Unfortunately we live in a polluted environment; it is not only the air we breathe, it is also water pollution and even noise pollution. Although air and noise pollutants cannot be gathered up and put in a box, pollution control tanks are used to treat the raw sewage to the point where it is once again safe to drink.
That sounds like a tall order but the treatment is so sophisticated today that even microscopic microorganism is eliminated. This is not true in all countries of course, but in first world countries like the United States, domestic waste is sent via an underground sewage system to a treatment plant where it is discharged into pollution control tanks. Although sewage treatment plants for large municipalities are done in purpose built facilities and the tanks are large concrete in-ground tanks, this is not true for all. Smaller municipalities and even companies that have a great deal of process waste have above ground facilities using large steel pollution control tanks often lined with a material which will not be harmed by the acrid mix.
As the untreated waste enters the facility the first step is to remove large objects that can easily damage the equipment if allowed to go through. A mechanical screen called a trash rake is employed, it collects any large objects. These objects are sent to a landfill site for disposal.
Once the sewage has been screened, it travels to another tank for primary treatment. Here, particles settle to the bottom of the tanks and form sludge; the sludge also is collected and treated off site. As oil and grease floats on water, it too is removed at this stage.
The waste water is now ready to move on to secondary treatment where it settles in pollution control tanks where biological matter breaks down. This is normally done by the introduction of bacteria which break the material down, eventually these bacteria precipitate out.
The final stage is to move into a tank where further filtration takes place as well as disinfection. This treatment includes the introduction of chlorine or to treat the water with UV light or subject it to ozone. All three of these treatments eliminate bacteria and any harmful organisms.
