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. A series of biological process zones lead to a secondary clarifier. Mixed liquor sludge, preferably from an aerobic zone, goes through a classifier or separator processing flow from the aerobic zone, to the secondary clarifier. In a sidestream process that can be included a portion of sludge preferably from an aerobic zone goes through a classifier or separator to selectively produce a granular-rich effluent, and the clarifier may also have a separator to further concentrate granular biomass, most of which is cycled back to an initial multi-stage anaerobic process zone. The anaerobic zone is structured and operated to encourage growth of granules in subsequent process zones.

Claims

1. A wastewater treatment system including a series of biological process zones and a downstream clarifier, and further comprising: a sidestream flow from an aerobic process zone of the series of process zones and receiving a selected portion of sludge exiting the aerobic process zone, the sidestream flow including a sidestream separator for separating granular sludge from floc sludge to produce a first separator effluent containing primarily floc sludge, the sidestream separator having a second effluent enhanced in granular content, the sidestream separator further including a recycle stream of the primarily floc sludge, recycled back to the sidestream flow into the sidestream separator, with a control for controlling flow via the recycle stream, a portion of the first effluent being a waste stream, at least intermittently, and the second effluent from the sidestream separator joining with a main flow from the aerobic process zone to the clarifier, so that flow entering the clarifier contains an enhanced proportion of granular sludge thus enhancing settling rate in the clarifier, tending to collect a granular-rich sludge in a bottom area of the clarifier, whereby settling of sludge in the clarifier is enhanced to increase clarifier efficiency, and control of granular sludge and floc sludge content in the process stream can be enhanced by adjustments in the operation of the sidestream.

2. The wastewater treatment system of claim 1, wherein the clarifier has a floc-rich region separated from the granular-rich sludge, and including a recycle line of floc sludge from the floc-rich region of the clarifier to at least one of the process zones.

3. The wastewater treatment system of claim 2, wherein said one of the process zones is an aerobic or anoxic zone.

4. The wastewater treatment system of claim 2, including a recycle flow of granular biomass from the bottom of the clarifier to an anaerobic process zone of the series of biological process zones, with a portion of the settled granular sludge from the clarifier being wasted.

5. The wastewater treatment system of claim 1, wherein the clarifier produces a clarified effluent, and the system includes a recycle of a portion of the clarified effluent to the separator for dilution of the flow into the separator.

6. The wastewater treatment system of claim 1, wherein the sidestream flow from the aerobic process zone is from an upper level of the aerobic process zone, above the level of the main flow from the aerobic process zone.

7. The wastewater treatment system of claim 1, further including a recycle line for the second effluent to an anaerobic zone of the series of process zones, for directing a portion of the second effluent to the anaerobic zone as desirable under particular conditions.

8. The wastewater treatment system of claim 1, wherein the main flow from the aerobic process zone goes to a second separator located within the clarifier, so that flow entering the clarifier contains an enhanced proportion of granular sludge thus further enhancing settling rate in the clarifier, the second separator being effective to further separate granular sludge from floc sludge such that granular sludge settles more rapidly to the bottom of the clarifier, with primarily floc sludge from the second separator being directed to a radially outward region of the clarifier so as to settle in an annular area of floc sludge radially outward from settled granular sludge, and the system including a recycle line of floc sludge from the outer annular area of the clarifier to at least one of the process zones, and a recycle flow of granular biomass from the bottom of the clarifier to an anaerobic zone of the series of process zones, with a portion of the settled granular sludge from the clarifier being wasted, whereby settling of sludge in the clarifier is further enhanced to increase clarifier efficiency.

9. The wastewater treatment system of claim 8, wherein the clarifier produces a clarified effluent, and the system includes a recycle of a portion of the clarified effluent to the sidestream separator for dilution of the sidestream flow into the sidestream separator.

10. The wastewater treatment system of claim 1, acting as a mainstream process for removing nitrogen and/or phosphorus, and further including a sidestream treatment incubator system for generating granular biomass for use in the mainstream process, comprising: a biological sludge process stream with one or a succession of incubator process zones, to remove nitrogen or nitrogen and phosphorus from activated sludge, with a continuous influent of solids processing reject water or influent wastewater into the incubator process zones, a first incubator zone of said incubator process zones being an anaerobic or anoxic zone, an incubator separator receiving sludge flow from the biological sludge incubator process zone(s), with sludge flowing through the incubator separator, in which granular sludge is separated from floc sludge, with granular-rich sludge collected in a bottom area of the incubator separator, a majority of the granular-rich sludge in the incubator separator being recycled to the first incubator zone so as to feed the granular biomass with influent soluble bCOD, and a portion of the granular-rich sludge being directed to the mainstream process.

11. The wastewater treatment process of claim 10, wherein the incubator separator has a primarily floc sludge overflow, separate from the granular-rich sludge, the primarily floc sludge overflow being directed to the mainstream process.

12. The wastewater treatment system of claim 11, wherein the primarily floc sludge overflow is directed to the clarifier of the mainstream process.

13. The wastewater treatment system of claim 10, wherein said portion of the granular-rich sludge is directed to an anaerobic zone of the series of biological process zones of the mainstream process.

14. A separator 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 separator 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 bottom plate and internal baffles configured to direct sludge in generally even 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 separator further including the clarifier having a granular sludge exit through the tank floor, near the center of the clarifier, and a floc sludge exit through the tank floor spaced outwardly from the granular sludge exit, and the separator 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.

15. The separator as in claim 14, 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.

16. The separator as in claim 14, wherein the energy dissipating inlet is submerged and 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.

17. The separator as in claim 14, 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.

18. 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, a biomass separator downstream of the process zones, to produce a mixed liquor, the mixed liquor in the process zones including a first type of sludge and a second, faster settling sludge that settles faster than the first type of sludge, a biomass separator downstream of the process zones, receiving mixed liquor with the first and second types of sludge, the separator having separation means for separating out the second type of sludge from the mixed liquor, so that the separator produces a first effluent with predominantly the first type of sludge and a second effluent enriched in the second type of sludge, and a stream of clarified liquid to join the mixed liquor entering the separator when needed for dilution of the flow into the separator to enhance separation.

19. The wastewater treatment system of claim 18, wherein the first type of sludge comprises floc biomass and the second type of sludge comprises granular biomass.

20. The wastewater treatment system of claim 18, further including a gravity settling clarifier downstream of the separator and receiving at least some of said first effluent from the separator, the clarifier producing a clarified effluent and the clarifier having a bottom where settled sludge is collected and can be discharged, and said stream of clarified liquid comprising clarified effluent from the clarifier.

21. The wastewater treatment system of claim 20, wherein bacteria in the first process zone are effective to produce granular biomass as said second type of sludge as well as flocculent biomass at said first type of sludge, 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, one of the plurality of process zones being an aerobic zone, the biomass separator separating out granular biomass from the mixed liquor, so that the separator produces the first effluent as predominantly flocculent biomass and the second effluent enriched in granular biomass, and a granular recycle carrying a portion of said second effluent from the separator back to the first process zone.

22. The wastewater treatment system of claim 19, acting as a mainstream process for removing nitrogen and/or phosphorus, and further including a sidestream treatment incubator system for generating granular biomass for use in the mainstream process, comprising: a biological sludge process stream with a succession of incubator process zones, to remove nitrogen and/or phosphorus from activated sludge, with a continuous influent of solids processing reject water or influent wastewater into the incubator process zones, a first incubator zone of said incubator process zones being an anaerobic or anoxic zone, an incubator separator receiving sludge flow from the incubator process zone(s), with sludge flowing through the incubator separator, in which granular sludge is separated from floc sludge, with granular-rich sludge collected in a bottom area of the incubator separator, and a majority of the granular-rich sludge in the incubator separator being recycled to the first incubator zone so as to feed the granular biomass with influent soluble bCOD, and a portion of the granular-rich sludge in the incubator separator being directed to the mainstream process.

23. A wastewater treatment process with a series of biological process zones, with continuous flow of wastewater through the series of zones, a first of the biological process zones being an anaerobic zone for encouraging selective growth of granular biomass, comprising: providing at least two successive stages in the anaerobic zone, including a first stage and a second stage, into a continuous flow of influent wastewater, introducing a first portion of a recycled activated sludge (RAS) stream from a downstream process zone of the series of biological process zones to produce a continuous combined raw influent/RAS flow into the first stage, the first stage being of limited volume, and dwell time in the first stage being no greater than 30 minutes, so as to provide for intimate contact between the incoming wastewater, rich in food, and the RAS, rich in biological activity, such that granular biomass present in the RAS is exposed to the food of the incoming wastewater for consumption and storage leading to growth of granules in further non-anaerobic zones, operating a mixer in the first stage to mix the RAS and incoming wastewater to provide a mixed liquor, moving the mixed liquor in continuous flow to the second stage, introducing to a bottom region of the second stage a second, remaining portion of the RAS to mix with the mixed liquor in the second stage, in the second stage, operating a mixer intermittently such that mixing of the incoming RAS and sludge from the first stage occurs for a time, then the mixer is shut off for a selected period of time whereby heavier granular biomass tends to settle deeper than floc biomass in the second stage, so that said remaining portion of RAS entering the second stage comes into intimate contact with the settled granular biomass and particulate BOD, and the proportions of incoming wastewater and RAS in the first stage being such as to create a food to mass ratio (F/M) of at least 5.

24. The process of claim 23, wherein the second, remaining portion of RAS is introduced into the second stage using a distributor that distributes the incoming RAS essentially uniformly across the width of the second stage and at said bottom region of the second stage.

25. The process of claim 23, including a third stage downstream of the second stage, mixed liquor being moved continuously from the second stage to the third stage.

26. The process of claim 25, including operating a mixer intermittently in the third stage.

27. The process of claim 23, wherein at least an aerobic process zone is positioned downstream of the anaerobic zone, and including a granular/floc separator downstream of the aerobic zone, and a clarifier connected to the separator such that the clarifier tends to concentrate granular-rich sludge in a bottom area of the clarifier, with at least a portion of the granular-rich sludge being directed back to the first stage of the anaerobic zone as said RAS.

28. The process of claim 27, wherein the series of biological process zones includes an anoxic zone between the anaerobic and aerobic zones.

29. The process zone of claim 23, wherein said first portion of the RAS is 10% to 50% of the RAS.

30. The process of claim 23, wherein said first portion of the RAS is 25% to 40% of the RAS.

Description

DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 shows stereo microscope photos comparing flocculent and self-aggregating aerobic granular sludge size and structure.

[0058] FIG. 2 is a graph showing relationship of granular size, settling velocity and bCOD loading rate.

[0059] 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.

[0060] FIG. 4 shows schematic of general arrangement of continuous flow combined granular/floc sludge process.

[0061] FIG. 5A shows schematic of a variation of the process for a phosphorus and nitrogen removal including simultaneous nitrification-denitrification.

[0062] 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.

[0063] FIG. 5C shows schematic of a variation of the process for nitrogen removal with anaerobic granule selector zone.

[0064] FIG. 5D shows schematic of a process for production of granular sludge in sidestream treatment for feeding granules to the main wastewater treatment process.

[0065] FIG. 6A shows schematic of a downflow granular sludge classifier.

[0066] FIG. 6B shows schematic of a upflow granular sludge classifier.

[0067] FIG. 7 shows schematic for locating the granular sludge classifier in the bioprocess.

[0068] FIG. 8A shows schematic of a downflow granular sludge classifier located in the secondary clarifier.

[0069] FIG. 8B shows schematic of a submerged upflow granular sludge classifier located in the secondary clarifier.

[0070] FIG. 9 shows schematic of a variation of the process for nitrogen removal with anoxic granule selector zone.

[0071] FIGS. 10A-10D show schematics of a radial flow energy dissipating inlet with radial flow for use in a granular sludge classifier or separator.

[0072] FIGS. 11A-11B show schematics of an energy dissipating inlet for a granular sludge classifier or separator utilizing a downflow separation design.

[0073] FIG. 12 is a schematic diagram showing a particular embodiment with a sidestream separator, which may be in addition to a separator in the clarifier.

[0074] FIG. 13 is an elevational section view showing a multiple-stage anaerobic zone for the system of the invention, to encourage selective growth of granular sludge.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0075] All of the combined granular/flocculent sludge processes shown are for continuous flow activated sludge treatment using hydraulic granular sludge classifier or separator 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.

[0076] 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.

[0077] 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.

[0078] 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 has a separation means that 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 via a line 26 for granular sludge wasting.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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. 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.

[0085] 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.

[0086] 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.

[0087] The classifier (separator) 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.

[0088] 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.

[0089] Anaerobic zone stages after the first 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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. FIG. 5C also shows a clarified effluent recycle line 57 for dilution of the influent to the classifier/separator 10, to achieve optimum dilution for separation of granules, as needed. This is an option for all of FIGS. 4 to 5C, and even for FIG. 5D, discussed below, in which clarified effluent from the main process can be cycled to the separator for dilution. Other sources of clarified liquid or water could also be used for this purpose. See dilution line 57 in FIG. 5D.

[0095] Embodiment 2 shown in FIG. 5D is used for growth of granules to add to the main treatment system and does not itself have a final secondary clarifier as in Embodiment 1. The system is a sidestream incubator for granular sludge. The first high loaded anaerobic reactor 42 is fed line 16a which may be, for example, a reject liquid from digestion dewatering or a small portion of the influent wastewater flow, or another wastewater stream, MLSS from one of the main process zones, or even industrial wastewater, with addition of other organics if necessary.

[0096] 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, e.g. to the main process systems of FIGS. 4 and 5A to 5C, preferably to an anaerobic zone as at the line 21 in FIGS. 4 to 5C. Effluent from the anaerobic zone is preferably fed to a short-SRT aerobic zone 52 but could also be fed first to an SND aerobic zone 40 followed by a longer-SRT aerobic zone 52. The classifier overflow final effluent line 23a is also fed to the main liquid treatment system, preferably to an aerobic or anoxic zone. 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 or separator 10 in FIG. 5D is directed to reactor 42 operated at a high soluble bCOD load.

[0097] The sludge classifier (separator) is the key component for the control and optimization of granular/flocculent activated sludge processes.

[0098] The sludge classifier or separator 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/separator 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] In a preferred embodiment of the system of the invention the classifier processes at least two times daily system influent volume per day.

[0103] 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.

[0104] 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.

[0105] 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. 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.

[0106] 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.

[0107] 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 FIG. 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.

[0108] 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.

[0109] FIG. 12 is a schematic diagram showing another wastewater treatment system of the invention including a classifier or separator for enhancing granular sludge content. In this case the system, the liquid side of a treatment system as shown, includes an influent flow 150 into a series of biological treatment zones, in this case shown as an anaerobic zone 152, an anoxic zone 154 and an aerobic treatment zone 156. The anoxic zone 154 could be a swing zone by having aeration at a controlled rate to have simultaneous nitrification/denitrification, and the two zones 154 and 156 could be a single anoxic/oxic swing zone. Note that each of the process zones may contain one or more tanks in series.

[0110] The system shown in FIG. 12 includes a sidestream generally identified as 158, receiving a flow from the zone 156, i.e. from the aerobic or anoxic/oxic zone. Effluent from the zone 156, indicated at 160, is divided such that a selected portion of this flow goes into the sidestream, at 162. A sidestream separator or classifier, for granule/floc separation, is indicated at 164, and the sidestream flow is directed into the separator via a flow line 166. A pump 168 may be provided for this purpose, although in some cases the flow to the separator 164 could be by gravity. The influent to the separator 164 is via an EDI 169, which can be configured as in some of the previously described embodiments, such that granular sludge is encouraged into a bottom region 170 of the separator vessel 172, while primarily floc sludge is collected at an upper end, indicated as overflowing into a floc collection launder at 174.

[0111] The drawing also shows an internal recycle flow at 176, from the primarily floc collection launder 174, dropping by gravity. This recycle flow 176 joins with the incoming sidestream feed flow 162 at a collection box 178. The pump 168 preferably is adjustable, and is set to maintain a prescribed flow rate, with recycle 176 and incoming feed flow 162, through the separator 164 for desired flow velocities in the separator to encourage separation of granular sludge from floc sludge. In conditions where sidestream flow 162 is minimal, volumetric flow into the separator should be kept substantially constant, thus the internal recycle flow loop 176. If conditions are such that the liquid level in the collection box 178 becomes too low as determined by a sensor, the pump can be automatically shut off.

[0112] As indicated in the drawing, a first effluent of the sidestream separator, indicated as SS effluent in the drawing, at 182, is enhanced in granular concentration and preferably is rejoined with the main flow 160, to be introduced as a combined flow 183 into a clarifier 184. A second effluent of the separator 164 preferably comes from the upper end of the separator, in the same manner as the recycle flow 176, and comprises primarily floc sludge. This is indicated as a wasted stream 186 in the drawing, F-WAS.

[0113] In one implementation of the invention, the combined flow 183 of granular-rich sludge and effluent sludge from the process zone 156 can be delivered into the illustrated clarifier 184 in a conventional manner, typically through an energy dissipating inlet (EDI). The sludge to be settled in the clarifier will be enhanced in granular content, and since granular sludge settles at a faster rate than floc, the central bottom 188 of the clarifier will tend to concentrate the granular sludge. However, in the illustrated embodiment the clarifier's EDI 190 is a special separator EDI, i.e. a further separator that works in conjunction with the geometry of the clarifier to concentrate granular sludge even further. For example, the EDI can be similar to the separators shown in FIGS. 11A and 11B, or the clarifier/separator combination can be essentially as shown in FIGS. 8A and 8B. In any event, the EDI/separator 190 tends to separate granular from floc sludge, depositing granular sludge downward essentially centrally in the clarifier, while floc sludge tends to drift outwardly and to be collected as primarily granular sludge in an outer annular region 192 of the clarifier. The clarifier can include a dividing ring 194 to mostly separate primarily floc sludge into the outer region 192, while primarily granular sludge drops to central bottom region 188.

[0114] In FIG. 12 a dashed line 196 is shown for withdrawal of MLSS from a desired level directly from the aerobic process zone 156.

[0115] FIG. 12 shows a recycle line 198 (F-RAS) from the primarily floc-settling region 192 of the clarifier to the process zone 156, which may be an aerobic zone. Also, from this line 198 is shown an effluent line 200 (F-WAS) for wasting a portion of the recycle sludge from the clarifier.

[0116] The drawing shows a secondary effluent dashed line 201 which may be included from the clarifier's outflow launder back to the sidestream, entering the recycle flow at 176. This is to dilute the sidestream separator feed to provide better separation characteristics. Note that such a dilution line can also be included in the systems described above, such as in FIGS. 4, 5A-5D and 9, to dilute the flow to the separator when needed for optimal granular separation. In all cases, the dilution water could come from another source of clarified water if desired.

[0117] It is also possible that the internal recycle of the sidestream could be eliminated in some treatment plants or daily flow conditions. The dilution stream 201 from the clarifier, and/or an increase in the rate of flow from the aerobic zone 156, can be used to increase flow through the sidestream separator 164 as needed to maintain a minimum flow therethrough.

[0118] Still further, a dashed line 202 is indicated from the SS effluent line 182, i.e. granular-enriched sludge from the sidestream separator 164. Since the sidestream includes a granular/floc separator, the primarily granular portion can be sent directly back to the anaerobic zone 152, without first going to the clarifier 184. If desired the flow could be divided, according to conditions, to direct a portion of the SS effluent 182 to the clarifier and another portion via the line 202 directly to the anaerobic zone 152 via G-RAS line 203.

[0119] Another optional recycle line is shown at 204, indicating that primarily floc recycle sludge in the F-RAS line 198 can be recycled to the anoxic zone (or anoxic/oxic zone) 154, rather than (or in addition to) recycling to the aerobic zone 156. Another dashed line 206 shows a preferred recycle of a portion of the sludge in the aerobic zone back to the anoxic or swing zone 154.

[0120] The granular separation system described achieves several advantages. First, it provides two stages of granule/floc separation, so that a better concentration of granular sludge can help all sludge settle more quickly in the clarifier and a higher concentration of granular sludge can be realized at the bottom of the clarifier, at 188. Second, by having a sidestream separator 164, the system provides an early opportunity to collect very light floc and to discharge a desired portion of that floc, as at 186, rather than allowing the lightweight, fluffy material to hinder settling of sludge in the clarifier. Third, the sidestream allows for adjustment of conditions of the incoming mixed liquor for initial startup of the granular/floc separator, which can require dilution to achieve optimum conditions for separation. Fourth, the sidestream provides for the possibility of operation for different conditions and solids retention times for the AGS and floc. The portion of the effluent flow from the aerobic zone 156 to be sent through the sidestream can be adjusted. To avoid significant variations in flow through the separator 164, the pump 168 maintains essentially consistent flow, increasing the internal sidestream recycle to balance lower flow from the line 160 to assure a prescribed range of flow through the separator.

[0121] Another aspect of the invention focuses on the anaerobic process zone 152, i.e. the zone which first receives the influent flow 150. See FIG. 13. Pursuant to the invention the anaerobic zone is a multi-stage zone configured to provide an environment to encourage the growth of granules, in further zones downstream. The multi-stage anaerobic zone 152 is designed to create intimate contact of the food-bearing incoming wastewater with the recycled activated sludge entering the anaerobic zone (G-RAS as in FIG. 12), with its granular sludge, and with granular biomass already present in the first anaerobic zone. The influent 150 is rich in readily biodegradable soluble food for the microbes, while the RAS is rich in microbes, as well as in granular biomass. The anaerobic tank and its inflows are configured to encourage further granule growth of sufficient size to provide good separation of granules in the separators downstream. The design encourages a high soluble volumetric BOD loading and also a high food-to-mass (F/M) ratio (mass of BOD applied/mass of MLVSS-day, i.e. mixed liquor volatile suspended solids-day), particularly at the influent end of the zone.

[0122] One preferred implementation is shown in FIG. 13. In this embodiment, the anaerobic tank 152 is divided into multiple stages, at least two, with FIG. 13 showing three. Incoming wastewater, which may be raw wastewater, is indicated at the left side of the drawing, at 150, and this is combined with a portion of the G-RAS recycle flow 203 (see FIG. 12). The influent wastewater (line 150) and RAS recycle (line 212) are thoroughly mixed for intimate contact before entry to the stage 215, which would occur in a pipe or a mixing box upstream of or within the anaerobic zone. The RAS portion indicated as 212 in the drawing is a preselected portion of the total RAS flow 203 as further discussed below. Note that the G-RAS in the recycle line 203 could have been treated in a nitrate removal tank (not shown) prior to reaching the anaerobic zone 152.

[0123] The influent wastewater and the RAS portion flow into the first stage 215 of the anaerobic zone, which is a small AGS feed stage with retention time preferably 30 minutes or less, possibly only about 15 minutes. From that stage the mixed liquor moves to a second anaerobic zone stage 213, which is shown as by flowing over a weir or baffle 216, although movement to the stage 218 could be other than over a weir.

[0124] Mixers 219 in the anaerobic stages allow mixing of the feed with the tank contents for further consumption of readily available soluble food and conversion of colloidal and particulate food to a soluble form for consumption by the microbes.

[0125] As noted above, only a selected portion of the RAS is introduced along with the incoming wastewater, at 212/150. The remainder of the RAS portion passes through a line 220, to be introduced into the second stage as illustrated. This is preferably via an appropriate form of distributer, e.g. a horizontal pipe 222 with multiple openings to evenly distribute the RAS across the bottom width of the tank. With a portion of the RAS introduced farther downstream than the influent, the proportions of RAS at 212 and 220 can be adjusted so as to achieve a high F/M ratio, particularly in the first stage 215. In a preferred embodiment the F/M ratio is at least 5 in that first stage 215. This might be achieved using a recycle split with, for example, about 25% to 40% (this could range from 10% to 50%) of the RAS introduced with the influent via the line 212 as a function of the influent wastewater conditions. As note above, the retention time in the first stage is short, no more than 30 minutes.

[0126] A third stage 224 is shown in the anaerobic zone in the illustrated embodiment, entering past a divider 225 which can be a weir as shown. An arrow 226 indicates exit flow of MLSS from the third stage 224 and from the anaerobic zone. It should be understood that further anaerobic zones or stages could be included downstream of that shown. Mixers 219 preferably are provided in each stage. In the second and third stages the mixers are turned off periodically. Flow continues through the stages whether the mixers are on or off In the first stage 215 it is important that all the microbes are in contact for consumption of influent soluble good food at highest F/M ratio, and the mixer need not be shut off In the second and third stages 218 and 224, mixers are turned off for a selected period of time, greater than one hour, at desired intervals. When the mixer is off heavier solids including granular sludge and unbiodegradable particulate food settle to the bottom of the tank, while the flow in and out of the tank continues to carry lighter solids and smaller granules to the next tank. The solids that settle provide time for intimate contact between the faster settling granular sludge and biodegradable particulate solids.

[0127] Under that condition the biodegradable solids from the influent are hydrolyzed, and the hydrolyzed products are fermented to provide additional sbCOD for the granules. During this time the granules are consuming the sbCOD at a deeper biofilm depth and have less competition for the food from flocculent sludge.

[0128] The consumed sbCOD (soluble biodegradable COD) in the anaerobic zone is stored as polyhydroxyalkanoates (PHAs) by the bacteria in the granules. During the subsequent mixing period these granules move to the downstream anoxic and aerobic zones where the PHAs are oxidized to result in the growth of new granules to increase the granular sludge biomass content.

[0129] Larger granules in a granular/floc activated sludge system have higher settling velocities and thus may be more easily separated from the floc. The size of the granule can be affected by the bulk liquid soluble biodegradable COD (sbCOD) concentration in the anaerobic zone where the influent wastewater and return activated sludge containing granules are first in contact. A higher bulk liquid COD concentration results in a greater diffusion depth for sbCOD into the granule biofilm and thus provides for growth at deeper depths leading to a larger granule. The anaerobic zone in this innovative process design achieves providing a higher sbCOD concentration for granular growth using two features in the first anaerobic stage in the anaerobic zone: 1) a relatively small initial volume in stage 1 to achieve a high soluble BOD loading in g/L-d or high F/M and 2) intimate contact between the granular sludge and particulate BOD during the mixer-off operation.

[0130] Terms used herein such as about or generally should be understood as meaning within 10% of the value stated.

[0131] 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.