BIOMASS SELECTION AND CONTROL FOR CONTINUOUS FLOW GRANULAR/FLOCCULENT ACTIVATED SLUDGE PROCESSES

Abstract

A continuous flow granular/flocculent sludge wastewater process selects for granule biomass capable of nitrogen and phosphorus removal and controls granule size and concentration of granular and flocculent sludge for optimal nutrient, organic, and solids removal in a smaller footprint. It includes anaerobic, anoxic, and aerobic process zones, a high soluble biodegradable COD loaded first reactor in anaerobic or anoxic zones, a granular sludge classifier with recycle of underflow granular sludge to the first reactor, a secondary clarifier to settle flocculent sludge and particulates and recycle of flocculent sludge from the secondary clarifier underflow to an aerobic process zone. Wasting of sludge from the two separate recycle lines controls the bioprocess flocculent and granular sludge concentrations and SRTs. Bypass around and recycle flow to the classifier to maintain desired flow under various influent flow conditions aid control of granule size. On/off mixer operation of anaerobic and anoxic reactors may be used.

Claims

1. A wastewater treatment system for biological treatment of wastewater including organic sewage, the system including a liquid process configuration for removal of at least nitrogen and for concentrating biomass, in a continuous flow process, comprising: a plurality of process zones, including a first process zone receiving influent wastewater in continuous flow and mixing the influent wastewater with biomass to produce a mixed liquor in the first process zone, and including bacteria in the first process zone effective to produce granular biomass as well as flocculent biomass, the first process zone being anaerobic or anoxic to encourage formation of granular biomass, the plurality of process zones including at least a second process zone receiving mixed liquor in continuous flow from the first process zone, including granular biomass and flocculent biomass, the process zones including an aerobic zone, a biomass classifier downstream of the process zones, receiving mixed liquor with granular and flocculent biomass, the classifier having separation means for separating out most of the granular biomass from the mixed liquor, so that the classifier produces a first effluent with predominantly flocculent biomass and a second effluent with predominantly granular biomass, a gravity settling clarifier downstream of the classifier and receiving said first effluent from the classifier, the clarifier having a bottom where settled sludge is collected, first recycle means carrying said second effluent from the classifier back to the first process zone, while at least periodically wasting a portion of the second effluent, second recycle means for moving a major portion of settled sludge collected in the clarifier bottom to the aerobic process zone, while a waste outlet of the clarifier at least periodically wastes another portion of the settled sludge from the clarifier, third recycle means for balancing variations in influent flow rate into the system when influent flow is below a desired range, either by recycling a selected portion of said first effluent from downstream of the classifier to upstream of the classifier or by increasing flow at said second recycle means, and a bypass line for moving a selected portion of biomass from the process zones in a bypass around the classifier, in an amount to balance variations in influent flow rate to the system above the desired range.

2. The wastewater treatment system of claim 1, wherein the second recycle means delivers a further portion of settled sludge from the clarifier bottom to an anaerobic process zone.

3. The wastewater treatment system of claim 1, wherein the classifier includes a classifier waste outlet enabling at least a periodic wasting of a part of said second effluent.

4. The wastewater treatment system of claim 1, wherein the biomass classifier includes an energy dissipating inlet directing said mixed liquor into the classifier, the mixed liquor flowing into and through the classifier at a generally consistent flow rate, such that mostly granular biomass, having a greater density than floc biomass, settles and collects at the bottom of the classifier to be discharged as said second effluent, while floc biomass exits the classifier near an upper end of the classifier at said first effluent.

5. The wastewater treatment system of claim 4, wherein the energy dissipating inlet for the mixed liquor is submerged and includes baffles to slow and distribute the flow of mixed liquor into the classifier, the energy dissipating inlet being configured to direct inflow upwardly and outwardly in the classifier, to promote separation of granular sludge from floc sludge.

6. The wastewater treatment system of claim 4, wherein the energy dissipating inlet for the mixed liquor is submerged and includes baffles to slow and distribute the flow of mixed liquor into the classifier, the energy dissipating inlet being configured to direct inflow outwardly and downwardly in the classifier, the baffles promoting separation of granular sludge from flow sludge.

7. The wastewater treatment system of claim 6, wherein the energy dissipating inlet is configured to direct incoming mixed liquor radially outwardly and evenly, horizontally in all directions with the baffles being at staggered positions in the path of radial flow, then to direct flow from an upper, outer annular part of the EDI downwardly and through a series of radially spaced openings to direct a primarily granular flow downwardly, and the outer annular part including an annular array of outlets for mixed liquor just downstream of the baffles, to release primarily flocculent mixed liquor.

8. The wastewater treatment system of claim 1, wherein the classifier has a wasting outlet connected to the classifier bottom, so that wasting of settled sludge at both the clarifier and the classifier can be adjusted to provide desired proportions of granular sludge and of floc sludge in the process zones.

9. The wastewater treatment system of claim 1, wherein the process zones include an anaerobic zone as a first zone and an aerobic zone downstream of the anaerobic zone, and wherein primarily granular sludge from the classifier is recycled to the anaerobic zone, while primarily floc sludge from the clarifier is recycled to the aerobic zone.

10. The wastewater treatment system of claim 1, wherein the process zones include an anaerobic zone, an anoxic zone downstream of the anaerobic zone, and an aerobic zone downstream of the anoxic zone.

11. The wastewater treatment system of claim 1, wherein the process zones include an anoxic zone and an aerobic zone, and wherein primarily granular sludge from the classifier is recycled to the anoxic zone, while primarily floc sludge from the clarifier is recycled to the aerobic zone.

12. The wastewater treatment system of claim 1, further including means for varying a flow rate of the second recycle means to balance variations in influent flow to the system.

13. The wastewater treatment system of claim 1, further including means for local recycle around the classifier in a selected amount to balance variations in influent flow to the system.

14. The wastewater treatment system of claim 1, wherein the first process zone is receiving influent wastewater at a soluble bCOD loading rate of at least 4.8 g/L/day.

15. The wastewater treatment system of claim 1, wherein the mixed liquor in the first process zone has a flocculent biomass concentration in the range of 500 to 2,000 mg/L.

16. The wastewater treatment system of claim 1, wherein the mixed liquor in the first process zone has a granular biomass concentration in the range of 2,000 to 12,000 mg/L.

17. The wastewater treatment system of claim 15, wherein the mixed liquor in the first process zone has a granular biomass concentration in the range of about 3,000 to 9,000 mg/L.

18. The wastewater treatment system of claim 1, wherein the granular biomass in the process zones is at a granule size in the range of about 0.3 to 3.0 mm.

19. The wastewater treatment system of claim 1, wherein the granular biomass in the process zones is at a granule size in the range of about 0.7 to 2.0 mm.

20. The wastewater treatment system of claim 1, wherein mixed liquor flow through the biomass classifier is at a rate greater than 1 meter per hour.

21. The wastewater treatment system of claim 20, wherein mixed liquor flow through the biomass classifier is at a velocity in the range of 5 to 20 meters per hour.

22. The wastewater treatment system of claim 1, wherein granular biomass concentration in the first process zone is two to three times floc biomass concentration.

23. In a biological wastewater treatment system, a classifier for separating granular sludge from flocculent sludge, comprising: a tank or vessel, having an infeed of biomass sludge to the tank including both granular and flocculent sludge, an energy dissipating inlet in the tank and receiving the infeed and dispersing it into the tank at a reduced velocity, the tank having an effluent outflow near the top of the tank, causing a flow pattern in the tank ultimately upwardly toward the outflow, such that the upward flow carries primarily floc biomass of less density than granular biomass to the outflow, while primarily granular biomass, with higher density than the floc biomass, settles toward the bottom of the tank to accumulate at the bottom of the tank, and at the bottom of the tank, a bottom outflow for removal or recycle of granular floc, whereby a majority of biomass at the bottom outflow of the tank is granular biomass, and a majority of biomass effluent exiting the outflow near top of the tank is floc biomass.

24. The system of claim 23, wherein the energy dissipating inlet is submerged, positioned generally centrally in the height of the tank, within 30% of the tank height from center.

25. The system of claim 23, wherein the energy dissipating inlet is submerged deeply in the tank, approximately to down through the depth of the tank, and configured to direct a current of sludge outwardly and upwardly from the energy dissipating outlet.

26. The system of claim 23, wherein the bottom of the tank tapers to a narrow bottom point, at the bottom outflow.

27. The system of claim 23, wherein the energy dissipating inlet comprises a generally circular body with a top having a sludge inlet leading to an interior of the body, a bottom defining a lower boundary of the body, and a series of vertically extending baffle plates extending between the bottom and top of the body to disperse sludge and establish a generally even distribution of sludge entering the tank.

28. The system of claim 23, including a recycle path returning effluent from the effluent outflow back to the classifier inlet, to recycle a portion of the effluent as needed to maintain a desired range of flow through the classifier even under varying diurnal flow conditions.

29. The system of claim 28, further including a bypass from upstream of the infeed to downstream of the effluent outflow, to bypass a portion of the infeed as needed to maintain a desired range of flow rate through the classifier even under varying diurnal flow conditions.

30. The system of claim 23, further including a bypass from upstream of the infeed to downstream of the effluent outflow, to bypass a portion of the infeed as needed to maintain a desired range of flow rate through the classifier even under varying flow conditions.

31. The system of claim 23, including a wasting line connected to the bottom outflow of the classifier tank.

32. The system of claim 23, wherein the submerged energy dissipating inlet for the mixed liquor includes baffles to slow and distribute the flow of mixed liquor into the classifier, the energy dissipating inlet being configured to direct inflow upwardly and outwardly in the classifier, to promote separation of granular sludge from floc sludge.

33. The system of claim 23, wherein the energy dissipating inlet is configured to direct incoming mixed liquor radially outwardly and evenly, horizontally in all directions with the baffles being at staggered positions in the path of radial flow, then to direct flow from an outer annular part of the EDI downwardly and through a series of radially spaced openings to direct a primarily granular flow downwardly, and the outer annular part including an annular array of outlets for mixed liquor just downstream of the baffles, to release primarily flocculent mixed liquor.

34. A method for enhancing biological nitrogen and/or phosphorus removal from sanitary sewage wastewater, in a continuous flow process, comprising: operating a biological MLSS process in one or a succession of process zones, to remove nitrogen or nitrogen and phosphorus from activated sludge, and continuously receiving new raw influent wastewater into the process zones, a first zone of said process zones being an anaerobic or anoxic zone, directing sludge flow from the biological MLSS process zone(s) through a classifier through which sludge flows and in which granular sludge is mostly separated from floc sludge, directing primarily granular sludge in a granular recycle flow from the classifier back to one of the biological process zones, directing primarily floc sludge out of the classifier and to a clarifier where sludge settles to the bottom of the clarifier, recycling a major portion of the settled sludge from the clarifier to one of the process zones, in a classifier recycle, increasing flow into the classifier either by returning a portion of the primarily floc sludge exiting the classifier to an input of the classifier or by increasing the recycle of settled sludge from the clarifier, when the classifier recycle is operated, with a classifier bypass line, bypassing a portion of sludge from the biological process around the classifier when the classifier bypass line is operated, operating the classifier recycle and the classifier bypass line to maintain a flow rate into the classifier within a desired range during influent flow variations, by increasing flow through the classifier recycle when influent flow falls below the desired range and increasing flow through the classifier bypass line when influent flow exceeds the desired range, operating the classifier such that granular sludge separated out in the classifier is in a size range from about 0.3 to 3.0 mm, and operating the classifier and wasting settled sludge from the classifier and from the clarifier at such rates as to establish a desired ratio of granular sludge to floc sludge in the process zones.

35. The method of claim 34, wherein said one of the process zones to which the primarily granular sludge is directed to an anaerobic zone.

36. The method of claim 34, wherein the granular sludge size range is about 0.7 to 2.0 mm.

37. A classifier within a clarifier in a system for biological treatment of wastewater including organic sewage, comprising: a clarifier tank with an inflow pipe receiving activated sludge from upstream liquid process zones of the system, the classifier including an energy dissipating inlet connected to the inflow pipe and receiving sludge having both floc and granular biomass, the energy dissipating inlet having a top plate and a bottom plate and internal baffles configured to direct sludge in generally open distribution radially outwardly into liquid volume of the clarifier, such that sludge solids settle by gravity to a tank floor sloped downwardly toward the center of the clarifier, with granular sludge settling faster than floc sludge and the floc sludge settling slower and more outwardly, the classifier further including the clarifier having a granular sludge exit through the tank floor, near the center of the classifier, and a floc sludge exit through the tank floor spaced outwardly from the granular sludge exit, the classifier further including an annular sludge dividing deflector plate extending up from the tank floor and positioned radially inwardly from the floc sludge exit, so that floc sludge, which tends to settle more slowly and travel farther outwardly in the clarifier than granular sludge, tends to settle on the tank floor outwardly of the dividing deflector plate while the denser granular sludge tends to settle inwardly of the dividing deflector plate, whereby sludge exiting the granular sludge exit has a higher concentration of granular sludge than sludge exiting at the floc sludge exit of the clarifier.

38. The classifier as in claim 37, wherein the clarifier has a rotating sludge removal arm positioned on and movable on the clarifier floor in a sweeping motion to bring settled granular sludge to the granular sludge exit, and including a floc sludge removal arm on the clarifier floor and movable in a sweeping motion to bring floc sludge to the floc sludge exit.

39. The classifier as in claim 37, further including an upper deflector plate in an annular configuration above and outward from the energy dissipating inlet, positioned to deflect sludge emerging from the energy dissipating inlet away from a liquid surface in the clarifier and outwardly in the clarifier.

40. (canceled)

41. The classifier as in claim 37, wherein the energy dissipating inlet has a downflow configuration, with internal baffles configured to direct floc biomass in generally even distribution radially outwardly and upwardly to exit a floc discharge opening into liquid volume of the clarifier and faucet baffles to direct granular biomass in generally even distribution radially inwardly and downwardly into the liquid volume.

42. In a wastewater treatment system, a sidestream treatment process for generating granular biomass for use in a mainstream process for removing nitrogen and/or phosphorus, comprising: operating a biological sludge process in one or a succession of process zones, to remove nitrogen or nitrogen and phosphorus from activated sludge, and continuously receiving solids processing reject water or influent wastewater into the process zones, a first zone of said process zones being an anaerobic or anoxic zone, directing sludge flow from the biological sludge process zone(s) through a classifier through which sludge flows and in which granular sludge is mostly separated from floc sludge, and collecting primarily granular sludge in a bottom area of the classifier, recycling a majority of the primarily granular sludge to the first zone so as to feed the granular biomass with influent soluble bCOD, and wasting a sidestream comprising some of the primarily granular sludge to the mainstream process.

43. The process of claim 42, wherein the classifier has a primarily floc sludge overflow, separate from the granular sludge, and including directing the primarily floc sludge overflow to the mainstream process.

Description

DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 shows stereo microscope photos comparing flocculent and self-aggregating aerobic granular sludge size and structure.

[0054] FIG. 2 is a graph showing relationship of granular size, settling velocity and bCOD loading rate.

[0055] FIG. 3 is a graph showing relationship of a system granular to floc SRT ratio as function of floc and granular sludge reject efficiency from a hydraulic separator of the feed.

[0056] FIG. 4 shows schematic of general arrangement of continuous flow combined granular/floc sludge process.

[0057] FIG. 5A shows schematic of a variation of the process for a phosphorus and nitrogen removal including simultaneous nitrification-denitrification.

[0058] FIG. 5B shows schematic of a variation of the process for a phosphorus and nitrogen removal including simultaneous nitrification-denitrification for treating wastewater with a lower soluble bCOD fraction.

[0059] FIG. 5C shows schematic of a variation of the process for nitrogen removal with anaerobic granule selector zone.

[0060] FIG. 5D shows schematic of a process for production of granular sludge in sidestream treatment for feeding granules to the main wastewater treatment process.

[0061] FIG. 6A shows schematic of a downflow granular sludge classifier.

[0062] FIG. 6B shows schematic of a upflow granular sludge classifier.

[0063] FIG. 7 shows schematic for locating the granular sludge classifier in the bioprocess.

[0064] FIG. 8A shows schematic of a downflow granular sludge classifier located in the secondary clarifier.

[0065] FIG. 8B shows schematic of a submerged upflow granular sludge classifier located in the secondary clarifier.

[0066] FIG. 9 shows schematic of a variation of the process for nitrogen removal with anoxic granule selector zone.

[0067] FIGS. 10A-10D show schematics of a radial flow energy dissipating inlet with radial flow for use in a granular sludge classifier.

[0068] FIGS. 11A-11B shows schematics of an energy dissipating inlet for a granular sludge classifier utilizing a downflow separation design.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0069] All of the combined granular/flocculent sludge processes shown are for continuous flow activated sludge treatment using hydraulic granular sludge classifier to control granule size and to provide granule recycle to a first high loaded anaerobic or anoxic reactor. By continuous is meant essentially continuous, possibly including starts and stops but not batch process. The classifier provides a means to control the size of the granular sludge and the flocculent and granular sludge concentrations in the treatment reactor activated sludge mixed liquor. A minimum flocculent sludge concentration is needed for efficient degradation of colloidal and suspended solids in the wastewater and to provide good effluent clarity.

[0070] The flocculent sludge concentration may vary as a function of the wastewater characteristics and will be typically in the range of 500-1,500 mg/L. A preferred range of flocculent sludge for solids clarification for capture of particulates and colloidal solids is 800 mg/L-1,200 mg/L. The granular size is controlled to provide a low SVI and a high MLSS concentration and for maintaining high efficiency simultaneous nitrification-denitrification (SND) and enhanced biological phosphorus removal (EBPR). The size must be large enough to provide a sufficient anoxic volume in the granules in the aerobic reactor for SND and PAO growth, but small enough to provide efficient use of biomass growth for EBPR and have enough surface area for efficient nitrification. The granules may have a size range from 0.3 mm-3.0 mm. The preferred size may be in the range of 0.7 mm-2.0 mm. The effluent from the classifier has a much higher concentration of flocculent sludge than granular sludge and these solids are settled in the secondary clarifier. The secondary clarifier can be circular, rectangular or square. Wasting of sludge from the bottom flow from the secondary clarifier results wasting more flocculent than granular sludge from the system to thus result in a much higher granule sludge concentration in the bioprocess. Concentrations and SRTs in the reactor mixed liquor. The granular sludge concentration in the mixed liquor may be 2-8 times the flocculent sludge concentration, or in the first process zone, typically 2-3 times. Due to the high settling rates and high thickness of the granular sludge the bioprocess may have a reactor mixed liquor concentration 2-3 times that of conventional flocculent activated sludge systems and up to a typical operating range of 6,000 mg/l-12,000 mg/L to save on treatment footprint and tank volume required. The hydraulic separator provides an upflow velocity that carries out mostly flocculent solids to be removed by the final clarification step.

[0071] Granule settling velocity changes with granule size and thus the hydraulics of the classifier are controlled to select for the desirable granular size. Other types of classifiers may be used in the combined/flocculent sludge processes for granule size selection and floc separation such as screens or hydrocyclones.

[0072] FIG. 4 shows a general arrangement of the process for granule selection and granule size and concentration control. Granular sludge recycle flow line 21 enters an anaerobic or anoxic reactor 36 at high soluble bCOD loading where it is mixed with the influent wastewater line 16. Flow from the high loaded reactor is further processed in a downstream aerobic or anoxic reactors and in aerobic reactors consisting of one or more baffled stages. The flow from the final aerobic process line 28 enters the classifier 10 which produces two outflow streams. One flow contains mostly flocculent sludge line 22 which is directed to the secondary clarifier. The other flow contains mostly granules which is directed to the first reactor via line 21 with possible removal of a small portion line 26 for granular sludge wasting.

[0073] Flow control methods are used to maintain the hydraulic loading on the classifier with possible upflow velocities in the range of 5-20 m/h (meters per hour) to control granule size selection and maximize the flocculent sludge rejection efficiency. Rejection represents the fraction of granule or floc solids from the influent line 28 that is in the classifier effluent line 22. A high rejection percentage occurs for the smaller size flocculent sludge and a lower rejection percentage occurs for the larger size faster settling granules. A portion of the flow leaving bioprocess may be bypassed around the classifier in a bypass line 30 to divert higher flows during diurnal flow variations or due to wet weather events to control the flow rate to the classifier. When the influent wastewater flow results in lower than a desired range of flow to the classifier, recycle may be provided from the classifier effluent line 32 and/or by increasing the flow of clarifier return sludge line 18. Short cut recycle from line 18 can be used to direct recycle sludge flow to the classifier via line 19.

[0074] Sludge wasting must be done to control the activated sludge MLSS concentration at its desired levels. The primary location for wasting excess solids is line 34 from the secondary clarifier. The classifier provides a higher percentage of flocculent sludge to the clarifier due to the higher reject efficiency for the smaller solids. Thus, the secondary clarifier underflow has a higher fraction of flocculent sludge and wasting from that line results in a bioprocess with a much higher granular sludge concentration than flocculent sludge.

[0075] The sludge management approach is also to select the solids wasting rate from the secondary clarifier underflow line 34 to meet the flocculent sludge concentration needed to provide good clarification and low TSS in the effluent. If the SRT and bioprocess concentration of the granular sludge is too high than additional granular sludge can be wasted from the classifier underflow line 26.

[0076] The embodiments illustrated in FIGS. 5A, 5B, 5C, FIG. 5D, and FIG. 9 are for continuous flow combined granular/flocculent activated processes with different process features to meet the specific treatment objectives, handle different types of wastewater characteristics and select for the preferred type of granular sludge. They all incorporate a high loaded first reactor and granular sludge classifier to control the granular sludge size and relative proportions of granular and flocculent sludge in the activated sludge mixed liquor. Granule size control is important for providing an aerobic reactor with SND, which reduces energy costs for aeration and internal recycle pumping and a simpler treatment scheme than conventional nitrification and denitrification processes for nitrogen removal.

[0077] The first embodiment shown in FIG. 5A is a continuous flow combined granule/flocculent sludge process to grow granules with PAOs and to allow SND to achieve for both biological nitrogen and phosphorus removal. The process has an anaerobic zone 38, an aerobic zone with SND 40, a final aerobic zone at higher DO 52, granular sludge classifier 10, and a secondary clarifier 14.

[0078] Granular sludge is recycled from the classifier line 21 to an anaerobic reactor 42 with a volume that result in a high soluble bCOD loading from the influent flow line 16. The anaerobic zone may have at least 3 stages (3 mixed reactors in series) with the first reactor at a high soluble bCOD loading of greater than 4.8 g soluble bCOD/L-day and less than 30 g soluble bCOD/L-day. The 2.sup.nd stage volume 44 is at least as large as the 1.sup.st stage and preferably no more than double. The 3.sup.rd stage 46 is much larger and can exist as a single tank or be divided into multiple stages. The high soluble bCOD loading assures a higher bulk liquid soluble bCOD concentration and creates a long enough diffusion gradient to drive substrate deeper into the granules for subsequent oxidation by NO.sub.3/NO.sub.2 for SND in the aerobic zone to enable larger size granules.

[0079] Mixed liquor from the anaerobic zone enters 38 enters an aerobic reactor 40 that has DO control to allow SND. If DO concentration is too high then oxygen penetrates too deep into the granule to limit use of NO.sub.3/NO.sub.2 by the PAOs. If too low the nitrification rate on the outer layer of the granules is too low to result in a low nitrification efficiency. A lower nitrification efficiency can lead to less nitrogen removal.

[0080] The aeration tank 40 can be a single aerated mixed tank or divided into a number of tanks in series. Aeration DO control maintains the DO concentration at set points in the range of 0.5 mg/L-2.5 mg/L depending on the MLSS and granular size so that SND occurs for nitrogen removal. Nitrifying bacteria growth is primarily on the outer layers of the granule, where the DO concentration is higher, and PAOs are generally in the inner core of the granule, which can use NO.sub.3/NO.sub.2 produced by nitrifying bacteria in the outer granule.

[0081] The classifier and secondary clarifier process and operation is the same as that described for FIG. 4 above. One exception is that the increased return activated sludge recycle flow to control the classifier velocity may also be provided in a separate flow line 19 from the return flocculent sludge recycle instead of only increasing the flow in line 18.

[0082] The sludge wasting to control the bioprocess granular and flocculent sludge concentrations is the same as described for the general configuration in FIG. 4 above.

[0083] Anaerobic zone stages after the 1.sup.st stage 42 may be operated with on/off mixing to allowed solids settling and fermentation of solids to produce more localized soluble bCOD for uptake by granules with PAOs. Some return activated sludge flow line 18a may be added to the anaerobic stage with on-off mixing to provide other solids that can be fermented to produce soluble bCOD.

[0084] A modification to Embodiment 1 for wastewater with a low influent soluble bCOD relative to the influent total organic and ammonia nitrogen is shown in FIG. 5B. The modification relies on the degradation of particulate and colloidal solids to provide degradable COD for denitrification. This process contains an anaerobic zone 38 anoxic zone 50, a SND aerobic zone 40, a second aerobic zone 52, a low DO zone 54, a granular sludge classifier 10, and a secondary clarifier 14.

[0085] This process is necessary for applications lacking enough soluble bCOD to enable high removal of nitrogen by SND with PAO granular sludge. Due to the low soluble bCOD:N ratio the amount of stored carbon by PAOs in the anaerobic zone cannot provide enough electron donor to consume a high percentage of the amount of NO.sub.3/NO.sub.2 produced in the aerobic zone. An internal recycle flow, line 56, from the low DO zone 54 within the second aerobic zone 52 provides NO.sub.3/NO.sub.2 to the unaerated mixed anoxic zone 50 for consumption of NO.sub.3/NO.sub.2 with oxidation of particulate and colloidal solids. The internal recycle flowrate may range from 50 to 500% of the wastewater influent flowrate. The anoxic and aeration zones may consist of a single reactor or a number of reactors operated in series.

[0086] Additional carbon is provided by biodegradable colloidal and suspended solids in the preanoxic zone 50 before the aerobic SND zone 40. The additional aerobic zone 52 operated at a higher DO concentration is provided after the SND aerobic zone for further NH.sub.3 oxidation and enhance further P uptake.

[0087] For this process all the features and operational conditions of the anaerobic zone 38, SND aerobic zone 40, final aerobic zone 52 described for FIG. 5A are applicable. Also, all the features and operational conditions described for the classifier and clarifier and sludge management are applicable and clarifier operation described in Embodiment 1 above with FIG. 5A are included.

[0088] A modification to Embodiment 1 for applications for which nitrogen removal and not phosphorus is required is shown in FIG. 5C. An anaerobic high loaded first reactor is used to select for PAO granules. Mixed liquor flows from anaerobic reactor 44 to an anoxic zone 50 that may be single or multiple stages. The PAO granules from reactor 44 use stored carbon obtain in reactors 42 and 44 for denitrification in zone 50.

[0089] Embodiment 2 shown in FIG. 5D is used for growth of granules to add to the main treatment system and does not have a final secondary clarifier as in Embodiment 1. The first high loaded anaerobic reactor 42 is fed line 16a which may be a reject liquid from digestion dewatering or a small portion of the influent wastewater flow. The process selects for PAO granules that are fed via line 26a to a liquid treatment system producing the treated effluent for the wastewater treatment plant. The classifier overflow final effluent line 23a is also fed to the main liquid treatment system. Treatment of influent flow 16a follows the same course as for the system in FIG. 5A to produce PAO granules. Recycle of underflow from the classifier 10 is directed to reactor 42 operated at a high soluble bCOD load. This sidestream granular generating system may be fed anaerobic digestions dewatering reject water supplemented with organic carbon, part of the wastewater plant influent stream or other.

[0090] The sludge classifier is the key component for the control and optimization of granular/flocculent activated sludge processes.

[0091] The sludge classifier uses a hydraulic design to control the relative capture efficiency of granules and floc and to also control the size of the granular sludge. The classifier is a downflow or upward feed and upflow effluent design that separates the appropriate solids size as a function of the apparatus upflow velocity. The upflow velocity is greater than 1.0 m/hr to minimize floc settling in the lower chamber. The classifier may be contained in the bioreactor tankage as shown in FIG. 7, located between the bioreactor and liquid/solids separation clarifier as shown in FIGS. 6A and 6B, or located within a conventional secondary clarifier as shown in FIGS. 8A and 8B.

[0092] A schematic of the granular/flocculent downflow classifier 10a located between the bioreactor and liquid/solids separation clarifier is shown in FIG. 6A. The effluent flow line 28, from the aerobic process zone plus classifier effluent recycle flow line 32, enters an energy dissipater 60, preferably but not necessarily submerged, that distributes a uniform down flow of the mixed liquor and promotes separation of granule and floc. The flow travels downward in the inner chamber 62 and the fast settling granules continue to settle to the bottom of the classifier. A majority of the flow from the inner chamber flows to the outer chamber 63 and the resulting liquid rise velocity in the outer chamber is greater than the floc settling velocity of floc, which causes floc to be carried upward and out with the flow over the effluent launder 64 to the secondary clarifier through the classifier effluent line 22. Due to the fact, granular sludge has a much higher settling velocity than flocculent sludge, the solids rising in the outer chamber will consist mainly of flocculent sludge. The rise rate can also be controlled to select for granular size by varying the recycle flow rate line 32. At very high flow rates, due to peak diurnal flow or wet weather flow, a portion of the influent flow to the classifier can be bypassed using the high flow bypass line 30 to the secondary clarifier so that the classifier's preferred rise rate is maintained. The granules are collected and thickened at the bottom of the classifier 10a and exits via line 20 to continuous flow recycle line to the high load granular biomass selector tank at the beginning of the upstream activated sludge process and also split to a waste line to be used as needed.

[0093] A schematic of the granular/flocculent sludge upflow classifier 10b located between the bioreactor and liquid/solids separation clarifier is shown in FIG. 6B. The influent feed from the activated sludge bioreactor line 28 plus the effluent recycle flow line 32 is introduced into the energy dissipater 68 preferably submerged and located at an appropriate depth within the classifier that distributes a uniform radial flow and promotes separation of granules and floc. Preferably the dissipater is between one-third and two thirds of the classifier tank liquid depth, or within 30% of center of the tank's depth. The classifier's dimension and total feed flow rate determine the upflow velocity in the upper region of the chamber 66 to separate granules and floc and determine the granule size. The granules with settling velocity greater than the upflow velocity are captured and thickened at the bottom of the classifier 10b and exits via line 20 to a continuous flow recycle line to the high load granular biomass selector tank at the beginning of the upstream activated sludge process and also split to a waste line to be used as needed. The rise rate can also be controlled to select for granular size by varying the recycle flow rate, line 32. At very high flow rates due to peak diurnal flow or wet weather flow a portion of the influent flow to the classifier can be bypassed using the peak flow bypass line 30 to the secondary clarifier so that the classifier desired rise rate is maintained.

[0094] In a preferred embodiment of the system of the invention the classifier processes at least two times daily system influent volume per day.

[0095] The general schematic in FIG. 7 illustrates that the classifier can be located in the bioprocess, typically after the last aeration reactor. Granular sludge recycle flow from the classifier line 21 enters a granular feed reactor 36 at a high soluble bCOD loading where it is mixed with the influent wastewater line 16. The granular feed reactor 36 may be anaerobic (as in FIGS. 5A, 5B, and 5C) or anoxic (as in FIG. 9). The bioprocess zone 48 after the granular feed reactor may contain a series of anaerobic, anoxic and aerobic reactors in some configuration. Mixed liquor flow from a final bioprocess reactor enters the classifier 10 and most or all of the flow in the classifier underflow line is in the granular sludge recycle line 21 or a lesser amount for granular sludge wasting line 26. Flow control to the classifier at low influent flow conditions may be provided by recycle of flow from the classifier effluent line 22 back to the classifier inflow via line 32 and/or by increasing the flocculent sludge recycle flow rate from the secondary clarifier 14 via line 18. At excessive high flow conditions bioprocess effluent flow beyond that desired for the classifier may be directed from the final bioprocess reactor to the clarifier 14 via line 30. The total influent flow line 23 to the clarifier 14 equals the clarifier effluent flow following solids settling line 24 plus clarifier underflow with a thicker flocculent sludge concentration in a recycle flow to the bioprocess 48 and a small amount of flow for mainly flocculent sludge wasting line 34.

[0096] A schematic of the granular/flocculent downflow classifier located within a conventional secondary clarifier is shown in FIG. 8A. The effluent flow line 28 from the activated sludge bioreactor plus clarifier floc recycle flow line 19 enters an energy dissipater 70 that distributes a uniform down flow of the mixed liquor and promotes separation of granules and floc. Alternatively, the recycle flow rate to the bioprocess in line 18 could be increased. The flow travels downward in the inner, classifier chamber 72, the granules are settling faster than the floc. Floc from the classifier chamber 72 flows into the outer, secondary clarifier chamber 74 with an upflow velocity that lifts particles with settling velocity less than the rise velocity. Flow is toward the effluent launder 76. Floc then is allowed to settle to the bottom of the secondary clarifier chamber 74 and the clarifier liquid is carried into the effluent launder and out through the clarified effluent line 96. Due to the fact that granular sludge has a much higher settling velocity than flocculent sludge, the solids leaving the classifier chamber 72, i.e. flowing outwardly between an upper annular deflector 80 and a lower annular sludge dividing deflector 82 will consist mainly of flocculent sludge. The rise rate in the classifier chamber 72 can also be controlled to select for granular size by varying the clarifier floc recycle flowrate line 32. At very high flow rates due to peak diurnal flow or wet weather flow a portion of the influent flow to the classifier can be bypassed using the high flow bypass line 30 to a separate secondary clarifier so that the classifier preferred rise rate is maintained. The granules are collected and thickened at the bottom 78 of the classifier chamber 72 and recycled, via line 84, to the high loaded first reactor of the upstream activated sludge process. The floc are also collected and thickened at the bottom of the secondary clarifier chamber 74 and recycled, via line 86, to the appropriate location in the upstream activated sludge process.

[0097] A schematic of a more preferred embodiment of a granular/flocculent upflow classifier located within a conventional secondary clarifier is shown in FIG. 8B. The effluent flow from the activated sludge bioreactor, line 28, plus clarifier floc recycle flow line 19 enters an energy dissipater, flow distribution, and granule/floc separation device 88 located at an appropriate depth within the inner, classifier chamber 92, preferably below center as shown. This combined influent flow enters the separation device 88 via ports (not shown) in the center influent 90 of the clarifier. The flow travels upward and outward, the granules are settling faster than the floc and tend to settle in the classifier chamber 92 of the clarifier. Floc from the classifier chamber 92 flows into the outer, secondary clarifier chamber 94 with an outward and upward flow velocity that lifts particles with settling velocity less than the rise velocity. Again, upper and lower annular deflector plates 80 and 82, respectively, help direct flow in and out of the classifier chamber 92. Floc flows out of the classifier chamber to the secondary clarifier chamber 94. Floc is allowed to settle to the secondary clarifier floor in the secondary clarifier chamber and the clarified liquid is carried into the effluent launder 76 and out through the clarified effluent line 96. Due to the fact that granular sludge has a much higher settling velocity than flocculent sludge, the solids leaving classifier chamber 92 will consist mainly of flocculent sludge. The rise rate in the classifier chamber 92 can also be controlled to select for granular size by varying the clarifier floc recycle flowrate line 19. At very high flow rates, due to peak diurnal flow or wet weather flow, a portion of the influent flow 28 to the classifier can be bypassed using a high flow bypass line 30 to a separate secondary clarifier so that the classifier preferred rise rate is maintained. The granules are collected and thickened at the bottom of the classifier chamber 92 and recycled line 84 to high loaded first reactor of the upstream activated sludge process. The floc are also collected and thickened at the bottom of the secondary clarifier chamber 94 and recycled, via line 86, to the appropriate location in the upstream activated sludge process.

[0098] Embodiment 3 shown in FIG. 9 is for a continuous flow combined granular/flocculent sludge process for nitrogen removal where phosphorus removal is not needed. No anaerobic zone is used in this case and the granules grown are based on the classifier operation and the soluble bCOD loading to the first stage reactor 54 of the anoxic zone 50. The process contains an anoxic zone 50, an aerobic zone 40, a granular sludge classifier 10 and secondary clarifier 14. The second anoxic reactor 58 may be single stage or divided into two or more stages. The aerobic zone 40 may also be single stage or divided into two or more stages.

[0099] All the features and operational conditions described for the classifier and clarifier and sludge management are applicable and clarifier operation described in Embodiment 1 above with FIG. 5A are included.

[0100] FIGS. 10A through 10D show an energy dissipating inlet (EDI) 110 that can be used in the preferred classifier shown in FIG. 6B. This is sometimes called a reverse energy dissipating inlet or reverse EDI, and can be used upright as in FIGS. 10A and 10B, or inverted as in FIGS. 10C and 10D. The EDI has a top plate 112, a top deflector plate 114 at the periphery of the top plate, a bottom plate 116 and a series of outer and inner baffle plates 118 and 120, offset in position as shown in FIG. 10D, which shows a preferred inverted condition of the EDI 110. The sectional view of FIG. 10D is also inverted, showing inner baffles at 120 and the outer baffles 118 in dashed lines, since they are in staggered positions with the inner baffles at baffle. In this position the top plate 112 is actually at the bottom. As can be seen from FIGS. 10C and 10D, flow is down through the influent pipe 122 to the interior of the EDI, where the baffles dissipate energy, slow and distribute the flow generally evenly into the volume of liquid, tending to separate the floc and granular sludge, with an upward and outward flow pattern.

[0101] FIGS. 11A and 11B show an energy dissipating inlet (EDI) 121 that can be used in the classifier shown in FIG. 6A and in the classifier area of the clarifier in FIG. 8A utilizing the downflow separation design. This is sometimes called a faucet energy dissipating inlet, and can be used with faucet baffles at bottom of the lower deflector 124 as in FIG. 11A, or at the bottom plate 116 as in FIG. 11B. The EDI 121 has a bottom plate and a series of outer and inner baffles (118 and 120) similar to the reverse EDI 110 shown in FIGS. 10A through 10D. EDI 121 also has more baffled layers 119 than EDI 110 with each baffled layer, from the most inner to the most outer, offset from each other to provide increased energy dissipation and optimum flow patterns to disrupt the granule/floc matrix for optimum separation of granules from the floc structure. In addition, upper faucet baffling system in FIG. 11A or a lower faucet baffling system in FIG. 11B is added to equalize flow distribution of the granules which have separated from the floc structure such that the granules settle over the entire classifier floor area. The faucet baffle system has openings which vary in size so that the beginning flow is restricted from exiting the closest opening and requires the flow to continue flowing to the next opening until the flow is equalized. The faucet layer can be placed at the lower exit of the EDI 121 which is referred to the lower faucet baffles 126 as shown in FIG. 11A, or this faucet baffle system can replace a portion of the bottom plate 116 at the upper exit which is referred to the upper faucet baffles 128 shown in FIG. 11B. The lower faucet baffles 126 in FIG. 11A receive the settled granules from the upper layer of radial baffles at the outer edge of the bottom plate 116. The lower faucet baffles 126, in this configuration, restrict all the granules from exiting at the outer edge of the lower deflector 124 requiring the flow to continue flowing to the next opening until the flow is equalized and the granules settle evenly over the entire classifier floor area. In contrast, the upper faucet baffles 128 in FIG. 11B allow the granules that have settled at each radial baffle layer to pass through the faucet opening while the floc is kept suspended, enters an outer annular part, still high up in the EDI as shown, and finally exits through an annular array of floc discharge outlets 131 along an upper deflector 130 which directs the floc 132 outwardly and downwardly into the clarifier area. After passing through the upper faucet baffles 128, the granules 134 then settle evenly over the entire classifier floor area of the tank with the lower deflector 124 preventing short circuiting into the clarifier area of the tank.

[0102] Terms used herein such as about or generally should be understood as meaning within 10% of the value stated.

[0103] The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.