Method for short-cut nitrification and rapid start-up and stable operation of thiocyanate-containing acrylonitrile wastewater

Abstract

The application discloses a method for short-cut nitrification rapid start and stable operation of thiocyanate-containing acrylic fiber wastewater, and belongs to the field of wastewater treatment. At least three batches of small tests are arranged, the nitrite accumulation rate of each small test is calculated, the lowest thiocyanate concentration greater than 50% is selected as the starting concentration, the initial sludge concentration is maintained at 3000 mg / L-4000 mg / L, four cycles are operated in one day, and the operation mode is full aerobic or anoxic-aerobic. After the short-cut nitrification is successfully started, if the initial thiocyanate concentration of the influent is lower than 90 mg / L, the thiocyanate concentration needs to be strengthened and maintained at 90-100 mg / L. The inherent thiocyanate in the acrylic fiber wastewater is used as a natural inhibitor without additional chemical agents, and the pollutants are simultaneously degraded. The intermediate product sulfide has selective inhibition on NOB, the double inhibition strengthens the short-cut nitrification, and the AOB activity is not affected. The short-cut nitrification is rapidly started in 10-12 cycles, and the long-term stable operation is maintained through dynamic adjustment of the SCN-concentration.

Description

Technical Field

[0001] This invention relates to a method for rapid start-up and stable operation of short-cut nitrification in acrylonitrile-containing wastewater containing thiocyanate, belonging to the field of wastewater treatment. Background Technology

[0002] Acrylic fiber wastewater is a typical industrial wastewater containing nitrogen and sulfur, with ammonia nitrogen (NH4) being the most abundant. + ) and thiocyanate (SCN) – Ammonia nitrogen is a characteristic nitrogen and sulfur pollutant in acrylonitrile wastewater. The concentration of ammonia nitrogen in acrylonitrile wastewater is approximately 100 mg / L. Excessive discharge of ammonia nitrogen can cause a decrease in dissolved oxygen in the water and lead to severe eutrophication. The concentration of thiocyanate in acrylonitrile wastewater is approximately 100–300 mg / L. It contributes not only to the total nitrogen in petrochemical wastewater but also to COD, and ultimately produces ammonia nitrogen through oxidative degradation. Thiocyanate is also a toxic and chemically stable pollutant that inhibits various enzyme systems, posing serious hazards to humans, plants, and aquatic organisms.

[0003] Traditional nitrification-denitrification (NDI) is currently the main biological process for treating acrylonitrile fiber wastewater. However, this process suffers from high energy consumption, low nitrogen removal efficiency, and failure to meet total nitrogen standards in the effluent. To meet the treatment and discharge requirements of acrylonitrile fiber wastewater, introducing low-carbon and efficient anaerobic ammonium oxidation (ANAO) technology holds promise for achieving economical and efficient nitrogen removal. Short-cut nitrification coupled with ANAO (PN / A) nitrogen removal has advantages over traditional NDI processes, including lower energy consumption, less residual sludge, no need for added organic carbon, and higher nitrogen removal efficiency, making it a promising technology for nitrogen removal in acrylonitrile fiber wastewater treatment.

[0004] The stabilization of short-cut nitrification is a crucial step in the PN / A process for nitrogen removal from acrylonitrile wastewater. Short-cut nitrification involves maximizing the activity of ammonia-oxidizing bacteria (AOB) while simultaneously inhibiting nitrite-oxidizing bacteria (NOB) to partially convert ammonia nitrogen into nitrite nitrogen, after which the conversion stops, providing a stable substrate of nitrite nitrogen for anaerobic ammonia oxidation. However, NOB often co-grows with AOB, disrupting the short-cut nitrification process. Currently effective strategies for inhibiting NOB include controlling dissolved oxygen levels, controlling sludge age, and strategies based on free ammonia and free nitrite. However, these strategies suffer from drawbacks such as long start-up periods (2–3 months) and low long-term stability.

[0005] Inhibitors can effectively and stably suppress NOB activity, but the exogenous application of inhibitors increases operating costs. SCN in acrylonitrile wastewater. – It is an effective inhibitor; studies have shown that SCN... – Within a certain concentration range, it significantly inhibits NOB activity while having little effect on AOB activity. Furthermore, SCN... – It is also a pollutant in acrylonitrile wastewater, SCN –intermediate product S generated by degradation 2– It has also been shown to promote short-cut nitrification. Therefore, SCN is used. – Promoting short-cut nitrification can achieve zero cost of inhibitors and SCN. – While degradation of thiocyanate is possible, there is currently a lack of effective short-cut nitrification initiation methods that utilize thiocyanate as an inhibitor. Therefore, this invention utilizes thiocyanate in acrylonitrile wastewater as an SCN inhibitor. – A novel short-cut nitrification inhibitor enables rapid start-up and stable operation of short-cut nitrification in acrylonitrile-containing wastewater containing thiocyanate. Summary of the Invention

[0006] The purpose of this invention is to solve the problems mentioned in the background art and to provide a method for rapid start-up and stable operation of short-cut nitrification of acrylonitrile-containing wastewater. The technical steps are as follows:

[0007] (1) Set up at least 3 batches of aerobic active nitrification pilot tests, calculate the nitrite accumulation rate of each pilot test, and select the lowest thiocyanate concentration with a nitrite accumulation rate greater than 50% as the thiocyanate concentration for reactor startup.

[0008] (2) An initial sludge concentration of 3000 mg / L–4000 mg / L was maintained by inoculating the activated sludge from the municipal wastewater treatment plant into a sequencing batch reactor.

[0009] (3) The sequencing batch reactor operates for 4 cycles a day, each cycle is 6 hours. Each cycle includes water inlet, anoxic stirring, aerobic stirring, sedimentation, drainage, and idle. The operating mode is either aerobic throughout or anoxic-aerobic.

[0010] (4) During the start-up phase, according to step (1), the initial ammonia nitrogen concentration in the influent is controlled to be 80–100 mg / L and the thiocyanate concentration is controlled to be 100–300 mg / L. The system is run for 10–12 cycles. The concentrations of ammonia nitrogen, nitrite, nitrate and thiocyanate in the reactor influent and effluent are monitored regularly. If the nitrite accumulation rate reaches more than 80%, it indicates that the short-cut nitrification system has been successfully started up.

[0011] (5) After the short-cut nitrification is successfully started, if the initial concentration of thiocyanate in the reactor after the water influent is less than 90 mg / L, the short-cut nitrification needs to be enhanced. The initial concentration of thiocyanate in the system is increased by 30–40 mg / L to enhance the short-cut nitrification until the initial concentration of thiocyanate is 90–100 mg / L.

[0012] (6) After the short-range nitrification enhancement is completed, maintain the initial thiocyanate concentration at a stable level of 90–100 mg / L.

[0013] Furthermore, in step (1) above, the initial ammonia nitrogen concentration of the active small-scale reaction is set to 100 mg / L, and the concentration range of thiocyanate is 100–300 mg / L;

[0014] Furthermore, in step (1) above, the batch-scale active test reaction lasted for 10 hours. During the reaction, the sludge mixture was taken every hour for filtration and the concentrations of ammonia nitrogen, nitrite, nitrate and thiocyanate were measured, and the nitrite accumulation rate was calculated.

[0015] Furthermore, in step (3) above, the water inlet time is 15 min, the sedimentation time is 30 min, and the drainage time is 5 min. The stirring and idle time and hydraulic retention time (HRT) are set according to the reactor operation mode. In the full-process aerobic mode: 0 min of anoxic stirring, 240 min of aerobic stirring, 70 min of idle time, and HRT is 10 h; in the anoxic-aerobic mode: 120 min of anoxic stirring, 180 min of aerobic stirring, 10 min of idle time, and HRT is 12.5 h.

[0016] Furthermore, in steps (2), (3), and (4) above, the reaction temperature is 23–26℃, the pH is 6.5–8.5, and the dissolved oxygen in the aerobic phase is 0.05–6 mg / L;

[0017] Furthermore, in steps (5) and (6) above, the reaction temperature is 23–26℃, the pH is 6.5–7.4, and the dissolved oxygen in the aerobic stage is controlled at 0.05–3 mg / L;

[0018] Furthermore, in step (5) above, after each increase of 30–40 mg / L of the initial thiocyanate concentration, an enhanced operation is performed for 20–25 days.

[0019] Furthermore, after the enhancement in step (6) above is completed, the stable operation mode is consistent with the operation mode in the start-up stage, and the operating conditions are controlled at reaction temperature of 23–26℃, pH of 6.5–8.5, and dissolved oxygen of 0.05–3 mg / L.

[0020] The principle of this invention for short-cut nitrification of acrylonitrile wastewater lies in the fact that thiocyanate, an endogenous pollutant in acrylonitrile wastewater, inhibits the activity and abundance of NOB within a certain concentration range, while having a smaller inhibitory effect on AOB. At the same time, hydrogen sulfide, an intermediate product of thiocyanate biodegradation, also has the same inhibitory effect. Therefore, by utilizing the difference in response of AOB and NOB to thiocyanate, ammonia nitrogen in the system is oxidized to nitrite and accumulated, thereby initiating in-situ short-cut nitrification of acrylonitrile wastewater.

[0021] This invention utilizes characteristic pollutants in acrylonitrile fiber wastewater to achieve rapid start-up and enhancement of short-cut nitrification in acrylonitrile fiber wastewater. The advantages of this invention are:

[0022] 1) Directly utilize the thiocyanate inherent in acrylonitrile wastewater as a natural inhibitor, eliminating the need for additional chemical agents, significantly reducing operating costs, and simultaneously achieving synergistic degradation of pollutants.

[0023] 2) SCN- and its degradation intermediate sulfides selectively inhibit NOB, thus enhancing short-cut nitration with dual inhibition, while not affecting AOB activity.

[0024] 3) By gradient control of SCN- concentration and real-time monitoring of effluent indicators, short-cut nitrification can be quickly started within 10–12 cycles, which significantly shortens the start-up time compared to traditional methods (2–3 months), and long-term stable operation can be maintained by dynamically adjusting SCN- concentration. Attached Figure Description

[0025] Figure 1 The minimum SCN required for reactor startup was determined in a batch aerobic activated nitrification pilot test in specific case 1 of this invention. – concentration;

[0026] Figure 2 In the specific case 1 of this invention, NH4 is used to start the short-cut nitrification process. + -N, NO2 – -N, NO3 – -N、SCN – Changes in concentration and nitrite accumulation rate;

[0027] Figure 3 This is a specific example of the invention, Case 2, involving the initiation of a short-cut nitrification process using water NH4. + -N, NO2 – -N, NO3 – -N、SCN – Changes in concentration and nitrite accumulation rate;

[0028] Figure 4 This is a specific example of the invention, Case 2, showing a typical cycle of NH4 after starting short-cut nitrification. + -N, NO2 – -N, NO3 – -N、SCN – -N concentration, pH, and dissolved oxygen changes. Detailed Implementation

[0029] The technical solution of the present invention will be described in detail below with reference to embodiments. It should be noted that the core concept of the present invention is explained below through specific implementation methods and data parameters, but this is not the only limitation of the present invention. Those skilled in the art, based on the technical principles of the present invention, can make equivalent substitutions and optimizations by adjusting process conditions or parameters without departing from its core idea. Therefore, the scope of protection of the present invention should be defined by the claims and is not limited by the specific details described in the embodiments.

[0030] Example 1:

[0031] The batch aerobic activated nitrification pilot test of this invention was conducted in glass bottles with an effective volume of 500 ml. The initial ammonia nitrogen concentration was maintained at 80 mg / L, while the initial thiocyanate concentration was set at 100, 200, and 300 mg / L, respectively. The inoculum sludge was ordinary municipal wastewater treatment plant sludge. The experimental procedure included washing the inoculum sludge three times with deionized water to remove residual substrate, and then diluting the sludge with distilled water to 500 ml glass bottles to maintain a sludge concentration of approximately 4000 mg / L. Aeration was continuously supplied during the reaction, and the operating temperature was maintained at approximately 26°C. The reaction lasted for 10 hours, during which samples were taken periodically from the mixture to determine the concentrations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and thiocyanate. Figure 1 As shown, when SCN was added at concentrations of 100, 200, and 300 mg / L... – Under these conditions, the nitrite accumulation rates at time 10 were 54%, 66%, and 68%, respectively. The lowest SCN with a nitrite accumulation rate greater than 50% was selected. – Concentration, i.e., 100 mg / L of SCN – As the start-up concentration for a short-cut nitrification reactor.

[0032] The short-cut nitrification reaction of this invention is carried out in a sequencing batch reactor with a total working volume of 10 liters. The reactor operates four cycles per day, each lasting 6 hours, in a fully aerobic mode. Each cycle includes 15 minutes of influent, 240 minutes of aerobic aeration, 30 minutes of sedimentation, 5 minutes of effluent, and 70 minutes of idle time. The hydraulic retention time is set to 10 hours. Wastewater containing 80 mg / L ammonia nitrogen and 100 mg / L thiocyanate is introduced into the reactor via a peristaltic pump, while the supernatant is discharged via a solenoid valve. During the aerobic aeration phase, an air pump regulated by a gas flow meter provides airflow, maintaining a stable gas flow rate of 200 ml / min. Simultaneously, a stirrer ensures uniform mixing of sludge and wastewater. A temperature-controlled heater is installed within the reactor to maintain a stable reaction temperature of approximately 26°C. Dissolved oxygen and pH are continuously monitored using dedicated sensors. Figure 2As shown, the pH during the start-up phase is 6.8–7.1, and the dissolved oxygen is 1.6–5.6 mg / L; during the enhancement phase, the pH is 6.5–7.4, and the dissolved oxygen is 0.1–2.9 mg / L. Figure 3 As shown, after 3 days (12 cycles), the nitrite accumulation rate of the system reached 88%, indicating that short-cut nitrification was successfully initiated. In the following 25 days, the influent concentration was 100 mg / L SCN. – Under operation, the nitrite accumulation rate increased from 88% to 93%. During the start-up phase, SCN... – The initial mixing concentration was approximately 30 mg / L, therefore, two enhancement cycles were performed at a gradient of 30 mg / L, each lasting 24 days. After the enhancement, the reaction continued in a fully aerobic mode, with the temperature maintained at 26°C, pH between 6.5 and 8.5, dissolved oxygen at approximately 0.1 mg / L, and the initial thiocyanate concentration at 90 mg / L. The nitrite accumulation rate remained above 97%. Throughout the entire operation, the thiocyanate removal rate remained above 98%. This invention provides a novel method for the rapid start-up and stable operation of short-cut nitrification of acrylonitrile fiber wastewater containing thiocyanate.

[0033] Example 2:

[0034] The short-cut nitrification reaction of this invention is carried out in a sequencing batch reactor with a total working volume of 10 liters. The operating temperature is maintained at approximately 26°C. The reactor operates for four cycles per day, each lasting 6 hours, in an anoxic-aerobic mode. Each cycle includes 15 minutes of influent, 120 minutes of anoxic agitation, 180 minutes of aerobic aeration, 30 minutes of sedimentation, 5 minutes of effluent, and 10 minutes of idle time. The hydraulic retention time is set to 12.5 hours. Wastewater containing 80 mg / L ammonia nitrogen and 100 mg / L thiocyanate is introduced into the reactor via a peristaltic pump, while the supernatant is discharged via a solenoid valve. During the aerobic aeration phase, an air pump regulated by a gas flow meter provides the airflow, maintaining a stable gas flow rate of 200 ml / min. Simultaneously, a stirrer ensures uniform mixing of sludge and wastewater. A temperature-controlled heater is installed within the reactor to maintain a stable reaction temperature of approximately 26°C. Figure 3 As shown, during the start-up phase, after 3 days (12 cycles), the nitrite accumulation rate reached 79%. After 15 days, the nitrite accumulation rate reached over 98% and remained stable for 35 days. During the start-up phase, SCN was mixed... – Concentrations above 90 mg / L do not require system enhancement. A typical system cycle on day 35 is as follows: Figure 4As shown, during the aerobic aeration phase of hours 2–5 in this cycle, nitrite continuously accumulates, with an accumulation rate as high as 99%. Throughout the entire operation, the thiocyanate removal rate remains above 98%, with dissolved oxygen levels in the aerobic phase ranging from 0.07–0.1 mg / L and pH from 7.6–8.5. This invention provides a novel method for the rapid start-up and stable operation of short-cut nitrification in acrylonitrile fiber wastewater containing thiocyanate.

Claims

1. A method for rapid start-up and stable operation of short-cut nitrification in acrylonitrile-containing wastewater, characterized in that, Includes the following steps: (1) Set up at least 3 batches of aerobic active nitrification pilot tests, calculate the nitrite accumulation rate of each pilot test, and select the lowest thiocyanate concentration with a nitrite accumulation rate greater than 50% as the thiocyanate concentration for reactor startup; (2) An activated sludge from a municipal wastewater treatment plant was inoculated using a sequencing batch reactor to maintain an initial sludge concentration of 3000 mg / L–4000 mg / L; (3) The sequencing batch reactor operates for 4 cycles a day, each cycle is 6 hours. Each cycle includes water inlet, aerobic stirring, sedimentation, drainage and idle. The operating mode is aerobic throughout. (4) During the start-up phase, according to step (1), the initial ammonia nitrogen concentration in the influent is controlled to be 80–100 mg / L and the thiocyanate concentration is controlled to be 100–300 mg / L. The system is run for 10–12 cycles. The concentrations of ammonia nitrogen, nitrite, nitrate and thiocyanate in the reactor influent and effluent are monitored regularly. When the nitrite accumulation rate reaches more than 80%, it indicates that the short-cut nitrification system has been successfully started. (5) After the short-cut nitrification is successfully started, if the initial thiocyanate concentration in the reactor after the influent is less than 90 mg / L, the short-cut nitrification needs to be enhanced. The initial thiocyanate concentration of the system should be increased in a gradient of 30–40 mg / L. After each increase of 30–40 mg / L in the initial thiocyanate concentration, the enhanced operation should be carried out for 20–25 days until the initial thiocyanate concentration reaches 90–100 mg / L and the enhancement is completed. (6) After the short-range nitrification enhancement is completed, maintain the initial thiocyanate concentration at 90–100 mg / L during operation.

2. The method according to claim 1, characterized in that, In step (1), the initial ammonia nitrogen concentration for the small-scale active reaction is set to 100 mg / L, and the thiocyanate concentration range is 100–300 mg / L.

3. The method according to claim 1, characterized in that, In step (1), the batch activity test reaction lasted for 10 hours. During the reaction, the sludge mixture was taken every hour for filtration and the concentrations of ammonia nitrogen, nitrite, nitrate and thiocyanate were measured. The nitrite accumulation rate was calculated.

4. The method according to claim 1, characterized in that, In step (3), the water inlet time is 15 min, the aerobic stirring time is 240 min, the sedimentation time is 30 min, the drainage time is 5 min, and the idle time is 70 min. The hydraulic retention time (HRT) is 10 h.

5. The method according to claim 1, characterized in that, In steps (2), (3), and (4), the reaction temperature is 23–26℃, the pH is 6.5–8.5, and the dissolved oxygen is 0.05–6 mg / L.

6. The method according to claim 1, characterized in that, In step (5), the reaction temperature is 23–26℃, the pH is 6.5–7.4, and the dissolved oxygen in the aerobic phase is controlled at 0.05–3 mg / L.

7. The method according to claim 1, characterized in that, After the enhancement in step (6) is completed, the stable operation mode is the same as the operation mode in the start-up stage. The operating conditions are controlled at a reaction temperature of 23–26℃, a pH of 6.5–8.5, and a dissolved oxygen of 0.05–3 mg / L.

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