Patent Application
20250091920
Wastewater treatment plants (WWTPs) are driven to cost-effectively optimize their treatment process to produce treated water for discharge to the environment which meets environmental regulations established by governmental bodies. As the understanding of the nutrient loadings that receiving water bodies can sustain before suffering environmental degradation continues to improve, more stringent regulations have been introduced for the permissible nutrient levels in the treated effluent discharged from WWTPs. The introduction of these stringent regulations has presented a challenge to many WWTPs to reliably meet low nutrient limits in their treated effluent.
Nutrients enter into wastewater primarily through human waste, synthetic detergents, and various industrial processes. Excess discharge of these nutrients to receiving water bodies can lead to eutrophication, which accelerates the degradation in the aquatic ecosystem diversity and overall quality of the water body. The treatment of the nutrients present in wastewater is accomplished through biological nutrient removal (BNR). In BNR, various environments are provided to selectively grow bacteria which perform biochemical reactions that result in the removal of nutrients from the wastewater. Many of the bacteria involved with BNR require simple organic compounds, primarily in the form of volatile fatty acids (VFAs), to perform biochemical nutrient removal process and gain energy to grow. However, many WWTPs receive insufficient biodegradable organic material in their influent wastewater to generate the quantity of VFAs necessary to achieve the level of BNR required to meet stringent environmental regulations.
Fermentation is a process in which VFAs are generated from the anaerobic digestion of organic material and consists of two primary steps: hydrolysis and acetogenesis. Hydrolysis involves the conversion of biodegradable organic material to soluble organic acids, where acetogenesis then converts these soluble organic acids into VFAs. If the anaerobic digestion process is allowed to continue, methanogenesis will proceed and the VFAs generated will subsequently be converted to methane. Thus, the solids retention time (SRT) of a fermentation process is a parameter which must be optimized to provide enough time allowing for maximal hydrolysis and acetogenesis but ensures that the time provided is insufficient to allow for methanogenesis. Traditional fermentation processes have utilized the sludge generated from primary sedimentation clarifiers to produce VFAs for use in downstream BNR processes. However, many WWTPs do not incorporate primary sedimentation clarifiers in their treatment processes and subsequently do not have the option to ferment primary sludge to generate VFAs.
Return activated sludge (RAS) or mixed liquor suspended solids (MLSS) fermentation is an alternative to primary sludge fermentation which enables WWTPs that do not have primary sedimentation clarifiers to have the ability to produce VFAs for use in their BNR processes. RAS fermentation is typically performed by sending a small percentage (≤ 10%) of the RAS flow to a side-stream fermentation tank, where the RAS solids are retained in the tank for more than two days to allow for anaerobic digestion to proceed. MLSS fermentation is typically performed by contacting RAS with influent wastewater in an anaerobic tank to form mixed liquor, where a small percentage (≤10%) of the anaerobic mixed liquor is then sent to a side-stream fermentation tank to ferment. While RAS fermentation can generate sufficient VFAs, MLSS fermentation may be better suited for the support of BNR processes. This is because in MLSS fermentation, RAS is first contacted with influent wastewater, where soluble, particulate, and colloidal biodegradable carbon is adsorbed by the activated sludge flocs. MLSS fermentation allows for these adsorbed biodegradable carbon sources to also be fermented to form VFAs in addition to the VFAs generated from the anaerobic digestion of the RAS. This enables MLSS fermentation to yield more VFAs than RAS fermentation alone, while also enhancing the survival of bacteria involved with BNR as there is more fermentable substrate.
With currently available technologies for MLSS fermentation, it is difficult to reliably produce a consistent stream of VFAs to meet the needs of BNR processes. This stems from the inability of these technologies to directly monitor the microbial activity occurring in mixed liquor fermenters. As such, many WWTP operators find it challenging to optimize these technologies as there is limited to no direct feedback from the microbial activity due to operational changes. Furthermore, these technologies do not provide an unambiguous way to control the SRT of the fermenter other than through controlling the influent flowrate of mixed liquor (i.e. HRT=SRT). Consequently, the footprints of MLSS fermentation tanks are often sufficiently larger than would be necessary in a system where the SRT can be controlled.
What is needed, but not yet available, is a method of monitoring the real-time microbial activity within a mixed liquor fermenter to allow for the fermentation performance to be optimized to produce a fermentate with the desired quantity of VFAs to support the varying BNR needs of WWTPs.
Discloses a BES for monitoring the response of exo-electrogenic bacteria to one or more agents in oxygenated water or wastewater in a water treatment system.
Method for detecting and addressing system imbalances due to delivery of cleaning agents.
Key disadvantage—Application is for oxygenated environments. Intended for the optimization of aerobic wastewater treatment processes. Not suited for anaerobic fermentation environments.
Although the real-time metabolic activity in wastewater treatment processes can be monitored with this invention, the main application of this disclosure appears to be for optimizing membrane-based wastewater treatment processes through detecting and addressing system imbalances due to delivery of cleaning agents to a fouled membrane or up-stream treatment equipment.
Discloses a BES for monitoring and controlling one or more organic carbon compounds in a wastewater treatment system.
Provides methods for controlling nitrogen and phosphorus removal processes in wastewater treatment processes through the controlled delivery of one or more organic carbon compounds.
Main disadvantage—Only monitors organic carbon compound levels in wastewater treatment processes to facilitate the controlled delivery of said organic carbon to facilitate nitrogen and phosphorus removal. Disclosure does not describe how the BES can be implemented to control fermentation for the production of organic carbon compounds (i.e. VFAs).
Only discloses a system and method for monitoring BOD using a BES. Does not detail how the BOD reading can be utilized for wastewater treatment process optimization.
Discloses the Unified Fermentation and Thickening (UFAT) process.
Requires WWTPs to have primary clarifiers to produce a stream of primary sludge to ferment to generate VFAs for use in BNR processes.
Many WWTPs do not have primary clarifiers in their process and thus this process is limited in its application.
Side-stream mixed liquor fermentation reactor operated at a long HRT (2-days) and without mixing to ensure an SRT is reached to allow for acetogenesis to occur. This is not ideal as it requires a large reactor footprint and/or low flowrates.
No mixing in side-stream mixed liquor fermentation reactor makes it difficult to control the SRT of the reactor. If solids stay too long in the system, then methanogenesis will occur and consume the generated VFAs, thus decreasing the VFA production efficiency.
Utilizes a dissolved air flotation (DAF) unit to separate solids from the influent wastewater and directs the floated solids to a side-stream fermenter. It is not ideal to have a DAF positioned on the main-stream treatment line as DAF units have limited capacity, are sensitive to temperature changes, can be complex and require skilled operators, and DAF units require the use of chemical coagulants or flocculants which can be operationally expensive.
Utilizes solid electrodes to provide reducing equivalents to yield tunable fermentation products within a microbial fuel cell (MFC) reactor configuration.
The downside to this invention is that solids electrodes are required to drive the fermentation process, which may be both expensive and complex to operate for full-scale implementations at WWTPs.
MFCs also have limited capacity and likely would not be suitable for mixed liquor fermentation applications.
This invention disclosure provides a system and method for controlling the fermentation of MLSS to optimize the endogenous production of VFAs for the BNR needs of WWTPs. The system provides an anaerobic mixed liquor fermentation tank (AnMLFT) which receives the controlled delivery of RAS and screened and de-gritted wastewater (SD-WW). The AnMLFT is equipped with a mixing device whose mixing intensity can be adjusted in a controlled manner with a variable frequency drive (VFD), motor, and/or solenoid valve. The system also incorporates a biosensor suspended in the AnMLFT basin to monitor the real-time soluble biodegradable carbon utilization rate (SBCUR). A control unit is incorporated into the system to allow for adjustments to be made to the operation of the AnMLFT at least partially in response to the real-time SBCUR data recorded by the biosensor. These operational adjustments may be initiated by the control unit when real-time SBCUR readings from the biosensor deviate beyond thresholds set to optimize the fermentation of MLSS. The system allows for automated adjustments to be made to the rate of flow of RAS and SD-WW to the AnMLFT in response to real-time SBCUR readings. The system also allows for automated adjustments to be made to the output from the mixing device(s) in the AnMLFT in response to the real-time readings from the biosensor. These operational adjustments allow for the hydraulic retention time (HRT), SRT, and influent RAS-to-SD-WW flow ratio to be modulated in real-time to optimize the fermentation of MLSS in the AnMLFT to yield a fermentate consisting of VFAs within a desired concentration range.
This invention may be embodied in either in-line or side-stream configurations within BNR processes. For in-line embodiments, MLSS fermentation is performed in cycles which coincide with the diurnal loading patterns of WWTPs. Under normal flow conditions, the AnMLFT operates as a typical anaerobic selector tank of an Anaerobic/Anoxic/Oxic (A20) BNR process, where 100% of the RAS and SD-WW are delivered to the tank for a specified HRT. Under low flow conditions (i.e. early morning, 2-4 AM), the soluble biodegradable carbon (SBC) loading to the AnMLFT will be significantly lower than under normal flow conditions, which will be detected by the biosensor through a sharp decrease in SBCUR readings. When this occurs, the control unit will initiate the system to proceed into fermentation mode. In fermentation mode, 100% of the RAS will proceed to the AnMLFT while the rate of flow of SD-WW may be modulated to target a specified HRT and/or RAS to SD-WW flow ratio which optimizes MLSS fermentation. The initiation of the system into fermentation mode will also include diverting the mixed liquor recycle (MLR) discharge location within the pre-anoxic basin of a BNR process to be diverted further downstream in the pre-anoxic basin such that a larger anaerobic volume can be developed. Fermentation mode will also signal to the mixing device(s) in the developed anaerobic volumes of a BNR process to adjust their output to provide a mixing intensity which allows for solids to accumulate such that an SRT which optimizes MLSS fermentation can be provided in the anaerobic volumes. When the influent to a WWTP begins to return to normal flow conditions in response to diurnal loading patterns, the SBC loading to the AnMLFT will be significantly higher than under low flow conditions, which the biosensor will detect through a sharp increase in SBCUR readings. When this occurs, the control unit will cease fermentation mode and return the system back to normal A2O operation. This embodiment allows WWTPs to perform MLSS fermentation within an existing plant footprint without making major infrastructure changes or sacrifice to effluent quality. Additionally, this embodiment enables WWTPs to harvest endogenous sources of VFAs to supplement their BNR processes to allow for enhanced process reliability, robustness, and intensification.
In side-stream embodiments of this invention, the AnMLFT is positioned off the main treatment path of a BNR process. The AnMLFT is equipped with a biosensor such that the real-time SBCUR in the tank can be monitored and utilized to optimize MLSS fermentation. Conduit equipped with flow control devices enables the controlled delivery of RAS and SD-WW from the main-stream BNR process to be made to the side-stream AnMLFT in response to real-time SBCUR readings from the biosensor. Mixing device(s) installed in the AnMLFT can modulate their output through VFDs, variable speed motors, or through solenoid valves to deliver a mixing output which enables solids to accumulate in the system such that an SRT which maximizes acetogenesis can be achieved through real-time SBCUR readings from the biosensor. Conversely, under completely mixed conditions when the HRT of the AnMLFT is equivalent to its SRT, the influent flowrate may be modulated such that the HRT of the AnMLFT is equivalent to the SRT which maximizes acetogenesis, determined through SBCUR readings from the biosensor. VFA-rich effluent from the AnMLFT is then conveyed to the anaerobic selectors of the mainstream BNR process. This side-stream embodiment of this invention enables real-time optimization of side-stream mixed liquor fermentation processes to consistently yield a VFA-rich effluent to support the BNR needs of WWTPs. Although additional infrastructure is required for this embodiment, the benefit lies with the continuous delivery of VFAs to a BNR process rather than intermittently as detailed in the previous embodiment.
The system and method provided in this disclosure enable MLSS fermentation to be continuously optimized through monitoring the real-time SBCUR within an AnMLFT using a biosensor. Real-time SBCUR readings enable operational changes to be made to an AnMLFT to maximize the production of VFAs through acetogenesis. These operational changes can include adjusting the reactor HRT, SRT, output delivered from mixing devices, and the flow ratio of RAS to SD-WW in the influent. Multiple biosensors may be incorporated into a mixed liquor fermentation system at the inlet, outlet, and/or throughout the system to provide better process control to maximize VFA production. Through optimizing the hydrolytic fermentation activity in MLSS fermentation reactors with this invention, WWTPs can achieve more robust and reliable BNR performance with less dependence on influent SBC loadings and exogenous chemical addition. Overall, this invention allows WWTPs to intensify their process through improving their carbon management efficiency to reliably meet stringent environmental regulations.
The biosensor may also be utilized to optimize the mixing intensity within a fermentation reactor, as depicted in
The invention disclosed herein provides multiple advantages over prior art. The primary advantage of the invention is that the real-time SBCUR within a mixed liquor fermentation reactor can be directly monitored such that the process can be optimized to yield the desired production of VFAs required for the BNR needs of a WWTP. Previous inventions incorporating mixed liquor fermenters for VFA production (see U.S. Pat. No. 7,285,215) are operated with low influent flowrates to yield reactor HRTs that are equivalent to the SRT needed for acetogenesis. While these previous inventions enable the production of VFAs from mixed liquor to support BNR, they are difficult to optimize with changing influent characteristics as there is no direct feedback from the microbial activity within the system. Furthermore, designing mixed liquor fermenters with an HRT equivalent to the SRT needed for acetogenesis (≥2 days) results in large reactor footprints (increased capital costs) and/or low flowrates.
This invention enables WWTPs which do not have primary sedimentation clarifiers, and subsequently access to primary sludge, incorporated into their treatment processes to have the ability to endogenously produce VFAs for use in their BNR processes in an optimized manner from mixed liquor fermentation. This allows for BNR processes to be more efficient, reliable, robust, and can move BNR process performance towards becoming independent from variable influent nutrient loadings.
Another advantage of the invention provided in this disclosure is that it can be retrofitted into existing in-line or side-stream mixed liquor fermentation reactors to optimize their performance without making major changes to the existing infrastructure.
A biosensor incorporated into an anaerobic mixed liquor fermentation reactor allows for the real time monitoring of the SBCUR within AnMLFTs, which can enable real time process optimization to yield the desired production of VFAs required for the BNR needs of a WWTP. Real-time microbial activity monitored through SBCUR readings using a biosensor allow for real-time process optimization of MLSS fermenters through modulating the reactor HRT, SRT, and the RAS-to-SD-WW flow ratio in the influent.
The method of MLSS fermentation control provided through this invention can be embodied as an in-line configuration within a wastewater treatment process, as depicted in
The in-line configuration of this invention may be best embodied through having effluent from the AnMLFT 306 flow into a modified Ludzack-Ettinger (MLE) process. Preferably, the pre-anoxic basin of MLE process would consist of two or more anoxic tanks in series where the MLR discharge location can be varied between the individual anoxic tanks with a flow diversion device 316, as depicted in
In an alternative embodiment, the method of MLSS fermentation control detailed in this disclosure can be applied in a side-stream configuration within a continuous flow biological wastewater treatment process, as depicted in
The side-stream embodiment of this invention allows for the continuous optimization of MLSS fermentation to yield the desired production of VFAs to support the BNR needs of a WWTP. The biosensor 417 suspended in the AnMLFT 415 detects real-time changes in the SBCUR. When the SBCUR readings from the biosensor 417 deviate beyond a threshold range set to optimize MLSS fermentation, specific changes are made to the operation of the AnMLFT 415 by the control unit 418. These operational changes can include modulating the influent flowrate (i.e. reactor HRT), reactor SRT, and influent RAS to SD-WW flow ratio. Operational changes to the AnMLFT 415 may also be implemented through the real-time SBC concentrations monitored in the influent SD-WW using the biosensor 426. These operational changes may be implemented to target a desired influent SBC loading to the AnMLFT 415 and/or to target a desired food-to-microorganism ratio (F:M) in the AnMLFT 415.
In either embodiment, the performance of the AnMLFT may be optimized through keeping the operating parameters constant while only allowing for one parameter to vary and observing the change in values measured using a biosensor. For instance, this can be done by keeping the reactor HRT (i.e. influent flowrate) and mixing intensity constant, while only allowing the percentage of RAS in the influent to vary. This will allow for the percentage of RAS in the influent flow which maximizes the production of VFAs through acetogenesis to be determined. With the optimum RAS percentage in the influent flow then held constant, the reactor HRT can then be varied to determine the HRT which maximizes acetogenesis and the production of VFAs. With the optimum reactor HRT then held constant, the mixing intensity can then be varied to determine the mixing intensity which maximizes acetogenesis. Furthermore, the SRT of the AnMLFT can also be varied through on/off cycling the mixing device to allow for the accumulation of solids in the reactor. The time interval between when the mixing device is on and when the mixing device is off determines the extent of solids accumulation in the reactor. By varying this time interval and recording the output from the biosensor, the optimum SRT of the fermentation reactor can be determined. Continuous optimization, whether manual or through an algorithm, allows for the continuous optimum production of VFAs through mixed liquor fermentation to supplement the BNR needs of a WWTP.
A flow chart which depicts how the control unit 311, 418 in either embodiment would perform the abovementioned performance optimization process is provided in
A comparator 706 may also be included in the control unit 311, 418 and be linked to the divider 702 and the memory 705 for comparing successive rates of SBCUR change per unit operational parameter adjustment quotients to determine whether the rates of SBCUR change are increasing or decreasing with respect to each unit of operational parameter adjustment. To change the variable operational parameter 701 to the end of maximizing the rate of SBCUR increase per unit of adjustment, the control unit 311, 418 is configured with an operating parameter reset module 707 to operate an actuator 708 which adjusts the variable operational control parameter 701. Operating parameter reset module 707 receives successive measures from the comparator 706 and memory 705 to determine the direction (increase or decrease) in which to adjust the variable operational control parameter 701. In this completely automated embodiment, the control unit 311, 418 automatically adjusts the actuator 708 in response to the rate of change in SBCUR per unit of adjustment made to the operational control parameter 701 as calculated by the divider 702. The comparator 706 automatically compares successive SBCUR rate change calculations and the operating parameter reset module 707 automatically adjusts the actuator 708 in accordance with the rates of SBCUR change per unit adjustment to the variable operational control parameter 701 as determined by the operation of the comparator 706.
In some cases, the variable operational control parameter 701 may be restrained by minimum or maximum values with respect to its operation. The control unit 311, 418 is equipped with an additional comparator 709 connected to the memory 705 and the parameter reset module 707 for ensuring that the pre-selected maximum or minimum values for the variable operational control parameter 701 are not exceeded. The comparator 709 compares a prospective operational adjustment from operating parameter reset module 707 with reference to values stored in memory 705 and informs the operating parameter reset module 707. If a minimum or maximum operational value would be breached by an impending adjustment, operating parameter reset module 707 determines additional prospective adjustments to avoid exceeding a minimum or maximum value. The various functional building blocks of the control unit 311, 418, particularly comparators 706, 709, divider 702, and parameter reset module 707 may take the form of hard-wired logic circuits or, alternatively, generic digital processing circuits of a microprocessor modified by programming to carry out the intended functions. Through performing the SBCUR optimization process described above and illustrated in
For control of the entire MLSS fermentation system, depicted in
To regulate each respective operational control parameter of the AnMLFT 306, 415 to the end of containing the SBCUR readings within a set threshold range, the control unit 311, 418 includes an operating parameter reset module 809 to operate various actuators 810, 811, 812 which adjust the output of each respective operational control parameter. Operating parameter reset module 809 receives successive data from comparator 808 and memory 807 and determines the adjustments needing to be made to each respective actuator 810, 811, 812 to elicit a change in SBCUR readings from the biosensor 310, 417 estimated to be sufficient to return them to within a set threshold range. In a completely automated embodiment, control unit 311, 418 automatically adjusts actuators 810, 811, 812 in response to real-time SBCUR readings from the biosensor 310, 417 and the input from each operational control parameter as determined by the divider 801.
A control process for MLSS fermentation optimization may include the setting of minimum and maximum RAS flowrates for restricting the MLSS loading to desired limits. In this case, control unit 311, 418 provides an additional comparator 814 connected to memory 807 and the operating parameter reset module 809 for ensuring that the pre-selected maximum or minimum RAS flow values are not exceeded. Comparator 814 compares a prospective adjustment to the RAS flow control device actuator 810 from the operating parameter reset module 809 with reference to values stored in memory 807 and informs the operating parameter reset module 809. If a RAS flowrate limit is met or exceeded by an impending adjustment, operating parameter reset module 809 determines additional prospective adjustments to actuators 810, 811, 812 which avoid exceeding pre-selected MLSS loading limits while still allowing for the SBCUR readings from the biosensor 310, 417 to be adjusted to within a set threshold range.
Similarly, a control process for MLSS fermentation optimization may include the setting of minimum and maximum SD-WW flowrates for restricting the SBC loading to desired limits. In this case, the control unit 311, 418 provides an additional comparator 815 connected to memory 807 and the operating parameter reset module 809 for ensuring that the pre-selected maximum or minimum SD-WW flowrates are not exceeded. Comparator 815 compares a prospective adjustment to the SD-WW flow control device actuator 811 from the operating parameter reset module 809 with reference to the values stored in memory 807 and informs the operating parameter reset module 809. If an SD-WW flowrate limit is met or exceeded by an impending adjustment, operating parameter reset module 809 determines additional prospective adjustments to actuators 810, 811, 812 which avoid exceeding pre-selected SBC loading limits while still allowing for the SBCUR readings from the biosensor 310, 417 to be adjusted back to within a set threshold range.
A control process for MLSS fermentation optimization may also include the setting of minimum and maximum outputs provided by the mixing device(s) for restricting the mixing output provided in the AnMLFT to desired limits. In this case, the control unit 311, 418 provides an additional comparator 816 connected to memory 807 and the operating parameter reset module 809 for ensuring that the pre-selected maximum or minimum mixing outputs are not exceeded. Comparator 816 compares a prospective adjustment to the mixing device actuator 812 from the operating parameter reset module 809 with reference to the values stored in memory 807 and informs the operating parameter reset module 809. If a mixing output limit is met or exceeded by an impending adjustment, operating parameter reset module 809 determines additional prospective adjustments to actuators 810, 811, 812 which avoid exceeding pre-selected mixing limits while still allowing for the SBCUR readings from the biosensor 310, 417 to be adjusted back to within a set threshold range.
For in-line embodiments of this invention, an additional actuator 813 which controls the MLR flow diversion device 316, and a timer 817 is incorporated into the operational flow of the control unit 311. The MLR diversion actuator 813 is operatively connected to the operating parameter reset module 809 such that the MLR flow diversion device 316 may be automatically adjusted by the control unit 311. The timer 817 is operatively linked to the divider 801, memory 807 and the operating parameter reset module 809. Under normal flow conditions, the control unit 311 sits idle and the output for the operational control parameters for the AnMLFT 306 are set to constant values established for A2O operation. Once the divider 801 receives inputs from SD-WW flowmeter 307 and/or the SD-WW biosensor 325 that are below a low-flow threshold, the divider 801 sends a signal which initiates the timer 817. The initiated timer 817 then directs the operating parameter reset module 809 to adjust the actuators of the operational control parameters 810, 811, 812, 813 to the outputs which were in place when the previous MLSS fermentation cycle terminated, as stored in the memory 807. The control unit 311 will then proceed to automatically adjust the operational control parameter actuators 810, 811, 812, 813 in response to the SBCUR readings from the biosensor 310. The control unit 311 will continue to remain in operation until the timer 817 reaches the average low-flow time, as stored in the memory 807. When the average low flow time expires, the operating parameter reset module 809 will adjust the operational control parameter actuators 810, 811, 812, 813 back to the constant output values established for normal A2O operation and the control unit 311 will then revert to idle mode. Alternatively, fermentation mode may also be terminated by the SD- WW flowmeter 307 and/or the SD-WW biosensor 325 readings rising above a low-flow threshold before the average low flow time expires on the timer 817.
For side-stream embodiments, the timer 817 incorporated into the control unit 418 may be utilized to specify the time interval between when adjustments may be made to the variable operational control parameters of the AnMLFT 415. For instance, when operating parameter reset module 809 makes an adjustment to the operational control parameter actuators 810, 811, 812 in response to real-time SBCUR readings from the biosensor 417, the timer 817 is initiated. The control unit 418 will then sit idle until a pre-determined period of time has elapsed, wherein the timer 817 will then reinitiate the operating parameter reset module 809 to continue to make adjustments if the SBCUR readings from the biosensor 417 are still outside of a set threshold range.
As the MLR flow diversion device 316 is not included in the side-stream embodiment of this invention, subsequently the MLR flow diversion actuator 813 would not be included in the operation of the control unit 418 for side-stream embodiments.
A WWTP has an in-line embodiment of the disclosed invention, similar to the process depicted in
With sufficient data collected under normal A2O operation by the control unit
311, the parameters for a control process for an in-line embodiment of cyclic MLSS fermentation can be determined and optimized. The initiation of the system to proceed from A2O operation into fermentation mode may be induced through SBC readings from the SD-WW biosensor 325 falling below a low flow SBCUR reading threshold (Y2) and/or SD-WW flowrate readings falling below a low flow threshold (Y1). When one or more low flow thresholds have been exceeded, fermentation mode is initiated, and the timer 817 is started. In this example, the RAS flowrate to the AnMLFT 306 is held constant from normal A2O operation and the SD-WW flowrate is not controlled. Thus, the mixing output provided in the AnMLFT 306 by the mixing device(s) 309 is the sole operational control parameter which may be varied under fermentation mode. With the initiation of the system into fermentation mode, the MLR discharge is diverted with the flow diversion device 316 from the first tank of the pre-anoxic basin 312 to the second tank, effectively increasing the anaerobic volume while maintaining a pre-anoxic volume sufficient to sustain the nitrogen removal required of the BNR process 302. Furthermore, the output from the mixing device(s) 309 is reduced from above a mixing output threshold (Y3) which completely-mixes the contents of the AnMLFT 306 and the first tank of the pre-anoxic basin 312 to below the mixing output threshold (Y4) which results in the formation of a sludge blanket, as illustrated in panel “c” in
A WWTP has a side-stream embodiment of the disclosed invention, similar to the process depicted in
For control of the AnMLFT 415, the SBCUR readings from the biosensor 417 are utilized to indicate when operational adjustments are needed. When an SBCUR threshold is exceeded, the mixing device output is adjusted by a predetermined magnitude (Δyt) estimated by the control unit 418 to bring the SBCUR readings back to within a threshold range. The control unit may make additional adjustments of a predetermined magnitude (Δyt) to the output of the mixing device 416 if after a predetermined interval of time (Δt) has elapsed and the SBCUR readings have not changed by an anticipated magnitude. For side-stream embodiments, the timer 817 in the control unit 418 may be utilized to keep track of the time that has elapsed since adjustments have been made to output from the mixing device 416 to inform the operating parameter reset module 809 when a predetermined interval of time (Δt) has been reached. In the case where the maximum SBCUR threshold (Y1) is exceeded, this would indicate that too much SBC is being generated in the AnMLFT 415 for the needs of the mainstream BNR process (402) and consequently that the SRT is too long for optimized MLSS fermentation. In this scenario, the SRT of the AnMLFT 415 would be incrementally reduced by the operation of the control unit 418 directing the mixing device 416 to incrementally increase its output such that more solids are wasted in the effluent of the AnMLFT 415. For the case where the SBCUR readings from the biosensor 417 fall below the minimum SBCUR threshold (Y2), this would indicate that insufficient SBC is being produced from MLSS fermentation to support the needs of the mainstream BNR process 402 due to the SRT of the AnMLFT 415 being too short. In this scenario, the SRT of the AnMLFT 415 would be incrementally increased by the operation of the control unit 418 directing the mixing device 416 to incrementally reduce its output such that more solids are retained within the AnMLFT 415. When the SBCUR readings from the biosensor 417 are within the maximum and minimum SBCUR thresholds (Y1 and Y2, respectively), the output from the mixing device 416 is held constant until future threshold deviations are detected.
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.
This application claims benefit of provisional application Ser. No. 63/539,233, filed Sep. 19, 2023.
| Number | Date | Country | |
|---|---|---|---|
| 63539233 | Sep 2023 | US |
