A2O sewage treatment system and process for sewage alkalinization carbon emission reduction

Abstract

The application discloses an A2O sewage treatment system and process for carbon emission reduction of sewage alkalization, and the system comprises sequentially connected anaerobic fermentation tanks, anoxic fermentation tanks, aerobic aeration tanks and sedimentation tanks, and the gas outlet of the anaerobic fermentation tank is connected with a gas production and purification column; magnesium-iron olivine is added into the aerobic aeration tank; the process uses alkaline minerals to purify the methane gas produced by the anaerobic tank in the anaerobic-anoxic stage, and at the same time, olivine is added in the aerobic process stage to improve the alkalinity of the treated sewage, and the regenerated water after alkalization is discharged into the sea to realize seawater alkalization and carbon sink increase, and offset part of the carbon emission in the sewage treatment process.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of sewage treatment and seawater alkalization carbon sink increase, and particularly relates to an A2O sewage treatment process for sewage alkalization carbon emission reduction. BACKGROUND

[0002] The greenhouse gas emission of a sewage treatment plant is related to the type of sewage treatment process. The A2O process is a short name of the "anaerobic-anoxic-aerobic" biological denitrification and phosphorus removal process. The A2O process is a popular urban sewage treatment method, and the total hydraulic retention time is shorter than that of other processes, and the sludge loading rate is large, and the process is operated under anaerobic, anoxic and aerobic conditions. Although the A2O process has high sewage treatment efficiency, the greenhouse gas emission is also large. Research results show that the A2O process produces about 0.39 kg of carbon dioxide equivalent greenhouse gas emission per 1 m 3 The sewage produces about 0.39 kg of carbon dioxide equivalent greenhouse gas emission. The greenhouse gases produced in the A2O sewage treatment process mainly include carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). CO2 mainly comes from microbial respiratory activity, and the CO2 emission in the aerobic tank is the highest, N2O comes from denitrification and nitrification stages, and CH4 mainly comes from anaerobic digestion.

[0003] The addition of alkaline minerals in the sewage treatment process can effectively reduce greenhouse gas emission and help achieve the carbon neutralization goal, that is, the sewage alkalization carbon sink technology. The sewage alkalization carbon sink technology is to increase the alkalinity of sewage by human intervention, increase the solubility of CO2 in the sewage system of the sewage treatment plant, and thus increase the carbon sink of sewage. At present, there are mainly two technical ways for A2O to add alkaline minerals to increase the carbon sink. The first one occurs in the anaerobic stage of the A2O process, that is, by adding alkaline minerals in the process of anaerobic digestion of activated sludge to in-situ store CO2 and increase CH4 production to realize energy recovery. The second one is to connect an alkalization tank or tank at the effluent outlet of the A2O process to increase the carbon sink of sewage. The alkalized sewage discharged into the sea will further increase the carbon sink in the offshore sea area. The first strategy can significantly increase CH4 production but is not conducive to the dissolution of alkaline minerals, the sewage alkalinity is slow to increase, and the carbon sink effect is not obvious. The second strategy does not change the existing sewage treatment process but has high energy consumption and low economic benefit. SUMMARY

[0004] The application is proposed to solve the problems in the prior art, and aims to provide an A2O sewage treatment system and process for sewage alkalization carbon emission reduction.

[0005] The application is implemented by the following technical scheme:

[0006] An A2O sewage treatment process for sewage alkalization carbon emission reduction comprises the following steps:

[0007] (i) Wastewater is discharged into an anaerobic fermentation tank and discharged into an anoxic fermentation tank after 0.5 to 2 days of anaerobic fermentation.

[0008] (ii) After 0.5 to 2 days of anaerobic fermentation, the mixture is discharged into the aerobic aeration tank;

[0009] (iii) Add magnesium iron olivine to the aerobic aeration tank, and after the wastewater is aerated and treated aerobically for 0.5 to 5 days, it is discharged into the sedimentation tank for separation.

[0010] (iv) The liquid separated from the sedimentation tank is directly discharged into the sea, and the undissolved olivine is returned to the aerobic aeration tank.

[0011] The retention time in each treatment tank is determined by the pollution level of the target wastewater.

[0012] In the above technical solution, the magnesium-iron olivine activated sludge separated in step (iv) is returned to the anaerobic fermenter (1), and the remaining sludge enters the sludge treatment and relief process.

[0013] In the above technical solution, the particle size of the magnesium iron olivine in step (ii) is 10μm to 2000μm.

[0014] In the above technical solution, the mass ratio of magnesium iron olivine in step (ii) is determined according to the target alkalinity of the effluent.

[0015] In the above technical solution, the target alkalinity of the effluent is calculated by subtracting the alkalinity of the unalkalized wastewater from the alkalinity of the dischargeable wastewater, which is determined based on the water temperature, salinity, and pH value of the target sea area.

[0016] In the above technical solution, the formula for calculating the mass ratio of the magnesium-iron olivine is as follows:

[0017]

[0018] Where: k is the percentage of olivine added to the aerobic aeration tank relative to the mass of wastewater treated, %; d0 is the olivine particle size, in μm;

[0019] TA0 is the target alkalinity of the effluent, expressed in mmol / L;

[0020] t represents the residence time in the aerobic aeration tank during the wastewater treatment process, expressed in days.

[0021] In the above technical solution, a portion of the suspended liquid in the anoxic fermenter is recycled to the anaerobic fermenter; a portion of the suspended liquid in the aerobic aeration tank is recycled to the anoxic fermenter. The proportion of the recycled suspended liquid to the total suspended liquid in the anoxic fermenter, i.e., the recycling ratio, is determined by the wastewater treatment target, and it is also possible to choose not to recycle; the recycling ratio in the aerobic aeration tank is the same.

[0022] An A2O wastewater treatment system for alkalization and carbon reduction includes an anaerobic fermenter, an anoxic fermenter, an aerobic aeration tank, and a sedimentation tank connected in sequence, with the gas outlet of the anaerobic fermenter connected to a gas purification column.

[0023] In the above technical solution, a suspension mixture return pipeline is provided between the anoxic fermenter and the anaerobic fermenter, as well as between the aerobic aeration tank and the anoxic fermenter; magnesium iron olivine is added to the aerobic aeration tank; and the sedimentation tank is a sedimentation machine.

[0024] In the above technical solution, the gas production and purification column is filled with alkaline mineral filler, which is any one or more of limestone, olivine, montmorillonite, attapulgite, or wollastonite; the particle size of the alkaline mineral filler is 1mm to 20mm; and the volume of the gas production and purification column is one-half to one-twentieth of the daily gas production of the anaerobic fermenter.

[0025] The beneficial effects of this invention are:

[0026] This invention provides a novel technology for increasing the alkalinity of wastewater in an A2O aerobic tank using alkaline minerals, achieving wastewater alkalization, carbon sequestration, and emission reduction. The design involves the partial return of suspended liquid from the anoxic fermenter to the anaerobic fermenter, and the partial return of suspended liquid from the aerobic aeration tank to the anoxic fermenter. This allows for the purification of gas in the anaerobic tank by alkaline minerals during the anaerobic-anoxic stage, the addition of olivine in the aerobic process to increase the alkalinity of the treated wastewater, and the discharge of the alkalized reclaimed water into the sea, achieving seawater alkalization and carbon sequestration, thus offsetting some of the carbon emissions during wastewater treatment. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the A2O wastewater treatment system for carbon reduction through wastewater alkalization according to the present invention.

[0028] in:

[0029] 1. Anaerobic fermenter; 2. Anaerobic fermenter; 3. Aerobic aeration tank; 4. Sedimentation tank; 5. Gas purification column.

[0030] For those skilled in the art, other related figures can be obtained from the above figures without any creative effort. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] An A2O wastewater treatment system for alkalization and carbon reduction includes an anaerobic fermenter 1, an anoxic fermenter 2, an aerobic aeration tank 3, and a sedimentation tank 4 connected in sequence. The gas outlet of the anaerobic fermenter 1 is connected to a gas purification column 5.

[0034] Suspended mixed liquor return pipelines are provided between the anoxic fermentation tank 2 and the anaerobic fermentation tank 1, as well as between the aerobic aeration tank 3 and the anoxic fermentation tank 2; that is, part of the sewage-sludge-olivine suspended mixed liquor of the anoxic fermentation tank 2 is returned to the anaerobic fermentation tank 1; part of the sewage-sludge-olivine suspended mixed liquor of the aerobic aeration tank 3 is returned to the anaerobic fermentation tank 1 and then returned to the anoxic fermentation tank 2.

[0035] Magnesium iron olivine is added to the aerobic aeration tank 3. During the aerobic treatment of sewage aeration, some of the olivine dissolves, alkalizes the sewage, fixes and seals the carbon dioxide in the water, and the remaining part flows into the sedimentation machine 4 with the sewage-sludge mixture.

[0036] The settling tank 4 is a settling machine, and a magnesium-iron olivine activated sludge return pipeline is installed between the settling tank 4 and the anaerobic fermentation tank 1.

[0037] The settling tank 4 uses mechanical threshing. The liquid is wastewater that has undergone alkalization and biological treatment and is discharged directly. Since the density difference between olivine and sludge is about 3 times, the solids are further separated by density difference. The solid waste with more olivine content and higher density is returned to the aeration tank, and the solid waste with more sludge content and relatively lower density is returned to the anaerobic tank. However, only a portion of the solid waste can be used for return, and the remainder enters the sludge digestion treatment stage. The amount of sludge returned is determined by the wastewater treatment target, and it is also possible not to return it.

[0038] Suspended mixed liquid return pipelines are provided between the anoxic fermentation tank 2 and the anaerobic fermentation tank 1, as well as between the aerobic aeration tank 3 and the anoxic fermentation tank 2.

[0039] The gas purification column 5 is filled with alkaline mineral filler, which is any one or more of limestone, olivine, montmorillonite, attapulgite, or wollastonite; the particle size of the alkaline mineral filler is 1 mm to 20 mm.

[0040] The volume of the gas-producing purification column 5 is 1 / 2 to 1 / 20 of the daily gas production of the anaerobic fermenter 1.

[0041] The A2O wastewater treatment system of this application enhances the degradation and purification of pollutants in the incoming wastewater by setting up return pipelines between the anoxic fermenter 2 and the anaerobic fermenter 1, and between the aerobic aeration tank 3 and the anoxic fermenter 2. At the same time, olivine is introduced into the anaerobic and anoxic fermenters to enhance the alkalization intensity of the wastewater. The presence of olivine in the fermenters purifies the purity of the methane produced by the fermenters. The gas purification column 5 with alkaline mineral packing further purifies the gas produced by the fermenters, thereby recovering methane.

[0042] Example 2

[0043] An A2O wastewater treatment process for carbon reduction through alkalization includes the following steps:

[0044] (i) Wastewater is discharged into an anaerobic fermentation tank, and after anaerobic fermentation for 0.5 to 2 days, it is discharged into an anoxic fermentation tank.

[0045] (ii) After 0.5 to 2 days of anaerobic fermentation, the mixture is discharged into an aerobic aeration tank;

[0046] (iii) Add magnesium iron olivine to the aerobic aeration tank, and after the wastewater is aerated and treated aerobically for 0.5 to 5 days, it is discharged into the sedimentation tank for separation.

[0047] (iv) The liquid separated from the settling tank is directly discharged into the sea, the undissolved olivine is returned to the aerobic aeration tank, the activated sludge containing magnesium iron olivine is returned to the anaerobic fermentation tank, and the remaining sludge is sent to the sludge treatment plant for mitigation.

[0048] In step (ii), the particle size of the ferrofer olivine is 10μm to 2000μm, and the mass ratio of ferrofer olivine is determined according to the target alkalinity of the effluent.

[0049] The target alkalinity of the effluent is calculated by determining the alkalinity of the dischargeable wastewater based on the water temperature, salinity, and pH value of the target sea area, and then subtracting the alkalinity of the un-alkalized reclaimed water.

[0050] The formula for calculating the mass ratio of the magnesium-iron olivine is as follows:

[0051]

[0052] Where: k is the percentage of olivine added to the aerobic aeration tank relative to the mass of wastewater treated, %; d0 is the olivine particle size, in μm;

[0053] TA0 is the target alkalinity of the effluent, expressed in mmol / L;

[0054] t represents the residence time in the aerobic aeration tank during the wastewater treatment process, expressed in days.

[0055] This embodiment of the treatment process is applied to scenarios where treated reclaimed water is discharged into the sea. It is an anaerobic-anoxic-aerobic (A2O) process that can reduce carbon emissions during wastewater treatment. During the aerobic treatment of wastewater aeration, some olivine dissolves, and the alkalized wastewater fixes and seals carbon dioxide in the water. The remaining part flows into a settling tank with the wastewater-sludge mixture. Through mechanical granulation in the settling tank, on the one hand, wastewater and sludge are separated, and the effluent after alkalization and biological treatment flows out. On the other hand, through density differences, undissolved olivine in the sludge is separated and returned to the aerobic aeration tank. Most of the sludge removed enters the sludge treatment process for mitigation, while a small portion is inoculated into the anaerobic fermenter. In the aerobic aeration tank, a portion of the wastewater-sludge-olivine suspension mixture is returned to the anoxic fermenter, and a portion of the mixture is also returned to the anaerobic fermenter. This enhances the degradation and purification of pollutants in the incoming wastewater, while simultaneously introducing olivine into both the anaerobic and anoxic fermenters, increasing the alkalization intensity of the wastewater. The presence of olivine in the fermenter also helps purify the methane produced by the fermenter. The gas purification column, filled with alkaline mineral packing, further purifies the gas produced by the fermenter, thereby recovering methane.

[0056] During the anaerobic-anoxic stage, alkaline minerals are used to purify the methane produced in the anaerobic tank. At the same time, olivine is added in the aerobic process stage to increase the alkalinity of the treated wastewater. The reclaimed water after alkalization is discharged into the sea to achieve seawater alkalization and carbon sequestration, thus offsetting part of the carbon emissions during the wastewater treatment process.

[0057] The fermenters for anaerobic and anoxic biological treatment contain magnesia-iron olivine refluxed from the aeration tank, while the gas outlet is connected to a purification column filled with alkaline minerals to adsorb and fix the carbon dioxide emitted from the fermenter.

[0058] This invention is a novel urban wastewater treatment process for increasing carbon sequestration in alkaline minerals, and it has been applied to increasing marine carbon sequestration in alkaline wastewater.

[0059] Application Example 1

[0060] This application example simulates the addition of olivine to an aerobic aeration tank in an A2O reactor, followed by limestone-filled purification columns. The study assesses the alkalization and absorption effect of wastewater in the aerobic aeration tank, as well as the purity of methane produced in the anaerobic digester. The specific process is as follows:

[0061] Using activated sludge from a wastewater treatment plant at a university in Shandong as the inoculum source, the following culture medium was prepared at a concentration of mg / L: (C6H 10 O5) n (175), C6H 12 O6(200), C 26 H 20N2O2S2(28), COH2)2(64), NH4Cl(150), KH2PO4(52.5), MgCl2·6H2O(150) and CaSO4·2H2O(50). The trace mineral solution contains (mg / L): MnCl2·4H2O(30), H3BO3(300), CoCl2·6H2O(10), CuCl2·2H2O(10), NiCl2·6H2O(10), ZnCl2(100) and FeSO4·7H2O(300). Mix them together and add 1 mL of trace mineral solution to each liter of wastewater to prepare synthetic wastewater.

[0062] The nearshore waters of the Yellow Sea, designated as the discharge area for biologically treated alkalized wastewater, have a salinity of 30, a pH of 8.0, and a summer water temperature of 25℃. Table 2 shows that the acceptable alkalinity for discharged wastewater is 5.8 mmol / L. The alkalinity of the untreated wastewater after biological treatment is 2.2 mmol / L. Therefore, the target alkalinity increase for the treated wastewater is 3.6 (=5.8-2.2) mmol / L. Using 30μm olivine, with a biological wastewater retention time of 5 days, the olivine feed rate, as per this invention, is 0.5% of the treated wastewater.

[0063] The changes in alkalinity and carbon dioxide emission reduction in the aerobic aeration tank after adding 0.5% magnesia-olivine are as follows:

[0064] Time Alkalinity of aerobic tank Carbon dioxide emission reduction 0 days 0.5 mmol / L sewage 0 mg / L sewage 1 day 2.8 mmol / L sewage 79 mg / L sewage 2 days 4.0 mmol / L sewage 111 mg / L sewage 3 days 4.6 mmol / L sewage 119 mg / L sewage 4 days 5.0 mmol / L sewage 128 mg / L sewage 5 days 5.9 mmol / L sewage 160 mg / L sewage

[0065] After 5 days of aeration treatment, the alkalinity test value of the discharged wastewater (5.9 mmol / L) was close to the theoretical value (5.8 mmol / L), and the carbon dioxide emission reduction (160 mg CO) was also significant. 2-eq L -1 The alkalinity of the treated wastewater increased by 3.6 mmol / L, which is consistent with the theoretical value (the target alkalinity increase for treated wastewater, 3.6 mmol / L).

[0066] Without adding magnesium ferrolithite to the anaerobic fermenter and without connecting an alkalizing mineral purification column to the gas outlet, the methane content in the gas produced by the fermenter was 74.5%. With olivine present in the treated wastewater, the methane content in the gas produced was 77.0%. When a limestone purification column was connected, with a column volume of one percent of the daily gas production and a limestone particle size of 2 mm, the methane content in the gas produced by the fermenter was 89.8%.

[0067] Application Example 2

[0068] The biological wastewater retention time was 3 days, and other conditions were the same as in Example 1. The olivine feed amount, as described in this invention, was 1% of the wastewater being treated. After adding 5% magnesian olivine to the aerobic aeration tank, the changes in alkalinity and carbon dioxide emission reduction in the aeration tank water were as follows:

[0069]

[0070]

[0071] After 3 days of aeration treatment, the alkalinity test value of the discharged wastewater (5.4 mmol / L) was close to the theoretical value (5.8 mmol / L), and the carbon dioxide emission reduction (155 mg CO) was also significant. 2-eq L -1 The alkalinity of the treated wastewater (i.e., the alkalinity of the treated wastewater increased by 3.5 mmol / L) is close to the theoretical value (the target alkalinity increase of the treated wastewater is 3.6 mmol / L), which can achieve the carbon emission reduction target of the A2O process.

[0072] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An A2O wastewater treatment process for alkalization and carbon reduction, characterized in that: Includes the following steps: (i) Wastewater is discharged into an anaerobic fermentation tank, and after anaerobic fermentation, it is discharged into an anoxic fermentation tank; (ii) After anaerobic fermentation, the contents are discharged into an aerobic aeration tank; (iii) Add magnesium iron olivine to the aerobic aeration tank, and after the wastewater is aerated and treated aerobically, it is discharged into the sedimentation tank for separation; (iv) The liquid separated from the sedimentation tank is directly discharged into the sea, and the undissolved olivine is returned to the aerobic aeration tank (3). The mass ratio of magnesium iron olivine in step (iii) is determined based on the target alkalinity of the effluent. The target alkalinity of the effluent is calculated by subtracting the alkalinity of the unalkalized reclaimed water from the alkalinity of the dischargeable wastewater, which is determined based on the water temperature, salinity, and pH value of the target sea area. The formula for calculating the mass ratio of the magnesium-iron olivine is as follows: In the formula: k is the percentage of olivine added to the aerobic aeration tank relative to the mass of wastewater being treated, %; d0 is the olivine grain size, in μm; TA0 is the target alkalinity of the effluent, expressed in mmol / L; t represents the residence time in the aerobic aeration tank during the wastewater treatment process, expressed in days.

2. The A2O wastewater treatment process for carbon reduction through alkalization of wastewater according to claim 1, characterized in that: The magnesium-iron olivine activated sludge separated in step (iv) is returned to the anaerobic fermenter (1), and the remaining sludge enters the sludge treatment process.

3. The A2O wastewater treatment process for carbon reduction through alkalization of wastewater according to claim 1, characterized in that: In step (iii), the particle size of the ferrofer olivine is 10 μm to 2000 μm.

4. The A2O wastewater treatment process for carbon reduction through alkalization of wastewater according to claim 1, characterized in that: In step (i), the anaerobic fermentation time in the anaerobic fermenter is 0.5 to 2 days; in step (ii), the anoxic fermentation time in the anoxic fermenter is 0.5 to 2 days; and in step (iii), the aerobic aeration treatment time of the wastewater in the aerobic aeration tank is 0.5 to 5 days.

5. An A2O wastewater treatment system for carbon reduction through alkalization of wastewater applied to any one of the A2O wastewater treatment processes described in claims 1 to 4, characterized in that: It includes an anaerobic fermenter (1), an anoxic fermenter (2), an aerobic aeration tank (3) and a sedimentation tank (4) connected in sequence, with the gas outlet of the anaerobic fermenter (1) connected to a gas purification column (5).

6. The A2O wastewater treatment system for carbon reduction through alkalization of wastewater according to claim 5, characterized in that: Suspended mixed liquid return pipelines are provided between the anoxic fermentation tank (2) and the anaerobic fermentation tank (1) and between the aerobic aeration tank (3) and the anoxic fermentation tank (2); magnesium iron olivine is added to the aerobic aeration tank (3); the sedimentation tank (4) is a sedimentation machine.

7. The A2O wastewater treatment system for carbon reduction through alkalization of wastewater according to claim 5, characterized in that: The gas-producing purification column (5) is filled with alkaline mineral filler, which is any one or more of limestone, olivine, montmorillonite, attapulgite or wollastonite; the particle size of the alkaline mineral filler is 1mm to 20mm; the volume of the gas-producing purification column (5) is one-half to one-twentieth of the daily gas production of the anaerobic fermenter (1).

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