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How Does the Sewer System Work?

Sewer systems are one of those things that virtually no one thinks about until a problem arises. That reality means most have a vague idea of how the sewage system works but could not explain it in very much detail. 


When you think about how important sewer services are to everyone, however, the importance of understanding how they work becomes obvious. Here is how a modern, municipal sewer system functions. Let’s continue and learn more about how does the Sewer System Work?

How Does the Sewer System Work

Why Sewage Systems Are Important

Raw sewage stinks. No matter its form, even if it did not start stinking, virtually all organic waste we create eventually stinks. If we just left it sitting in our backyards, everywhere humans live would become uninhabitable. 


Worse, raw sewage contains many critters that can do a lot of damage to human beings. Some can even kill humans if they ever get a foothold. Additionally, some liquids have chemicals that are poisonous to waterways and humans.


A few of the dangers of untreated sewage are:


  • Disease 
  • Bacterial infections
  • Parasite infections
  • Aquatic life is killed off
  • Drinking water is made undrinkable
  • Other animals becoming poisoned

Sewage Systems and Our Homes

Each use of the toilet, sink, shower, etc., introduces a liquid form of waste to the sewage system. Each form of liquid waste has a specific chemical makeup. All of it must be treated and released back into nature.


To get to the sewage system, waste must pass from a toilet or sink into a home’s pipes to the main sewage pipe (also called a main). From there, the waste moves along until it ends up in a municipal water treatment facility. Once in the facility, the waste gets treated, stored, and released.

Gravity and Pressure

The driving forces behind municipal sewage services that deal with all sorts of refuse are gravity and pressure. Gravity forces waste down towards a certain point. Pressure does that same work when the slope to move waste becomes too steep for gravity alone to work. 


Ultimately, that waste ends up in a wastewater treatment facility where it is processed, cleaned, and released back into the environment, usually via a waterway. 


Ideally, gravity is the driving force getting the waste and wastewater to wherever it is headed. When gravity is not sufficient, though, sewer services use pumping stations but do so sparingly because human waste is solid, which can cause a problem in pumps. 


Additionally, pump turbulence can create deadly gases when certain bacteria grow in it, and a pressurized environment can become volatile as chemicals become unstable.

Sewage Piping and Sewer Mains

Piping from buildings allows sewage to flow to a sewer main, which. The sewer main is 3 to 5 feet in diameter. The piping from the building that connects to the main is 6 to 12 inches in diameter. 


Sewer mains run underneath roadways or alongside them. When sewer mains are underground, workers can access them via manholes. Manholes are vertical shafts that descend from the road to the sewage system. The type of work performed in the sewage system can include but is not limited to unclogging sewer mains and installing piping and equipment.

Pump Stations

While a continuous flow downhill to a water treatment facility is ideal, it rarely happens. Often, the geography of a town or city is uneven, and some sewage mains fall below the central sewage piping system. 


When that happens, the volume of sewage exceeds gravity’s ability to pull the sewage down through the system. To remedy this, pumping stations that use pressurization give gravity a little help. 


Pumps elevate the sewage flow to a point above the rest of the system. Once there, the sewage gets reintroduced to the overall sewage system flow. Gravity then pulls all the sewage until it reaches its destination, or another pumping station helps it along. 


Eventually, municipal sewer mains flow into larger pipes. These vary in size, depending on the volume the sewage system receives. Sewage is pushed through the pipe system until it reaches the wastewater treatment plant.

Wastewater Treatment 

A wastewater treatment plant is usually located next to another body of water and has specific stages and holding containers used for treating wastewater. The goal is to have the water sterilized and free of sediment for reintroduction into the general water supply.


Chemicals treat wastewater and leave it disinfected. The disinfection effectively kills any living organisms in the water.


Filtering wastewater usually includes several stages of letting the water settle and pushing it through various types of filters. The filters strain unwanted organisms that might have survived disinfection and some sediment.

Sedimentation Tanks

These let the water settle, and physical particles or liquids heavier than water will fall and settle on the sediment tank floor.


Not all sewer services have this second level of filtration. Its purpose is to catch stragglers that somehow have evaded disinfection and the first round of filtration but have not sunk into the sediment tank.


At this stage, machines add chemicals to the water to prompt debris and dirt to collect together in a group called a floc.

Body of Water

The water is then run through one more filtration process to collect the floc, and it is ready for release into a lake, river, or reservoir. 


Water gets tested for foreign matter, debris, dirt, bacteria, parasites, and viruses throughout the wastewater treatment process. Once released into the water system, it is also periodically checked to ensure the wastewater treatment plant is doing its job correctly.


Testing is accelerated whenever a wastewater facility gets flooded. When floodwaters breach wastewater treatment tanks, the water we take for granted can become contaminated. When there is a flood, environmental personnel test the water supply for the presence of harmful chemicals, bacteria, parasites, and viruses. 


Each testing personnel is looking to determine if the water is safe for drinking, cooking, bathing, or general washing.

Final Thoughts

Until a problem develops, sewage systems are out of sight, out of mind for most people. Understanding how the sewage system works is important for residents’ peace of mind and municipal transparency.