Method for quick start and stable operation of short-cut nitrification of thiocyanate-containing acrylic fiber wastewater

Abstract

The invention discloses a short-cut nitrification rapid starting and stable operation method for thiocyanate-containing acrylic fiber wastewater, and belongs to the field of sewage treatment. According to the method, at least three batches of small tests are set, the nitrite accumulation rate of each small test is calculated, and the lowest thiocyanate concentration larger than 50% is selected as the starting concentration; the initial sludge concentration is kept at 3000 mg / L to 4000 mg / L; the operation is performed for four cycles per day, and the operation mode is whole-course aerobic or anoxic-aerobic; after the short-cut nitrification is successfully started, if the concentration of the initial thiocyanate is lower than 90 mg / L after water is fed, strengthening is needed, and the operation is carried out by keeping the concentration of the initial thiocyanate at 90-100 mg / L. According to the method, inherent thiocyanate in the acrylic fiber wastewater is used as a natural inhibitor, no extra chemical agent needs to be added, and synergistic degradation of pollutants is achieved at the same time. The intermediate product sulfide has selective inhibition on NOB, double inhibition strengthens short-cut nitrification, and meanwhile, the activity of AOB is not influenced. According to the method, short-cut nitrification is rapidly started within 10-12 cycles, and long-term stable operation is maintained by dynamically adjusting the SCN-concentration.

Description

Technical Field

[0001] The present invention relates to a method for rapid start-up and stable operation of short-cut nitrification of acrylonitrile fiber wastewater containing thiocyanate, belonging to the field of sewage treatment. Background Art

[0002] Acrylonitrile fiber wastewater is a typical industrial wastewater containing nitrogen and sulfur. Among them, ammonia nitrogen (NH4 + ) and thiocyanate (SCN – ) are characteristic nitrogen and sulfur pollutants in acrylonitrile fiber wastewater. The concentration of ammonia nitrogen in acrylonitrile fiber wastewater is about 100 mg / L. The excessive discharge of ammonia nitrogen will cause a decrease in dissolved oxygen in water and trigger serious water eutrophication and other hazards. The concentration of thiocyanate in acrylonitrile fiber wastewater is about 100–300 mg / L. It not only contributes to the total nitrogen of petrochemical wastewater but also contributes to COD, and finally produces ammonia nitrogen after oxidative degradation. Thiocyanate is also a toxic and chemically stable pollutant, which will inhibit a variety of enzyme systems and has serious hazards to humans, plants, aquatic organisms, etc.

[0003] The traditional nitrification-denitrification process is the main biochemical process for treating acrylonitrile fiber wastewater at present. However, this process has problems such as high energy consumption, low denitrification efficiency, and unqualified total nitrogen in the effluent. To meet the treatment and discharge requirements of acrylonitrile fiber wastewater, introducing the low-carbon and high-efficiency anaerobic ammonium oxidation technology is expected to achieve economic and efficient nitrogen removal of acrylonitrile fiber wastewater. The short-cut nitrification coupled with anaerobic ammonium oxidation denitrification (PN / A) process has the advantages of low energy consumption, less residual sludge, no need to add organic carbon, and high denitrification efficiency compared with the traditional nitrification-denitrification process, and has application prospects in the denitrification treatment of acrylonitrile fiber wastewater.

[0004] The stability of short-cut nitrification is the key step for the PN / A process to treat acrylonitrile fiber wastewater for denitrification. The short-cut nitrification process is to exert the activity of ammonia-oxidizing bacteria (AOB) while inhibiting nitrite-oxidizing bacteria (NOB) to achieve the conversion of part of ammonia nitrogen into nitrite nitrogen and then stop, and no longer continue to be converted into nitrate nitrogen, providing the substrate nitrite nitrogen for the stability of anaerobic ammonium oxidation. However, NOB often grows together with AOB, thus destroying the short-cut nitrification process. Currently, effective strategies for inhibiting NOB include controlling low dissolved oxygen, controlling sludge age, strategies based on free ammonia and free nitrous acid, etc. However, these strategies have defects such as long start-up periods (2–3 months) and low long-term stability.

[0005] Using inhibitors can efficiently and stably inhibit the activity of NOB, but the external addition of inhibitors increases the operating cost. SCN – in acrylonitrile fiber wastewater is an effective inhibitor. Existing studies have shown that SCN – has a significant inhibitory effect on the activity of NOB within a certain concentration range and has little effect on the activity of AOB. Moreover, SCN – is also a pollutant in acrylonitrile fiber wastewater. SCN –Intermediate product S produced by degradation 2– has also been proven to be able to promote shortcut nitrification. Therefore, using SCN – to promote shortcut nitrification can achieve zero cost of inhibitors and degradation of SCN – , but currently there is a lack of a method for starting shortcut nitrification that effectively uses thiocyanate as an inhibitor. Therefore, in the present invention, the SCN in acrylic fiber wastewater is used as – a new type of shortcut nitrification inhibitor to achieve rapid start-up and stable operation of shortcut nitrification of acrylic fiber wastewater containing thiocyanate. Summary of the Invention

[0006] The purpose of the present invention is to solve the problems in the above-mentioned background technology and provide a method for rapid start-up and stable operation of shortcut nitrification of acrylic fiber wastewater containing thiocyanate. The technical steps are as follows:

[0007] (1) Set at least 3 batches of aerobic activated nitrification bench-scale tests, calculate the nitrite accumulation rate of each test, and select the lowest thiocyanate concentration with a nitrite accumulation rate greater than 50% as the thiocyanate concentration for reactor start-up;

[0008] (2) Use a sequencing batch activated sludge reactor to inoculate the activated sludge from a municipal wastewater treatment plant and maintain the initial sludge concentration at 3000mg / L–4000mg / L;

[0009] (3) The sequencing batch reactor operates 4 cycles a day, each cycle is 6h, and each cycle includes influent, anoxic stirring, aerobic stirring, sedimentation, drainage, and idling. The operation mode is full aerobic or anoxic-aerobic;

[0010] (4) In the start-up stage, control the initial ammonia nitrogen concentration in the influent to be 80–100mg / L and the thiocyanate concentration to be 100–300mg / L according to step (1), and operate for 10–12 cycles; regularly detect the ammonia nitrogen, nitrite, nitrate, and thiocyanate concentrations at the inlet and outlet of the reactor. When the nitrite accumulation rate reaches more than 80%, it indicates that the shortcut nitrification system has been successfully started;

[0011] (5) After the shortcut nitrification is successfully started, if the initial concentration of thiocyanate mixed evenly in the reactor after influent is lower than 90mg / L, the shortcut nitrification needs to be strengthened. The initial thiocyanate concentration of the system is increased in gradients of 30–40mg / L to strengthen the shortcut nitrification until the initial thiocyanate concentration reaches 90–100mg / L to end the strengthening;

[0012] (6) After the shortcut nitrification strengthening is completed, maintain a stable operation at an initial thiocyanate concentration of 90–100mg / L;

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

[0014] Further, in the above step (1), the batch activated bench-scale reaction lasts for 10 hours. During the reaction, the sludge mixture is filtered every 1 hour to measure the concentrations of ammonia nitrogen, nitrite, nitrate, and thiocyanate, and the nitrite accumulation rate is calculated;

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

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

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

[0018] Further, in the above step (5), after increasing the initial thiocyanate concentration by 30–40 mg / L each time, the enhanced operation is carried out for 20–25 days;

[0019] Further, in the above step (6), after the enhancement ends, the operation mode of the stable operation is the same as that in the startup stage. The operating conditions control the reaction temperature at 23–26 °C, the pH at 6.5–8.5, and the dissolved oxygen at 0.05–3 mg / L;

[0020] The principle of realizing short-cut nitrification of acrylic fiber wastewater in the present invention is that the endogenous pollutant thiocyanate in acrylic fiber wastewater will inhibit the activity and abundance of NOB within a certain concentration range while having less inhibition on AOB. At the same time, the intermediate product hydrogen sulfide generated by the biodegradation of thiocyanate also has the same inhibitory effect. Therefore, by utilizing the response difference of AOB and NOB to thiocyanate, the ammonia nitrogen in the system is oxidized to nitrite and accumulated, so as to achieve the startup of in-situ short-cut nitrification of acrylic fiber wastewater.

[0021] The present invention realizes the rapid startup and enhancement of short-cut nitrification of acrylic fiber wastewater by utilizing the characteristic pollutants in acrylic fiber wastewater. The advantages of the present invention are as follows:

[0022] 1) Directly utilize the inherent thiocyanate in acrylic fiber wastewater as a natural inhibitor, without the need to additionally add chemical agents, significantly reducing the operating cost while achieving the co-degradation of pollutants.

[0023] 2) SCN- and the sulfide intermediate products generated by its degradation have selective inhibition on NOB, and the dual inhibition strengthens shortcut nitrification without affecting the activity of AOB.

[0024] 3) By gradient regulating the SCN- concentration and real-time monitoring the effluent indexes, shortcut nitrification can be quickly started within 10 - 12 cycles. Compared with the traditional method (2 - 3 months), the start-up time is significantly shortened, and long-term stable operation can be maintained by dynamically adjusting the SCN- concentration. Description of the Drawings

[0025] Figure 1 It is for determining the lowest SCN concentration for reactor start-up in the batch aerobic activated nitrification bench-scale test of Specific Case 1 of the present invention; – concentration;

[0026] Figure 2 It is for the variation of NH4 + -N, NO2 – -N, NO3 – -N, SCN – concentration and nitrite accumulation rate during the start-up of shortcut nitrification in Specific Case 1 of the present invention;

[0027] Figure 3 It is for the variation of NH4 + -N, NO2 – -N, NO3 – -N, SCN – concentration and nitrite accumulation rate during the start-up of shortcut nitrification in Specific Case 2 of the present invention;

[0028] Figure 4 It is for the variation of NH4 + -N, NO2 – -N, NO3 – -N, SCN – -N concentration, as well as the variation of pH and dissolved oxygen during a typical cycle after the start-up of shortcut nitrification in Specific Case 2 of the present invention. Detailed Embodiments

[0029] The technical solution of the present invention will be described in detail below in conjunction with embodiments. It should be noted that the core concept of the present invention is explained below through specific implementation manners and data parameters, but this is not the only limitation of the present invention. Based on the technical principle of the present invention, those skilled in the art can make equivalent replacements and optimize the implementation by adjusting process conditions or parameters without departing from its core idea. Therefore, the protection scope of the present invention shall be defined by the claims and shall not be limited by the specific details described in the embodiments.

[0030] Example 1:

[0031] The batch aerobic active nitrification bench test of the present invention was carried out in a glass bottle with an effective volume of 500 ml. The initial ammonia nitrogen concentration was maintained at 80 mg / L, while the initial thiocyanate concentration (set at 100, 200, and 300 mg / L respectively). The inoculated sludge was the sludge from a common urban sewage treatment plant. The test process included washing the inoculated sludge three times with deionized water to remove residual substrates, and then diluting the sludge into a 500-ml glass bottle with distilled water, so as to maintain the sludge concentration at about 4000 mg / L. Oxygen was continuously supplied during the reaction process, and the operating temperature was maintained at about 26°C. The reaction lasted for 10 hours. During this period, samples were taken regularly from the mixed liquor to measure the concentrations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and thiocyanate. As Figure 1 shown, when adding 100, 200, 300 mg / L of SCN – the nitrite accumulation rates at the 10th hour were 54%, 66%, and 68% respectively. Select the lowest SCN – concentration with a nitrite accumulation rate greater than 50%, that is, 100 mg / L of SCN – as the starting concentration of the shortcut nitrification reactor.

[0032] The shortcut nitrification reaction of the present invention was carried out in a sequencing batch reactor with a total working volume of 10 liters. The reactor operates 4 cycles per day, each cycle lasting 6 hours, and the operation mode is fully aerobic. Each cycle includes 15 minutes of influent, 240 minutes of aerobic aeration, 30 minutes of sedimentation, 5 minutes of drainage, and 70 minutes of idling. The hydraulic retention time was set at 10 hours. The wastewater containing 80 mg / L of ammonia nitrogen and 100 mg / L of thiocyanate was introduced into the reactor through a peristaltic pump, and the supernatant was discharged through a solenoid valve. During the aerobic aeration stage, an air pump regulated by a gas flow meter was used to provide air flow, maintaining a stable gas flow rate of 200 ml / min. At the same time, a stirrer was used to ensure uniform mixing of the sludge and the wastewater. A temperature control heater was installed in the reactor to maintain a stable reaction temperature of about 26°C. The dissolved oxygen and pH value were continuously monitored through special sensors. As Figure 2As shown, the pH in the startup stage is 6.8 - 7.1, and the dissolved oxygen is 1.6 - 5.6 mg / L. The pH in the intensification stage is 6.5 - 7.4, and the dissolved oxygen is 0.1 - 2.9 mg / L. As Figure 3 shown, after 3 days of operation, that is, 12 cycles, the nitrite accumulation rate of the system reached 88%, indicating that the shortcut nitrification was successfully started. In the following 25 days with an influent of 100 mg / L SCN – operation, the nitrite accumulation rate increased from 88% to 93%. In the startup stage, the initial mixing concentration of SCN – was about 30 mg / L. Therefore, two intensifications were carried out at a gradient of 30 mg / L, with each intensification lasting 24 days. After the intensification ended, the reaction operation mode was still the full aerobic mode, the temperature was maintained at 26 °C, the pH was 6.5 - 8.5, the dissolved oxygen was about 0.1 mg / L, the initial concentration of thiocyanate was 90 mg / L, and the nitrite accumulation rate remained above 97%. The removal rate of thiocyanate during the entire operation stage was maintained above 98%. The present invention provides a new method for the rapid startup and stable operation of shortcut nitrification of acrylonitrile wastewater containing thiocyanate.

[0033] Example 2:

[0034] The shortcut nitrification reaction of the present invention is carried out in a sequencing batch reactor with a total working volume of 10 liters. The operating temperature is maintained at about 26 °C. The reactor operates 4 cycles per day, each cycle lasting 6 hours, and the operation mode is anoxic-aerobic. Each cycle includes 15 minutes of influent, 120 minutes of anoxic stirring, 180 minutes of aerobic aeration, 30 minutes of sedimentation, 5 minutes of drainage, and 10 minutes of idling. The hydraulic retention time is set to 12.5 hours. Wastewater containing 80 mg / L of ammonia nitrogen and 100 mg / L of thiocyanate is introduced into the reactor through a peristaltic pump, while the supernatant is discharged through a solenoid valve. During the aerobic aeration stage, an air pump regulated by a gas flow meter is used to provide an air flow, maintaining a stable gas flow rate of 200 ml / min. At the same time, a stirrer is used to ensure uniform mixing of the sludge and wastewater. A temperature control heater is installed in the reactor to maintain a stable reaction temperature of about 26 °C. As Figure 3 shown, in the startup stage, after 3 days of operation, that is, 12 cycles, the nitrite accumulation rate reached 79%. After 15 days of operation, the nitrite accumulation rate reached above 98% and remained stable for 35 days. The mixing concentration of SCN – in the startup stage was above 90 mg / L. Therefore, the system did not need to be intensified. The typical cycle of the system on the 35th day is as Figure 4As shown, during the aerobic aeration stage from the 2nd to the 5th hour of this cycle, nitrite continued to accumulate, with an accumulation rate as high as 99%. The removal rate of thiocyanate was maintained above 98% throughout the operation stage. The dissolved oxygen in the aerobic section was 0.07 - 0.1 mg / L, and the pH was 7.6 - 8.5. The present invention provides a new method for the short-cut nitrification rapid startup and stable operation of acrylonitrile wastewater containing thiocyanate.

Claims

1. A method for rapid startup and stable operation of short-range nitrification of thiocyanate-containing acrylic wastewater, characterized in that: The following steps are involved: (1) Setting up at least three batches of aerobic active nitrification tests, calculating the nitrite accumulation rate of each test, and selecting the lowest thiocyanate concentration at which the nitrite accumulation rate is greater than 50% as the thiocyanate concentration for starting the reactor; (2) A sequencing batch activated sludge reactor was used to inoculate activated sludge from a municipal sewage plant, maintaining an initial sludge concentration of 3000 mg / L–4000 mg / L; (3) The sequencing batch reactor runs four cycles a day, each cycle lasting 6 hours. Each cycle includes water inlet, anoxic stirring, aerobic stirring, sedimentation, drainage, and idleness. The operation mode is either full aerobic or anoxic-aerobic. (4) During the startup phase, 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 according to step (1), and the operation is performed for 10-12 cycles; the concentrations of ammonia nitrogen, nitrite, nitrate and thiocyanate in the influent and effluent of the reactor are regularly tested, and when the nitrite accumulation rate reaches more than 80%, it indicates that the short-range nitrification system has been successfully started; (5) After the short-range nitrification is successfully started, if the initial mixed thiocyanate concentration in the reactor after the water enters is lower than 90 mg / L, the short-range nitrification needs to be enhanced by increasing the initial thiocyanate concentration of the system by 30-40 mg / L to enhance the short-range nitrification until the initial thiocyanate concentration reaches 90-100 mg / L. (6) After the short-term nitrification enhancement is completed, the initial thiocyanate concentration is maintained at 90–100 mg / L.

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

3. The method according to claim 1, characterized in that The batch activity test in step (1) was reacted for 10 hours. During the reaction, the sludge mixed solution was filtered every hour and the concentrations of ammonia nitrogen, nitrite, nitrate and thiocyanate were measured to calculate the nitrite accumulation rate.

4. The method according to claim 1, characterized in that In step (3), water is introduced for 15 minutes, sedimentation is carried out for 30 minutes, and drainage is carried out for 5 minutes. The stirring, idle time and hydraulic retention time (HRT) are set according to the reactor operation mode. In the full aerobic mode, anoxic stirring is carried out for 0 minutes, aerobic stirring is carried out for 240 minutes, idle time is carried out for 70 minutes, and HRT is carried out for 10 hours. In the anoxic-aerobic mode: anoxic stirring for 120 min, aerobic stirring for 180 min, idle for 10 min, and HRT is 12.5 h.

5. The method according to claim 1, characterized in that In steps (2), (3), and (4), the reaction temperature is 23–26°C, 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°C, the pH is 6.5-7.4, and the dissolved oxygen in the aerobic stage is controlled at 0.05-3 mg / L.

7. The method according to claim 1, characterized in that In step (5), the intensified operation is performed for 20-25 days after each increase of the initial thiocyanate concentration by 30-40 mg / L.

8. The method according to claim 1, characterized in that After the strengthening in step (6) is completed, the operation mode of the stable operation is consistent with the operation mode of the startup phase, and the operating conditions control the reaction temperature to 23-26°C, the pH to 6.5-8.5, and the dissolved oxygen to 0.05-3 mg / L.

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