Wastewater (Sewage) Treatment (at 34.47 minute)
Originally established by the Royal Commission on
Sewage Disposal (1898-1915), the objectives of sewage
treatment are:
•Avoid pestilence and nuisance (disease and odour)
•The protection of potable water sources from pollution
by sewerage discharge and
•To produce effluents, which after dilution with river water are suitable for abstraction as
sources of potable supply.
Sewage is a complex mixture of suspended and dissolved materials; both categories
constitute organic pollution. Sewage is 99.9% water and the wastewater treatment process
is designed to treat the 0.1% solids. The strength of the sewage and the purity of the
sewage effluent are described in terms of their suspended solids (SS) and
biological oxygen demand (BOD).
The Royal Commission devised measures for both:
•Suspended Solids (SS): Determined by filtration, drying and weighing of a known sample
volume, which is expressed in mg l-1
•Biochemical Oxygen Demand (BOD): The amount of oxygen required by aerobic
microorganisms to decompose the organic matter in a sample of water.