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How does a wastewater treatment plant work?

According to the Environmental Protection Agency (EPA), wastewater treatment is one of the most common forms of pollution control in the United States. Lakeside Equipment Corporation is proud to offer equipment and systems used nationwide in wastewater treatment plants, facilities that clean wastewater before it is discharged into the environment.
The need for wastewater treatment plants: past and present
Wastewater treatment plants have not always been necessary. In the past, bacteria and other organisms in waterways would break down wastewater into harmless by-products in a naturally occurring purification process. However, bacteria and other organisms could not keep up with the growth in population and sewage generation. Wastewater is now sent to wastewater treatment plants - many of which use the same purification processes as nature to clean the water.
Most wastewater treatment plants prepare wastewater for reuse in two distinct stages: primary and secondary.
Primary stage of wastewater treatment
As soon as wastewater arrives at a wastewater treatment facility, it enters the primary treatment stage. First, it is conveyed through a screen designed to remove large pieces of debris that could damage the Lakeside equipment used elsewhere in the facility. Some facilities have installed multiple screens to remove different sized objects and materials from the effluent.
After passing through the screens, the effluent enters a grit sink. Grit can include sand, gravel, eggshells or any other type of solid material that can pass through the screening process. There are several different types of grit settling tanks, but Lakeside's aeration grit settling tank is the most popular. Wastewater flows in a spiral pattern in this chamber. Air is slowly introduced into one side of the chamber, creating a vertical pattern that separates the heavier material from the rest of the water. The heavier material or grit then sinks to the bottom of the chamber.
Even though the wastewater has passed through the screens and grit settling tanks, it still contains other materials that need to be removed. The wastewater slowly flows through the settling tank and as it does so, the solids that remain in the water begin to drift toward the bottom of the settling tank.
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This is the final step in the primary stage of the wastewater treatment process. At this point, most of the solids have been removed from the water. However, the water is still not clean enough to be released back into the environment, so it enters the secondary stage for further purification.
Secondary stage of wastewater treatment
The second stage of the treatment process aims to remove up to 85% of the organic matter remaining in the wastewater. There are many different ways to achieve this goal, but many facilities use trickling filters or activated sludge methods.
If the facility uses the trickling filter method, the wastewater is pumped into an area containing 3 to 6 feet of stones after leaving the settling tank. Bacteria and other small organisms grow on these stones, so they consume or break down the organic matter in the water flowing through the tank. The water is then piped out of the trickling filter and sent back to the settling tank for another round of purification.
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Most facilities use an activated sludge process, which takes place immediately after the settling tanks in the primary treatment stage. The wastewater enters an aeration tank where it is mixed with sludge. Air is then pumped into the aeration tank to promote the growth of bacteria and other small organisms within the sludge. The bacteria and other microorganisms break down the organic matter in the water into harmless by-products. The wastewater will remain in the aeration tank for three to six hours, which gives the bacteria and microorganisms enough time to break down all of the remaining organic material. After the wastewater leaves the aeration tank, it is usually sent to another settling tank to separate the solids from the water.
Regardless of which method is used, the wastewater goes through another round of treatment before being released back into the environment. In the secondary stage of the treatment process, the water leaves the settling tank and is sent to a pond where it is exposed to chlorine. Wastewater typically stays in these tanks with chlorine for 15-20 minutes. This chemical kills harmful bacteria that may be lurking in the water and also removes unpleasant odors from the wastewater. Wastewater treatment plants can kill up to 99 percent of the bacteria in the water with chlorine, so this is an important step in the process.
Some facilities do not use chlorine to kill bacteria in the final stage of the treatment process. Instead, these facilities use alternatives such as ultraviolet (UV) light or ozone to kill bacteria in the water before releasing it into the environment. These alternatives do not involve the use of chemicals and are therefore considered safer for the environment and wildlife.
After passing through this final stage, the water is discharged into community waterways. The final stage ensures that the vast majority of bacteria in the water is killed so that once discharged, it will not harm humans, animals or the environment.
Anaerobic granular sludge is an aggregate of highly active anaerobic bacteria formed in the treatment of organic wastewater. As a micro-ecosystem, it is enriched with various anaerobic microbial populations and has self-balancing properties to degrade various organic pollutants in raw wastewater. It is used to start anaerobic reactors in high concentration organic wastewater treatment systems. Anaerobic granular sludge is a form of microbial immobilization, slightly heavier than water, with good settling properties and methanogenic activity.

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