The entire treatment process starts with a pre-treatment phase. It’s the stage which works to remove materials conveniently collected from raw wastewater so that they can’t clog or damage skimmers or pumps of primary sewage treatment clarifiers. These materials could be leaves, tree limbs, trash etc. The sewage water gets thoroughly strained to sift out large objects that are carried through sewage stream. An automatic mechanical raked-bar screen is the most common aide here, especially for modern sewage treatment plants. However, smaller plants might go for manual screening.
The solids collected are disposed in landfills or else are incinerated. The pre-treatment phase generally comprises of grit removal.