It consists of removal of floating material (like dead animals, tree branches, papers, plastics, wood pieces, vegetables peels etc) and also the heavy settleable inorganic solids (grit etc). Preliminary treatment includes: Screening, Comminutors, Grit Removal, Skimming Tank etc
The process of absorbing oxygen from air is known as aeration. High amount of O2 is provided in the aeration tank because of high BOD in sewage. Three methods for aeration in activated sludge process Diffused Air Aeration, Mechanical aeration & Combine aerator
The separation or cutting of rail due to friction and abnormal heavy load is called wear. There are three types of wears of rail, Wear of rails at the Top, Wear of rails at the end and Wear at the side of head of rails.