn continuously or periodically from the fluidized bed zone 12.2 via pipe 18 either for further treatment or disposal.
From the above description of the prefered apparatus and the associated process hydraulics it i.s evident that the ~noxic-Aerobic Activated Sludge System of the presen-t invention does not re~uire the traditional secondary clarifier, does not xequire the traditional compressors and air diffusers and/or surface aerators for aeration of the reactor liquor, does not require the traditional mixers to maintain the biolo~ical activity in the denitrification stages of the treatment in the anoxic zone 11, does not require the traditional pumps and piping for recir-culation of -the reactor liquor and sludge between the Anoxic and Aerobic stages, does not require sludge return pumps/ sludge scrapers and the associated piping as commo~n in all current art systems.
It is also evident that the described apparatus of t~e present invention does not use equipment or parts that wou].d .~
~L ~ 5 ~
require maintenance or parts that can fail.
From the described hydraulics it is also evident that the efficiency in utilization of energy in recirculation of the reactor liquor and sludge between the Anoxic and Aerobic stages, in mixing o~ the reactor liquor and sludge in the Anoxic and Aerobic stages and in aeration of the reactor liquor and sludge in the aeration zones is much better than that in current art systems. It is also evident from the described Anoxic-~erobic Activated Sludge Process used in the apparatus of the present invention that the performance offered by the present apparatus is much higher than that offered by current art systems. It therefore follows that the capital and operating costs for the described system may be expected to be much lower than that of the current art systems.
Reference is now made to Fig. 4 which represents another embodiment of the apparatus of the present invention in which a large Anoxic-Aerobic Activated Sludge System is provided by joining four modular units utilizing the apparatus of the present in~ention shown in Fig. 2 and 3.
; As shown schematically in Fig. 4 a single reaction tank 100 is formed by joining four modular units lO to form a single anoxic zone ll located between eight aerobic zones 12. Each aerobic zone 12 has the same arrangement of parts as those shown in Fig. 2 and Fig. 3 with two endless belts 5 located in each aerobic zone.
Baffles 30 may be pro~ided :in the anoxic zone 11 to utilize a small portion of the kinetic energy of the ro-tating reactor liquor to induce a longitudinal circulation of the rotating liquo~ in the anoxic zone ll shown by arrows 31 to further improve the mixlng ~ ~5$576 of the anoxic zone content. ~aste water inlet 7 may be directed into the waste water distribution channel 7.1 from which waste water is distributed into the anoxic zone via openings 7.2. The clarified effluent flows out from each aerobic stage 12 via in-dividual exits 8 into a common trench 8.1 and the excess sludgemay be withdrawn via pipe 18.
It should be apparent that an efficient apparatus for bio-logical purification of waste waters can be constructed also by other modifications of the anoxic and aerobic stages or by modifi-cation of other parts of the described apparatus. It should be also apparent that the apparatus of the present inventicn can be combined with any current art apparatus designed for pretreatment of the incoming waste water and/or designed for further treatment o:E the effluent to achieve higher effluent quality.
Having described the prefered embodiments of the present in-vention it should be apparent to those skilled in the art that the sa~e permits modification in arrangement and details. I
therefore claim as my invention all such modifications as come within the -true spirit and scope of the following claims.
.
~5~7~
ABLE 1 - Comparison of the Anoxic-Aerobic Systems (A-A-S) vs Complete Mix Nitrifying Activated Sludge System (N.A.S.S.) Design Base: Flow = 454 m3/d Domestic Waste Water;
T = 15C; BODs - 300 mg/l; TSS = 250 mg/l;
USS = 200 mg/l; TKN = 50 mg/1, PO4P = 10 mg/l; Alkalinity = 200 mg/l COMPLETE COMPLETE COMPLETE
OXIDATION TREATMENT MIX
PROCESS PARAMETER A-A-S A-A-S N.A.S.S.
1. Sludge Age -Areation Days 16 8.8 8.8 2. Sludge Age -Denitrification Days 9 6.2
3. Av.BOD in Effluent mg/l 4.2 5.0 8.0
4. Av.SS in Effluent mg/l 5.0 5.0 10.0
5. Av.TKN in Effluent mg/l 0.1 0.3 0.3
6. Av.NO3-N in Effluent mg/l 1.6 1.2 28.3
7. Av.NH~-N in Eff~uent mg/l 0.1 0.3 0.3
8. Av.TN in Effluent mg/l 1.8 1.8 29.0
9. Av.PO4P in Effluent mg/1 2.6 1.3 6.4
10. Av~ BOD Load kg BODs/kg VSS day 0.16 0.22 0.20
11. Av. BOD Load kg BODs/m3 day 1.22 1.67 0.37
12. Design MLSS gr/lit 20.0 20.0 3.0
13. Desi~n 2 Concentration mg/l 1.0 1.0 2.0
14. Oxygen Uptake kg/kg VSS day 0.2 0.2 0.2
15. Oxygen Uptake kg/m3 day1.44 1.63 0.5
16. Oxygen Uptake kg/day 132.2 110.0 150.0
17. Excess Sludge kg/day 77.1 92.6 104.4
18. Excess Sludge kg/kg VSS day 0.07 0.11 0.12 1~. Aeration Volumem3 58.2 39.2 301.0 20. Anoxic Volume m3 33.4 28.3 21. Clarifier Volume m3 - - 45.0 22. Total System Volume m3 91.6 67.5 346.0 23. Total HydrauIic Retention Time hr 4.8 3.6 18.2 24. Sludge Recirculation Ratio Qs/Q 5 5 0.5 725. Mixed Liquor Recir-culation Rat~o Ql/Q 30 30 JL
Claims (9)
1. Apparatus for treatment of waste waters including means defining a reaction tank, waste water inlet means for introducing waste water into said reaction tank, said reaction tank equipped with two first solid wall partitions attached to two side walls of said reaction tank and dividing said reaction tank into a single centrally located anoxic zone and two aerobic zones located at the two end sides of said reaction tank, said two aerobic zones each divided by second solid wall partition means attached to said side walls of said reaction tank into a downflow aeration zone and an upflow fluidized bed zone followed by a clear well zone, said clear well cone located above said fluidized bed zone, said anoxic zone being in communication with said each aerobic zone via openings located in the upper part of said first solid wall partition and via an opening located in the lower part of said first solid wall partition, each said aeration zone being equipped at the top with a throat means located between said first solid wall partition and said second solid wall partition means, each said aeration zone being in communication with its respective said fluidized bed zone at the top via funnel means located at the top of said fluidized bed zone and connected to said throat means and at the bottom via an opening formed between the bottom of said second solid wall partition means and the bottom of said reaction tank, said clear well zones being in communication with said aeration zones via openings in said second solid wall partition means located at the liquid level of said clear well zones and via said throat means, each said aerobic zone being equipped with at least one endless belt means, said endless belt means comprising a pair of endless chains joined with a plurality of horizontal pipe means, said pipe means being kept in position with said chain links to prevent rotation of said pipe means, said pipe means being a chamber having openings located along their length thereof, said endless belt means being positioned within said reaction tank with their top portion located above the liquid level of said reaction tank and with their bottom portion ex-tending near the bottom of said reaction tank, said belt means being held in position by support means permitting rotation of said belt means around said first solid wall partitions down-wardly in said aeration zones then through said bottom opening located in the bottom part of said first solid wall partitions into said anoxic zone then upwardly in said anoxic zone and out of the liquid held in said anoxic zone then around said top endless belt support means and down into said aeration zones, said endless belt support means being rotated by motor means, said endless belt means with said pipe means being arranged to recirculate the reactor liquor and sludge solids between said aerobic zones and said anoxic zone, to rotate the content of said anoxic zone, to pump the atmospheric air into said aeration zones and to disperse the air in form of bubbles into a downwardly recirculated liquor and sludge in said aeration zones, to recirculate the liquor and sludge solids in a loop downwardly through said aeration zone and upwardly through said fluidized bed zone then via said funnel means and said throat means back into said aeration zone, and said belt means being arranged to skim the floating solids from said clear well zones and to recycle said skimmed solids back into said aeration zones, said clear well zones each being equipped with a weir means for collecting the clarified effluent and with means for discharging the effluent out of said reaction tank and at least one of said fluidized bed zones being equipped with means for withdrawal of the excess sludge.
2. An Anoxic-Aerobic process hydraulics of the apparatus of claim 1 comprising:
continuously rotating the content of said anoxic zone in a double hydraulic loop maintained by said plurality of horizontal pipe means moving upwardly in said anoxic zone and down-wardly in said aerobic zones, said double loop rotation offering reduced hydraulic resistance in mixing of said anoxic zone content with improved contact of sludge solids with the reactor liquor and with incoming waste water, feeding by gravity the incoming waste water into said anoxic zone to utilize the kinetic energy of the incoming waste water in maintaining said double loop rotation of the reactor liquor in said anoxic zone, continuously flowing by gravity the mixed liquor from said anoxic zone via said openings located in said upper part of said first solid wall partitions into said aeration zones to eliminate the hydrostatic pressure difference between said anoxic and aerobic zones and to reduce the hydraulic resistance in recirculating the mixed liquor from said anoxic zone into said aerobic zones, continuously pumping by said plurality of horizontal pipe means air into said aeration zones and continuously releasing said air from said pipe means via said openings in form of bubbles into a downwardly recirculated ractor liquor and sludge and simultaneously replacing said air in said pipe means with liquor and sludge as said pipe means are moving downwardly through said aeration zones, continuously moving by said pipe means the reactor liquor and sludge from said aeration zones into said anoxic zone, and then releasing said liquor and sludge from said pipe means into said anoxic zone when said pipe means are emerging out of the reactor liquor held in said anoxic zone, continuously recirculating by said cavities formed between said horizontal pipe means and said chain links the liquor and sludge in a hydraulic loop downwardly through said aeration zone and upwardly through said fluidized bed zone, continuously flowing by gravity the floating solids from said clear well zones via said openings located in said second solid wall partition means into said aeration zones, continuously flowing by gravity the clarified effluent collected by said weir means via said effluent discharging means out of said reaction tank, and flowing the excess sludge from at least one of said fluidized bed zones via said excess sludge withdrawal means out of said reaction tank.
continuously rotating the content of said anoxic zone in a double hydraulic loop maintained by said plurality of horizontal pipe means moving upwardly in said anoxic zone and down-wardly in said aerobic zones, said double loop rotation offering reduced hydraulic resistance in mixing of said anoxic zone content with improved contact of sludge solids with the reactor liquor and with incoming waste water, feeding by gravity the incoming waste water into said anoxic zone to utilize the kinetic energy of the incoming waste water in maintaining said double loop rotation of the reactor liquor in said anoxic zone, continuously flowing by gravity the mixed liquor from said anoxic zone via said openings located in said upper part of said first solid wall partitions into said aeration zones to eliminate the hydrostatic pressure difference between said anoxic and aerobic zones and to reduce the hydraulic resistance in recirculating the mixed liquor from said anoxic zone into said aerobic zones, continuously pumping by said plurality of horizontal pipe means air into said aeration zones and continuously releasing said air from said pipe means via said openings in form of bubbles into a downwardly recirculated ractor liquor and sludge and simultaneously replacing said air in said pipe means with liquor and sludge as said pipe means are moving downwardly through said aeration zones, continuously moving by said pipe means the reactor liquor and sludge from said aeration zones into said anoxic zone, and then releasing said liquor and sludge from said pipe means into said anoxic zone when said pipe means are emerging out of the reactor liquor held in said anoxic zone, continuously recirculating by said cavities formed between said horizontal pipe means and said chain links the liquor and sludge in a hydraulic loop downwardly through said aeration zone and upwardly through said fluidized bed zone, continuously flowing by gravity the floating solids from said clear well zones via said openings located in said second solid wall partition means into said aeration zones, continuously flowing by gravity the clarified effluent collected by said weir means via said effluent discharging means out of said reaction tank, and flowing the excess sludge from at least one of said fluidized bed zones via said excess sludge withdrawal means out of said reaction tank.
3. Apparatus of claim 1 in which said reaction tank is being equipped with said two first solid wall partitions attached to said two side walls of said reaction tank and dividing said reaction tank into at least one centrally located anoxic zone and at least four aerobic zones located at said two end side walls of said reaction tank, with each said aerobic zone being formed by two solid side wall partitions attached to said first solid wall partition and to said end side wall of said reaction tank, each said aerobic zone being divided by said second solid wall partition means attached to said two solid side wall parti-tions into said downflow aeration zone and said upflow fluidized bed zone followed by said clear well zone, said anoxic zone being in communication with each said aerobic zone and said anoxic zone in addition being equipped with tangetial baffles to induce longitudinal circulation of the rotating liquor in said anoxic zone to improve mixing of the content therein.
4. Apparatus according to claim 1 comprising in addition means for disinfection of the effluent.
5. Apparatus according to claim 3 comprising in addition means for disinfection of the effluent.
6. Apparatus according to claim 1 comprising in addition means for filtration and means for disinfection of the effluent.
7. Apparatus according to claim 3 a comprising in addition means for filtration and means for disinfection of the effluent.
8. Apparatus according to claim 1 comprising in addition means for pretreatment of the incoming raw waste water, said pretreatment means comprising removing, storing and treating the settleable and floatable solids present in the incoming raw waste water and said excess sludge withdrawn from said fluidized bed zone.
9. Apparatus according to claim 3 comprising in addition means for pretreatment of the incoming raw waste water, said pretreatment means comprising removing, storing and treating the settleable and floatable solids present in the incoming raw waste water and said excess sludge withdrawn from said fluidized bed zone.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000405406A CA1155976A (en) | 1982-02-17 | 1982-02-17 | Apparatus for anoxic-aerobic activated sludge process and treatment of waste waters |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000405406A CA1155976A (en) | 1982-02-17 | 1982-02-17 | Apparatus for anoxic-aerobic activated sludge process and treatment of waste waters |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1155976A true CA1155976A (en) | 1983-10-25 |
Family
ID=4123033
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000405406A Expired CA1155976A (en) | 1982-02-17 | 1982-02-17 | Apparatus for anoxic-aerobic activated sludge process and treatment of waste waters |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1155976A (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1994018130A1 (en) * | 1993-02-15 | 1994-08-18 | Svatopluk Mackrle | Method and apparatus for biological activation waste water treatment |
| WO1996003352A1 (en) * | 1994-07-26 | 1996-02-08 | Johann Schwabegger | Method and device for purifying waste water, in particular for fully biological domestic sewage treatment systems |
| CN102689985A (en) * | 2011-02-18 | 2012-09-26 | 中国石油化工股份有限公司 | Sewage processing technology by anoxic-aerobic biological fluidized bed |
| CN105668788A (en) * | 2016-01-28 | 2016-06-15 | 浦华环保股份有限公司 | Activated sludge biochemical pond |
| CN106565023A (en) * | 2016-10-06 | 2017-04-19 | 浙江大学 | Module combination type microcirculation biological nitrogen removal reactor and method thereof |
| CN111634994A (en) * | 2020-06-11 | 2020-09-08 | 武汉轻工大学 | Reactor, system and method for improving biodegradability of refractory organic wastewater |
| CN117049707A (en) * | 2023-07-26 | 2023-11-14 | 山西资环科技股份有限公司 | Integrated cultivation wastewater treatment reactor and application thereof in cultivation wastewater treatment |
-
1982
- 1982-02-17 CA CA000405406A patent/CA1155976A/en not_active Expired
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1994018130A1 (en) * | 1993-02-15 | 1994-08-18 | Svatopluk Mackrle | Method and apparatus for biological activation waste water treatment |
| AU681375B2 (en) * | 1993-02-15 | 1997-08-28 | Svatopluk Mackrle | Method and apparatus for biological activation waste water treatment |
| WO1996003352A1 (en) * | 1994-07-26 | 1996-02-08 | Johann Schwabegger | Method and device for purifying waste water, in particular for fully biological domestic sewage treatment systems |
| CN102689985A (en) * | 2011-02-18 | 2012-09-26 | 中国石油化工股份有限公司 | Sewage processing technology by anoxic-aerobic biological fluidized bed |
| CN105668788A (en) * | 2016-01-28 | 2016-06-15 | 浦华环保股份有限公司 | Activated sludge biochemical pond |
| CN105668788B (en) * | 2016-01-28 | 2023-10-31 | 浦华环保股份有限公司 | Biochemical pool of activated sludge |
| CN106565023A (en) * | 2016-10-06 | 2017-04-19 | 浙江大学 | Module combination type microcirculation biological nitrogen removal reactor and method thereof |
| CN111634994A (en) * | 2020-06-11 | 2020-09-08 | 武汉轻工大学 | Reactor, system and method for improving biodegradability of refractory organic wastewater |
| CN111634994B (en) * | 2020-06-11 | 2022-07-05 | 武汉轻工大学 | Reactor, system and method for improving biodegradability of refractory organic wastewater |
| CN117049707A (en) * | 2023-07-26 | 2023-11-14 | 山西资环科技股份有限公司 | Integrated cultivation wastewater treatment reactor and application thereof in cultivation wastewater treatment |
| CN117049707B (en) * | 2023-07-26 | 2024-03-26 | 山西资环科技股份有限公司 | Integrated cultivation wastewater treatment reactor and application thereof in cultivation wastewater treatment |
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