The aerated grit chamber is a kind of long channel. Along the whole length direction of one side of the channel wall, an aerator is installed 60-90cm from the bottom of the chamber, and a sand collecting hopper is set at the bottom of the chamber, with a slope of I = 0.1-0.5, so as to ensure the sand sliding in.
Due to aeration, organic particles in wastewater are often in suspension state. Sand particles rub with each other and bear the shear force of aeration. The organic pollutants attached to the sand particles can be removed, which is conducive to obtaining relatively pure sand particles. Under the centrifugal force of swirling flow, these dense sand particles are thrown to the outside and sink into the sand collecting tank, while the less dense organic matter flows forward with the water flow and is carried to the next treatment unit. In addition, aeration in water can deodorize, improve water quality, facilitate subsequent treatment, and also play a role of pre aeration.
There are 15% organic matters in the sand retained by the ordinary sand settling tank, which makes the subsequent treatment of the sand more difficult. The aerated sand settling tank can overcome this disadvantage to a certain extent.
Characteristic
The aerated grit chamber has been used since 1950s. Its characteristics are as follows:
(1) The content of organic matter in sediment is less than 5%
(2) Because the tank is equipped with aeration equipment, it has the functions of pre aeration, deodorization, defoaming and accelerating the separation of oil and scum in sewage.
Advantages: the aerated grit chamber provides favorable conditions for the normal operation of the subsequent sedimentation tank, aeration tank and sludge nitrification tank and for the final disposal of the grit.
Disadvantages: aeration consumes energy and has adverse effects on the operation of anaerobic or anoxic section of biological nitrogen and phosphorus removal system.
Design parameters
(1) The horizontal velocity can be taken as 0.08-0.12m/s, generally 0.1m/s;
(2) The retention time of the maximum flow sewage in the tank is 2-4min, and that of the combined sewage in rainy days is 1-3min. If it is used as a pre aeration tank at the same time, the retention time is 10-30min;
(3) The effective water depth of the pool should be 2.0-3.0m. The ratio of pool width to pool depth is 1 ~ 1.5, and the ratio of pool length to width can be up to 5. When the ratio of pool length to width reaches 5, lateral baffles can be considered.
(4) Multiple empty pipes are often used for aeration in the aeration settling basin, with a perforation diameter of 2.5! 6.0mm and a distance of about 0.6-0.9m from the bottom of the basin. Each group of aeration pipes shall be equipped with regulating valves.
(5) The amount of aeration required per cubic meter of sewage should be 0.1-0.2 cubic meters of air, or 3-5 cubic meters per hour per square meter of pool surface area.
As far as possible, the shape of the aeration grit chamber shall not produce dead angle and bias flow, the direction of water inflow shall be consistent with the direction of swirl flow in the chamber, the direction of water outflow shall be vertical to the direction of water inflow, and baffles shall be set to prevent short flow.
