AERATED LAGOONS
Aerated lagoons have been successfully used for the treatment of domestic or industrial wastewater
An aerated lagoon is a wastewater treatment plant in which mechanical or diffused-air aeration is used to artificially supplement the oxygen supply. Aerated lagoons are of the following four types:
Aerated lagoons have great depth resulting in lesser surface area than waste stabilization ponds.They are relatively shallow earthen basins varying in depth from 2 to 5m and provided with mechanical aerators on floats or fixed platforms. The mechanical aerators are used to provide oxygen for the biological treatment of wastewater and also to keep the suspended solids in suspension.Sometimes diffused aeration is also used.
Facultative aerated lagoons
In this case, the power input per unit volume is enough only for diffusing the required amount of oxygen in the wastewater but not for maintaining all solids in suspension. Therefore, the solids settle down and undergo anaerobic decomposition. These ponds exhibit partly aerobic and partly anaerobic activity. Hence, they are called facultative. They are also referred to as aerobic lagoons. They remove 70 to 90% of the BOD load.
Aerobic lagoons with recycling of solids are similar to (Extended aeration activated sludge process) aerobic flow-through plants. The power level is high to keep all suspensed solids under suspension. Solids are prevented from escaping out with effluent. Hence the concentration of solids is high. Arrangements are incorporated for settling and recycling of solids. High BOD removal, as high as 95 to 98% can be acheved in these lagoons.In these lagoons, an earthen lined basin is used in place of a RCC reactor basin.The Hydraulic Retention Time is longer than that used in conventional extended aeration process. The aeration requirement for these lagoons should be higher than those for all other types of lagoons. In these type of lagoons, most of the solids are maintained in suspension.The aerobic lagoon with recycling of solids is the same as the activated sludge process.
- -Facultative aerobic lagoons
- -Aerobic, flow-through lagoons
- -Dual-powered lagoons
- -Aerobic lagoons with recycling of solids
Aerated lagoons have great depth resulting in lesser surface area than waste stabilization ponds.They are relatively shallow earthen basins varying in depth from 2 to 5m and provided with mechanical aerators on floats or fixed platforms. The mechanical aerators are used to provide oxygen for the biological treatment of wastewater and also to keep the suspended solids in suspension.Sometimes diffused aeration is also used.
Facultative aerated lagoons
In this case, the power input per unit volume is enough only for diffusing the required amount of oxygen in the wastewater but not for maintaining all solids in suspension. Therefore, the solids settle down and undergo anaerobic decomposition. These ponds exhibit partly aerobic and partly anaerobic activity. Hence, they are called facultative. They are also referred to as aerobic lagoons. They remove 70 to 90% of the BOD load.
Aerobic lagoons with recycling of solids are similar to (Extended aeration activated sludge process) aerobic flow-through plants. The power level is high to keep all suspensed solids under suspension. Solids are prevented from escaping out with effluent. Hence the concentration of solids is high. Arrangements are incorporated for settling and recycling of solids. High BOD removal, as high as 95 to 98% can be acheved in these lagoons.In these lagoons, an earthen lined basin is used in place of a RCC reactor basin.The Hydraulic Retention Time is longer than that used in conventional extended aeration process. The aeration requirement for these lagoons should be higher than those for all other types of lagoons. In these type of lagoons, most of the solids are maintained in suspension.The aerobic lagoon with recycling of solids is the same as the activated sludge process.
Aerobic flow through dual power aerated lagoons
In case of aerobic, flow-through type lagoons, the power
supplied is sufficient to diffuse enough oxygen but also keep all
suspended solids in suspension. They are similar to activated sludge
aeration tanks. There is no settlements of solids in these types of
aerated lagoons. The aeration period is 2 to 5 days. The wastewater
leaves along with the suspended solids. The BOD removal is around 50 -
60 %. This process is normally followed by facultative aerated lagoons
or algal ponds or converted into aerobic lagoons with recycling of
solids.
Dual powered aerobic lagoons are a special case of aerobic, flow-through lagoons where the first lagoon is an aerobic flow through lagoon followed by a facultative aerated lagoon in series. These lagoons are given the name dual powered since power maintained in first lagoon is different from that in subsequent lagoons. Detention time in both lagoons may be different. 1 to 3 days in aerated lagoons and 3 to 4 days in subsequent lagoons is adopted to meet desired final effluent quality.
Dual powered aerobic lagoons are a special case of aerobic, flow-through lagoons where the first lagoon is an aerobic flow through lagoon followed by a facultative aerated lagoon in series. These lagoons are given the name dual powered since power maintained in first lagoon is different from that in subsequent lagoons. Detention time in both lagoons may be different. 1 to 3 days in aerated lagoons and 3 to 4 days in subsequent lagoons is adopted to meet desired final effluent quality.
This type of lagoon is essentially an extended aeration activated sludge process. In these cases, an earthen basin is used instead of a RCC reactor basin.The Hydraulic Retention Time (HRT) is longer that that used in conventional extended aeration process.The aeration requirement for an aerobic lagoon with recycle is higher than that required by the aerobic flow through lagoons so that all the solids are maintained under suspension.
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