System and method for upgrading a conventional activated sludge plant

Abstract

Traditional activated sludge wastewater treatment equipment is upgraded by adding one or more of a membrane filtration unit, a membrane aerated biofilm reactor (MABR) unit, and a screen. The membrane filtration unit is added between the process tank and the secondary clarifier. The membrane filtration unit extracts treated effluent at a rate of up to 25% of the inflow rate. Since the MLSS concentration is still below 4000 mg / L, the equipment is not converted to a membrane bioreactor (MBR). The membrane aerated biofilm reactor (MABR) unit is added to the process tank of the equipment and provides attached-growth biological treatment. The screen extracts solids from the water flowing into the process tank. When optionally used in combination, the added units and processes increase the equipment's capacity for primary separation, biological treatment, and secondary separation. The inflow rate can be increased.

Description

[0001] This application is a divisional application of a patent application filed on April 21, 2017 (application number 2017800898670, invention title "System and method for upgrading conventional activated sludge equipment"). Technical Field

[0002] This manual relates to the use of activated sludge processes for treating wastewater, such as sewage or industrial wastewater. Background Technology

[0003] The activated sludge process is a biological treatment process and is standard practice in many countries worldwide. In a conventional activated sludge wastewater treatment plant (WWTP), wastewater passes through one or more biological process tanks maintained under various oxidizing and mixing conditions. Organisms grow in the suspended solids within the process tanks. The combination of wastewater and organisms is called mixed liquor. The mixed liquor is separated in a secondary clarifier to produce treated effluent and activated sludge. A portion of the activated sludge (returned activated sludge or RAS) is recycled to one or more process tanks. Another portion of the activated sludge (waste activated sludge or WAS) is discarded. The recycling of activated sludge results in a organism residence time greater than the hydraulic residence time of the equipment. The mixed liquor suspended solids (MLSS) concentration is typically less than 4000 mg / L. Alternatively, wastewater may pass through a primary clarifier before being treated in the process tanks. The primary clarifier produces primary sludge and primary effluent. The primary effluent flows to the process tanks. Summary of the Invention

[0004] This specification describes methods and systems that can be added to conventional activated sludge (CAS) equipment to upgrade it. Upgraded equipment can produce higher quality effluent, treat wastewater at higher rates, or both. The various systems and methods described herein can be used individually or in any combination of two or more.

[0005] In one example, a membrane filtration unit is added between the process tank and the secondary clarifier. At this point, the biological treatment is essentially complete, or at least essentially complete as it would be in the secondary clarifier. The membrane filtration unit extracts the treated effluent from the mixed liquid prior to secondary clarification. The treated effluent extracted by the membrane filtration unit can be mixed with the treated effluent from the secondary clarifier. Extracting the treated effluent from the membrane filtration unit as permeate reduces the hydraulic loading rate of the secondary clarifier, or both the hydraulic and solids loading rates (depending on whether the solids removed by the membrane are sent to the secondary clarifier or to the return activated sludge (RAS) line). The amount of treated effluent extracted by the membrane filtration is preferably less than 25% of the inflow rate. Because the system operates under CAS operating conditions (e.g., MLSS < 4000 mg / L), the device is not converted into a membrane bioreactor (MBR).

[0006] In another example, a membrane aerated biofilm reactor (MABR) unit is added to the device, for example, by immersion in a process tank. The MABR unit adds biological treatment via attached growth to conventional suspension growth.

[0007] In another example, one or more filters, such as microporous sieves, are added to extract solids from the water flowing in or to the process tank. In one option, the microporous sieve is added in parallel with a primary clarifier. In another option, a portion of the RAS is screened before returning to the process tank. Using either or both of these methods reduces the solids load on the process tank.

[0008] When used in combination, the above units and their corresponding processes enhance the equipment's primary separation, biological treatment, and secondary separation capabilities. This can increase the inflow rate of the equipment. Attached Figure Description

[0009] Figure 1 It is a schematic process flow diagram of a traditional activated sludge equipment based on existing technology.

[0010] Figure 2a is a schematic process flow diagram of a traditional activated sludge equipment upgraded with primary micro-sieving.

[0011] Figure 2b is a schematic process flow diagram of a traditional activated sludge equipment upgraded with side-flow screening.

[0012] Figure 3 This is a schematic process flow diagram of a traditional activated sludge equipment upgraded with MABR membranes.

[0013] Figure 4A This is a schematic process flow diagram illustrating the upgrade of traditional activated sludge equipment by using membrane filtration outside the bioreactor.

[0014] Figure 4B This is a schematic process flow diagram illustrating the upgrade of traditional activated sludge equipment by using membrane filtration within a bioreactor. Detailed Implementation

[0015] Traditional activated sludge (CAS) is a common biological wastewater treatment process. CAS typically involves three treatment steps, although the primary treatment step described below can optionally be omitted. Pretreatment uses mechanical means such as coarse screening, sand removal, and grease flotation to remove larger particles. Primary treatment (usually in a clarifier) ​​removes suspended solids (including some organic matter) through physical separation. One or more bioreactors using microorganisms to remove organic matter (e.g., COD / BOD) typically operate under aerobic conditions in at least one reactor. The bioreactor may also include multiple zones or tanks, optionally with one or more recirculation loops between them, where environmental conditions are controlled (i.e., between aerobic, anoxic, and anaerobic conditions) to favor different biological pathways for the removal of nutrients (such as nitrogen and phosphorus). Secondary treatment (typically in a clarifier) ​​separates the mixed liquid suspended solids (MLSS) from the final effluent, recycling a portion as recirculated activated sludge (RAS) and discarding a portion (WAS) to control sludge retention time (SRT).

[0016] exist Figure 1 The wastewater treatment plant (WWTP) 10 shown is an example of a conventional CAS plant. The treatment unit includes a primary clarifier 12, a process tank 14, and a secondary clarifier 16. Although only one process tank 14 is shown, multiple process tanks or other forms of bioreactors may optionally be present. When only one process tank 14 is present, it is typically aerated to provide suspended growth under aerobic conditions. Optionally pretreated influent wastewater 18 flows into the primary clarifier 12. Primary sludge 17 is separated from primary effluent 20. Primary effluent 20 flows into process tank 14 and becomes part of the mixed liquid 22 therein. Mixed liquid 22 also flows to the secondary clarifier 16, where it is separated into activated sludge and treated effluent 24. Optionally, spent activated sludge (WAS) 28 exits the plant 10. Returned activated sludge (RAS) 26 is recycled back to process tank 14.

[0017] CAS (Chemical Access Control) equipment frequently requires upgrades or expansions. Upgrades are needed when treatment targets or effluent regulations become more stringent and the level of treatment achieved by the equipment is insufficient. Expansions are also necessary when the inflow rate of wastewater and / or the concentration of contaminants increases. Upgrading and expanding CAS equipment can be complex and expensive, as it involves adding storage and mechanical components. In many cases, CAS equipment is located in locations with very limited space available.

[0018] Upgrading a CAS (Chemical Acrylamide) device may involve adding one or more products to the CAS device. These products target the three treatment steps described above (primary separation, biological treatment, and secondary separation). They can be used individually or in combination of two or more. One type of product involves microporous sieves, or other sieves, which can be added to supplement the primary treatment to further reduce solids in the process tank or to protect the added membrane from solids. Another type of product involves media that support attached growth, such as membrane aeration biofilm modules, to supplement the bioreactor. Another type of product involves membrane filtration to supplement secondary clarification. The primary clarifier in the examples described below is optional.

[0019] Microsieving, side-flow sieving, MABR, and membrane filtration are described in other above-mentioned documents, such as U.S. Patents 6,942,786, 6,814,868, and 6,645,374, which are incorporated herein by reference. In this specification, they may optionally be used together to upgrade or expand CAS equipment.

[0020] In one example, using micro-screening products involves installing micro-screens in parallel with primary processing to remove suspended solids. Figure 2A In the example, a rotating belt screen (RBS) 32, such as GE Water's LEAP PRIMARY RBS, is added, but other configurations of microporous screens, such as drums or discs, may also be used. The microporous screen may optionally have pores of approximately 300 micrometers or smaller, or approximately 200 micrometers or smaller, or approximately 100 micrometers or smaller. A portion 30 of the influent wastewater 18 is transferred to the RBS 32. Microscreen sludge 33, containing solids removed by the RBS 32, may be added to the primary sludge 17. The RBS effluent 34 flows to the process tank 14. Parallel microscreens may operate continuously or only during peak periods to increase the hydraulic capacity of the primary treatment. Alternatively, parallel microscreens may contribute to increased chemically promoted primary treatment, i.e., by adding phosphorus-precipitated chemicals or polymers to the influent wastewater 18, by preventing an increase in solids to the primary clarifier 12 (which would otherwise result in some of the influent wastewater 18 being diverted from the primary clarifier 12).

[0021] In another example, a microporous sieve or other sieve is used to extract solids from the feed liquid or RAS. Removing these solids can supplement primary treatment or replace primary treatment if the equipment does not have one. Alternatively or additionally, screening the feed liquid or RAS can remove debris and larger particles from the feed liquid to protect the membrane in or added to the equipment. The sieve may optionally have pores of approximately 300 micrometers or smaller, or approximately 200 micrometers or smaller, or approximately 100 micrometers or smaller. In cases where only membrane protection is required, the sieve may optionally have pores up to 1000 micrometers in size. Figure 2BIn the example, a portion 38 of RAS26 is transferred to a rotary drum screen 36. Solids 37 removed by the screen 36 can be mixed with primary sludge 17. Filtrate 40 flows to process tank 14. If it is necessary to reduce the waste content in the mixed liquor to inhibit damage to the membrane module, this version of the primary treatment upgrade or extension is useful, for example, in combination with one or both of these other types of products involving biofilm support or filtration membranes.

[0022] Adding a supported biomass medium enhances the biological processing capacity of device 10. Figure 3 In the example, a membrane aerated biofilm module (MABR) module 42, such as GE Water's ZEELUNG module, is immersed in process tank 14. The MABR module provides additional nitrification and BOD removal capabilities. In the example shown, the MABR module 42 is immersed in the anoxic zone at the front end of process tank 14. Process tank 14 is aerobic downstream of the MABR module 42.

[0023] Membrane filtration products are used to extract treated effluent from mixed feed solutions. An example of a membrane filtration product is GE Water's ZEEWEED immersion ultrafiltration (UF) or microfiltration (MF) module. Figure 4A In the example, membrane tank 44 is located outside process tank 14 and contains either an immersed membrane in an open tank or a membrane contained in a sealed tank. A portion 46 of the mixture 22 is pumped out of the end of process tank 14 (where biotransformation is substantially complete) or through a conduit between process tank 14 and secondary clarifier 16 and is treated by an MF / UF membrane. Reject 48 may be mixed with RAS 26 or WAS 28. Adding membrane filtration in this manner reduces both the hydraulic and solids loading rates of secondary clarifier 16. Alternatively, some or all of the reject 48 may flow to secondary clarifier 16, which reduces the hydraulic loading on secondary clarifier 16 but only reduces the solids loading on secondary clarifier 16 to the extent that some reject 48 (if present) is mixed with RAS 26 or WAS 28. Permeate 50 may be mixed with the treated effluent 24.

[0024] exist Figure 4B In this example, membrane module 54 is directly immersed in the mixture 22 of process tank 14. This avoids pumping the mixture and the need for additional storage. In this case, the mixture can be only slightly concentrated and flows to the secondary clarifier. In this embodiment, adding membrane filtration only reduces the hydraulic load rate on the secondary clarifier.

[0025] exist Figure 4A and 4BIn this process, the permeate 50 is mixed with the treated effluent 24, thus improving the overall quality of the discharged effluent. Alternatively, in either example, the permeate 50 may be kept separate from the treated effluent 24. Due to the high quality of the permeate 50, it can be reused directly (e.g., for irrigation) or further treated by reverse osmosis for other types of reuse (e.g., groundwater refilling).

[0026] Adding a filter membrane to treat a small portion of the feed solution 22 does not convert the CAS device into a membrane bioreactor (MBR). The fraction of the inflow rate (Q) extracted as permeate 50 is limited to 25% (or one-third of the treated effluent 24 discharged from the secondary clarifier 16). The MLSS concentration of the feed solution 22 is optionally not increased, or at least not substantially increased. The MLSS concentration of the modified device is approximately 2000 to 4000 mg / L (typical for CAS), rather than 6000 to 12000 mg / L (typical for MBR).

[0027] Two or all three product types can be combined to improve the utilization of existing infrastructure. While existing CAS (Chemical Access Regulator) devices may be subject to different limitations, these limitations can potentially be addressed to increase device throughput by up to 25%. Optionally, products can be installed without substantially disrupting the operation of the CAS devices. Both MABRs and filter membranes can be configured as floating cartridges.

[0028] This specification uses examples to disclose the invention, including the best practices, and also enables those skilled in the art to practice the invention, including making and using any apparatus or system and performing any of the included methods. The patentable scope of the invention is defined by the claims and may include other examples that would occur to those skilled in the art. These other examples are intended to be within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

Claims

1. A method for upgrading a conventional activated sludge (CAS) device and treating wastewater, wherein the CAS device includes one or more biological process tanks and a secondary clarifier, the method comprising the following steps: Add a membrane filtration unit to the CAS device; Wastewater is passed through one or more biological process tanks and the wastewater is biologically treated to produce a mixed liquid; The first portion of the mixed liquid is separated by the filtration membrane of the membrane filtration unit; as well as The second portion of the mixed liquid is separated by the secondary clarifier; The first part comprises at most 25% of the combined first and second parts.

2. The method according to claim 1, wherein, The mixture has a solids concentration of 4000 mg / L or lower.

3. The method according to claim 1 or 2, further comprising recycling a portion of the activated sludge back to the one or more bioprocess tanks.

4. The method of claim 3, further comprising the return portion of screening the activated sludge upstream of the one or more bioprocess tanks.

5. The method of claim 1 or 2, further comprising screening the wastewater in parallel with a primary clarifier before passing the wastewater through the one or more biological process tanks.

6. The method according to claim 5, wherein, The screening includes micro-screening the wastewater.

7. The method according to claim 1 or 2, wherein, The biological treatment of the wastewater includes attached and suspended growth biological processes.

8. The method according to claim 1 or 2, wherein, The biological treatment of the wastewater includes treatment using a membrane aeration biofilm module.

9. The method according to claim 1 or 2, wherein, The filtration membrane is an ultrafiltration or microfiltration membrane.

10. The method according to claim 1 or 2, wherein, The first portion of the mixture liquid separated by the filter membrane produces permeate.

11. The method according to claim 1 or 2, further comprising causing the solids separated by the filter membrane to flow to the secondary clarifier.

12. The method according to claim 1 or 2, wherein, The second portion of the mixed liquid is separated by the secondary clarifier to produce activated sludge and effluent.

13. The method of claim 12, further comprising mixing the solids separated by the filter membrane with a return portion of the activated sludge.

14. The method of claim 12, further comprising mixing the solids separated by the filter membrane with the waste portion of the activated sludge.

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