Process flow:
Water inflow → (adding demulsifier, flocculant and coagulant aid) → air flotation tank → biochemical reaction tank (CASS process can be adopted) → sedimentation tank → water outlet.
1.CASS process, also known as circulating activated sludge process, refers to a charging-discharging intermittent activated sludge treatment process equipped with a variable volume biological selector and operated in a sequencing batch aeration-non-aeration mode, which completes the treatment functions of biodegradation of organic pollutants and mud-water separation in a reactor. Its predecessor was the ICEAS process, both of which were developed by Professor Goronszy of the United States and patented in the United States and Canada respectively. CASS tank is a batch reactor, in which the activated sludge process repeatedly combines the biological reaction process and the sludge-water separation process in a tank according to the aeration-non-aeration stage, so it is an updated variant of SBR process and ICEAS process. With the increasing popularity of computers, CASS process has attracted more and more attention because of its low investment, low operating cost and high treatment efficiency, especially its excellent nitrogen and phosphorus removal function. This process has been widely used in the treatment of urban sewage and various industrial wastewater. At present, there are more than 400 CASS sewage treatment plants in operation or under construction in the world. ]
2. The reactor of CASS process is mainly composed of biological selection zone and main reaction zone. According to actual needs, it can also be arranged in front of the main reaction zone-facultative zone.
[The backflow sludge in the biological selection area is mixed with influent, which makes full use of the rapid adsorption of activated sludge to accelerate the removal of soluble substrates, which has a good hydrolysis effect on refractory organic matter, and at the same time, the phosphorus in the sludge is effectively released under anaerobic conditions; Effectively inhibit the proliferation of filamentous bacteria, overcome sludge bulking and improve system stability. A small amount of nitrate nitrogen (about 2ml/L) in the returned sludge is denitrified (the denitrification amount can reach about 20% of the whole system)]
The facultative zone has the buffering effect of the biological selection zone operating under anaerobic or facultative conditions on the quality and quantity of influent, and also has the function of promoting the further release of phosphorus and strengthening the denitrification of nitrogen. ]
[The main reaction zone is the main place where the organic substrate is finally removed. During operation, by adjusting aeration intensity and dissolved oxygen, the main liquid in the area is in aerobic state, so that two gradients of dissolved oxygen and nitrate are formed inside and outside the sludge floc, and the degradation of organic pollutants and nitrification and denitrification are carried out simultaneously. ]
Three, CASS operation cycle can generally be divided into four steps:
Inflow aeration stage
The aeration device fills the reaction tank with oxygen. At this time, organic pollutants are oxidized and decomposed by microorganisms, and NH3-N in sewage is transformed into NO3-N by nitrification of microorganisms.
Precipitation stage
At this time, aeration is stopped, 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 carry out denitrification reaction. The activated sludge gradually sinks to the bottom of the pool, and the upper water becomes clear.
Decapitation stage
After precipitation, the decanter placed at the end of the reaction tank began to work, and the supernatant was gradually discharged from top to bottom. At this time, the reaction tank gradually transits to anaerobic state, and nitrogen removal continues.
Idle stage
Idle stage is the stage when the decanter rises to the original position, and the duration of this stage can be adjusted according to the actual production needs.
Fourth, the characteristics of CASS process:
1, sludge bulking is not easy to occur.
2, sludge sedimentation performance is good.
3. Strong external impact resistance and flexible operation.
4, the nitrogen and phosphorus removal performance is good.
5. The treatment effect of multi-tank series operation is stable and the volume utilization rate is high.
6. Simple technological process, less construction investment and high degree of automation.