Method of efficient denitrification and rapid and long-term sludge expansion control in urban waste water active sludge process

Abstract

To provide a method of efficient denitrification and rapid and long-term sludge expansion control in urban waste water active sludge process to realize an efficient use of dissolved oxygen and efficient removal of total nitrogen from urban waste water and to improve sludge settleability quickly in a driving condition of a low dissolved oxygen.SOLUTION: In an urban waste water continuous flow active sludge process comprising a continuous flow oxygen-free / aerobic active sludge reactor 2 and a secondary precipitation pond 3, active sludge in expansion state is inoculated, influent is simulation urban waste water, an oxygen-free partition part and an aerobic partition part are provided in a reactor, dissolved oxygen in the aerobic partition part is 0-0.8 mg / L, and aeration energy consumption is saved by improving travel speed of oxygen. A sludge in the secondary precipitation pond is refluxed to an influent port by an external reflux pump, a nitrification liquid in an aerobic section is refluxed to an oxygen-free section by using an inner reflux pump 5, diatomaceous earth heavy medium and a polyferric sulfate flocculant are added to a reactor, and sludge expansion is immediately controlled in a driving condition of low dissolved oxygen.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and relates to a method for efficient denitrification and rapid and long-term sludge bulking control in the urban sewage activated sludge process.

Background Art

[0002] For the biological denitrification of municipal domestic sewage, an activated sludge process is generally adopted. Under aerobic conditions, nitrifying bacteria use oxygen to oxidize ammonia nitrogen to nitrate nitrogen, and under anoxic conditions, denitrifying bacteria use a carbon source to reduce nitrates and nitrites to nitrogen. Under low dissolved oxygen conditions, the activated sludge process has the advantages of saving aeration energy consumption and high denitrification efficiency. Compared with the operating conditions of high dissolved oxygen, the operating conditions of low dissolved oxygen have a higher oxygen transfer rate and a higher energy-saving effect. Under the operating conditions of low dissolved oxygen, in the aerobic zone, relatively good simultaneous nitrification and denitrification can be achieved, and the denitrification effect of the entire system can be improved. However, under the operating conditions of low dissolved oxygen and high load, the activated sludge system is prone to the phenomenon of sludge bulking. When the SVI value of the activated sludge (the volume occupied by 1 g of dry sludge, mL / g) exceeds 150 mL / g, it indicates that the activated sludge is about to be in an expanded state or is already in an expanded state, the sedimentation performance of the activated sludge deteriorates, and it will be lost together with the effluent of the secondary sedimentation tank. Severe sludge bulking may cause the collapse of the entire sewage treatment system.

[0003] In recent years, methods for rapidly controlling activated sludge bulking by adding diatomaceous earth heavy media have been reported. Diatomaceous earth has a huge specific surface area, high porosity, and high adsorption capacity for activated sludge. Activated sludge adsorbs on the surface of diatomaceous earth, and the sedimentation performance is effectively improved. The addition of diatomaceous earth rapidly improves the sedimentation performance of sludge. However, in long-term experiments, the sedimentation performance of sludge gradually deteriorates. The reason is that the dielectric constant of water is much larger than that of diatomaceous earth, so negative charges are formed on the surface of diatomaceous earth, and electrostatic repulsive forces are formed between diatomaceous earth particles, which may inhibit the aggregation of sludge. According to research, adding polyaluminum chloride to activated sludge can neutralize the negative charges in the sludge, enhance the aggregation ability of the sludge, and improve the sedimentation performance of the sludge. However, when adding polyaluminum chloride, it takes two weeks to obtain the effect of controlling sludge bulking. Ferric polysulfate is a phosphorus removal chemical commonly used in sewage treatment, which has characteristics such as high efficiency, low dosage, and non-toxicity. Currently, there are few studies on the rapid control strategy of sludge bulking in continuous flow reactors, and it only has a short-term improvement effect on the sedimentation performance of sludge.

Summary of the Invention

[0004] The present invention can achieve energy conservation and efficient denitrification in the urban sewage activated sludge process under low dissolved oxygen operating conditions, rapidly control the sludge bulking of activated sludge, improve the removal effects of ammonia nitrogen and total nitrogen, and maintain good sludge sedimentation performance in the long term. The present invention relates to a method for efficient denitrification and rapid and long-term control of sludge bulking in the urban sewage activated sludge process, which has the following steps.

[0005] (1) Adopt an urban sewage continuous flow activated sludge process composed of a continuous flow activated sludge reactor and a secondary sedimentation tank. The effective volume of the continuous flow activated sludge reactor is 54 L. The reactor consists of six partition parts, and the volume of each partition part is 9 L. The sludge is mixed by a mechanical stirrer, and the rotation speed of the stirring blade is set to 200 r / min. The effective volume of the secondary sedimentation tank is 22 L.

[0006] (2) The sludge was activated sludge in an expanded state in the laboratory. The inoculation volume was 20 L, the sludge concentration was 14,000 mg / L, and the sludge dilution sludge volume index was 170 - 190 mL / g.

[0007] (3) The influent of the reactor was simulated municipal domestic sewage. The concentration of influent ammonia nitrogen was 50 - 70 mg / L, the concentration of nitrate nitrogen was less than 1 mg / L, the concentration of nitrite nitrogen was less than 1 mg / L, and the concentration of COD was 160 - 250 mg / L. The specific influent components were NH 4 + -N (NH 4 Cl): 50 - 70 mg / L, COD (NaCH 3 COO): 160 - 250 mg / L, KH 2 PO 4 : 30 mg / L, CaCl 2 : 90 mg / L, MgSO 4 ·7H 2 O: 140 mg / L, trace elements: 1 mL / L, and the concentration of the trace element components was Na 2 -EDTA: 50 g / L, FeSO 4 ·7H 2 O: 5 g / L, CoSO 4 ·5H 2 O: 1.9 g / L, MnCl 2 ·4H 2 O: 5.1 g / L, CuSO 4 ·5H 2 O: 1.6 g / L, ZnSO 4 ·7H 2 O: 5 g / L, NaMoO 4 ·2H 2 O: 1.1 g / L.

[0008] (4) The temperature in the reactor was controlled at 25°C. The first partition section, the second partition section, and the third partition section of the reactor were anaerobic ponds without aeration, while the fourth partition section, the fifth partition section, and the sixth partition section of the reactor were aerobic ponds with aeration by an aeration pump. The aeration rate was 2 L / min, and the dissolved oxygen in the aerobic partition section was 0 - 0.8 mg / L. The return sludge from the secondary sedimentation tank was externally refluxed to the inlet by a peristaltic pump, and the flow rate ratio of the externally refluxed sludge to the influent water was set to 1. The nitrified liquid in the sixth partition section was internally refluxed to the first partition section by a peristaltic pump, and the flow rate ratio of the internally refluxed sludge to the influent water was set to 2. The hydraulic retention time of the reactor was controlled at 6 h.

[0009] (5) Rapid control measures for sludge bulking: Diatomaceous earth with a particle size of 200 mesh (74 μm) was added to the reactor at one time to make the concentration of diatomaceous earth in the reactor reach 4000 mg / L. Next, a concentrated ferric polysulfate solution was added to the sixth partition section of the reactor every day, and the concentration of ferric polysulfate in the entire continuous flow reactor was made 125.0 mg / L by external reflux.

[0010] (6) Definition of the dilution volume index of sludge: The sludge sedimentation ratio of activated sludge is closely related to the sludge concentration. To facilitate the comparison of changes in sludge sedimentation performance, the sludge mixed liquor in the reactor was taken and tap water was added to control the sludge concentration at 4000 mg / L. After standing for 30 min, the diluted sludge sedimentation ratio of the activated sludge was obtained. The ratio of the diluted sludge sedimentation ratio to the sludge concentration was defined as the diluted sludge volume index.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0012] 1. The reactor device is shown in Figure 1.

[0013] 2. The operation procedure for adopting the above method is as follows. (1) Experimental device: As shown in Figure 1, the municipal sewage treatment process consists of a continuous flow activated sludge reactor and a secondary sedimentation tank. The effective volume of the continuous flow activated sludge reactor is 54 L. The reactor consists of six partition parts, and the volume of each partition part is 9 L. The sludge is mixed by a mechanical stirrer, and the stirring blade rotation speed is set at 200 r / min. The effective volume of the secondary sedimentation tank is 22 L.

[0014] (2) The seed sludge is activated sludge in an expanded state in the laboratory. The inoculation volume is 20 L, and the sludge concentration is 14,000 mg / L.

[0015] (3) Inflow into the reactor: The inflow into the reactor is simulated municipal domestic sewage. The concentration of influent ammonia nitrogen is 50 - 70 mg / L, the concentration of nitrate nitrogen is less than 1 mg / L, the concentration of nitrite nitrogen is less than 1 mg / L, and the concentration of COD is 160 - 250 mg / L. The specific inflow components are NH 4 + -N (NH 4 Cl): 50 - 70 mg / L, COD (NaCH 3 COO): 160 - 250 mg / L, KH 2 PO 4 : 30 mg / L, CaCl 2 : 90 mg / L, MgSO 4 ·7H 2 O: 140 mg / L, trace elements 1 mL / L. The concentration of the trace element components is Na 2 -EDTA: 50 g / L, FeSO 4 ·7H 2 O: 5 g / L, CoSO 4 ·5H 2 O: 1.9 g / L, MnCl 2 ·4H 2 O: 5.1 g / L, CuSO 4 ·5H 2 O: 1.6 g / L, ZnSO 4 ·7H 2 O: 5 g / L, NaMoO4 ·2H 2 O is 1.1 g / L.

[0016] (4) Reactor operating parameters: The temperature inside the reactor was maintained at 25°C. The first, second, and third partition sections of the reactor were anaerobic ponds and not aerated, while the fourth, fifth, and sixth partition sections of the reactor were aerobic ponds and aerated by an aeration pump. The aeration rate was 2 L / min, and the dissolved oxygen in the aerobic partition section was 0 - 0.8 mg / L. In the latter three aerated partition sections, the activated sludge oxidized ammonia nitrogen to nitrate nitrogen and nitrite nitrogen. Due to the low dissolved oxygen concentration, the activated sludge could also perform simultaneous nitrification and denitrification. The return sludge from the secondary sedimentation tank was externally returned to the inlet by a peristaltic pump, and the flow rate ratio of the externally returned sludge to the influent water was set to 1. The nitrified liquid from the sixth partition section was internally returned to the first partition section by a peristaltic pump to remove nitrate nitrogen and nitrite nitrogen in the nitrified liquid with the carbon source in the influent water. The flow rate ratio of the internally returned sludge to the influent water was set to 2, and the hydraulic retention time of the reactor was maintained at 6 h. In the first three anaerobic partition sections, the activated sludge could perform denitrification using nitrate nitrogen (nitrate nitrogen and nitrite nitrogen) in the internal return and the carbon source in the influent water.

[0017] (5) Definition of the dilution volume index of sludge: The sludge sedimentation ratio of activated sludge is closely related to the sludge concentration. To facilitate the comparison of changes in sludge sedimentation performance, the sludge mixed liquor in the reactor was taken and tap water was added to control the sludge concentration at 4000 mg / L. After standing for 30 min, the diluted sludge sedimentation ratio of the activated sludge was obtained. The ratio value of the diluted sludge sedimentation ratio to the sludge concentration was defined as the dilution volume index of the sludge.

[0018] (6) Reactor operating conditions: The operation of the reactor was divided into two stages. Stage 1 (1 - 10 d) was the activated sludge expansion stage. The activated sludge was in an expanded state, and the dilution volume index of the sludge was 170 - 190 mL / g. From the 1st day to the 10th day, the sludge concentration in the reactor was 3500 - 4600 mg / L, the effluent ammonia nitrogen concentration was 6.1 - 9.7 mg / L, the ammonia nitrogen removal rate was 85.2% - 90.0%, and the total nitrogen removal rate was 74.0% - 77.6%.

[0019] Stage 2 (11 - 34d) is the rapid control stage of sludge bulking, and the sedimentation performance was significantly improved. On the 11th day, diatomaceous earth with a particle size of 200 mesh (74 μm) was added to the reactor at one time, and the concentration of diatomaceous earth in the reactor was set to 4000 mg / L. Next, a concentrated ferric polysulfate solution was added to the 6th partition of the reactor every day, and the concentration of ferric polysulfate in the entire continuous flow reactor was set to 125.0 mg / L by external reflux. On the 11th day, the diluted sludge volume index of the activated sludge decreased to 80.0 mg / L, and the sludge concentration in the reactor increased to 5600 mg / L. However, from the 11th day to the 34th day, the diluted sludge volume index of the activated sludge was stably maintained below 80 mL / g. From the 21st day to the 34th day, the sludge concentration in the reactor decreased to 5900 - 8240 mg / L, the effluent ammonia nitrogen concentration decreased to 0.1 - 2.1 mg / L, the ammonia nitrogen removal rate was 97.0% - 99.1%, and the total nitrogen removal rate was 74.4% - 82.4%. Compared with Stage 1, in Stage 2, the sedimentation performance of the sludge decreased significantly, was stably maintained, the effluent ammonia nitrogen concentration decreased significantly, and the total nitrogen removal rate increased.

[0020] The composite addition strategy of diatomaceous earth and ferric polysulfate proposed in this application can rapidly control sludge bulking and maintain good sludge sedimentation performance in the long term. Its internal mechanism is as follows. After adding diatomaceous earth, the expanded activated sludge adsorbs on the diatomaceous earth to form aggregates with high density, and the sludge sedimentation performance can be rapidly improved. In long-term experiments, the surfaces of the sludge and diatomaceous earth form negative charges, forming an electrostatic repulsive force, which inhibits the aggregation of the sludge. Ferric polysulfate is added to the reactor every day. Ferric polysulfate generates iron ions with positive charges, and these positive charge ions neutralize the electricity with the sludge and diatomaceous earth whose surfaces have negative charges to "destabilize". Furthermore, the polymerized ferric salt forms a large number of polynuclear complexes and iron hydroxide colloids, causing the activated sludge and diatomaceous earth to collide and adsorb with each other under the action of forces such as van der Waals force, colloid attraction, and Brownian motion, destroying the stable suspension state of the activated sludge, gradually aggregating into large particles, and forming dense aggregates, which helps to improve the sludge sedimentation performance over a long period.

[0021] (7) Based on the above principle, it is possible to make other forms of changes and variations. These changes and modifications are within the scope of the present invention.

Description of Reference Numerals

[0022] 1 Inlet pump, 2 Continuous flow activated sludge reactor, 3 Secondary sedimentation tank, 4 Internal reflux pump, 5 External reflux pump, 6 Aeration pump, 7 Heating rod, 8 Mechanical stirrer, 9 Effluent from the secondary sedimentation tank

Claims

1. 1) A continuous-flow activated sludge process for urban wastewater is adopted, which is composed of a continuous-flow activated sludge reactor and a secondary sedimentation tank. The effective volume of the continuous-flow activated sludge reactor is 54 L, the reactor is composed of six partitions, each of which has a volume of 9 L. The sludge is mixed by a mechanical stirrer, and the rotation speed of the stirring blade is 200 r / min. 2) The seed sludge is activated sludge in an expanded state in the laboratory, the inoculation volume is 20 L, the sludge concentration is 14,000 mg / L, and the diluted sludge volume index of the sludge is 170-190 mL / g; 3) The inlet water to the reactor is simulated urban wastewater, with the inlet ammonia nitrogen concentration of 50-70 mg / L, the nitrate nitrogen concentration of less than 1 mg / L, the nitrite nitrogen concentration of less than 1 mg / L, and the COD concentration of 160-250 mg / L; 4) The temperature inside the reactor is kept at 25°C; the first, second and third partitions of the reactor are anoxic ponds and are not aerated; the fourth, fifth and sixth partitions of the reactor are aerobic ponds and are aerated by an aeration pump; the aeration rate is 2L / min; the dissolved oxygen in the aerobic partitions is 0-0.8mg / L; the reflux sludge of the secondary settling tank is refluxed to the water inlet by a peristaltic pump; the flow rate ratio of the externally refluxed sludge to the inlet water is 1; the nitrification liquid in the sixth partition is refluxed inside the first partition by a peristaltic pump; the flow rate ratio of the internally refluxed sludge to the inlet water is 2; and the hydraulic retention time of the reactor is kept at 6h; 5) Rapid control measures for sludge expansion: adding diatomaceous earth with a particle size of 200 mesh (74 μm) to the reactor at one time to make the concentration of diatomaceous earth in the reactor 4000 mg / L; adding concentrated polyferric sulfate solution to the sixth partition of the reactor every day to make the concentration of polyferric sulfate in the entire continuous flow reactor 125.0 mg / L by external reflux; Includes A method for efficient denitrification and rapid and long-term control of sludge expansion in a municipal wastewater activated sludge process.

2. The inlet water is artificially distributed, and the concentration of the components is NH ４ ＋ -N(NH ４ Cl): 50-70mg / L, COD (NaCH ３ COO): 160-250mg / L, KH ２ P.O. ４ :30mg / L, CaCl ２ :90mg / L, MgSO ４ ・7H ２ O: 140 mg / L, trace elements: 1 mL / L. The concentrations of trace elements are: Na ２ -EDTA: 50g / L, FeSO ４ ・7H ２ O: 5g / L, CoSO ４ ・5H ２ O: 1.9g / L, MnCl ２ ・4H ２ O: 5.1g / L, CuSO ４ ・5H ２ O: 1.6g / L, ZnSO ４ ・7H ２ O: 5g / L, NaMoO ４ ・2H ２ O: 1.1 g / L 2. The method for efficient denitrification and rapid and long-term sludge expansion control in a municipal wastewater activated sludge process according to claim 1.

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