System and process for controlling the quality of treated wastewater discharged from a biological reactor via an upflow gravitational separation device

Abstract

A method of treating wastewater in a moving bed bioreactor (MBBR) is described. The MBBR includes one or more upflow gravitational separation devices disposed about the discharge area of the reactor. As treated effluent flows upwardly through the one or more gravitational separation devices, suspended solids in the treated effluent are separated. The present invention entails a method or process where the effective cross-sectional area of the one or more gravitational separation devices can be varied and controlled. This in turn varies and controls the upflow velocity of the treated effluent. By varying and controlling the effective cross-sectional area of the one or more gravitational separation devices, the degree to which suspended solids are separated from the treated effluent is controlled.

Description

[0001] SYSTEM AND PROCESS FOR CONTROLLING THE QUALITY OF TREATED WASTEWATER DISCHARGED FROM A BIOLOGICAL REACTOR VIA AN UPFLOW GRAVITATIONAL SEPARATION DEVICE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an efficient system and process for biologically treating wastewater in a moving bed bioreactor (MBBR) containing biofilm carriers, and more particularly to one or more upflow gravitational separation devices for discharging treated water from the MBBR and which also functions to retain the biofilm carriers in the MBBR and generally control the amount of suspended solids retained in the MBBR.

[0004] BACKGROUND OF THE INVENTION

[0005] A moving bed bioreactor (MBBR) is a type of biological reactor for treating wastewater that includes biofilm carriers that support microorganisms that remove biodegradable organic matter and nutrients from the wastewater. MBBRs are typically mixed and there is a continuous flow of wastewater through the MBBR. Biofilm carriers are typically retained in the MBBR by a screen through which the treated effluent flows. Generally, suspended solids, including suspended biomass, in the MBBR pass through the screen and are discharged with the treated effluent.

[0006] SUMMARY OF THE INVENTION

[0007] The inventors recognized that the quality or characteristics of treated effluent flowing from an MBBR is impacted by the suspended solids (including the biomass therein) in the biological reactor. That is, the amount of suspended solids in the MBBR determine to a significant degree the quality or characteristics of the treated effluent. The inventors hypothesize that the quality or characteristics of the effluent could be controlled to a certain degree by controlling the discharge of suspended solids from the MBBR. For example, in some cases the desired quality or characteristics of the effluent can be achieved by accumulating suspended solids in the MBBR. In other cases, the desired quality or characteristics of the effluent can be enhanced or maintained by selectively discharging suspended solids, and the biomass thereof, from the MBBR. With this in mind, the inventors sought to design a system and process that not only retains the biofilm carriers in the reactor, but also could selectively control the amount of suspended solids separated from the effluent being discharged from the MBBR.

[0008] The present invention addresses this problem by incorporating one or more gravitational separation devices about the discharge area of the MBBR. Each gravitational separation device includes what is referred to as an effective cross-sectional area. The effective cross-sectional area is the cross-sectional area of the upflow portion or the upflow section of the separation device through which the effluent flows as it is being discharged from the MBBR. The inventors determined that, by varying and controlling the effective cross-sectional area of the gravitational separation device or devices, this would enable the upflow velocity of the effluent flowing through the gravitational separation device or devices to be controlled, which in turn could be used to control the amount of suspended solids that are separated from the treated water being discharged from the MBBR.

[0009] In one embodiment, there is provided a bank of two or more gravitational separation devices disposed about the discharge area of the MBBR. These gravitational devices are controlled such that one or more of the separation devices can be selectively removed from service at any time. By varying the operative state (i.e. an on state or off state) of one or more of the gravitational separation devices, the effective cross-sectional area of the bank of gravitational separation devices is varied.

[0010] In another embodiment, there is provided a single gravitational separation device about the discharge area of the biological reactor. In this case, the present invention entails a gravitational separation device wherein the effective cross-sectional area of the separation device can be mechanically altered.

[0011] When the MBBR employs a plurality of gravitational separation devices, one or more of the separation devices can be closed, which effectively prevents treated water from flowing through them. That is, by closing one or more of the upflow gravitational devices, this removes the one or more separation devices from service. Furthermore, if a finer adjustment is desired, mechanical means can be employed to partially close flow to one or more of the gravitational separation devices or mechanically alter the effective cross- sectional area of a separation device.

[0012] Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a side elevational view of an MBBR having an upflow gravitational separation device disposed about a discharge area.

[0015] Figure 1A is an enlarged view of the upflow gravitational separation device shown in Figure 1 and illustrates the separation of biofilm carriers and suspended solids from the upflowing treated effluent. Figure 1 B is a schematic illustration of the cross-sectional area of an upflow gravitational device and schematically illustrates how the effective cross-sectional area of the separation device can be varied.

[0016] Figure 2 is a schematic illustration of a control system for controlling the effective cross-sectional area of a bank of gravitational separation devices.

[0017] DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0018] With reference to Figure 1 , a biological wastewater treatment system is shown therein. In this case, the wastewater treatment system is an MBBR. Details of the MBBR system and process are not dealt with here in detail because such is not perse material to the present invention, and MBBR systems and processes are well known and appreciated by those skilled in the art. Suffice it to say that an MBBR process is an attached growth biological treatment process. That is, microorganisms that carry out the treatment are attached to a medium which is referred to herein as a biofilm carrier. The biofilm carrier is kept suspended in the wastewater by a diffused aeration system for an aerobic process or by a mechanical mixing system for an anoxic or anaerobic process. As depicted in the drawings, the circles represent biofilm carriers. Besides the targeted contaminants (e.g. organic matter, nutrients, etc.), the wastewater may include what is broadly referred to herein as suspended solids even though the wastewater treated in the MBBR might have been subjected to pretreatment upstream of the MBBR. The term “suspended solids”, as used herein, is to be broadly interpreted and includes particles, particulate matter, and biomass.

[0019] The MBBR system shown in the drawings is referred to generally by the numeral 10. Wastewater contained in the MBBR is generally sufficiently mixed and flows continuously through the MBBR. As shown in the drawings, the MBBR includes an influent inlet 12 and an aeration system indicated generally by the numeral 14. Air is supplied from an air source to one or more conduits disposed in the bottom portion of the MBBR. From the conduits, the air is dispersed throughout the MBBR.

[0020] Disposed about the discharge end of the MBBR is one or more upflow gravitational separation devices, each being identified generally by the numeral 20. Each gravitational separation device 20 is designed such that treated wastewater flows upwardly through the separator as it is discharged from the MBBR. More particularly, the upflow gravitational separation device is designed to: (1) selectively separate suspended solids from the effluent prior to the effluent exiting the gravitational separation device, and (2) retain the biofilm carriers in the MBBR. That is, as the treated wastewater moves upwardly through the gravitational separation device 20, suspended solids may fall out through the bottom opening 35 in the gravitational separation device and remain suspended in the wastewater in the MBBR. As discussed more fully below, the upflow velocity of the effluent through the gravitational separation device 20 can be controlled and that in turn can generally determine the amount of suspended solids that are separated from or remain entrained with the effluent. Also, the upflow gravitational separation device 20 is designed such that the biofilm carriers are generally prevented from being discharged with the effluent. There may be occasions or circumstances when it is desirable to discharge at least some of the biofilm carriers from the MBBR. In those cases, the effective cross-sectional area of one or more of the upflow gravitational separation devices can be adjusted accordingly.

[0021] Viewing the gravitational separation device 20 in more detail, it is seen that the same includes an inlet 22 and an outlet 24. Note that the outlet 24 is positioned below the general level of wastewater contained in the MBBR. A front panel 34 forms the front of the gravitational separation device 20 and extends below the water level in the bioreactor allowing water to enter the gravitational separation device 20. A guide panel 26 extends above the water level in the reactor for guiding the water downwards into the upflow part of the gravitational separation device 20. A back panel 28 forms the back of the gravitational separation device 20 and in the embodiment illustrated herein, the back panel 28 is formed by a wall of the MBBR, or could be a separate back panel that forms a part of the separation device. The gravitational separation device 20 can be closed on opposite sides by a pair of side panels. Typically, the upflow gravitational separation device assumes the generally form of a vertical column which, in the example shown, includes the guide panel 26, back panel 28 and side panels.

[0022] A line and arrow, denoted by A (Figures 1 and 1A), illustrates the flow of treated water into and through the gravitational separation device 20. Since the MBBR is generally a continuous flow reactor, treated wastewater enters the inlet 22 and turns downwardly so as to flow downwardly between the front panel 34 and the guide panel 26. Thereafter, the treated wastewater turns upwardly and flows upwardly between the guide panel 26 and the front panel 28 to where the wastewater is discharged out the outlet 24. Front panel 24 of the gravitational separation device 20 also functions as an air deflector. Front panel 34 prevents the air being dispersed in the MBBR from interfering with the separation of suspended solids and biofilm carriers occurring in the gravitational separation device.

[0023] One concept underlying the present invention is that suspended solids entrained in the treated water entering the gravitational separation device 20 can be selectively separated from the treated water. Fundamentally, this entails varying the velocity of the treated effluent flowing upwardly through the gravitational separation device 20. The higher the upflow velocity of the effluent passing through the upflow gravitational separation device 20, the greater the tendency of the suspended solids to remain entrained with the effluent. Likewise, the lower the upflow velocity of the effluent, the less the tendency of the suspended solids to remain entrained with the effluent being discharged. Since MBBRs are generally continuous flow reactors, the inventors envisioned that the upflow velocity of the effluent through the gravitational separation devices can be dynamically controlled by controlling the effective cross-sectional area through which the treated effluent flows.

[0024] In the case of a single gravitational separation device 20, the inventors envisioned that the effective cross-sectional area can be varied mechanically. There are various ways of mechanically varying the effective cross-sectional area of the upflow gravitational separation device 20. Figure 1 B schematically shows how the structure and components of the separation device 20 can be mechanically adjusted so as to vary the effective cross- sectional area of the separation device. Opposite sides of the separation device can be moved or articulated between multiple positions by a motor, electric actuator, etc. By selectively actuating, the opposite sides of the separation device, the effective cross- sectional area of the separation device can be adjusted. Note in Figure 1 B where the effective cross-sectional area of the separation device can be varied from the illustration on the left to the illustration on the right. The effective cross-sectional area of the separation device on the right is substantially greater than the cross-sectional area of the separation device shown on the left. Note that the cross-sectional area shown on the left is superimposed by dotted lines on the cross-sectional area on the right. Again, as noted above, Figure 1 B is simply a high level simple schematic illustration showing how the effective cross-sectional area of the upflow gravitational separation device can be varied. There are many ways to accomplish this mechanically with moveable panels, motors and mechanical actuators, etc.

[0025] There are various approaches to controlling the degree of suspended solids separation that occurs in the gravitational separation device 20. At a high level, the separation of suspended solids can be a function of various effluent parameters, such as total suspended solids, turbidity, particle counts, color, opaqueness, etc. In other cases, the degree of suspended solids separation can be based on variations of the influent flow or hydraulic load. In the end, one aim is to enhance the quality of the treated effluent. This is achieved by proactively selecting the amount of suspended solids separated by the upflow gravitational separation device or devices.

[0026] Figure 2 is a schematic illustration showing a control system for controlling a bank of three gravitational separation devices 20. The system includes a programmable logic controller (PLC) that is designed or configured to receive input data and based on the input data, to output operating instructions, which in this case effectively controls the effective cross-sectional area of the gravitational separation devices 20. The PLC includes internal logic programmed to control the gravitational separation devices based on various inputs. In the example shown in Figure 2, various parameters or process variables of the treated effluent are measured online. The effluent parameters that are measured can include, for example, total suspended solids, turbidity, color, and opaqueness. It is understood and appreciated by those skilled in the art that other effluent parameters or process variables could be measured and data representing the measurements inputted into the PLC. Programmed logic contained in the PLC analyzes and manipulates the data to generate one or more output signals. The output signals in this case are directed to three actuators that are operatively associated with the three gravitational separation devices 20. Each of the actuators are in turn operative to adjust and vary the effective cross-sectional area of the associated gravitational separation device based on the output signals from the PLC. For example, each of the separation devices is provided with means that enable the separation device to be completely closed or partially closed. When completely closed, the separation device is offline or out of service. An actuator can be operatively associated with each separation device. Output signals from the PLC drive the various actuators, which in turn are operative to vary the effective cross-sectional area of the three separation devices. As discussed above, by varying the effective cross-sectional area of the separation device, the velocity of the effluent flowing upwardly through the separation device is adjusted to yield a selected degree of suspended solids separation. That is, based on the input data, the programmable logic controller determines the appropriate effective cross-sectional area of the three separation devices in order to achieve the necessary separation of suspended solids passing through the separation device in order to yield a treated effluent having certain qualities and characteristics. In similar fashion, the effective cross-sectional area of the three upflow gravitational separation devices can be adjusted to assure that the biofilm carriers that happen to enter the upflow gravitational device are separated from the treated effluent and are returned to the MBBR.

[0027] As noted above, various data can be used to drive the PLC and control the quality and characteristics of the treated effluent. Another example of an input to the PLC is shown in Figure 2. Here, the influent flow is measured and data representative of the influent flow is inputted into the PLC. Based on that data, the program logic in the PLC directs signals or instructions to the actuators that in turn adjusts and controls the effective cross-sectional area of the gravitation separation devices so as to yield a treated effluent having selected qualities and characteristics.

[0028] There are many advantages to the present invention. First, by controlling the effective cross-sectional area of the gravitational separation device 20, a partial separation of particles forming the suspended solids can be achieved and controlled in the case where full separation is not desired or when the hydraulic load is varying. This can be used to decrease the amount of suspended solids in the MBBR by flushing them to the effluent, or by increasing the amount of suspended solids in the MBBR by accumulating influent suspended solids. Another advantage of the present invention is that separation of distinctly different fractions of particles in the suspended solids can be achieved. For example, the effective cross-sectional area of the gravitational separation device or devices can be varied so as to distinguish between light and heavy bacteria conglomerates in a system. This method or process can be used in order to favor particles with a high sinking velocity to be accumulated in a system at the expense of particles with lower sinking velocity (for instance, flocs). Finally, the present invention is employed in an MBBR system, the gravitational separation devices can be used to retain the biofilm carriers. The biofilm carriers are heavier than water and consequently the invention is used to retain the biofilm carriers in the MBBR while lighter suspended solids are entrained with the effluent and are discharged from the MBBR. In some cases, the present invention can be used to reduce the amount of biofilm carriers in the system when such is necessary.

[0029] The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

Claims

CLAIMSWhat is claimed is:1 . A method of treating wastewater containing suspended solids in a moving bed bioreactor (MBBR) containing biofilm carriers, comprising: directing the wastewater into the MBBR; biologically treating the wastewater in the MBBR by contacting the wastewater with the biofilm carriers; directing the wastewater containing suspended solids through one or more upflow gravitational separation devices with each separation device including a cross-sectional area through which the wastewater flows; separating at least some of the suspended solids from the wastewater flowing through the one or more separation devices to yield a treated effluent; and varying the amount of suspended solids separated from the wastewater flowing through the one or more separation devices by varying the effective cross-sectional area of the one or more separation devices through which the wastewater flows, which in turn varies the upflow velocity of the wastewater flowing through the one or more separation devices.

2. The method of claim 1 including maintaining the effective cross-sectional area of the one or more gravitational separation devices at a level that maintains substantially all of the biofilm carriers in the MBBR.

3. The method of claim 1 wherein varying the cross-sectional area of the one or more separation devices through which the wastewater flows is a function of one or more wastewater parameters.

4. The method of claim 3 wherein varying the cross-sectional area of the one or more separation devices through which the wastewater flows is a function of the flow rate of wastewater into the MBBR.

5. The method of claim 1 including two or more gravitational separation devices and wherein varying the cross-sectional area of the two or more separation devices through which the wastewater flows includes preventing wastewater from flowing through at least one of the separation devices.

6. The method of claim 1 including a plurality of gravitational separation devices where one or more of the separation devices includes on and off states, and wherein the cross- sectional area of the plurality of separation devices through which wastewater flows can bevaried by selectively switching between on and off states of the one or more separation devices that include an on and off state.

7. The method of claim 1 wherein the cross-sectional area of at least one separation device through which the wastewater flow is varied mechanically.

8. The method of claim 1 wherein there is one gravitation separation device associated with the MBBR and wherein said one separation device includes a housing structure that includes a wastewater inlet and an effluent outlet and a surrounding wall structure that defines an area through which the wastewater flows as the wastewater flows through the separation device, and wherein at least a portion of the housing structure is moveable in order to effectively vary the cross-sectional area of the housing structure through which the wastewater flows.

9. The method of claim 1 further including controlling the velocity of the wastewater flowing through the one or more upflow gravitational separation devices such that the biofilm carriers are separated from the effluent and remain in the MBBR.

10. The method of claim 1 wherein there is provided a sieve or screen operatively associated with the MBBR to prevent the biofilm carriers from being discharged from the MBBR; wherein the upflow gravitational separation device is relegated to varying the amount of suspended solids separated from the wastewater flowing through the one or more separation devices.

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