Comparison of various activated sludge processes

Main Operation Modes of Activated Sludge Process

1. Various activated sludge processes

So far, in the field of activated sludge process engineering, a variety of unique operating methods have been applied. There are mainly the following: ① Traditional push flow activated sludge method; ② Completely mixed activated sludge method; ③ Stage aeration activated sludge method; ④ Adsorption-regeneration activated sludge method; ⑤ Delayed aerated activated sludge method ⑥ High load activated sludge method; ⑦ Pure oxygen aerated activated sludge method; ⑧ Shallow low pressure aerated activated sludge method; ⑨ Deep water aerated activated sludge method; ⑩ Deep well aerated activated sludge method.

1. Traditional push flow activated sludge method:

  1. Process flow:
  2. Supply and demand curve:
  3. Main advantages: 1) Good treatment effect: The removal rate of BOD5 can reach 90-95%; 2) The degree of wastewater treatment is more flexible and can be adjusted according to requirements.
  4. Main problems: 1) In order to avoid the anaerobic state at the head of the pool, it is not appropriate to use too high organic load, so the pool capacity is large and the area is large; 2) The oxygen supply rate may appear higher than the aerobic rate at the end The phenomenon of speed will waste the power cost; 3) The adaptability to shock load is weak.
  5. Generally used design parameters (treatment of urban sewage):

2. Completely mixed activated sludge method

  1. Main features: a. The organic matter degradation reaction in the reactor can be conveniently controlled by adjusting F / M conveniently; b. As soon as the water enters the aeration tank, it is immediately diluted by a large amount of mixed liquid. Therefore, it has a certain resistance to impact loads; c. It is suitable for treating higher concentrations of organic industrial wastewater.
  2. Main structural forms: a. Joint construction type (aerated sedimentation tank): b. Sub-construction type

3.Stage aeration activated sludge method-also known as staged activated sludge method or multi-point activated sludge method

  1. Process flow:
  2. Main features: a. Wastewater is injected into the aeration tank in sections along the length of the tank, and the load distribution of organic matter is more balanced, which improves the contradiction between the feeding rate and the aerobic rate and is beneficial to reducing energy consumption. Adaptability of aeration tank to impact load;
  3. Main design parameters:

4, adsorption regeneration activated sludge method-also known as biological adsorption method or contact stabilization method.

The main feature is that the two processes of degradation of organic pollutants by the activated sludge process-adsorption and metabolic stability-are carried out in their respective reactors.

  1. Process flow:
  2. Main advantages: a. The contact time of wastewater and activated sludge in the adsorption tank is short, the volume of the adsorption tank is small, and the regeneration tank only accepts the return sludge with a higher concentration, so the volume of the regeneration tank is also smaller. The sum of the volume of the adsorption tank and the regeneration tank is lower than the volume of the traditional method aeration tank, and the capital cost is low; b. It has a certain ability to withstand the impact load. When the activated sludge in the adsorption tank is damaged, it can be supplemented by the sludge in the regeneration tank.
  3. The main disadvantage: the treatment effect is lower than the traditional method, especially for the wastewater with a higher content of dissolved organic matter, the treatment effect is worse.
  4. Main design parameters:

5. Delayed aeration activated sludge method-complete oxidation activated sludge method

  1. Main features: a. The organic load rate is very low, the sludge is continuously in an endogenous metabolic state, and the remaining sludge is small and stable, and no further treatment is required; b. Treatment of effluent and effluent water has good stability and has strong adaptability to the impact load of wastewater; c. In some cases, it is not necessary to set up a primary sedimentation tank.
  2. The main disadvantages: Large tank capacity, long aeration time, high construction and operating costs, and large land area; generally suitable for small town sewage and industrial sewage with high water quality requirements, the water volume is generally below 1000m3 / d.
  3. Main design parameters:

6.High load activated sludge method-also known as short-time aeration method or incomplete aeration activated sludge method

  1. Main features: high organic load rate, short aeration time, and poor treatment effect; but it is basically the same as the traditional method in terms of process flow and aeration tank structure.
  2. Main design parameters:

7, pure oxygen aerated activated sludge method

① Main features:

a. The partial pressure of oxygen in pure oxygen is about 5 times higher than air. Pure oxygen aeration can greatly improve the efficiency of oxygen transfer;

b. The oxygen transfer rate can be increased to 80 ~ 90%, while the general blast aeration is only about 10%;

c. The activated sludge concentration in the aeration tank can be as high as 4000 ~ 7000mg / l, which can greatly increase the volume load of the aeration tank;

d. The remaining sludge production is small, and the SVI value is also low. Generally, there is no concern about sludge expansion.

② Structure of aeration tank:

③ Main design parameters:

8. Shallow low pressure aeration method

① Theoretical basis: Only at the moment when bubbles are formed and broken, the oxygen transfer rate is the highest, so there is no need to extend the rising distance of bubbles in water;

② The aeration device is generally installed at 0.8 ~ 0.9 meters underwater, so low pressure fans with a wind pressure of less than 1 meter can be used, and the power efficiency is high, which can reach 1.80 ~ 2.60kgO2 / kw.h;

③ its oxygen transfer rate is low, generally only 2.5%;

④ There is a deflector in the tank to make the mixed liquid flow in a circulating state.

9.Deepwater aerated activated sludge method

① Main features: a. The aeration tank water depth is more than 7 ~ 8m, b. Due to the large water pressure, the transfer rate of the ocean can be increased, and the degradation rate of organic matter can be accelerated accordingly;

② Generally there are two forms: a. Deep water aeration method: b. Deep water deep aeration method:

10.Deep well aeration activated sludge method-also known as ultra-deep water aeration method

① Process flow: Generally the plane is circular, the diameter is about 1 ~ 6m, and the depth is generally 50 ~ 150m.

② Main features: a. High oxygen transfer rate, about 10 times that of the conventional method; b. High power efficiency, small footprint, easy maintenance and operation; c. Impact resistance, low mud production; d. Establish a primary sedimentation tank; e. However, it is limited by geological conditions.

③ Main design parameters

Design parameters of various activated sludge processes (treatment of urban sewage, for reference only)

Design parameters Traditional activated sludge method Completely mixed activated sludge method Stage aeration activated sludge method

BOD5—SS load (kgBOD5 / kgMLSS.d) 0.2 ~ 0.4 0.2 ~ 0.6 0.2 ~ 0.4

Volume load (kgBOD5 / m3.d) 0.3 ~ 0.6 08 ~ 2.0 0.6 ~ 1.0

Sludge age (d) 5 ~ 15 5 ~ 15 5 ~ 15

MLSS (mg / l) 1500 ~ 3000 3000 ~ 6000 2000 ~ 3500

MLVSS (mg / l) 1200 ~ 2400 2400 ~ 4800 1600 ~ 2800

Reflow ratio (%) 25 ~ 50 25 ~ 100 25 ~ 75

Aeration time HRT (h) 4 ~ 8 3 ~ 5 3 ~ 8

BOD5 removal rate (%) 85 ~ 95 85 ~ 90 85 ~ 90

Design parameters Adsorption and regeneration activated sludge method Delayed aeration activated sludge method High load activated sludge method

BOD5—SS load (kgBOD5 / kgMLSS.d) 0.2 ~ 0.6 0.05 ~ 0.15 1.5 ~ 5.0

Volume load (kgBOD5 / m3.d) 1.0 ~ 1.2 0.1 ~ 0.4 1.2 ~ 2.4

Sludge age (d) 5 ~ 15 20 ~ 30 0.25 ~ 2.5

MLSS (mg / l) Adsorption pond 1000 ~ 3000 Regeneration pond 4000 ~ 10000 3000 ~ 6000 200 ~ 500

MLVSS (mg / l) Adsorption cell 800 ~ 2400 Regeneration cell 3200 ~ 8000 2400 ~ 4800 160 ~ 400

Reflow ratio (%) 25 ~ 100 75 ~ 100 5 ~ 15

Aeration time HRT (h) Adsorption tank 0.5 ~ 1.0 Regeneration tank 3 ~ 6 18 ~ 48 1.5 ~ 3.0

BOD5 removal rate (%) 80 ~ 90 95 60 ~ 75

Design parameters Pure aeration activated sludge method Deep well aeration activated sludge method

BOD5—SS load (kgBOD5 / kgMLSS.d) 0.4 ~ 1.0 1.0 ~ 1.2

Volume load (kgBOD5 / m3.d) 2.0 ~ 3.2 3.0 ~ 3.6

Sludge age (d) 5 ~ 15 5

MLSS (mg / l) 6000 ~ 10000 3000 ~ 5000

MLVSS (mg / l) 4000 ~ 6500 2400 ~ 4000

Reflow ratio (%) 25 ~ 50 40 ~ 80

Aeration time HRT (h) 1.5 ~ 3.0 1.0 ~ 2.0

DO (mg / l) 6 ~ 10

SVI (ml / g) 30 ~ 50

BOD5 removal rate (%) 75 ~ 95 85 ~ 90

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