Coking Wastewater Treatment A 2 Rapid Recovery Method for Abnormal Operation of the Biochemical Section of the O Process

Abstract

The present invention discloses a method for rapidly restoring the abnormal operation of the biochemical section of the coking wastewater treatment A2 / O process. By utilizing the characteristics of good activity and no toxic and harmful substances of municipal sludge, the present invention adds municipal sludge for sludge re-domestication, rapidly restores the nitrification and denitrification reactions of the system, simultaneously reduces the content of S2− in the influent water that inhibits the biological nitrogen removal process, further improves the contact condition between dissolved oxygen and activated sludge, rapidly restores the biological nitrogen removal process of the system and improves the operation stability of the system. The above method also realizes the resource utilization of municipal sludge.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for rapidly restoring abnormal operation of biological nitrogen removal in the biochemical section of an anaerobic-anoxic-aerobic process in a coking wastewater system. Background Art

[0002] Coking wastewater is one of the main wastewaters discharged by iron and steel enterprises, mainly including ammonia distillation wastewater, coal washing wastewater, coke quenching wastewater, tar processing wastewater, gas final cooling circulating water, crude benzene separation water, refined benzene separation water, ammonium sulfate wastewater, etc. Ammonia distillation wastewater is the main source of coking wastewater. The pollutants contained in coking wastewater include phenols, polycyclic aromatic compounds, and heterocyclic compounds containing nitrogen, oxygen, and sulfur, cyanides, etc., which is a typical industrial wastewater containing toxic substances and refractory organic compounds. Ammonia distillation wastewater is the wastewater discharged after the distillation of mixed surplus ammonia water. Generally, the water quality of ammonia distillation wastewater in coking plants is: CODcr 3500 - 4500 mg / L, phenol 700 - 1400 mg / L, cyanide 7 - 20 mg / L, oil less than 30 mg / L, ammonia nitrogen about 150 mg / L, TKN about 300 mg / L. However, the water quality of coking wastewater varies greatly due to differences in the process flow and production operation mode of each plant.

[0003] For the treatment of coking wastewater, a mode of pretreatment + biochemical treatment + advanced treatment is mostly adopted. Among them, the biochemical treatment method, which is the secondary treatment in the coking wastewater treatment system, plays a very crucial role in the whole wastewater treatment. The biochemical treatment method (biological treatment method) is a method of using microorganisms to oxidize and decompose the organic matter in the wastewater (mainly for nitrogen removal). Compared with other nitrogen removal processes, the anaerobic-anoxic-aerobic process (A 2 O process) has the advantages of short total hydraulic retention time, simple structure, low operation cost, small control complexity, and not easily generating sludge bulking, and has been widely applied. The anaerobic-anoxic-aerobic process is specifically as follows: in the aerobic section, nitrifying bacteria convert the ammonia nitrogen in the influent and the ammonia nitrogen ammoniated from organic nitrogen into nitrate through biological nitrification; in the anoxic section, denitrifying bacteria convert the nitrate brought in by the internal reflux into nitrogen gas and escape into the atmosphere through biological denitrification, so as to achieve the purpose of nitrogen removal; in the anaerobic section, polyphosphate-accumulating organisms release phosphorus and absorb easily degradable organic matters such as low-level fatty acids; while in the aerobic section, polyphosphate-accumulating organisms absorb phosphorus in excess and remove phosphorus through the discharge of excess sludge.

[0004] In the treatment of coking wastewater, the stability of the entire system depends to a large extent on the operation of the biochemical system. In addition, the dry quenching process is currently widely used in coking. After the abnormal operation of the coking wastewater system, the water balance of the system operation and the progress of the front-end production will be severely affected. Therefore, the research and development of how to improve the biological nitrogen removal operation stability of the biochemical system using the anaerobic-anoxic-aerobic process and how to quickly recover after the abnormal operation of biological nitrogen removal have important practical significance and extremely high application value.

[0005] Currently, the municipal sludge generated by sewage treatment plants in China exceeds 30 million tons (with a moisture content of 80%) per year. With the increase in sewage treatment volume, the surplus sludge also increases significantly, and the situation of sludge treatment and disposal is very serious. The current methods of sludge treatment and disposal in China mainly include landfill, composting, incineration, and sludge building materials utilization, etc. Generally, there are situations of relatively low treatment level and limited treatment capacity. Finding new ways of sludge resource utilization is an effective way to increase the treatment volume of municipal sludge. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present invention provides a method for quickly restoring the abnormal operation of the biochemical section of the A 2 / O process for coking wastewater treatment. By utilizing the characteristics of good activity of municipal sludge and no toxic and harmful substances, municipal sludge is added for sludge re-domestication to quickly restore the nitrification and denitrification reactions of the system, and at the same time reduce the content of S 2- in the influent water that inhibits the biological nitrogen removal process. It also further improves the contact situation between dissolved oxygen and activated sludge, quickly restores the biological nitrogen removal process of the system and improves the operation stability of the system. The above method also realizes the resource utilization of municipal sludge.

[0007] The technical solution of the present invention is: a method for quickly restoring the abnormal operation of the biochemical section of the A 2 / O process for coking wastewater treatment, which is characterized by including the following steps:

[0008] (1) After dissolving the municipal sludge with the secondary sedimentation tank water, add it to the front end of the aerobic tank to quickly restore the nitrification and denitrification reactions of the system; after adding the sludge, the nitrification liquid reflux and sludge reflux are suspended, aeration is carried out for 8 - 24 h, and after the aeration is completed, the nitrification liquid reflux and sludge reflux are restored; after the sludge addition is completed, the biochemical system does not discharge sludge within one week;

[0009] (2) After the ammonia nitrogen at the outlet of the aerobic tank returns to the normal level of 0 mg / L, adjust the nitrification liquid reflux ratio to 3 ± 0.2, and adjust the sludge reflux ratio to 2 ± 0.2; and gradually increase the treatment load of the system; at the same time, adjust the dissolved oxygen content at the inlet of the aerobic tank to 0.5 - 1 mg / l, the dissolved oxygen content from the inlet to the middle of the aerobic tank to 5 - 6 mg / l, and the dissolved oxygen content from the middle to the end of the aerobic tank to 6 - 6.5 mg / l;

[0010] (3) By controlling the pH value of the coking wastewater between 7.5 and 8 before it enters the biochemical system, the content of S which inhibits the biological denitrification process is reduced. 2- .

[0011] Furthermore, the municipal sludge in the above step (1) needs to be odorless and have good biological activity under microscopic examination. It is preferably the sludge pressed out by a spiral press, and no chemicals such as lime are added during the treatment of the municipal sludge. For the A 3 / h 2 O process section, the amount of municipal sludge input is 30 ± 5 tons.

[0012] Furthermore, in the above step (2), the treatment load of the system is increased. Specifically: for the A 3 / h 2 O process section, within the first 48 hours, the treatment volume can be quickly restored to 11 ± 1 m 3 / h; within 48h - 96h, it operates stably at a load of 11 ± 1 m 3 / h for 24 hours, and then the volume is increased to 15 ± 1 m 3 / h at 72 hours, and further increased to 20 ± 1 m 3 / h at 96 hours; after the treatment volume reaches 20 ± 1 m 3 / h, the operation load of the system is restored by increasing the treatment volume by 5 ± 0.5 m 3 / h every 24 hours.

[0013] Furthermore, the preferred method for adjusting the pH value between 7.5 and 8 in the above step (3) is: for the ammonia stripping wastewater, the pH value of the effluent from the front - end ammonia stripping system can be adjusted between 7.5 and 8. Utilizing the characteristic that lead acetate test paper turns black when encountering sulfide ions (S 2- ) in the solution, the detection of the effluent quality of the ammonia stripping wastewater is strengthened. If the test paper turns black, the caustic soda dosage in the ammonia stripping process is adjusted in a timely manner for control.

[0014] The technical solution of the present invention is:

[0015] 1. The purpose of adding municipal sludge in the present invention is to quickly restore the activity of the system. By utilizing the characteristics of good activity and no toxic and harmful substances of the municipal sludge, the microorganisms in the abnormally operating system are supplemented and the toxic and harmful substances in the abnormally operating system are diluted, so as to quickly restore the activity of the system (nitrification and denitrification). As Figure 3 shown, before and after adding the sludge, the ammonia nitrogen content in the aerobic tank and the anoxic tank decreases rapidly. In addition, the present invention makes full use of the municipal sludge, opening up a new perspective for the resource utilization of the municipal sludge, eliminating secondary pollution and reducing primary energy consumption.

[0016] 2. The present invention starts from reducing the maximum growth rate constant μ of nitrifying bacteria and denitrifying bacteria A , the denitrification and nitrification rates, the content and distribution of substances that play an inhibitory role in ammonia oxidation and hydroxylamine oxidation, adjusts the operation of the front-end process parameters, and reduces the S 2- content in the influent water. Controlling the pH helps to improve the operational stability of biochemical nitrogen removal. At the same time, compared with the original iodometric method, indirect flame atomic absorption spectrometry, and meteorological molecular absorption spectrometry, which have a long detection process time for S 2- and cannot conduct high-frequency inspections to timely guide production, the present invention uses lead acetate test paper to quickly conduct a qualitative detection of S 2- in the ammonia distillation wastewater, improving the immediacy of the effluent water quality control of the ammonia distillation tower.

[0017] 3. In traditional theory, the dissolved oxygen required for nitrification reaction is about 2 mg / l. However, it is found in practice that this does not have a good effect on nitrification. The present invention adjusts the dissolved oxygen content according to the characteristics of coking wastewater with high oil content. High dissolved oxygen content is beneficial to improving the mass transfer effect, reducing the hindrance of oil substances in coking wastewater, and better combining with microorganisms for nitrification reaction.

[0018] 4. After the ammonia nitrogen at the outlet of the aerobic tank returns to the normal level of 0 mg / L, adjust the nitrification liquid reflux ratio to about 3 to increase the uniformity of microorganism distribution in the system, improve the removal rate of COD by denitrifying bacteria, and avoid the inhibition of nitrification by high ammonia nitrogen concentration; adjust the sludge reflux ratio to about 2 to reduce the residence time of sludge in the secondary sedimentation tank.

[0019] In summary, when the biological nitrogen removal process in the biochemical system of the A 2 O process for coking wastewater treatment shows abnormalities, through the resource utilization of municipal sludge, the nitrification and denitrification processes of the system are quickly restored. At the same time, the content of substances that play an inhibitory role in the biological nitrogen removal process in the influent water is reduced, and the contact condition between dissolved oxygen and activated sludge is further improved, quickly restoring the biological nitrogen removal process of the system and improving the operational stability of the system. The above method also realizes the resource utilization of municipal sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic process flow diagram of the present invention;

[0021] Figure 2 shows the ammonia nitrogen change in the anoxic tank and aerobic tank from 0 to 250 h (municipal sludge was added to the aerobic tank at 195 h);

[0022] Figure 3 shows the ammonia nitrogen change in the anoxic tank and aerobic tank from 140 to 300 h (municipal sludge was added to the aerobic tank at 195 h);

[0023] Figure 4 It is the regulation situation of the nitrification liquid reflux ratio, sludge reflux ratio and treatment capacity from 200h to 435h;

[0024] Figure 5 For S 2- 、HS - 、The distribution coefficients of H2S under different pH values;

[0025] Figure 6 It is the distribution situation of the nitrite nitrogen content at the outlet of the aerobic tank. Specific implementation mode

[0026] The following combines examples and drawings to illustrate its effects.

[0027] Example 1:

[0028] For the treatment method of coking wastewater, the mode of pretreatment + biochemical treatment + advanced treatment is mostly adopted. As Figure 1 shown, the pretreatment includes an oil removal tank and a homogenization tank, and the biochemical treatment includes an anaerobic tank, an anoxic tank, an aerobic tank and a secondary sedimentation tank. The surplus ammonia water discharged from the blast condensation is subjected to ammonia distillation treatment in the ammonia distillation unit, and the distilled ammonia water enters the accident tank for storage.

[0029] The pretreatment of coking wastewater is specifically as follows: after removing light and heavy tar through the oil removal tank, it enters the homogenization tank to adjust the water volume and homogenize the water quality.

[0030] The biochemical treatment of coking wastewater is specifically as follows: for the coking wastewater pretreated as above, in the aerobic section, nitrifying bacteria convert the ammonia nitrogen in the influent and the ammonia nitrogen ammoniated from organic nitrogen into nitrate through biological nitrification; in the anoxic section, denitrifying bacteria convert the nitrate brought in by the internal reflux into nitrogen gas through biological denitrification and escape into the atmosphere, so as to achieve the purpose of nitrogen removal; in the anaerobic section, polyphosphate-accumulating bacteria release phosphorus and absorb easily degradable organic matters such as low-level fatty acids; while in the aerobic section, polyphosphate-accumulating bacteria absorb phosphorus in excess and remove phosphorus through the discharge of excess sludge. The wastewater treated by nitrogen removal undergoes mud-water separation in the secondary sedimentation tank to clarify the mixed liquid, concentrate the sludge and return the separated sludge to the aerobic tank in the biological treatment section. The wastewater treated by biochemical treatment subsequently enters the advanced treatment.

[0031] Taking the accident tank 3645m at the front end of the coking wastewater treatment system 3 and the oil removal tank 302m 3 and the homogenization tank 524m 3 and the anaerobic tank 829m 3 and the anoxic tank 3370m 3 and the aerobic tank 6740m 3 with a designed maximum treatment capacity of 60m 3 / h of A 2Taking the O process section as an example (the influent ammonia nitrogen content is 80 - 100 mg / l), the specific implementation plan and steps are as follows:

[0032] 1. Recovery stage of the effluent ammonia nitrogen index

[0033] After dissolving the municipal sludge with the water from the secondary sedimentation tank, pump it into the front end of the aerobic tank to quickly restore the nitrification and denitrification reactions of the system. The amount of municipal sludge input is 30 tons. The municipal sludge should be odorless and have good biological activity under microscopic examination. Select the sludge pressed by a spiral press, and no chemicals such as lime are added during the treatment of municipal sludge. After the sludge is input, the nitrification liquid is refluxed, and the sludge reflux is suspended. Aerate for 8 - 24 h. After the sludge input is completed, the biochemical system does not discharge sludge within one week. After the aeration is completed, restore the nitrification liquid reflux and sludge reflux.

[0034] Within 0 - 250 h, the changes in the ammonia nitrogen content of each tank are as Figure 2 shown. The highest ammonia nitrogen content in the east aerobic tank reaches 34.89 mg / l, the highest ammonia nitrogen content in the west aerobic tank reaches 36.72 mg / l, and the highest ammonia nitrogen content in the anoxic tank reaches 36.72 mg / l. After the abnormality occurred in the biological denitrification process, 30 tons of municipal sludge was added to the aerobic tank at 195 h. After adding the municipal sludge, the ammonia nitrogen content in each tank first increased slightly and then decreased rapidly.

[0035] From Figure 3 it can be seen that before and after adding the sludge, the ammonia nitrogen content in each tank decreased rapidly. Compared with 200 h, at 219 h, the ammonia nitrogen in the anoxic tank decreased from 36.72 mg / l to 25.52 mg / l, the ammonia nitrogen in the west aerobic tank decreased from 26.82 mg / l to 14.06 mg / l, and the ammonia nitrogen in the east aerobic tank decreased from 21.87 mg / l to 7.55 mg / l. At 243 h, the ammonia nitrogen at the outlets of the west aerobic tank and the east aerobic tank was zero and remained stable.

[0036] 2. System load increase stage

[0037] After the ammonia nitrogen at the outlet of the aerobic tank returns to the normal level of 0 mg / L, start to adjust the operating parameters such as the nitrification liquid reflux ratio, sludge reflux ratio, and treatment volume, and gradually increase the treatment volume. The adjustment process from 200 h to 435 h is as Figure 4 shown.

[0038] During the period of increasing the operating load, according to the test indexes and combined with the system water balance requirements, the following adjustments were made to the parameters such as the treatment volume, sludge reflux, and nitrification liquid reflux. The specific adjustment situation is as follows: During the process of initially restoring the treatment volume, it can be quickly increased to a low load of about 11 m 3 / h. After operating stably at a load of 11 m 3 / h for 24 h, the flow rate is increased to 15 m 3 / h, and after stabilizing for 24 hours, increase the flow rate to 20 m 3 / h. After the processing volume reaches 20 m 3 / h, adopt the method of increasing the processing volume by 5 m 3 / h every 24 hours to restore the operating load of the system.

[0039] After the system runs stably and then stabilizes again, the nitrification liquid reflux ratio is 300% (to increase the uniformity of microorganism distribution in the system, improve the removal rate of COD by denitrifying bacteria, and avoid the inhibition of nitrification by high ammonia nitrogen concentration), and the sludge reflux ratio is 200% (to reduce the residence time of sludge in the secondary sedimentation tank).

[0040] At the same time, adjust the dissolved oxygen content at the inlet of the aerobic tank to 0.5 - 1 mg / l, the dissolved oxygen content from the inlet to the middle of the aerobic tank to 5 - 6 mg / l, and the dissolved oxygen content from the middle of the aerobic tank to the end of the aerobic tank to 6 - 6.5 mg / l.

[0041] 3. Reduce the content of S 2-

[0042] By adjusting the pH value of the effluent from the front-end ammonia stripping system to be between 7.5 and 8, and utilizing the influence of the pH value on the hydrolysis and ionization of sulfur-containing compounds, reduce the content of S 2- 2- has an inhibitory effect on the maximum growth rate constant μ A of nitrifying bacteria and denitrifying bacteria, the nitrification and denitrification rates, ammonia oxidation, and hydroxylamine oxidation; utilize the characteristic that lead acetate test paper turns black when encountering sulfide ions (S 2- ) in the solution, strengthen the detection of the effluent quality of the ammonia stripping wastewater, and if the test paper turns black, adjust the caustic soda dosage in the ammonia stripping process in time to control the pH.

[0043] First of all, there are many substances that inhibit activated sludge, such as various heavy metal substances, organic compounds, inorganic ions, etc. According to the characteristics of coking wastewater, based on the analysis and testing of the influent water quality, this invention grasps the substance S 2- that plays a major inhibitory role to improve the influent water quality.

[0044] After testing, the distribution coefficients of S Figure 5 , HS 2- , and H2S under different pH values are obtained as shown. According to the two process index requirements of controlling the mass fraction of S - and maintaining the influent ammonia nitrogen not too high, control the pH value within the range of 7 - 8 (if the pH is too low, the influent ammonia nitrogen is too high, and the biochemical system will also be inhibited). 2-

[0045] 4. System operation conditions

[0046] ​​1) Outlet nitrate nitrogen and nitrite nitrogen content

[0047] The oxidation of ammonia nitrogen to nitrite nitrogen can release 242.8 - 351.7 kJ / mol of energy, and nitrite bacteria can obtain 5% - 14% of the energy from it. The energy released during the oxidation of nitrite nitrogen to nitrate nitrogen is 64.5 - 87.5 kJ / mol. Nitrate bacteria can utilize 5% - 10% of it, which is 20% - 25% of the energy effectively utilized by nitrite bacteria. To achieve the same energy consumption, the amount of nitrite oxidized by nitrate bacteria must reach 4 - 5 times the amount of ammonia nitrogen oxidized by nitrite bacteria. Therefore, there will be no accumulation of nitrite under steady state.

[0048] During the operation of the system, by sampling and analyzing the outlet of the aerobic tank, within 180 days, through the analysis of 76 outlet nitrite nitrogen data, it was found that in the above samples, the average value of nitrite nitrogen content was 0.058 mg / l, the standard deviation of the samples was 0.024, and in most cases, the nitrite nitrogen content ≤ 0.1 mg / l. The specific distribution of nitrite nitrogen content is as Figure 6 shown. From the perspective of the content of nitrite nitrogen, the system operates stably and well.

[0049] 2) Outlet alkalinity and ammonia nitrogen

[0050] Sampling and analyzing the outlet of the aerobic tank, the outlet alkalinity is 250 - 350 mg / l, and the outlet ammonia nitrogen content is 0 mg / l.

[0051] 3) Operating load

[0052] Under the high treatment load of an influent flow rate of 60 m 3 / h, an influent ammonia nitrogen content of 80 - 100 mg / l, and a dilution water dosage of ≤ 10 m 3 / h, and a water temperature of ≤ 37°C, the stable operation time can reach 180 days.

Claims

1. A rapid recovery method for abnormal operation of the biochemical section of the AO process for treating coking wastewater, characterized in that, 2 It includes the following steps: ​ (1) After dissolving municipal sludge in water, add it to the front end of the aerobic tank to quickly restore the nitrification and denitrification reactions of the system; after adding the sludge, the return of nitrified liquid and sludge is suspended, and aeration is carried out for 8 - 24 h. After the aeration is completed, the return of nitrified liquid and sludge is restored; (2) After the ammonia nitrogen at the outlet of the aerobic tank returns to the normal level of 0 mg / L, adjust the nitrified liquid return ratio to 3 ± 0.2 and the sludge return ratio to 2 ± 0.2; gradually increase the treatment load of the system; at the same time, adjust the dissolved oxygen content at the inlet of the aerobic tank to 0.5 - 1 mg / l, the dissolved oxygen content from the inlet to the middle of the aerobic tank to 5 - 6 mg / l, and the dissolved oxygen content from the middle to the end of the aerobic tank to 6 - 6.5 mg / l; The processing load of the lifting system is specifically as follows: for the A 2 O process section with a flow rate of 60 m3 / h, within the first 48 hours, the processing volume quickly recovers to 11 ± 1 m 3 / h; within 48 h - 96 h, after operating stably at a load of 11 ± 1 m 3 / h for 24 hours, the flow rate is increased to 15 ± 1 m3 / h at 72 h and to 20 ± 1 m3 / h at 96 h; after the processing volume reaches 20 ± 1 m3 / h, the operating load of the system is restored by increasing the processing volume by 5 ± 0.5 m3 / h every 24 hours; (3) By controlling the pH between 7.5 and 8 before the coking wastewater enters the biochemical system, the content of S which inhibits the biological nitrogen removal process is reduced; the lead acetate test paper is used to detect the water quality by virtue of the characteristic that it turns black when encountering sulfide ions S in the solution. 2- in the solution; 2- The lead acetate test paper is used to detect the water quality by virtue of the characteristic that it turns black when encountering sulfide ions S in the solution.

2. The quick recovery method according to claim 1, characterized in that, In step (1), the municipal sludge needs to be odorless, have good biological activity under microscopic examination, and no chemicals are added during the treatment of the municipal sludge.

3. The quick recovery method according to claim 2, characterized in that, In step (1), the municipal sludge is the sludge pressed by a spiral press.

4. The quick recovery method according to claim 3, characterized in that, The said step (1) is aimed at the A of 60 m3 / h 2 O process section, and the input amount of municipal sludge is 30 ± 5 tons.

5. The quick recovery method according to claim 1, characterized in that, In step (1), the municipal sludge is dissolved with the secondary sedimentation tank water.

6. The rapid recovery method according to claim 1, characterized in that, After the sludge addition in step (1) is completed, the biochemical system does not discharge sludge within one week.

7. The quick recovery method according to claim 1, characterized in that In step (3), the pH is adjusted between 7.5 and 8. For the ammonia distillation wastewater, the pH value of the effluent from the front-end ammonia distillation system is adjusted to be between 7.5 and 8. When lead acetate test paper is used, it reacts with sulfide ions S in the solution 2- Strengthen the detection of the effluent quality of the ammonia distillation wastewater. If the test paper turns black, promptly adjust the caustic soda dosage in the ammonia distillation process for control.

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