Method and apparatus for partial nitrification using a membrane aerated biofilm reactor

Abstract

This specification describes a membrane-aerated biofilm reactor (MABR) and method for nitrosation, nitrosation-denitrosation, or deammonification. Oxygen supply through a gas transfer membrane is limited to inhibit growth of nitrite oxidizing bacteria (NOB). Exhaust gas from the MABR unit can have an oxygen concentration of 4% or less. The method can optionally include one or more of the following: intermittent (batch) feed process air; process air conditioning; process air direction reversal; process air recirculation; and, process air step flow. The method can optionally include adding inoculum sludge containing anammox to the reactor, optionally after pretreatment and selection.

Description

[0001] Related applications

[0002] This application claims the benefit and priority of U.S. Provisional Patent Application No. 62 / 972,719, filed February 11, 2020, entitled “Process and Apparatus for Nitritation Using Membrane Aerated Biofilm Reactor,” which is incorporated herein by reference. Technical Field

[0003] This manual relates to membrane aerated biofilm reactors (MABRs) and related equipment, as well as wastewater treatment using membrane aerated biofilms. Background Technology

[0004] Nitrogen compounds typically exist in the form of ammonia and are routinely removed from wastewater via nitrification-denitrification. Conventional nitrification involves two steps: nitrite production via ammonia-oxidizing bacteria (AOB), followed by the oxidation of nitrite to nitrate by nitrite-oxidizing bacteria (NOB). Nitrification, or partial nitrification, occurs solely through the first step using AOB to produce nitrite. In nitrification-denitrification, or short-cut denitrification, nitrite is directly converted to gaseous nitrogen by ordinary heterotrophic bacteria (OHB) without the production of nitrate. Anaerobic ammonia oxidation (anammox) is a microbial process in which nitrite and ammonium are converted into diatomic nitrogen and water. The abbreviation can also refer to the bacteria that perform the anaerobic ammonia oxidation process. Some nitrates are also produced as respiratory products of anaerobic ammonia oxidizing bacteria. Denitrification (or partial nitrification-anaerobic ammonium oxidation) refers to a process that combines partial nitrification (i.e., nitrification of some, but not all, of the ammonium in the wastewater supply without producing large amounts of nitrate) with anaerobic ammonium oxidation of nitrite and residual ammonium. Nitrification-denitrification and denitrification are difficult to implement in practice because NOB is prone to growth and tends to convert these processes into complete nitrification-denitrification.

[0005] In membrane biofilm reactors (MBfR), a gas transfer membrane is used to support the biofilm while one or more gases are supplied to the biofilm through the membrane. Aerated membrane biofilm reactors (MABR) are a subset of MBfR where an oxygen-containing gas (generally air) is used for the biological reaction. Li et al. recently reviewed efforts to use MABRs for deammoniation (2018). Efforts to address the challenge of suppressing NOB in biofilms include controlling the air pressure within the membrane to match the ammonia and oxygen transfer rates (Gilmore et al., 2013) and periodically shutting off the air (or oxygen) supply, for example, shutting off the air for one day in a 1.5-day cycle (Pellicer-Nacher 2010). Summary of the Invention

[0006] The following paragraphs are intended to introduce the invention and the following specific embodiments to the reader, rather than to limit or define any claimed invention.

[0007] The inventors have observed that the methods for controlling NOB as described above are not effective in practice. For example, controlling air pressure or airflow rate can prevent significant NOB growth in the biofilm during the reactor start-up phase (which may take several months) and in the months that follow. However, a significant NOB population eventually emerges, transforming the process into complete nitrification-denitrification. The reactor must then be shut down, typically for a period of 4–8 weeks, to disrupt the NOB population in the biofilm. But after restarting the reactor, the NOB population generally reappears after several months, leading to another reactor shutdown. Multiple reactor shutdowns for several weeks each year severely impact the process productivity. Similarly, shutting off the air for 12–24 hours in 1.5–2 day cycles severely impacts process productivity. Although NOB growth is suppressed during the shutdown period, AOB does not convert ammonia to nitrite during the shutdown period.

[0008] This specification describes methods for operating a MABR. MABRs can be used for the biotransformation of ammonia in water, such as by nitrification (incomplete nitrification), with or without complete nitrification-denitrification or deammoniation reactions. In these methods, it is useful to inhibit or control the growth of NOB and, in the case of deammoniation, to support the growth of anaerobic ammonia-oxidizing bacteria. One method involves supplying an oxygen-containing gas or gas mixture (optionally referred to as process air) to a device containing a membrane-aerated biofilm medium, such as a gas transfer membrane (optionally referred to as a MABR unit), to inhibit NOB growth and, in some instances, encourage the growth of anaerobic ammonia oxidation. This specification also describes a device, such as an MABR or MABR unit. The device includes one or more tools, such as a network of conduits, metering devices, valves, sensors, and flow control instruments, for supplying air to the membrane-aerated biofilm medium as needed to implement the method.

[0009] In some of the examples described herein, the methods may include one or more of the following: intermittent or batch feeding of process air over short cycles; process air conditioning; process air reversal; nitrogen enrichment (or oxygen dilution) of process air, for example, through process air recirculation; stepped flow of process air; and maintaining exhaust oxygen concentration below 4%. Process air is air supplied to the interior of the MABR unit for transfer to the biofilm, rather than air supplied by generating bubbles outside the MABR unit to flush the biofilm. Exhaust is the portion of process air that is not delivered to the biofilm and leaves the MABR unit. These methods can be used in various arrangements and combinations. For example, stepped flow of process air can be combined with any other method, optionally with the MABR medium (i.e., one or more gas transfer membranes) or a MABR unit less than 0.5 m in length. In another example, reverse flow of process air can be combined with any other method.

[0010] This specification describes a method for batch feeding process air within a short cycle. In this method, air is supplied to the MABR unit for a first time period, and then the valves upstream and downstream of the MABR unit are closed for a second time period. Optionally, the total cycle time can be between 0.1 and 2 hours.

[0011] This specification describes a method for process air conditioning. In this method, air is supplied to a MABR unit at a first rate for a first time period and at a second rate for a second time period. Optionally, the total cycle time can be between 0.5 and 10 days.

[0012] This specification describes a method for reversing the direction of process air flow. In this method, process air flows through a MABR unit in one direction for a first time period, and then flows through the MABR unit in the opposite direction for a second time period. Optionally, the total cycle time can be between 0.5 and 10 days.

[0013] This specification describes a method for nitrogen enrichment in process air. In this method, nitrogen-enriched (or oxygen-diluted) air is supplied to the MABR for a continuous period of time. The nitrogen-enriched air can be supplied continuously. Optionally, nitrogen-enriched air is supplied to the MABR unit for a first period of time, and ambient air is supplied to the MABR unit for a second period of time, for example, the total cycle length is between 0.5 and 10 days. In some instances, the nitrogen-enriched air is supplied via process air recirculation, i.e., at least some exhaust gas flows from the outlet of the MABR unit into the inlet of the MABR unit. Optionally, the process air velocity during the second period of time does not decrease relative to the first period of time, such that the air velocity through the MABR unit increases during the exhaust gas recirculation period.

[0014] This specification describes a method for stepped flow of process air. In some instances, process air is supplied to multiple MABR units connected in series, for example, by connecting the port of one MABR unit to the port of another MABR unit.

[0015] Short start-up phases also benefit from the use of deammoniation to treat water, as anammox produces slow-growing, low-yield microorganisms, and the start-up time of deammoniation reactors is generally significant. In some instances, this specification describes a method that can be used to shorten reactor start-up time or to shorten the time required for a reactor to recover from a failure involving a reduction in anammox bacteria. This method may include adding inoculum sludge containing anammox bacteria to the reactor, optionally after pretreatment and selection of the inoculum sludge, optionally after inoculating the reactor with nitrified sludge. Alternatively or additionally, the method may include pre-inoculating MABR media or units separately from the inoculated reactor.

[0016] Not intended to be theoretically limited, the methods described herein exert pressure on NOB by subjecting at least some, but preferably most or all, of the biofilm attached to the MABR unit to periodic exposure to low oxygen availability. However, the entire MABR unit is rarely (if any) fully exposed to low oxygen availability, thus AOB remains active. In some instances, the method utilizes spatial differences within the MABR unit, such as upstream sections receiving process air with higher oxygen concentrations than downstream sections. Methods such as stepped process air flow, batched process air feed, process air conditioning, and nitrogen enrichment of process air can help ensure that downstream sections of the MABR unit are at least temporarily exposed to air with low oxygen concentrations (e.g., 4% or less oxygen). Reversing the process air direction or exhaust recirculation can cause the low oxygen concentration region to shift to the previously upstream end of the MABR unit, thereby suppressing NOB throughout most or all of the biofilm. Attached Figure Description

[0017] Figure 1 A graph showing the flux of DO and O2 along the membrane cord in the experimental setup.

[0018] Figure 2 A graph showing the variation of oxygen flux at a certain frequency in batches of process air feed.

[0019] Figure 3 This is a graph showing the oxygen flux over time in a process air conditioning method.

[0020] Figure 4 This is a graph showing the distribution of oxygen flux along the membrane length during reversed process airflow direction.

[0021] Figure 5A graph showing oxygen flux along the membrane length with and without process air recirculation.

[0022] Figure 6A and 6B These are diagrams illustrating batch feeding of process air with open and closed media, respectively.

[0023] Figure 7 This is a diagram of process air conditioning. The left side shows continuous but low process airflow, while the right side shows intermittent but high process airflow.

[0024] Figure 8 This is a diagram illustrating the reversal of the process airflow direction.

[0025] Figure 9A and 9B This is a diagram of process air recirculation. The left side shows continuous process air with recirculation, while the right side shows batch feeding of pure oxygen with recirculation.

[0026] Figure 10A , 10B The diagrams for 10C and 10C represent the flow patterns of process air in three stages: a flow pattern of process air with recirculation and a flow pattern of process air with reversed direction.

[0027] Figure 11A , 11B 11C and 11C are schematic diagrams of experimental MABRs configured for startup, process air direction reversal, and batch process air feeding, respectively.

[0028] Figure 12 for Figure 11A A graph showing the experimental results during MABR operation.

[0029] Figure 13 for Figure 11B A graph showing the experimental results during MABR operation.

[0030] Figure 14 for Figure 11C A graph showing the experimental results during MABR operation.

[0031] Figure 15 A graph showing the experimental results of a MABR with process air conditioning and, in some cases, reversed process air direction.

[0032] Figure 16 This demonstrates an experimental MABR with reversed process air direction.

[0033] Figure 17 Display configurations include reversed process air direction and stepped process air flow. Figure 16 Experimental MABR.

[0034] Figure 18 for Figure 16 and 17 The chart shows the experimental results of MABR.

[0035] Figure 19 A graph showing the experimental results during the startup of another MABR.

[0036] Figure 20 This includes a period of time during which the air direction is reversed in the process. Figure 19 The chart shows the experimental results of MABR.

[0037] Figure 21 For process air nitrogen enrichment over a period of time Figure 19 The chart shows the experimental results of MABR. Detailed Implementation

[0038] Membrane aerated biofilm media (optionally referred to as MABR media) generally comprise one or more gas transfer membranes. The gas transfer membrane can be a hydrophobic porous membrane, a densely walled material, or a material with sufficiently small pore sizes (i.e., <40 Å) to prevent bulk water flow. The gas transfer membrane can have any shape. For example, the gas transfer membrane can be in sheet form, as in products manufactured by Fluence, or in the form of discrete hollow fibers, as in products manufactured by 3M or Oxymem. Alternatively, the gas transfer membrane can be multiple hollow fiber gas transfer membranes in a strip, as in the ZeeLung sold by Suez. TM In the product. This type of tape is described in International Publication No. WO 2015 / 142586 A2, which is incorporated herein by reference. In the case of the tape or another structure having multiple gas transfer membranes with a thickness less than the expected biofilm thickness, the gas transfer surface can be represented by a smooth surface covering a single membrane. The use of tape to support nitrification is described in International Publication No. WO 2020 / 086407 A2, which is incorporated herein by reference. MABR media can be deployed in tanks with or without suspended biomass. Nitrification, nitrification-denitrification, or deammoniation can occur in the biofilm.

[0039] Factors that inhibit or remove NOB include, for example, solids retention time (SRT), dissolved oxygen (DO) concentration (especially during different lag periods of AOB and NOB), temperature, pH, alkalinity, free nitrite, and free ammonia. However, in MABRs, many of these factors are impractical or difficult to adjust. Restricted oxygen supply can be used for NOB control in MABRs. However, excessive oxygen restriction also reduces the ability of AOB to convert ammonia to nitrite. Furthermore, restricting oxygen supply alone is generally not effective in achieving and maintaining high-velocity nitrification over extended periods while minimizing complete nitrification in MABRs.

[0040] In membrane aerated biofilm processes, oxygen diffuses through the membrane wall into the biofilm, while substrates such as ammonium enter the biofilm from the bulk liquid in the opposite direction—a phenomenon known as reverse diffusion. If oxygen is not consumed immediately, it accumulates at the base of the biofilm. When the local oxygen level becomes sufficiently high, NOB begins to grow and may proliferate at the base of the biofilm. A challenge in MABRs is that while higher airflow rates can increase the oxygen transfer rate (OTR), they can also lead to more oxygen accumulation at the base of the biofilm. Even under controlled low airflow rates, significant NOB populations can still establish themselves in the biofilm after prolonged operation.

[0041] In particular, NOB can proliferate near the inlet of the MABR unit even at low airflow rates. At the inlet of the MABR unit, the oxygen concentration of the process air and the resulting oxygen transfer driving force are high. Figure 1 This displays the oxygen flux and DO concentration along the length of the hollow fiber gas transfer membrane at the base of the biofilm. Figure 1 As can be seen, the oxygen flux and DO concentration are high near the MABR unit inlet (i.e., at the gas transfer membrane inlet) and become lower at the outlet. Although the overall method conditions (i.e., average oxygen flux or DO concentration) can be optimized to selectively suppress NOB, the oxygen flux and DO concentration near the MABR unit inlet remain high, which can lead to long-term NOB growth starting from one end of the membrane. However, some or all of the methods described below help to suppress NOB growth in the long term and reduce it to a minimum, or optionally increase the total oxygen transfer rate (OTR).

[0042] For example, intermittent or batch feeding of process air over a period of 0.1-2 hours will create a cycle in the biofilm where the OTR (Oxygen Flow Rate) changes over time, including a period of high OTR (aeration on-time), a period of OTR decreasing to zero (aeration transition period), and optionally a short period of OTR remaining at zero (aeration off-time). An example of this variation in oxygen flow rate through the membrane is... Figure 2 As shown. The duration of the aeration on-off and off-off periods is a controllable parameter for the success of the method and can be optimized for specific equipment. Generally, the duration of the aeration off-off period should be 25% or less of the total cycle time, or 10% or less. The total cycle duration is optionally 30 minutes or less. The process air conditions during the aeration on-off period, including process airflow rate and operating pressure, can be higher than those of methods using continuous process air to suppress NOB. Thus, the overall OTR and throughput of a MABR unit using batch-feed process air do not necessarily decrease compared to methods using continuous process air.

[0043] Figure 6A and 6B This shows two methods for providing an aeration transition period. In Figure 6AIn one method shown, the supply of process air 15 to the MABR unit 6 is stopped, for example by closing the intake valve 20, while keeping the exhaust outlet 18 of the MABR unit open. Figure 6B In another method shown, the supply of process air 15 to the MABR unit 6 is stopped, for example by closing the inlet valve 20, and the exhaust outlet of the MABR unit is also closed, for example by closing the exhaust valve 22. The naming of the inlet and outlet of the MABR unit 6 relative to the direction of the process air flowing through the MABR unit 6 can vary as further described below. However, the inlet and outlet are located at opposite ends of the gas transfer membrane in the MABR unit 6. Therefore, when inlet valve 20 and exhaust valve 22 are closed, the process air is trapped within the MABR unit, and oxygen continues to permeate through the gas transfer membrane to the biofilm. The resulting aeration transition period, within a short cycle, can continue into the next aeration start period, resulting in no aeration shutdown period. Figure 6A In this arrangement, a pressure control valve is typically present at the outlet of MABR unit 6. This valve can be adjusted to prolong the aeration transition period, ensuring that any aeration shutdown period is less than 25% of the total cycle time, optionally less than 10%. However, in either case ( Figure 6A Alternatively, a 6B aeration cycle can be used, with a total cycle time of 2 hours or less, or 30 minutes or less, because in longer cycles, the aeration transition period is unlikely to be a significant part of the cycle. If present, the aeration transition period and aeration shut-off period inhibit NOB growth.

[0044] Figure 3 and 7 This indicates process air conditioning. Process air conditioning is performed over relatively long cycles, such as cycles between 0.5 and 10 days or between 1 and 7 days. Process air conditioning does not have an aeration shutdown period. Figure 3 As shown, during the repetitive cycle, the process airflow rate is adjusted between relatively high and relatively low rates. Figure 7 As shown, during the low flow period ( Figure 7 Compared to the pressure within MABR unit 6 on the left, the high-flow-rate period generally corresponds to a higher pressure within MABR unit 6. Figure 7 (Right side). In at least a portion of MABR unit 6, the lower OTR period in the process air conditioning is controlled at a level that inhibits NOB, i.e., limits NOB growth, and optionally temporarily stops or reverses NOB growth. The higher OTR period increases the average OTR without causing excessive NOB proliferation. Optionally, the process air conditioning can be combined with batched process air feed to produce a method with high OTR periods, low OTR periods, aeration transition periods, and aeration shutdown periods. Optionally, the process air conditioning can be combined with process air direction reversal (as described below). In this case, a lower flow rate can be selected such that NOB is inhibited only at the downstream end of MABR unit 6.

[0045] The low OTR threshold limiting NOB growth varies with many parameters, including membrane material and configuration, as well as operating conditions such as temperature, pH, DO, and ammonium concentration in the bulk. The acceptable level of complete nitrification also influences the chosen OTR threshold. Therefore, the operating conditions for achieving low OTR can vary depending on the influencing parameters. However, the inventors observed that NOB can be suppressed in at least a portion of the MABR unit when the exhaust oxygen concentration is 4% or lower. When the exhaust oxygen concentration is 2% or lower, NOB is likely to be suppressed in at least the downstream portion of the MABR.

[0046] Reference Figure 8 During the process air reversal, in the first time period, process air 15 enters the first port 24 of MABR unit 6 while exhaust air 18 exits from the second port 26 of MABR unit 6. Figure 8 (Left side). During the second time period ( Figure 8 (On the right side), process air 15 enters the second port 26 of the MABR unit 6, while exhaust air 18 exits from the first port 24 of the MABR unit 6. The airflow direction through the membrane aeration biofilm medium (i.e., hollow fiber membrane or belt) is reversed during the repetition cycle.

[0047] As mentioned above, stable nitrification can be achieved at continuous but relatively low process gas flow rates. However, compromises are often made with continuous aeration to allow for a certain level of complete nitrification, maximizing OTR (and the conversion of ammonia to nitrite) while only partially controlling NOB. Complete nitrification can occur primarily in the biofilm near the upstream end of MABR Unit 6, where process air 15 is introduced into the membrane aeration biofilm medium; this phenomenon is hereinafter referred to as the "inlet effect." The inlet effect occurs because the oxygen flux is higher at the inlet of MABR Unit 6 and decreases at the outlet as the oxygen partial pressure in MABR Unit 6 decreases along the gas flow direction.

[0048] like Figure 4As shown, when the process airflow direction is reversed, the oxygen flux distribution along the length of the gas transfer membrane switches. The biofilm at both ends of the membrane receives only intermittently relatively high oxygen flux, followed by a period of relatively low oxygen flux. If the low oxygen flux period is long enough to destroy any NOB that may have begun to grow in the biofilm during the high oxygen flux period, the NOB population will not establish itself at either end of the membrane. The frequency of reversal operations may vary depending on the equipment, but generally should not exceed 20 days between reversals. Optionally, the total treatment time (i.e., the sum of the first and second time periods) is in the range of 0.5–10 days or 1–7 days. Overall process air conditions can also be selected to increase the OTR relative to methods with continuous process air. To implement process air direction reversal, a suitable network of valves and piping can be connected to MABR unit 6 and the controller to provide automatic reversal of the flow through the membrane.

[0049] When a large gradient exists along the length of the medium in the OTR (Oxygen Tolerance), such as due to variations in oxygen concentration along the membrane length, reversing the process air direction can be more effective. Large partial pressure differences along the membrane length can create a non-uniform DO (Dissolved Oxygen) distribution within the biofilm attached along the membrane length. With the process air direction reversed, the regions near the upstream and downstream ends of MABR unit 6 exhibit a non-uniform DO distribution over time. The temporary presence of extremely low DO is manageable for AOB (Active Oxygen Absorption Deficiency) but detrimental to NOB (Novel Coronavirus B). However, a significant portion of the biofilm exhibits high DO at any given time in this method and exhibits active AOB. The non-uniform DO distribution along the membrane length within the biofilm, combined with the process air direction reversal, helps suppress NOB growth in critical sections of the biofilm near the inlet of MABR unit 6 without reducing activity throughout MABR unit 6.

[0050] The oxygen concentration in exhaust gas 18 can be used as an indicator of the presence of a substantially non-uniform DO distribution along the length of the biofilm. For example, the oxygen concentration in the exhaust gas may be 0.5-4% or lower, or 0.5-2% or lower, optionally about 1-2%. In automated methods, sensors can be used to measure the oxygen concentration in exhaust gas 18. Control methods can use an exhaust oxygen concentration setpoint, for example, within the range of 1-2%, to control the flow rate and / or pressure of process air 15. Automating process airflow based on exhaust oxygen concentration helps provide a stable and reliable method.

[0051] The inlet effect can also be mitigated by temporary or continuous nitrogen enrichment of process air. Process air is relatively nitrogen-rich or oxygen-diluted relative to ambient air. For example, at the inlet of a MABR unit, the oxygen concentration in the process air can be in the range of 5-15%. Nitrogen-rich process air can be provided, for example, by flowing process air through a gas exchange membrane unit or by adding nitrogen to the process air. Optionally, nitrogen enrichment of process air can be provided through exhaust gas recirculation. The exhaust gas is either oxygen-depleted or nitrogen-rich. Figure 9AThis illustrates a method for recirculating process air. In this method, a portion of exhaust air 18 is continuously mixed with fresh process air 15. The nitrogen-rich mixture of fresh process air 15 and exhaust air 18 flows through MABR unit 6. Figure 9B This illustrates another method for process air recirculation. In this method, a batch of process air 15 is pumped into the MABR unit 6. The inlet valve 20 and outlet valve 22 are closed, and exhaust gas 18 is recirculated through the MABR unit 6 for a period of time, optionally adding some process air 15 to replenish the volume of oxygen leaking from the MABR unit 6. After a period of time, a new batch of fresh process air 15 is added. Figure 9A The method generates a continuous supply of nitrogen-enriched process air at a typically constant nitrogen concentration over the duration of nitrogen enrichment in the process air. Figure 9B The method generates process air with increased nitrogen concentration during the duration of nitrogen enrichment in process air. Optionally, a first duration of nitrogen enrichment in process air can be provided, followed by a second duration in a repeating cycle, such as 0.5-10 days or 1-7 days.

[0052] Figure 5 This shows a comparison of oxygen flux along the membrane length with and without nitrogen enrichment in the process air. In this example, the flow rate of fresh process air does not decrease when nitrogen is added or recirculated exhaust. Thus, the total mass flow rate through the MABR unit increases, but the oxygen mass transfer flow rate does not increase, or does not increase to the same extent. When the process air is recirculated (or diluted with nitrogen), the oxygen partial pressure at the membrane inlet decreases, and if the mass flow rate increases, the gas velocity in the membrane increases. This results in a lower oxygen flux at the membrane inlet and a more uniform oxygen flux distribution along the membrane length. This maintains the overall OTR rate while suppressing NOB growth upstream of the membrane.

[0053] Process air recirculation can be as follows Figure 9A As shown, exhaust gas 18 is recirculated to inlet 24 of MABR unit 6 using air pump 28, for example, by connecting the exhaust gas line to the process air line or directly to the membrane manifold of MABR unit 6. However, process air recirculation can be performed in different ways depending on the oxygen source. If air is used as the oxygen source, a continuous process air flow rate and continuous exhaust gas recirculation can be used in the system, such as... Figure 9A As shown. If pure oxygen is used as the oxygen source, then batch-fed pure oxygen can be used and recycled, such as... Figure 9B As shown. If an inert gas (such as nitrogen) is added to dilute the process air, additional gas lines and flow controls will be required.

[0054] Figure 10A , 10BAmong the three alternative methods for stepped airflow in the 10C display process, generally speaking, it uses the exhaust gas 18 of the first MABR unit as the air supply for the next MABR unit 6, and operates two or more MABR units 6 in series. Figure 10A In this configuration, the outlet 26 of one MABR unit is connected to the inlet 24 of another MABR unit. The names of the inlet 24 and outlet 26 can vary depending on the reference direction of the airflow within the MABR unit. For example, although the gas... Figure 10A In the two MABR units 6, the gas flows downwards, or it may flow downwards in one MABR unit 6 and upwards in the other MABR unit 6. Optionally, such as Figure 10B As shown, some of the exhaust gas 18 can also be recirculated to the inlet 24 of the first MABR, while another portion of the exhaust gas 18 flows to the next MABR unit 6. Optionally, the direction of the process air through one or two MABR units 6 and / or the order of the MABR units can be varied. Figure 10C As shown, process air 15 is relative to Figure 10A The air flows through MABR unit 6 in the opposite order and in the opposite direction. The process air stepped flow can be combined with any or more other methods described herein. For example, by […] in the repeating cycle... Figure 10A configuration and Figure 10C The configurations are alternated to combine stepped flow of process air with reverse flow of process air. The repetition cycle can be, for example, 0.5-10 days or 1-7 days.

[0055] Some rapid start-up strategies include optimizing conditions and selecting and pretreating the inoculum sludge. Quantitative polymerase chain reaction (qPCR) technology can be used to identify and quantify different anaerobic ammonium oxide (ANA) or other species in the inoculum sludge and biofilm. Inoculum sludge rich in fast-growing ANA species, such as... Ca. Brocadia Sinica This can shorten start-up time. In addition, pretreatment by breaking the inoculated sludge into small particles will enhance initial adhesion and thus also shorten start-up time.

[0056] In another approach, off-site startup accelerates field startup in full-scale applications by providing a subset of pre-inoculated MABR units, and in some cases, eliminates field startup by providing all pre-inoculated MABR units.

[0057] Deammoniation was carried out on a laboratory scale using high-strength ammonium synthesis wastewater as feed at a temperature range of 30-35°C. Stable deammoniation was achieved under optimized process air conditions (optimal process gas flow and pressure). Two strategies for the rapid formation of a single biofilm containing both ammonium-oxidizing bacteria (AOB) and anaerobic ammonium oxidation on the ZeeLung membrane belt were tested and proved successful. The two strategies were (1) first forming AOB in the biofilm and then forming anaerobic ammonium oxidation, and (2) first forming anaerobic ammonium oxidation in the biofilm and then forming AOB. TIN removal was approximately 3.5 gN / m³. 2 / d. TIN removal appears to be limited by the rate of nitrite formation in the biofilm. To increase the nitrite formation rate, a higher process gas flow rate than the optimal continuous process gas flow can be provided intermittently. Increasing the gas flow rate only from the optimal continuous process gas flow rate results in poor nitrification.

[0058] In the cycle described in this article, the duration of the first time period: the duration of the second time period can be in the range of 1:4 to 4:1, or in the range of 1:2 to 2:1, or about 1:1.

[0059] Example 1

[0060] Figure 11A , 11B The 11C model showcases a membrane-aerated biofilm reactor at experimental scale, configured for operation in three different modes. Figure 11A In this configuration, the reactor is set to operate with a continuous supply of process air to the MABR. Figure 11B In this reactor configuration, the reactor is designed to operate under conditions of process air conditioning and process air reversal. Figure 11C In this reactor, the reactor is configured to provide an intermittent supply of process air.

[0061] Reference Figure 11A Wastewater is supplied from feed tank 1 to open tank 4 by feed pump 2 through valve 3. The feed water is treated in tank 4 and exits the tank as effluent 17. MABR unit 6 is located in tank 4 and remains submerged in the feed water. In this embodiment, MABR unit 6 is a ZeeLung from Suez. TMMembrane module. Process air 15 is compressed and fed to the inlet of MABR unit 6 via mass flow controller 5. The process air flows from the inlet through the lumen of the gas transfer membrane in MABR unit 6 to the outlet of MABR unit 6. As the process air passes through the MABR unit, oxygen passes through the gas transfer membrane to the feed water and then to the biofilm outside the gas transfer membrane. The process air flows from the outlet of MABR unit 6 through pressure gauge 7, mass flow meter 8, and needle valve 9, and is released as exhaust gas 18. The exterior of MABR unit 6 is periodically flushed with nitrogen bubbles to remove excess biofilm. To generate bubbles, compressed nitrogen 16 is supplied to the coarse bubble aerator 13 via pressure regulator 10 and rotor flow meter 11.

[0062] Figure 11B The reactor in Figure 11A The reactors are similar to those in the reactor. Figure 11B The reference number in refers to, for example, for Figure 11A The aforementioned components. Additionally... Figure 11B The reactor in the reactor has two three-way valves 13 and associated piping. The three-way valves can be configured to alternately (a) supply process air 15 to the inlet of the MABR unit 6 and release exhaust gas 18 from the outlet of the MABR unit 6 or (b) supply process air 15 to the outlet of the MABR unit 6 and release exhaust gas 18 from the inlet of the MABR unit 6.

[0063] Figure 11C The reactor in Figure 11A The reactors are similar to those in the reactor. Figure 11C The reference number in refers to, for example, for Figure 11A The aforementioned components. Additionally... Figure 11C The reactor in the reactor has a solenoid valve 14. The solenoid valve can be configured to alternately (a) supply process air to the inlet of the MABR unit 6 and release exhaust gas 18 from the outlet of the MABR unit 6 or (b) seal the inlet and outlet of the MABR unit 6.

[0064] reactor with Figure 11A Start-up configuration. Continuously supply process air 15 to MABR unit 6. As described below, except when inoculating the reactor with nitrifying sludge and anaerobic ammonium oxidation sludge, supply feed water to tank 4. The feed water is synthetic wastewater containing approximately 100 mg N / L of NH4-N and NaHCO3. Except when the reactor is being inoculated, adjust the feed water flow rate to maintain the NH4-N concentration in tank 4 above 50 mg N / L. The water temperature in tank 4 is 30-35°C. The pH of the water in tank 4 is above 6.7 and above 7.5 most of the time. The continuous process airflow rate is 4.2 L / m³. 2 / h (based on the area of ​​the gas transfer membrane in MABR unit 6). The pressure in the MABR unit, as measured by pressure gauge 7, is approximately 3 psi (21 kPa).

[0065] At the start of the process, nitrified inoculum sludge from an activated sludge membrane bioreactor was added to tank 4. Following inoculation, the mixed liquor suspended solids (MLSS) concentration in the reactor was approximately 3 g MLSS / L. The reactor was operated in batch mode for 10 days to maintain the inoculum sludge in tank 4. After 10 days of batch operation, feed pump 2 was started, and the reactor was switched to continuous feed and effluent operation. Suspended solids from the nitrified inoculum sludge were removed from the reactor over several days.

[0066] On the 46th day of operation, the feed water flow was stopped, and water taken from Demon was used. TM Anaerobic ammonia oxidation sludge inoculation tank 4 of the granular sludge reactor. After inoculation, the MLSS concentration in the reactor is approximately 3 g MLSS / L. The reactor is operated in batch mode for 30 days to maintain the inoculated sludge in tank 4. After 30 days of batch operation, feed pump 2 is started and the reactor is switched to continuous flow-through operation. Suspended solids in the nitrifying inoculated sludge are removed from the reactor within a few days.

[0067] Figure 12 The results show the reactor operation over 150 days. The total inorganic nitrogen (TIN) removal rate began to increase after inoculation with anaerobic ammonia oxidation sludge on day 46. Figure 12 The results showed that a partial nitrification / anammox (PN / A) biofilm formed in approximately 80 days, with nitrification inoculum sludge sequentially inoculated on day 0, followed by anammox sludge inoculation starting on day 46. Prior to inoculation with the anammox sludge, TIN removal was approximately zero, indicating the absence of anammox activity for nitrogen removal in the reactor. The TIN removal rate began to increase during the anammox sludge inoculation period (days 46–76). After the anammox inoculum sludge was discharged at approximately day 80, TIN removal stabilized.

[0068] A NO2-N / NOx ratio close to 1.0 indicates that NOB is completely suppressed. A NO2-N / NOx ratio close to 0 indicates that NOB is not suppressed. During anammox inoculation, the NO2-N / NOx ratio decreases. However, after the reactor is restored to normal operation and the anammox sludge is discharged, the NO2-N / NOx ratio recovers.

[0069] The reactor operated for 450 days, including the aforementioned 150-day phase. A continuous supply of process air was provided for approximately 325 days. During the first 200 days of operation, the NO2-N / NOx ratio was approximately 0.7, but decreased to approximately 0.3 on day 325 when both process air conditioning and process air reversal began. The reactor configuration is as follows... Figure 11B As shown. According to the process air conditioning, during the repetition cycle, the process air is supplied at a rate of 3.2 L / m³.2 / h supply for 3 days, and then at 1.6 L / m 2 The supply lasts for 3 days per hour. During the repetitive cycle, the process airflow direction is reversed once per day; that is, process air travels from the inlet to the outlet of MABR 6 for one day, and then from the outlet back to the inlet for one day. (Refer to...) Figure 13 When process air conditioning is introduced and the process air direction is reversed, the NO2-N / NOx ratio begins to increase. By day 450, the NO2-N / NOx ratio exceeds 0.9. NO2-N formation also increases when process air conditioning is introduced and the process air direction is reversed.

[0070] The setup and operation of the second reactor are as described for the reactor described above, except that the reactor configuration is as follows: Figure 11C As shown. Furthermore, during reactor startup, process air is supplied in batches rather than continuously. Specifically, during repetition cycles, process air is supplied at a rate of 13.2 L / m³. 2 / h provides 8 minutes, and then closes solenoid valve 14 to maintain pressurized process air within the MABR module for 10 minutes. Figure 14 The NO2-N / NOx ratios of a second reactor with a batch supply of process air during startup and a first reactor with a continuous supply of process air were compared. During startup with a batch supply of process air, NOB was almost completely suppressed, while some NOB was present in the biofilm when continuous air was supplied during startup.

[0071] Example 2

[0072] The MABR reactor was operated at pilot scale and fed with lagoon supernatant from an anaerobic digestion process. The reactor has three ZeeLungs in a single reactor tank. TM MABR unit. The reactor tank is fed with lagoon supernatant at a constant rate. Each MABR unit has independent process air control, allowing for different gas flow conditions within each unit. Each MABR unit has exhaust oxygen concentration monitoring. Reactor temperature is maintained using a recirculation loop and an online heater. The method is started by inoculating the reactor with 3 g / L nitrification MLSS, which is then diluted from the system after 5 days. Following initial inoculation, the pilot reactor is operated in a flow-through configuration.

[0073] The reactors were configured and operated under the conditions described in Table 1. MABR Unit 1 was operated with the process air direction reversed every 24 hours. MABR Unit 2 was operated with the process air direction reversed every 48 hours. MABR Unit 3 was operated without process air direction reversal. Exhaust oxygen concentration was measured as an indicator of biofilm growth. In particular, low exhaust oxygen concentrations, such as 2% or lower, indicated the elimination of stable partial nitrifying and nitrite-oxidizing bacteria (NOB).

[0074] Table 1

[0075] parameter numerical values unit Number of MABR units 3 # Surface area per MABR unit 40 <![CDATA[m 2 ]]> Total membrane surface area 120 <![CDATA[m 2 ]]> Feed flow rate 50 L / h Inflow ammonia concentration 900 mg / L Process airflow rate 1.35 <![CDATA[L / m 2 / h]]> Intake pressure 45 kPa Exhaust pressure 20 kPa MABR 1 air reversal frequency 24 Hour MABR 2 air reversal frequency 48 Hour MABR 3 Air Reversal Frequency N / A Hour Reactor temperature 30 ℃

[0076] Figure 15 The data shows the exhaust oxygen concentration for each of the three MABR units and the ratio of nitrite produced to total NOx produced throughout the reactor. MABR units 1 and 2 achieved low exhaust oxygen concentrations most rapidly and consistently. MABR unit 3 did not achieve such low exhaust oxygen concentrations. These results indicate that, for a given airflow, air reversal achieves lower exhaust oxygen concentrations, demonstrating that reversing the process air direction can more effectively suppress NOB. The reactor achieving a nitrate to NOx ratio exceeding 0.85 also indicates effective NOB suppression.

[0077] Example 3

[0078] A laboratory-scale MABR reactor was operated to treat high-intensity concentrate from anaerobic digestion sludge dewatering in a municipal wastewater treatment facility. The reactor consisted of four laboratory-scale MABR units 6 within a single tank 4. Each laboratory-scale MABR unit 6 was 0.5 m long (measured as the length of the membrane exposed to water between manifolds). In contrast, ZeeLung... TM The MABR unit is 2.0 m long. An electric heating blanket is used to control the temperature of tank 4. The concentrate (feed water 1) is continuously pumped into tank 4. The initial configuration has the following characteristics: Figure 16 The diagram shows four MABR units 6 arranged in parallel. The process air direction is reversed every 24 hours (i.e., a total cycle time of 2 days) by varying the position of the three-way valve 27. The reactor is initially inoculated with 3 g / L of nitrified MLSS, which is then removed from the system after 3 days.

[0079] After 3 months of operation, such as Figure 17 The reactor is reconfigured as shown, so that MABR unit 6 operates with a stepped flow of process air (i.e., series process air flow). MABR unit 6 is connected in series with the outlet 26 of one MABR unit 6, and outlet 26 is connected to the inlet 24 of the next MABR unit 6. The process air direction is also reversed every 24 hours (i.e., a total cycle time of 2 days) by changing the position of the three-way valve 27. The reactor operating conditions are summarized in Table 2.

[0080] Table 2

[0081] parameter numerical values unit Number of MABR units 4 # Surface area per MABR unit 0.25 <![CDATA[m 2 ]]> Total membrane surface area 1 <![CDATA[m 2 ]]> Concentrate flow rate 0.5 L / h Inflow ammonia concentration 750 mg / L Process airflow rate 0.5 <![CDATA[L / m 2 / h]]> Intake pressure 45-55 kPa Exhaust pressure 25-50 kPa Air reversal frequency 24 Hour Reactor temperature 34 ℃

[0082] Figure 18The diagram shows the types of nitrogen generated due to ammonia conversion and the concentration of emitted oxygen from the MABR unit. A high emitted oxygen concentration was observed when four MABR units received oxygen in parallel. Initially, the reactor exhibited good nitrification, such as... Figure 18 As shown, a large proportion of nitrite is produced during the first two months of operation. After approximately two months, a decrease in nitrite and complete nitrification occur, as... Figure 18 As shown, the proportion of nitrate produced increased while the proportion of nitrite produced decreased. Reconfiguring the four MABR units in series resulted in a longer effective membrane length, leading to a decrease in emitted oxygen concentration, recovery of nitrification, and subsequent growth of anaerobic ammonium oxidation (AOB). The increased portion of ammonia converted to nitrogen indicates the growth of AOB, demonstrating the conversion of ammonia and nitrite in AOB and AOB.

[0083] The combination of tandem MABR units, low emission oxygen concentration, and reversed airflow direction led to the intrinsic growth of anaerobic ammonia-oxidizing bacteria, indicating that the NOB population was controlled and provided with suitable conditions for the growth of anaerobic ammonia oxidation.

[0084] Example 4

[0085] The test equipment was operated to treat a high-strength concentrate from anaerobic digestion sludge dewatering in a municipal wastewater treatment facility. The test equipment consisted of three ZeeLung reactors in a single reactor tank. TM The MABR unit is composed of a feed concentrate fed at a constant rate. The MABR unit has a common process air feed and exhaust, and the process air is uniformly distributed among the three components. A recirculation loop and an online heater are used to maintain the reactor temperature. The method is started by inoculating the reactor with 3 g / L nitrification MLSS, which is then diluted from the system after 5 days. Following the initial inoculation, the experiment is operated in a flow-through configuration.

[0086] The test reactor was reconfigured to test the effects of process air direction reversal and nitrogen enrichment. During nitrogen enrichment, a nitrogen dilution stream was added to the process air, followed by nitrogen-enriched process air feed into the MABR unit. The airflow arrangement ensured that the MABR unit had the same oxygen mass flow rate, but with a lower oxygen concentration at the point where the process air entered the gas transfer membrane lumen. The reactor was operated under the conditions shown in Table 3.

[0087] Table 3

[0088] parameter numerical values unit Number of MABR units 3 # Surface area per MABR unit 40 <![CDATA[m 2 ]]> Total membrane surface area 120 <![CDATA[m 2 ]]> Concentrate flow rate 40-50 L / h Inflow ammonia concentration 500-700 mg / L air velocity 1.6 <![CDATA[L / m 2 / h]]> Process gas dilution flow rate (when applied) 1.6 <![CDATA[L / m 2 / h]]> Intake pressure 40 kPa Exhaust pressure 28 kPa Air reversal frequency 24 Hour Reactor temperature 31 ℃

[0089] After inoculation, the reactor was operated in feed water flow-through mode. The MABR unit was initially operated by introducing process air at the top of the MABR unit and collecting exhaust gas from the bottom of the MABR unit. For the first 60 days of operation, nitrification was stable with no nitrate buildup. However, over time, NOB adapted to the process conditions and nitrate buildup occurred. Figure 19 As shown, nitrate accumulation begins around day 80 and continues until around day 120. During this period, nitrate concentrations exceed 100 mgN / L.

[0090] Starting from day 120, the airflow direction is reversed. Process air is fed into the bottom of the MABR unit and discharged from the top in the opposite direction. This airflow direction is reversed every 24 hours. Until day 120, the exhaust oxygen concentration is <2%, meaning that bacteria at the bottom of the MABR unit receive oxygen transfer from the gas with an oxygen concentration below 2%. Due to the low oxygen concentration, the ecology at the bottom of the MABR unit is likely to modulate to eliminate NOB, which is more sensitive to hypoxia, while AOB may consume limited oxygen to oxidize ammonia.

[0091] When the process air direction is reversed and air containing 20.9% oxygen is introduced to the bottom of the MABR unit, nitrate production from the MABR unit immediately decreases, but slowly re-accumulates over time. With the change in airflow direction, the oxygen concentration at the top of the module is lower, creating NOB-limiting conditions. Therefore, this strategy utilizes the oxygen-deficient period at the top of the module compared to the bottom to avoid NOB activity and thus prevent nitrate accumulation.

[0092] Figure 20 This shows the effect of periodically (i.e., every 24 hours) reversing the process air direction. Between July 14th and August 23rd, nitrite concentrations reached 250 mgN / L, but nitrate concentrations exceeded 100 mgN / L. A transition period from August 23rd to October saw intermittent reversals of the process air direction. Continuous reversals of the process air direction occurred between October 22nd and December 1st. During this period, nitrite concentrations again reached 250 mgN / L, but nitrate concentrations stabilized and remained at approximately 70 mgN / L.

[0093] Reference Figure 21 Between August 14th and September 2nd, the experiment was reconfigured to test the effectiveness of process air nitrogen enrichment. No process air direction reversal occurred during the process air nitrogen enrichment period. Figure 21Two process air nitrogen enrichment tests were conducted during the time period highlighted in the report. Air dilution tests resulted in high ammonia and nitrogen removal rates. Between day 90 and day 110, the 90th percentiles of the performance data for ammonia and nitrogen removal rates were 0.62 kg / d / m³. 3 and 0.47 kg-N / d / m 3 During the first dilution period, the 25th percentile of ammonia and nitrogen removal rates were 0.65 kg-N / d / m³, respectively. 3 and 0.45 kg-N / d / m 3 This indicates that during the period without air dilution, the removal rate is significantly higher than the 90th percentile removal rate. The performance during the air dilution period shows a significant change in the reactor's performance regarding ammonia and nitrogen removal, which is the opposite when dilution removal is performed. A second, shorter process air dilution period shows the same trend.

Claims

1. A method for nitrification using a membrane-aerated biofilm reactor, comprising the following steps: The device containing the membrane aeration biofilm medium, the "MABR unit", is immersed in water containing ammonia; The MABR unit is supplied with an oxygen-containing gas, "process air"; and, The bacterial population, including ammonia-oxidizing bacteria, "AOB", is allowed to grow outside the MABR unit. The method includes reversing the process air direction, wherein the process air flows through the MABR unit in one direction for a first time period, and then flows through the MABR unit in the opposite direction for a second time period; thereby switching the distribution of oxygen flux along the length of the gas transfer membrane, with the biofilm at both ends of the membrane receiving only intermittently relatively high oxygen flux, followed by a period of relatively low oxygen flux.

2. The method of claim 1, further comprising feeding process air in batches over a short period of time, wherein air is supplied to the MABR unit for a first time period, and then the valves upstream and downstream of the MABR unit are closed for a second time period.

3. The method according to claim 2, wherein the total cycle time of the batch feeding process air is between 0.1 and 2 hours.

4. The method of claim 1, further comprising process air conditioning, wherein process air is supplied to the MABR unit at a first rate for a first time period and at a second rate for a second time period.

5. The method according to claim 4, wherein the total cycle time for process air conditioning is between 0.5 and 10 days.

6. The method according to claim 1, wherein the total cycle time for reversing the process air direction is between 0.5 and 10 days.

7. The method of claim 1, further comprising nitrogen enrichment of process air, wherein nitrogen-enriched air is provided to the MABR unit.

8. The method of claim 7, wherein a first process air is supplied to the MABR unit for a first time period and a second relatively nitrogen-rich process air is supplied to the MABR for a second time period.

9. The method of claim 8, wherein the total cycle time for supplying nitrogen-enriched air to the MABR unit is between 0.5 and 10 days.

10. The method of claim 8, wherein the first process air is ambient air.

11. The method of claim 7, wherein the nitrogen-enriched air is provided via process air recirculation, comprising causing at least some exhaust gas to flow from the outlet of the MABR unit into the inlet of the MABR unit.

12. The method according to any one of claims 8-10, wherein the second process air velocity is higher than the first process air velocity.

13. The method of claim 1, further comprising a stepped flow of process air between a plurality of MABR units, wherein process air is supplied to the plurality of MABR units connected in series.

14. The method of claim 13, further comprising connecting a port of one MABR unit to a port of another MABR unit.

15. The method according to claim 13 or 14, wherein each MABR unit is less than 0.5 m in length, or wherein the series-connected MABR units are greater than 1 m in length.

16. The method of claim 1, further comprising, in combination with at least one of the following: batch feeding of process air in short cycles; process air conditioning; nitrogen enrichment of process air; and maintaining exhaust oxygen concentration below 4%.

17. The method of claim 1, further comprising combining with at least one of the following: batch feeding of process air in short cycles; process air conditioning; nitrogen enrichment of process air; stepped flow of process air; and maintaining exhaust oxygen concentration below 4%.

18. The method of claim 1, further comprising maintaining the exhaust oxygen concentration below 4%.

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