How To Calculate Aerobic Tank Aeration Volume

How To Calculate Aerobic Tank Aeration Volume

Aerobic tank is a structure for sewage treatment using activated sludge method. The tank provides a certain sewage residence time to meet the oxygen required by aerobic microorganisms and the mixing conditions of sewage and activated sludge in full contact. Aeration is a means of making strong contact between air and water, the purpose of which is to dissolve the oxygen in the air in the water, or to banish unwanted gases and volatile substances from the water into the air. In other words, it is a means of facilitating the exchange of substances between gases and liquids, in addition to a number of other important roles, such as mixing and stirring.

Data:

(1) Water flow: 46m3/h

(2) COD: 1200mg/L

(3) No data for BOD,here we assume BOD=0.5*COD=600mg/L

Four Calculate Methods:

Method One: Calculate According To The Air-Water Ratio:

Contact oxidation Tank 15:1,so the air volume is: 15*46=690m3/h

Activated sludge tank is 10:1, then the air volume is: 10*46=460 m3/h

The adjustment tank is 5:1, then the air volume is: 5*46=230 m3/h

The total air volume is: 690+460+230=1380 m3/h=23 m3/min

Method Two: Calculated by removing 1 kg of BOD and 1.5 kg of O2

The removal amount of BOD per hour is 0.6kg/m3*1100m3/d÷24=27.5kgBOD/h

Oxygen demand: 27.5*1.5=41.25kgO2

The weight of oxygen in the air is: 0.233kg O2/kg air,

Then the required air volume is: 41.25 kgO2÷0.233 O2/kg air=177.04 kg air

The density of air is 1.293 kg/m3

Then the air volume is: 177.04kg÷1.293 kg/m3=136.92 m3

The oxygen utilization rate of the microporous aeration head is 20%,

Then the actual air demand is: 136.92 m3÷0.2=684.6m3=11.41m3/min

Method Three: Calculate the aeration intensity according to the unit tank area

The aeration intensity is generally 10-20 m3/m2h, taking the middle value, the aeration intensity is 15 m3/m2h

The total area of contact oxidation tank and activated sludge tank is: 125.4 m2

Then the air volume is: 125.4*15=1881 m3/h=31.35 m3/min

The aeration intensity of the regulating tank is 3m3/m2h, and the area is 120m2, the air volume is 3*120=360m3/h=6m3/min

A total of 37.35 m3/min is required

Method 4: Calculate according to the number of aeration heads

Calculate the pool capacity according to the residence time, and then calculate that a total of 350 aeration heads are required, and the air demand is 3 m3/h.

Then the total required air is 350×3=1050 m3/h=17.5 m3/min

In addition, the gas demand of the regulating tank is 6 m3/min,

Total required air: 23.5 m3/min

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