Wastewater treatment system, method for controlling it and method for retrofitting a wastewater treatment system

Abstract

A wastewater treatment system comprising:a sequencing batch reactor vessel configured to perform biological treatment of wastewater in a series of treatment phases including a fill phase, a bioreaction phase, a sludge settling phase in which solids settle from the wastewater to form a sludge and a low-solids supernatant, a low-solids supernatant withdrawal phase, and a standstill phase, wherein the fill phase comprises introducing a non-predetermined amount of wastewater into the vessel;a liquid level sensor configured to measure a liquid level in the vessel and provide an indication of the level of the liquid to a controller;anda sludge detector configured to measure a position of an interface between the sludge and the low-solids supernatant in the vessel and provide an indication of the position of the interface to the controller, and further determine a severity of the interface and provide an indication of the severity of the interface to the controller,wherein the controller is configured to make a comparison between the level of the liquid and the position of the interface and, based on the comparison, control an amount of low-solids supernatant removed from the vessel during the withdrawal phase, and vary a rate of removal of the low-solids supernatant based at least in part on the severity of the interface.;

Description

This patent application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application Serial No. 62 / 219,735, entitled "VARYING WATER LEVEL SOLIDS AND TRACKING CONTROL" (Control of Solids and Tracking at Varying Water Level), filed Sep. 17, 2015, which is incorporated herein by reference in its entirety for all purposes.BACKGROUNDAspects and embodiments disclosed herein are generally directed to the structure and operation of sequencing batch reactors (SBR) and control systems therefor.EP 2 078 702 A1 relates to a method for biological waste water treatment plants with so-called SBR (sequencing batch reactor). Document US 5 205 936 A also describes an SBR container. Furthermore, U.S. Pat. No. 5,421,995 A likewise discloses a sequencing batch reactor vessel.SUMMARYAccording to one aspect of the present invention there is provided a system for waste water treatment according to claim 1. The system includes a sequencing batch reactor vessel configured to perform biological processing of wastewater in a series of processing phases including a fill phase, a bio-reaction phase, a sludge settling phase in which solids settle out of the wastewater such that a sludge and low solids supernatant form, a low solids supernatant withdrawal phase, and a still phase. The filling phase comprises introducing an amount of non-predetermined waste water into the container. The system further includes a liquid level sensor configured to measure a liquid level in the container and provide an indication of the level of the liquid to a controller, and a slurry detector configured to measure a position of an interface between the slurry and the low solids supernatant in the container and provide an indication of the position of the interface to the controller. The control device is configured to perform a comparison between the level of the liquid and the position of the interface and to control an amount of low-solids supernatant removed from the container during the withdrawal phase based on the comparison. The mud detector is further configured to determine a degree of sharpness of the interface and provide an indication of the degree of sharpness of the interface to the controller. Further, the controller is further configured to vary a rate of removal of the low solids supernatant based at least in part on the sharpness level of the interface.In some embodiments, the controller is further configured to initiate removal of the low solids supernatant in response to the sharpness level of the interface exceeding a predetermined level.In some embodiments, the controller is further configured to control a rate of sludge removal from the container based at least in part on the sharpness level of the interface.In some embodiments, the controller is further configured to draw low solids supernatant from the container at a rate that maintains a substantially constant depth of supernatant above the interface.In some embodiments, the controller is further configured to control an amount of sludge removed from the container based at least in part on the position of the interface.In some embodiments, the slurry detector includes a plurality of suspended solids sensors, each located at different fixed locations within the vessel. The plurality of suspended solids sensors may include one or more optical or ultrasonic sensors.In some embodiments, the slurry detector includes a sensor that moves vertically in response to a change in the liquid level in the container. The mud detector may include one of an ultrasonic level sensor or a radar level sensor.In some embodiments, the liquid level sensor includes an ultrasonic sensor.In some embodiments, the liquid level sensor includes a plurality of sensors each disposed at different fixed levels in the container.In some embodiments, the liquid level sensor and the mud sensor are comprised of a same sensor.In some embodiments, the mud detector includes an ultrasonic level detector having an operating frequency between about 50 kHz and about 800 kHz.In some embodiments, the mud detector includes a high intensity compressed radar pulse sonar unit.According to another aspect there is provided a method of enabling control of a waste water treatment system according to claim 15. The method includes introducing a volume of wastewater into a sequencing batch reactor vessel of the wastewater treatment system, biologically treating the wastewater in the vessel, maintaining sufficiently quiet conditions in the vessel such that solids settle in the wastewater and form a blanket of settled sludge and a low solids supernatant, measuring a liquid level in the vessel, providing an indication of the level of the liquid to a controller, measuring a position of an interface between the blanket of settled sludge and the low solids supernatant in the vessel, providing an indication of the position of the interface to the controller, performing a comparison between the level of the liquid and the position of the interface with the controller, withdrawing the low solids supernatant from the container and controlling an amount of the low solids supernatant withdrawn from the container based on the comparison. The method further includes determining a degree of sharpness of the interface and providing an indication of the degree of sharpness of the interface to the controller. The method further includes varying a rate of withdrawal of the low-solids supernatant based at least in part on the sharpness level of the interface.In some embodiments, the method further includes introducing the wastewater into the container at a non-predetermined rate.The method may further include initiating the stripping of the low solids supernatant in response to the sharpness level of the interface exceeding a predetermined level. In some embodiments, the method further includes controlling a rate of sludge removal from the container based at least in part on the sharpness level of the interface.In some embodiments, the method further includes controlling an amount of sludge removed from the container based at least in part on the position of the interface.In some embodiments, introducing the volume of waste water into the container includes introducing a non-predetermined volume of waste water into the container.In some embodiments, the method includes controlling a rate of withdrawing low-solids supernatant from the sequencing batch reactor vessel to maintain a substantially constant depth of low-solids supernatant above the interface during settling of the slurry.According to another aspect, there is provided a method of retrofitting a waste water treatment system according to claim 22. The method includes installing a control system in a sequencing batch reactor vessel of the waste water treatment system. The sequencing batch reactor vessel is configured to perform biological processing of wastewater in a series of processing phases including a fill phase, a bioreaction phase, a sludge settling phase in which solids settle out of the wastewater and form a sludge blanket and a low-solids supernatant, a low-solids supernatant withdrawal phase, and a stall phase, wherein the fill phase includes introducing an unrepredicted amount of wastewater into the vessel. The control system includes a liquid level sensor configured to measure a liquid level in the container and provide an indication of the level of the liquid to a controller, and a sludge detector configured to measure a position of an interface between the sludge blanket and the low solids supernatant in the container and provide an indication of the position of the interface to the controller, and further determine a degree of sharpness of the interface and provide an indication of the degree of sharpness of the interface to the controller. The controller is configured to perform a comparison between the level of the liquid and the position of the interface and to control an amount of the low solids supernatant removed from the container during the withdrawal phase based on the comparison and to vary a rate of removal of the low solids supernatant based at least in part on the sharpness level of the interface.BRIEF DESCRIPTION OF THE DRAWINGSIt is not intended that the accompanying drawings be drawn to scale. In the drawings, each identical or approximately identical component illustrated in different figures is represented by an equal number. For clarity, not every component in each drawing may be labeled. Illustrated in the drawings are: FIG. 1A shows a first preparation phase of a sequencing batch reactor; FIG. 1B shows another processing phase of a sequencing batch reactor; FIG. 1C shows another processing phase of a sequencing batch reactor; FIG. 1D shows another processing phase of a sequencing batch reactor; FIG. 1E shows another processing phase of a sequencing batch reactor; FIG. 1F shows another processing phase of a sequencing batch reactor; FIG. 2 shows an embodiment of a wastewater treatment tank; FIG. 3 shows an embodiment of a sensor element used in the wastewater treatment tank in FIG. 2 ; FIG. 4 shows another embodiment of a waste water treatment tank; FIG. 5 shows an embodiment of a wastewater treatment tank; FIG. 6 shows an embodiment of a wastewater treatment tank; FIG. 7 shows an embodiment of a wastewater treatment tank; FIG. 8 illustrates a control system for embodiments disclosed herein; FIG. 9 shows a storage system for the control system in FIG. 8 ; FIG. 10 illustrates levels of liquid and sludge in a sequencing batch reactor measured over time with embodiments of a sensor system disclosed herein; FIG. 11 shows a comparison of depth measurements of a sensor with manual measurements of liquid and sludge depth; and FIG. 12 predictively illustrates sludge and liquid levels in an operating mode of an SBR as disclosed herein.DETAILED DESCRIPTIONAspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of the components set forth in the following descriptions or illustrated in the drawings. Aspects and embodiments disclosed herein may be practiced or carried out in various ways. Also, the terminology and terminology used herein is for the purpose of description and is not to be regarded as limiting. The use herein of "comprising," "including," "having," "including," "including," and variations thereof is intended to include the items listed thereafter and equivalents thereof, as well as additional items.Sequencing batch reactors (SBR) are containers used in some waste water treatment systems. SBRs are often used to perform the mining of solids using an activated sludge process. Wastewater treated in SBR can comprise, for example, dirty water or output from anaerobic digestion vessels or mechanical biological treatment plants. Wastewater is typically processed in batches in an SBR. In many reactions, in an SBR, a mixture of wastewater and activated sludge is sparged with oxygen to degrade organic matter, often measured as biochemical oxygen demand (BOD) or chemical oxygen demand (COD), such that an excess sludge and a pre-purified wastewater, referred to herein as a low solids supernatant, are produced.SBR typically operate in a series of conditioning phases including: A. Fill B. React C. Settling D. Stripping E. StallIn the filling phase (see Fig. 1A), an inlet to an SBR tank 10 is opened and waste water is introduced into the SBR tank 10 and mixed with activated sludge 15 either present in the tank or introduced with the waste water and possibly with supernatant 20 remaining in the tank 10 from a previous cycle to form a mixed liquid 25. The mixing of the waste water, activated sludge 15 and residual supernatant 20 can be performed mechanically under anoxic, anaerobic or aerobic conditions during and / or after the waste water is / has been introduced into the SBR container 10. In various implementations, the volume and / or rate of introduction of wastewater into the SBR vessel 10 may not be known in advance.In the reaction phase (see FIG. 1B ), the mixed liquid 25 can be supplied with aerators at the surface of the mixed liquid, for example floating surface aerators (not shown), or with oxygen from a venting system 30 by bubbling the mixed liquid 25 with an oxygen-containing gas, for example air. The oxygen is used by aerobic microbes to oxidize organic solids in the mixed liquid 25. In some embodiments, the SBR is operated under anoxic and / or anaerobic conditions and no oxygen is introduced into the mixed liquid 25.During the settling phase (see FIG. 1C ), solids suspended in the mixed liquid 25 are allowed to settle by terminating aeration or mechanical agitation of the mixed liquid. The suspended solids form a sludge blanket 15 on the bottom of the SBR vessel 10 and a low solids supernatant 20 is formed over the sludge layer 15. Microorganisms in the settled sludge 15 can consume substantially all the oxygen in the sludge 15, thereby causing anaerobic processes, for example denitrification, 15 to proceed in the settled sludge.The low-solids supernatant 20 is removed from the container during the removal phase (see FIG. 1D ), for example by opening an outlet valve of the container 10 or by pumping. In some embodiments, supernatant is removed from or near the surface of the supernatant in the SBR container 10. The supernatant may be discharged into the environment or further processed, for example to remove dissolved solids or chemical species if necessary to meet local regulations for discharge into the environment.Settled sludge 15 can be removed from the container 10 during or after the settling or withdrawal phase as excess activated sludge (ÜS) (see FIG. 1E ), for example by opening an outlet valve of the container 10 or by pumping. The OS can be disposed of or further processed.After the low solids supernatant 20 has been removed from the SBR vessel, the SBR can enter a standstill phase (see FIG. 1F ) in which it waits for a next waste water batch to be introduced. The SBR container 10 may include residual supernatant 20 and sludge 15 during the shutdown phase.In many existing SBR systems, the amount of time provided for the settling and withdrawal phases is typically fixed. Variations in process conditions, for example, the liquid level in the SBR and the type and amount of solids in the wastewater may result in either too much or too little supernatant and / or UV being removed. If too much supernatant is removed, there is a risk that the level of supernatant in the SBR will be lowered to a point where some suspended solids can be removed from the settled sludge with the supernatant. The withdrawn supernatant may thus exceed a maximum allowable level of suspended solids and may require additional treatment or retreatment, leading to an increase in treatment costs and time. Different complexes may have different allowable maximum suspended solids levels for supernatant to be discharged to the environment, for example between 5 mg / L and 30 mg / L. If a quantity of supernatant abundantly below a volume that would result in a risk of withdrawing supernatant at an undesirably high level of suspended solids is removed from the SBR vessel, the SBR would not produce the quantity of supernatant that it would be capable of running less efficiently than desired, thereby reducing a quantity of wastewater that could be processed or requiring an increased number of SBR in a wastewater treatment plant to handle a given wastewater flow. If too little UV is removed, the SBR canister may accumulate an unnecessarily high level of solids, which may increase the time required for solids settling and thus increase the cycle time of the SBR. If too much UV is removed, an insufficient bacterial population may remain in the SBR vessel to properly treat incoming waste water.Aspects and embodiments disclosed herein are generally directed to an automated process for controlling the removal of low-solids supernatant in a system to which varying amounts of waste water are supplied, by continuously monitoring the liquid level and the level of settling or settled solids in the system, and to an apparatus configured to perform such a process. Aspects and embodiments of this method and apparatus can be used in SBRs, where varying operating water levels often occur, to optimize settling, stall and drain cycles. The time that suspended solids may take to settle out of the wastewater in an SBR may vary based on process conditions, for example, a solids concentration in the wastewater, ambient temperature or temperature of liquid in the SBR, a volume of wastewater introduced into the SBR, a type and / or quantity of bacteria in the SBR, etc. The amount of low-solids supernatant produced in an SBR and the time used to produce the low-solids supernatant may also vary based on factors such as a solids concentration in the wastewater, ambient temperature or temperature of liquid in the SBR, a volume of wastewater introduced into the SBR, a type and / or quantity of bacteria in the SBR, etc. Aspects and embodiments disclosed herein provide for withdrawing low solids supernatant from an SBR or other treatment system once solids have settled to a desired degree from the supernatant by monitoring or measuring the amount of sludge settled to the bottom of the SBR and / or the sludge settling rate, rather than relying on blinders for a predetermined amount of time for settling of the solids. Aspects and embodiments disclosed herein provide for the withdrawal of an amount of low-solids supernatant consistent with the amount of low-solids supernatant actually produced from a waste batch by monitoring or measuring the total liquid level and sludge level in an SBR or other treatment system and calculating the amount of available low-solids supernatant, rather than simply withdrawing for a predetermined amount of time. Systems disclosed herein may thus operate more efficiently than prior art systems by withdrawing low solids supernatant at an appropriate time and in an appropriate amount and / or at an appropriate rate so that a larger amount of low solids supernatant may be recovered at a desired low solids content than may be achievable by relying on fixed settling and withdrawal times. Systems disclosed herein may also or alternatively operate with a reduced cycle time compared to conventional SBR by performing the sludge settling and solids-lean supernatant stripping phases at least partially simultaneously.In one embodiment, an automatic control system utilizes sensors or switches to determine the position of solids to optimize the removal of low solids supernatant from a system with varying or fixed water level. The solids position sensors or switches may be suspended solids sensors positioned at fixed locations in a waste water treatment vessel, tank or reactor. In another embodiment, either single or multiple sensors or switches may be movable to different levels in a waste water treatment tank, tank or reactor.The sensors or switches for determining the position of solids may include one or more ultrasonic mud level sensors. The ultrasonic sludge level sensors may be operated at a frequency or frequencies that provide a desired level of accuracy and / or sensitivity for determining the position of an interface between settling or settled sludge and supernatant in the wastewater treatment vessel, tank or reactor. It has been observed that ultrasonic level sensors operating at high frequencies, for example above 750 kHz, may not be able to provide a reliable measurement of the position of a sludge blanket with a low level of suspended solids as might be present when the sludge has first begun to settle in an SBR. It has been observed that ultrasonic level sensors operating at lower frequencies, for example between 5 kHz and 800 kHz, are better able to provide reliable measurement of the position of a sludge blanket with a low level of suspended solids than ultrasonic level sensors operating at higher frequencies. Accordingly, in some embodiments, sensors or switches used in the systems and methods disclosed herein for determining the position of solids may include one or more ultrasonic slurry level sensors operating at a frequency between about 5 kHz and about 800 kHz, between about 50 kHz and about 800 kHz, between about 50 kHz and about 200 kHz, or between about 200 kHz and about 455 kHz. In some embodiments, sensors or switches used in the systems and methods disclosed herein for determining the position of solids may include one or more ultrasonic slurry level sensors operating at frequencies at which commercially available ultrasonic transducers operate, for example, 50 kHz, 200 kHz, 455 kHz, or 800 kHz, or combinations thereof.In other embodiments, the sensors or switches for determining the position of solids may include one or more compressed high-intensity radar pulse (CHIRP) sonar units. CHIRP sensors include a transducer that outputs a progressively increasing frequency in a specific range (e.g., 28 kHz-60 kHz, 42 kHz-65 kHz, or 130 kHz-210 kHz) such that a variety of frequencies are used to obtain further resolution with respect to the depth and position of submerged objects compared to ultrasonic level sensors operating at a single frequency.In some embodiments, ultrasonic level sensors are used that continuously travel with the varying water level. In some embodiments, ultrasonic level sensors, radar level sensors, floating level sensors, and / or fixed level sensors or switches may be used alone or in combination to detect both the solids level and the water level in a wastewater treatment tank, tank, or reactor. One or more liquid level sensors may be used in combination with an instrument or sensor for detecting the position of solids so that the solids level and position of the supernatant-solids interface in a waste water treatment vessel, tank or reactor may be determined. The sensors or switches may be connected either by cable or wirelessly to a control system and may be anchored or mounted within the waste water treatment tank, tank or reactor so that they may float and drive at the varying water levels.When used in an SBR, the solids and liquid level or position sensors can provide a profile of the location of settling solids and the interface between settling solids and supernatant formed over the settling solids. Knowing this information, it is possible to optimize the removal of low-solids supernatant and / or solids, for example UV from the wastewater treatment vessel, tank or reactor. For example, a control system in communication with the liquid level and / or solids level sensors may trigger the start and end of the removal of the low solids supernatant based on the relative level of liquid and settled solids in the waste water treatment vessel, tank or reactor. In another embodiment, a controller may control the rate of removal of the low solids supernatant based at least in part on, for example, a degree of sharpness of an interface between a sludge blanket and supernatant in the wastewater treatment vessel, tank, or reactor. In another embodiment, the sensors and control system may be used to trigger the start and end of the removal of solids, and may also control the rate at which the solids are removed.In some embodiments, a "buffer layer" may be defined over the interface between a mud blanket and supernatant in a container, and low solids supernatant is removed from the container only at depths above the buffer layer. The thickness of the buffer layer can be determined based on the sharpness degree of the interface between the sludge blanket and the supernatant. If the interface between the sludge blanket and the supernatant is not very sharp, withdrawal of supernatant from a region near the interface could risk withdrawing supernatant at an undesirably high concentration of suspended solids, and therefore the buffer layer or minimum depth over the sludge blanket from which supernatant should be withdrawn can be defined to be greater in depth than if the interface between the sludge blanket and the supernatant were sharper. If the interface between the sludge blanket and the supernatant is very sharp, supernatant can be withdrawn from a position near the interface between the sludge blanket and the supernatant with a low risk of withdrawing supernatant with an undesirably high concentration of suspended solids, and therefore the buffer layer or minimum depth above the sludge blanket from which supernatant should be withdrawn can be defined with a depth less than if the interface between the sludge blanket and the supernatant were less sharp.In some embodiments, the control system may use data from the liquid level and / or solids level sensors to determine a degree of sharpness of an interface between a sludge blanket and supernatant in a wastewater treatment vessel and a desired minimum depth above the sludge layer or blanket from which supernatant should be drawn to avoid pulling supernatant with an undesirably high concentration of suspended solids. The control system may operate the waste water treatment vessel or a withdrawal subsystem thereof to withdraw low solids supernatant from the vessel at a time and / or at a rate such that the level of supernatant in the vessel is maintained at or just above the desired minimum depth above the sludge layer or blanket during at least a portion or during substantially all of the withdrawal phase.The degree of sharpness of an interface between a sludge blanket and supernatant in a wastewater treatment vessel may vary due to various factors, for example, changes in the content of wastewater introduced into the vessel, age of sludge in the vessel, changes in environmental conditions, for example, temperature, and / or changes in the types or quantity of bacteria present in the vessel (which may vary based on the age and / or temperature of the sludge). Accordingly, the desired minimum depth above the sludge layer or blanket in a container from which supernatant should be withdrawn to avoid withdrawal of supernatant with an undesirably high concentration of suspended solids may vary with time, for example with seasons. In some embodiments, the control system of the wastewater treatment vessel may use data from the liquid level and / or solids level sensors to periodically or continuously recompute a degree of sharpness of an interface between a sludge blanket and supernatant in the vessel and the desired minimum depth above the sludge layer or blanket from which supernatant should be drawn to avoid pulling supernatant with an undesirably high concentration of suspended solids to account for changes in the degree of sharpness of the interface between the sludge blanket and supernatant over time. The controller may use the recomputed value of the desired minimum depth above the sludge layer or blanket from which supernatant should be drawn to avoid drawing supernatant at an undesirably high concentration of suspended solids to periodically or continuously adjust the time and / or rate of drawing low solids supernatant to maintain the level of supernatant in the container at least during part or during substantially all of the drawing phase at or just above the recomputed desired minimum depth above the sludge layer or blanket.In some embodiments, the system may be operated in batch mode, wherein nonpredicted and varying amounts of wastewater are introduced into the wastewater treatment vessel, tank or reactor at unknown and varying flow rates. In some embodiments, a ballast material, for example magnetite or other high density material, may be added to the wastewater treatment vessel, tank or reactor to increase the settling rate of the solids.Aspects and embodiments disclosed herein are not limited to use in an SBR and may be used in aerobic and / or anaerobic digestion vessels to optimize thickening and waste cycles of these tanks. Aspects and embodiments disclosed herein are not limited to the type, number, location, and combination of sensors or switches used.In some embodiments, a wastewater treatment system includes a wastewater treatment vessel, tank or reactor equipped with a system for determining and / or continuously monitoring a total liquid level as well as a depth or level of a blanket of settling sludge in the vessel, tank or reactor. The terms "container", "tank" and "reactor" are used interchangeably herein and are understood to include SBR. The system may be further configured to determine a change in suspended solids concentration with depth in the vessel and quantify a degree of sharpness of an interface between settled or settling sludge and a supernatant in the vessel. As used herein, a degree of sharpness of a solids-liquid or solids-supernatant interface is defined by a change in the concentration of suspended solids with depth across the interface. As used herein, a low solids supernatant, low solids supernatant, or simply supernatant is wastewater in a wastewater treatment vessel from which solids have been at least partially removed, for example, by settling. When wastewater comprising suspended solids is left under quiet conditions in a wastewater treatment vessel, solids having a relatively greater density than water typically settle to the bottom of the vessel over time, resulting in a "sludge blanket" at the bottom of the vessel covered by a layer of low solids supernatant, for example, low solids water. The term "low solids content" is a relative term used herein to refer to supernatant as opposed to solid rich sludge in a waste water treatment vessel.A system for monitoring the liquid and sludge levels may include one or more sensors. In some embodiments, one type of sensor may be used to monitor or measure the total liquid level in the container and another type of sensor may be used to monitor or measure a level or depth of a sludge layer or an interface between sludge and supernatant in the container. The total level of liquid in the container will typically correspond to the top surface of the supernatant in the container. In other embodiments, similar or the same types of sensors may monitor or measure the total liquid level in the container and the level or depth of a sludge layer or interface between sludge and supernatant in the container. In other embodiments, the same sensor may monitor or measure the total liquid level in the container and the level or depth of a sludge layer or interface between sludge and supernatant in the container.The level or depth sensors of the system for monitoring the liquid and sludge levels may be in communication with a control device of the waste water container via wires or wirelessly and may communicate data including indications of the measured liquid or sludge levels, depths or concentrations of suspended solids or sludge to the control device. The controller may be programmed to control various operating parameters of the container based at least in part on data received from one or more of the sensors, for example, the time or rate of introducing waste water into the container, the time or rate of removing supernatant or sludge from the container, the time or rate of aeration or mixing of the container, or any other operating parameters of interest.In one embodiment, illustrated in Figure 2, a wastewater treatment vessel 10 includes a total liquid level or supernatant level sensor 35 and a sludge level or suspended solids concentration sensor 40 respectively. The suspended solids level sensor 40 (hereinafter, the "sludge sensor") includes a plurality of sensor elements 40a fixedly attached to a wall 12 of the container 10. The mud sensor 40 or a controller with which the mud sensor 40 communicates may determine a location of a top surface 50 of a mud layer 15 (also referred to herein as the interface between the mud layer 15 and the supernatant 20) by comparing measurements of the concentration of suspended solids provided by the different sensor elements 40 a. The sludge sensor 40 may also be used to determine a degree of sharpness of the interface between the sludge layer 15 and the supernatant 20 by providing an indication of how the level of suspended solids changes from one sensor element 40a to the next, and thus how the concentration of suspended solids changes with depth.The sensor elements 40 aof a mud sensor 40 may include, for example, optical (e.g., infrared) or ultrasonic sensors. In an example illustrated in FIG. 3, the sensor elements 40 aof the mud sensor 40 may include a signal transmitter 42 (e.g., an infrared light transmitter or an ultrasonic transducer) and a signal receiver 44 (e.g., an infrared or ultrasonic receiver) separated from the signal transmitter 42 by a distance 46. Liquid in a container in which sensor element 40 ais disposed fills the distance 46 between the signal transmitter 42 and signal receiver 44. the sensor elements 40 amay provide output signals indicative of a degree of attenuation of the signal (infrared light or ultrasound) from the signal transmitter 42 received by the signal receiver 44. The degree of attenuation of the signal can be correlated with the concentration of suspended solids or turbidity of the liquid in the container 10. The difference in signal attenuation at the different sensor elements 40 aof the mud sensor 40 in FIG. 2 may be used to determine a suspended solids profile or mud concentration versus depth in the vessel 10, and thus may be used to determine a position and / or sharpness level of the mud-supernatant interface 50. The sensor elements 40 aof the mud sensor 40 are not limited to optical or ultrasonic sensors and may include any type of sensor capable of providing a signal indicative of a concentration of suspended solids or mud at locations in the container 10. More or fewer sensor elements 40 athan illustrated, for example 64 or more sensor elements 40 amay be provided. The sensor elements 40 aof the mud sensor 40 may be disposed on a single wall 12 of the container 10, as illustrated, or on more than one wall. The sensor elements 40 amay include wipers (not shown in FIG. 3 ) or other self-cleaning mechanisms to remove contaminants from the signal transmitter 42 and / or signal receiver 44 as desired.The sensor elements 40 amay additionally or alternatively be used to detect a liquid level in the container 10. If a signal transmitted from a signal transmitter 42 to a signal receiver 44 in a first sensor element 40 aupward of a second sensor element 40 ais not attenuated or not substantially attenuated, while the signal transmitted from the signal transmitter 42 to the signal receiver 44 in the second sensor element 40 ais substantially attenuated more than that of the first sensor element 40 a, it can be concluded that the liquid surface is between the first and second sensor elements.The total liquid level or supernatant level sensor 35 may also be immovably attached to a wall 12 of the container, which may be the same as or a different wall than that to which the sludge sensor 40 is attached. The total liquid level or protrusion level sensor 35 may alternatively be suspended from a rod, cable, scaffold, or other mechanism above the liquid surface in the container 10. The sensor 35 may be an ultrasonic sensor, a radar sensor, an optical sensor, or any other type of sensor capable of providing an indication of the height or level of the top surface 45 of the supernatant 20 or wastewater in the container 10. In some embodiments, for example, in the embodiment illustrated in FIG. 2, the level sensor 35 may be disposed at a position above an expected upper liquid level in the container 10.Together, the mud sensor 40 and level sensor 35 may be used to determine a protrusion depth D 1, a mud layer thickness or depth D 2, and a total liquid depth D 3 in the container 10. In some embodiments, the protrusion depth D 1 and / or depth of the slurry-protrusion interface is determined by a controller by subtracting a slurry layer thickness D 2 determined from an output of the slurry sensor 40 from the liquid level D 3 determined from an output of the level sensor 35.In another embodiment, illustrated in Figure 4, the mud sensor 40 comprises an elongate member, for example a rod, rod or cable, which is mounted in the container 10 at a position offset from the walls 12 of the container. Sensing elements 40a, which may be similar in construction and operation to the sensing elements 40a discussed with respect to the embodiment illustrated in Figure 2, may be located at different positions along the length of the elongate element and thus at different depths in the container 10. In a particular example, the mud sensor 40 may be similar to the automated slide blanket level detector available from Markland Specialty Engineering Ltd. with 64 photodetector sensor elements over a four foot (1.2 meter) length.The liquid level sensor 35 illustrated in FIG. 4 is a liquid pressure sensor. As the liquid level in the container 10 increases, the liquid pressure at the bottom of the container 10 increases. The liquid level sensor 35 illustrated in FIG. 4 is configured to measure or monitor the liquid pressure at the bottom of the container 10 or near the bottom of the container 10 and provide data comprising an indication of the pressure to a controller that can determine the liquid level (wastewater or sludge and supernatant) in the container based on the pressure indication. The liquid level sensor 35 is illustrated in Figure 4 adjacent a wall 12 of the container but may be located at differing locations in various embodiments.In the embodiment illustrated in FIG. 5, the level sensor 35 is similar in construction and operation to the level sensor 35 illustrated in FIG. 2. the mud sensor 40 in the embodiment illustrated in FIG. 5 at least partially reaches the liquid in the container 10. The propagation speed of ultrasonic pulses transmitted from the ultrasonic transceiver may be different in sewage, low solids supernatant 20, and sludge 15. The mud sensor 40 in FIG. 5 may measure a time between transmitting an ultrasonic pulse and receiving an echo of the ultrasonic pulse to determine the amount of mud 15 in the container 10 and thus the height of the mud blanket 15. In some embodiments, a controller may use knowledge of a position of the mud sensor 40 in a calculation of the height of the mud ceiling 15 and / or depth of the mud-supernatant interface calculated from the data provided by the mud sensor 40. For example, if the mud sensor 40 is positioned above X meters of liquid in the container 10 and if it were expected that an ultrasonic pulse transmitted from the mud sensor 40 takes Y milliseconds to be reflected from the bottom of the container and return to the mud sensor 40 if the container were filled with low solids supernatant, the controller could compare an actual amount of time Z between pulse transmission and echo detection to time Y given the expected propagation speed of the ultrasonic pulse through low solids supernatant and mud to determine the height of the mud blanket 15. In some embodiments, the mud sensor 40 may be similar to the SONATAX™ sc Sl Blanket Level Probe available from Hach. The mud sensor 40 in FIG. 5 may include a wiper (not shown in FIG. 5 ) or other self-cleaning mechanisms to remove contaminants from its signal transmitter, receiver, or transceiver as desired.Figure 6 illustrates an embodiment in which both the level sensor 35 and the sludge sensor 40 comprise floating elements which move vertically with the liquid level in the container 10. The level sensor 35 of the embodiment in Fig. 6 is a float sensor comprising a float 32 mounted on a rod 36. The rod 36 may be secured to a wall 12 of the container 10 or otherwise immovably secured within the container 10. The float 32 includes one or more magnets and the rod 36 includes one or more magnetic sensors, for example reed switches, at known locations along its length. As the liquid level in the container 10 varies, the float 32 moves up and down the rod 36. As the one or more magnets in the float 32 approach a magnetic sensor in the rod 36, the magnetic sensor may provide a signal to a controller that may interpret the signal to determine the position of the float 32 and thus the liquid level in the container 10.The mud sensor 40 in FIG. 6 may include, for example, a float mounted ultrasonic transceiver or separate transmitters and receivers. The mud sensor 40 in FIG. 6 may float on the liquid in the container 10 and rise and fall with the total liquid level in the container 10. The mud sensor 40 in FIG. 6 may operate in a similar manner to the mud sensor 40 in FIG. 5 described above. In some embodiments, a controller may use data received from the level sensor 35 regarding the total liquid level in the reservoir 10 to refine a calculation of the height of the mud blanket 15 and / or depth of the mud-supernatant interface calculated from the data provided by the mud sensor 40. For example, if the data received from the level sensor 35 indicates that D3 meters of liquid are in the container 10, and if an ultrasonic pulse transmitted from the mud sensor 40 were expected to take X milliseconds to be reflected from the bottom of the container and return to the mud sensor 40 if the container were filled with low solids supernatant, the controller could compare an actual amount of time Y between pulse transmission and echo detection to time X given the expected propagation speed of the ultrasonic pulse through low solids supernatant and mud to determine the height of the mud blanket 15. The floating sludge sensor 40 in Fig. 6 may be operable in a greater range of liquid levels than, for example, the sludge sensor 40 in Fig. 5 which could be located outside the liquid in the container if the liquid level increased too far. Furthermore, a floating mud sensor may be operable to measure flatter layers of supernatant than a fixed mud sensor. For example, a floating mud sensor may be used in a control system configured to remove or withdraw supernatant during the settling phase of an SBR cycle. The supernatant may be drained while maintaining only a supernatant depth, for example, about six inches (15.2 cm), sufficient to provide drained low solids supernatant with a desired low solids concentration. The level of suspended solids of the withdrawn low solids supernatant can be controlled or minimized by providing a sufficient depth of supernatant above the supernatant-sludge interface to avoid withdrawal of sludge or suspended solids from a mixed layer around the supernatant-sludge interface, which may comprise an undesirably high amount of suspended solids. The mud sensor 40 in FIG. 6 may include a wiper (not shown in FIG. 6 ) or other self-cleaning mechanisms to remove contaminants from its signal transmitter, receiver, or transceiver as desired. In other embodiments, a mud sensor comprising an ultrasonic transducer may be built into the float 32 of the level sensor 35 to generate a combination liquid level sensor mud depth sensor, and a separate mud sensor 40 may be omitted.In another embodiment, illustrated in Figure 7, a mud sensor 40 and / or level sensor 35 may comprise a plunger 45 suspended from a cable into the liquid in the container 10. A winch 50 may be used to lower the plunger 45 to different depths within the container and may include a sensor to track the depth to which the plunger 45 has been lowered. In one embodiment, the immersion element 45 may comprise a suspended solids concentration monitor with optical or ultrasonic transducers and receivers, similar to the sensor element 40a illustrated in Figure 3. In another embodiment, the dip 45 may additionally or alternatively comprise a liquid level sensor, for example a pressure sensor, to provide an indication of a depth of the dip 45 below a liquid surface in the container 10. Additionally or alternatively, the plunger 45 may have a density between that of the supernatant 20 and the slurry 15 in the container. The plunger 45 may be lowered from the winch 50 into the liquid in the container until it comes to rest and floats on the surface of the sludge layer 15 below the supernatant 20, thereby providing an indication of a depth of the sludge-supernatant interface. The plunger 45 and / or winch 50 may / may provide data to a controller of the vessel 10 indicative of the liquid level in the vessel, the depth of the slurry supernatant interface or height of the slurry layer, and / or a profile of suspended solids concentration versus depth.Data provided by any of the level sensors and mud sensors disclosed herein regarding the liquid level in the container 10 and the depth of the mud-supernatant interface or height of the mud layer may be utilized by a control system to control the operation of the container 10. For example, an indication of the concentration of suspended solids in wastewater introduced into the vessel provided by an embodiment of any of the sensors disclosed herein may be utilized by the control system to determine a desired amount or time of aeration or mixing or estimate a desired time for settling of the solids. An indication of a severity of the mud-supernatant interface provided by an embodiment of any of the sensors disclosed herein may be utilized by the control system to determine when to begin withdrawing the low solids supernatant. Withdrawal of the low solids supernatant may be initiated by the control system as soon as the sludge-supernatant interface attains a desired degree of sharpness, so that a low solids supernatant can be withdrawn with a desirably low amount of suspended solids.An indication of the severity of the sludge-supernatant interface provided by an embodiment of any of the sensors disclosed herein may be utilized by the control system to determine how quickly to withdraw low-solids supernatant from the container. The control system may initiate withdrawal of low solids supernatant while solids are in the process of settling from the waste water. The control system can first draw off the low-solids supernatant slowly, so that the high-solids supernatant is not drawn off further down in the container until the solids settle in the high-solids supernatant. The rate of withdrawal of the low solids supernatant can be increased by the control system as the sludge-supernatant interface becomes sharper, since there will be greater confidence that supernatant withdrawn from the container will not contain an undesirable concentration of solids.An indication of a depth of the mud-supernatant interface provided by an embodiment of any of the sensors disclosed herein may be utilized by the control system to determine how much low-solids supernatant may be drawn off without risking, along with the low-solids supernatant, sludge being drawn off. An indication of a depth of the mud-supernatant interface provided by an embodiment of any of the sensors disclosed herein may be utilized by the control system to determine when and how much mud is to be drained or removed from the container 10 to provide a desired amount of mud (and microorganisms) in the container. An indication of the severity of the mud-supernatant interface provided by an embodiment of any of the sensors disclosed herein may be utilized by the control system to determine how quickly to drain or remove mud from the container 10. If the slurry-supernatant interface is not sharp, it may be desirable to drain the slurry from the vessel 10 at a relatively slow first rate in order not to introduce turbulence into the vessel that can remix the slurry and supernatant. If the slurry-supernatant interface is sharp, it may be desirable to discharge the slurry from the container 10 at a relatively higher second rate, which is higher than the first rate, such that the slurry is removed before it can remix with the supernatant.Various operating parameters of the wastewater treatment vessels or SBRs disclosed herein may be controlled or adjusted by an associated control system or controller based on various parameters measured by various sensors located in different portions of the vessel. The control apparatus used to monitor and control the operation of the various elements of a container 10 or a waste water treatment system comprising a container 10 may comprise a computerized control system. Various aspects of the controller may be implemented as special purpose software executed in a general purpose computer system 100 such as that shown in FIG. 8. The computer system 100 may include a processor 102 connected to one or more storage devices 104, such as a disk drive, semiconductor memory, or other device for data storage. Memory 104 is typically used to store programs and data during operation of computer system 100. Components of the computer system 100 may be coupled by an interconnect mechanism 106, which may include one or more buses (e.g., between components integrated within a same machine) and / or a network (e.g., between components residing on separate discrete machines). The interconnect mechanism 106 enables communications (e.g., data, instructions) to be exchanged between system components of system 100. Computer system 100 also includes one or more input devices 108, for example, a keyboard, mouse, trackball, microphone, touch screen, and one or more output devices 110, for example, a printing device, display screen, and / or speaker. Additionally, computer system 100 may include one or more interfaces (not shown) that connect computer system 100 to a communication network in addition to or as an alternative to interconnection mechanism 106.The dispensers 110 may also include valves, pumps, or switches that may be used to introduce waste water into a treatment tank, mix or ventilate the waste water in the tank, and / or remove supernatant or sludge from the tank. The one or more input devices 108 may also include any of the liquid level or mud sensors disclosed herein.Storage system 112 shown in more detail in FIG. 9 typically includes a computer readable and writable non-transitory recording medium 202 storing signals defining a program executed by processor 102 or information processed by the program. The medium may include, for example, a disk or flash memory. In operation, the processor typically causes data to be read from the non-volatile recording medium 202 into another memory 204 that allows the processor to access the information more quickly than does the medium 202. This memory 204 is typically a volatile random access memory such as a dynamic random access memory (DRAM) or a static memory (SRAM). It may reside in storage system 112 as shown or in storage system 104. The processor 102 generally processes the data within the memory integrated circuit 204 and then copies the data onto the medium 202 after processing is complete. A variety of mechanisms for managing data movement between the medium 202 and the memory integrated circuit element 204 are known, and aspects and embodiments disclosed herein are not limited thereto. Aspects and embodiments disclosed herein are not limited to a particular storage system 104 or storage system 112.The computer system may include specially programmed special purpose hardware, for example an application specific integrated circuit (ASIC). Aspects and embodiments disclosed herein may be implemented in software, hardware, or firmware, or any combination thereof. Furthermore, such methods, acts, systems, system elements, and components thereof may be implemented as part of the computer system described above or as an independent component.Although computer system 100 is shown by way of example as one type of computer system upon which various aspects and embodiments disclosed herein may be practiced, it should be appreciated that aspects and embodiments disclosed herein are not limited to being implemented on a computer system as shown in FIG. 8. Various aspects and embodiments disclosed herein may be practiced on one or more computers having a different architecture or components than those shown in FIG. 8.Computer system 100 may be a general purpose computer system that is programmable using a high level computer programming language. Computer system 100 may also be implemented using specially programmed special purpose hardware. In computer system 100, processor 102 is typically a commercially available processor such as the well known Pentium™ class, Core™ class, or Atom™ class processors available from Intel Corporation. Many other processors are available, including programmable logic controllers. Such a processor typically executes an operating system, which may be, for example, the Windows 7 operating system, the Windows 8 operating system, or the Windows 10 operating system available from Microsoft Corporation, the MAC OS System X available from Apple Computer, the Solaris operating system available from Sun Microsystems, or the UNIX available from various sources. Many other operating systems may be used.The processor and operating system together define a computer platform for which application programs are written in higher level programming languages. It should be understood that the invention is not limited to a particular computer system platform, processor, operating system, or network. It should also be apparent to those skilled in the art that aspects and embodiments disclosed herein are not limited to a specific programming language or computer system. Furthermore, it should be appreciated that other suitable programming languages and other suitable computer systems could also be used.One or more portions of the computer system may be distributed over one or more computer systems (not shown) coupled to a communication network. These computer systems may also be general purpose computer systems. For example, various aspects of the invention may be distributed over one or more computer systems configured to provide a service (e.g., server) to one or more client computers or perform an overall task as part of a distributed system. For example, various aspects and embodiments disclosed herein may be performed on a client-server system that includes components distributed over one or more server systems that perform various functions according to various aspects and embodiments disclosed herein. These components may be executable code, intermediate code (e.g., IL), or interpreted code (e.g., Java) that communicate over a communication network (e.g., the Internet) using a communication protocol (e.g., TCP / IP). In some embodiments, one or more components of computer system 100 may communicate with one or more other components via a wireless network, including, for example, a cellular telephone network.It should be appreciated that the aspects and embodiments disclosed herein are not limited to execution on any particular system / group of systems. It should also be appreciated that the aspects and embodiments disclosed herein are not limited to any particular architecture(s), network, or communication protocol(s). Various aspects and embodiments disclosed herein may be programmed using an object oriented programming language such as SmallTalk, Java, C++, Ada, or C# (C-Sharp). Other object oriented programming languages may also be used. Alternatively, functional, scripting, and / or logical programming languages may be used, for example, ladder logic. Various aspects and embodiments disclosed herein may be implemented in a non-programmed environment (e.g., HTML, XML, or other format created documents that, when viewed in a window of a browser program, render graphical user interface (GUI) aspects or perform other functions). Various aspects and embodiments disclosed herein may be implemented as programmed or non-programmed elements or a combination thereof.Example 1: Measurement of System PerformanceTo illustrate the variability of liquid level and sludge level between cycles in an SBR, liquid level and sludge level sensors were installed in an SBR in a waste water treatment plant and liquid level and sludge level measurements were taken over a two day period. The liquid level sensor was an ultrasonic level sensor SITRANS LU™ model number 7ML522-2AA18 manufactured by Siemens AG. The liquid level sensor was placed 17 feet, 3 inches (5.26 meters) above the bottom of the SBR container, abundantly above the upper liquid level reached in the container during testing, which was about 11 feet (3.35 meters). The sludge level sensor was a SONATAX™ sc Sl Blanket Level Probe from Hach. The mud level sensor was mounted on floats and the ultrasonic transceiver of the mud level sensor extended between 3 and 8 inches (between 7.6 cm and 20.3 cm) below the surface of the liquid in the SBR. Measurements were taken using the liquid level sensor and slurry sensor during normal operation of the SBR with a 2.5 hour clocked fill phase, a one hour clocked reaction phase, a one hour clocked settling phase, and a 25 minute clocked drain / stall phase.As can be seen from Figure 10, over the two day period, the liquid and sludge level in the SBR varied from cycle to cycle and was not predetermined. The liquid level varied between about 9.3 feet and about 10.5 feet at the end of each fill cycle (the peaks in the curve of water depth). The sludge level at the end of each fill cycle varied from about eight feet to just over nine feet. At the end of each withdrawal cycle, the liquid level decreased to about 8.5 feet with some variation between cycles and the sludge level decreased to between about 5.5 feet and about 5.8 feet.Example 2: Measurement accuracyThe accuracy of the ultrasonic level sensor SITRANS LU™ and the SONATAX™ sc Sl Blanket Level Sample for measuring the liquid level and sludge level, respectively, was investigated by comparing the readings of these sensors with manually made physical measurements of the liquid and sludge level during the settling and withdrawal phase of a cycle of the same SBR as used in Example 1. FIG. 11 illustrates a comparison between the sensor readings and the physical measurements of liquid level and mud depth. As can be seen from these data, apart from some variations in the depth of the sludge blanket at the beginning of the settling phase and at the end of the withdrawal phase, the sensor measurements closely matched the physically observed liquid and sludge levels. Without being bound by any particular theory, it is believed that these deviations are a consequence of the SONATAX™ sc Sl Blanket Level Sample utilizing an operating frequency at which it is impossible for him to accurately determine the level of the low solids concentration sludge blanket at the beginning of the settling phase and at the end of the withdrawal phase when mixing of the liquid in the SBR began. These data illustrate that the sensors used can be used to accurately measure the liquid level and the mud depth at least during a majority of an operating cycle in an SBR.Example 3: Predictive Amount of Cycle Time SavingsA control system of an SBR may be configured to begin withdrawal of low solids supernatant during the settling phase of an SBR once the slurry-supernatant interface has sunk to a depth, for example between about six inches (15.24 cm) and about three feet (91.4 cm), below the surface of the liquid in the SBR. This depth may be selected based on the sharpness degree of the supernatant-sludge interface such that low-solids supernatant contains a desired low solids content, for example, a suspended solids content below the content for discharging the supernatant into the environment required by the regulations in a region where the waste water treatment system including the SBR is located. The low-solids supernatant may be drained from the surface or near the surface of the liquid in the SBR container via a drain valve or pump. The severity of the supernatant-sludge interface may vary based on, for example, the type of wastewater and amount and type of suspended solids, ambient temperature or temperature within the SBR, and other factors. If the slurry and / or liquid level sensor determines that the desired depth of supernatant having the desired low solids content has formed, the control system of the SBR initiates withdrawal of the low solids supernatant. The flow rate of the low solids supernatant withdrawn is controlled so that the desired depth of supernatant having the desired low solids content is maintained during the withdrawal process.FIG. 12 illustrates liquid and sludge levels in a predictive example of this process. In Fig. 12, the dotted line represents the total liquid level in a conventionally operated SBR during one cycle of operation. The SBR is filled, aerated and the sludge is then allowed to settle. After the settling time has elapsed, the SBR withdraws the prescribed volume of low solids supernatant in preparation for the next cycle. The line labeled "sludge level" in Figure 12 represents the depth of the sludge-supernatant interface. The solid line labeled "Liquid Level (predictive)" represents a potentially revised liquid level profile that is achievable while monitoring the mud depth and withdrawing the low solids supernatant so that a fixed supernatant depth is maintained in the SBR. Knowing where the sludge-supernatant interface is during the settling cycle, the withdrawal cycle can be performed partially or wholly simultaneously with the settling cycle.In a particular predictive example, an SBR is normally operated with a 2.5 hour clocked fill phase, a one hour clocked reaction phase, a one hour clocked settling phase, and a 25 minute clocked drain / stall phase. The sludge precipitates to form low solids supernatant with a sufficiently low solids content to provide regulatory environmental requirements at a linear rate of about two inches / min. (5.1 cm / minute). The time to reach six inches of supernatant during the settling cycle would thus be about 3 minutes. If the system were modified to operate in accordance with one or more of the embodiments disclosed herein, then the withdrawal phase could begin 3 minutes after the settling phase and the rate of removal of the low solids supernatant would be adjusted so that the six inches of supernatant having the sufficiently low solids content is maintained above the sludge-supernatant interface. The withdrawal phase would end at substantially the same time as the settling phase.The SBR cycle time would thus be reduced from four hours and 55 minutes to 4.5 hours, a reduction of 8.5%. A larger wastewater flow can thus be processed in an identically designed SBR or the design of the SBR can be reduced by 8.5% and achieve the same wastewater processing flow. For example, the number of SBR cycles could be increased from about 10 every two days to about 11 every two days, an increase of about 180 cycles per year. This reduction in cycle time would be greater for systems in which sludge would settle more quickly, for example, in systems in which magnetite was added to the sludge to increase settling, and less for systems in which sludge settling would settle at a lower rate or in which it would be desired to maintain a greater depth of supernatant above the sludge-supernatant interface during stripping, for example, to meet more stringent guidelines for the solids content of low solids supernatant to be discharged to the environment.Example 4: Predictive Increase of Supernatant RecoveryThe amount of low solids supernatant withdrawn during each cycle of an SBR is typically set to a fixed value. The fixed value is typically set so that during stripping, the level of supernatant does not drop to a level close enough to the highest expected depth of the sludge-supernatant interface so that the stripped low solids supernatant does not comprise any more suspended solids than is permitted by local regulatory guidelines. Due to the variability in the depth of the slurry-supernatant interface below the liquid surface in a typical SBR after a typical clocked settling phase, the slurry-supernatant interface between the supernatant and the settled slurry may be below the highest expected depth during many cycles. Withdrawal of the solid low solids supernatant level in cycles where the sludge-supernatant interface between the supernatant and the settled sludge is below the highest expected depth may result in low solids supernatant that would meet the regulatory requirements for discharge remaining in the SBR after the withdrawal phase, and the SBR may thus operate below its optimal capacity and efficiency for low solids supernatant production and waste water treatment. By monitoring the depth of the sludge-supernatant interface, an amount of low-solids supernatant that is drawn off can be varied based on the observed depth of the sludge-supernatant interface, which results in a greater amount of low-solids supernatant that meets regulatory guidelines being drawn off, and increases the capacity and efficiency of the SBR for low-solids supernatant generation and waste water treatment.In a particular predictive example, the depth of the slurry-supernatant interface after settling of the slurry in an SBR having an average liquid fill volume of 1,000 ft 3(28,3 m 3) and an average liquid fill height of 10 feet (with, for this example, negligible cycle-to-cycle fill height variation) has an average depth D of five feet (1.5 meters) with a standard deviation δ of one foot (0.3 meters). In order for low solids supernatant having a solids content meeting regulatory guidelines to be stripped at 99.9% confidence level, an adjusted volume of low solids supernatant is stripped such that stripping ends when the level of supernatant reaches one foot above D+3δ or nine feet. If the level of the sludge-supernatant interface were monitored, the low solids supernatant could be drawn off on average until the level of supernatant reached one foot above D, or six feet, while still meeting the regulatory requirements for solids content. This would result in the withdrawal of an average of 300 ft 3(8,5 m 3) of low-solids supernatant in addition per cycle. If each cycle took 6 hours on average, this would result in an increased capacity for SBR production of low solids supernatant and a capacity for wastewater treatment of about 438,000 ft 3(12 402 m 3) per year.The terminology and terminology used herein is for the purpose of description and is not to be regarded as limiting. As used herein, the term "plurality" refers to two or more things or components. The terms "include", "comprise", "carry", "have", "contain" and "involve", whether in the written description or in the claims and the like, are open terms, i.e., they are intended to mean "include, but not limited to.". Thus, the use of such terms is intended to include the items listed thereafter and equivalents thereof, as well as additional items. Only the transitional terms "consisting of" and "consisting essentially of" are terms closed and semi-closed, respectively, with respect to the claims. The use of ordinal terms such as "first(r / s)", "second(r / s)", "third(r / s)", and the like in the claims to modify an element of a claim does not mean any priority, priority, or order of one element of one claim over another, or the chronological order in which actions of a method are performed, but are used merely as a label to distinguish an element of a claim having a certain name from another element having a same name (except for using the ordinal term) to distinguish the elements of one claim from each other.Having thus described several aspects of at least one embodiment, it will be appreciated that various changes, modifications and improvements will readily occur to those skilled in the art. For example, it should be appreciated that each of the level sensors and sludge sensors disclosed herein may be included in a wastewater treatment tank or SBR with any other of the level sensors and sludge sensors disclosed herein. Any feature described in any embodiment may be included in or substituted for any feature of any other embodiment. In other embodiments, existing wastewater treatment systems or containers may be retrofitted to include features of the wastewater containers disclosed herein. Such alterations, modifications and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are exemplary only.

Claims

A wastewater treatment system comprising: a sequencing batch reactor vessel configured to perform biological treatment of wastewater in a series of treatment phases comprising a fill phase, a bioreaction phase, a sludge settling phase in which solids settle out of the wastewater such that sludge and low solids supernatant form, a low solids supernatant withdrawal phase, and a stall phase, wherein the fill phase comprises introducing a non-predetermined amount of wastewater into the vessel; a liquid level sensor configured to measure a liquid level in the vessel and provide an indication of the level of the liquid to a controller; and a slurry detector configured to measure a position of an interface between the slurry and the low solids supernatant in the vessel and provide an indication of the position of the interface to the controller and further determine a degree of sharpness of the interface and provide an indication of the degree of sharpness of the interface to the controller, wherein the controller is configured to perform a comparison between the level of the liquid and the position of the interface and to control an amount of low solids supernatant removed from the vessel during the withdrawal phase based on the comparison and to vary a rate of removal of the low solids supernatant based at least in part on the degree of sharpness of the interface.The system of claim 1, wherein the controller is further configured to initiate removal of the low solids supernatant in response to the sharpness level of the interface exceeding a predetermined level.The system of claim 1, wherein the controller is further configured to control a rate of sludge removal from the container based at least in part on the sharpness level of the interface.The system of claim 1, wherein the controller is further configured to draw low solids supernatant from the container at a rate that maintains a substantially constant depth of supernatant above the interface.The system of claim 1, wherein the controller is further configured to control an amount of sludge removed from the container based at least in part on the position of the interface.The system of claim 1, wherein the sludge detector includes a plurality of suspended solids sensors each located at different fixed locations within the vessel.The system of claim 6, wherein the plurality of suspended solids sensors include one or more optical or ultrasonic sensors.The system of claim 1, wherein the slurry detector includes a sensor that moves vertically in response to a change in the liquid level in the container.The system of claim 8, wherein the mud detector includes one of an ultrasonic level sensor or a radar level sensor.The system of claim 1, wherein the liquid level sensor comprises an ultrasonic sensor.The system of claim 1, wherein the liquid level sensor includes a plurality of sensors disposed at different fixed levels in the container, respectively.The system of claim 1, wherein the liquid level sensor and the mud sensor are comprised by a same sensor.The system of claim 1, wherein the mud detector includes an ultrasonic level detector having an operating frequency between 50 kHz and 800 kHz.The system of claim 1, wherein the mud detector includes a high intensity compressed radar pulse sonar unit.A method of controlling the waste water treatment system of any one of claims 1 to 14, the method comprising: introducing a volume of waste water into a sequencing batch reactor vessel of the waste water treatment system; biologically treating the waste water in the vessel; maintaining quiet conditions in the vessel sufficient for solids in the waste water to settle and form a ceiling of settled sludge and a low solids supernatant; measuring a liquid level in the vessel; providing an indication of the level of the liquid to a controller; measuring a position of an interface between the ceiling of settled sludge and the low solids supernatant in the vessel; providing an indication of the position of the interface to the controller; Making a comparison between the level of the liquid and the position of the interface with the controller; withdrawing the low solids supernatant from the container; controlling an amount of the low solids supernatant withdrawn from the container based on the comparison; the method characterized by the steps of: determining a degree of sharpness of the interface; providing an indication of the degree of sharpness of the interface to the controller; and varying a rate of withdrawal of the low solids supernatant based at least in part on the degree of sharpness of the interface.The method of claim 15, further comprising introducing the waste water into the container at a non-predetermined rate.The method of claim 15, further comprising initiating the stripping of the low solids supernatant in response to the sharpness level of the interface exceeding a predetermined level.The method of claim 15, further comprising controlling a rate of sludge removal from the vessel based at least in part on the sharpness level of the interface.The method of claim 15, further comprising controlling an amount of sludge removed from the container based at least in part on the position of the interface.The method of claim 15, wherein introducing the volume of waste water into the container comprises introducing a non-predetermined volume of waste water into the container.The method of claim 15, comprising controlling a rate of withdrawing low solids supernatant from the sequencing batch reactor vessel to maintain a substantially constant depth of low solids supernatant above the interface during settling of the slurry.A method for retrofitting a waste water treatment system, the method comprising: installing a control system in a sequencing batch reactor vessel of the waste water treatment system, wherein the sequencing batch reactor vessel is configured to perform biological treatment of waste water in a series of treatment phases comprising a fill phase, a bioreaction phase, a sludge settling phase in which solids settle out of the waste water and form a sludge blanket and a low solids supernatant, a draw phase of the low solids supernatant, and a stall phase, wherein the fill phase comprises introducing a non-predetermined amount of waste water into the vessel, and wherein the control system comprises: a liquid level sensor configured to:, a level of liquid in the container and providing an indication of the level of the liquid to a controller; and a sludge detector configured to measure a position of an interface between the sludge blanket and the low solids supernatant in the container and provide an indication of the position of the interface to the controller, and further determine a degree of sharpness of the interface and provide an indication of the degree of sharpness of the interface to the controller, wherein the controller is configured to perform a comparison between the level of the liquid and the position of the interface and control an amount of the low solids supernatant removed from the container during the withdrawal phase based on the comparison and vary a rate of removal of the low solids supernatant based at least in part on the degree of sharpness of the interface.

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