The most complete sewage treatment process introduction

4. High idle rate of equipment;

5. Sewage lifting head loss is greater.

CASS process

CASS process is called circulating activated sludge process. Based on the sequencing batch activated sludge method (SBR), the reaction tank is designed into two parts along the long direction of the tank, the front is the biological selection area, also known as the pre-reaction area, the back is the main reaction area, and the rear of the main reaction area is installed with an automatic skimming device. The whole process of aeration, precipitation, drainage and other processes in the same tank cycle cycle, eliminating the conventional activated sludge method of secondary sedimentation tank and sludge return system; At the same time can be continuous water, intermittent drainage.

Process flow:

1. Aeration stage: The aeration device is used to oxygenate the reaction tank. At this time, organic pollutants are oxidized and decomposed by microorganisms, and NH3-N in sewage is converted to NO3--N through the nitrification of microorganisms.

2. Precipitation stage: aeration is stopped at this time, and microorganisms use the remaining DO in the water for oxidative decomposition. The reaction tank gradually changed from aerobic state to anoxic state, and began to conduct denitrification reaction. Activated sludge gradually sinks to the bottom of the pool, and the upper water becomes clear.

3. Decanting stage: After the precipitation is over, the decanter placed at the end of the reaction tank begins to work and gradually drains the supernatant from top to bottom. At this time, the reaction pond gradually transitioned to an anaerobic state to continue denitrification.

4. Idle stage: Idle stage is the stage when the decanter rises to the original position.

CASS process advantages:

1. Simple process, small footprint, low investment, low operating costs

2. The driving force of biochemical reaction is large

3. Good precipitation effect

4. Flexible operation, strong impact resistance

5. It is not easy to cause sludge swelling

6. Wide range of application, suitable for phased construction

7. Low sludge yield and stable sludge properties

CASS process disadvantages:

1. The complex relationship between microbial populations remains to be studied

2. Biological nitrogen removal efficiency is difficult to improve

3. Phosphorus removal efficiency is difficult to improve

4. Single control mode

AO process

A/O process: The sewage through anaerobic, aerobic two biological treatment processes (referred to as A/O), to achieve the purpose of removing BOD, nitrogen and phosphorus at the same time.

A/O process advantages:

1. High efficiency

2. Simple process, investment saving, low operating costs

3. The anaerobic denitrification process has a high degradation efficiency for pollutants

4. High volume load

5. Anoxic/aerobic process has strong load impact resistance

A/O process disadvantages:

1. Because there is no independent sludge return system, sludge with unique functions cannot be cultivated, and the degradation rate of refractory substances is low

2. In order to improve the efficiency of nitrogen removal, the internal circulation ratio must be increased, thus increasing the operating cost

AAO process

A2/O sewage treatment system: The sewage through anaerobic, anaerobic and aerobic three biological treatment processes (referred to as A2/O), to achieve the purpose of removing BOD, nitrogen and phosphorus at the same time.

A2/O process advantages:

1 High pollutant removal efficiency, stable operation, good impact load resistance.

2. Good sludge settling performance.

3. The organic combination of anaerobic, anoxic and aerobic environmental conditions and different types of microbial flora can simultaneously remove organic matter, nitrogen and phosphorus.

4. The nitrogen removal effect is affected by the reflux ratio of the mixed liquid, and the phosphorus removal effect is affected by the inclusion of DO and nitric acid oxygen in the reflux sludge, so the nitrogen and phosphorus removal efficiency cannot be very high.

5. In the process of deoxygenation and phosphorus removal of organic matter at the same time, the process is the simplest, and the total hydraulic residence time is less than other similar processes.

6. Under the anaerobic - anoxic - aerobic alternating operation, filamentous bacteria will not multiply, SVI is generally less than 100, and sludge swelling will not occur

7. The phosphorus content in sludge is high, generally more than 2.5%

A2/O process disadvantages:

1. The volume of the reaction tank is larger than that of the A/O nitrogen removal process

2. The sludge internal return flow is large and the energy consumption is high

3. High cost for small and medium-sized sewage plants

4. The economic efficiency of biogas recycling is poor

5. The sludge exudate needs chemical phosphorus removal

Oxidation ditch process

Oxidation ditch: It is an improved activated sludge method, and its aeration tank is a closed ditch shape, in which the sewage and activated sludge mixture flow, so it is called "oxidation ditch", also known as "ring aeration tank".

The oxidation ditch HRT and SRT are longer, organic matter can be removed more thoroughly, the discharged sludge has been highly stable, the overall power density is low, and energy saving. However, it is easy to cause problems such as sludge swelling, uneven flow rate, sludge deposition, foam and sludge floating.