(1) batch activated sludge process
Batch activated sludge process, also known as sequencing batch reactor -SBR, consists of one or more SBR tanks. During operation, wastewater enters each pool in batches and goes through five independent stages: water inflow, reaction, precipitation, drainage and idle. Water level control is adopted for water inflow and drainage, and time control is adopted for reaction and precipitation. The time of an operation cycle varies according to the load and effluent requirements, which is generally 4 ~ 12h, in which the reaction accounts for 40%, and the effective tank volume is the sum of the influent and the required sludge quantity in this cycle.
Compared with the continuous flow method, the reaction speed is faster, the treatment efficiency is higher and the load impact resistance is stronger; Because of the high concentration of substrate, large concentration gradient and alternating anoxic and aerobic States, it can inhibit the excessive reproduction of obligate aerobic bacteria and is beneficial to biological nitrogen and phosphorus removal. Moreover, due to the short age of sludge, filamentous bacteria can not become an advantage, so sludge is not easy to swell. Compared with continuous flow method, SBR method has the advantages of short process, simple equipment structure, only one batch reactor, no special sedimentation tank and regulating tank, no sludge reflux when the water volume is small, and low operating cost.
(2) Adsorption regeneration (contact stabilization) method
This method makes full use of the initial removal ability of activated sludge. In a short time (10 ~ 40 min), the suspended and colloidal organics in wastewater were removed by adsorption, and then the wastewater was purified by liquid-solid separation, and BOD5 could be removed by about 85% ~ 90%. Some saturated activated sludge that needs to be refluxed is introduced into the regeneration tank for further oxidative decomposition to restore its activity; The other part of the excess sludge is discharged into the sludge treatment system without oxidative decomposition.
In two tanks (adsorption tank and regeneration tank) or in two parts of the same tank. Strong adaptability to load impact, and can also save the primary sedimentation tank. The main advantage is that it can greatly save capital investment, and it is most suitable for treating wastewater containing more suspended substances and colloidal substances, such as tannery wastewater and coking wastewater, and 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 extended aeration method. Its plane is like a runway, and there are two rotating aeration brushes (disks) in the ditch. There are also surface aerators, ejectors or riser aerators. When the aeration equipment works, the ditch liquid is pushed to flow rapidly, so as to realize oxygen supply and stirring.
Compared with ordinary aeration method, oxidation ditch has the advantages of less capital investment, convenient maintenance and management, stable treatment effect, good effluent quality, less sludge output, good nitrogen and phosphorus removal effect and strong adaptability to load impact.
(4) Extended Aeration Activated Sludge Process (ICEAS) with continuous water inflow and periodic circulation.
There is a pre-reaction zone in the front of the ICEAS reactor (10% of the tank volume). The reaction tank is composed of a pre-reaction zone and a main reaction zone to realize continuous water inflow and intermittent drainage. The pre-reaction zone is generally in anaerobic and anoxic state, and organic matter is adsorbed by activated sludge. The area also has the functions of biological selection, inhibiting the growth of filamentous bacteria and preventing sludge bulking. The adsorbed organic matter is oxidized and decomposed by activated sludge in the main reaction zone.
Continuous water inflow in the reaction solved the contradiction between water inflow and intermittent water inflow. However, the sedimentation effect and purification effect of this process are poor, sludge bulking is easy to occur, sludge load is low, reaction time is long, equipment volume is increased, and investment is large.
(5) Biological nitrogen and phosphorus removal process (A/A/O)
Sewage first enters the anaerobic tank and is mixed with the returned sludge. Under the action of facultative anaerobic fermentation bacteria, the easily biodegradable macromolecular organic substances in sewage are transformed into phosphorus accumulating bacteria, which can absorb small molecular organic substances (such as VFA) and store them in the body in the form of PHB, and the energy required by them comes from the decomposition of phosphorus accumulating chains. Then, the wastewater enters the anoxic zone, and the denitrifying bacteria use the organic matrix in the wastewater to denitrify NO3- brought in with 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 PHB in vivo for bacterial proliferation. At the same time, they absorb the dissolved phosphorus in the surrounding environment into the body, store it in the form of phosphorus chain, and then discharge it from the system in the form of excess sludge. The low concentration of organic matter in the aerobic zone of the system is beneficial to the growth of autotrophic nitrifying bacteria in this zone.
Organic matter, nitrogen and phosphorus can be removed at the same time under three different environmental conditions: anaerobic, anoxic and aerobic, and with the organic cooperation of different kinds of microbial flora; Simple process and short hydraulic retention time; SVI is generally less than 100, and sludge bulking will not occur; The phosphorus content in sludge is high, generally above 2.5%; Anaerobic-anoxic tank only needs to be gently stirred and mixed without increasing dissolved oxygen; The sedimentation tank should avoid anaerobic-anoxic state, prevent phosphorus accumulating bacteria from releasing phosphorus, reduce the effluent quality, and denitrification will produce N2, which will interfere with sedimentation. The effect of nitrogen removal is affected by the reflux ratio of mixed liquor, while the effect of phosphorus removal is affected by DO and nitrate oxygen carried in the returned sludge, which cannot improve the effect of nitrogen and phosphorus removal.