Water treatment

A sewage treatment plant in northern Portugal.

Water treatment describes those processes used to make water more acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the concentration of such contaminants so the water becomes fit for its desired end-use. One such use is returning water that has been used back into the natural environment without adverse ecological impact.

The processes involved in treating water for drinking purpose may be solids separation using physical such as settling and filtration, chemical such as disinfection and coagulation.

Biological processes are also employed in the treatment of wastewater and these processes may include, for example, aerated lagoons, activated sludge or slow sand filters.

Potable water purification

Main article: Water purification

Abandoned Water Purification Plant Springfield, Tennessee

Water purification is the removal of contaminants from untreated water to produce drinking water that is pure enough for its intended use, most commonly human consumption. Substances that are removed during the process of drinking water treatment include bacteria, algae, viruses, fungi, minerals such as iron, manganese and sulphur, and man-made chemical pollutants including fertilizers.

It is important to take measures to make available water of desirable quality at the consumer end. That leads to protection of the treated water during conveyance and distribution after treatment. It is common practice to have residual disinfectants in the treated water in order to kill any bacteriological contamination after water treatment.

World Health Organization (WHO) guidelines are generally followed throughout the world for drinking water quality requirements. In addition of the WHO guidelines, each country or territory or water supply body can have their own guidelines in order for consumers to have access to safe drinking water.

Processes for drinking water

The combination of following processes is used for municipal drinking water treatment worldwide:

• Pre-chlorination - for algae control and arresting any biological growth
• Aeration - along with pre-chlorination for removal of dissolved iron and manganese
• Coagulation - for flocculation
• Coagulant aids also known as polyelectrolytes - to improve coagulation and for thicker floc formation
• Sedimentation - for solids separation, that is, removal of suspended solids trapped in the floc
• Filtration - for removal of carried over floc
• Disinfection - for killing bacteria

There is no unique solution (selection of processes) for any type of water. Also, it is difficult to standardise the solution in the form of processes for water from different sources. Treatability studies for each source of water in different seasons need to be carried out to arrive at most appropriate processes.

Sewage treatment

Main article: Sewage treatment

Sewage treatment is the process that removes the majority of the contaminants from wastewater or sewage and produces both a liquid effluent suitable for disposal to the natural environment and a sludge. To be effective, sewage must be conveyed to a treatment plant by appropriate pipes and infrastructure and the process itself must be subject to regulation and controls. Some wastewaters require different and sometimes specialized treatment methods. At the simplest level, treatment of sewage and most wastewaters is carried out through separation of solids from liquids, usually by settlement. By progressively converting dissolved material into solids, usually a biological floc which is then settled out, an effluent stream of increasing purity is produced.

In developing countries

As of 2006, waterborne diseases are estimated to cause 1.8 million deaths each year. These deaths are attributable to inadequate public sanitation systems and it is clear that proper sewerage (or other options as small-scale water treatment) need to be installed.

Appropriate technology options in water treatment include both community-scale and household-scale point-of-use (POU) designs. Military surplus water treatment units like the ERDLator are still seen in developing countries. Newer military style Reverse Osmosis Water Purification Units (ROWPU) are portable, self-contained water treatment plants are becoming more available for public use.

In order for the decrease of waterborne diseases to have long term effects, water treatment programs implemented by research and development groups in developing countries must be sustainable by its own residents. This can ensure the efficiency of such programs after the departure of the research team as monitoring is difficult because of the remoteness of many locations.

See also

• Agricultural wastewater treatment
• Ecological sanitation
• Industrial wastewater treatment
• Peak water
• Water pollution
• Water quality
• Water supply network

External links

• International Water Association Professional / research organization
• [1] - WHO Guidelines
• Nanotechnology-enabled Water Treatment-Project NeWT, Center for Biological and Environmental Nanotechnology (CBEN), Rice University
• NSF International - Independent non-profit standards organization
• Photo essay of water treatment system - by photographer Marc Steinmetz
• Water Environment Federation - Professional association focusing on wastewater treatment