What are the common sewage treatment processes?

1, traditional activated sludge process

2、A/O

A/O stands for anoxic/aerobic. Its advantage is that it not only degrades organic pollutants, but also has a certain function of nitrogen and phosphorus removal. It uses anaerobic hydrolysis technology as pretreatment of activated sludge, so A/O method is an improved activated sludge method.

Basic principle: In the A/O process, the first anoxic stage and the second aerobic stage are connected in series, the DO in the A stage is not more than 0.2mg/L, and the DO in the O stage is 2 ~ 4 mg/L.. In the anoxic stage, heterotrophic bacteria hydrolyze suspended pollutants such as starch, fiber, carbohydrate and soluble organic matter in sewage into organic acids, so that macromolecular organic matter is decomposed into micromolecule organic matter and insoluble organic matter is converted into soluble organic matter. When these products after anoxic hydrolysis enter the aerobic tank for aerobic treatment, the biodegradability of sewage is improved and the oxygen efficiency is improved. In the anoxic stage, heterotrophic bacteria ammoniate pollutants such as protein and fat (N in organic chain or amino in amino acid) and release ammonia (NH3 and NH4+). Under the condition of sufficient oxygen supply, the nitrification of autotrophic bacteria oxidizes NH3-N(NH4+) into NO3-, and returns to pool A through reflux control. Under anoxic conditions, denitrification of heterotrophic bacteria reduces NO3- to molecular nitrogen (N2).

Main process disadvantages: the anoxic tank is in front, and the organic carbon in the sewage is utilized by denitrifying bacteria, which can reduce the organic load of the subsequent aerobic tank, and the alkalinity produced by denitrification can compensate the demand for alkalinity in nitrification of aerobic tank. After aerobic treatment in anoxic tank, the residual organic pollutants in denitrification can be further removed and the effluent quality can be improved. The removal rate of BOD5 is higher than 90 ~ 95%, but the effect of nitrogen and phosphorus removal is a little poor, with nitrogen removal efficiency of 70 ~ 80% and phosphorus removal of only 20 ~ 30%. Nevertheless, because the A/O process is relatively simple and has its outstanding characteristics, it is still a widely used process. The process can also combine the anoxic tank and the aerobic tank into one, with a baffle in the middle, which reduces the project cost, so this form is conducive to the transformation of the existing plug-flow aeration tank.

Influencing factors: The operation of A/O process should be controlled not to cause sludge swelling and loss, and its organic matter degradation rate is high (90 ~ 95%), but its disadvantage is poor nitrogen and phosphorus removal effect. If the phosphorus concentration of raw sewage is

①MLSS should generally be above 3000mg/L, below which the nitrogen removal effect of A/O system is obviously reduced.

②TKN/MLSS load rate (tkn- Kjeldahl nitrogen refers to the sum of ammonia nitrogen and organic nitrogen in water): the load rate should be 0.05gTKN/(gMLSS? D) below.

③BOD5/MLSS loading rate: In the nitrification reaction, the main factor affecting nitrification is the existence and activity of nitrifying bacteria, because the minimum specific growth rate of autotrophic nitrifying bacteria is 0.21/d; The minimum specific proliferation rate of heterotrophic aerobic bacteria is 1.2/d, and the specific proliferation rate of the former is much smaller than that of the latter. In order to make nitrifying bacteria survive and dominate, the sludge age is required to be greater than 4.76 d; But for heterotrophic aerobic bacteria, the sludge age is only 0.8d d. In the traditional activated sludge process, because the sludge age is only 2 ~ 4 days, nitrifying bacteria can not survive and have an advantage, and can not complete the nitrification task.

In order to make nitrifying bacteria propagate well, it is necessary to increase MLSS concentration or increase the volume of aeration tank to reduce the organic load and increase the sludge age. Sludge loading rate (BOD5/MLSS) should be less than 0. 18KgBOD5/KgMLSS? d

④ Mud age ts: In order to keep a sufficient number of nitrifying bacteria in the nitrification tank to ensure the smooth nitrification, the mud age should be determined as 3 times of the generation time of nitrifying bacteria, and the average generation time of nitrifying bacteria is about 3.3d(20℃).

If the winter water temperature is 10℃ and the generation time of nitrifying bacteria is 10d, the design sludge age should be 30d.

⑤ Total nitrogen concentration of sewage inflow: TN should be less than 30 mg/L. Excessive NH3-N concentration will inhibit the growth of nitrifying bacteria and reduce the denitrification rate to below 50%.

⑥ The reflux ratio of mixed liquid: R directly affects the denitrification effect. With the increase of R, the denitrification rate increases, but with the increase of R, the power consumption and operating cost increase.

⑦ bo D5/ NOx-N N N ratio in anoxic tank: H>4 ensures sufficient C/N ratio, otherwise the denitrification rate will decrease rapidly; However, when entering the nitrification tank, the BOD5 value should be controlled below 80 mg/L. When the BOD5 concentration is too high, heterotrophic bacteria multiply rapidly, inhibiting the growth of autotrophic bacteria and stopping the nitrification reaction.

⑧ Dissolved oxygen in the nitrification tank: DO>2 mg/L, generally sufficient oxygen supply DO should be kept at 2 ~ 4 mg/L to meet the requirements of nitrification oxygen demand. According to calculation, oxidation of 1gNH4+ requires 4.57g of oxygen.

⑨ hydraulic retention time: hydraulic retention time of nitrification reaction >: 6h; The hydraulic retention time of denitrification is 2 hours, and the ratio of the two is 3: 1, otherwise the denitrification efficiency will decrease rapidly.

⑩PH: HNO3 _ 3 produced during nitrification reduces the PH of the mixed solution, while nitrifying bacteria are very sensitive to pH, and the optimum pH for nitrification is 8.0 ~ 8.4. In order to keep proper pH value, corresponding measures should be taken. According to calculation, the alkalinity of complete nitrification of 1g ammonia nitrogen (NH3-N) is about 7. 1g (calculated by CaCO3). The alkalinity (3.75g alkalinity /GNOX-N) produced during denitrification can compensate about half of the alkalinity consumed by nitrification. The optimum pH for denitrification is 6.5 ~ 7.5, and should not be greater than 8 or less than 7.

○ 1 1 temperature: the nitration reaction is 20 ~ 30℃, and it almost stops below 5℃; Denitrification is carried out at 20 ~ 40℃, and the denitrification rate decreases rapidly below 65438 05℃.

Therefore, measures should be taken to maintain the denitrification rate in winter, such as increasing the age of denitrification sludge ts, reducing the load rate and increasing the hydraulic retention time.

3、A2/O

A2O method, also called AAO method, is the abbreviation of the first letter anaerobic-anoxic-aerobic (anaerobic-anoxic-aerobic method). It is a commonly used secondary sewage treatment process, which can be used for secondary sewage treatment or tertiary sewage treatment and reclaimed water reuse, and has good nitrogen and phosphorus removal effect. This method was developed by some American experts on the basis of AO process in 1970s.

The function of each reactor unit

1. Anaerobic reactor. Raw sewage and phosphorus-containing sludge discharged from the sedimentation tank enter simultaneously. The main function of the reactor is to release phosphorus and ammoniate some organic matter at the same time.

2, anoxic reactor, the primary function is to remove nitrogen, nitrate nitrogen is sent by aerobic reactor through internal circulation, and the circulating mixed liquid volume is large, generally 2Q(Q is the raw sewage flow);

3. Aerobic reactor-aeration tank. This reaction unit is multifunctional. BOD removal, nitrification and phosphorus absorption are all carried out here. The mixed liquid with the flow rate of 2Q flows back to the anoxic reactor from here.

4. Sedimentation tank, which is used to separate mud from water. Part of the sludge flows back to the anaerobic reactor, and the supernatant is discharged as treated water.

technical characteristics

1, which is the simplest simultaneous nitrogen and phosphorus removal process in the system, and the total hydraulic retention time is less than other processes;

2. Under the condition of anaerobic (anoxic) and aerobic alternate operation, filamentous bacteria can't proliferate in large quantities, and filamentous bulking of sludge is not easy to occur, and the SVI value is generally less than100;

3. The sludge has high phosphorus content and high fertilizer efficiency;

4. During operation, there is no need to add chemicals, only two sections A need to be gently stirred, which will not increase dissolved oxygen, and the operation cost is low;

Existing problems to be solved:

1, the phosphorus removal effect is difficult to improve, and the sludge growth is limited, especially when the P/BOD value is high;

2. It is difficult to further improve the denitrification effect, and the internal circulation is generally limited to 2Q, which should not be too high;

3. The treated water entering the sedimentation tank should maintain a certain dissolved oxygen concentration, reduce the residence time, and prevent anaerobic state and phosphorus release from sludge, but the dissolved oxygen concentration should not be too high, so as to prevent the circulating mixed liquid from interfering with the anoxic reactor.

4. Styrene butadiene rubber

Intermittent activated sludge process is a kind of activated sludge wastewater treatment technology with intermittent aeration according to time.

superiority

1. The ideal plug-flow process increases the driving force and efficiency of biochemical reaction, and anaerobic and aerobic conditions in the tank are in alternating state, so the purification effect is good.

2, the operation effect is stable, the sewage is precipitated in an ideal static state, the required time is short, the efficiency is high, and the effluent quality is good.

3. Impact load resistance. There is stagnant treated water in the pool, which can dilute the buffered sewage and effectively resist the impact of water quantity and organic pollutants.

4. Each process in the process can be adjusted according to the water quality and quantity, and the operation is flexible.

5. Less processing equipment, simple structure and convenient operation, maintenance and management.

6. The concentration gradient of DO and BOD5 exists in the reaction tank, which effectively controls the expansion of activated sludge.

7.SBR system itself is also suitable for combined construction, which is beneficial to the expansion and transformation of sewage treatment plant.

8. Nitrogen and phosphorus removal, properly control the operation mode, realize the alternation of aerobic, anoxic and anaerobic states, and have good nitrogen and phosphorus removal effect.

9. Simple process and low cost. There is only one sequencing batch batch reactor as the main equipment, and there is no secondary sedimentation tank and sludge reflux system, and the regulating tank and primary sedimentation tank can also be omitted, so the layout is compact and the occupied area is saved.

Insufficient:

1, which requires high automatic control.

2. The drainage time is short (intermittent drainage), and it is required not to stir the precipitated sludge layer during drainage, so special drainage equipment (decanter) is needed, and the requirements for decanter are very high.

3. There are many requirements for post-treatment equipment: if the disinfection equipment is large, the contact pool volume is also large, and drainage facilities such as drainage pipes are also large.

4. The decanting depth is generally 1~2m, which wastes the head loss and increases the total lift.

5. Because there is no primary sedimentation tank, scum is easy to appear, and the problem of scum has not been properly solved.

craftsmanship

Due to the above technical characteristics, SBR system further broadens the application scope of activated sludge process. As far as the current technical conditions are concerned, SBR system is more suitable for the following situations:

1) Domestic sewage from small and medium-sized towns and industrial wastewater from factories and mines, especially in places with intermittent discharge and large flow changes.

2) Places with better water quality than Gao Quan, such as scenic spots, lakes and harbors, should not only remove organic matter, but also remove phosphorus and nitrogen from water to prevent eutrophication of rivers and lakes.

3) Where water resources are scarce. SBR system can carry out physical and chemical treatment after biological treatment without increasing facilities, which is convenient for water recycling.

4) Where land is scarce.

5) Transform the existing continuous flow sewage treatment plant, etc.

6) It is very suitable for treating industrial wastewater with small amount of water and intermittent discharge and scattered point source pollution.

5. Cass

The reactor of SBR was divided into two parts along the length direction by circulating activated sludge method. The former part is the biological selection area, also called the pre-reaction area, and the latter part is the main reaction area. A lifting decanter device is installed at the back of the main reaction zone to realize the periodic circulation operation of continuous water inflow and intermittent drainage, integrating aeration, sedimentation and drainage.

6. Oxidation ditch

Characterized in that the mixed liquid continuously circulates in the ditch to form anaerobic, anoxic and aerobic sections.

Second, the biofilm method

1, contact biological method

Contact biological method is a new type of wastewater biochemical treatment method with the characteristics of activated sludge method and biofilm method. The main equipment of this method is biological contact oxidation filter. The closed aeration tank is filled with fillers such as coke, gravel and plastic honeycomb. The filler is submerged by water, and the bottom of the filler is aerated and oxygenated by a blower.

2. Membrane bioreactor

It is a new water treatment technology that combines membrane separation unit and biological treatment unit.

Third, anaerobic.

Anaerobic biological treatment takes advantage of the metabolic characteristics of anaerobic microorganisms, takes the reduced organic matter as hydrogen acceptor and produces methane gas with energy value without providing external energy.

1, septic tank

2、UASB

3. Integrated circuit internal circulation reactor

Fourth, advanced treatment.

On the basis of primary and secondary treatment, further treatment of refractory organic matter, phosphorus and nitrogen and other nutrients. It mainly includes filtration and disinfection.

I hope I can help you.