Sewage Treatment Objectives
As populations increase by leaps and bounds, it places more pressure on the environment and threatening sources of fresh water supplies, it was recognized that the problem of 'human waste' needed proper management.
From the early 1900s there has been a steady evolution of sewage treatment into today's modern sewage treatment plants producing high quality effluent, which can be safely discharged to the environment or reused.
More recent developments in sewage treatment have been to improve the reliability and efficiency of treatment systems to treat sewage to meet standards and reduce the land area occupied by treatment works through accelerating natural treatment rates under controlled conditions.
However, despite these developments sewage treatment systems are still mainly concerned with the removal of suspended and floatable materials, the treatment of biodegradable organic and in some cases the elimination of pathogenic organisms.
Sewage treatment methods may be classified into physical unit operations, chemical unit processes and biological unit processes.
Physical Unit Operations
Physical unit operations are treatment methods, which use the application of physical forces to treat sewage. These include screening, mixing, flocculation, sedimentation, filtration and flotation.
Chemical Unit Processes
Treatment methods in which the removal or conversion of pollutants by the addition of chemicals or by chemical reactions are known as Chemical Unit Processes. These include precipitation, adsorption and disinfection.
Biological Unit Processes
Biological unit processes describe methods, which remove pollutants by biological activity. Biodegradable organic substances are converted into gases that escape to the atmosphere and cell tissue is removed by settling.
Basic Biological Reaction in an Oxidation Pond