If you are in Beijing, Yanqing Sewage Treatment Plant does SBR. I have visited it. You can search and contact us.
The following is a brief introduction to SBR, I hope it will be helpful.
Abstract: SBR-Sequencing Batch Reactor is a water treatment process invented as early as 1914 by British scholars Ardern and Locket. In the early 1970s, Professor R. Irvine of Natre Dame University in the United States conducted systematic and in-depth research on the SBR process on a laboratory scale. In 1980, with funding from the U.S. Environmental Protection Agency (EPA), he renovated and renovated the SBR process in Culwer City, Indiana. The world's first SBR sewage treatment plant was put into operation. The SBR process is run in sequence. An operation process is divided into five stages: water inlet, reaction, precipitation, decanting, and idle.
Keywords: SBR process Sequencing Batch Reactor (SBR—Sequencing Batch Reactor) is a water treatment process invented as early as 1914 by British scholars Ardern and Locket. In the early 1970s, Professor R. Irvine of Natre Dame University in the United States conducted systematic and in-depth research on the SBR process on a laboratory scale. In 1980, with funding from the U.S. Environmental Protection Agency (EPA), he renovated and renovated the SBR process in Culwer City, Indiana. The world's first SBR sewage treatment plant was put into operation. The SBR process is run in sequence. An operation process is divided into five stages: water inlet, reaction, precipitation, decanting, and idle.
Due to the operation process of SBR, the operating time of each stage, the change of mixed liquid volume in the reactor and the operating status can all be determined according to the nature of the specific sewage, effluent quality, effluent quality and operation function requirements, etc. Flexible to change. For the SBR reactor, it is only timing control and there are no spatial control obstacles, so it can be controlled flexibly. Therefore, the SBR process has developed extremely rapidly, and many new SBR treatment processes have been derived.
Intermittent Cyclic Extended Aeration Activated Sludge (ICEAS-Intermittent Cyclic Extended System) was developed in 1968 by the University of New Wales in Australia and the American ABJ Company. In 1976, the world's first ICEAS process wastewater plant was put into operation. Compared with traditional SBR, the biggest feature of ICEAS is that a pre-reaction zone is set up at the water inlet end of the reactor. The entire treatment process is continuously fed with water and is drained intermittently. There is no obvious reaction stage and idle stage, so the treatment cost is lower than that of traditional SBR. Due to the continuous water inflow throughout the entire process, the separation of mud and water during the sedimentation stage is poor, which limits the amount of water inflow.
The intermittent aerobic aeration system (DAT-IAT—Demand Aeration Tank-Intermittent Tank) is a new SBR technology proposed by Tianjin Municipal Engineering Design and Research Institute. The main structure is composed of an aerobic tank DAT tank and an intermittent aeration tank IAT tank. The DAT tank continuously inflows water for continuous aeration, and its outlet water enters the IAT tank from the intermediate wall. The IAT tank continuously inflows water and drains water intermittently. At the same time, the sludge from the IAT pool returns to the DAT pool. It has the characteristics of strong impact resistance and has the function of removing phosphorus and denitrification.
The Cyclic Activated Sludge System (CASS—Cyclic Activated Sludge System) was developed by Professor Gotonszy on the basis of the ICEAS process and is a new form of SBR process. Replace the pre-reaction area of ??ICEAS with a biological selector with smaller volume and more reasonable and optimized design. Usually, the CASS pool is divided into three reaction zones: biological selector, anoxic zone and aerobic zone. The volume ratio is generally 1:5:30. The entire process operates intermittently, with water aeration and sludge return at the same time. The treatment system has nitrogen and dephosphorization functions.
The UNITANK unit pool activated sludge treatment system was proposed by the Belgian SEGHERS company. It is another variation of the SBR process. It combines the characteristics of the SBR process and the oxidation ditch process. The integrated design allows the entire system to continuously enter and discharge water, while a single pool has intermittent water inflow and intermittent drainage.
This system can flexibly control time and space, appropriately increase the hydraulic retention time, and achieve nitrogen and phosphorus removal in sewage.
Modified Sequencing Batch Reactor (MSBR-Modified Sequencing Batch Reactor) is a more ideal sewage treatment method developed by C.Y. Yang and others based on the characteristics of SBR technology combined with the A2-O process. system. It adopts single-pool multi-square mode and operates continuously under constant water level. Usually the MSBR tank is divided into main aeration tank, sequence batch tank 1, sequence batch tank 2, anaerobic tank A, anaerobic tank B, anoxic tank, and mud-water separation tank.
Each cycle is divided into 6 periods, and every 3 periods is a half-cycle. Operation status of one and a half cycles: sewage first enters anaerobic tank A for denitrification, then enters anaerobic tank B for phosphorus removal, enters the main aeration tank for aerobic treatment, and then enters the sequence batch tank. The two sequence batch tanks operate alternately (lack of Oxygen-aerobic/sedimentation-effluent). The ability to remove nitrogen and phosphorus is stronger.
Advantages of SBR process
1. The ideal push flow process increases the driving force of biochemical reactions and improves efficiency. The anaerobic and aerobic conditions in the pool are in an alternating state, and the purification effect is good.
2. The operation effect is stable. The sewage settles in an ideal static state, which requires a short time, high efficiency, and good effluent quality.
3. Resistant to impact loads. There is stagnant treated water in the pool, which dilutes and buffers sewage and effectively resists the impact of water volume and organic pollutants.
4. Each process in the process can be adjusted according to water quality and quantity, and the operation is flexible.
5. Less processing equipment, simple structure, easy operation, maintenance and management.
6. There is a concentration gradient of DO and BOD5 in the reaction tank, which effectively controls the expansion of activated sludge.
7. The SBR method system itself is also suitable for combined construction methods, which is conducive to the expansion and renovation of wastewater treatment plants.
8. For nitrogen and phosphorus removal, properly control the operation mode to achieve alternating aerobic, anoxic and anaerobic states, with good nitrogen and phosphorus removal effects.
9. The process is simple and the cost is low. The main equipment has only one sequencing batch batch reactor, no secondary sedimentation tank and sludge return system. The regulating tank and primary sedimentation tank can also be omitted. The layout is compact and the floor space is saved.
The scope of application of the SBR system
Due to the above technical characteristics, the SBR system further broadens the scope of application of the activated sludge method. In terms of recent technical conditions, the SBR system is more suitable for the following situations:
1) Domestic sewage in small and medium-sized towns and industrial wastewater from factories and mines, especially places with intermittent discharge and large flow changes.
2) Places that require higher effluent quality, such as scenic spots, lakes and harbors, not only need to remove organic matter, but also require phosphorus and nitrogen removal in the effluent to prevent eutrophication of rivers and lakes.
3) Places where water resources are scarce. The SBR system can perform physical and chemical treatment after biological treatment without adding facilities, which facilitates water recycling.
4) Places where land is tight.
5) Renovation of existing continuous flow sewage treatment plants, etc.
6) It is very suitable for treating small water volumes, intermittent discharge of industrial wastewater and the treatment of scattered point source pollution.
SBR design key points and main parameters
SBR design key points
1. Determination of the operating cycle (T)
SBR operating cycle It is determined by water filling time, reaction time, sedimentation time, drainage time and idle time. The water filling time (tv) should have an optimal value. As mentioned above, the water filling time should be determined according to the specific water quality and the aeration method used during operation. When limited aeration is used and the concentration of pollutants in the incoming water is high, the water filling time should be appropriately longer; when non-limited aeration is used and the concentration of pollutants in the incoming water is low, the water filling time can be Make it shorter as appropriate. The water filling time is generally 1 to 4 hours. Reaction time (tR) is a very important process design parameter for determining the volume of the SBR reactor. The determination of its value also depends on factors such as the nature of the sewage during operation, the concentration of sludge in the reactor, and the aeration method. For easy-to-treat wastewater such as domestic sewage, the reaction time can be shorter. On the contrary, for wastewater containing refractory substances or toxic substances, the reaction time can be appropriately longer. Generally within 2 to 8 hours.
The sedimentation drainage time (tS+D) is generally designed as 2 to 4 hours. The idle time (tE) is generally designed as 2h. The time required for one cycle tC≥tR+tS+tD, the number of cycles n=24/tC
2. Calculation of reaction tank volume
Assuming that the amount of sewage in each series is q, then in each series The amount of sewage entering each reaction tank in one cycle is q/n·N. The volume of each reaction tank is:
V: The capacity of each reaction tank
1/m: Discharge ratio
n: Number of cycles (cycles/d)
N: The number of reaction tanks in each series
q: The sewage inlet volume of each series (designed maximum daily sewage volume) (m3/d)
3. Aeration system
In the sequential batch activated sludge process, the capacity of the aeration device should be the oxygen demand that can be supplied within the specified aeration time. In the design, high-load operation The BOD of water inlet per unit is 0.5~1.5kgO2/kgBOD, and it is 1.5~2.5kgO2/kgBOD during low load operation.
In the sequential batch activated sludge method, since the aeration and sedimentation of activated sludge are carried out in the same reaction tank, the aeration device must be difficult to block, and the mixing performance of the reaction tank must be taken into consideration. Commonly used aeration systems include gas-liquid mixed jet type, mechanical stirring type, perforated aeration pipe, and microporous aerator. Jet aeration is generally selected because it has a mixing effect when not aerated and avoids clogging.
4. Drainage system
⑴The supernatant discharge device should be able to discharge the supernatant liquid within the set drainage time without the activated sludge floating. The methods include gravity discharge and water pump discharge.
⑵ In order to prevent the failure of the supernatant discharge device, an accident drainage device should be installed.
⑶ The supernatant liquid discharge device should be equipped with a mechanism to prevent scum from flowing out.
The sequential batch activated sludge discharge device should discharge the supernatant separated from the activated sludge during the sedimentation and drainage period, and have the following characteristics:
1) It should be able to It neither disturbs the settled sludge nor makes the sludge float, and discharges the supernatant liquid according to the specified flow rate. (Quantitative drainage)
2) In order to obtain clear treated water after separation, the water collection mechanism should be as close to the water surface as possible and can drain as the water level changes after the supernatant is discharged. (Performance of following water level)
3) The actions of draining and stopping drainage should be smooth, accurate, and durable. (Reliability)
The structural form of the drainage device, depending on the way of lifting, includes float type, mechanical type and fixed type without lifting.
5. Sludge discharge equipment
Designed sludge dry solid volume = designed sewage volume The sludge production is calculated as 1 kg per inflow of 1 kg of SS when 0.4 kg-BOD/kg-ss·d), and calculated as 1 kg of sludge per inflow of 1 kg of SS during low load operation (0.03~0.1 kg-BOD/kg-ss·d). 0.75 kg calculation.
A simple sludge concentration tank is installed in the reaction tank to obtain 2 to 3% concentrated sludge. Since the sequential batch activated sludge method does not have a primary sedimentation tank, it is easy for more debris to flow into the sludge pump, so the sludge pump should be of a pump type that is not easy to clog.
Main parameters of SBR design
The design parameters of the sequential batch activated sludge process must consider the regional characteristics and design conditions of the treatment plant (land area, maintenance management, treatment water quality indicators, etc. ) appropriate determination.
The design parameters used for facility design should be based on the following values:
Project parameters
BOD-SS load (kg-BOD/kg-ss·d ) 0.03～0.4
MLSS (mg/l) 1500～5000
Discharge ratio (1/m) 1/2～1/6
Safety height ε (cm) (minimum water depth above the activated sludge interface) 50 or more
The sequential batch activated sludge method is a method that varies from low load (equivalent to oxidation ditch method) to This method can be operated within the range of high load (equivalent to standard activated sludge method).
The BOD-SS load of the sequential batch activated sludge process is considered as the reaction time, so the definition formula is as follows:
QS: sewage inlet volume (m3/d)
< p>CS: Average BOD5 of the incoming water (mg/l)CA: Average MLSS concentration of the mixed liquid in the aeration tank (mg/l)
V: Aeration tank volume< /p>
e: Aeration time ratio e=n·TA/24
n: Number of cycles TA: Aeration time of one cycle
Sequential batch activated wastewater The load conditions of the sludge process are determined based on the ratio of the reaction tank volume to the sewage inlet volume and the number of daily cycles in each cycle. In addition, in the sequential batch activated sludge process, it is easy to maintain good MLSS in the tank. concentration, so through changes in MLSS concentration, the organic matter load can also be adjusted. Furthermore, since the aeration time is easy to adjust, the organic matter load can also be adjusted by changing the aeration time.
When denitrification and desulfurization are targeted, in addition to the organic matter load, the discharge ratio, number of cycles, daily aeration time, etc. must also be studied.
In facilities with limited land area, it is suitable for high-load operation. In small-scale facilities with small water inlet flow and large load changes, it is best to operate at low load. Therefore, the effective way is to operate at low load in the initial stage of production, and as the water volume increases, it can also be operated at high load.
Characteristics under different load conditions
Organic matter load conditions (water inlet conditions) High load operation, low load operation
Intermittent water inlet, intermittent water inlet, continuous< /p>
Operating conditions BOD-SS load (kg-BOD/kg-ss·d) 0.1～0.4 0.03～0.1
Number of cycles is large (3～4) small (2～3)
Discharge ratio
Treatment characteristics: Organic matter removal treatment water BOD<20mg/l, relatively high removal rate
Denitrification is low and high
High dephosphorization is lower
How much sludge is produced
Maintenance and management resistance to load changes is better than low load difference. It has stronger adaptability to load changes and greater operational flexibility
The land area of ??the reaction tank is small, and the space-saving reaction tank has a large volume
The scope of application can effectively treat sewage of medium scale or above, and is suitable for facilities with a treatment scale of about 2000m3/d or more. In small sewage treatment plants, the treatment scale is about 2000m3/d or less, which is suitable for facilities that do not require denitrification
Problems that require special attention in SBR design
(1) Main facilities and Equipment
1. Composition of facilities
In principle, this method does not include a primary sedimentation tank. The main reason why this method is applied to small sewage treatment plants is that the facilities are relatively simple and the maintenance and management are relatively centralized. . In order to adapt to changes in flow rate, the volume of the reaction tank should be left with a margin or methods such as setting the operating cycle should be adopted. However, for places where traffic changes greatly, such as tourist destinations, the setting of the flow adjustment pool should be studied based on maintenance management and economic conditions.
2. Reaction pool
The reaction pool is a completely mixed type. The reaction pool is very compact and occupies very little space. The shape is rectangular, the ratio of pool width to pool length is approximately 1:1 to 1:2, and the water depth is 4 to 6 meters.
If the water depth of the reaction tank is too deep, it is uneconomical for the following reasons: ① If the water depth of the reaction tank is large and the depth of the discharged water increases accordingly, the settling time required for solid-liquid separation will increase. ②The dedicated supernatant discharge device is subject to structural limitations, and the depth of the supernatant discharge water cannot be too deep.
It is undesirable for the reaction tank water depth to be too shallow for the following reasons: ① During the drainage period, due to the restriction of the minimum water depth above the activated sludge interface, the depth of supernatant discharge cannot be too deep. ② Compared with other treatment methods with the same BOD-SS load, the advantage is that it requires less land area.
The number of reaction tanks, taking into account cleaning and maintenance, should be set at least 2 in principle. When the scale is small or the amount of sewage is small in the initial stage of production, a pool can also be built.
3. Drainage device
The drainage system is an important part of the SBR treatment process design. It is also the most distinctive part of its design and a key part related to the success or failure of the system operation.
At present, the SBR drainage devices reported at home and abroad can be roughly summarized into the following categories: (1) Submersible pump single-point or multi-point drainage. This method consumes a lot of power and is easy to suck out the settled sludge; ⑵ There are multiple fixed valves at the end (side) of the tank for drainage, and the valves are opened from top to bottom. Disadvantages: It is inconvenient to operate, and drainage is easy to bring mud; (3) Special equipment decanter. The decanter is a water outlet weir that can be adjusted as the water level changes. The outlet is submerged under the water to a certain depth to prevent scum from entering. The ideal drainage device should meet the following conditions: ① The water output per unit time is large, the flow rate is small, and the settled sludge will not be turned up again; ② The water collection port decreases with the water level, and the static sedimentation state during the reaction is always maintained during drainage; ③The drainage equipment is sturdy and durable, and the drainage volume can be adjusted steplessly, with a high degree of automation.
When setting the drainage time of a cycle, you must pay attention to the following items:
①The overflow load of the supernatant discharge device - determine the number of equipment required;
②The minimum water depth at the activated sludge interface - mainly to prevent sludge from floating, is determined by the supernatant discharge device and overflow load. In terms of performance, the water depth should be as small as possible;
③As the overflow load of the supernatant discharge device increases, the discharge volume of treated water per unit time increases, which can shorten the drainage time, and the corresponding capacity of the subsequent treatment structure must be expanded;
④ In drainage During this period, the floating of precipitated activated sludge occurs when drainage is about to end. Drainage starting from the middle of the sedimentation process is in line with the operating principle of the SBR method.
Aerobic demand and oxygen supply in the SBR process
The degradation rules of organic matter in the SBR process are similar to those of the push-flow aeration tank. The push-flow aeration tank is spatially (length) Push flow, while the SBR reaction tank is a push flow in a time sense. Since the concentration of organic matter in the SBR process changes gradually, in the early stage of the reaction, the concentration of organic matter in the pool is relatively high. If the oxygen supply rate is less than the oxygen consumption rate, the dissolved oxygen in the mixed solution is zero. For a single microorganism, it is impossible to obtain oxygen. It is intermittent, and the oxygen supply rate determines the degradation rate of organic matter. As the aerobic process progresses, the concentration of organic matter decreases, the oxygen supply rate begins to be greater than the oxygen consumption rate, dissolved oxygen begins to appear, and microorganisms begin to receive sufficient oxygen supply. The level of organic matter concentration becomes an important factor affecting the degradation rate of organic matter. From the perspective of the relationship between oxygen consumption and oxygen supply, maintaining sufficient oxygen supply in the SBR reaction tank in the early stages of the reaction can increase the degradation rate of organic matter. With the emergence of dissolved oxygen, gradually reducing the oxygen supply can save operating costs and shorten the reaction time. time. Through the design of the aeration system, the SBR reaction tank adopts gradually decreasing aeration, which is more economical and reasonable.
Selection of SBR process discharge ratio (1/m)
The SBR process discharge ratio (1/m) determines the concentration of organic matter in the early stage of the SBR process reaction. The discharge ratio is small, and the initial organic matter concentration is low, and vice versa. According to the law of microbial degradation of organic matter, when the concentration of organic matter is high, the degradation rate of organic matter is large and the aeration time can be reduced. However, when the concentration of organic matter is high, the oxygen consumption rate is also high, and the conflict between oxygen supply and oxygen consumption may be greater. In addition, the settling properties of different wastewater activated sludges are also different. If the sludge settling performance is good, there will be more supernatant liquid after settling, so a smaller discharge ratio should be selected, otherwise a larger discharge ratio should be used. The choice of discharge ratio is also related to the sludge loading rate and mixed liquid sludge concentration selected in the design.
SBR reaction tank mixed liquid sludge concentration
According to the basic principle of the activated sludge method, the mixed liquid sludge concentration determines the size of the biochemical reactor volume. The same is true for the SBR process. When the mixed liquid sludge concentration is high, the required aeration reaction time is short and the SBR reaction tank capacity is small. On the contrary, the SBR reaction tank capacity is large. However, when the concentration of mixed liquid sludge is high, the oxygen consumption rate increases in the early stage of the biochemical reaction, and the contradiction between oxygen supply and oxygen consumption becomes greater. In addition, the concentration of mixed liquid sludge in the tank also determines the settling time. A high sludge concentration requires a long settling time, and vice versa. When the settling performance of the sludge is good, the discharge ratio is small, the concentration of organic matter is low, and the oxygen supply rate is high, a larger value can be selected, and vice versa, a smaller value should be selected. The selection of SBR process mixed liquor sludge concentration should be considered based on various factors.
About the selection of sludge loading rate
The sludge loading rate is the main parameter that affects the aeration reaction time. The size of the sludge loading rate is related to the final effluent organic concentration of the SBR reaction tank. of high or low.
When the required concentration of organic matter in the effluent is low, the sludge loading rate should be a low value; when the wastewater is easy to biodegrade, the sludge loading rate increases. The selection of sludge loading rate should be determined based on the biodegradability of wastewater and the required effluent quality.
The combination of SBR process with regulation and hydrolysis and acidification processes
The SBR process uses intermittent water inflow and intermittent drainage. The SBR reaction tank has a certain adjustment function, which can play a certain role in The role of balancing water quality and quantity. Through the design of the air supply system, the mixing system, the design of the automatic control method, and the selection of the idle period, the SBR process can be combined with the adjustment and hydrolysis and acidification processes, so that the three can be built together, thereby saving investment and operation and management costs. .
During the water inlet period, an underwater stirrer is used for stirring, and the water inlet electric valve is closed using liquid level control. The aeration start time is determined based on the time required for hydrolysis and acidification, and the adjustment, hydrolysis and acidification process is combined with SBR. Craftsmanship is organically combined. The start of water inflow into the reaction pool marks the end of the idle period so that the entire system can operate normally. The specific operation method is as follows:
The start of water inflow is the end of idle time, and is controlled by the end time of water inflow in the previous group of SBR pools;
The end of water inflow is controlled by the liquid level. The overall water intake time may vary.
The hydrolysis and acidification time starts from the water inlet to the aeration reaction, including the water inlet period. This period can be determined according to the changes in water volume and the required hydrolysis and acidification time. It should not be less than the time required to fill the tank at the minimum flow rate. The time required for the SBR reaction tank.
The aeration reaction starts when the hydrolysis, acidification and stirring end, and the aeration reaction time can be calculated based on the calculation.
The settling time is determined based on the sludge settling performance and the sludge concentration of the mixed liquid. Its beginning is the end of the aeration reaction.
The drainage time is determined by the performance of the decanter, and the end of decanting can be controlled by the liquid level.
The time selection of the idle period is the key to the combination of adjustment, hydrolysis, acidification and SBR processes. The length of the idle time should be determined according to the changes in wastewater. In actual operation, the idle time often changes. Through adjustments during the idle period, the water inlet of the SBR reaction pool is reasonably arranged so that the entire system can operate normally and avoid disorder in the entire operation process.
SBR debugging procedures and precautions
(1) Cultivation and domestication of activated sludge
The mechanism of organic matter removal in the SBR reaction tank is basically the same as that of the ordinary activated sludge method Similarly, the main mass-proliferating microbial groups degrade the organic matter in the sewage.
The first task of the activated sludge treatment system before it is officially put into production is to cultivate and domesticate the activated sludge. The cultivation and domestication of activated sludge can be summarized into asynchronous training, synchronous training and inoculation. The asynchronous method is to cultivate first and then domesticate, the synchronous method is to cultivate and domesticate at the same time or alternately, and the inoculation method uses other sewage treatment methods. The remaining sludge from the plant is then properly trained.
Cultivation of activated sludge requires bacteria and nutrients required by the bacteria. For urban sewage, the bacteria and nutrients are available and can be cultured directly. For industrial wastewater, due to the lack of specialized strains and sufficient nutrients, in addition to cultivating sufficient activated sludge with general strains and required nutrients when it is put into production, the cultivated activated sludge should also be domesticated so that The activated sludge microbial community gradually forms an enzyme system that metabolizes specific industrial wastewater and has certain specializations.
(2) Trial operation
After the activated sludge is cultured and acclimated, the trial operation will begin. The purpose of the trial run is to determine the best operating conditions.
In the operation of the activated sludge system, there are many influencing factors, such as mixed liquid sludge concentration, air volume, sewage volume, sewage nutrition, etc. The activated sludge method requires maintaining an appropriate ratio of nutrients to microorganisms in the aeration tank, supplying the required oxygen, allowing the microorganisms to be in good contact with organic matter, and maintaining an appropriate contact time uniformly throughout.
For the SBR treatment process, the determination of the operation cycle is also related to the sedimentation, drainage and sludge discharge time and idle time, as well as the number of SBR reactors designed in the treatment process. The determination of the operating cycle must not only ensure the stability of the operation and the treatment effect during the treatment process, but also ensure the continuity of the water filling sequence of each pool. That is, a reasonable operating cycle should meet the requirements to avoid two or more problems during the operation. The phenomenon of water entering the pool at the same time or the water entering the first pool and the last pool being disconnected.
At the same time, by changing the aeration time and drainage time, different reaction tests are conducted on the sewage to determine the best operation mode to achieve the best effluent quality and the most economical operation mode.
(3) Control of sludge settling performance
Good settling performance of activated sludge is one of the prerequisites to ensure the normal operation of the activated sludge treatment system. If the settling performance of the sludge is not good, it will be difficult for the sludge to settle after the reaction period of the SBR. The tightness of the sludge will be poor, and the removal of the supernatant liquid will be restricted. The cement ratio will decrease, resulting in the amount of sewage processed in each operation cycle. decline. If the flocculation performance of the sludge is poor, the suspended solids (SS) content in the effluent will increase and the COD will increase, resulting in a decrease in the quality of the treated effluent.
There are many reasons for the deterioration of sludge settling performance, but they are all reflected in the increase of sludge volume index (SVI). Due to the repeated presence of high-concentration substrates in the SBR process, in the ecological environment where colloidal bacteria and filamentous bacteria exist, filamentous bacteria are generally not easy to reproduce, so the possibility of expansion of sludge filamentous bacteria is Very low. SBR is more prone to high viscosity expansion problems. This may be because the SBR method is a transient process, and the matrix in the mixed liquid gradually degrades. The concentration of the matrix in the liquid phase decreases, but this does not completely indicate that the matrix has been oxidized and removed. In addition, many sewage pollutants are easily adsorbed by activated sludge. and absorption. In a short period of time, the matrix concentration in the mixed liquid can be reduced to a very low level. From the perspective of sewage treatment, the treatment effect has been achieved, but this is only a phase transfer. The reduction in matrix concentration is only a superficial phenomenon. It can be considered that during the sewage treatment process, the formation and growth of bacterial gel clusters requires the accumulation of a certain amount of organic matrix in the system to form polysaccharide polymers outside the cells (otherwise, the bacterial gel clusters will not grow or even bacteria will appear. Dispersed growth phenomenon, turbid water). In the actual operation process, excessive accumulation of substrate is often caused by improper selection of water filling time or aeration method or improper operation, resulting in high viscosity expansion of sludge.
The accumulation of pollutants in the mixed liquid is gradual and is generally difficult to manifest immediately within a cycle. It can only be manifested by observing the changes in sludge settling performance during each operating cycle. In order to ensure that the sludge has good settling performance, attention should be paid to the SVI change trend of the sludge during each operation cycle, and the operation mode should be adjusted in a timely manner to ensure good treatment effects.