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I. Intermittent activated sludge process (SBR)

Intermittent activated sludge process, also known as Sequencing Batch Reactor-SBR, consists of one or more SBR pools. When running, wastewater enters into the pool in batches, and goes through five independent stages in turn, i.e. water inflow, reaction, sedimentation, drainage and idle. Influent and drainage water level control, reaction and sedimentation time control, the time of a operation cycle varies according to load and effluent requirements, generally 4-12 hours, of which the reaction accounts for 40%, the effective tank volume is the sum of the water inflow and sludge volume required in the cycle.

Compared with the continuous flow method, the reaction speed is faster, the treatment efficiency is higher, and the ability to withstand the impact of load is stronger. Because of the high concentration of substrate, the gradient of concentration is larger, and the alternation of anoxic and aerobic conditions can inhibit the excessive reproduction of specific aerobic bacteria, which is conducive to biological denitrification and phosphorus removal. Because of the short mud age, filamentous bacteria can not be an advantage, so sludge is not easy to expand; Compared with the continuous flow method, SBR is not easy to The process is short and the device is simple. When the water volume is small, only one batch reactor is needed, no special sedimentation tank and regulating tank are needed, no sludge reflux is needed, and the operation cost is low.

2. Adsorption Regeneration (Contact Stabilization) Method

This method makes full use of the initial removal capacity of activated sludge. In a short time (10-40 minutes), suspended and colloidal organic matter in wastewater can be removed by adsorption, and then the wastewater can be purified by liquid-solid separation. BOD5 can be removed by about 85%-90%. Some of the activated sludge adsorbed saturated need to be refluxed. The regeneration tank is introduced to further oxidize and decompose to restore its activity. The other part of the excess sludge is discharged into the sludge treatment system without oxidative decomposition.

They are carried out in two pools (adsorption pool and regeneration pool) or in two sections of the same pool. It has a strong ability to adapt to load shock and can save the primary sedimentation tank. The main advantage is that it can greatly save capital investment and is most suitable for treating wastewater containing suspended and colloidal substances, such as tannery wastewater, coking wastewater and so on. The process is flexible. However, due to the short adsorption time, the treatment efficiency is not as high as that of the traditional method.

3. Oxidation ditch

Oxidation ditch is a special type of delayed aeration method. Its plane is like a runway. There are two rotating aeration brushes (discs) in the ditch. There are also surface aerator, jet or riser aerator. When the aeration equipment works, it promotes the ditch liquid to flow rapidly, and realizes the function of oxygen supply and stirring.

Compared with the conventional aeration method, the oxidation ditch has the advantages of less capital investment, easy maintenance and management, stable treatment effect, good effluent quality, less sludge output, better removal of N and P, and strong adaptability to load impact.

IV. Continuous Influent Cycle Delayed Aeration Activated Sludge Process (ICEAS)

There is a pre-reaction zone in the front of the ICEAS reactor (10% of the tank volume). The reactor consists of the pre-reaction zone and the main reaction zone, and realizes continuous water inflow and intermittent drainage. Pre-reaction zone is generally in anaerobic and anoxic state, where organic matter is adsorbed by activated sludge. It also has biological selectivity, inhibits filamentous bacteria growth and prevents sludge bulking. The adsorbed organic matter is oxidized and decomposed by activated sludge in the main reaction zone.

The incompatibility between the incoming water and the intermittent water was solved by continuous reaction. However, the process has poor sedimentation effect, poor purification effect, easy to produce sludge bulking, low sludge load, long reaction time, increased equipment volume and large investment.

Biological nitrogen and phosphorus removal process (A/A/O)

Sewage first enters anaerobic tank and mixes with reflux sludge. Under the action of facultative anaerobic fermentation bacteria, macromolecular organisms easily biodegradable in wastewater can be converted into phosphorus accumulating bacteria, which can absorb small molecular organisms (such as VFA) and store them in the form of PHB. The energy needed comes from the decomposition of phosphorus accumulating chain. Subsequently, the wastewater enters the anoxic zone, and denitrifying bacteria use the organic matrix in the wastewater to denitrify the NO3 - carried by the reflux mixture. When the wastewater enters the aerobic tank, the concentration of organic matter in the wastewater is low. Phosphorus accumulating bacteria mainly obtain energy by decomposing the PHB in the body for bacterial proliferation. At the same time, soluble phosphorus in the surrounding environment is absorbed into the body, stored in the form of phosphorus accumulating chain, and then discharged into the system in the form of excess sludge. The low concentration of organic matter in the aerobic zone of the system is conducive to the growth of autotrophic nitrifying bacteria in this area.

Anaerobic, anoxic and aerobic three different environmental conditions and the organic combination of different microbial flora can simultaneously remove organic matter and nitrogen and phosphorus; the process is simple and the hydraulic retention time is short; SVI is generally less than 100, and sludge bulking does not occur; phosphorus content in sludge is high, generally more than 2.5%; anaerobic-anoxic tank only needs gentle stirring to mix, but not to mix. Increasing dissolved oxygen concentration; avoiding anaerobic-anoxic state in sedimentation tank to avoid phosphorus accumulating bacteria releasing phosphorus and reducing effluent quality and denitrification producing N2 to interfere with precipitation; the effect of nitrogen removal is affected by the recirculation ratio of mixed liquor, while the effect of phosphorus removal is affected by DO and Nitric Oxygen in recirculating sludge, so the effect of nitrogen and phosphorus removal can not be improved.