Development and evolution of activated sludge process
2022-12-14 05:06:17
Development and evolution of activated sludge process
Since the invention of the activated sludge process, various variants have been developed depending on the reaction time, the water inlet mode, the aeration equipment, the source of oxygen, the type of the reaction tank, etc., and some of these variants are still widely used, and new The developed processing technology is still tested in practice in the project. It needs to be treated differently when it is used, and it should be chosen according to the time.
1, traditional push flow
In the traditional push-flow activated sludge process, sewage and return sludge enter at the front end of the aeration tank, flow into the pool at the end of the tank, and are aerated and stirred by a blower through a diffusion device or a mechanical aerator. Because the aspect ratio of the corridor is 5~10 , 3~5 corridors are generally used. Adsorption, flocculation and oxidative decomposition of organic pollutants in the aeration tank, and finally into the secondary sedimentation tank for separation of treated sewage and activated sludge, part of the sludge is returned to the aeration tank, and part of the sludge is discharged as excess sludge . The main problems in the traditional push-flow operation are: the flow pattern in the pool is push-flow type, the first end organic pollutant load is high, and the oxygen consumption rate is high; second, the sewage and return sludge can not be immediately after entering the aeration tank. The entire aeration tank mixture is well mixed, susceptible to impact loads, and poor in adaptability to changes in water quality and quantity; third, the oxygen demand of the mixture is gradually reduced in the length direction, and the oxygenation equipment is usually uniform along the length of the tank. Arranged, so there will be insufficient oxygen supply in the first half, and oxygen supply in the second half will exceed the required phenomenon.
2, gradually reduce the aeration method
In order to change the gap between oxygen supply and aerobic demand in the traditional push-flow activated sludge process, a decreasing aeration method can be adopted, and the arrangement of the oxygenation equipment is matched with the oxygen demand along the length direction of the pool, so that the distribution of the gas gradually decreases. It is close to the aerobic rate, and the total air usage is reduced, which can save energy and improve processing efficiency.
3. Stage aeration method
To reduce the peak oxygen demand at the inlet end of the traditional push-flow aeration tank, a stepwise water inlet method can also be adopted, and the inflow sewage enters in the aeration tank at 3 to 4 points, which equalizes the load and needs of the organic pollutants in the aeration tank. The oxygen rate improves the ability of the aeration tank to impact the water quality and water volume. The stage aeration push-flow aeration tank generally adopts 3 or more corridors. After the first inlet point, the MLSS concentration of the mixed liquid can be as high as 5000~9000mg/L , and the sludge concentration in the back corridor is along with the sewage. Reduced by multiple entry. In the case of the same volume of the tank body, the stage aerated activated sludge process system can have a higher total sludge volume than the conventional push flow type, so that the sludge age can be higher.
The stage aeration method can also only inject water into the rear corridor, so that the system operates according to the adsorption regeneration method. In the high season of the rainy season, the influent water can be surpassed to the rear corridor, thereby reducing the solid load entering the secondary settling tank and avoiding the loss of suspended solids in the aeration tank mixture.
4, high load aeration method
The high-load aeration method (also known as the modified aeration method) is the same as the conventional push-flow activated sludge method in the system and aeration tank construction, but the aeration stay time is only 1.5~3.0h , and the aeration tank activated sludge is at The period of growth is strong. The main feature of the process is that the organic volume load or sludge load is high, the aeration time is short, but the treatment effect is low. Generally, the removal rate of BOD 5 does not exceed 70 % ~ 75 %. In order to maintain the stability of the system, sufficient agitation and must be ensured. Aeration.
5, delayed aeration method
The delayed aeration method is similar to the traditional push-flow method. The difference is that the activated sludge of the process is in the endogenous respiration period of the growth curve, the organic matter load is very low, and the aeration reaction time is long, generally more than 24h , the sludge The mud is long and the SRT is between 20 and 30 days . The design of the aeration system is determined by the agitation requirements of the system rather than the oxygen demand. Since the activated sludge is in the endogenous respiration period for a long time in the pool, the amount of excess sludge is small and stable, and the excess sludge is mainly the residue of endogenous metabolism of microorganisms which are difficult to biodegrade. Therefore, it can be said that the process is sewage and sludge. Integrated aerobic treatment system. The process also has the advantages of high stability of the treatment process, strong adaptability to changes in the influent water quality and water quantity, and no need for a primary sedimentation tank; however, there are also disadvantages such as a large volume of the tank body, high capital cost and high operating cost, and the like is generally applicable. For small sewage treatment systems.
6. Adsorption regeneration method
The adsorption regeneration method, also known as the stable contact method, appeared in the expansion and reconstruction of the US sewage treatment plant in the late 1940s .
The characteristic of the process is that the adsorption time of sewage and activated sludge in the adsorption tank is short ( 30~60min ), the volume of the adsorption tank is small, and the regeneration tank receives the return sludge which has been excluded from the excess sludge, and the sludge concentration is relatively High, therefore, the volume of the regeneration tank is also small; the adsorption regeneration method has a certain impact load resistance capacity, and if the adsorption tank sludge is destroyed, it can be supplemented by the regeneration tank.
However, due to the short adsorption contact time, the degradation of organic matter and the nitrification of ammonia nitrogen are limited, and the treatment effect is lower than the conventional method. For the sewage treatment with more dissolved organic pollutants, the process is not applicable.
7, complete mixing method
After the sewage and return sludge enter the aeration tank, they are thoroughly mixed with the mixed liquid in the tank. The mixing in the tank is also the treated water to be separated from the muddy water.
The process has the following characteristics:
(1) The sewage entering the aeration tank is quickly diluted and homogenized by the existing mixed liquid in the pool, and the composition change of the pool liquid is small when the inflow occurs, because the sudden increase of the load can be the whole pool mixture. Sharing, rather than just relying on partial return sludge in the push flow, the process has a strong adaptability to impact loads and is suitable for treating industrial wastewater, especially industrial wastewater with higher concentration.
(2) The sewage is evenly distributed in the aeration tank, the F/M value is equal, the degradation conditions of organic pollutants in all parts are the same, and the composition and quantity of the microbial population are almost the same. Therefore, it is possible to adjust the F/M value. The working conditions of the entire aeration tank are controlled under optimal conditions to better utilize the purification function of the activated sludge.
(3) The aerobic rate of the mixed liquid in the aeration tank is balanced.
The fully mixed activated sludge process system is generally located in the stationary phase or the senescence phase of the growth curve because of the low organic matter load, and the activated sludge is prone to expansion.
The shape of the fully mixed activated sludge tank can be round or square, and can be combined or divided with the sedimentation tank.
8, deep aeration method
The economic depth of the aeration tank is determined by infrastructure and operating costs. According to long-term experience and through various technical and economic comparisons, the economic depth is generally 5~6m . But with the development of the city, the general feeling shortage of land, in order to save the land, from the 1960s he began to study the development of deep aeration.
Generally, the depth of the deep aeration tank can reach 10~20m , but the ultra-deep aeration method, also known as shaft or deep well aeration, has a diameter of 1.0~6.0m and a water depth of 150~300m , which greatly saves the land area. At the same time, due to the large increase in water depth, the oxygen transfer rate can be promoted, and the treatment function is hardly affected by climatic conditions. The process is suitable for treating high concentration organic wastewater.
In the deep well aeration method, the activated sludge undergoes a large change in pressure, sometimes pressurized, and sometimes decompressed. Practice shows that there is no abnormal change in the activity and metabolic capacity of the microorganism at this time. However, there are certain changes in the distribution of synthesis and energy. During the operation, it is found that the amount of carbon dioxide produced is 30 % more than that of normal aeration, and the sludge production is low.
In the deep well aeration tank, the gas-liquid turbulence is large, the night film is updated rapidly, and the K La value is increased. At the same time, the gas-liquid contact time increases, and the saturated oxygen concentration increases with the depth. Dozens of deep well aeration treatment plants have been built abroad, and there are also applications in China. However, when the well wall is corroded or damaged, whether the sewage will penetrate through the well wall and pollute the groundwater, this problem must be taken seriously.
9, pure oxygen aeration method
Replacing air with pure oxygen can increase the rate of biological treatment. Pure oxygen aeration uses a closed tank. The aeration time is short, about 1.5~3.0h , and the MLSS is higher, about 6000~8000mg/L . Therefore, the design and operation of the second settling tank should attract attention.
One of the main advantages of a pure oxygen aeration tank is that the purity of oxygen is over 90 %. In a closed container, the dissolved oxygen saturation concentration can be increased, the driving force of oxygen transfer is also increased, and the oxygen transfer rate is increased, thus processing The effect is good, the sedimentation performance of the sludge is good, and the amount of excess sludge generated is small. Pure aeration does not change the nature of the activated sludge or microorganisms, but allows the microorganisms to fully function.
The disadvantage of pure oxygen aeration is that the pure oxygen generator is prone to failure, the device is complicated, and the operation management is troublesome. The top of the pool must be sealed and airtight, and the structure requirements are high. If a large amount of volatile hydrocarbons are mixed into the influent water, it is easy to cause an explosion. At the same time, the carbon dioxide generated in the biological metabolism will increase the partial pressure of carbon dioxide in the gas, and dissolve in the solution, which will cause the pH to drop, hinder the normal operation of the biological treatment, especially the process that affects the nitrification reaction, so it is necessary to exhaust and carry out in time. pH adjustment.
10. Kraus law
The Krauss engineer added the anaerobic digestion ammonia-rich supernatant to the return sludge for aeration and nitration, and then added to the aeration tank. In addition to providing a nitrogen source, the nitrate can also act as an electron acceptor and participate in organic matter. Degradation. After the process transformation, the sludge expansion problem caused by high carbohydrates was successfully overcome. In addition, the amount of digested sludge in the supernatant of the digester is large, which has the effect of improving the sedimentation performance of the mixture.
11. Adsorption - biodegradation process ( AB method)
The main features of the AB treatment process are:
(1) The whole sewage treatment system is divided into three sections: pretreatment section, A grade and B grade. In the pretreatment section, only processing equipment such as grid and sediment is provided, and no primary sedimentation tank is provided;
(2) Class A consists of an adsorption tank and an intermediate sedimentation tank, and Class B consists of an aeration tank and a secondary settling tank;
(3) Class A and Class B each have independent sludge return systems, each of which is capable of producing unique microbial populations that are suitable for the water quality characteristics of this class.
Class A operates at high load or super high load, the aeration stay time is 2~4h , and the sludge mud age is 15~20d .
The process has stable treatment effect and anti-impact load capacity and is widely used in Europe. The process can also be built in phases according to economic strength.
12. Sequencing batch activated sludge process ( SBR method)
The sequential batch activated sludge process appeared earlier than the continuous activated sludge process, but was replaced by a continuous flow system due to limitations in operational management conditions at the time. With the improvement of the level of automatic control, the SBR method has attracted people's attention and carried out more in-depth research and improvement.
Compared with the continuous flow activated sludge process, the SBR process has some advantages: 1 the process system is simple in composition, the aeration tank has the function of the secondary settling tank, and there is no sludge returning device; 2 the impact load is under normal conditions (including Industrial wastewater treatment) No need to set up the regulating tank; 3 The reaction driving force is large, and it is easy to obtain the effluent water quality superior to the continuous flow system; 4 The operation is flexible, and the effect of nitrogen and phosphorus removal can be achieved by appropriately adjusting the operating state of each stage; In a running cycle, the mud has good sedimentation performance and low SVI value, which can effectively prevent the expansion of filamentous bacteria. 6 The process can be automatically controlled by computer and easy to maintain and manage.
13, oxidation ditch
Developed in the 1950s oxidation ditch is a special form of aeration delay, the general round or oval corridor, elongated cell body, deep shallow pool, provided with a mechanical aeration in the trench and advancing In recent years, there have also been modes of operation using local area blast aeration plus underwater propellers. The arrangement of the pool body and the aeration and agitation devices are all beneficial to the one-way flow of the mixed liquid in the corridor. The flow rate of 0.25~0.30m/s is formed in the corridor by aeration or agitation, so that the activated sludge is suspended. Under such corridor flow rate, the mixed liquid completes a cycle within 5~15min , and a large number of corridors The mixture can be diluted 20 to 30 times, and the water flow in the corridor is pushed, but the process kinetics is close to the complete mixing tank. When the sewage leaves the aeration zone, the dissolved oxygen concentration decreases, and denitrification may occur.
In most cases, the oxidation ditch system requires a secondary settling tank, but in some cases it can be settled in the gallery to complete the mud-water separation process.
14. Circulating activated sludge process ( CAST or CASS )
CAST modified SBR process is a process, in vivo cell walls separated by a biological selection area, and three areas of the zone and the main reaction zone, the volume ratio of the three regions is approximately 1: 2: 20 mixture of the The three zones are returned to the first zone, and the reflux ratio is generally 20 %. The activated sludge in the first zone is mixed with the incoming fresh sewage, and the conditions for competing for survival of the microbial population in a high concentration and high load environment are selected. The unique biological system suitable for the system can effectively inhibit the excessive proliferation of filamentous bacteria, avoid the occurrence of sludge swelling and improve the stability of the system.
The biological selection zone has the function of releasing phosphorus under high sludge concentration and fresh water inflow conditions. The facultative zone can further promote the release and denitrification of phosphorus. If the system is required to achieve a certain purpose of nitrogen and phosphorus removal, the main reaction zone needs Corresponding to the design of anoxic, anaerobic and aerobic environment, the denitrification reaction of the system is not only carried out in the facultative zone, but also in the sludge layer in the sedimentation and hydrophobic stages, and can be controlled well. The dissolved oxygen level in the oxygen phase achieves simultaneous nitrification and denitrification.
Excerpt from Water Pollution Control Engineering
For more information, please pay attention: Yingnuo Instrument (Shanghai) Co., Ltd.
Website: http://
Since the invention of the activated sludge process, various variants have been developed depending on the reaction time, the water inlet mode, the aeration equipment, the source of oxygen, the type of the reaction tank, etc., and some of these variants are still widely used, and new The developed processing technology is still tested in practice in the project. It needs to be treated differently when it is used, and it should be chosen according to the time.
1, traditional push flow
In the traditional push-flow activated sludge process, sewage and return sludge enter at the front end of the aeration tank, flow into the pool at the end of the tank, and are aerated and stirred by a blower through a diffusion device or a mechanical aerator. Because the aspect ratio of the corridor is 5~10 , 3~5 corridors are generally used. Adsorption, flocculation and oxidative decomposition of organic pollutants in the aeration tank, and finally into the secondary sedimentation tank for separation of treated sewage and activated sludge, part of the sludge is returned to the aeration tank, and part of the sludge is discharged as excess sludge . The main problems in the traditional push-flow operation are: the flow pattern in the pool is push-flow type, the first end organic pollutant load is high, and the oxygen consumption rate is high; second, the sewage and return sludge can not be immediately after entering the aeration tank. The entire aeration tank mixture is well mixed, susceptible to impact loads, and poor in adaptability to changes in water quality and quantity; third, the oxygen demand of the mixture is gradually reduced in the length direction, and the oxygenation equipment is usually uniform along the length of the tank. Arranged, so there will be insufficient oxygen supply in the first half, and oxygen supply in the second half will exceed the required phenomenon.
2, gradually reduce the aeration method
In order to change the gap between oxygen supply and aerobic demand in the traditional push-flow activated sludge process, a decreasing aeration method can be adopted, and the arrangement of the oxygenation equipment is matched with the oxygen demand along the length direction of the pool, so that the distribution of the gas gradually decreases. It is close to the aerobic rate, and the total air usage is reduced, which can save energy and improve processing efficiency.
3. Stage aeration method
To reduce the peak oxygen demand at the inlet end of the traditional push-flow aeration tank, a stepwise water inlet method can also be adopted, and the inflow sewage enters in the aeration tank at 3 to 4 points, which equalizes the load and needs of the organic pollutants in the aeration tank. The oxygen rate improves the ability of the aeration tank to impact the water quality and water volume. The stage aeration push-flow aeration tank generally adopts 3 or more corridors. After the first inlet point, the MLSS concentration of the mixed liquid can be as high as 5000~9000mg/L , and the sludge concentration in the back corridor is along with the sewage. Reduced by multiple entry. In the case of the same volume of the tank body, the stage aerated activated sludge process system can have a higher total sludge volume than the conventional push flow type, so that the sludge age can be higher.
The stage aeration method can also only inject water into the rear corridor, so that the system operates according to the adsorption regeneration method. In the high season of the rainy season, the influent water can be surpassed to the rear corridor, thereby reducing the solid load entering the secondary settling tank and avoiding the loss of suspended solids in the aeration tank mixture.
4, high load aeration method
The high-load aeration method (also known as the modified aeration method) is the same as the conventional push-flow activated sludge method in the system and aeration tank construction, but the aeration stay time is only 1.5~3.0h , and the aeration tank activated sludge is at The period of growth is strong. The main feature of the process is that the organic volume load or sludge load is high, the aeration time is short, but the treatment effect is low. Generally, the removal rate of BOD 5 does not exceed 70 % ~ 75 %. In order to maintain the stability of the system, sufficient agitation and must be ensured. Aeration.
5, delayed aeration method
The delayed aeration method is similar to the traditional push-flow method. The difference is that the activated sludge of the process is in the endogenous respiration period of the growth curve, the organic matter load is very low, and the aeration reaction time is long, generally more than 24h , the sludge The mud is long and the SRT is between 20 and 30 days . The design of the aeration system is determined by the agitation requirements of the system rather than the oxygen demand. Since the activated sludge is in the endogenous respiration period for a long time in the pool, the amount of excess sludge is small and stable, and the excess sludge is mainly the residue of endogenous metabolism of microorganisms which are difficult to biodegrade. Therefore, it can be said that the process is sewage and sludge. Integrated aerobic treatment system. The process also has the advantages of high stability of the treatment process, strong adaptability to changes in the influent water quality and water quantity, and no need for a primary sedimentation tank; however, there are also disadvantages such as a large volume of the tank body, high capital cost and high operating cost, and the like is generally applicable. For small sewage treatment systems.
6. Adsorption regeneration method
The adsorption regeneration method, also known as the stable contact method, appeared in the expansion and reconstruction of the US sewage treatment plant in the late 1940s .
The characteristic of the process is that the adsorption time of sewage and activated sludge in the adsorption tank is short ( 30~60min ), the volume of the adsorption tank is small, and the regeneration tank receives the return sludge which has been excluded from the excess sludge, and the sludge concentration is relatively High, therefore, the volume of the regeneration tank is also small; the adsorption regeneration method has a certain impact load resistance capacity, and if the adsorption tank sludge is destroyed, it can be supplemented by the regeneration tank.
However, due to the short adsorption contact time, the degradation of organic matter and the nitrification of ammonia nitrogen are limited, and the treatment effect is lower than the conventional method. For the sewage treatment with more dissolved organic pollutants, the process is not applicable.
7, complete mixing method
After the sewage and return sludge enter the aeration tank, they are thoroughly mixed with the mixed liquid in the tank. The mixing in the tank is also the treated water to be separated from the muddy water.
The process has the following characteristics:
(1) The sewage entering the aeration tank is quickly diluted and homogenized by the existing mixed liquid in the pool, and the composition change of the pool liquid is small when the inflow occurs, because the sudden increase of the load can be the whole pool mixture. Sharing, rather than just relying on partial return sludge in the push flow, the process has a strong adaptability to impact loads and is suitable for treating industrial wastewater, especially industrial wastewater with higher concentration.
(2) The sewage is evenly distributed in the aeration tank, the F/M value is equal, the degradation conditions of organic pollutants in all parts are the same, and the composition and quantity of the microbial population are almost the same. Therefore, it is possible to adjust the F/M value. The working conditions of the entire aeration tank are controlled under optimal conditions to better utilize the purification function of the activated sludge.
(3) The aerobic rate of the mixed liquid in the aeration tank is balanced.
The fully mixed activated sludge process system is generally located in the stationary phase or the senescence phase of the growth curve because of the low organic matter load, and the activated sludge is prone to expansion.
The shape of the fully mixed activated sludge tank can be round or square, and can be combined or divided with the sedimentation tank.
8, deep aeration method
The economic depth of the aeration tank is determined by infrastructure and operating costs. According to long-term experience and through various technical and economic comparisons, the economic depth is generally 5~6m . But with the development of the city, the general feeling shortage of land, in order to save the land, from the 1960s he began to study the development of deep aeration.
Generally, the depth of the deep aeration tank can reach 10~20m , but the ultra-deep aeration method, also known as shaft or deep well aeration, has a diameter of 1.0~6.0m and a water depth of 150~300m , which greatly saves the land area. At the same time, due to the large increase in water depth, the oxygen transfer rate can be promoted, and the treatment function is hardly affected by climatic conditions. The process is suitable for treating high concentration organic wastewater.
In the deep well aeration method, the activated sludge undergoes a large change in pressure, sometimes pressurized, and sometimes decompressed. Practice shows that there is no abnormal change in the activity and metabolic capacity of the microorganism at this time. However, there are certain changes in the distribution of synthesis and energy. During the operation, it is found that the amount of carbon dioxide produced is 30 % more than that of normal aeration, and the sludge production is low.
In the deep well aeration tank, the gas-liquid turbulence is large, the night film is updated rapidly, and the K La value is increased. At the same time, the gas-liquid contact time increases, and the saturated oxygen concentration increases with the depth. Dozens of deep well aeration treatment plants have been built abroad, and there are also applications in China. However, when the well wall is corroded or damaged, whether the sewage will penetrate through the well wall and pollute the groundwater, this problem must be taken seriously.
9, pure oxygen aeration method
Replacing air with pure oxygen can increase the rate of biological treatment. Pure oxygen aeration uses a closed tank. The aeration time is short, about 1.5~3.0h , and the MLSS is higher, about 6000~8000mg/L . Therefore, the design and operation of the second settling tank should attract attention.
One of the main advantages of a pure oxygen aeration tank is that the purity of oxygen is over 90 %. In a closed container, the dissolved oxygen saturation concentration can be increased, the driving force of oxygen transfer is also increased, and the oxygen transfer rate is increased, thus processing The effect is good, the sedimentation performance of the sludge is good, and the amount of excess sludge generated is small. Pure aeration does not change the nature of the activated sludge or microorganisms, but allows the microorganisms to fully function.
The disadvantage of pure oxygen aeration is that the pure oxygen generator is prone to failure, the device is complicated, and the operation management is troublesome. The top of the pool must be sealed and airtight, and the structure requirements are high. If a large amount of volatile hydrocarbons are mixed into the influent water, it is easy to cause an explosion. At the same time, the carbon dioxide generated in the biological metabolism will increase the partial pressure of carbon dioxide in the gas, and dissolve in the solution, which will cause the pH to drop, hinder the normal operation of the biological treatment, especially the process that affects the nitrification reaction, so it is necessary to exhaust and carry out in time. pH adjustment.
10. Kraus law
The Krauss engineer added the anaerobic digestion ammonia-rich supernatant to the return sludge for aeration and nitration, and then added to the aeration tank. In addition to providing a nitrogen source, the nitrate can also act as an electron acceptor and participate in organic matter. Degradation. After the process transformation, the sludge expansion problem caused by high carbohydrates was successfully overcome. In addition, the amount of digested sludge in the supernatant of the digester is large, which has the effect of improving the sedimentation performance of the mixture.
11. Adsorption - biodegradation process ( AB method)
The main features of the AB treatment process are:
(1) The whole sewage treatment system is divided into three sections: pretreatment section, A grade and B grade. In the pretreatment section, only processing equipment such as grid and sediment is provided, and no primary sedimentation tank is provided;
(2) Class A consists of an adsorption tank and an intermediate sedimentation tank, and Class B consists of an aeration tank and a secondary settling tank;
(3) Class A and Class B each have independent sludge return systems, each of which is capable of producing unique microbial populations that are suitable for the water quality characteristics of this class.
Class A operates at high load or super high load, the aeration stay time is 2~4h , and the sludge mud age is 15~20d .
The process has stable treatment effect and anti-impact load capacity and is widely used in Europe. The process can also be built in phases according to economic strength.
12. Sequencing batch activated sludge process ( SBR method)
The sequential batch activated sludge process appeared earlier than the continuous activated sludge process, but was replaced by a continuous flow system due to limitations in operational management conditions at the time. With the improvement of the level of automatic control, the SBR method has attracted people's attention and carried out more in-depth research and improvement.
Compared with the continuous flow activated sludge process, the SBR process has some advantages: 1 the process system is simple in composition, the aeration tank has the function of the secondary settling tank, and there is no sludge returning device; 2 the impact load is under normal conditions (including Industrial wastewater treatment) No need to set up the regulating tank; 3 The reaction driving force is large, and it is easy to obtain the effluent water quality superior to the continuous flow system; 4 The operation is flexible, and the effect of nitrogen and phosphorus removal can be achieved by appropriately adjusting the operating state of each stage; In a running cycle, the mud has good sedimentation performance and low SVI value, which can effectively prevent the expansion of filamentous bacteria. 6 The process can be automatically controlled by computer and easy to maintain and manage.
13, oxidation ditch
Developed in the 1950s oxidation ditch is a special form of aeration delay, the general round or oval corridor, elongated cell body, deep shallow pool, provided with a mechanical aeration in the trench and advancing In recent years, there have also been modes of operation using local area blast aeration plus underwater propellers. The arrangement of the pool body and the aeration and agitation devices are all beneficial to the one-way flow of the mixed liquid in the corridor. The flow rate of 0.25~0.30m/s is formed in the corridor by aeration or agitation, so that the activated sludge is suspended. Under such corridor flow rate, the mixed liquid completes a cycle within 5~15min , and a large number of corridors The mixture can be diluted 20 to 30 times, and the water flow in the corridor is pushed, but the process kinetics is close to the complete mixing tank. When the sewage leaves the aeration zone, the dissolved oxygen concentration decreases, and denitrification may occur.
In most cases, the oxidation ditch system requires a secondary settling tank, but in some cases it can be settled in the gallery to complete the mud-water separation process.
14. Circulating activated sludge process ( CAST or CASS )
CAST modified SBR process is a process, in vivo cell walls separated by a biological selection area, and three areas of the zone and the main reaction zone, the volume ratio of the three regions is approximately 1: 2: 20 mixture of the The three zones are returned to the first zone, and the reflux ratio is generally 20 %. The activated sludge in the first zone is mixed with the incoming fresh sewage, and the conditions for competing for survival of the microbial population in a high concentration and high load environment are selected. The unique biological system suitable for the system can effectively inhibit the excessive proliferation of filamentous bacteria, avoid the occurrence of sludge swelling and improve the stability of the system.
The biological selection zone has the function of releasing phosphorus under high sludge concentration and fresh water inflow conditions. The facultative zone can further promote the release and denitrification of phosphorus. If the system is required to achieve a certain purpose of nitrogen and phosphorus removal, the main reaction zone needs Corresponding to the design of anoxic, anaerobic and aerobic environment, the denitrification reaction of the system is not only carried out in the facultative zone, but also in the sludge layer in the sedimentation and hydrophobic stages, and can be controlled well. The dissolved oxygen level in the oxygen phase achieves simultaneous nitrification and denitrification.
Excerpt from Water Pollution Control Engineering
For more information, please pay attention: Yingnuo Instrument (Shanghai) Co., Ltd.
Website: http://
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