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.