What Happens to Wastewater During Treatment?
Wastewater undergoes a number of different treatments in different stages, each of which is designed to remove pollutants and other harmful elements from the water. The goal is to produce water that is safe for discharge into waterways and that does not pose a threat to the environment or to human health.
There are seven key steps of the wastewater treatment process:
1. Screening and Pumping
In the earliest stage, the water passes through screening equipment, where the largest materials — like plastics, rags, and wood fragments — are removed and sent to a landfill.
2. Grit Removal
The remaining water passes through a more refined filter, where materials like sand and gravel are removed. These materials, too, are sent to a landfill.
3. Primary Settling
During this stage, the wastewater becomes less agitated, giving the remaining material in the water a chance to settle to the bottom of the tank. The settled material, also called primary sludge, is pumped from the bottom of the tank while grease and other floating debris are skimmed off the top. The remaining water is then treated with chemicals to remove phosphorus, and the water exits from the top of the tank to the next stage. The primary and activated sludge must be treated separately.
4. Aeration / Activated Sludge
The aeration/activated sludge stage is where most of the wastewater treatment will take place. During this stage, oxygen is pumped into the wastewater, providing the necessary ingredients for biological microorganisms to grow and develop. The microorganisms replicate in the tank the same activity they perform at the bottom of lakes and rivers: consuming pollutants and turning them into cell tissue, water, and nitrogen. This process is known as biological degradation.
While biological degradation within a natural environment (like a lake or river) can take years, the process is much faster within a wastewater treatment setting thanks to high-efficiency water aeration. We will revisit this phase in more detail below.
5. Secondary Settling
During this stage, the treated wastewater separates from the biological microorganisms and is sent to another tank, called the secondary clarifier. The water is now over 90% treated.
The water passes through the most refined filter yet, capable of removing particles as small as 10 microns in diameter.
Last, the treated wastewater is disinfected via an ultraviolet treatment process. This kills any remaining bacteria, allowing the water to safely discharge back into the natural environment.
What Role Does Aeration Play in Wastewater Treatment?
Let’s return to Step 4, the aeration/activated sludge stage. How does proper aeration impact the outcome of this critical stage?
Wastewater aeration tanks are designed to mix air with the wastewater in an oxygen-rich environment, increasing the rate of biological activity. Without it, there would be no bacteria or other biological microorganisms to break down organic matter and perform the bulk of the wastewater treatment process.
The resulting bacteria also requires oxygen to complete its biodegradation process, using the gas to break organic matter down into carbon dioxide and water. While degradation can occur without sufficient oxygen, it’s slower, less sanitary, and more odorous. Imagine the difference between a stagnant pond and a flowing river.
Aeration Solutions for Wastewater Treatment
Unsurprisingly, the right aeration system is one of the most crucial elements of the wastewater treatment and activated sludge process. If the system can’t evenly and consistently deliver a powerful oxygen supply, the microorganisms will not be able to thrive.
What makes a particular aeration system the “right” one for the job? To answer that, let’s explore the three main types of water aeration:
Surface aerators agitate the water at the surface, introducing a large amount of oxygen in a short amount of time. Because aeration at the surface is unlikely to reach the depths of a tank, this type of aeration is most useful for shallow water applications. It can also be used in tandem with a course or fine bubble diffuser.
Coarse Bubble Diffusers
Coarse bubble diffusers oxygenate the water by displacing and churning the water, producing bubbles ranging from 10 to 50 millimeters in diameter (compared to fine bubble diffusers like Aero-Tube®, which produces bubbles averaging 3 millimeters in diameter).
Coarse bubble diffusers perform well in conventional aeration applications like wastewater treatment, but they cannot oxygenate as much surface area as fine bubble diffusers. Given this, coarse bubble diffusers are less energy-efficient than fine bubble diffusers.
Fine Bubble Diffusers
Fine bubble diffusers like Aero-Tube® are the ideal next-generation water aerator for wastewater treatment. Unlike coarse bubble diffusers, which rely on churning the water to introduce oxygen, fine bubble diffusers are fully submersible systems that disperse diffused oxygen evenly via very fine bubbles, or micro bubbles.
These hundreds of thousands of micro bubbles cover a greater surface area than the bubbles made by coarse bubble diffusers, and at a fraction of the energy output. Micro bubbles also take longer to rise and stay intact for longer, maximizing the rate at which oxygen is exposed to the water. This is the ideal solution for applications like wastewater treatment.
Aero-Tube® Fine Bubble Diffusers for Wastewater Treatment
If you’re an engineer or wastewater treatment plant operator, there are three main factors to consider as you choose or replace your aeration system:
- How much oxygen can be transferred?
- How energy efficient and cost-effective is the system?
- How easy is the system to maintain?
On all three counts, Aero-Tube® stands out as an industry leader. By combining the micro bubble technology with best-in-class hose and grid systems, Aero-Tube® has been able to produce one of the most powerful and efficient fine bubble diffusers on the market.
What’s more, Aero-Tube® does not contain any moving parts, resulting in a very low maintenance requirement. Compared to technologies like paddle wheels, surface aerators or even other fine bubble diffusers, the cost of maintaining Aero-Tube® — not to mention the chances of dealing with unexpected, expensive mechanical issues — is minimal.
The proper treatment of wastewater is a crucial way to avoid harming the environment and prevent disease. Untreated wastewater can impact aquatic and human life through pollutants that include chemicals, viruses, bacteria, and parasites. Literally and figuratively, the price of using an old or outdated wastewater treatment system is simply too high.