Sewage treatment is divided into the following technologies
1, adsorption regeneration (contact stability) method
This way to make full use of the initial removal capacity of activated sludge, in a short time (10~40min), by adsorption removal of suspended and colloidal organic matter in wastewater, and then through liquid-solid separation, wastewater purification, BOD5 can remove about 85%~90%. Adsorption saturated activated sludge, part of the need to reflux, into the regeneration tank for further oxidation and decomposition, restore its activity; The other part of the surplus sludge is discharged into the sludge treatment system without oxidation decomposition.
Either in two pools (adsorption and regeneration) or in two sections of the same pool. It has strong ability to adapt to load impact and can also save the initial sedimentation tank. The main advantage is that it can greatly save capital construction investment and is suitable for the treatment of wastewater containing suspended and colloidal substances, such as tanning wastewater, coking wastewater, etc., with flexible process. However, due to the short adsorption time, the treatment efficiency is not as high as the traditional method.
2, biological nitrogen and phosphorus removal process (A/A/O)
The wastewater first enters the anaerobic tank and is mixed with the reflux sludge. Under the action of facultative anaerobic fermentation bacteria, the biodegradable macromolecular organic matter in the wastewater is transformed into phosphorous accumulating bacteria, which can absorb small molecular organic matter (such as VFA) and store it in the body in the form of PHB. The energy required comes from the decomposition of phosphorous accumulating chain. Then, the wastewater enters the anoxic zone, and denitrifying bacteria use the organic matrix in the wastewater to denitrify the 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 the PHB in the body for bacterial proliferation, and absorb the dissolved phosphorus in the surrounding environment into the body, and store it in the form of phosphorus accumulating chain, and then discharge the system in the form of surplus sludge. The concentration of organic matter in the aerobic zone of the system is low, which is favorable to the growth of autotrophic nitrifying bacteria.
Anaerobic, anoxic, aerobic three different environmental conditions and different kinds of microbial flora organic coordination, can simultaneously have the function of removing organic matter, nitrogen and phosphorus; Simple process, short hydraulic retention time; SVI is generally less than 100, and sludge bulking does not occur. Sludge phosphorus content is high, generally more than 2.5%; The anaerobic-anoxic tank only needs to be gently stirred to mix without increasing dissolved oxygen; The anaerobic-anoxic state should be avoided in the sedimentation tank to avoid the release of phosphorus by phosphorus accumulating bacteria, which would reduce the effluent quality and denitrify N2, which would interfere with precipitation. The effect of nitrogen removal is affected by the reflux ratio of mixed liquid, and the effect of phosphorus removal is affected by DO and nitric oxygen in the reflux sludge, so the effect of nitrogen removal and phosphorus removal cannot be improved.
3. Batch activated sludge process (SBR)
Sequencing Batch reactor-SBR method is also called Sequencing Batch reactor-SBR method. It consists of one or more SBR tanks. During operation, wastewater enters into the tank in batches and goes through 5 independent stages successively, namely influent, reaction, precipitation, drainage and idle. The water level for water intake and drainage is controlled, and the time for reaction and precipitation is controlled. The time of a running cycle varies according to the load and effluent requirements, generally 4-12h, in which reaction accounts for 40%. The effective pool volume is the sum of the water intake and sludge volume required within the cycle.
Compared with the continuous flow method, the reaction speed is faster, the processing efficiency is higher, and the ability to withstand the impact of load is strong. Due to the high substrate concentration and large concentration gradient, the state of hypoxia and aerobic occurs in turn, which can inhibit the excessive reproduction of obligate aerobic bacteria and is conducive to biological nitrogen and phosphorus removal. Moreover, due to the short mud age, filamentous bacteria cannot become the dominant, so the sludge is not easy to expand. Compared with the continuous flow method, THE SBR method has the advantages of short process and simple device structure. When the water quantity is small, only one intermittent reactor is required, no special sedimentation tank and regulating tank is required, no sludge reflux is required, and the operation cost is low.
4. Continuous influent cyclic delay aeration activated sludge method (ICEAS)
A pre-reaction zone (10% of the tank volume) is located at the front of the ICEAS reactor. The reaction pool is composed of the pre-reaction area and the main reaction area, and the realization of continuous water, intermittent drainage. The pre-reaction zone is generally in anaerobic and anoxic states, where organic matter is adsorbed by activated sludge. The zone also has a biological selection effect, which inhibits the growth of filament-like bacteria and prevents sludge bulking. The adsorbed organic matter is oxidized and decomposed by activated sludge in the main reaction zone.
The contradiction between water inflow and intermittent water inflow is solved. However, this process has poor precipitation effect, poor purification effect, prone to sludge bulking, low sludge load, long reaction time, equipment volume increase, large investment.
5, oxidation ditch
Oxidation ditch is a special type of delayed aeration method. Its plane is like a runway, and two aeration swivel brushes (disk) are arranged in the groove. It is also useful for surface aerator, jet or riser tube aeration device. When the aeration equipment is working, it promotes the rapid flow of ditch liquid to realize oxygen supply and stirring.
Compared with the common aeration method, oxidation ditch has the advantages of less capital construction investment, easy maintenance and management, stable treatment effect, good effluent water quality, less sludge yield, better removal of N and P, and strong ability to adapt to load impact.