Oxidation ditch type energy-saving carbon-reducing efficient denitrification reaction tank and sewage treatment method

Abstract

The invention discloses an oxidation ditch type energy-saving carbon-reducing efficient denitrification reaction tank and a sewage treatment method. The reaction tank comprises an anaerobic zone, a first anoxic zone, a first aerobic zone, a second aerobic zone and a second anoxic zone; sewage sequentially flows through the anaerobic zone, the first anoxic zone, the first aerobic zone, the second aerobic zone and the second anoxic zone to be treated, and part of nitrification liquid in the first aerobic zone flows back to the first anoxic zone in the treatment process. The existing oxidation ditch type A2 / O process town sewage treatment plant is transformed, the area of the aerobic zone is reduced, and the reduced aerobic zone is transformed into the second aerobic zone and the second anoxic zone which are connected end to end and circularly flow, so that the consumption of excessive carbon sources in the aerobic stage is avoided, the denitrification performance is improved, and the denitrification efficiency is improved. The aeration energy consumption, external carbon source and indirect carbon emission in the town sewage treatment process are reduced, so that the operation cost of a town sewage treatment plant is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and in particular relates to an oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool and a sewage treatment method. Background Art

[0002] Urban wastewater treatment is a typical high-energy-consuming industry, contributing nearly 1% to 2% of total greenhouse gas emissions, significantly impacting the ecological environment. my country's focus on developing a high-quality urban wastewater treatment system inevitably places higher demands on the daily operation and maintenance of wastewater treatment plants.

[0003] The oxidation ditch process is a common biological denitrification process. It has the characteristics of "end-to-end connection and circular flow", which can effectively improve the denitrification performance of the system and is widely preferred by urban sewage design practitioners. After decades of development, this process has been 2 Oxidation ditch type A 2 / O, so that it has the function of removing nitrogen and phosphorus.

[0004] However, these oxidation ditch process projects that have been put into production still have the phenomenon of exchanging high energy consumption for high water quality. The main reason is that the electron donors for denitrification mainly include the carbon source of the activated sludge system influent and the external carbon source. When the carbon source in the sewage comes into contact with the activated sludge, there is an initial adsorption phenomenon, and the organic matter is enriched in the activated sludge and flows with the sewage through the anoxic zone and aerobic zone at the back end of the system. During the rapid construction of urban sewage treatment plants in the past 20 years, in order to effectively remove pollutants and ensure that the effluent meets the standards, the designers usually set the safety factor (F) of the aerobic zone too large, resulting in excessive consumption of carbon sources in the aerobic stage. At the same time, more external carbon sources must be added in the anoxic stage to meet the demand for electron donors in the denitrification process. This design model objectively increases the electricity consumption and drug consumption of the sewage treatment plant.

[0005] Therefore, there are many engineering cases in my country where the carbon source distribution of the influent does not match the functional zoning of the biological phosphorus removal and denitrification system. Generally speaking, the biological denitrification system designed in this way is not efficient. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide an oxidation ditch type energy-saving carbon reduction and high-efficiency denitrification reaction tank and sewage treatment method, to improve the existing oxidation ditch type A 2 The transformation of urban sewage treatment plants using the / O process can significantly reduce aeration energy consumption, external carbon sources and indirect carbon emissions in the urban sewage treatment process, while ensuring that the effluent meets the standards, and promote the low-carbon operation of urban water systems.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention discloses an oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool, wherein the reaction pool comprises an anaerobic zone, a first anoxic zone, a first aerobic zone, a second aerobic zone and a second anoxic zone;

[0009] The water outlet of the anaerobic zone is connected to the water inlet of the first anoxic zone through a first water hole, the water outlet of the first anoxic zone is connected to the water inlet of the first aerobic zone through a second water hole, the water outlet of the first aerobic zone is connected to the second aerobic zone through an overflow weir, and the second aerobic zone and the second anoxic zone are connected end to end to form a circulating flow channel;

[0010] The first aerobic zone is provided with MBBR filler, and the outlet end of the first aerobic zone is provided with a nitrification liquid reflux pump for returning the nitrification liquid from the first aerobic zone to the first anoxic zone;

[0011] Aeration devices are respectively provided in the first aerobic zone and the second aerobic zone;

[0012] The first anoxic zone and the second anoxic zone are respectively provided with a carbon source adding device.

[0013] As a preferred technical solution, a pre-denitrification zone is further provided before the anaerobic zone.

[0014] As a preferred technical solution, a flow propeller is provided at the end where the second aerobic zone and the second anoxic zone meet.

[0015] As a preferred technical solution, the anaerobic zone, the first anoxic zone and the first aerobic zone are respectively provided with corridor partition walls to separate the anaerobic zone, the first anoxic zone and the first aerobic zone into two zones connected end to end, and a flow pusher is provided at the end where the two zones are connected.

[0016] The present invention also discloses a sewage treatment method based on the oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction tank. The sewage flows through the anaerobic zone, the first anoxic zone, the first aerobic zone, the second aerobic zone and the second anoxic zone in sequence for treatment. During the treatment process, part of the nitrification liquid in the first aerobic zone flows back to the first anoxic zone, and the reflux ratio is 150% to 250%. When the C / N ratio of the influent is unbalanced, a carbon source is added to the first anoxic zone and the second anoxic zone.

[0017] As a preferred technical solution, the activated sludge is returned to the pre-denitrification zone with a return ratio of 70% to 100%.

[0018] The beneficial effects of the present invention are:

[0019] The present invention improves the existing oxidation ditch type A 2The urban sewage treatment plant with the / O process was renovated to reduce the area of ​​the aerobic zone and transform the reduced aerobic zone into a second aerobic zone and a second anoxic zone with end-to-end circulation, thereby avoiding excessive consumption of carbon sources in the aerobic stage. While improving the denitrification performance, it also reduced the aeration energy consumption, external carbon sources and indirect carbon emissions in the urban sewage treatment process, thereby reducing the operating costs of the urban sewage treatment plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention provides the following drawings for illustration:

[0021] Figure 1 For the existing oxidation ditch type A 2 Schematic diagram of the / O process reaction pool;

[0022] Figure 2 It is a schematic plan view of the oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool of the present invention;

[0023] Figure 3 It reflects the basic operation status of the urban sewage treatment plant that was continuously monitored during the renovation and commissioning period;

[0024] Figure 4 It reflects the continuous monitoring of pollutant removal at the urban sewage treatment plant during the renovation and commissioning period;

[0025] Figure 5 It reflects the impact of different process parameters on energy-saving and carbon-reduction transformation methods during the transformation and commissioning period;

[0026] Figure 6 It reflects the system operation status of continuous monitoring for 10 hours during the renovation and commissioning period. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0028] like Figure 1 As shown, the existing oxidation ditch type A 2 The 1 / 2 O process reactor consists of an anaerobic zone 1, an anoxic zone 2, and an aerobic zone 3. The aerobic zone 3 is equipped with MBBR filler 4 and a nitrification liquid return pump 5, which returns the nitrification liquid from the aerobic zone 3 to the anoxic zone 2. The aerobic zone 3 is also equipped with an aeration device, while the anoxic zone 2 is equipped with a carbon source dosing device. Wastewater flows sequentially through the anaerobic zone 1, anoxic zone 2, and aerobic zone 3 for treatment. During this process, a portion of the nitrification liquid from the aerobic zone 3 returns to the anoxic zone 2. If the C / N ratio of the influent is unbalanced, a carbon source is added to the anoxic zone 2.

[0029] like Figure 2 As shown, the oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction tank of the present invention includes an anaerobic zone 6, a first anoxic zone 7, a first aerobic zone 8, a second aerobic zone 9 and a second anoxic zone 10; the water outlet of the anaerobic zone 6 is connected to the water inlet of the first anoxic zone 7 through a first water hole, the water outlet of the first anoxic zone 7 is connected to the water inlet of the first aerobic zone 8 through a second water hole, the water outlet of the first aerobic zone 8 is connected to the second aerobic zone 9 through an overflow weir, and the second aerobic zone 9 and the second anoxic zone 10 are connected end to end to form a circulating flow ditch.

[0030] The first aerobic zone 8 is provided with MBBR filler 11, and the water outlet of the first aerobic zone 8 is installed with a nitrification liquid reflux pump 12 for returning the nitrification liquid from the first aerobic zone 8 to the first anoxic zone 7; the first aerobic zone 8 and the second aerobic zone 9 are respectively provided with an aeration device; the first anoxic zone 7 and the second anoxic zone 10 are respectively provided with a carbon source addition device.

[0031] The anaerobic zone 6, the first anoxic zone 7, and the first aerobic zone 8 are respectively provided with corridor partition walls to separate the anaerobic zone 6, the first anoxic zone 7, and the first aerobic zone 8 into two partitions connected end to end, and a flow pusher 13 is provided at the end-to-end connection of the two partitions; a flow pusher 14 is provided at the end-to-end connection of the second aerobic zone 9 and the second anoxic zone 10.

[0032] The sewage flows through the anaerobic zone 6, the first anoxic zone 7, the first aerobic zone 8, the second aerobic zone 9 and the second anoxic zone 10 in sequence for treatment. During the treatment process, part of the nitrification liquid in the first aerobic zone 8 flows back to the first anoxic zone 7, and the reflux ratio is 150% to 250%. When the C / N balance of the influent is unbalanced, a carbon source is added to the first anoxic zone 7 and the second anoxic zone 10.

[0033] A pre-denitrification zone 15 is provided before the anaerobic zone 6. The function of the pre-denitrification zone 15 is to return the activated sludge to the pre-denitrification zone 15. The return ratio is 70% to 100%.

[0034] Implementation Cases:

[0035] A single biochemical pool of a certain urban sewage treatment plant was renovated. The plant has a design capacity of 50,000 m 3 / d, the existing oxidation ditch type A 2 The / O process reaction pool is transformed into the oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool of the present invention.

[0036] Figure 3 It reflects the basic operation status of the urban sewage treatment plant during the continuous monitoring of the renovation and commissioning period, including temperature, dissolved oxygen, MLSS, power consumption, internal recirculation ratio and external carbon source dosage. Figure 3As shown in the figure, the inlet water temperature of the sewage treatment plant is much higher than the temperature of its location. The commissioning started in autumn and ended in winter. The inlet water temperature dropped from 24.5℃ to 17.1℃. During the commissioning period, the daily low temperature was as low as 2℃, but the sewage temperature was still maintained at around 17℃, which was not lower than the minimum water temperature limit taken when the plant was designed; MLSS was controlled in the range of 4500mg / L to 6000mg / L; from the changing trend of power consumption during the commissioning process, it can be seen that as the temperature decreases, the aeration energy consumption and specific energy consumption of the system increase accordingly; the internal reflux ratio is controlled between 150% and 300%; from the use of carbon source, as the transformation progresses, the amount of carbon source added gradually decreases, which preliminarily confirms that the present invention has a positive impact on energy conservation and carbon reduction in sewage treatment plants.

[0037] Figure 4 This reflects the continuous monitoring of pollutant removal at the urban sewage treatment plant during the renovation and commissioning period. Figure 4 As shown, the plant's effluent complies with the surface water level Class IV standard, which has strict requirements for ammonia nitrogen removal, and the ammonia nitrogen removal rate must be guaranteed to be 100%. The average instantaneous total nitrogen concentration in the inlet and outlet water is 41.2 mg·L -1 and 9.9 mg·L -1 The average total nitrogen removal rate was 70.7%, and the nitrate nitrogen concentration in the second anoxic zone was controlled below 11 mg·L -1 , which can meet the effluent total nitrogen requirement of 15mg·L -1 Effluent limit. During the renovation period, the total nitrogen removal rate did not decrease significantly, and as the water temperature continued to decrease, the amount of carbon source added did not increase but decreased, indicating that the system's utilization of carbon sources in sewage increased. There is almost no nitrate nitrogen and nitrite nitrogen in the influent of urban sewage treatment plants, so the organic nitrogen in the total nitrogen needs to be converted into ammonia nitrogen through ammonification and then removed by nitrification and denitrification. By continuously monitoring the total nitrogen, nitrate nitrogen and ammonia nitrogen concentrations in the effluent of the secondary sedimentation tank, it was found that the average level of difficult-to-degrade organic nitrogen in the influent of the plant during the renovation period was only 2.0 mg·L -1 , accounting for 10.62% of the dissolved inert organic matter in the influent. This part of the total nitrogen cannot be removed by biochemical methods, so the regulatory limit of nitrate nitrogen should be 13 mg·L -1 To ensure production safety, 11 mg·L -1 In summary, during the renovation and commissioning process, none of the pollutant indicators exceeded the effluent standards, indicating that the addition of MBBR filler enhanced the nitrification performance of the system and met the denitrification needs of the system under winter water temperature conditions.

[0038] Figure 5The data reflect the influence of different process parameters on the energy-saving and carbon-reduction transformation methods during the transformation and commissioning period. (ab) are the effluents at each stage with sludge concentrations of 4745 and 5156 mg / L; (cd) are the effluents at each stage with internal recirculation ratios of 197% and 247%; (ef) are the effluents at each stage with dissolved oxygen of 0.5-1.0 and >2 mg / L.

[0039] like Figure 5 As shown in Figures 5a and 5b, except for the slight difference in sludge concentration and influent total nitrogen concentration, the other operating parameters are almost the same. Comparing the water quality data along the system operating at different sludge concentrations, the total nitrogen concentration of the secondary sedimentation tank effluent is 8.2 mg·L -1 , 7.2mg·L -1 , 7.0mg·L -1 and 6.7 mg·L -1 ; Nitrate nitrogen concentration was 6.5 mg·L -1 , 6.0mg·L -1 , 6.9mg·L -1 and 4.6 mg·L -1 . The denitrification capacity and denitrification performance of the system after the transformation are better than before the transformation, which once again proves that the distribution of carbon sources in the system sewage has been optimized after the transformation. In addition, the denitrification performance of high MLSS is better than that of low MLSS conditions. This is because under the same aeration volume conditions, the residual DO at the MBBR effluent under high MLSS conditions is less than that under low MLSS conditions, resulting in the DO brought into the anoxic zone through internal recirculation being less than that under low MLSS conditions, affecting the denitrification capacity of the anoxic zone. Moreover, under low MLSS conditions, it is necessary to increase aeration to ensure that the effluent ammonia nitrogen meets the standards, which further aggravates the impact of DO on the function of the anoxic zone. Therefore, under winter water temperature conditions, high MLSS conditions should be used, about 5500mg / L~6000mg / L.

[0040] like Figure 5 As shown in c and 5d, the water quality data along the system with different internal recirculation ratios are compared. The total nitrogen concentration of the effluent from the secondary sedimentation tank is 7.0 mg·L -1 , 6.3mg·L -1 , 8.3 mg·L -1 and 6.5 mg·L -1 ; Nitrate nitrogen concentration was 6.4 mg·L -1 , 6.3mg·L -1 , 7.6mg·L -1 and 5.7 mg·L -1The denitrification capacity and denitrification performance of the system after the transformation were better than those before the transformation, both under high and low internal reflux ratio conditions. This shows that even if the internal reflux ratio is increased, the carbon reduction method of the present invention effectively avoids the impact of the denitrification functional area on the DO of the reflux nitrification liquid, and changes the distribution of carbon sources in the system wastewater. In addition, the denitrification performance of the system before the transformation decreased with the increase of the internal reflux ratio, while the system after the transformation was not greatly affected. After the transformation, the total nitrogen in the effluent did not decrease with the increase of the internal reflux ratio.

[0041] like Figure 5 As shown in e and 5f, the water quality data along the system under different DO conditions are compared. The ammonia nitrogen concentration of the secondary sedimentation tank effluent is 0.80 mg·L -1 , 0.36mg·L -1 , 0.37mg·L -1 and 0.41 mg·L -1 ; Total nitrogen concentration was 6.7 mg·L -1 , 5.7mg·L -1 , 11.1 mg·L -1 and 9.6 mg·L -1 . It shows that when the system DO increases, its nitrification performance improves, but DO inhibits the denitrification process, resulting in an increase in the total nitrogen concentration in the effluent. The modified system still has strong nitrification performance under low dissolved oxygen conditions because the energy-saving and carbon reduction strategy of the present invention changes the spatial distribution of carbon sources in the system inlet water, and more carbon sources are used by denitrifying bacteria in the anoxic zone. At this time, the amount of organic matter entering the aerobic zone is reduced, resulting in an increase in the relative abundance of nitrifying bacteria in the aerobic zone during long-term operation, thereby enhancing the nitrification performance. In addition, even under high DO conditions, the denitrification performance of the modified system is better than before the modification, indicating that the modification can effectively reduce the oxidation of organic matter by aerobic respiration of heterotrophic microorganisms. On the other hand, if the aeration intensity is further increased, the total nitrogen in the modified system may still exceed the standard. In addition, for urban sewage, DO has almost no effect on the COD removal performance.

[0042] Figure 6 It reflects the system operation status of continuous monitoring for 10 hours during the renovation and commissioning period. The monitoring items are inlet flow, inlet and outlet COD concentration, inlet and outlet nitrogen concentration, dissolved oxygen concentration and carbon source dosage. Figure 6 As shown, the sludge concentration in the system on the day of the test was 5500 mg·L -1 The influent COD / TN was 6.52. After 10 hours of continuous monitoring, the MLSS concentrations of the control group and the modified group were almost the same. The DO of the biochemical pool effluent was between 0.51 and 3.34 mg·L -1 The carbon source dosage of the control group increased the COD of the sewage by 85.53 mg·L -1 The modified group only increased COD by 3.24 mg·L-1 After the transformation, the system almost does not need to add carbon source. The denitrification sludge load of the transformation group and the control group were 0.008286kg N / kg MLSS·d -1 and 0.008280kgN / kg MLSS·d -1 The results are almost the same. Even under the condition of such a huge difference in carbon source dosage, the denitrification performance of the modified group is still better than that of the control group, which proves that the modification has clarified the role of each functional area and enhanced the system's utilization of carbon sources in sewage.

[0043] In summary, the direct economic benefits and carbon reduction benefits brought about by the above-mentioned sewage treatment plant renovation are calculated. After the renovation, the denitrification performance is improved by 7.5%, and the specific energy consumption of the sewage treatment plant is reduced by 13.0% (0.54kWh·m -3 Reduced to 0.47 kWh·m -3 ), and the transformation group does not need to add external carbon source, which greatly reduces the amount of carbon source added to the sewage treatment plant. The cost of composite carbon source is 1000 yuan·t -1 The electricity fee is 0.55 yuan per kWh. -1 The invention has saved the sewage treatment plant more than 1.5 million yuan per year and reduced carbon emissions by 795.04t CO2·a under the same influent water quality and quantity. -1 (Only indirect carbon emissions from electricity consumption are calculated).

[0044] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. An oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction tank, characterized by: The reaction tank includes an anaerobic zone, a first anoxic zone, a first aerobic zone, a second aerobic zone and a second anoxic zone; The water outlet of the anaerobic zone is connected to the water inlet of the first anoxic zone through a first water hole, the water outlet of the first anoxic zone is connected to the water inlet of the first aerobic zone through a second water hole, the water outlet of the first aerobic zone is connected to the second aerobic zone through an overflow weir, and the second aerobic zone and the second anoxic zone are connected end to end to form a circulating flow channel; The first aerobic zone is provided with MBBR filler, and the outlet end of the first aerobic zone is provided with a nitrification liquid reflux pump for returning the nitrification liquid from the first aerobic zone to the first anoxic zone; Aeration devices are respectively provided in the first aerobic zone and the second aerobic zone; The first anoxic zone and the second anoxic zone are respectively provided with a carbon source adding device.

2. The oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool according to claim 1 is characterized in that: A pre-denitrification zone is also provided before the anaerobic zone.

3. The oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool according to claim 1 is characterized in that: A flow propeller is provided at the end where the second aerobic zone and the second anoxic zone meet.

4. The oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction pool according to claim 1 is characterized in that: The anaerobic zone, the first anoxic zone and the first aerobic zone are respectively provided with corridor partition walls to separate the anaerobic zone, the first anoxic zone and the first aerobic zone into two zones connected end to end, and a flow pusher is provided at the end where the two zones are connected end to end.

5. A sewage treatment method based on the oxidation ditch type energy-saving, carbon-reducing and high-efficiency denitrification reaction tank according to any one of claims 1 to 4, characterized in that: The sewage flows through the anaerobic zone, the first anoxic zone, the first aerobic zone, the second aerobic zone and the second anoxic zone in sequence for treatment. During the treatment process, part of the nitrification liquid in the first aerobic zone flows back to the first anoxic zone, and the return ratio is 150% to 250%. When the C / N balance of the influent is unbalanced, a carbon source is added to the first anoxic zone and the second anoxic zone.

6. The sewage treatment method according to claim 5, wherein: The activated sludge is returned to the pre-denitrification zone with a return ratio of 70% to 100%.

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