Aeration and Types of Aerators

Aeration and its types

1. WELCOME

2. Aeration and Types of Aerators Presented by Kari Venkata Sai 2016-18-015

3. Aeration The process of  absorbing oxygen  from air is known as aeration. (or) The process of bringing water and air into close contact in order to remove dissolved gases, such as carbon dioxide, and to oxidize dissolved metals such as iron. It can also be used to remove volatile organic chemicals (VOC) in the water.

4. Aeration serves three important functions  : Mixing the returned sludge with effluent from primary treatment. Keeping the activated sludge in suspension . Supplying the oxygen to the biochemical reactions necessary for the stabilization of the wastewater

5. Why we use Aeration? Oxidation of organic matter. To increase dissolved oxygen content. To reduce the concentration of taste and odor causing substances, such as hydrogen sulfide and various organic compounds, by volatilization/stripping or oxidation. To oxidize iron and manganese, rendering them insoluble.

6. Aerators generally falls into two categories Air into Water – This method creates small bubbles of air that are injected into the water stream. Water into Air – This method is designed to produce small drops of water that fall through air. All aerators are designed to create a greater amount of contact between the air and water to enhance the transfer of gases.

7. Types of Aerators

8. Gravity Aerators 1. Cascade aerators A cascade aerator consists of a series of steps that the water flows over. In all cascade aerators, aeration is accomplished in the splash zones. Cascade aerators can be used to oxidize iron and to partially reduce dissolved gases.

9. 2. Cone aerators Cone aerators are used primarily to oxidize iron and manganese from the ferrous state to the ferric state prior to filtration. The water being pumped to the top of the cones and then being allowed to cascade down through the aerator.

10. Spray aerators This type of aerator has one or more spray nozzles connected to a pipe manifold. The water is sprinkled in fine jets through nozzles to a height of about 2 m to 2.5 m. The nozzles are generally operated at a pressure of 0.07 to 0.14 N/mm 2 . The discharge through nozzle will depend upon its design and available head of water.

11. Diffused air aeration system The perforated pipes are installed at the bottom of tanks. The compressed air is blown through these pipes. The air bubbles while coming up from the bottom of tank come into close contact of water contained in the tank and aeration of water is thus achieved. The depth of aeration tanks is generally about 2.5 m to 3 m and they generally work on the principle of continuous flow with minimum detention period of 15 minutes. The quantity of air consumed per 1000 litres of water varies from 0.3 m 3 to 0.6 m 3 .

12. Mechanical aerators Mechanical aerators are of two general types; surface aerators and turbine aerators. Surface aerators consist of submerged or partially submerged impellers, which are centrally mounted in the aeration tank. Surface aerators agitate the wastewater vigorously, entraining air in the wastewater and causing a rapid change of the air-water interface to facilitate solution of the air. Turbine aerators are usually up flow types that rely on violent agitation of the surface and air entrainment for their efficiency. A draft tube may be utilized to control the flow pattern of the circulating liquid within the aeration tank. The draft tube is a cylinder with flared ends mounted concentrically with the impeller, and extending from just above the floor of the aeration tank to just beneath the impeller.

13. Mechanical Aerators types

14. DIFFUSED AERATION MECHANICAL AERATION 1. Superior Mixing full mixing for any depth full basin utilization Limited mixing depth Limited energy location- poor distribution 2. Major Energy Saving Approx 40% energy saving Low energy demand High energy cost High energy demand 3. Possible Flexibility Can turn down or throttle entire system Loss of air when unit are turn off No throttling possible 4. Capital Cost If used in deep basin very economical Short payback period If used in deep basin very costly Comparatively high payback period .

15. Common operating problems Super saturation. Slow removal of the hydrogen sulfide. Algae production. Clogged filters. Overuse of energy.

16. Thank You