The treatment of wastewater in “sewage treatment plants” or “wastewater treatment plants” involves different steps including physical, biological and chemical processes. Before wastewater enters a treatment facility, it typically flows through a screen, which removes large floating objects like sticks, cans, bottles and plastic packets (Preliminary Treatment). Geneally, screens are placed in a chamber or channel and vary in form and size. The inclined screen allows debris to be caught on the upstream surface of the screen and allows access for manual or mechanical cleaning. (Tchobanoglous et al. 2003 & EPA 2004) There are up to four treatment steps involved before the water is released into the environment.

• Primary treatment

• Secondary treatment

• Tertiary treatment

• Fourth treatment stage