A method for realizing quick start and stable maintenance of urban sewage short-cut nitrification at normal temperature by using quaternary ammonium salt

Abstract

The application discloses a method for realizing quick start and stable maintenance of short-cut nitrification of municipal sewage at normal temperature by using quaternary ammonium salt, and belongs to the technical field of sewage biological treatment. The method is as follows: inoculating full-nitrification activated sludge in a sequencing batch biochemical reactor, mixing QACs with water into the full-nitrification system, adding QACs (concentration: 2-4 mg / L) into the system in each cycle, regularly monitoring the water quality change of effluent, and determining that the start of short-cut nitrification of municipal sewage at normal temperature is successful when the nitrite accumulation rate in the system is greater than 80%. The method can start short-cut nitrification in about 10 days, and the started short-cut nitrification can be stably maintained for a long time.

Description

Technical Field

[0001] This invention belongs to the field of biological wastewater treatment and relates to a method for rapidly starting and stably maintaining short-cut nitrification of urban wastewater at room temperature using quaternary ammonium salt disinfectants. This invention is primarily suitable for biological denitrification processes in urban wastewater with low carbon-to-nitrogen ratios. Background Technology

[0002] Excessive levels of nitrogen and phosphorus in water bodies lead to eutrophication, causing serious harm to the aquatic environment. Therefore, wastewater denitrification and phosphorus removal are necessary. In urban wastewater treatment, biological denitrification is one of the most important methods. However, traditional nitrification-denitrification processes require energy for aeration and carbon source consumption to ensure denitrification, significantly increasing wastewater treatment costs. Therefore, a more efficient and energy-saving wastewater denitrification method is needed to treat urban wastewater with a low carbon-to-nitrogen ratio. Many novel denitrification processes have been applied to current wastewater treatment, such as short-cut nitrification-denitrification and short-cut nitrification-anaerobic ammonium oxidation processes, with short-cut nitrification being the core. Studies show that compared to full nitrification-denitrification processes, short-cut nitrification can save approximately 25% of aeration, thereby reducing wastewater treatment costs. The key to achieving short-cut nitrification lies in two aspects: rapid start-up and stable maintenance. The core mechanism for achieving short-cut nitrification is to suppress the activity of nitrite-oxidizing bacteria (NOB) without excessively suppressing the activity of ammonia-oxidizing bacteria (AOB), thereby achieving stable nitrite accumulation during wastewater treatment. However, since wastewater biological treatment systems are cultivation systems where multiple bacteria are mixed together, the symbiotic relationship between AOB and NOB is quite complex. Therefore, developing a new treatment method to rapidly and stably achieve short-cut nitrification deserves in-depth research attention.

[0003] Previous studies have indicated that methods for achieving short-cut nitrification mainly include increasing temperature, decreasing dissolved oxygen (DO), and reducing sludge time (SRT). When the temperature in the activated sludge system exceeds 25°C, the growth rate of aerobic nitrification (AOB) in the reactor is significantly higher than that of nitrogen oxides (NOB). Therefore, the higher temperature in the system makes AOB more competitive than NOB, gradually washing NOB out of the reactor and achieving short-cut nitrification. Ma et al. also achieved short-cut nitrification and a nitrite accumulation rate (NAR) of over 95% by reducing the DO in the system to around 0.4-0.7 mg / L. However, lower DO also inhibits the activity of AOB, thereby suppressing ammonia oxidation performance and reducing wastewater denitrification performance. In addition, in activated sludge systems, since AOB and NOB have different SRTs, short-cut nitrification can be achieved by adjusting the SRT. However, achieving short-cut nitrification through these traditional methods has drawbacks such as long start-up time, low maintenance capacity after start-up, and severe impact on the performance of wastewater biological treatment after start-up.

[0004] Achieving short-cut nitrification using short-cut nitrification inhibitors has become a key research focus. Currently researched short-cut nitrification inhibitors include formic acid, sulfides, chlorates, free ammonia (FA), free nitrite (FNA), and hydroxylamine. Formic acid, as a fatty acid, has strong corrosive properties and volatility, making it hazardous during experiments and unsuitable for storage. While sulfides can achieve short-cut nitrification, they also produce hydrogen sulfide gas, posing a threat to human health and environmental safety. Furthermore, sulfides in wastewater may promote the growth of filamentous sulfur bacteria, leading to sludge bulking and affecting effluent quality. Chlorate is a potentially explosive chemical, posing significant safety hazards during use. Studies have shown that NOB is adaptable to the inhibition of FA and FNA; 0.75 mg / L of FNA can successfully initiate short-cut nitrification, but as the reaction proceeds, the abundance of NOB in the system gradually increases, ultimately disrupting the short-cut nitrification process. Previous studies have also used hydroxylamine to experiment with short-cut nitrification processes. For example, using 10 mg / L hydroxylamine as a short-cut nitrification inhibitor can achieve short-cut nitrification of granular sludge. However, hydroxylamine is chemically unstable and decomposes rapidly at room temperature after absorbing water and carbon dioxide. In addition, hydroxylamine is also expensive, costing approximately 14 yuan per gram. In summary, these inhibitors have many drawbacks, such as difficulty in storage, easy adaptation to NOB, and high usage costs. Therefore, finding safe and efficient new short-cut inhibitors has significant practical implications. Quaternary ammonium compounds (QACs) are commonly used disinfectants with broad-spectrum bactericidal effects and are widely used in household and hospital disinfection. Alkyltrimethylammonium compounds (ATMAC) and dialkyldimethylammonium compounds (DADMAC) are commonly used in daily life and frequently detected in the environment. However, there are few reports on using QACs to achieve rapid start-up and stable maintenance of short-cut nitrification. Therefore, this invention selects QACs as a novel short-cut nitrification inhibitor, aiming to study its ability to achieve rapid start-up and stable maintenance of ambient temperature short-cut nitrification in urban wastewater. Summary of the Invention

[0005] To achieve rapid start-up and stable maintenance of short-cut nitrification of urban wastewater at ambient temperature, this invention proposes a method using quaternary ammonium salt disinfectants. By adding QACs to the reactor, this invention can inhibit NOB activity without excessively inhibiting AOB activity during the reaction, and gradually wash NOB out of the reactor, thereby achieving rapid start-up and stable maintenance of short-cut nitrification.

[0006] The technical steps of this invention are as follows:

[0007] (1) First, activated sludge is inoculated into the sequencing batch reactor so that the sludge concentration in the reactor is 2500-3500 mg / L;

[0008] (2) Use artificially synthesized water as the feed water of the reactor. The feed water contains ammonia nitrogen, COD (chemical oxygen demand) and trace elements. When the ammonia nitrogen removal rate (ARE) in the system reaches more than 95%, it is considered that the activated sludge system in the reactor has good full-process nitrification activity. Then, a certain concentration of QACs mother liquor is mixed with artificially synthesized water and added to the reactor to start the short-cut nitrification start-up process.

[0009] (3) The operating cycle of the sequencing batch bioreactor includes five stages: water inlet, aeration, sedimentation, drainage and idle. The specific operating mode is as follows: water inlet time is 5-15 min, aeration time is 130-200 min, sedimentation time is 10-30 min, drainage time is 5-10 min, and idle time is 80-150 min.

[0010] (4) Regularly monitor the influent and effluent water quality of the reactor and calculate the nitrite accumulation rate (NAR) using the formula. When the NAR in the reactor system reaches more than 80%, it is considered that the short-cut nitrification of urban sewage at room temperature has been officially started. The short-cut nitrification can be started in about 10 days and then maintained for more than 30 days.

[0011] Furthermore, the inoculated sludge in step (1) above was taken from the fully nitrified activated sludge in the secondary sedimentation tank of a municipal sewage treatment plant. After being taken back, it was washed three times with clean water to remove the interference of the original impurities in the sludge.

[0012] Furthermore, in step (1) above, the quaternary ammonium compounds (QACs) are selected from alkyltrimethyl ammonium compounds (ATMAC) and dialkyldimethyl ammonium compounds (DADMAC).

[0013] Furthermore, in step (2) above, the ammonia nitrogen concentration in the influent is approximately 55-80 mg / L, the COD concentration is approximately 150-350 mg / L, the QACs concentration is 2-4 mg / L, and the QACs are added once per cycle.

[0014] Furthermore, in step (3) above, the reactor runs four cycles a day. Artificial water is pumped into the reactor by a peristaltic pump. Then, the dissolved oxygen (DO) in the reactor system is adjusted by regulating the gas rotor flow meter. After aeration, the reactor is allowed to settle for 30 minutes. Then, mud-water separation is performed, and the supernatant of the reactor is discharged from the drain outlet by an electric ball valve.

[0015] Furthermore, in steps (1), (2) and (3) above, the reactor drainage ratio is 50%, and the DO and temperature during operation are 2-6 mg / L and 18-25℃, respectively.

[0016] Furthermore, the formula in step (4) above is:

[0017]

[0018] Furthermore, QACs, as a commonly used disinfectant, can enhance the metabolic activity of microorganisms under appropriate concentrations. The QACs concentration selected in this invention is a safe dosage, and the short-cut nitrification achieved by adding QACs has good maintenance ability, which can be maintained for more than 30 days.

[0019] The principle of this invention for achieving short-cut nitrification of urban wastewater is as follows: Adding quaternary ammonium salt disinfectant to the reactor will inhibit the activity of AOB and NOB to a certain extent. Since AOB has a stronger ability to adapt to drug stress, it will preferentially and quickly recover its activity, while NOB is more sensitive, and the inhibitory effect of the drug on it will take longer. By utilizing the difference in response of AOB and NOB to QACs, the efficiency of ammonia nitrogen to nitrite nitrogen and the efficiency of nitrite nitrogen to nitrate nitrogen in the system will differ, thereby causing nitrite nitrogen to gradually accumulate in the system, and finally achieving rapid start-up and stable maintenance of short-cut nitrification of urban wastewater at room temperature.

[0020] This invention achieves rapid start-up and stable maintenance of short-cut nitrification in urban wastewater by adding quaternary ammonium salt disinfectant to the reactor. The advantages of this invention are:

[0021] 1) It is suitable for rapid start-up of low ammonia nitrogen urban wastewater short-cut nitrification at room temperature, and provides a stable source of nitrite for the mainstream urban wastewater treatment process—anaerobic ammonia oxidation;

[0022] 2) The reaction system has simple process control conditions, low operating costs, strong operability, and stable operation. Quaternary ammonium salt disinfectant is safer than other short-cut nitrification inhibitors.

[0023] 3) It does not require precise control of the pH parameters during the reaction process, and short-cut nitrification can still be stably achieved even with high DO levels;

[0024] 4) It has good short-cut nitrification stability after startup, requires less dosage and does not cause secondary pollution;

[0025] 5) Even in full nitrification systems containing antibiotics, this method can still quickly start and stably maintain short-cut nitrification.

[0026] 6) It has good maintenance ability after starting short-cut nitrification and can maintain it for more than 30 days. Even if the addition of quaternary ammonium salt disinfectant to the reactor is stopped, short-cut nitrification can still be maintained for about 20 days. Attached Figure Description

[0027] Figure 1 This is a typical cycle of NH4 in specific case 1 of the present invention when QACs (DADMAC) are not added to the reactor. + -N, NO2 - -N, NO3 - The graph showing the variation of -N;

[0028] Figure 2 In specific case 1 of this invention, the addition of QACs (DADMAC) to the reactor successfully initiated a typical short-cut nitrification cycle with NH4. + -N, NO2 - -N, NO3 - The graph showing the variation of -N;

[0029] Figure 3 This invention presents a specific example of the changes in nitrite nitrogen, nitrate nitrogen, and NAR in the effluent during short-cut nitrification by adding QACs (DADMAC) to the reactor.

[0030] Figure 4 This is a specific example of the invention, showing the changes in nitrite nitrogen, nitrate nitrogen, and NAR in the effluent during short-cut nitrification by adding QACs (DADMAC) to the reactor.

[0031] Figure 5 This is a specific example of the invention, Case 3, showing the changes in nitrite nitrogen, nitrate nitrogen, and NAR in the effluent during the short-cut nitrification process when QACs (ATMAC) are added to the reactor. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to experimental examples, but the present invention is not limited to these embodiments.

[0033] Example 1:

[0034] The seed sludge in this embodiment of the invention is activated sludge from a wastewater treatment plant in Beijing. The influent is artificially synthesized water. The complete nitrification process in the system before DADMAC addition is as follows: Figure 1 As shown.

[0035] The short-cut nitrification system in this invention employs a sequencing batch reactor (SBR) made of plexiglass with an effective volume of 9L. The reactor's supporting equipment includes a peristaltic pump, an aeration pump, an aeration disc, a constant-temperature heating belt, and an effluent ball valve. The inoculated sludge is taken from the secondary sedimentation tank of a municipal wastewater treatment plant and is fully nitrified activated sludge. After being retrieved, it is washed three times with clean water to remove interference from existing impurities. The sludge concentration in the system is maintained at approximately 3000 mg / L. The system operates four cycles per day, each cycle consisting of five stages: an influent stage of 15 minutes, an aeration stage of 150 minutes, a sedimentation stage of 30 minutes, a effluent stage of 10 minutes, and a rest stage of 155 minutes. Artificially synthesized water is used as the reactor influent, containing NH4+. + The concentration of -N is approximately 70 mg / L, and the concentration of COD is approximately 250 mg / L. The reactor is aerated using an aeration pump and aeration discs, with the DO concentration maintained at 2-6 mg / L, the pH maintained between 6.0 and 8.0, and the temperature maintained between 18-25℃.

[0036] First, synthetically produced water is pumped into the reactor using a peristaltic pump. Aeration gradually restores the full-process nitrification activity of the activated sludge. When the ARE (acetic acid level) in the system reaches over 95%, the nitrification activity of the sludge returns to normal. A certain concentration of DADMAC mother liquor is then added to the water, and DADMAC is subsequently added to the reactor system to treat the sludge, initiating short-cut nitrification of municipal wastewater. In the first cycle of startup, 2 mg / L of DADMAC is added to the reactor. During the first 5 days of reaction, nitrite begins to accumulate, and NAR (nitrite alkaloids) gradually increases, reaching 81.78% on day 10. At this point, short-cut nitrification has successfully started. A typical cycle in the short-cut nitrification process after DADMAC treatment is shown below. Figure 2 As shown, the NAR (Nutritional Amount) during this cycle is 83%. The changes in effluent nitrite nitrogen, nitrate nitrogen, and NAR in the short-cut nitrification system are as follows: Figure 3 As shown, after successful start-up of short-cut nitrification, it remained stable for 20 days. After adding 4 mg / L of DADMAC to the reactor, the NAR continued to increase and remained above 85% for 40 days. Even after removing DADMAC from the system, short-cut nitrification still operated stably for 20 days. This means that adding DADMAC to the full-process nitrification system to treat the activated sludge can successfully start up urban wastewater at ambient temperature in about 10 days, and the short-cut nitrification has good maintenance capacity, remaining stable for about 60 days after successful start-up. Even after removing DADMAC from the system, it can still operate stably for about 20 days. This invention provides a new method for the rapid start-up and stable maintenance of urban wastewater at ambient temperature short-cut nitrification.

[0037] Example 2:

[0038] The seed sludge used in this embodiment of the invention is activated sludge from a wastewater treatment plant in Beijing. This wastewater treatment plant mainly treats wastewater containing the antibiotic ciprofloxacin (CIP). The influent is artificially synthesized water, and the activated sludge used for inoculation is fully nitrified sludge.

[0039] The system parameters for reactor operation are the same as in Example 1.

[0040] First, synthetically produced water is pumped into the reactor using a peristaltic pump. Aeration gradually restores the full-process nitrification activity of the activated sludge. When the ARE (Acid Reduction) in the system reaches over 95%, the nitrification activity of the sludge returns to normal. Throughout the operation, the system contains 0.2 mg / L of CIP. Then, a certain concentration of DADMAC mother liquor is added to the water, and DADMAC is started to treat the sludge in the reactor system, initiating the short-cut nitrification of municipal wastewater. The changes in nitrite nitrogen, nitrate nitrogen, and NAR in the effluent of the DADMAC-treated short-cut nitrification system containing CIP are shown below. Figure 4 As shown, after the start-up of the first cycle, 2 mg / L of DADMAC was added to the reactor. During the first week of reaction, the NAR in the system gradually increased, reaching 84.2% on day 8, at which point short-cut nitrification was successfully initiated. The NAR was then maintained above 80% for 20 days. Afterwards, the addition of 4 mg / L of DADMAC to the reactor maintained stable short-cut nitrification for approximately 20 days. In other words, adding DADMAC to a full-process nitrification system containing environmental concentrations of CIP to treat activated sludge can successfully initiate ambient-temperature short-cut nitrification of municipal wastewater approximately 8 days later, and the short-cut nitrification has good maintenance capacity, remaining stable for approximately 40 days after successful start-up. This invention provides a new method for the rapid start-up and stable maintenance of ambient-temperature short-cut nitrification of municipal wastewater.

[0041] Example 3:

[0042] The seed sludge used in this embodiment of the invention is activated sludge from a wastewater treatment plant in Beijing. This wastewater treatment plant mainly treats wastewater containing the antibiotic ciprofloxacin (CIP). The influent is artificially synthesized water, and the activated sludge used for inoculation is fully nitrified sludge.

[0043] The system parameters for reactor operation are the same as in Example 1.

[0044] First, synthetically produced water is pumped into the reactor using a peristaltic pump. Aeration gradually restores the full-process nitrification activity of the activated sludge. When the ARE (Acid Reduction) in the system reaches over 95%, the nitrification activity of the sludge returns to normal. Throughout the operation, the system contains 0.2 mg / L of CIP. Then, a certain concentration of ATMAC mother liquor is added to the water, and ATMAC is started to be added to the reactor system to treat the sludge, initiating the short-cut nitrification of municipal wastewater. The changes in nitrite nitrogen, nitrate nitrogen, and NAR (Non-Acid Reduction) in the effluent of the ATMAC-treated short-cut nitrification system containing CIP are shown below. Figure 5 As shown, at the start of the first cycle, 2 mg / L of ATMAC was added to the reactor. During the first 10 days of the reaction, the NAR in the system gradually increased, reaching 80% on day 14, at which point short-cut nitrification was successfully initiated. The NAR was then maintained above 80% for 15 days. Afterwards, 4 mg / L of DADMAC was added to the reactor, and the NAR continued to increase, remaining above 80% for nearly 15 days, indicating good stability of short-cut nitrification. In other words, adding ATMAC to a full-process nitrification system containing environmental concentrations of CIP to treat activated sludge can successfully initiate ambient-temperature short-cut nitrification of municipal wastewater approximately 14 days later, and this stable initiation can be maintained for approximately 30 days. This invention provides a new method for the rapid start-up and stable maintenance of ambient-temperature short-cut nitrification of municipal wastewater.

Claims

1. A method for rapidly initiating and stably maintaining short-cut nitrification of urban wastewater at ambient temperature using quaternary ammonium salts, characterized in that, Includes the following steps: (1) First, activated sludge is inoculated into the sequencing batch reactor so that the sludge concentration in the reactor is 2500-3500 mg / L; (2) Use artificially synthesized water as the feed water of the reactor. The feed water contains ammonia nitrogen, COD (chemical oxygen demand) and trace elements. When the ammonia nitrogen removal rate (ARE) in the system reaches more than 95%, it is considered that the activated sludge system in the reactor has good full-process nitrification activity. Then, a certain concentration of quaternary ammonium salt compound (QACs) mother liquor is mixed with artificially synthesized water and added to the reactor to start the short-cut nitrification start-up process. (3) The operating cycle of the sequencing batch bioreactor includes five stages: water inlet, aeration, sedimentation, drainage and idle. The specific operating mode is as follows: water inlet time is 5-15 min, aeration time is 130-200 min, sedimentation time is 10-30 min, drainage time is 5-10 min, and idle time is 80-150 min. (4) Regularly monitor the influent and effluent water quality of the reactor and calculate the nitrite accumulation rate (NAR) using the formula. When the NAR in the reactor system reaches more than 80%, the short-cut nitrification of urban sewage at room temperature is considered to have officially started; then it can be maintained stably thereafter. In step (2), the quaternary ammonium salt compounds QACs are selected from ATMAC and DADMAC; the concentration of QACs is 2-4 mg / L, and the QACs are added once per cycle; Step (2) The influent contains the antibiotic ciprofloxacin.

2. The method according to claim 1, characterized in that, The inoculated activated sludge in step (1) is the fully nitrified activated sludge from the secondary sedimentation tank of the urban sewage treatment plant. After taking it back, it is washed with clean water three times to remove the interference of the original impurities in the sludge.

3. The method according to claim 1, characterized in that, In step (2), the ammonia nitrogen concentration of the influent is 55-80 mg / L and the COD concentration is 150-350 mg / L.

4. The method according to claim 1, characterized in that, In step (3), the reactor runs four cycles a day. Artificially synthesized water is pumped into the reactor by a peristaltic pump. The dissolved oxygen (DO) in the system is 2-6 mg / L. After aeration, the system is allowed to settle for 30 minutes. Then, mud and water are separated and the supernatant from the reactor is discharged from the drain outlet by an electric ball valve.

5. The method according to claim 1, characterized in that, In steps (1), (2) and (3) above, the reactor drainage ratio is 50%, and the DO and temperature during operation are 2-6 mg / L and 18-25 ℃, respectively.

6. The method according to claim 1, characterized in that, The formula in step (4) above is: 。 7. The method according to claim 1, characterized in that, In step (4), short-cut nitrification can be started in 10 days and then maintained stably for more than 30 days.

8. The method according to claim 1, characterized in that, In step (4), even if the addition of quaternary ammonium compounds to the reactor is stopped during the stabilization phase, short-cut nitration can still be maintained for 20 days.

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