Method and system for enhanced denitrification by CASS (cyclic activated sludge system) process

Abstract

The invention discloses a method and a system for enhancing nitrogen removal by a CASS (cyclic activated sludge system) process, the method comprises CASS post-denitrification, the CASS post-denitrification comprises a water inlet stage, an aeration stage, a stirring stage, a precipitation stage and a water decanting stage, a carbon source is added into sewage after the aeration stage is ended, and the carbon source is added into the sewage after the aeration stage is ended. And carrying out denitrification reaction by utilizing the mud-water mixing areas in the precipitation stage and the water decanting stage. According to the method for enhancing nitrogen removal through the CASS process, CASS post-denitrification is adopted, the mud-water mixing time and space in the precipitation stage and the water decanting stage are fully utilized, denitrification is more thorough, and the nitrogen removal effect of the CASS process is enhanced. According to the system disclosed by the invention, each CASS pool is provided with an independent feeding pipeline and a control system, the feeding pipeline ensures that a carbon source can be accurately and quickly fed into the CASS pool, and the control system can accurately control the feeding time and feeding amount of the carbon source according to the running state and water quality monitoring data of the CASS pool so as to adapt to different inlet water quality and treatment requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and particularly to a method and system for enhancing denitrification in the CASS process. Background Art

[0002] In the field of sewage treatment, the CASS (Cyclic Activated Sludge System) process is widely used. In the process of upgrading and improving the standard, sewage treatment plants using the CASS process add denitrification filters in the advanced treatment process or reduce the treatment volume of the CASS tank to achieve the upgrade from Class B to Class A. A certain sewage treatment plant uses the CASS process with a designed scale of 4.5×10 4 m³ / d. Although the upgrade was completed in 2019 by adding agitators and building a high-efficiency sedimentation tank, etc., to improve the effluent standard from Class B to Class A, as the influent water quality concentration approaches the design value and the treatment water volume needs to reach the design value, there is great pressure to meet the total nitrogen (TN) standard.

[0003] There are many limitations in the pre-denitrification of the traditional CASS process. Due to strict time control, within the limited denitrification time, the carbon source cannot be fully utilized, and the denitrification nitrogen removal amount is only 36% of the theoretical value. At the same time, the content of easily degradable COD in domestic municipal sewage accounts for about 11%. When using urban domestic sewage as the carbon source, the denitrification rate is low, and a large denitrification volume is often required, that is, a long denitrification reaction time. Starting the agitator in the pre-denitrification process takes about 4 minutes for the CASS tank to change from static to fully mixed, further compressing the denitrification time.

[0004] In actual operation, although measures such as increasing the sludge concentration, supplementing the carbon source, and reducing the influent load are taken when the sewage treatment plant alternates between autumn and winter, the total nitrogen compliance is still unstable. Especially in autumn and winter when the influent TN concentration is the highest, the microbial activity and sedimentation performance are poor, and the pressure to meet the total nitrogen standard is greater. Therefore, there is an urgent need for a new method to enhance the denitrification effect of the CASS process. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above background art, and provide a method and system for enhancing denitrification in the CASS process. The method adopts post-denitrification, makes full use of the mixing time and space of the mud and water in the precipitation stage and the decantation stage, makes the denitrification more thorough, solves the deficiency of difficult total nitrogen compliance in the existing CASS process, and enhances the denitrification effect of the CASS process.

[0006] To achieve the above object, a method for enhancing denitrification in the CASS process provided by the present invention includes post-denitrification in CASS. The post-denitrification in CASS includes an influent stage, an aeration stage, a stirring stage, a sedimentation stage, and a decantation stage. After the aeration stage ends, a carbon source is added to the sewage, and the mixed sludge-water zone in the sedimentation stage and the decantation stage is used for the denitrification reaction.

[0007] Further, the carbon source is sodium acetate with a concentration of 15-20%.

[0008] Further, the addition time of the carbon source is no more than 10 min.

[0009] Further, after the carbon source is added, the COD concentration of the sewage in the CASS tank is 10-15 mg / L.

[0010] Further, the total time of the post-denitrification in CASS is 4 h.

[0011] Further, the time of the aeration stage is 90 min, the time of the stirring stage is 30 min, the time of the sedimentation stage is 60 min, and the time of the decantation stage is 60 min.

[0012] Further, the influent stage and the aeration stage are started simultaneously, the time of the influent stage is 50 min, and after the influent stage ends, the aeration stage continues for another 40 min.

[0013] The present invention also provides a system for implementing the above method, including a plurality of CASS tanks. A carbon source addition pipeline is provided on each CASS tank, and a dosing valve is provided on the carbon source addition pipeline. The carbon source addition pipeline is used to add a carbon source into the CASS tank.

[0014] Still further, a PLC control system is also provided on each CASS tank. The control signal output end of the PLC control system is connected to the control signal input end of the dosing valve on the CASS tank; the carbon source is quantitatively added by controlling the dosing valve through the PLC control system.

[0015] Even further, a plurality of stirrers are provided in each CASS tank.

[0016] Compared with the prior art, the present invention has the following advantages: First, the method for enhancing denitrification in the CASS process of the present invention can increase the denitrification amount. Under the same conditions, the denitrification amount of post-denitrification is twice that of pre-denitrification. Through post-denitrification, the mixed sludge-water time and space in the sedimentation and decantation stages are fully utilized, making the denitrification more complete.

[0017] Second, the method for enhancing denitrification in the CASS process of the present invention can improve the utilization rate of carbon sources: the carbon source for post-denitrification is utilized more thoroughly. According to the ASM1 model calculation, the result of the biodegradable substrate switching function in the post-denitrification process is better than that in the pre-denitrification process. When adding carbon sources after the aeration ends, the CASS pool is in a mixed state, and there is no need for additional time to make the pool reach a fully mixed state, avoiding the compression of denitrification time caused by stirring and mixing in the pre-denitrification process, thereby improving the utilization efficiency of carbon sources.

[0018] Third, the method for enhancing denitrification in the CASS process of the present invention can stably meet the total nitrogen standard. From the perspective of the utilization rate of external carbon sources and the total nitrogen removal effect, post-denitrification in the CASS pool is superior to the pre-denitrification process. Using this method, even under adverse conditions such as increased influent water quality concentration and decreased water temperature, the total nitrogen removal efficiency can be effectively improved, making the total nitrogen in the effluent more stably meet the standard, and solving the problem of difficult stable compliance of total nitrogen in sewage treatment plants under full-load production conditions.

[0019] Fourth, the enhanced denitrification system of the CASS process of the present invention is equipped with a separate dosing pipeline and control system for each CASS pool. The dosing pipeline ensures that the carbon source can be accurately and quickly dosed into the CASS pool. The control system can precisely control the dosing time and dosing amount of the carbon source according to the operating status of the CASS pool and water quality monitoring data to adapt to different influent water qualities and treatment requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the method for enhancing denitrification in the CASS process of the embodiment of the present invention; Figure 2 is the schematic diagram of each stage process of CASS post-denitrification in the embodiment of the present invention; Figure 3 is the schematic diagram of the enhanced denitrification system of the CASS process of the embodiment of the present invention; In the figure: CASS pool 1, carbon source dosing pipeline 2, dosing valve 3, PLC control system 4, stirrer 5. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following will describe the implementation of the present invention in detail in combination with implementation cases, but they do not constitute a limitation to the present invention, and are only for illustration. At the same time, the advantages of the present invention will become clearer and easier to understand.

[0022] Taking a certain sewage treatment plant as an example, as Figure 1The figure shows the process flow of a sewage treatment plant after adopting the method of enhancing nitrogen removal by the CASS process of the present invention, demonstrating the entire treatment process of sewage from inlet to outlet, including treatment units such as coarse screens, fine screens, CASS tanks, bio-magnetic high-efficiency sedimentation tanks, etc., providing a basis for understanding the process environment of the present invention. The main process parameters of each unit in this embodiment are as follows: Main parameters of the coarse screen: 2 rotary grid cleaners, single-pass flow rate through the grid: Q = 950 m³ / h, grid width: B = 900 mm, grid bar gap: b = 20 mm, water depth in front of the grid: h = 1200 mm, grid inclination angle: a = 75°, head loss through the grid: Δhmax = 150 mm, single-unit power: 15 kW. Main parameters of the influent pump house: 4 submersible sewage pumps, N = 75 kW, Q = 950 m³ / h, H = 15 m. Main parameters of the fine screen and aerated grit chamber: 2 drum grid cleaners, single-pass flow rate through the grid: Q = 0.36 m / s, grid width: B = 1400 mm, grid bar gap: b = 6 mm, water depth in front: h = 750 mm, grid inclination angle: a = 35°, flow-through loss: Δhmax = 200 mm, 1 grid residue conveyor, conveying capacity W = 15 m³ / h, 1 bridge-type sand suction machine, N = 0.37 kW, L = 52 m, traveling speed 3 m / min, 1 screw-type sand and water separator, water treatment capacity: 20 m³ / h, 2 sand suction pumps, N = 15 kW, Q = 30 m³ / h, H = 6 m. Main parameters of the CASS tank: A total of 8 CASS tanks, sludge load 0.1 kg BODs / kg MLVSS·d, sludge return ratio: R = 20%, suspended solid concentration MLSS = 3500 mg / L, water filling ratio: 0.3, dimensions: L×B×H = 61.95 m×42.5 m×7.0 m, each single tank is equipped with 2 agitators, power 11 kW. Main parameters of the intermediate lift pump house: 3 submersible sewage lift pumps, 2 in use and 1 standby, power: N = 37 kW, flow rate: Q = 1315 m³ / h, head: H = 6 m, pump house dimensions: L×B×H = 80 m×50 m×50 m. Main parameters of the bio-magnetic high-efficiency sedimentation tank: Surface load of the sedimentation tank 18 m³ / ㎡ / h, adding PAC + PAM + magnetic powder. Main parameters of the precision filter: 3 R200 Fajiesi precision filters (2 in use and 1 standby), single-unit treatment capacity 20,000 tons per day, P = (1.5 + 2.2) kW, 3 backwash pumps, N = 3 kW, Q = 10.6 m³ / h, H = 63 m. Main parameters of the contact disinfection tank: Dimensions: L×B×H = 30.5 m×12.2 m×4.0 m.

[0023] As Figure 2The time flow of each stage of CASS post-denitrification in this embodiment is shown, visually presenting the process of CASS post-denitrification. CASS post-denitrification includes the time distribution of the influent stage, aeration stage, stirring stage, sedimentation stage, and decantation stage. This figure reflects that the CASS tank is in different biochemical processes at different time stages. All the above biochemical processes are carried out in the CASS tank, and the total time of CASS post-denitrification is 4 hours. In the present invention, a carbon source is added to the sewage after the aeration stage, and the denitrification reaction is carried out using the mud-water mixing zone in the sedimentation stage and the decantation stage. Figure 2 The shown flow chart helps to clarify the position and time nodes of the carbon source addition and denitrification process in the entire CASS process cycle in the present invention, and specifically includes the following processes: Preparation stage: In the CASS tank system of the sewage treatment plant, a separate carbon source addition pipeline and control system are installed for each CASS tank. 20% sodium acetate is selected as the carbon source, and a carbon source solution with a COD concentration of 20×10 4 mg / L is prepared for standby.

[0024] Operation stage: After the aeration ends, the control system starts the addition pipeline, and quickly adds 200 L of the carbon source solution to the CASS tank within 10 minutes. At the same time, the stirrer is turned on and stirred for 30 minutes. The COD concentration of the sewage in the CASS tank is 10 - 15 mg / L. After adding the carbon source, the stirrer is stirred for 30 minutes to create a denitrification environment. After the stirring ends, the CASS tank enters the sedimentation stage (60 minutes) and the decantation stage (60 minutes). During the sedimentation stage, the denitrification reaction continuously occurs in the mud-water mixing zone, and the denitrification process is made more sufficient by utilizing the time and space of the sedimentation and decantation stages. During the entire operation process, the influent water quality and the water quality parameters in the CASS tank (such as total nitrogen, ammonia nitrogen, SCOD, etc.) are monitored in real time through the control system, and the carbon source addition amount and the operation parameters of the CASS tank are adjusted in a timely manner according to the monitoring data to ensure the best total nitrogen removal effect. In this embodiment, the TN removal rate of CASS post-denitrification using the method of the present invention is about 51%, while the effect of pre-denitrification is relatively poor.

[0025] As Figure 3As shown in the figure, an enhanced denitrification system for CASS process includes several CASS tanks 1. A carbon source dosing pipeline 2 is arranged on each CASS tank 1, and a dosing valve 3 is arranged on the carbon source dosing pipeline 2. The carbon source dosing pipeline 2 is used to dose carbon source into the CASS tank 1. A PLC control system 4 is also arranged on each CASS tank 1. The control signal output end of the PLC control system 4 is connected to the control signal input end of the dosing valve on the CASS tank 1; the carbon source is dosed quantitatively by controlling the dosing valve through the PLC control system. Several agitators 5 are also arranged in each CASS tank. The enhanced denitrification system for CASS process of the present invention is configured with a separate dosing pipeline and control system for each CASS tank. The dosing pipeline ensures that the carbon source can be accurately and quickly dosed into the CASS tank. The control system can accurately control the dosing time and dosing amount of the carbon source according to the operating status of the CASS tank and the water quality monitoring data to adapt to different influent water qualities and treatment requirements.

[0026] The above is only the specific embodiment of the present invention. It should be noted that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The rest not detailed is the prior art.

Claims

1. A method for enhancing denitrification in the CASS process, characterized in that: It includes post - denitrification in CASS. The post - denitrification in CASS includes an influent stage, an aeration stage, a stirring stage, a sedimentation stage, and a decantation stage. After the aeration stage, a carbon source is added to the sewage, and the mixed zone of mud and water in the sedimentation stage and the decantation stage is used for denitrification reaction.

2. The method for enhancing denitrification by the CASS process according to claim 1, characterized in that: The carbon source is sodium acetate with a concentration of 15 - 20%.

3. The method for enhancing denitrification by the CASS process according to claim 2, characterized in that: The dosing time of the carbon source is no more than 10 min.

4. The method for enhancing denitrification by CASS process according to claim 3, characterized in that: After the carbon source is added, the COD concentration of the sewage in the CASS tank is 10 - 15 mg / L.

5. The method for enhancing nitrogen removal by the CASS process according to any one of claims 1 to 4, characterized in that: The total time of the post - denitrification in CASS is 4 h.

6. The method for enhancing denitrification by the CASS process according to claim 5, characterized in that: The time of the aeration stage is 90 min, the time of the stirring stage is 30 min, the time of the sedimentation stage is 60 min, and the time of the decantation stage is 60 min.

7. The method for enhancing denitrification by CASS process according to claim 6, characterized in that: The influent stage starts simultaneously with the aeration stage. The time of the influent stage is 50 min. After the influent stage ends, the aeration stage continues for another 40 min.

8. A system for implementing the method for enhancing denitrification in the CASS process according to any one of claims 1 to 7, characterized in that: It includes several CASS tanks. A carbon - source dosing pipeline is arranged on each CASS tank, and a dosing valve is arranged on the carbon - source dosing pipeline. The carbon - source dosing pipeline is used to add the carbon source into the CASS tank.

9. The system according to claim 8, wherein: A PLC control system is also arranged on each CASS tank. The control - signal output end of the PLC control system is connected to the control - signal input end of the dosing valve on the CASS tank; the carbon source is quantitatively dosed by controlling the dosing valve through the PLC control system.

10. The system according to claim 9, wherein: Several stirrers are also arranged in each CASS tank.

Images