System and method for intensifying a sequencing batch reactor

Abstract

Systems and methods to overcome the limitations of a sequencing batch reactor, SBR, to accommodate nutrient removal and higher loading rates by separating the sludge residence time, SRT, of slow growing organisms, often nutrient removing organisms, and SRT of faster growing organisms. SRT uncoupling is achieved by introducing a biofilm support media with a specific gravity more than one (1), retaining the biofilm support media inside the SBR during regular operation, adding a controllable mixer to maintain the support in suspension and adjust mixing power for different stages of operation of the SBR as needed to optimize biofilm performance, adding a support media mixed liquor separator for retaining the biofilm support media within the SBR during sludge wasting.

Description

SYSTEM AND METHOD FOR INTENSIFYING A SEQUENCING BATCH REACTOR CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of US Provisional Patent Application Serial No.63 / 750,287 filed January 28, 2025, entitled “SYSTEM AND METHOD FOR INTENSIFYING A SEQUENCING BATCH REACTOR”. The above-identified patent application is hereby incorporated by reference in its entirety into the present patent application.BACKGROUND

[0002] Existing water resource recovery facilities, WRRF, often face the need to expand their treatment process to accommodate the new regulatory effluent requirements or to accommodate larger loads and flows reaching the facility or both. Many of these facilities have limited space for expanding their footprint to accommodate additional process functionality or flow and load capacity. Intensification of existing treatment processes is then an option where new processes are developed with more process flexibility for achieving removal of contaminants, for example enhanced removal of nutrients, and / or more capacity to treat larger flows and mass loads to the process. The present invention describes a novel intensification process for enhanced removal of nutrients and enhanced capacity for processing flows and loads in sequencing batch reactors.

[0003] The sequencing batch reactor (SBR) is a type of activated sludge process for wastewater treatment where aeration, settling, and decanting occur in a single tank in a time-sequenced manner. This process operates in a series of discrete phases, each serving a specific purpose in the treatment cycle, FIG.l. The typical operational phases of an SBR are: Fill Phase where wastewater to be treated is introduced to the tank. React Phase where active microbial treatment of wastewater takes place, microorganisms grow and form flocs, sludge, mixing with the wastewater forming a mixture customarily referred to as mixed liquor. Settle phase where separation of water and sludge flocs in the mixed liquor takes place. Decant Phase where the clarified treated wastewater, substantially devoid of flocs, is removed from the system as treated water. Idle Phase is an optional phase where the tank is waiting to receive more influent wastewater. It is important to emphasize for the purpose of this invention that a parallel phase takes place when excess sludge floc produced as a result of bacterial growth and accumulation of non-degradable components in the influent wastewateris removed from the system. Removal of excess sludge is commonly referred to as wasting sludge or simply as wasting. The ratio of the total amount of sludge inside a tank in the SBR to the amount of sludge that is wasted is the sludge residence time or SRT. SRT is a critical variable in the operation of an SBR, in particular when nutrient removal is part of the treatment objectives of the SBR. These phases are repeated in a cycle, with the duration of each phase depending on factors such as the influent characteristics, treatment goals, and system design.

[0004] The SBR's flexibility in operational timing allows for customizable treatment processes, making it suitable for a wide range of wastewater applications among others removal of nutrients, nitrogen and phosphorus. Sequencing batch reactors usually experience limitations for accommodating flows and loads increases beyond design as reaction and clarification of wastewater occurs in the same tank. Microorganisms responsible for biological degradation of contaminants and removal of nutrients grow and aggregate forming flocs, customarily referred to as sludge, and when mixed with wastewater in process of treatment with the SBR, the mixture is referred to as mixed liquor. In an SBR treated water and sludge flocs are separated by settling in the same reaction tank. Two layers are formed in the tank, one a sludge layer in the bottom and a clarified treated wastewater layer on the top. Time for settling can be limiting for treatment. With increase in flows and loads settling the velocity of the sludge layer is often limiting the overall capacity of the SBR system. Increase loads to the SBR result in a more concentrated mixed liquor, slowing clarification, leading to overall limitations.

[0005] One way of controlling the concentration of mixed liquor at increased flows and loads is to reduce the sludge residence time, SRT, by removing, wasting, from the tank more of the sludge, e.g. increase wasting of mixed liquor. However, SRT, reduction has process limits when nutrient removal is necessary. The microorganisms responsible for nutrient removal are usually slow growing and too much removal of sludge to reduce SRT might compromise the presence and activity of the microorganisms in the mixed liquor and the achievement of treatment objectives. This is further limited by cold temperatures in wastewater as growth rates of nutrient removing organisms slow down considerably with low temperatures.Nitrification processes, for example, are catalyzed by slow growing bacteria that are further slowed during cold weather. As a result, accommodating flows and loads and achieving nutrient removal criteria is often a challenge for SBR technology.SUMMARY OF THE INVENTION

[0006] In the present invention the limitations of SBR to accommodate nutrient removal and higher loading rates during are overcome by providing means for separating the SRT of slow growing organisms, often nutrient removing organisms, and SRT of faster growing organisms. This is achieved by adding a biofilm support media to the SBR where slow growing organisms can grow attached to the surface of the support forming a biofilm, and the faster growing organisms can be present in the mixed liquor sludge. Mixed liquor and the support media move freely in the tank. The biofilm support media is designed with a specific gravity such that it settles to the bottom of the tank, in the settling phase of the SBR, carrying along the biofilm and retaining the slow growing organisms. Two additional features are necessary to make the process work. One is the provision of additional mixing in the tank to keep the biofilm support in suspension during the different phases of SBR operation. Because of the settling characteristics of the support media under non-aeration modes, the normal SBR mixing intensity is not sufficient to keep the support media in suspension during operation, in particular during anoxic or anaerobic phases of the SBR cycle. Mixing control is desirable also to avoid excessive scouring of the biofilm on the media when in aerobic cycles of the SBR. The second additional feature is the provision of means for separating the mixed liquor from the support media for wasting sludge, and it is of critical importance to this invention as separation of support media and flocs during wasting enables separation of SRTs, e.g one SRT for the microorganisms in the floc and a different SRT for the microorganisms in the biofilm. A screen or a differential settling device are exemplary embodiments of the mixed liquor-support separator, FIG.4 to FIG.6. The separator enables wasting the mixed liquor at faster rates, lowering the SRT of the mixed liquor, as a result the faster growing organisms tend to be in the mixed liquor flocs while the slow growing organisms tend to be attached to the biofilm. This separation of SRTs enables reduction in mixed liquor concentrations^ providing room for additional flows and loads, while giving the slow growing organisms the ability to stay in the system at long SRTs of the biofilm in the support media.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG.1 is an illustration of prior art, a sequencing batch reactor, SBR, and the main phases of operation.

[0008] FIG. IB is an illustration of an exemplary embodiment of the present invention sequencing batch reactor SBR with an main phases of operation.

[0009] FIG. 2 is an illustration of a biofilm support media that can be used in an embodiment of the present invention showing shapes and characteristics.

[0010] FIG.3 illustrates an exemplary embodiment of a controllable mixing installed on a sequencing batch reactor undergoing intensification with the methods and systems of the this invention.

[0011] FIG.4 illustrates an exemplary embodiment of a mixed liquor support media separator installed in a sequencing batch reactor undergoing intensification with the methods and systems of this invention.

[0012] FIG.5 further provides details of the mixed liquor support media separator shown in FIG.4.

[0013] FIG.6 further presents an alternative exemplary mixed liquor support media separator of a differential settling type.

[0014] FIG.7 illustrates a time series of the performance of an SBR prior to the intensification modifications according to this invention.

[0015] FIG.8 further illustrates the time series performance of the same SBR of FIG.7 after undergoing intensification modifications according to the methods and systems of the present invention.DETAILED DESCRIPTION

[0016] FIG.1 illustrates prior art, a sequencing batch reactor and the main phases of operation. The typical operational phases of an SBR are: Fill Phase 105 where wastewater to be treated 101 is introduced to the SBR vessel 107; in this phase typically the sludge 102 microbial floc has settle to the bottom of the tank and the initial water level 103 in the tank is low. The level in the tank is brought to a higher level 104 with the influent wastewater 101 finalizing the fill phase 105. React Phase 109 usually follows the fill phase and typically mixing of the contents of the bioreactors take place forming a mixed liquor 108 by resuspending the sludge flocs containing microorganism, mixing can be accomplished by aeration 109 when the react phase is aerobic or by mechanical means when the react phase includes anoxic or anaerobic reactions. During the react active microbial treatment of wastewater takes place, microorganisms grow and form flocs, sludge, mixing with the wastewater forming a mixture customarily referred to as mixed liquor 108. Settle phase 111 typically follows the react phase and separation of water and sludge flocs in the mixed liquor takes place. Decant Phase 112 where the clarified treated wastewater, substantially devoid of flocs, is removed from the system as treated effluent 114. The level is reduced from andinitial high level 115 to a final lower level 116. Optionally and from time-to-time sludge wasting 113 is usually practiced in this phase. Idle Phase, not shown, is an optional phase where the SBR tank 107 is waiting to receive more influent wastewater. It is important to emphasize for the purpose of this invention that a parallel phase takes place when excess sludge floc produced as a result of bacterial growth and accumulation of non-degradable components in the influent wastewater is removed from the system. Removal of excess sludge is commonly referred to as wasting sludge or simply as wasting 113. The ratio of the total amount of sludge inside a tank in the SBR to the amount of sludge that is wasted is the sludge residence time or SRT, and it is a critical variable in the operation of an SBR, when nutrient removal is part of the treatment objectives of the SBR. Sludge wasting is a fundamental way of controlling SRT and with it the presence of certain microorganisms depending on the growth characteristics. Organisms used for removing nitrogen and phosphorus compounds have slower growth rates and too much wasting of sludge might remove them out of the bioreactor faster than they can reproduce. These phases are repeated in a cycle, with the duration of each phase depending on factors such as the influent characteristics, treatment goals, and system design.

[0017] FIG. IB illustrates an exemplary embodiment of the present invention and an exemplary operation phase sequence, as other exist, similar to those presented in FIG.l for prior art. Three main components of the embodiment of the invention are illustrated, a biofilm support media 110 with a specific gravity such that it settles with the mixed liquor sludge in the settle phase 111, a controllable mixer 301 with capacity to keep the biofilm support media in suspension during the react phase, and a mixed liquor biofilm support separator 401, configured to retain the biofilm support media within the SBR vessel 107 when wasting of sludge 113. Sludge wasting is more advantageously conducted when the sludge has settled as shown in the decant phase 112 but alternative wasting can be practiced as illustrated in FIG.6. This enables separation of SRTs of the biofilm organisms attached to the support media and those organisms that are removed in the wasted sludge. A short SRT for the sludge floc waste lowers the MLSS concentration in the reactor enabling enhanced capacity for influent wastewater treatment. Slow growing organisms can still remain in the system as part of the biofilm attached to the system.

[0018] FIG.2 illustrates a picture and specification of one exemplary embodiment of a biofilm support media 110 that can be used for this invention, as other biofilm supports are possible and someone skilled in the art could find alternative supports. The biofilm support media in this case has a specific gravity of 1.01 - 1.03 to 1.04 -1.06 in the shape of rings ofsize of 25 mm diameter by 4 - 8 mm in thickness. The combination of size and specific gravity enables fast settling of the media in the tank and mixing energy in the order of 5-50 W / m3 is necessary to re-suspend the media after the settle / decant phase. This mixing intensity is usually larger than the mixing necessary to have the mixed liquor flocs in suspension and as a result increased mixing is necessary as part of the intensification method and system in this invention. Increased mixing is advantageously achieved in this invention by installing a controllable mixer 301. The ratio of the volume in a tank taken by the media to the total useful liquid volume of the tank is called to fill ratio and it is an important variable in the design of the intensification process according to this invention.

[0019] FIG.3 illustrates a reduction to practice of an exemplary embodiment of a controllable mixer 301 installed on a sequencing batch reactor undergoing intensification with the methods and systems of this invention.

[0020] FIG.4 illustrates a reduction to practice of an exemplary embodiment of a mixed liquor support media separator 401 installed in a sequencing batch reactor undergoing intensification with the methods and systems of this invention. The separator is installed within the SBR tank and enables mixed liquor to pass into an isolated compartment elevated from the floor through a perforated plate acting as a perforated screen 402. The perforated screen 402 walls surround an existing SBR pump used for wasting mixed liquor and effectively isolating the compartment from turbulence in the main SBR reaction chamber. Mixed liquor passes through the walls while the support media 110 stays behind, within the main reaction tank of the SBR. The mixed liquor inside the isolated compartment settles allowing wasting 113 of a more concentrated sludge, beneficial for the overall performance of excess sludge processing downstream.

[0021] FIG.5 further provides details of the mixed liquor support media separator 401 shown in FIG.4 and used in the reduction to practice of this invention. The perforated plate 402 used in this embodiment is illustrated here, separation is exemplary achieved here by sieving, size and dimensions of the perforated portion of the device can change according to design to effectively allow settled mixed liquor sludge to pass through while retaining outside the support media 110.

[0022] FIG.6 further presents and alternative exemplary mixed liquor support media separator of differential settling type. A set of baffles is installed within the SBR tank form a support media settler 601 creating a quiescent zone 602. Mixed liquor 108 and media enter the quiescent zone and velocities of settling in the quiescent zone are calculated to allow mixed liquor to pass through and support media 110 with much higher settling velocities tosettle and return by gravity to the main SBR reaction chamber. Influent 101 displaces support free mixed liquor 603 and wasting of sludge can be achieved this way. Other types of differential settling devices can be designed including cyclonic type devices as this is only an illustration of a differential settling application for support media separation for wasting.

[0023] FIG.7 illustrates a time series of performance of an SBR prior to the intensification modifications according to this invention. The plant is in the state of Pennsylvania and is subject to strict limits of ammonia discharge. The graph shows data for water temperature, and ammonia concentration in the effluent of the SBR plant for April of 2021 to April of 2024. It is observed that the plant nitrifies ammonia during the summer but in the fall as the water temperature drops ammonia concentration increases indicating loss of nitrification activity through fall, winter and spring, and only recovering until the summer. Three annual cycles are observed in the graph with similar performance.

[0024] FIG.8 further illustrates the time series of performance of the same SBR illustrated in FIG.3, FIG.4 and FIG.7 after undergoing the intensification modifications according to the methods and systems of the present invention compared to the performance of the same unit in the previous year, 2023 for the same season. Intensification modifications were installed in the fall of 2024 in one SBR. The arrow points to the black round data points showing the performance of the intensified SBR. Ammonia nitrification was achieved shortly after the modifications despite low temperatures indicating the benefits of this invention.

[0025] Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Claims

CLAIMSWhat is claimed is:

1. A method for intensifying a sequencing batch reactor by:a. adding a biofilm support media with specific gravity higher than 1 to a sequencing batch reactor forming a mixture of mixed liquor and support media,b. retaining the biofilm support media in the sequencing batch reactor during operation,c. adding a mixed liquor biofilm support media separator to the sequencing batch reactor for separating the mixed liquor from the media for wasting of mixed liquor,d. wasting mixed liquor from the sequencing batch reactor to independently control the mixed liquor sludge residence time, e. adding one or several mixers to control mixing intensity in the sequencing batch reactor as needed.

2. The method of Claim 1 where the specific gravity of the media is between 1.01 and 1.1.

3. The method of Claim 1 where the fill ratio of media in the sequencing batch reactor is between 1% and 5%, or between 5% and 10%, or between 10% and 50%.

4. The method of Claim 1 where the retention of the media during operation of the sequencing batch reactor is by settling.

5. The method of Claim 1 where the separation of the media and the mixed liquor form mixed liquor wasting is conducted by sieving or by settling or by floating or by centrifugal force.

6. The method of Claim 1 where the sludge residence time of the mixed liquor is controlled between 1 and 10 days.

7. The method of Claim 6 where the sludge residence time is adjusted seasonally to induce nitrification.

8. The method of Claim 1 where the mixing intensity of the mixers is adjustable between 0 to 50 W / m3.

9. The method of Claim 4 where the selection of the media specific gravity and the settling time of the sequencing batch reactor is controlled to separate themedia and a substantial portion of the mixed liquor is earned away with the effluent.

10. The method of Claim 8 where the mixing intensity is adjusted during aerobic, or anoxic or anaerobic operation stages.

11. A system for intensifying a sequencing batch reactor comprising: a sequencing batch reactor, a source of biofilm support media with specific gravity higher than 1, a separator of mixed liquor and support media, an adjustable mixing subsystem configured to control mixing in the sequencing batch reactor and maintain the biofilm support media in suspension as needed, and pipes, valves, fittings, connectors, pumps and appurtenances to fluidly connect the above- mentioned parts of the system, an optional set of electrical instrumentation and controls to integrate the operation of the parts, and where:a. the sequencing batch reactor is configured to receive and retain the biofilm support media, andb. the separator of support media and mixed liquor is fluidly connected to the sequencing batch reactor, and.c. the separator of support media and mixed liquor is configured to retain the support media in the sequencing batch reactor when wasting mixed liquor, andd. the adjustable mixing subsystem is electrically controlled.

12. The system of Claim 11 where wasting of mixed liquor is conducted to control mixed liquor SRT between 1 day and 10 days13. The system of Claim 11 where the biofilm support media has a specific gravity between 1.01 and 1.1.

14. The system of Claim 11 where the biofilm support is delivered to till between 1% and 5% or the volume of the sequencing batch reactor, or between 5% and 10%, or between 10% and 50%.

15. The system of Claim 11 where the mixing subsystem intensity is adjustable between 0 to 50 W / m3.

16. The system of Claim 11 where the separator of mixed liquor and support media is a perforated plate, or a screen.

17. The system of Claim 11 where the separator of mixed liquor and support media is differential settling or a cyclonic device.

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