Water Treatment

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Water Treatment Factsheets


Conventional water treatment and what it involves.


Flotation involves the formation of small bubbles in water that has to be flocculated. The bubbles attach to the floc causing them to rise to the surface where they are collected as a froth that is removed from the top of the flotation unit.


Sedimentation is a suitable process for the removal of flocs formed from silt and clay particles that are relatively heavy and settle readily.  However, certain flocs are relatively light and do not settle readily and a process such as flotation must be used for their removal.

Coagulation & Flocculation

Coagulation is the process by means of which the colloidal particles are destabilised (i.e. the nature of the colloidal particles is changed so that they form flocs through the process of flocculation that can be separated from the water). Destabilisation is achieved through the addition of chemicals (called coagulants) to the water.

Coagulation: Important factors and the beaker test

“The process of adding chemicals to water to destabilize charges on naturally occurring particles to facilitate their subsequent aggregation and removal by flocculation or filtration. There are a number of very important factors to consider when you want to ensure proper and successful coagulation.

Coagulation Chemicals

Different chemicals can be used as coagulants. The most common coagulants are aluminium sulphate, ferric chloride, lime and polyelectrolytes. Coagulant-aids are also sometimes used. These are substances added in very small quantities to improve the action of the primary coagulant.

Disinfection: Overview

Disinfection of water entails the addition of the required amount of a chemical agent or disinfectant (e.g. Chlorine gas, Cl2, ozone, chlorine dioxide and other chlorine compounds such as calcium hypochlorite (HTH), sodium hypochlorite (bleach) and monochloramine) to the water and allowing contact between the water and disinfectant for a predetermined period of time (under specified conditions of pH and temperature).

Disinfection: Chlorination

Chlorine is a strong oxidising agent and it reacts and oxidises some of the essential systems of micro-organisms, thereby inactivating or destroying them. The different forms, in which chlorine is used for disinfection, have different oxidising powers.

Disinfection: Ozone

Oxygen in the air (O2) is composed of two oxygen molecules. Under certain conditions, three oxygen atoms can be bound together instead, forming ozone (O3). It is also referred to as activated or enriched oxygen.  Ozone occurs naturally in the earth’s atmosphere and protects us from the sun’s harmful rays. Thousands of tons of ozone are produced daily during thunderstorms or around high-tension lines.  Ozone is applied commercially as a disinfectant instead of chlorine and other disinfectants. It is used in air and water purification. It destroys algae, bacteria, molds and mildews, eliminates spores, yeast and fungus and inactivates viruses and cysts.

Disinfection: UV

Ultraviolet or UV-light is light outside the range usually detectable by the human eye. It can be used to deactivate protozoans so that they can’t reproduce and to significantly reduce the bacteria in water. UV radiation kills or inactivates micro-organisms, provided each organism receives a minimum amount of radiation. UV radiation functions on the principle that each unit of water must be exposed to the radiation for a minimum amount of time at minimum dosage intensity.

Residual Handling and Treatment

What waste products are generated during water treatment and how can waste be handled and disposed of?

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