Micropollutants in water: treatment processes

The technologies employed for the treatment of micropollutants in water depend on the physico-chemical characteristics of each compound present in water.  In the same family, many varieties of components can be found: hydrophilic or hydrophobic – adsorbable – volatile or semi-volatile – biodegradable – refractory – high or low molecular weight. The treatment processes used are:

 

  • Biological Degradation
  • Adsorption
  • Oxidation
  • The membrane separation technique

 

The Biological Degradation treatment of micropollutants in water

Biological treatment utilizes a great variety of microorganisms, mainly bacteria. These microorganisms convert matter that is biodegradable by absorption of the soluble or suspended constituents into wastewater into simple products such as carbon dioxide and additional biomass, or nitrate and nitrogen gas if the necessary conditions are present.


As certain bacteria in activated sludge have enzymes with affinities for a particular micropollutant, they can degrade or convert those substances. Other bacteria mineralize micropollutants by using them as a source of carbon and energy.

 

The Adsorption treatment of micropollutants in water

Adsorption is the adhesion of molecules onto the surface of an adsorbent solid using various processes of differing intensity (using Van der Waals forces of attraction = physical adsorption, or same type forces which are involved in the formation of chemical attractions = chemical adsorption).

 

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In wastewater treatment, activated carbon is widely proposed for adsorption of the micropollutants.   This material can either be in granular form in a filter or in powder form usually in an activated carbon contactor/separator.

 

The Oxidation treatment of micropollutants in water

In addition to disinfection, oxidation by physico-chemical means is also used for water treatment to decolour and degrade the organic compounds and to convert non-biodegradable pollutants into substances that can be assimilated by the bacteria in a downstream biological treatment process.

 

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The choice of oxidant to be used is dictated by the good selectivity towards the targeted pollution.


The membrane separation treatment of micropollutants in water

The membrane separation technique applies selective resistance to the transfer of different constituents of a liquid or gaseous fluid and thus separates some of the elements composing such fluid. The separation process creates a pressure which constitutes the driving force enabling the fluid to pass through the membrane. The membranes provide a real physical barrier for impurities and pathogenic germs.

 

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Microfiltration and ultrafiltration membranes eliminate micropollutants in the water mainly by retaining the suspended solids to which they are attached. Performance is limited, however, as the majority of micropollutants are smaller than the cut-off threshold of the microfiltration or ultrafiltration membranes.


Due to their low cut-off level, nanofiltration and reverse osmosis retain, in a more efficient way, a broad spectrum of soluble micropollutants.

 

January 2013

 

 

 

<-- Special Topics: Water, technologies, Partnerships

 

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Liste des micropolluants dans l'eau

 

More information on the micropollutants presence in the natural environment and the list of micropollutants here


 

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