A method for performing short-cut nitrification in a continuous flow process

Abstract

The present application relates to the field of sewage denitrification technology, and particularly relates to a method for carrying out short-cut nitrification in a continuous flow process. The method controls the hydroxylamine addition concentration by monitoring the nitrite accumulation rate in the aerobic zone in real time, achieves the purpose of quickly starting and maintaining short-cut nitrification while ensuring that the ammonia nitrogen in the effluent meets the standard, and further reduces the aeration and carbon source costs of the system.

Description

Technical Field

[0001] This invention relates to the field of wastewater denitrification technology, specifically to a method for short-cut nitrification in a continuous flow process. Background Technology

[0002] With the development of society and the economy, and the gradual improvement of people's living standards, the public's attention to environmental issues has been increasing. Improving water quality has become an urgent priority for sustainable social development. Eutrophication, caused by excessive nitrogen emissions, is a pressing water pollution problem. To address this, various nitrogen removal processes, including physicochemical and biological methods, have been designed. Physicochemical wastewater treatment systems include ion exchange and breakpoint chlorination, but the chemical reagents used are expensive and produce various byproducts, easily causing secondary pollution of water bodies. Therefore, nitrogen removal in urban wastewater treatment plants currently typically employs biological technologies.

[0003] Traditional biological nitrogen removal processes include nitrification and denitrification units. The former utilizes microorganisms to denitrify ammonia nitrogen (NH4). + -N (or NH3-N) is oxidized stepwise to nitrite NO2. - -N and nitrate nitrogen NO3 - -N, specifically, ammonia-oxidizing bacteria will convert NH4+ into nitrogen dioxide. + -N is converted to NO2 - -N, and thus, under the action of nitrite-oxidizing bacteria, NO2 is converted. - -N is converted to NO3 - The process of reducing NO2 by -N requires a large amount of oxygen, resulting in high energy costs. The latter process, however, uses denitrifying bacteria to convert the produced NO2... - -N and NO3 - -N is reduced to gaseous nitrogen such as nitrogen gas (N2). This process requires a large amount of carbon source. However, the carbon source in the raw wastewater cannot meet the requirements, so the nitrogen removal rate is often not high.

[0004] To address the issue of high oxygen and carbon input requirements, researchers have developed a short-cut nitrification-denitrification process. This process utilizes the symbiotic relationship between ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, controlling the nitrification process to NO2 production by inhibiting the activity of the latter. - The -N stage, on the one hand, reduces the amount of NO2 produced during nitrification. - -N is converted to NO3 - -N reduces energy consumption and avoids the release of NO3 during denitrification. - -N is reduced to NO2 - -N is further converted into N2, consuming excess carbon sources.

[0005] Currently, methods for achieving short-cut nitrification and denitrification mainly include dissolved oxygen control, temperature control, and sludge age control. These methods are often affected by large fluctuations in the water quality and quantity of actual urban wastewater treatment plants, making effective nitrogen removal difficult. In addition, inhibitors such as free ammonia (FA) and free nitrite (FNA) can be added to achieve short-cut nitrification; however, these mainstream inhibitors are highly toxic and are often used in scenarios involving high-nitrogen-concentration wastewater treatment.

[0006] Therefore, some studies have adopted the method of adding hydroxylamine (H2N-OH) in the treatment system of low-concentration urban wastewater. As an intermediate product of nitrification, hydroxylamine can inhibit the activity of nitrite-oxidizing bacteria, achieve short-cut nitrification, thereby saving aeration energy consumption, reducing carbon source addition, and lowering system operating costs.

[0007] However, while hydroxylamine inhibits the activity of nitrite-oxidizing bacteria, it also reduces the ability of ammonia-oxidizing bacteria to treat ammonia nitrogen, resulting in substandard ammonia nitrogen content in the effluent. Furthermore, existing wastewater denitrification systems often use hydroxylamine as an auxiliary method in conjunction with intermittent influent to remove nitrogen, but this is limited by its intermittent nature and cannot achieve continuous wastewater treatment. Although some studies have used hydroxylamine in continuous flow systems, it often requires combination with intermittent aeration or influent ammonia nitrogen control methods, placing high demands on the automation system and incurring significant costs. Meanwhile, influenced by various parameters such as temperature and pH, current short-cut nitrification-denitrification processes typically require approximately 100 days to adjust parameters, resulting in long start-up times and operational instability. These problems limit the application of hydroxylamine in short-cut nitrification processes and urgently need to be addressed. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and solve at least one of the defects in the above-mentioned background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for short-cut nitrification in a continuous flow process includes: S1, a preparation stage: inoculating aerobic activated sludge into an aerobic zone and aerating it, and inoculating anoxic activated sludge into an anoxic zone downstream of the aerobic zone, wherein the aerobic activated sludge includes nitrifying denitrifying bacteria and the anoxic activated sludge includes denitrifying denitrifying bacteria; S2, a short-cut nitrification start-up stage: adding hydroxylamine into the aerobic zone to present it at a first concentration, and monitoring the nitrite accumulation rate of the effluent from the aerobic zone until the nitrite content of the effluent from the aerobic zone is greater than the nitrate content; S3, a short-cut nitrification maintenance stage: presenting hydroxylamine in the aerobic zone at a second concentration, the second concentration being less than the first concentration, and monitoring the nitrogen concentration of the effluent from the anoxic zone.

[0011] Preferably, in step S2, the first concentration is 7-9 mgN / L.

[0012] Preferably, in step S3, the second concentration is 1-3 mgN / L.

[0013] Preferably, in step S2, the hydroxylamine is added once every 5-7 hours, and the duration of each addition is less than 10 minutes.

[0014] Preferably, in step S2, the nitrite accumulation rate is greater than 90%.

[0015] Preferably, in step S1, the concentration of suspended solids in the mixed solution in the aerobic zone and the anoxic zone is 2500-4500 mg / L.

[0016] Preferably, in step S1, the dissolved oxygen concentration in the aerobic zone is 1-3 mg / L.

[0017] Preferably, step S1 further includes maintaining the hydraulic residence time of the system at 12-16 hours.

[0018] Preferably, step S3 further includes maintaining the average concentration of suspended solids in the mixture of the system at 4000-6000 mg / L.

[0019] Preferably, step S3 further includes maintaining the sludge retention time of the system at 25-40 days.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] (1) The method provided by the present invention can ensure that the ammonia nitrogen in the effluent meets the standard while avoiding intermittent water intake, and thus can be applied to the sewage treatment of continuous flow systems, thereby improving the overall adaptability of the system.

[0022] (2) The method provided by the present invention does not require strict control of the influent ammonia nitrogen load and the dissolved oxygen content in the aerobic zone, saving the cost of the automatic control system and reducing the operating cost of the system.

[0023] (3) The present invention adopts the addition method of hydroxylamine to reduce the concentration, which shortens the start-up time of traditional short-range nitrification to about 30 days, greatly improving the operating efficiency of the system.

[0024] (4) The method provided by the present invention can stably maintain the nitrite accumulation rate at about 95%, thereby continuously utilizing short-cut nitrification for wastewater denitrification treatment. Attached Figure Description

[0025] Figure 1 A flow chart of an anaerobic-aerobic-anoxic AOA process containing a hydroxylamine dosing unit;

[0026] Figure 2 shows the relationship between hydroxylamine and ammonia oxidation rate (ARE) and nitrite accumulation rate (NAR). Figure 2a When the hydroxylamine concentration is 8 mg N / L, Figure 2b When the hydroxylamine concentration is 5 mg N / L, Figure 2c This refers to the case where hydroxylamine is not added externally;

[0027] Figure 3 shows the relationship between hydroxylamine and the contents of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the effluent. Figure 3a When the hydroxylamine concentration is 8 mg N / L, Figure 3b When the hydroxylamine concentration is 5 mg N / L, Figure 3c This refers to the case where hydroxylamine is not added externally;

[0028] Figure 4 shows the relationship between hydroxylamine and the ammonia nitrogen content and ammonia nitrogen removal rate in the effluent. Figure 4a When the hydroxylamine concentration is 8 mg N / L, Figure 4b When the hydroxylamine concentration is 5 mg N / L, Figure 4c This refers to the case where hydroxylamine is not added externally;

[0029] Figure 5 This is a graph showing the relationship between low concentrations of hydroxylamine and the NAR (nitrite accumulation rate).

[0030] Figure 6 This is a graph showing the relationship between low concentrations of hydroxylamine and the ammonia oxidation rate (ARE).

[0031] Figure 7 This is a graph showing the relationship between low concentrations of hydroxylamine and the contents of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the effluent.

[0032] Explanation of reference numerals in the attached figures:

[0033] 11-Water inlet tank; 12-Water inlet pump;

[0034] 21-Anaerobic zone; 22-Aerobic zone; 221-Aeration pump; 23-Anoxic zone 1; 24-Anoxic zone 2;

[0035] 31-Secondary sedimentation tank; 32-First sludge return pump; 33-Second sludge return pump;

[0036] 41-Drug storage tank; 42-Drug dosing pump. Detailed Implementation

[0037] The technical solution of this patent will be further described in detail below with reference to specific embodiments. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0038] Generally speaking, nitrogen in wastewater is mainly ammonia nitrogen (NH4). + -N (or NH3-N), nitrite nitrogen NO2 - -N and nitrate nitrogen NO3 - It exists in multiple forms such as -N, and NH4 + -N is the main form of nitrogen in urban wastewater. Furthermore, the three types of nitrogen can interconvert through nitrification, such as NH4+ contained in raw wastewater. + -N is oxidized into NO2 by ammonia-oxidizing bacteria. - -N, which is then oxidized to NO3 by nitrite-oxidizing bacteria. - -N. The short-cut nitration process controls the above reaction before the second oxidation reaction, i.e., NH4+. + -N is converted to NO2 - -N, but does not further convert to NO3. - -N, thereby reducing energy consumption in the subsequent denitrification process.

[0039] To control the progress of nitrification, it is necessary to regulate the activities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. Specifically, the ammonia oxidation rate (ARE) and nitrite accumulation rate (NAR) can be used as indicators. The ammonia oxidation rate refers to the amount of NH4+ oxidized bacteria. + -N is converted to NO2 - The higher the -N ratio, the higher the activity of ammonia-oxidizing bacteria; the nitrite accumulation rate refers to the NO2 content in the system. - The higher the nitrite content, the lower the activity of nitrite-oxidizing bacteria. When the nitrite accumulation rate is greater than 50% and remains stable, it indicates that short-cut nitrification has been successfully initiated.

[0040] In addition, in the evaluation of wastewater treatment systems, besides considering the start-up time and operational stability of short-cut nitrification, the removal efficiency of nitrogen in wastewater should also be tested. Ammonia nitrogen removal rate and total nitrogen (TN) removal rate can usually be used as indicators.

[0041] In this scheme, the nitrite accumulation rate in the aerobic section of the short-cut nitrification unit of the continuous flow system was monitored in real time. Hydroxylamine was added to the bioreactor in a reduced concentration manner. While ensuring that the ammonia nitrogen and total nitrogen in the effluent met the standards, the relative activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria was effectively regulated, thereby shortening the start-up time of short-cut nitrification to about 30 days and reducing the cost of subsequent processes.

[0042] Example 1:

[0043] This embodiment provides a method for short-cut nitrification in a continuous flow process, employing an anaerobic-aerobic-anoxic (AOA) process device containing a hydroxylamine dosing unit. It should be understood that this method is also applicable to other wastewater treatment processes containing a post-anoxic stage.

[0044] See appendix Figure 1 The device includes an influent unit, a bioreactor, a sludge treatment unit, and a hydroxylamine dosing unit. The bioreactor comprises an anaerobic zone 21, an aerobic zone 22, an anoxic zone 1 23, and an anoxic zone 24 connected in sequence, with a volume ratio of 1:1:2 for the anaerobic, aerobic, and anoxic zones. Furthermore, the anaerobic zone 21, anoxic zone 1 23, and anoxic zone 24 are equipped with agitators, and the aerobic zone 22 is equipped with an aeration device, specifically an aeration pump 221 connected to an aeration head via a rotor flow meter to supply oxygen to the aerobic zone 22.

[0045] The inlet tank 11 of the inlet unit is connected to the anaerobic zone 21 via the inlet pump 12, thereby transporting wastewater to the bioreactor. The anoxic zone 24 is connected to the secondary sedimentation tank 31 of the sludge treatment unit via an overflow pipe. Simultaneously, the treated wastewater in the upper layer of the secondary sedimentation tank 31 is discharged through a drain pipe, while the sludge in the lower layer is divided into three streams: one stream is returned to the anaerobic zone 21 via the first sludge return pump 32, another stream is returned to the anoxic zone 23 via the second sludge return pump 33, and the remaining stream is periodically discharged through the sludge discharge pipe. The hydroxylamine dosing unit's storage tank 41 is connected to the aerobic zone 22 via the dosing pump 42.

[0046] Using the above-mentioned anaerobic-aerobic-anoxic (AOA) process device, this embodiment provides a method for short-cut nitrification in a continuous flow process, including a preparation stage, a short-cut nitrification start-up stage, and a short-cut nitrification maintenance stage.

[0047] (1) Preparation stage

[0048] Sludge is inoculated into the bioreactor to achieve a mixed liquor suspended solids (MLSS) concentration of 2500-4500 mg / L. Specifically, anaerobic activated sludge, including polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria, is inoculated into anaerobic zone 21; aerobic activated sludge, including polyphosphate-accumulating bacteria, ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria, is inoculated into aerobic zone 22; and anoxic activated sludge, including polysaccharide-accumulating bacteria, is inoculated into anoxic zones 1 (23) and 24 (24). Polyphosphate-accumulating bacteria are used as phosphorus-removing agents, ammonia-oxidizing and nitrite-oxidizing bacteria are used as nitrifying agents, and polysaccharide-accumulating bacteria are used as denitrifying agents. Other wastewater denitrification and dephosphorization agents can also be added according to the actual needs of each zone in the bioreactor. Furthermore, fluidized bed packing is added to aerobic zone 22 to increase the biomass of nitrifying bacteria and improve nitrification stability.

[0049] Under the action of the influent pump 12, the domestic sewage in the influent tank 11 is fed into the bioreactor, and the hydraulic retention time (HRT) of the bioreactor is controlled to be 12-16 hours. This embodiment uses domestic sewage from a university in Shenzhen as the treatment target. The influent water quality is shown in Table 1, where COD is the chemical oxygen demand, pH is the hydrogen ion concentration index, and [NH4+] is the hydrogen ion concentration index. + -N] represents the ammonia nitrogen concentration, [NO3] represents the NO3 concentration. - -N] represents the nitrate nitrogen concentration, and TIN represents the total inorganic nitrogen concentration.

[0050] Table 1 Influent Water Quality

[0051]

[0052] In addition, aeration pump 221 is used to aerate the aerobic zone 22, and the dissolved oxygen concentration (DO) is controlled to be 1-3 mg / L by a rotor flow meter. At the same time, under the action of the first sludge return pump 32 and the second sludge return pump 33, the sludge in the secondary sedimentation tank 31 is mixed into the anaerobic zone 21 and the anoxic zone 23 at a return ratio of 50%-150% to maintain the average mixed liquor suspended solids concentration (MLSS) in the bioreactor at 4000-6000 mg / L, and the sludge retention time (SRT) is controlled at 25-40 days.

[0053] When wastewater enters the anaerobic zone 21, polyphosphate-accumulating bacteria release phosphorus anaerobicly, while polysaccharide bacteria store intracellular carbon sources. Then, it enters the aerobic zone 22, where polyphosphate-accumulating bacteria aerobically absorb phosphorus, and ammonia-oxidizing bacteria and nitrite-oxidizing bacteria oxidize ammonia nitrogen into nitrite nitrogen and nitrate nitrogen step by step. Then, it enters the anoxic zone 1 23 and anoxic zone 24, where polysaccharide bacteria use the carbon sources stored in their cells to perform endogenous denitrification of the generated nitrite nitrogen and nitrate nitrogen, thereby converting the above-mentioned nitrogen into gaseous nitrogen such as nitrogen gas.

[0054] (2) Short-range nitrification start-up stage

[0055] Hydroxylamine was added. A high-concentration hydroxylamine hydrochloride stock solution was prepared in storage tank 41. Then, the dosage of the dosing pump 42 was adjusted to achieve an initial concentration of 8 mg N / L in the aerobic zone 22. The dosing frequency was four times a day, i.e., once every 6 hours, with each dosing session lasting less than 5 minutes. As a control, the dosing frequency and duration were kept constant, and the initial hydroxylamine concentration in the aerobic zone 22 was controlled at 0 and 5 mg N / L. In addition to hydroxylamine hydrochloride, hydroxylamine sulfate, hydroxylamine phosphate, and other hydroxylamine agents could also be used. It should be noted that the hydroxylamine concentrations used in this embodiment are all equivalent concentrations, expressed in milligram equivalents per liter.

[0056] Monitor the nitrite accumulation rate (NAR). Maintain the hydraulic retention time (HRT), sludge retention time (SRT), and dissolved oxygen (DO) concentration in the aerobic zone 22 of the bioreactor constant, and continuously monitor the nitrite accumulation rate (NAR) in the effluent from the aerobic zone 22. When this value is greater than 95%, or when the nitrate content in the effluent from the aerobic zone 22 is less than 1 mg / L, short-cut nitrification is considered to have been successfully initiated. At this point, the activity of nitrite-oxidizing bacteria is sufficiently inhibited and washed away, and the effluent from the aerobic zone 22 is dominated by nitrite nitrogen, with nitrate nitrogen as a secondary component.

[0057] (3) Short-range nitrification maintenance stage

[0058] The hydroxylamine dosing strategy was changed. When the nitrite accumulation rate (NAR) was greater than 95%, the hydraulic retention time (HRT), sludge age (SRT), and dissolved oxygen concentration (DO) in the aerobic zone 22 of the bioreactor were kept constant. The hydroxylamine dosing concentration was reduced so that the hydroxylamine concentration in the aerobic zone 22, i.e., the second concentration, was 2 mgN / L, thereby stabilizing the short-cut nitrification process.

[0059] Monitor the nitrite accumulation rate (NAR). Monitor the effluent from aerobic zone 22. When the nitrite accumulation rate (NAR) is greater than 50% and remains stable, it indicates that the nitrification process is successfully maintained.

[0060] Monitor the effluent. Monitor the nitrogen content of the supernatant in the secondary sedimentation tank 31. When the ammonia nitrogen removal rate reaches 95% and the total nitrogen removal rate reaches 60% and remains stable, it indicates that the nitrification and denitrification process is operating successfully.

[0061] The following explains the results of the experimental and control groups obtained using the above method.

[0062] Figure 2 shows the relationship between hydroxylamine and ammonia oxidation rate (ARE) and nitrite accumulation rate (NAR). The horizontal axis represents the hydroxylamine dosage time, the vertical axis of the bar chart represents the ammonia oxidation rate (ARE), and the vertical axis of the line graph represents the nitrite accumulation rate (NAR). Figures 2a-2c The figures show the cases where the hydroxylamine concentration is 8, 5, and 0 mgN / L, respectively. Statistical results of the data in Figure 2 are shown in Table 2.

[0063] Table 2. Effects of hydroxylamine concentration on NAR and ARE in the aerobic zone.

[0064]

[0065] As shown above, during the optimal treatment period of 0 to 30 days, the ammonia oxidation rate (ARE) obtained by different hydroxylamine concentrations all reached over 85%, demonstrating relatively good nitrification activity and thus being able to oxidize ammonia nitrogen in wastewater to nitrite nitrogen. However, when hydroxylamine was added to the system again 10 days after the optimal treatment period, the ARE results of different hydroxylamine concentrations showed significant differences. When the hydroxylamine concentration was 5 mgN / L or no hydroxylamine was added, the ARE of the system remained above 85% for 41 days, indicating that the inhibitory effect of adding low concentrations of hydroxylamine on ammonia-oxidizing bacteria was not significant. However, when the hydroxylamine concentration was 8 mgN / L, although the ARE of ammonia oxidation was maintained at 87.8% from 0 to 30 days, it showed a downward trend thereafter, dropping to an average of 69.4%. This indicates that excessive addition of high concentrations of hydroxylamine leads to insufficient activity of ammonia-oxidizing bacteria, inhibiting the oxidation of ammonia nitrogen and thus failing to achieve effective nitrogen removal.

[0066] Furthermore, observation of the nitrite accumulation rate (NAR) at different hydroxylamine concentrations revealed that without hydroxylamine, the NAR was almost zero, and even with low concentrations of hydroxylamine, the NAR was less than 3%. This indicates that when the hydroxylamine concentration is too low, most of the nitrite nitrogen produced by ammonia-oxidizing bacteria is further oxidized to nitrate nitrogen by nitrite-oxidizing bacteria. In other words, the activity of nitrite-oxidizing bacteria is higher than that of ammonia-oxidizing bacteria, thus preventing the accumulation of nitrite nitrogen in the aerobic zone and hindering the initiation of short-cut nitrification in the short term. When the hydroxylamine concentration was 8 mg N / L, the nitrite accumulation rate (NAR) reached approximately 95% on day 20 and remained above 90% for the following 20 days. This indicates that the activity of nitrite-oxidizing bacteria was inhibited, with only a small amount of nitrite nitrogen being converted to nitrate nitrogen, allowing nitrite to accumulate and be used for denitrification in subsequent stages.

[0067] In summary, adding an appropriate amount of high-concentration hydroxylamine (approximately 8 mg N / L) can inhibit the activity of nitrite-oxidizing bacteria for about 30 days, thereby accumulating nitrite and rapidly initiating short-cut nitrification. After 30 days, the concentration of hydroxylamine should be reduced to maintain the activity of ammonia-oxidizing bacteria, thus ensuring that the nitrogen content of the effluent meets the standards.

[0068] Figure 3 shows the relationship between hydroxylamine and the concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the influent and effluent. The horizontal axis represents the hydroxylamine dosing time, and the vertical axes of the triangle, square, and circle-marked line graphs represent the influent ammonia nitrogen concentration, influent nitrite nitrogen concentration, and influent nitrate nitrogen concentration, respectively. For comparison, Figures 3a-3cThe figures represent hydroxylamine concentrations of 8, 5, and 0 mg N / L, respectively, all under the same influent water quality conditions. It can be seen that the influent ammonia nitrogen concentration is the highest, remaining at 15-30 mg / L, while nitrite and nitrate nitrogen contents are relatively low. This indicates that the primary target for nitrogen removal from this domestic wastewater is ammonia nitrogen, and the purpose of short-cut nitrification is to convert it into nitrite nitrogen, which is then subsequently converted into gaseous nitrogen.

[0069] Furthermore, in Figure 3, the vertical axes of the black, light gray, and dark gray bars represent the effluent ammonia nitrogen concentration, effluent nitrite nitrogen concentration, and effluent nitrate nitrogen concentration, respectively. It can be observed that when a low concentration of hydroxylamine is added, the effluent from the aerobic zone is mainly composed of nitrate nitrogen, indicating that under this concentration condition, the activity of nitrite-oxidizing bacteria is relatively high, thus preventing the rapid accumulation of nitrite nitrogen in the aerobic zone. Adding a high concentration of hydroxylamine can rapidly accumulate nitrite nitrogen within 15-30 days, but adding excessive amounts of high-concentration hydroxylamine will affect the nitrogen content, leading to substandard ammonia nitrogen levels in the aerobic zone effluent.

[0070] Figure 4 shows the removal effect of hydroxylamine at different concentrations. The horizontal axis represents the hydroxylamine addition time. The vertical axes of the line graphs marked with black and white squares represent the influent ammonia nitrogen concentration and the effluent influent ammonia nitrogen concentration, respectively. The vertical axis of the bar graph represents the ammonia nitrogen removal rate. Figures 4a-4c The figures show the cases where the hydroxylamine concentration is 8, 5, and 0 mgN / L, respectively. The statistical results of the data in Figure 4 are shown in Table 3.

[0071] Table 3. Effect of hydroxylamine dosage concentration on effluent ammonia nitrogen

[0072]

[0073] As shown in the chart, adding a high concentration of hydroxylamine (8 mg N / L) reduces the ammonia nitrogen removal rate. This indicates that high concentrations of hydroxylamine inhibit the activity of ammonia-oxidizing bacteria to some extent, preventing the influent ammonia nitrogen from being converted into nitrite and nitrate nitrogen. Consequently, it cannot be reduced to gaseous nitrogen in the post-denitrification unit in the anoxic zone and is discharged from the system in an untreated state. Furthermore, this inhibitory effect of high concentrations of hydroxylamine on ammonia nitrogen removal is more pronounced during the excess period, with the ammonia nitrogen removal rate dropping to as low as 69.4%. This suggests that continuously high concentrations of hydroxylamine further inhibit the activity of ammonia-oxidizing bacteria, thus affecting the effluent ammonia nitrogen content.

[0074] In contrast, the ammonia nitrogen removal efficiency without hydroxylamine addition in the aerobic zone remained above 95% for 0-41 days, confirming that hydroxylamine inhibits the activity of ammonia-oxidizing bacteria, thus affecting the effluent ammonia nitrogen content. Compared to not adding hydroxylamine, the effluent ammonia nitrogen removal efficiency was slightly reduced with appropriate or excessive addition of a low concentration of 5 mg N / L hydroxylamine, but it still maintained a high removal rate of over 90%, indicating that adding low concentrations of hydroxylamine only slightly inhibits the effluent ammonia nitrogen removal efficiency.

[0075] In summary, after rapidly initiating short-cut nitrification with a high concentration of hydroxylamine (approximately 8 mg N / L), it is appropriate to reduce the hydroxylamine dosage to maintain the stability of the short-cut nitrification process. Specifically, when the nitrite accumulation rate (NAR) is greater than 95%, the single hydroxylamine dosage should be reduced from 8 mg N / L to an even lower concentration.

[0076] To further determine the optimal low-concentration hydroxylamine dosage range for maintaining stable short-cut nitrification, under the influent water quality conditions shown in Table 4, the nitrite accumulation rate (NAR), ammonia oxidation rate (ARE), and effluent ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen content were analyzed by adding hydroxylamine at concentrations of 0.5, 1, and 2 mg N / L. (Note: COD is the chemical oxygen demand, and [NH4+] is the nitrogen content in the effluent.) + -N] represents the ammonia nitrogen concentration, [NO3] represents the NO3 concentration. - [-N] represents the concentration of nitrate nitrogen.

[0077] Table 4 Influent Water Quality

[0078]

[0079] Figure 5 The graph shows the relationship between low concentrations of hydroxylamine and the average nitrite accumulation rate (NAR) in the aerobic zone. The horizontal axis represents the time of hydroxylamine administration, and the vertical axis represents the average nitrite accumulation rate (NAR). Hydroxylamine was administered at a concentration of 2 mg N / L from day 1 to 34, at a concentration of 1 mg N / L from day 35 to 67, and at a concentration of 0.5 mg N / L from day 68 to 93. Figure 5 The statistical results of the data are shown in Table 5.

[0080] Table 5. Effects of low-concentration hydroxylamine dosage on NAR in aerobic zones.

[0081]

[0082] As shown above, a low concentration of hydroxylamine (2 mg N / L) can maintain a stable short-cut nitrification effect, with the nitrite accumulation rate (NAR) consistently above 97.1%, and mostly around 99.9%. A hydroxylamine dosage of 1 mg N / L can also maintain a high nitrite accumulation rate (NAR) for a long time, but the value can be observed to continuously decrease from 100% to 93.1%. A hydroxylamine dosage of 0.5 mg N / L cannot maintain stable nitrite accumulation, with the NAR decreasing from 93.1% to 84.0%. This phenomenon may be due to the reduced inhibitory effect of excessively low concentrations of hydroxylamine on the activity of nitrite-oxidizing bacteria, leading to an increased ability to oxidize nitrite nitrogen and a continuous decrease in the proportion of nitrite nitrogen in the aerobic zone effluent.

[0083] Figure 6The graph shows the relationship between low concentrations of hydroxylamine and the ammonia oxidation rate (ARE) in the aerobic zone. The horizontal axis represents the time of hydroxylamine addition, and the vertical axes of the square and circular line graphs represent the average ammonia oxidation rate (ARE) and the influent ammonia nitrogen concentration, respectively. Hydroxylamine was added at a rate of 2 mg N / L from day 1 to 34, 1 mg N / L from day 35 to 67, and 0.5 mg N / L from day 68 to 93. Figure 6 The statistical results of the data are shown in Table 6.

[0084] Table 6. Effects of low-concentration hydroxylamine dosage on ARE in the aerobic zone.

[0085]

[0086] As shown in the table, under similar influent ammonia nitrogen concentrations of 43.8-44.5 mg / L, the ammonia oxidation rates (AREs) in the aerobic zone after adding low concentrations of hydroxylamine (0.5, 1, and 2 mg / L) were 95.1%, 93.8%, and 95.2%, respectively, indicating similar ammonia nitrogen removal efficiencies across the different groups. Compared to the control group's 94.8%, the addition of low concentrations of hydroxylamine did not inhibit ammonia nitrogen removal in the aerobic zone; therefore, the addition of this low concentration of hydroxylamine did not inhibit the nitrification effect of the process.

[0087] Figure 7 The graph shows the relationship between low concentrations of hydroxylamine and the concentrations of ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen in the effluent from the aerobic zone. The horizontal axis represents the time of hydroxylamine addition. The vertical axes of the line graphs marked with squares, rhombuses, and triangles represent the influent ammonia nitrogen concentration, influent nitrite nitrogen concentration, and influent nitrate nitrogen concentration, respectively. The vertical axes of the bar graphs marked with diagonal lines, white background with black dots, and black background with white dots represent the average effluent ammonia nitrogen concentration, average effluent nitrite nitrogen concentration, and average effluent nitrate nitrogen concentration, respectively. Specifically, hydroxylamine was added at a concentration of 2 mg N / L from day 1 to 34, 1 mg N / L from day 35 to 67, and 0.5 mg N / L from day 68 to 93. Figure 7 The statistical results of the data are shown in Table 7.

[0088] Table 7. Effects of low-concentration hydroxylamine dosage on ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen content in the effluent from the aerobic zone.

[0089]

[0090] The charts show that continuous addition of low concentrations of hydroxylamine (0.5, 1, and 2 mg N / L) can maintain the nitrite nitrogen concentration in the aerobic zone effluent within a certain range, thus exhibiting a sustained inhibitory effect on the activity of nitrite-oxidizing bacteria. However, the inhibitory effect of hydroxylamine on nitrite-oxidizing bacteria activity weakens as the concentration of hydroxylamine decreases. When hydroxylamine is added at concentrations of 1 and 2 mg N / L, the average nitrite nitrogen concentration in the aerobic zone effluent is 1.1 and 0.4 mg / L, respectively, at which point the activity of nitrite-oxidizing bacteria is continuously inhibited. When 0.5 mg N / L of hydroxylamine is added, the nitrite nitrogen concentration in the aerobic zone effluent continuously increases, thus failing to effectively inhibit the activity of nitrite-oxidizing bacteria and making it difficult to maintain the short-cut nitrification effect of the process.

[0091] Therefore, this scheme adopts a reduced concentration method for adding hydroxylamine. Specifically, when the nitrite accumulation rate (NAR) is greater than 95%, the single hydroxylamine dosage is reduced from 8 mg N / L to 2 mg N / L. On the one hand, the high concentration of hydroxylamine enables rapid start-up of short-cut nitrification in about 30 days, reducing aeration consumption and carbon source waste in the system. On the other hand, the relatively low concentration of hydroxylamine ensures stable operation of short-cut nitrification and compliance with ammonia nitrogen standards in the effluent.

[0092] In summary, this invention provides a method for short-cut nitrification in a continuous flow process, comprising a preparation stage, a short-cut nitrification start-up stage, and a short-cut nitrification maintenance stage. The start-up stage utilizes a high concentration of hydroxylamine to achieve rapid initiation and stable operation of short-cut nitrification, while the maintenance stage utilizes a low concentration of hydroxylamine to control the ammonia nitrogen content in the effluent.

[0093] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for short-range nitrification in a continuous flow process, the method employing an anaerobic-aerobic-anoxic (AOA) process unit containing a hydroxylamine dosing unit, characterized in that... Methods include S1. Preparation stage: Inoculate aerobic activated sludge into the aerobic zone and perform aeration treatment; add fluidized packing material into the aerobic zone; inoculate anoxic activated sludge into the anoxic zone located downstream of the aerobic zone; the aerobic activated sludge includes nitrifying denitrifying bacteria; the anoxic activated sludge includes denitrifying denitrifying bacteria; the dissolved oxygen concentration in the aerobic zone is 1-3 mg / L. S2, Short-cut nitrification start-up stage: Hydroxylamine is added to the aerobic zone to make it exist at a first concentration of 7-9 mgN / L, and the nitrite accumulation rate of the effluent from the aerobic zone is monitored until the nitrate content of the effluent from the aerobic zone is less than 5 mg / L. The hydroxylamine is added once every 5-7 hours, and the duration of each addition is less than 10 minutes. The nitrite accumulation rate is greater than 90%. S3, Short-cut nitrification maintenance stage; Maintain the hydraulic retention time, sludge retention time and dissolved oxygen concentration in the aerobic zone of the bioreactor at a constant level, so that hydroxylamine exists in the aerobic zone at a second concentration of 1-3 mgN / L, which is less than the first concentration, and monitor the nitrogen concentration in the effluent from the anoxic zone. The device includes an influent unit, a bioreactor, a sludge treatment unit, and a hydroxylamine dosing unit. The bioreactor includes an anaerobic zone, an aerobic zone, an anoxic zone 1, and an anoxic zone 2 connected in sequence, with a volume ratio of 1:1:2 for the anaerobic, aerobic, and anoxic zones. The anoxic zone 2 is connected to the secondary sedimentation tank of the sludge treatment unit via an overflow pipe. The treated wastewater in the upper layer of the secondary sedimentation tank is discharged through a drain pipe, while the sludge in the lower layer is divided into three streams: one part is returned to the anaerobic zone via a first sludge return pump, one part is returned to the anoxic zone 1 via a second sludge return pump, and the remaining part is periodically discharged from the sludge discharge pipe.

2. The method according to claim 1, characterized in that, In step S1, the concentration of suspended solids in the mixed liquid in the aerobic zone and the anoxic zone is 2500-4500 mg / L.

3. The method according to any one of claims 1-2, characterized in that, Step S1 further includes maintaining the hydraulic residence time of the system at 12-16 hours.

4. The method according to claim 3, characterized in that, Step S3 further includes maintaining the average concentration of suspended solids in the mixture of the system at 4000-6000 mg / L.

5. The method according to claim 4, characterized in that, Step S3 further includes maintaining the sludge retention time of the system at 25-40 days.

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