Aeration in waste water treatment and different methods

Aeration is the process of mixing air into a liquid or substance that acts like a fluid, such as soil. It can also refer to the process of adding tiny air pockets to fats and oils. Uses of aeration
Soil
Aeration improves the exchange of gases between the soil and the atmosphere. It also helps to reduce soil compaction and promote stronger roots.
Water
Aeration is used to remove unwanted gases from water. It can also be used to oxidize iron and manganese, and to reduce ammonia and hydrogen sulfide.
Food
Aeration is used to create light and fluffy textures in foods like cakes and desserts.
Sewage
Aeration is used to break down organic matter in wastewater.
How aeration works
In soil, aeration occurs through molecular diffusion and convection.
In fats and oils, aeration is achieved by creaming the mixture together with a wooden spoon or electric whisk.
In water, aeration is achieved by bringing air and water into intimate contact.
The word aeration comes from the Latin word aer which means "air".
Aeration creates holes down into the soil to alleviate compaction so air, water and nutrients can reach grass roots. Deprived of their basic needs by compacted soil, lawn grasses struggle in stressful situations, such as heat and low rainfall, and lose their healthy, rich color.
Meringues: Meringues are a classic example of how aeration can transform a preparation. By beating egg whites and adding sugar, we create a light, fluffy structure that can be folded into mousses or soufflés or baked for a crisp outside and soft inside.
Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid or substance.

Aeration brings water and air in close contact in order to remove dissolved gases and to oxidize dissolved metals, including iron, hydrogen sulfide, and volatile organic chemicals (VOCs). This process is typically the first major process at drinking water treatment plant, and occurs in the secondary treatment processes of activated sludge treatment in wastewater treatment plants. An evenly distributed oxygen supply in an aeration system is essential to effective wastewater treatment for fostering microbial growth.

According to the Missouri Rural Water Association, the efficiency of aeration depends on the amount of surface contact between air and water. This is primarily controlled by the size of the water drop or air bubble. Aeration brings water and air in close contact by exposing drops or thin sheets of water to the air or by introducing small bubbles of air and letting them rise through the water. Dissolved gases are then removed from the solution and allowed to escape into the surrounding air.
Aeration is the interchange of various gases between the atmosphere and soil and the various reactions that either consume or produce gases in the soil. The composition of soil air depends on the relative magnitude of both the sources and sinks of the various gas components, the interchange between soil air and atmose

1. AERATION Anagha R Roll No 3 1

2. AERATION 2 Aeration is often the first major process at the treatment plant. It is 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 in the water. During aeration, constituents are removed or modified before they can interfere with the treatment processes.

3. WHY WE USE AERATION? 3 Oxidation of organic matter To increase dissolved oxygen content in the water To remove those compounds that may interfere with the subsequent water treatment To oxidize iron and manganese, rendering them insoluble To reduce the concentration of taste and odour causing substances, such as hydrogen sulphide and various organic compounds, by volatilization/ stripping or oxidation

4. Different m ethods of Aeration 4

5. SPRAY NOZZLE AERATOR This type of aerator has one or more spray nozzles connected to a pipe manifold. Moving through the pipe under pressure, the water leaves each nozzle in a fine spray and falls through the surrounding air, creating a fountain effect. In general, spray aeration is successful in oxidizing iron and manganese. Up to 90% CO2 in water can be removed. 5

6. CASCADE AERATOR 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. Removes up to 60% - 70% CO2 6

7. Process Description With Cascade Aerators, aeration is accomplished by natural draft units that mix cascading water with air that is naturally inducted into the water flow Cascade water is pumped to the top of the aerator, and cascades over a series of trays Air is naturally inducted into the water flow to accomplish iron oxidation and some reduction in dissolved gasses 7

8. AIR DIFFUSION A common way to aerate water is via diffused air. In these systems air is pumped through some sort of diffuser to generate small bubbles. These diffusers are porous ceramics, cloth or plastic. Types of diffused aeration: (a) Fine bubble (b) Coarse bubble Efficiency of fine bubble aeration is 10 to 20 times greater than that of coarse bubble diffused aeration system. 8

9. Fine bubble aeration system Diameter of bubbles is approximately 2 mm to 2.5 mm A mass of many small bubbles has a much larger cumulative surface area than a few larger ones. This increased surface area allows for a higher rate of oxygen transfer as the air and water come into contact across the surfaces of the bubbles.  Smaller bubbles rise at a slower rate than larger ones. This slow rate of speed results in a greater amount of contact time between air and water and permits more oxygen to be distributed throughout the water column. Coarse bubble aeration system They have slightly lower aeration efficiency than fine bubble aerators, but cheaper in cost and less liable to clogging. 9

10. Fine bubble aeration system 10

11. GRAVEL BED AERATOR (TRICKLING BEDS) Water is sprayed at the top, and it trickles down the bed of coke or anthracite. The thickness of gravel bed is 1 to 1.5 m 3 – 4 trays are kept filled with coke or stone. Water is sprayed from the distribution pipe at the top. Allow water to trickle down through perforated trays arranged vertically in series. During downward movement, air get mixed up. This enhances the biological treatment process and promotes the breakdown of organic matter in the water. 11

12. THANK YOU 12