Trying to clean Civilization's Waste Water

Not only do we clean water from rivers so that we can use it, we also can clean waste water that we use. This is done at sewage treatment plants.
Note: Much of the information on this page came from the Johnstown Sewage Treatment Plant home page

First, waste water is collected from homes and industries through the sewer system, which is a collection of pipes that runs throughout a city to each home or business. These pipes join together to enter the treatment plant in a single huge pipe... the one in Johnston County Pennsylvania has a diameter of 60 inches (that's 5 feet across, or 1.52 meters)!

When the sewage enters the plant, it runs through several grinding pumps, whose blades chop up any large solids to keep them from damaging other pumps. The heavy mixture is immediately sent to a tank called the primary settler tank, were the heaviest solid pieces of waste fall to the bottom of the tank. These solids are moved to a "sludge thickening tank", where they will be collected and disposed of, usually in a landfill.

The water is then pumped off of the top to a different tank, where it is mixed with the chemical chlorine. Chlorine is the same chemical that is put into pools that you swim in! Chlorine acts as a disinfectant, which kills many bacteria (types of microorganisms), and also helps chemical reactions take place that will "digest" some of the waste in the water.

Some sewage treatment plants utilize a special room called the Pure Oxygen Reactor. These plants pump the water from the chlorine tank into a buried room where 98 % of the air is oxygen gas! Certain bacteria which were not killed by the chlorine will now help digest any other solid matter in the water. The 98% oxygen in the air helps the bacteria to work better!

Now the water is sent to a clarifying tank, where the water is allowed to sit and remaining solids settle to the bottom. Oil and greases are skimmed off of the top, and more chlorine is added. The water is then sent off into the river!

Visit the Johnstown Sewage Treatment Plant Tour for more information and pictures...