Aeration Tank (MBBR TANK)
Aeration in water treatment
The water from the equalization tank is pumped into the aeration tank where treatment of the sewage water begins.
- The aeration tank consists of the bio media suspended in the water and agitated by aeration.
- Aeration is performed through fine bubble diffusers fitted in sets at the bottom of the tank.
- Bio-mass growth on the biomedia helps breakdown the impurities in the water, rendering it clean.
- A baffle is provided near the inlet of the tank to aid in settling and to prevent short circuiting the sewage.
- The inlet and outlet pipes are positioned farther most apart from each other.
- Aeration is provided in cycles to allow for nitrification and de-nitrification cycles to take place.
- Free board of nearly 7 feet is provided to cope with any accidental overloading of incoming sewage.
- Outlet of the tank is covered by a mesh to prevent the escape of biomedia.
- Inlet of the tank is covered by mesh.
- The inlet pipe brings sewage from the raw sewage lift pump (sewage from the equalization tank). The pipe is bent downward, so that the sewage does not get propelled toward the outlet pipe (6).
- The baffle wall does not let the incoming sewage and sludge go across the tank toward the outlet pipe (6). The wall forces the mix toward the bottom of the tank; thus ensuring maximum retention.
- The tank is always filled till this level (which is set by the top of the launder (4). So the remaining height of the tank serves as freeboard (height margin to ensure that the tank does not overflow immediately under moderate emergencies.)
- The Outlet Launder collects the sewage and delivers it to the outlet pipe (6). Note that the outlet launder is located farthest from the inlet pipe (1) to minimize short circuiting of flow from the inlet to the outlet of the tank.
- The net prevents entry of debris in the outlet pipe (6). The operator should remove debris collected in the launder (4) periodically; otherwise eventually the mesh will be blocked with accumulated debris, resulting in a rise of water-level in the aeration tank. In the extreme case, this will cause overflow from the tank.
- The outlet pipe takes the sewage to the settling tank/secondary clarifier.
- The fine bubble diffusers are actually rigid pipes with long slots, which are then covered with tubular synthetic rubber membranes. The compressed air is released in the form of fine bubbles throughout the length of the diffusers, through minute holes punched in the rubber membrane. The figure shows an array of eight diffusers. The array is strapped to cement blocks (ballasts) to keep the entire assembly anchored to the bottom of the tank.
- In the case of fixed diffusers, compressed air is supplied through a header pipe at the bottom of the tank, as shown.