CN113845218A

CN113845218A - Multistage AO sewage treatment system and process thereof

Info

Publication number: CN113845218A
Application number: CN202110976145.5A
Authority: CN
Inventors: 张伟; 吴卫君; 杨曹玲
Original assignee: Wuxi Huishan Environmental Water Co ltd
Current assignee: Wuxi Huishan Environmental Water Co ltd
Priority date: 2021-08-24
Filing date: 2021-08-24
Publication date: 2021-12-28

Abstract

The invention relates to the technical field of sewage treatment, in particular to a multi-stage AO sewage treatment system and a process thereof, which comprises a pre-anoxic tank, an anaerobic tank, an anoxic tank, an aerobic tank, an anoxic tank, a post-aerobic tank and a secondary sedimentation tank which are sequentially connected in series along the sewage flow treatment direction; a water inlet area is arranged at the front end of the pre-anoxic tank; a water outlet area is arranged at the rear end of the secondary sedimentation tank; in the running process, a multi-stage AO process is formed by the stage treatment of each sewage treatment tank, sewage is preferably pretreated by an anoxic pre-tank and then enters a first-stage sewage treatment unit and a second-stage sewage treatment unit to form an anoxic and aerobic alternate form, the multi-stage reaction is realized to achieve the effects of denitrification and dephosphorization, and finally, the high-quality effluent is obtained by the treatment of a secondary sedimentation tank, the reduction of sludge can be realized, so that the effluent can reach the discharge standard, and the comprehensive use cost is lower.

Description

Multistage AO sewage treatment system and process thereof

Technical Field

The invention relates to the technical field of sewage treatment, in particular to a multi-stage AO sewage treatment system and a process thereof.

Background

The problem of water environment pollution has serious influence on the development of economy in China, and simultaneously, harm and inconvenience are brought to the life of people, so that the government correspondingly improves the discharge standard of nitrogen and phosphorus in sewage, and new challenge and opportunity are brought to the water treatment industry. In the present day of the improvement of the sewage treatment standard, the water treatment world pays more attention to research and development of a new denitrification and dephosphorization treatment process and expects the effect of the new denitrification and dephosphorization treatment process in the aspect of engineering application. At present, the A2O (anaerobic-anoxic-aerobic method) process or the improved A2O process, the CASS process, the oxidation ditch process and the like are widely applied to sewage treatment plants.

In recent years, as a multistage AO process of sectional water inflow developed abroad to overcome the defects of the traditional nitrogen and phosphorus removal, data shows that Japan is one of the most extensive countries applying the multistage AO process in the world, according to statistics of Japan sewer service groups, the number of sewage plants adopting the multistage AO process of sectional water inflow built and built in Japan reaches more than 20 by 2004, and the total treated water amount reaches more than 400 million t/d. The method is widely popularized and applied in the transformation and upgrading of sewage plants in China.

For sewage with small scale, large change of water quality and water quantity, high pollutant concentration, especially high nitrogen and phosphorus concentration, and high-quality effluent water quality, the conventional A2/O process has difficulty in realizing stable standard reaching and high-quality effluent, especially has difficulty in reaching high removal rate of total nitrogen, and is inconvenient for flexible process transformation according to the change of water quality and water quantity.

Disclosure of Invention

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

the invention provides a multistage AO sewage treatment system, which comprises a pre-anoxic tank, an anaerobic tank, an anoxic tank, an aerobic tank, an oxygen elimination tank, a post-anoxic tank, a post-aerobic tank and a secondary sedimentation tank which are sequentially connected in series along the sewage flow treatment direction; a water inlet area is arranged at the front end of the pre-anoxic tank; a water outlet area is arranged at the rear end of the secondary sedimentation tank; the anaerobic tank, the anoxic tank and the aerobic tank form a primary sewage treatment unit; the rear anoxic tank and the rear aerobic tank form a secondary sewage treatment unit; a certain sewage concentration gradient is formed between the primary sewage treatment unit and the secondary sewage treatment unit.

Further, a multi-stage AO sewage treatment process, carries out sewage treatment through a multi-stage AO sewage treatment system.

Furthermore, the water inlet area is divided into sections and is fed with water in proportion, and the sections respectively enter the pre-anoxic tank, the anaerobic tank and the anoxic tank.

Further, a carbon source is added into the anoxic pond and the post-anoxic pond.

Further, the oxygen elimination tank can reflux mixed liquor into the oxygen-deficient tank.

Further, the secondary sedimentation tank can make a part of sludge enter the pre-anoxic tank through an external return sludge return pipe; the secondary sedimentation tank can also discharge residual sludge to a sludge concentration tank.

Further, the internal reflux ratio of the mixed liquid refluxed into the anoxic tank by the oxygen elimination tank is 100-300%.

Further, the sludge reflux ratio of the secondary sedimentation tank to the pre-anoxic tank is 50-100%.

Further, glacial acetic acid is adopted as the carbon source.

The invention has the advantages or beneficial effects that:

the multistage AO sewage treatment system provided by the invention forms a multistage AO process through the stage treatment of each sewage treatment tank in the operation process, sewage is preferably subjected to the pretreatment of an anoxic tank, then enters a first-stage sewage treatment unit and a second-stage sewage treatment unit to form an anoxic and aerobic alternate form, and is subjected to multistage reaction to achieve the effects of denitrification and dephosphorization, and finally, high-quality effluent is obtained through the treatment of a secondary sedimentation tank, and simultaneously, the reduction of sludge can be realized, so that the effluent can reach the discharge standard, and the comprehensive use cost is lower.

Drawings

The invention and its features, aspects and advantages will become more apparent from reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference symbols in the various drawings indicate like elements. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a schematic diagram of a multi-stage AO sewage treatment system provided in embodiment 1 of the present invention;

FIG. 2-FIG. 5 are the water inflow distribution data diagrams of the multi-stage AO sewage treatment process provided in this example 1;

FIGS. 6-7 are comparative graphs of carbon source addition equivalent for the multi-stage AO wastewater treatment process provided in this example 1;

FIG. 8-FIG. 9 are comparative graphs of the reflux ratio of mixed liquor in the multi-stage AO sewage treatment process provided in this example 1;

fig. 10 to fig. 11 are analysis diagrams of nitrogen and phosphorus changes in the whole process of the system in the multi-stage AO wastewater treatment process provided in this embodiment 1;

FIG. 12 to FIG. 15 are analysis diagrams of the water quality treatment effect in the multi-stage AO sewage treatment process provided in this example 1;

fig. 16-17 are functional area simulation index test analysis diagrams in the multi-stage AO wastewater treatment process provided in this example 1.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application.

It will be understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

As used herein, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like are used in the positional or orientational relationship illustrated in the figures to facilitate the description of the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be construed as limiting the invention.

The appearances of the terms first, second, and third, if any, are used for descriptive purposes only and are not intended to be limiting or imply relative importance.

Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The technical solutions in the embodiments of the present invention are described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the invention without making creative efforts, belong to the protection scope of the invention.

Example 1

The invention provides a multi-stage AO sewage treatment system, as shown in figure 1, comprising a pre-anoxic tank, an anaerobic tank, an anoxic tank, an aerobic tank, an anoxic tank, a post-aerobic tank and a secondary sedimentation tank which are sequentially connected in series along the sewage flow treatment direction; a water inlet area is arranged at the front end of the pre-anoxic tank; a water outlet area is arranged at the rear end of the secondary sedimentation tank; the anaerobic tank, the anoxic tank and the aerobic tank form a primary sewage treatment unit; the rear anoxic tank and the rear aerobic tank form a secondary sewage treatment unit; a certain sewage concentration gradient is formed between the first-stage sewage treatment unit and the second-stage sewage treatment unit.

The sewage is first treated in a pre-anoxic and anaerobic way, phosphorus accumulating bacteria release phosphorus in the body with small amount of carbon source in an anoxic tank, nitrate as electron acceptor produces anaerobic respiration to produce phosphorus absorbing reaction, phosphorus absorbing and ammoniating organic nitrogen in an aerobic tank, nitrification and BOD and COD degradation are performed simultaneously, the mixed liquid after complete reaction and lower section water enter the next section of post-anoxic tank for reaction, effluent flows into a secondary sedimentation tank for solid-liquid separation, and supernatant is discharged from a water outlet pipe of the secondary sedimentation tank and flows into the next sewage treatment unit.

In the running process, a multi-stage AO process is formed by the stage treatment of each sewage treatment tank, sewage is preferably pretreated by an anoxic pre-tank and then enters a first-stage sewage treatment unit and a second-stage sewage treatment unit to form an anoxic and aerobic alternate form, the multi-stage reaction is realized to achieve the effects of denitrification and dephosphorization, and finally, the high-quality effluent is obtained by the treatment of a secondary sedimentation tank, the reduction of sludge can be realized, so that the effluent can reach the discharge standard, and the comprehensive use cost is lower.

In this example 1, the main process parameters in each treatment tank are shown in Table 1

TABLE 1

Preferably, the multi-stage AO sewage treatment process carries out sewage treatment by a multi-stage AO sewage treatment system.

In the embodiment 1, the total HRT of the multi-stage AO is 17 hours, so that the requirement of the quality of the effluent from town sewage treatment to surface IV-class water can be met. Table 2 HRT configuration times for each treatment tank:

TABLE 2

Preferably, in the multi-stage AO sewage treatment process provided in this embodiment 1, as shown in fig. 2 to 5, the water inlet region is divided into sections and fed with water in proportion, and the sections are fed into the pre-anoxic tank, the anaerobic tank and the anoxic tank, respectively.

The flow distribution ratio is the key of stable operation and effective denitrification of the process, and the nitrification rate of the process is obviously and positively correlated with the sludge load and the volume load. The flow ratio is optimal, the carbon source can be efficiently utilized, and the total nitrogen of the effluent is reduced. In this example 1, 3 points of inlet water enter the pre-anoxic tank, the anaerobic tank and the anoxic tank, and the flow distribution ratio of inlet water is controlled to be i 3:2:5, ii 5:3:2 and iii 3:5:2, which are shown in the figure for comparison:

when the ratio of the inflow water flow rate to the distribution ratio is 5:3:2 and 3:5:2, the average removal rate of COD is higher;

when the water inflow rate is distributed in a ratio of 3:5:2, the average total nitrogen removal rate is highest;

when the ratio of the inflow water to the flow rate is 5:3:2 and 3:5:2, the average TP removal rate is higher;

the multi-stage water inlet can improve the concentration of the suspended solid of the mixed liquid in the reaction tank while distributing the carbon source of each stage in proportion. And the reflux of the sludge and the extension of the hydraulic retention time enable nitrate nitrogen generated by the aerobic tank to be repeatedly denitrified, thereby improving the denitrification efficiency. Phosphorus is discharged out of the body by phosphorus accumulating bacteria in an anaerobic environment, and phosphorus is excessively taken in an aerobic environment, so that the anaerobic reaction and the aerobic reaction are alternately performed, and the phosphorus removal efficiency is greatly improved.

Preferably, in the multi-stage AO sewage treatment process provided in this embodiment 1, as shown in fig. 6 to 7, a carbon source is added to the anoxic tank and the post-anoxic tank, and the carbon source is glacial acetic acid.

In the embodiment 1, glacial acetic acid is used as a carbon source, and on the premise that the adding equivalent of carbon source COD (chemical oxygen demand) is the same, the total nitrogen removal rate is high, the carbon source adding point is located in the middle of an anoxic zone, and compared with the conventional method of adding a carbon source at the front end of an anoxic tank, the adding equivalent of carbon source COD can be saved by 20mg/L, that is, the adding equivalent of COD in the anoxic zone is 60mg/L, and the adding equivalent of COD in the anoxic zone is 10mg/L, so that the effluent standard that the total nitrogen is less than 10mg/L can be met.

Preferably, in the multi-stage AO sewage treatment process provided in this embodiment 1, the mixed liquid may flow back from the oxygen-poor tank to the anoxic tank, and the internal reflux ratio of the mixed liquid flowing back from the oxygen-poor tank to the anoxic tank is 100-300%. In this example 1, as shown in fig. 8-9, when the reflux ratio of the mixed liquid is 300%, the nitrogen and phosphorus removal effect is the best, but the reflux ratio of the mixed liquid is 200% which can meet the requirement of nitrogen and phosphorus removal treatment corresponding to the standard of the effluent of the landmark type iv water;

and sludge is discharged for 30min in each period, the corresponding total sludge age (the ratio of the total amount of the activated sludge in the steam pool to the sludge amount discharged every day, and the average retention time) is 19.9d, and the overall treatment efficiency of the system is higher.

Preferably, in the multistage AO sewage treatment process provided in this embodiment 1, the secondary sedimentation tank may allow a portion of sludge to enter the pre-anoxic tank through the external reflux sludge return pipe; the secondary sedimentation tank can also discharge residual sludge to a sludge concentration tank, and the sludge reflux ratio of the secondary sedimentation tank to the pre-anoxic tank is 50-100%. In this example 1, excess sludge was treated in 2 portions, one portion of the excess sludge was discharged into a sludge concentration tank, and the other portion was introduced into the beginning (pre-anoxic tank) of a multi-stage AO reaction tank through an excess sludge return pipe to maintain the amount of microorganisms in the reaction tank. And an aeration pipe connected from the blower room is aerated to the aerobic tanks in the AO tanks at all levels by the aeration discs to keep a certain dissolved oxygen concentration.

Test example 1

1. The nitrogen and phosphorus change condition of the system whole flow is analyzed, as shown in fig. 10-11:

variation of nitrogen along the way: the concentration of the inlet water STN is 31.9mg/L, and the main component is NH₃90.6 percent of-N, 0.54mg/L of nitrate nitrogen at the tail end of the anoxic zone and NH at the tail end of the aerobic tank₃the-N is 0.42mg/L, the denitrification effect of the system is stable, the total nitrogen removed by the secondary AO is about 1-2 mg/L, the STN of the final effluent of the secondary sedimentation tank is 4.36mg/L, and the NH content₃N is 0.41 mg/L.

Variation of phosphorus along the way: the STP of inlet water is 2.16mg/L, and the main component is PO₄ ^3-81.5% by weight, passing through an anaerobic zone PO₄ ^3-The increment is 0.33mg/L and passes through an anoxic zone PO₄ ^3-The concentration is reduced by about 0.23mg/L and the oxygen passes through an aerobic zone PO₄ ^3-The concentration is reduced by 0.45mg/L, the overall biological phosphorus removal effect of the system is more obvious, and the final STP (STP) of the effluent of the secondary sedimentation tank is 0.64 mg/L.

2. The analysis of the water quality treatment effect is shown in figures 12-15:

PAC is added for auxiliary chemical phosphorus removal at the same time in a continuous operation period, the adding amount is 10-15 mg/L, the COD of the effluent in the continuous operation period is 54.60mg/L at most, and the average removal rate is 73.23%; the maximum ammonia nitrogen of the effluent is 4.32mg/L, and the average removal rate is 96.46%; the maximum total nitrogen of effluent is 9.78mg/L, and the average removal rate is 75.73%; the maximum total phosphorus of the effluent is 0.54mg/L, and the average removal rate is 85.79%; the indexes of COD, BOD, total nitrogen, ammonia nitrogen and total phosphorus of the effluent of the system can reach the expected treatment.

3. The functional area simulates the index test analysis,

for nitrification rate data as shown in table 3:

TABLE 3

Table 3 corresponds to that shown in fig. 16.

Nitration rate: the nitrification rate of the activated sludge of the multistage AO system is 4.81 mg/gVSS.h, and compared with the nitrification rate average value of the activated sludge of the sewage treatment plant in the Tai lake basin, the nitrification rate average value is 2-4 mg/gVSS.h, the activated sludge nitrification flora of the multistage AO system is higher in relative abundance and better in nitrification performance.

Table 4 is the denitrification rate data:

TABLE 4

Table 4 corresponds to that shown in fig. 17.

Denitrification rate: the denitrification rate of the activated sludge of the multistage AO system is 6.26 mg/gVSS.h, and the average value of the denitrification potential of the activated sludge of the sewage treatment plant in the Tai lake basin is 4-6 mg/gVSS.h, which shows that the activated sludge denitrification performance of the system is better and the growth of denitrification flora is good.

The above description is only for the preferred embodiment of the present invention and is not intended to limit the scope of the present invention, and all equivalent structural changes made by using the contents of the present specification and the drawings, or any other related technical fields, are included in the scope of the present invention.

Claims

1. A multi-stage AO sewage treatment system is characterized by comprising a pre-anoxic tank, an anaerobic tank, an anoxic tank, an aerobic tank, an anoxic tank, a post-aerobic tank and a secondary sedimentation tank which are sequentially connected in series along the sewage flow treatment direction; a water inlet area is arranged at the front end of the pre-anoxic tank; a water outlet area is arranged at the rear end of the secondary sedimentation tank;

the anaerobic tank, the anoxic tank and the aerobic tank form a primary sewage treatment unit; the rear anoxic tank and the rear aerobic tank form a secondary sewage treatment unit; a certain sewage concentration gradient is formed between the primary sewage treatment unit and the secondary sewage treatment unit.

2. A multi-stage AO wastewater treatment process characterized by performing wastewater treatment by the multi-stage AO wastewater treatment system according to claim 1.

3. The multi-stage AO sewage treatment process of claim 2 wherein the influent section is staged to provide proportionate influent to the pre-anoxic tank, the anaerobic tank and the anoxic tank, respectively.

4. The multi-stage AO sewage treatment process of claim 2 wherein a carbon source is added to the anoxic tank and the post-anoxic tank.

5. The multi-stage AO sewage treatment process of claim 2 wherein the anoxic tank is operable to return mixed liquor to the anoxic tank.

6. The multi-stage AO sewage treatment process of claim 2, wherein the secondary sedimentation tank may have a part of sludge introduced into the pre-anoxic tank through an external return sludge return pipe; the secondary sedimentation tank can also discharge residual sludge to a sludge concentration tank.

7. The multi-stage AO sewage treatment process of claim 5, wherein the internal reflux ratio of the mixed liquid refluxed from the anoxic tank into the anoxic tank is 100-300%.

8. The multi-stage AO sewage treatment process of claim 6, wherein the sludge reflux ratio of the secondary sedimentation tank to the pre-anoxic tank is 50-100%.

9. The multi-stage AO sewage treatment process of claim 4, wherein the carbon source is glacial acetic acid.