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Discharge treatment

The first technique to reduce the emissions of pollutants in the water is the reduction “at source”, which requires better control of the processes and results in the reduced production of wastewater.
The hazard level of certain products or the sensitivity of certain milieus can lead to banning their discharge or even their usage in certain areas.
With the exception of certain activity sectors, total reduction in liquid industrial wastewater remains limited.

Therefore, treatment processes consist of trapping, concentrating or transforming the pollutants in order to reduce the polluting nature of the industrial wastewater before discharge.
In most cases, these techniques result in the production of waste which must also be disposed of (sludge, salts, concentrates, used filters etc.).

There are two main categories of liquid wastewater treatments:

  • biological treatment processes, aimed at degrading the organic material and certain mineral compounds by the action of specific micro-organisms. The pollution is transferred from the liquid wastewater to an insoluble phase (biological sludge) that must be extracted and treated.
  • physical-chemical treatment processes, aimed at trapping (settling, filtration, adsorption, ion-exchange resins) or chemically transforming the pollutants (chemical oxidation, neutralisation, precipitation). Depending on the nature of the pollutants and required remediation level, these treatments can be combined.
Type of pollutionBiological treatmentPhysical-chemical treatment
Organic Depending on biodegradability Yes
Nitrogenous Yes Ammonia stripping
Phosphorus Alternately anaerobic / aerobic Precipitation-settling
Metallic No Oxidation/precipitation/settling Concentration by recycling, ion-exchange resins, membrane techniques, electrolysis Activated carbon adsorption
Pesticides, PAH, benzene and organochlorines No Powerful chemical oxidation Activated carbon adsorption Nanofiltration, reverse osmosis (significant cost)
VOC Attached growth Stripping Chemical oxidation Activated carbon adsorption
PCB No Specific high temperature incineration Activated carbon adsorption
Arsenic No Precipitation Adsorption ion-exchange resins Membrane filtration