What does Sewage Treatment involve?
Sewage treatment involves: The removal of solids by physical screening or sedimentation The removal of soluble and fine suspended organic pollutants by a biological oxidation process. Both forms of treatment produce sludge as by-products and these have to be treated and disposed of separately in an economical and environmentally acceptable way. (See the description below on sludge treatment.) The following describes a typical sewage treatment sequence which is illustrated in Figure 1. In practice, there are many process variations employed according to locality and the standard of effluent required. Preliminary Treatment Screening Large solids (plastics, rag, woody material) are removed first by mechanical screens. Traditionally, screening was used to remove only large solid material (> 25-30mm) in order to protect downstream operations. Nowadays, much finer screens (6mm mesh) are commonly employed to remove smaller inert solids. The material retained (‘screenings’) is usually washed t
