Method for promoting continuous flow sewage short-process denitrification by using formate conditioning activated sludge

Abstract

The invention discloses a method for promoting continuous flow sewage short-process denitrification by using formate conditioning activated sludge, which is characterized in that on the basis of keeping the normal operation process and reaction unit structure of a continuous flow AO (Anaerobic Oxidation) process, part of return sludge is treated by using formate, and finally, the treated sludge is returned to a continuous flow AO reactor. Formate is regularly added into sludge which flows back to the anoxic tank from the secondary sedimentation tank, and then the pH value is adjusted, so that efficient accumulation of nitrite nitrogen in the aerobic tank can be quickly realized, and the oxidation rate of ammonia nitrogen is not obviously influenced. The method provided by the invention has no specific requirement on the ammonia nitrogen concentration in the sewage, and has the advantages of low cost and no secondary pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a method for promoting short-process denitrification of continuous-flow sewage by conditioning activated sludge with formate. Background Art

[0002] Nitrogen in water bodies is a key factor causing eutrophication, so nitrogen-containing sewage must be treated to meet standards before it can be discharged. At present, most sewage treatment plants in the world use nitrification-denitrification denitrification process to treat sewage biochemically. During the nitrification process, ammonia-oxidizing bacteria in activated sludge can oxidize ammonia nitrogen to nitrite nitrogen under aerobic conditions. At the same time, nitrite-oxidizing bacteria oxidize nitrite nitrogen to nitrate nitrogen under aerobic conditions. The generated nitrate nitrogen is then converted into nitrite nitrogen, nitric oxide, nitrous oxide and nitrogen gas by denitrifying bacteria in anoxic conditions, thereby completely removing nitrogen from the water. During the nitrification process, oxygenation facilities such as Roots blowers and jet aerators are required to maintain the dissolved oxygen in the reaction solution above 2 mg / L; and during the denitrification process, organic carbon sources need to be added as electron donors to ensure the full reduction of nitrogen oxides. The energy consumption cost of the nitrification-denitrification denitrification process generally accounts for 30% to 60% of the operating cost, so it is particularly necessary to carry out energy saving and consumption reduction for the realization of the "dual carbon" strategy.

[0003] Since nitrite is a common intermediate product of nitrification and denitrification, if the oxidation of nitrite during nitrification is inhibited and then reduced to nitrogen through denitrification, a short-process biological denitrification can be achieved, thereby reducing a large amount of aeration electricity consumption and carbon source addition costs.

[0004] At present, CN106865773 B discloses a method of adding 10 mg / L of hydroxylamine hydrochloride to a sequencing batch nitrification reactor to achieve the effect of inhibiting the activity of nitrite-oxidizing bacteria. However, the average daily sewage treatment capacity of urban sewage treatment plants is from tens of thousands to millions of tons. In order to make the agent reach the set concentration range, a large amount of agent needs to be added, which not only increases the cost of sewage treatment, but also poses a risk of secondary pollution. Therefore, the above method is completely unfeasible and has no practical application value.

[0005] CN105923752 B discloses a method for achieving stable short-range nitrification by adding 0.2-0.3 mL / L of formic acid to a sequencing batch nitrification reactor. However, this method cannot be applied in urban sewage treatment plants, and formic acid, as a single-carbon organic matter, is easily oxidized and decomposed by heterotrophic bacteria in activated sludge under aerobic conditions, and can be used as an electron donor by denitrifying bacteria to participate in the reduction of nitrogen oxides under anoxic conditions and in the presence of nitrogen oxides. Therefore, a large amount of excess sludge is generated, and formic acid needs to be continuously supplemented during the reaction process.

[0006] CN101284697 B discloses a method of controlling the pH of sludge digestion liquid to inhibit the activity of nitrite-oxidizing bacteria by combining free ammonia and free nitrite. However, this method is not applicable to sewage with low ammonia nitrogen concentration, and many studies have shown that nitrite-oxidizing bacteria will develop tolerance to free ammonia and free nitrite during long-term operation. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to provide a method for promoting the denitrification of continuous flow sewage in a short process by conditioning activated sludge with formate in view of the shortcomings of the prior art. The method of the present invention has no specific requirements on the concentration of ammonia nitrogen in sewage, and has the advantages of low cost and no secondary pollution.

[0008] The continuous flow AO process is currently the most mainstream biological denitrification process in sewage treatment plants. The present invention, while maintaining the normal operating flow and reaction unit structure of the process, only uses formate to treat part of the return sludge, and finally returns the treated sludge to the continuous flow AO reactor. It has the advantages of low reagent usage, simple operation, and no secondary pollution.

[0009] Technical solution: The purpose of the present invention is achieved through the following technical solution:

[0010] The present invention provides a method for promoting short-process denitrification of continuous flow sewage by conditioning activated sludge with formate. On the basis of maintaining the normal operating process and reaction unit structure of the continuous flow AO process, part of the return sludge is treated with formate, and finally the treated sludge is returned to the continuous flow AO reactor.

[0011] The method of using formate to treat part of the returned sludge in the present invention is: regularly adding formate to the sludge returned from the secondary sedimentation tank to the anoxic tank, and then adjusting the pH value to achieve efficient accumulation of nitrite nitrogen in the aerobic tank.

[0012] The method of the present invention comprises the following steps:

[0013] (1) Extract part of the sludge from the secondary sedimentation tank and place it in the sludge conditioning tank, add formate once, the dosage is 30-50mM, add acid solution or alkaline solution to make the pH of the sludge in the range of 7-9, and stir to mix the agent and sludge evenly;

[0014] (2) The sludge in the sludge conditioning tank is stirred once every hour and after 24 to 48 hours of treatment, it is all transferred to the anoxic tank;

[0015] (3) Repeat steps (1) and (2) until the denitrification efficiency remains stable for one month and then stop using formate to treat the sludge.

[0016] The formate is one or both of calcium formate and sodium formate.

[0017] In step (1), the volume of sludge extracted from the bottom of the sludge hopper of the secondary sedimentation tank to the sludge conditioning tank is determined according to the sludge concentration in the anoxic tank or the aerobic tank and the total volume of the anoxic tank and the aerobic tank. The specific calculation formula is:

[0018] V s =r×C s ×(V a +V o ) / ρ

[0019] Where V s is the volume of sludge extracted, in m 3 ; r is the sludge volume coefficient, ranging from 0.2 to 0.3, dimensionless; C s The concentration of sludge in the anoxic or aerobic tank, in kg / m 3 ; V a and V o are the volumes of the anoxic pool and the aerobic pool, respectively, in m 3 ; ρ is the sludge density coefficient, ranging from 10 to 30, in kg / m 3 .

[0020] In step (1), the acid solution added is hydrochloric acid or sulfuric acid solution, and the alkali solution added is sodium hydroxide or potassium hydroxide solution.

[0021] A preferred implementation of the present invention is that, in a continuous flow AO process, after 2000-3000 mg / L of activated sludge is inoculated into an anoxic tank and an aerobic tank respectively, sewage is pumped into the anoxic tank, and the submerged flow pump in the anoxic tank is started, so that sewage and activated sludge are repeatedly mixed to obtain a mud-water mixture; after the mud-water mixture flows from the anoxic tank into the aerobic tank, the aerator in the aerobic tank is started, so that the dissolved oxygen in the mud-water mixture is maintained at 3-4 mg / L; a part of the mud-water mixture in the aerobic tank is returned to the anoxic tank, and the other part flows into the secondary sedimentation tank, and the activated sludge settles to the bottom of the secondary sedimentation tank, and the effluent flows out from the top of the secondary sedimentation tank; a part of the activated sludge at the bottom of the secondary sedimentation tank is discharged as residual sludge, and the other part is discharged into the sludge conditioning tank; formate and acid / alkali are added to the sludge conditioning tank, and the activated sludge is returned to the anoxic tank after being treated for 24-48 hours.

[0022] A preferred implementation of the present invention is that during the first 60 days of operation of the continuous flow AO process, no sludge conditioning is performed; starting from the 61st day, sludge is extracted from the sludge hopper of the secondary sedimentation tank into the sludge conditioning tank every 24 hours.

[0023] Beneficial effects:

[0024] (1) The present invention utilizes formate to condition activated sludge to achieve short-range nitrification, and the dosage of reagents and the cost are relatively low.

[0025] (2) During the long-term operation of the denitrification process of the present invention, the denitrification efficiency remains in a stable state.

[0026] (3) In the present invention, the sludge after formate conditioning is directly returned to the anoxic tank, and the residual formate therein can be used as an organic carbon source and a denitrification electron donor, and can be further removed in the aerobic tank, so there is no risk of secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the process and apparatus of the method of the present invention;

[0028] Among them, 1-water inlet, 2-anoxic tank, 3-aerobic tank, 4-secondary sedimentation tank; 5-water outlet, 6-wastewater return, 7-sludge conditioning tank, 8-sludge return, 9-residual sludge discharge, 10-submerged flow pump, 11-aerator, 12-formatate addition port, 13-acid / alkali addition port. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is described in detail below through specific embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0030] The continuous flow AO process is currently the most mainstream biological denitrification process in sewage treatment plants. The present invention, while maintaining the normal operating flow and reaction unit structure of the process, only uses formate to treat part of the return sludge, and finally returns the treated sludge to the continuous flow AO reactor.

[0031] Figure 1 The figure is a schematic diagram of the process and apparatus of the method of the present invention.

[0032] After inoculating 3000 mg / L of activated sludge into the anoxic tank 2 and the aerobic tank 3 respectively, the sewage is pumped into the anoxic tank 2 from the water inlet 1, and the submerged flow pump 10 in the anoxic tank 2 is started to repeatedly mix the sewage and the activated sludge to obtain a muddy water mixture; after the muddy water mixture flows from the anoxic tank 2 into the aerobic tank 3, the aerator 11 in the aerobic tank 3 is started to maintain the dissolved oxygen in the muddy water mixture at 3-4 mg / L; a part of the muddy water mixture in the aerobic tank 3 flows back to the anoxic tank 2 (see sewage return 6 ), and another part flows into the secondary sedimentation tank 4, after which the activated sludge settles to the bottom of the secondary sedimentation tank, and the effluent flows out from the top of the secondary sedimentation tank 4 through the outlet 5; a part of the activated sludge at the bottom of the secondary sedimentation tank is discharged as residual sludge (see residual sludge discharge 9), and the other part is discharged into the sludge conditioning tank 7; the sludge conditioning tank 7 is respectively subjected to formate addition via the formate addition port 12 and acid / alkali addition port 13, and the activated sludge is returned to the anoxic tank 2 after being treated for 24 to 48 hours (see sludge return 8).

[0033] The low carbon-nitrogen ratio simulated sewage prepared in the laboratory was used as the influent of the AO process, in which the ammonia nitrogen concentration was 136.5±4.3 mg / L and the COD concentration was 318±21 mg / L.

[0034] The volumes of the anoxic tank 2 and aerobic tank 3 of the AO process are 6L and 12L respectively, and the initial sludge concentration therein is 2863mg / L. The inlet flow rate is 1L / h, the sludge-water mixture reflow ratio is 200%, and the sludge age is 30 days. During the first 60 days of operation, no sludge conditioning was performed, and the ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent of the aerobic tank were 2.4mg / L, 0.3mg / L and 62.4mg / L respectively. The results show that high concentrations of ammonia nitrogen do not achieve the accumulation of nitrite nitrogen, and due to the low COD concentration, denitrification is insufficient. Starting from the 61st day, 0.5L of sludge was extracted from the mud hopper of the secondary sedimentation tank 4 to the sludge conditioning tank 7 every 24h.

[0035] The method of the present invention is used to treat the sludge in the sludge conditioning tank 7 .

[0036] The volume of sludge extracted from the bottom of the sludge hopper of the secondary sedimentation tank 4 to the sludge conditioning tank 7 is determined according to the sludge concentration in the anoxic tank 2 or the aerobic tank 3 and the total volume of the anoxic tank 2 and the aerobic tank 3. The specific calculation formula is:

[0037] Vs=r×C s ×(V a +V o ) / ρ

[0038] Where V s is the volume of sludge extracted, in m 3 ; r is the sludge volume coefficient, ranging from 0.2 to 0.3, dimensionless; Cs The concentration of sludge in the anoxic or aerobic tank, in kg / m 3 ; V a and V o are the volumes of the anoxic pool and the aerobic pool, respectively, in m 3 ; ρ is the sludge density coefficient, ranging from 10 to 30, in kg / m 3 .

[0039] Example 1

[0040] Add 30mM sodium formate to the sludge conditioning tank 7, adjust the pH to 8.5 with 1M hydrochloric acid solution while mechanically stirring, and stir to mix the agent and sludge evenly. Stir the sludge once every hour for 5 minutes each time. After the sludge has been conditioned for 24 hours, it is all pumped into the anoxic tank 2. Then extract 0.5L of sludge from the bottom of the mud hopper of the secondary sedimentation tank 4 and repeat the above steps. After the sewage treatment process has been running continuously for 12 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitric nitrogen in the effluent of the aerobic tank are 1.6mg / L, 1.0mg / L and 45.5mg / L, respectively. After continuing to operate for 60 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitric nitrogen in the effluent are stabilized at 1.3mg / L, 0.8mg / L and 26.8mg / L. Then the sludge conditioning time was changed to once every 48 hours, and after 60 days of operation under this condition, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent remained at a low level, 0.5 mg / L, 0.9 mg / L and 28.1 mg / L respectively. At the same time, no sodium formate was detected in the effluent during the entire operation cycle.

[0041] Example 2

[0042] Add 50mM sodium formate to the sludge conditioning tank 7, adjust the pH to 7 with 1M hydrochloric acid solution while mechanically stirring, and stir to mix the agent and sludge evenly. Stir the sludge once every hour for 5 minutes each time. After the sludge has been conditioned for 36 hours, it is all pumped into the anoxic tank 2. Then extract 0.5L of sludge from the bottom of the mud hopper of the secondary sedimentation tank 4 and repeat the above steps. After the sewage treatment process has been running continuously for 12 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent of the aerobic tank are 4.1mg / L, 0.4mg / L and 36.1mg / L, respectively. After continuing to operate for 60 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent are stabilized at 3.0mg / L, 0.5mg / L and 21.2mg / L. Then the sludge conditioning time was changed to once every 48 hours, and after continuing to operate under this condition for 60 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent remained at a low level, at 2.7 mg / L, 0.4 mg / L and 19.4 mg / L respectively. At the same time, no sodium formate was detected in the effluent during the entire operation cycle.

[0043] Example 3

[0044] Add 30mM calcium formate to the sludge conditioning tank 7, adjust the pH to 9 with 1M hydrochloric acid solution while mechanically stirring, and stir to mix the agent and sludge evenly. Stir the sludge once every hour for 5 minutes each time. After the sludge has been conditioned for 24 hours, it is all pumped into the anoxic tank 2. Then extract 0.5L of sludge from the bottom of the mud hopper of the secondary sedimentation tank 4 and repeat the above steps. After the sewage treatment process has been running continuously for 12 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent of the aerobic tank are 3.3mg / L, 0.8mg / L and 43.0mg / L, respectively. After continuing to operate for 60 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent are stabilized at 4.0mg / L, 0.6mg / L and 36.2mg / L. Then the sludge conditioning time was changed to once every 48 hours, and after continuing to operate under this condition for 60 days, the concentrations of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen in the effluent remained at a low level, at 2.9 mg / L, 0.8 mg / L and 32.5 mg / L respectively. At the same time, no sodium formate was detected in the effluent during the entire operation cycle.

[0045] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes in form and details may be made without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A method for promoting short-process denitrification of continuous-flow sewage by conditioning activated sludge with formate, characterized in that: On the basis of maintaining the normal operation process and reaction unit structure of the continuous flow AO process, part of the return sludge is treated with formate, and finally the treated sludge is returned to the continuous flow AO reactor.

2. The method according to claim 1, characterized in that The method of using formate to treat part of the returned sludge is: regularly adding formate to the sludge returned from the secondary sedimentation tank to the anoxic tank, and then adjusting the pH value to achieve efficient accumulation of nitrite nitrogen in the aerobic tank.

3. The method according to claim 1 or 2, characterized in that: The following steps are involved: (1) Extract part of the sludge from the secondary sedimentation tank and place it in the sludge conditioning tank, add formate once, the dosage is 30-50mM, add acid solution or alkaline solution to make the pH of the sludge in the range of 7-9, and stir to mix the agent and sludge evenly; (2) The sludge in the sludge conditioning tank is stirred once every hour and after 24 to 48 hours of treatment, it is all transferred to the anoxic tank; (3) Repeat steps (1) and (2) until the denitrification efficiency remains stable for one month and then stop using formate to treat the sludge.

4. The method according to claim 3, characterized in that The formate is one or both of calcium formate and sodium formate.

5. The method according to claim 3, characterized in that: In step (1), the volume of sludge extracted from the bottom of the sludge hopper of the secondary sedimentation tank to the sludge conditioning tank is determined according to the sludge concentration in the anoxic tank or the aerobic tank and the total volume of the anoxic tank and the aerobic tank. The specific calculation formula is: V s =r×C s ×(V a +V o ) / ρ Where V s is the volume of sludge extracted, in m 3 ; r is the sludge volume coefficient, ranging from 0.2 to 0.3, dimensionless; C s The concentration of sludge in the anoxic or aerobic tank, in kg / m 3 ; V a and V o are the volumes of the anoxic pool and the aerobic pool, respectively, in m 3 ; ρ is the sludge density coefficient, ranging from 10 to 30, in kg / m 3 .

6. The method according to claim 3, characterized in that In step (1), the acid solution added is hydrochloric acid or sulfuric acid solution, and the alkali solution added is sodium hydroxide or potassium hydroxide solution.

7. The method according to claim 1 or 2, characterized in that: In the continuous flow AO process, after 2000-3000 mg / L of activated sludge is inoculated into the anoxic tank and the aerobic tank respectively, the sewage is pumped into the anoxic tank, and the submerged pump in the anoxic tank is started to repeatedly mix the sewage and the activated sludge to obtain a mud-water mixture; after the mud-water mixture flows from the anoxic tank into the aerobic tank, the aerator in the aerobic tank is started to maintain the dissolved oxygen in the mud-water mixture at 3-4 mg / L; a part of the mud-water mixture in the aerobic tank is returned to the anoxic tank, and the other part flows into the secondary sedimentation tank, after which the activated sludge settles to the bottom of the secondary sedimentation tank, and the effluent flows out from the top of the secondary sedimentation tank; a part of the activated sludge at the bottom of the secondary sedimentation tank is discharged as residual sludge, and the other part is discharged into the sludge conditioning tank; formate and acid / alkali are added to the sludge conditioning tank, and the activated sludge is returned to the anoxic tank after being treated for 24-48 hours.

8. The method according to claim 1 or 2, characterized in that: During the first 60 days of operation of the continuous flow AO process, no sludge conditioning was performed; starting from the 61st day, sludge was pumped from the sludge hopper of the secondary sedimentation tank to the sludge conditioning tank every 24 hours.

Images