Wastewater Treatment

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Wastewater Treatment Factsheets


The treatment of sewage involves the systematic removal or conversion of the harmful constituents present in sewage.

Coarse Screens

Sewage passes through bar screens for removal of larger objects (rags, plastics, tins, wood, etc.) Automatic or manual bar screen cleaners remove the larger objects from the raw sewage.  The collected material is temporarily stored to be transferred later to a landfill site.


Wastewater grit materials (known as detritus) include sand, silt, cinders, stones, glass metal particles and other large-sized, relatively non-putrescible organic and inorganic substances.

Biological Filters

The filter consists of an outer shell normally made of concrete. Under-drains on the floor of the filter allow for the collection of the effluent from the bottom of the filter and allow for the free passage of air through the filter, which is important, as the micro-organisms, which grow in a filter, require oxygen from the air to live.

Activated Sludge – Overview

The process was discovered by the aeration of holding tanks for distributing raw sewage onto land.  It was noticed that the nature of the sewage improved during aeration, which was applied mainly to prevent odours from forming.

Sludge digestion – Overview

In wastewater treatment considerable quantities of sludge are constantly being produced.  In their raw state the sludge are putrescible and rapidly develop strong and obnoxious odours.  Sludge also contain pathogenic (disease-causing) organisms harmful to man.  It is therefore necessary to contain and treat these wastes.

Sludge Thickening and Handling

Thickening is the process used to increase the solids content of sludge by the separation and removal of a portion of the liquid phase.  Gravity thickening makes use of the force of gravity as the main agent in the settling and thickening process.

Effluent Disinfection

The disinfection treatment process will remove or inactivate pathogenic micro-organisms. Not all organisms are killed during disinfection, as is the case with water sterilization. The purpose of disinfection is to kill or inactivate all the primary micro-organisms, such as bacteria, viruses and protozoan cysts.

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