WO2008141413A1

WO2008141413A1 - Wastewater treatment with aerobic granules

Info

Publication number: WO2008141413A1
Application number: PCT/CA2007/000893
Authority: WO
Inventors: Pierre Lucien Cote; Henry Behmann; Sheng Chang
Original assignee: Zenon Technology Partnership
Priority date: 2007-05-18
Filing date: 2007-05-18
Publication date: 2008-11-27

Abstract

A wastewater treatment system using aerobic granules has a large number of sequencing batch reactor tanks with high volumetric exchange rate, a variable cycle length and constant batch volume. The batch reactors are operated for C, N removal and P is removed chemically. SS are removed in a downstream separation step. A continuous flow reactor may comprise an aerobic zone, an alternately aerobic and anoxic zone or discrete aerobic and anoxic zones, and a settling zone. An anaerobic zone may be located at the bottom of a mass of settled granules. Feed may be introduced through the settled granules. An aerobic/anoxic zone may be like a CSTR but with aeration varying in space or time. Sludge granules may move intermittently from an aerobic zone to an aerobic/anoxic zone. A settling zone may have an upflow rate to wash off flocculated biomass. A dual sludge process may be used in which a fraction of unsettled floc is recycled to a region upstream of the granules settler. A fermentation zone may be used to pre-treat feed water or to treat a recycled waste stream, for example a waste stream contain floc.

Description

TITLE: WASTEWATER TREATMENT WITH AEROBIC GRANULES

FIELD

[0001] This specification relates to wastewater treatment.

BACKGROUND

[0002] The following discussion is not an admission that anything discussed below is citable as prior art or part of the knowledge of people skilled in the art. Any statements regarding the results, performance or inventiveness etc., relating to patents or publications discussed below, are statements found in those patents or publications and the present inventor does not admit that any such statements are true. [0003] Granules are dense agglomerates of biomass. Compared to floe or activated sludge, granules are denser, stronger and settle at a higher velocity. Individual granules may be roughly spherical with a diameter of 1-2 mm, a density of 60-90 g/L or 1.004 to 1.065 and a settling velocity of 30-40 m/hr. Granules may be aerobic or anaerobic as determined by the primary mode of digestion of microbes in the biomass. Anaerobic granules have been commercialized in upflow anaerobic sludge blanket (UASB) reactors.

[0004] U.S. Patent No. 6,566,119 relates to a method of acquiring granular growth of a microorganism in a reactor containing a liquid medium. Aerobic microorganisms are induced to granular growth by maintaining specific culture conditions. During a first step an oxygen-containing gas is supplied and the reactor contents are kept in turbulence. In a second step, after a short settling period, the top part of the reactor medium is discharged.

[0005] U.S. Patent No. 6,793,822 describes a method of producing aerobic biogranules for the treatment of waste water comprising the steps of: a) introducing waste water into a reactor; b) seeding the reactor with a active biomass material; c) supplying the oxygen-containing gas to the reactor to provide a mixing action to the suspension of biomass material in said waste water, the supply of oxygen-containing gas providing a superficial upflow gas velocity greater than 0.25 cm/s; d) initiating a period of nutrient starvation of the biomass material while continuing to supply oxygen-containing gas; e) allowing formed aerobic granules to settle in a settling zone in said reactor; f) discharging at least a portion of the waste water; g) repeating steps (a) to (f) until at least a portion of the biogranules in said settling zone are within predetermined properties; and h) recovering said biomass granules within those predetermined properties.

[0006] International Publication No. WO 2004/024638 relates to a method for the treatment of wastewater comprising an organic nutrient. According to the invention, the waste water is in a first step fed to sludge granules, after the supply of the waste water to be treated the sludge granules are fluidised in the presence of an oxygen-comprising gas, and in a third step, the sludge granules are allowed to settle in a settling step. This makes it possible to effectively remove not only organic nutrients but optionally also nitrogen compounds and phosphate. [0007] U.S. Patent No. 6,780,319 describes a method of purifying wastewater charged with organic matter which comprises a step of biologically treating the water, during which the organic matter contained in the water is degraded by micro-organisms thereby producing sludge, and a water-sludge separation step, the sludge coming from the separation step being recycled in the biological treatment step, this method being characterized in that it further comprises a step of degrading the sludge, coming either from the biological treatment step or from the separation step, during which the sludge is brought into contact with an ozonated gas under conditions making it possible to obtain a floe consisting of granules whose mean size is greater than 200 microns, the volatile matter content is between 50 and 65%, the thickening factor of this granular sludge, after 30 minutes of settling, always being greater than 4, the conditions for obtaining the said granular sludge consisting in: treating between 0.1 and 2 times the mass of sludge present in the biological treatment step per day and preferably between 0.7 and 1.5 and, applying an ozone dose of between 3 and 100 grams of ozone per kilogram of treated suspended matter (SM), preferably between 4 and 10 grams of ozone per kilo of treated SM.

[0008] U.S. Patent No. 5,985,150 is directed to a process for the aerobic purification of wastewater in a reactor containing unsupported granular active sludge. The oxygen necessary for maintaining aerobic conditions within the reactor is provided in the form of an oxygen-containing gas. The oxygen-containing gas is preferably introduced into the reactor at such a place that the oxygen-containing gas provides at least some mixing action in the reactor. The invention also provides a reactor suitable for this process.

SUMMARY

[0009] The following summary is intended to introduce the reader to this specification but not to limit or define any claim. One or more inventions may reside in a combination or sub-combination of apparatus elements or process steps described in this summary or in other parts of this document, for example the detailed description or the claims.

[0010] Various mechanisms promote growth of granules. The inventors believe that mechanisms that provide granule growth may include one or more of (a) the selection of species that tend to aggregate by periodically washing-off less dense floe; (b) cycling between periods of feasting and fasting; (c) selecting slow-growing organisms through a long anaerobic period; and, (d) applying a minimum level of shear at least from time to time. Attempting to provide these conditions, however, creates various challenges. For example, some conditions may be provided by using a batch process. For large applications, such as municipal wastewater, matching the feed flow to flow through a batch reactor is difficult. For further example, washing off floe also washes off suspended solids. The washed off material cannot be returned to a reactor containing the granules or species selection will be compromised. Yet further, because granules have a low growth rate, granule wastage does not remove significant amounts of phosphorous. [0011] This specification describes one or more apparatuses or processes that may address one or more of these issues or the desire to treat wastewater with aerobic granules. In general, granules can be grown in a sequencing batch reactor having 3 phases. In a first phase, a feed can be provided to the reactor in a generally plug flow form without air while effluent is simultaneously drawn from the reactor. This simultaneously charges the reactor with feed, removes treated effluent from a previous batch and provides a period of anaerobic digestion. In a second phase, the reactor can be aerated and mixed. The aeration rate can be cycled to provide aerobic and anoxic conditions to oxidize COD and provide nitrification and denitrificaton. In a third phase, mixing and aeration can be stopped to allow the granules to settle and allow treated effluent to rise to the top of the reactor.

[0012] To adapt a batch process to large continuous, possibly variable rate, feed flows, a number of reactors are provided in parallel and fed in sequence. For example, feed may be fed upwards through a bed of settled granules at a high velocity; for example, at a nominal velocity of 4 m/hr or more, or about 4-6 m/hr. The reactor volume exchange height and the feed velocity may be chosen to provide a feed time that, when multiplied by the number of reactors, equals the total cycle time. In this way, feed can be cycled through the reactors to avoid or reduce the need for feed equalization. The high feed velocity also washes off almost all flocculated biomass to enhance the selection of granules in the reactor.

[0013] To deal with washed-off suspended solids, the washed-off stream is treated in a downstream separation step. This downstream step may comprise a filtering membrane or a fine mesh screen. The separation device may operate in dead end flow or without recirculation to the granule reactor.

[0014] To remove phosphorous from the feed, advantage is taken of the fact that, for example during an anaerobic step, a small amount of liquid can be extracted from the reactor. Phosphorous can be precipitated from this liquid chemically. [0015] This specification also includes descriptions of continuous flow reactors or methods that promote aerobic granule formation. One or more of the mechanisms that promote granule growth discussed above may be performed in a continuous flow through the reactor. The reactor may comprise multiple, for example three or four, zones that may comprise one or more of an aerobic zone, an alternately aerobic and anoxic zone or discrete aerobic and anoxic zones, an anaerobic zone and a settling zone. The reactor may have a single sludge removal flow. An anaerobic zone may be located at the bottom of a mass of settled granules. Feed may be introduced through the settled granules generally in a plug flow. An aerobic/anoxic zone may be structured or operated partially like a continuously stirred tank reactor (CSTR) but with aeration varying in space or time. Sludge granules may move intermittently from an aerobic zone to an aerobic/anoxic zone, for example by an air lift pump. A settling zone may have an upflow of >4 m/hr or > 5 m/hr and wash off flocculated biomass.

[0016] This specification also describes reactors or methods involving a dual sludge process, or a process having granules and retained light floe. In a generally granular system, unsettled floe from the granules settling zone is wasted from the system. In a dual sludge process, a fraction of unsettled floe is recycled to achieve a concentration of the floes in a region or zone of the reactor prior to the granules settler. The floes in a dual sludge process may be separated by, for example, a secondary settler or a membrane filtration system, optionally operated as a membrane bioreactor (MBR), after the granules settler. The recycled floes may increase the concentrations of certain organisms in the receiving zones and improve the mass transfer limitation of the granular process to enhance COD and solids removal.

[0017] This specification also describes the use of a fermentation zone to pretreat feed to a process involving granules or to treat a recycled waste stream, for example a waste stream containing floe. BRIEF DESCRIPTION OF THE DRAWINGS [0018] Figure 1 shows a schematic plan and elevation view of a treatment system.

[0019] Figure 2 is an enlarged elevation view of part of the system shown as Part A in Figure 1. [0020] Figure 3 is an elevation view of Part B of Figure 1.

[0021] Figure 4 shows a schematic plan and elevation view of a flow through treatment system.

[0022] Figure 5 shows a schematic elevation view of another treatment flow through system. [0023] Figure 6 shows a schematic elevation view of another flow through treatment system.

[0024] Figure 7 shows a schematic view of another flow through rector.

[0025] Figure 8 shows schematic views of another flow through system.

[0026] Figure 9 shows a schematic view of another flow through system.

[0027] Figure 10 shows a schematic view of another flow through system.

[0028] Figure 11 shows a schematic view of a pre-fermenter.

[0029] Figure 12 shows a schematic view of an experimental set up for a granule producing sequencing batch reactor.

DETAILED DESCRIPTION

[0030] Various apparatuses or processes will be described below including an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that are not described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses or processes described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. All rights are reserved in any invention disclosed in an apparatus or process that is not claimed in this document. Any one or more features of any one or more embodiments can be combined with any one or more features of any one or more other embodiments.

[0031] The description below relates to a design for a 4,800 m³/d (200 m³/h) plant illustrated in Figures 1 , 2 and 3. A peaking factor of up to 3 is assumed. Design details are given in Table 1 and key aspects are described below. For larger plants, the number of granulators may remain the same, but their size may be increased to maintain the same HRT.

[0032] The general layout (Figure 1) involves a number of parallel granulators 12 that can accommodate continuous flow without equalization. The feed flow is directed by gravity from a feed channel 14 to the granulators 12 on a rotation basis. As one granulator 12 is fed, it displaces treated water that overflows into an effluent channel 16 and is directed to a downstream separation step 18.

[0033] Each granulator 12 is an in-ground, rectangular tank 20. It is equipped with a mechanism, for example an airlift pump or a gate valve, to transfer feed flow from the feed channel 14 to the tank 20. Once in the tank 20, the feed is directed via one or several pipes 22 that runs along the wall to the bottom of the tank 20 and are evenly distributed along the length of the tank 20 (Figure 2).

[0034] Figure 3 shows another cross-section of the tank 20 with the position of the feed pipe 22, aerators 24 and effluent collection troughs 26. Optionally, aerators 24 may be used as conduits to introduce feed into the tank 20. It also shows an extraction grid 28 at mid-height that is used for:

• Extracting phosphate-rich liquor for chemical precipitation

• Extracting treated effluent during periods of extreme low flow (when the fill/draw velocity is too low to wash off the flocculated biomass, for example, when the fill/draw velocity is about 4 m/h or less) • Extracting excess granules (the grid level determines the maximum level of settled granules in the tank)

[0035] The number of granulators 12 is determined by the total cycle time and the tank 20 depth. With the assumptions listed in Table 1, the plant would have 6 granulators 12.

[0036] The granulator 12 tanks 20 are built as elongated rectangles

(2.9m x 11.5m) to facilitate vertical plug flow during fill/draw although other shapes might also be used. [0037] The feed may rise at a velocity of about 6 m/h (Average Daily

Flow - ADF) and displace the treated water from the tank to the effluent channel. The flow rate to a single granulator is limited to 1.5 x ADF (9 m/h) in order to promote plug flow and avoid washing off granules. At flow rates > 1.5 ADF (determined for example by monitoring the level in the feed channel), 2 granulator tanks may be operated in parallel. Under these conditions, the maximum flow can be increased without exceeding the maximum fill/draw velocity. Under peaking conditions, for example rain weather flow, the plant HRT drops and the treatment sequence may be modified (e.g., reduce the denitrification periods to ensure complete COD removal). [0038] Provisions may be made to wash off the flocculated biomass during extended periods of low flow. If the flow drops below 0.5 ADF (or fill/draw velocity < about 3 m/h) washing off may be compromised and the mid-height extraction grid (Figure 3) can be used to extract the treated water.

Table 1 - Design for a granule-based plant

[0039] The cycle times indicated below are calculated based on the average daily flow (ADF); these can vary, for example they may be reduced at higher flow as indicated in Table 1.

[0040] Step 1 : Fill and Draw (50 min) • Air is off

• Feed is from the bottom

• Velocity is 5-15 m/h (nominal 10 m/h)

• Flow is through the settled granule bed

• Flocculated biomass is washed off • Treated water (with flocculated biomass) overflows into the collection trough 26 [0041] Step 2: Anaerobic React - Optional (30 min)

• This step is introduced if the fill/draw step is too short to effect PO4 release • Feed is off

• Short burst of air to remix the tank but minimize O₂ transfer

• Substrate impregnates the granules

• PAOs take up VFA and release PO₄

[0042] Step 3: PO4 Extraction - Optional (10 min) [0043] This step is optional because it is possible that the wastage of flocculated biomass (along with the eroded portion of granules), and the direct wastage of granules is sufficient to meet less stringent discharge criteria for phosphorus discharge (e.g. 2 mg/L). For tighter discharge criteria, or to implement nutrient recovery, the following method is used. • At the end of the anaerobic phase, PO4 has been released and its concentration in solution can reach up to about 10 times that of the feed concentration (i.e. up to 180 mg/L P-PO₄)

• A volume of PO₄-rich supernatant is drawn off the mid-height extraction grid 28 (this volume should be equivalent to 10-20% of the tank volume; see mass balance in Appendix I)) • The extracted volume can be processed a number of different ways:

1) precipitated with a coagulant (FeCb, alum) and put back in the granulator

2) as 1), but put back into the influent channel 14 (simpler valve arrangement)

3) as 1), but discharged to the effluent channel 16 (increases COD and NH₄)

4) precipitated with a magnesium salt to form struvite (Mg NH₄ PO₄- 6H₂O) [0044] Step 4: Aerobic/Anoxic React (200 minutes)

• Process air is turned on and off to oxidize COD, nitrify/denitrify, and cause PO₄ re-absorption

• Dissolved oxygen is high (for example >2.0 mg/L) during periods of aeration to promote penetration into the granules • This step also ensures proper shearing of the granules and a sufficient fasting time at the end

• This step may end with an air-off period to minimize the presence of NO₃ in the effluent and in the reactor at the beginning of the anaerobic period. [0045] Step 5: Settle (10 minutes)

• Air is off to allow granules to settle before starting fill/draw

[0046] The suspended solids that need to be continuously removed from the granulators 12 include the feed SS, the flocculated biomass and the sheared off portions of the granules. It is estimated that this could be as high as 100 mg/L. As well, this stream will contain trash if the granulators work without fine screening,

[0047] The downstream separation step is different from typical MBR or tertiary filtration processes because the membrane reject is not recycled back to the granulators 12. The reject is concentrated and taken out as sludge. [0048] In the separation system 18 there may be a static screen 30 to take out trash as a pretreatment to a membrane step 32. This could be a sufficient treatment for discharge to meet 25 mg/L SS, especially with a tight screen mesh in the static screen 30. The membrane filtration unit 32 may be designed to:

• Tolerate high SS • Work at high recovery

• Operate in dead-end to minimize energy

[0049] Benefits of the design described above may include one or more of the following:

• Since flocculated biomass is generally eliminated from the reactor, a larger concentration of granules may be maintained (for example up to

20 g/L)

• The VER may be > 75%, which translates into a higher volumetric loading rate (>2 kg COD/m³/d)

• The process may be very stable with variable flow rate in terms of maintaining the granules in the reactor and washing off the flocculated biomass

• Process control is simplified

• SS solids are removed in a downstream unit process

• High biomass (≥15 g/L) with easy separation • Low SS to effluent offering the opportunity to reduce cost of final separation

• C₁ N and P treatment without recirculation of mixed liquor

• Reliable chemical P removal enhanced by bioP principles (low stoichiometric ratio of coagulant) • Low loading and low sludge yield

• Ability to implement nutrient recycle by struvite precipitation

• Sequencing batch reactors (SBR) without need for equalization, upstream or downstream

• Excellent ability to peak without washing off biomass [0050] Design and operating philosophies may include one or more of: • Large number of small SBR tanks with high volume exchange ratio (VER) (for example >75%), a variable cycle length and constant batch volume to deal with variable flow

• Focus granulator on C, N removal, remove P chemically (under BioP enhanced conditions) and remove SS in a downstream step

[0051] A phosphorous mass balance for the reactor is as shown below.

P.. -P o,ut

"m ~ "eff ⁺ ^SS ⁺ °WG ⁺ "act Pj_n: mass of phosphorous in the feed

PefT mass of phosphorous dissolved in effluent

Pss: mass of phosphorous in effluent suspended solids

PWG: mass of phosphorous present in wasted granules

Pext: mass of phosphorous extracted (during anaerobic step) [0052] Defining x as the fraction of the feed flow that needs to be extracted during the anaerobic step

P_1n=Q-C_1n

P_eff =(l-x)'Q'C_eff

-C_bacl

[0053] PWG is assumed to be negligible as granules are very low growth not wasted in significant amount

Λ_*-**β'C«,

Q'C,_n=(\-x)'Q'C_eff+(\-x)'Q'SS_eff*C_{hocl +}x'Q'C_exl χ_ C_ιn-(C_{eff +}SS_ejr'C_hacl)

EXAMPLE

C_1n= 10mg/L

Cext = 50 mg/L (soluble P after anaerobic release) Ceff = 0.1 mg/L (soluble P in effluent (after aerobic uptake)) SSeff = 50 mg/L

Cbact = 0.02 mg/L (P in flocculated bacteria in effluent) x = 18.2%

[0054] Figure 4 shows a flow-through aerobic granulator (FTAG) designed to be implemented in a relatively shallow tank (for example where depth is less than either length or width). The sizes shown correspond to a 4,800 m³/d plant with 2 FTAGs in parallel, each treating a flow rate of 100 m3/h in a volume of 500 m3 to provide a retention time of 5 hours. Each tank is 6m deep, 10m long and 8.3m wide.

[0055] The feed is introduced at the bottom of the tank through an influent distribution grid.

[0056] Also at the bottom of the tank, there is an airlift pumping grid, optionally interlaced with the feed distribution grid. The airlift grid may comprise a series of coarse bubble aerators, each fitted with a section of pipe that extends from Level A (tank bottom) to near Level B (about 1/4 of the tank depth; 1.5m in the example given).

[0057] Also at Level B, there is a uniform grid of fine bubble process aerators.

[0058] Along the long side of the tank, there is a series of parallel plates that act as a plate settler. In the example shown, the plates occupy a surface area of 10 m² (10m x 1m). The effluent rises through this section at a velocity of about 10 m/h (100 m³/h/10m²). The settling zone is isolated from the reaction zone by a wall that extends down to about Level C to promote a vertical rising velocity within the settling zone.

[0059] The 3 grids described above do not extend across or below the settling zone.

[0060] The FTAG is designed to be operated with a high concentration of granules. The granules concentration may be determined by the interface level of settled granules (both sources of air off) which is controlled (by periodic wastage) to Level C (in the example given, Level C is about half of the tank depth or 3m).

[0061] From a process point of view, the FTAG may comprise 3 zones: i. An anaerobic zone below Level B ii. A mixed, or CSTR like, aerobic / anoxic zone above Level B iii. A narrow settling zone along one or two long sides.

[0062] At any point in time during operation of the FTAG, a fraction of the granules (for example between 25-50%) are settled below Level B and the complement is in suspension above Level B.

[0063] The influent introduced through the feed distribution grid rises in a generally plug flow mode through the settled granule bed between Levels A and B. The airlift pumps are off. The rise velocity may be about 1.2 m/h (100m³/h / 83 m²) for a maximum rise time of 1.5 hour. [0064] Above Level B, aerobic / anoxic conditions prevail as the fine bubble aeration system is cycled on/off. The settling time in this region is 5- 10min (4m/30m/h) and the cycling period may be such that granules are regularly re-suspended. This can be done be cycling the air between the two FTAG in parallel at a cycling time smaller than the settling time. In this region, CSTR like conditions prevail but with varying dissolved oxygen concentration; COD is removed, nitrogen is reduce by nit/denit and PO4 is absorbed by PAO.

[0065] A flow equal to the feed flow continuously rises through the settler and overflow as treated effluent. The design velocity of the settler allows granules to return to the reactor, but flocculated biomass is entrained.

[0066] Periodically, the airlift pumps are turned on to transfer the granules sitting at the bottom of the tank into the aerobic/anoxic zone, above Level B. The displaced granules are replaced by granules from the aerobic / anoxic zone that settle to just below Level B. The frequency and duration of airlift pumping are controlled to provide sufficient granule retention time below Level B (where anaerobic conditions prevail so PAO can uptake VFA and release PO₄). For example, the airlift pumps may be activated for a few minutes every 30-60 minutes. [0067] The flow-through aerobic granulator (FTAG) implements in a controllable way one or more of the 5 mechanisms of granule formation listed above: i. Selection pressure is applied to keep granules in the reactor and wash-off light floe in the settling zone ii. Feasting takes place when the granules are exposed to undiluted feed below Level B. Fasting happens before the airlift pumps are activated and the levels of COD in the aerobic/anoxic section reaches a minimum (DO in the reactor should reach a maximum) iii. The long anaerobic period is provided below Level B. iv. High substrate concentration is provided below Level B; high DO concentration above Level B v. Shearing is provided during aeration, above Level B.

[0068] Another version of a FTAG is designed to be implementable in a broader range of tank configurations, rectangular or circular, shallow or deep and of varying sizes. This version contains 4 distinct zones: 1. Anaerobic, 2. Anoxic, 3. Aerobic, and 4. Settling and is shown, in two variations, in Figures 5 and 6.

[0069] The anaerobic zone (1) is a defined by a baffle which encloses a closed chamber open at the top. Incoming feed (11) and settling unit underflow is distributed to the top of this zone. Air lift pumps are situated at suitable intervals along the length of this zone (22). The airlift pumps (12) are situated such that their inlets are at the bottom of the anaerobic zone and their discharge (13) is at the top of the aerobic/anoxic zone (2). The sides of the bottom may be sloped to reduce dead zones and facilitate solids flow. In the case where the settler (4) is placed above the anaerobic zone, the air discharge from the air lift pumps is routed around the settler so not to affect its function. [0070] The anoxic zone (2) is situated between the anaerobic zone (1) and the well mixed aerobic zone (3). It is open at the top and the bottom to induce downward circulation. This zone does not contain aeration elements. This zone provides a zone for the mixing of the anaerobic zone effluent (1) and the recirculating liquor from the aerobic zone (3). The zone provides an area of reduced dissolved oxygen content for continuous denitrification of the recirculating liquor from the aerobic zone. The passages between the aerobic and anoxic zones are sized to generate the required conditions for denitrification.

[0071] The aerobic zone (3) takes up the balance of the tank. It contains a uniform grid of fine bubble aerators (15) covering its bottom surface. This zone is uniformly mixed to effect complete dispersal of the granules and to maintain a high dissolved oxygen concentration.

[0072] The settling zone (4) may be situated on top of the anaerobic zone. This can be quite small if inclined plates (16) are used. It is sized to remove generally all solids with a settling velocity of less than 5 m/hr. The supernatant is discharged (17) and the settled granules are recycled to the anaerobic zone 1.

[0073] The individual zones are sized to provide the required anaerobic, anoxic/aerobic and settling functions. Flow between zones is also controlled to maintain the required reaction times.

[0074] Figures 5 and 6 illustrate reactors as described above in two examples of configurations. Figure 5 shows an installation in a rectangular tank whereas Figure 6 illustrates a circular tank implementation

[0075] The basic system consists of 4 zones: i. Anaerobic plug flow zone ii. Anoxic plug flow zone iii. Aerobic completely mixed zone iv. Settling zone

[0076] The feed (11) is introduced into the solids stream of the settling zone (22) for example directly under the settling unit (4). There it is mixed with the separated aerobic granules and introduced into an anaerobic zone

(1). A specific level of settled solids is maintained in this zone, controlled by airlift pumps (12) which pump from the bottom of this zone to the top of the anoxic zone (2) through the airlift ejector parts (13). The airlift pumps are controlled to maintain the required anaerobic contact time in this zone.

[0077] The pumped liquor is mixed with a recirculating stream from the aerobic zone (3) and flows downward through the anoxic zone (2). The bottom of the anoxic zone (2) is open to the aerobic zone (3) and is sized to allow a circulation which generates the required anoxic denitrification times. The upper part of the anoxic zone (2) is open to the settling unit (4). Essentially no aeration takes place in the anoxic zone.

[0078] The mixture from the anoxic zone (2) is introduced through the bottom connection into the completely mixed aerobic zone (3). This zone contains over its bottom a fine bubble aeration grid to provide efficient oxygen transfer and complete dispersal of the granules.

[0079] The aerobic zone (3) is connected to the settling zone (4) which is usually situated over the anoxic (2) and the anaerobic zone (1). This settling zone is sized for retaining solids with a settling velocity greater than 5 m/hr and is consequently small in size. Effluent is discharged from the overflow of the settling zone. Inclined plate settlers (16) may be used for compactness. The solids (19) are directed by baffles (18) to the anaerobic zone (1). Excess granules fall into the anoxic zone (2).

[0080] Solids wasting is effected by intercepting and discharging a portion of the settler underflow before feed introduction or discharging directly from the aerobic zone. [0081] This process is continuous in all operations except the air lift pumps which operate intermittently to maintain the required flow and level of granules in the anaerobic zone.

[0082] Further reactors shown in Figures 7 to 10 may be characterized by one or more of the following characteristics:

^■ FTAG with tanks in series;

• Granular sludge or dual sludge (granular and floe) processes with secondary separation (i.e. settling a membrane filtration)

^■ selection - Fast settling

- Combined Anaerobic/aerobic zone

- High shear

- High substrate exposure

^■ Nitrification/denitrification - Controlled DO exposure for simultaneous nitrification and denitrification in the aerobic zone

^■ P removal:

- Chemical precipitation from phosphorous concentrated feed;

- Granule waste; ■ Pre treatment;

- Cycling the process waste solids to a pre-fermentation zone

^■ Direct effluent discharge, post treatment or post treatment with recycle. [0083] Figures 7 to 10 show versions of a FTAG designed to apply the selection principles described herein to a plug-flow reactor with selection of fast settling bio-agglomerates to form a granular process, optionally with a post polishing process or to form a dual sludge process by retaining a fraction of biologically active light floe in the system. The post polishing process may be, for example, one or more of solids separation, biological treatment, membrane filtration, a membrane bioreactor or a physical or chemical treatment step. Floe may be retained in the system by, for example, a secondary settler or a membrane filtration process, with recycle, the membrane filtration process optionally operated as a light MBR. Combining various biological treatment zones in a generally plug flow reactor or process provides flexibility or control over biological reaction times and over the retention times of the selected bio-agglomerates and optionally floe biomass in different reaction zones. This flexibility or control assists in adapting the systems or processes to a variety of wastewater characteristics.

[0084] As shown in Figures 7 to 10, a pre-fermentation zone, an anaerobic zone, one or more alternating aerobic and anoxic zones, and a settling zone or, as an alternative, a pre-fermentation zone, an anaerobic zone, an aerobic zone with controlled DO concentration, and a settling zone may be included in the process. Other or fewer zones may also be present. Each zone can be in separate tanks or in one or more reaction areas separated by baffles or just distinguished based on operation conditions without a physical wall between them. The size and arrangement of different zones may be varied according to different wastewater characteristics and treatment objectives. In general, the arrangement of different zones may form a U or multi U shaped mixed liquor flow channel(s) with the settling zone next to the feeding anaerobic zone. Fine or medium aerators may be installed in the aerobic zones. Mechanical mixers or intermittent aeration may be used in the anoxic and anaerobic zones to suspend the biomass. For the intermittent aeration mixing, the aeration frequency may be in the range of 2 to 60 1/hr with an aeration duration of 5 to 120 seconds. Gravity may be used to drive liquid flow through the anaerobic, alternated aerobic and anoxic, and settling zones to a post treatment zone. The flow rate, and zone sizes, may be determined according to the reaction times required in the different zones based on the wastewater characteristics and removal requirements.

[0085] A granule or fast settling zone may be arranged next to a feeding anaerobic zone. A baffle or multiple baffle plates, oriented vertically or with a slope, may be installed on the top of the settler. The bottom of the settler may be shaped with a slope to facilitate collecting the settled solids. There may be single or multiple solids collection points. An airlift or other transport device may be used to transport the settled solids to the downstream anaerobic zone to mix with a continuous feeding wastewater flow. [0086] In Figures 7 to 10, a process can be operated as a sole granular sludge process as in Figure 9 or a dual sludge process (a combined granular and floe process) as in Figures 7, 8 and 10. The difference between these two processes is that, for the sole granular process, generally all of the unsettled light floes from the fast settler are wasted from the system, while for the dual sludge process a fraction of the light floes are recycled to achieve a concentration of the floe in a region prior to the fast settler. The floe in a dual sludge process can be separated by, for example, a gravity secondary settler or a membrane filtration system which could be a submerged or external membrane filtration system operated under suction, or gravity, or constant pressure condition.

[0087] For a sole granular process, the FTAG may be operated independently, that is with a direct discharge of the effluent, or coupled to a post treatment processes. The post treatment processes can be, for example, membrane filtration, gravity clarifier, and coagulant-assisted settling process. When membranes are used for the post treatment, the membrane filtration tank can be separated from the settling tank or combined with the settling tank. For a separated filtration tank design, a flow channel may be used to distribute effluent from the FTAG into the membrane tank. For a combined membrane tank and settler, baffles may be used to divide the tank into settling zone and membrane filtration zone. As an alternative to using membranes for post treatment, a gravity clarifier or coagulant-assisted settling process may be used to remove the suspended solids from the effluent before final discharge of the effluent.

[0088] For a dual sludge process with a secondary settler (Figure 10), the floe is separated by the gravity settling. A recirculation pump is used to recycle the settled floes to the final aerobic zone or the next anoxic zone before the fast settler. The waste of the floes may be controlled based on the floe concentration or the floe SRT required.

[0089] For a membrane dual sludge process (Figure 7), membrane filtration is used to replace the secondary gravity settling. The membrane filtration can use, for example, submerged or external cross flow or air lift membrane filtration systems.

[0090] In Figures 7 to 10, the feed is input continuously into the feeding anaerobic zone and mixes with granules from the fast settling zone. The mixed feed and granular biomass flows through the anaerobic and aerated regions with, for example, between 30 to 300 minutes or 30 to 180 minutes and 1 to 10 hours or 3 to 6 hours contact time for anaerobic and aerobic reaction respectively. Denification may be achieved through one or more alternated aerobic and anoxic zones or through an aerobic zone with controlled DO concentration. The anaerobic and anoxic zones provides metabolic selection for phosphate-accumulating organisms (PAO) and denitrifying floc-forming organisms which plays an important role in the formation of the aerobic granules and fast settling floes. To facilitate kinetic selection and nutrients removal, a multi-point feeding strategy can also be used to introduce substrate to the anaerobic and anoxic zones where the process function is identified to be limited by the substrate concentration.

[0091] Enhanced biological phosphorus removal can be achieved by two approaches. The first approach is to waste a certain amount of granules after the aeration periods when the granule is rich in P content which also helps control the granule age in the range of 5 or more days or between 20 to 200 days. The second approach is to extract a certain amount of liquid feed at the end of the anaerobic period where the feed has a high concentration of P due to the P releasing action of the granules during the anaerobic period. The extracted high P concentration feed may be treated by precipitation. Approaches 1 and 2 can also be used in the same process. [0092] A short settling time of 1 to 30 minutes or 1 to 10 minutes applied by sizing the fast settler exerts a strong hydrodynamic selection pressure to select fast settling bio-agglomerates. The fast settler is designed to remove solids of various shapes with settling velocity of less than 2 to 10 m/hr or 5 to 10 m/hr. The settled biomass is collected by the sloped bottom of the settler at a single or multiple collection points. The fast settled solids are transferred to the next anaerobic feeding zone by the air-lift or other transport device. The transport device may be sized to obtain a process exchange ratio ranging from 20% to 80% or from 30% to 80%.

[0093] For a sole granular process, as in Figure 9, the overflow effluent from the fast settler can be directly discharged, or treated with a post process, for example by a membrane filter, by a membrane bioreactor, or by a secondary gravity clarifier, or by a coagulant assisted settler, depending on the wastewater characteristics and treatment requirement.

[0094] For post membrane treatment, a single stage concentration process, for example with a recovery of 80 to 98% may be used. Alternately, a two or more stage membrane filtration process may be used. A first stage may be operated in continuous (continuous feed, permeation and retentate bleed) mode and a second in a batch (dead end filtration with periodic tank drain and refill or other deconcentration step) mode. Both of the membrane filtration stages may be designed to operate at a recovery larger than 80%, for a total recovery larger than 96%. For effluent with a relatively high concentration of soluble organic matters and fine colloids, coagulation can be used to form a combined coagulation and membrane process for effluent purification.

[0095] For a dual sludge process as in Figures 7, 8 and 10, the waste rate of the light floe may be controlled to provide conditions resembling a light

MBR, that is an MBR operated at a solids concentration of 10,000 mg/L or less. The floe solids concentration may be in the range of 200 to 5000 mg/L and the floe SRT may be in the range of 10 to 200 days. The floe biomass can be separated from the treated effluent by a secondary settler (Figure 10) or by membrane filtration (a light MBR) (Figure 7), which could be a submerged and external membrane processes operated under either of suction or gravity, and constant pressure. A recycling pump may be used to circulate the mixed liquor, which is separated by the secondary settler or the membrane process, to the aerobic or the anoxic zone before the fast settler. The mixed liquor recycled to the aerobic or anoxic zone increases the light floe concentration in the receiving zones, which will improve the treatment performance of these zones without competing for the food sources of the PAOs since the PAOs store the SCOD in the anaerobic zone and will use the stored food during the aerobic aeration.

[0096] If required, the wasted solids from a post treatment process or a dual sludge process can be recycled to a pre-fermentation zone, where an acidification reaction will reduce the suspended solids in the wastewater and increase the contents of the soluble COD in the feed. The pre-fermentation process may include a number of fermenters and two or more thickners to provide redundancy. The solid retention time in the fermenters may be controlled in a range of 1 to 25 days. The sludge in the fermenters is discharged into a thickner for removal of the liquid containing the VFA. If the process VFA can not meet the requirement of nutrients removal, acetate or acetic acid may be used as a supplemental VFA source. A pre-fermentation zone may also be used to perform similar functions for the feed water, that is converting suspended solids into soluble COD. This may be useful because granules are more effective at removing soluble COD than suspended solids. A pre-fermenter may be added in the feed stream of any reactor described herein.

[0097] Figure 8 shows another FTAG which operates generally as described for Figure 7 but with a different arrangement of zones as shown and without a pre-fermenter.

[0098] Figure 11 shows an optional two stage pre-fermenter that may be used with the systems of Figure 7, 9 or 10.

[0099] An experimental set-up as shown in Figure 12 consists of a bubble column, a feed tank, an effluent tank, and a feeding pump, an acetate dosing pump, and liquid circulation loop. The liquid circulation pump will be on during the anaerobic reaction period to enhance the feed-granule contact. There are 5 sampling outlets at different heights of the column for sampling from different sections. The aeration will use air from a compressed air system. The main set-up parameters include: - Inner diameter: 250 mm,

- Height of overflow outlet: 1.8 m

- Effective working volume: 90 L

- Flow rate of feeding pump: up to 16 cm/min

[00100] The reactor was inoculated with anaerobic granules with a start bed volume of 60 cm. The operation cycle of the granular sequencing batch reactor (GSBR) reactor consists of an anaerobic filling/decanting, anaerobic reaction, aerobic reaction, and settling. The influent feeds the bottom through the settled bed, while the treated effluent is overflowed from the top overflow outlet. Table 1 shows the main operation steps and control status. Table 2 operation steps and control status

[00101] The feeding velocity is set at 5 m/hr. Plug flow of the influent displaces the treated effluent within the granule bed to form an anaerobic environment in the granule bed. This gives priority to the PAO to store rbCOD during the first feeding and reaction period. An anoxic step is introduced after the second feeding step for denitrification. The total feeding height during a cycle is 83 cm, corresponding to an exchange ratio of 50%. [00102] The setting period was initially set at 10 minutes in the beginning of a start-up period to avoid excess washing-out of the biomass. The settling time was gradually reduced based on the settling characteristics of the biomass. [00103] The total cycle time is about 7.2 hours and there are 3.3 cycles per day. The total treated volume per cycle is about 45 L, corresponding to a HRT of 14 hour.

Claims

CLAIMS: We claim:

I . A system or granulator configuration having any feature described herein.

2. A process for treating wastewater having any feature described herein.

3. A phosphorous removal method having any feature described herein.

4. A process of applying granulation mechanisms in a continuous flow reactor.

5. A reactor having 3 or 4 zones in the same reactor including one or more of anaerobic, aerobic/anoxic, aerobic, anoxic or settling.

6. A flow through granulator reactor having a single sludge stream.

7. A reactor having an anaerobic zone at the bottom comprising settled granules.

8. A process comprising feed introduction through settled granules generally in plug flow.

9. A reactor having an aerobic/anoxic zone with aeration alternating in space or time.

10. A process or reactor wherein sludge granules moved intermittently from anaerobic zone to an aerobic/anoxic or aerobic or anoxic zone using an airlift pump.

I I . A process wherein granules are settled against an upflow of >4 m/hr or > 5 m/hr and flocculated biomass is washed off.

12. An apparatus for performing the process of any of claims 4, 8, 10 or 11.

13. A process used in the apparatus of any of claims 5-7 or 9.

14. A process or apparatus comprising one or more apparatus elements or process steps chosen from a set of all process steps and apparatus elements described in this document.

15. A generally continuous wastewater treatment reactor comprising; a) an aerobic feeding zone; b) aerobic or anoxic zones or both; and, c) a granules settling zone.

16. A process or apparatus of any preceding claim having pre-fermentation of feed.

17. A process or apparatus of any preceding claim wherein a portion of effluent from settling granules is recycled to upstream of the granules settling zone.

18. A process or apparatus as in claim 17 wherein waste solids are recycled through a fermetner.

19. A process or apparatus as in any previous claim wherein retained sludge from a filtration membrane is recycled to an aerobic or anoxic or aerobic/anoxic zone upstream of a granule settling zone.

20. A process or apparatus of any previous claim wherein liquid is removed from an anaerobic zone and phosphorous is precipitated from the liquid.

21. A process or apparatus according to any previous claim having a membrane filter in communication with an aerobic tank having an HRT of at least 4 hours.

22. A process in which granules or other dense bio-agglomerates are transported continuously or intermittently from a granule settler to an anaerobic zone.

23. A process having granular and biologically active flocculent sludges comprising steps of recycling biologically active floes retained by a membrane or floe settler downstream of a granule settler to an aerobic or anoxic or anaerobic/anoxic zone upstream of the granule settler.

24. Any process or apparatus comprising one or more process steps or apparatus elements selected from the set of all apparatus elements and process steps discussed in this document.