Preliminary treatment includes wastewater screening and blank

The main process of preliminary treatment is the removal of coarse solids and other large materials found in raw wastewater.

Explanation:

The preliminary treatment is used to protect operation of wastewater treatment plants. This is done by removing from wastewater any things that damage pumps, or interfere with subsequent treatment process.

The treatment process include coarse screening, grit removal, and used to remove excess amount of oils and greases.

Wastewater screening is the first operation used at wastewater treatment plants. In this process the object such as rags, paper, plastics and metals are removed to prevent damage and clogging of downstream equipment, piping. The modern treatments use both coarse screens and fine screens.