Ivan Bandura
Aeration refers to circulating or mixing air in a substance. This process is a common drinking and wastewater treatment method that helps remove contaminants and increase oxygen levels. The efficiency of an aeration system largely depends on the surface contact between air and water.
How Aeration Is Used in Wastewater Treatment
Aeration occurs in the secondary (activated sludge) treatment process. Air is pumped into a body of water to foster microbe growth.
When performed correctly, these naturally occurring microorganisms feed on organic pollutants in the wastewater. Over time, collected materials form “flocks” that are recirculated throughout the aeration system. This process boosts decomposition rates, ultimately helping improve water quality.
Types of Aeration
Wastewater treatment may involve either subsurface or surface aeration. While both systems work by increasing oxygen levels, their installation and mechanisms vary slightly.
Subsurface Aeration
Subsurface aeration involves pushing compressed air into diffusers via air pumps or blowers. These systems are placed at the bottom of lagoons, tanks, or other bodies of water to maximize surface area and oxygen exchange.
Fine Bubble Diffusers
During the secondary water treatment phase, a fine bubble (pore) diffuser creates and uses oxygen-rich bubbles to feed microorganisms in the wastewater. These beneficial bacteria feed on this oxygen to produce enzymes that break down organic matter.
These systems are desirable because they significantly lower energy consumption. This reduction is possible due to a higher Standard Aeration Efficiency (SAE) and Standard Oxygen Transfer Efficiency (SOTE).
Essentially, fine bubble diffusers produce small bubbles, typically measuring 1 to 3 millimeters in diameter. This abundance of tiny bubbles creates more surface area, resulting in a higher rate of oxygen transfer into the water column. Due to this increased SOTE, less compressed air is required to facilitate transfer, thus translating into energy savings.
Coarse Bubble Diffusers
Unlike fine bubble diffusers, a coarse bubble (pore) diffuser produces large bubbles between 3 and 50 millimeters. These systems are less energy efficient but more resistant to fouling.
Because of larger perforations, bacteria and biosolids do not become encrusted as often as in fine bubble diffusers. This quality also means coarse bubble diffusers require less cleaning, maintenance, and replacement.
However, this type of aeration supplies lower oxygen levels compared to fine bubble diffusion. This difference manifests as higher energy consumption to produce the same results.
Surface Aeration
Surface aeration systems are installed on the surface of a tank or lagoon, not along the bottom. Wastewater is broken up by spray nozzles, jets, or small waterfalls before mixing with the air to increase oxygen levels. This equipment is effective at achieving a high SOTE but is limited to the area surrounding the aerator.
Why Aeration Is Important in Wastewater Treatment
Aeration is beneficial for a few reasons. First, this process is cost-effective and chemical-free. Secondly, aeration causes little, if any, environmental damage because only oxygen and naturally occurring microorganisms are involved in treatment.
Maintaining Aeration Water Systems
As with any equipment, regular maintenance is necessary for preserving efficiency. Leaving minor issues unaddressed can lead to substantial problems down the line, such as expensive breakdowns, sludge buildup, and corroded or clogged filters.
Below is a maintenance checklist for an aeration system:
- Replace hardened or stretched rubber and/or brittle plastic
- Routinely assess discharge pressure, bubble patterns, and solid levels
- Avoid over-aeration
- Drain and pump tanks every 3 to 4 years
- Keep filters clean
- Ensure blowers and pumps are debris-free
- Maintain a log of maintenance and cleaning
In Conclusion
Aeration is a valuable tool in wastewater treatment. Depending on water volume, tank size, and efficiency requirements, facilities may opt for a different type of system. Regardless, both surface and subsurface methods effectively reduce contaminants and serve a valuable function in ensuring water quality.
