This causes some of the dissolved gases (such as hydrogen sulfide, which smells like rotten eggs) that taste and smell bad to be released from the water. One of the first steps that a water treatment facility can do is to just shake up the sewage and expose it to air. From here on, gravity takes over to move the wastewater through the treatment process.
If the plant is built above the ground level, the wastewater has to be pumped up to the aeration tanks (item 3). So wastewater-treatment plants are located on low ground, often near a river into which treated water can be released. The wastewater system relies on the force of gravity to move sewage from your home to the treatment plant. Most of these materials are sent to a landfill. Unless they are removed, they could cause problems later in the treatment process. Wastewater entering the treatment plant includes items like wood, rocks, and even dead animals.
