Have you ever stopped to ask what happens after you flush the toilet, or let out the dishwater? Today we're going to discuss how sewer and septic systems work.
Some people might wonder why we can't simply dump wastewater onto the ground outside, or something similar, which leads us to the three reasons why we use sewer and septic systems:
1. Bad odors. Wastewater quickly becomes smelly when released directly into the environment.
2. Bacteria. Human waste contains E.coli and other coliform bacteria that can contaminate water and become a health hazard that causes disease and even death.
3. Pollution. Wastewater contains phosphates and nitrogen, two fertilizers algae need to thrive. When algae grow excessively, it blocks out sunlight, which causes water to become foul. Organic material in the water will start decomposing, which consumes the oxygen in the water that fish need to survive. All these factors combine to destroy the ecosystem of the lake or stream, causing it to no longer be able to support wildlife, and that is why we use sewer and septic systems.
How Do Septic Systems Work?
Septic systems are usually installed in rural areas, where homes are far apart and where it is impractical and expensive to create infrastructure for sewer systems. Therefore, a septic tank acts as the family's own private sewage treatment plant.
What is a Septic Tank?
A septic tank is a large steel or concrete tank, which is buried near the home. It holds around 4,000 liters of water. Two pipes are suspended from different ends of the tank; with wastewater flowing in from the one end (originating from the home's sewer pipes) and leaving from the other when new water displaces existing water, to a drain field. The drain field is made up of perforated pipes that are buried in gravel-filled trenches. The water is slowly absorbed by the ground in the drain field.
If you were to look at a cross-section of the tank, you would note three layers:
Scum - Items that float will rise to the top of the tank.
Sludge - Heavier solids will sink to form a sludge layer.
Clear - The middle section of water is fairly clear, although it contains bacteria, as well as chemicals such as phosphorous and nitrogen.
As you can imagine, the gasses from the septic tank smell foul, and that's why P-traps in the sinks are designed to keep the gasses from entering the home.
Most septic systems are powered by gravity.
How Do Sewer Systems Work?
Urban and suburban areas use sewer systems, a practical solution in areas with many people living close together, creating lots of wastewater. The municipal system carries wastewater to nearby treatment facilities.
The system starts in the home, from where pipes flow into the sewer main. As the system nears the treatment facility, pipes are larger in diameter until it reaches the plant, where it undergoes several stages of treatment. The primary plant has the same function as a septic tank, using a screen to sift out solids. Water is then sent to a series of ponds or pools that allow the solids to settle.
During secondary treatment removes nutrients and organic materials, using bacteria in aerated tanks. This stage can help remove up to 90% of organic materials and solids.
Finally, during the tertiary treatment phase, the water will be treated according to the needs of the community and the wastewater composition. In most cases, chemicals are added to remove nitrogen and phosphorous from the water. However, the system may also include other types of treatment. Before the water is discharged, chlorine is added to kill whatever bacteria is left, and water is tested to ensure the efficacy of the plant.