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Originally a natural phenomenon

Eutrophication is an   aging phenomenon that affects water bodies (lakes, ponds).

For thousands of years, on a geological age scale, sediments gradually settle in the lakes as well as organic waste from different origins. Eutrophication is in fact a natural aging of water bodies. This  aging  process results in a gradual increase in the lake’s or pond of crop production.

With an abundance of nutrients; nitrogen (contained in ammonium, nitrates, and nitrites) and phosphorus, aquatic plants and algae multiply at a great scale , gradually modify the ecosystem of the water body, and generate in the medium to long term significant changes in water quality. This phenomenon jeopardizes the survival of miscellaneous animal species residing there.

A phenomenon amplified by human activities

Since the advent of industrial revolutions in the 19th century, our societies moved from the artisanal and agricultural era to mass production based on industrialisation in all areas.

This radical change in human activities has certainly contributed to the development of our civilization, but also had an  important impact on our ecosystems. Impact whose magnitude and diversity we measure today. Nitrates are particularly soluble and thus easily carried by

runoff or infiltration water. Above 5 mg/l NO3 in the water of a river it can lead to algae blooms.

Phosphorus (contained in phosphates) is easily carried to watercourses by effluent discharges, and rustle.

These responsible elements, generated by our activities, come from various sources:

– Municipal and industrial wastewater

– Detergents; laundry and soaps

– Industrial discharges

– Domestic fertilizers

– Agricultural fertilizers (fertilizers, manure spreading)

– Abusive deforestation

– Landfill of waste

The effects of eutrophication

When a biological imbalance involving phosphorus and nitrogen occurs in a body of water or a river, plants and algae reach an overabundance of easily assimilable nutrients and will therefore proliferate.

This proliferation affects water quality, transparency and reduces oxygenation. The algae grow on the surface and limit the diffusion of light essential to the chlorophyllous function.

Below the surface, aerobic bacteria that feed on  dead algae and vegetable waste proliferate and consume an increasing amount of oxygen.

The water body becomes oxygen-depleted.

Plants produce oxygen by photosynthesis and consume it by breathing.

At night, plants consume large quantities of oxygen. The water is less oxygenated, a chain reaction begins that affects the fauna and flora of the water body.

To some degree of eutrophication, the body of water “literally chokes”, thus generating

sometimes significant deaths among its inhabitants (invertebrates, fish).

Eutrophication also affects some specific  regions with the proliferation of algae;  for instance it is the case  of sargasso seaweed in the Caribbean, blue-green algae in Canada and  green algae in Brittany. As these algae rot, they release toxic gases such as hydrogen  sulphide. Temperature amplifies the  phenomenon. Thus, in a context of proven global warming, in the absence of control procedures, eutrophication is expected to intensify.

How to fight  eutrophication

The Government of Quebec has adopted an intervention plan against blue-green algae.

The intervention plan recommends the following measures:

  • It is required to reduce phosphorus concentrations in wastewater discharged into

surface water when  such a protection is needed by  the receiving environment (body of water)

  • The best available technology, taking into account technical economic and environmental  constraints, must be put in place to reduce phosphorus concentrations in wastewater;
  • If this is not already the case, equip municipal wastewater treatment facilities with dephosporization equipment, particularly in the case of wastewater discharging into or upstream a lake.
  • Review the requirements related to  the discharge of wastewater  for  water treatment facilities that discharge into or upstream a lake when dephosphorization equipment is already present and if technology allows it.

Treatment of contaminated water involves various methodologies

  • Chemical dephosphatizing by precipitation with iron or aluminium salts, or with lime.
  • Biological dephosphatizing  using bacteria
  • Methanation, which consists of transforming organic matter from waste  of industries or agricultural effluents into bio gas.

Let us mention the important role of Solugen which, with its process  to treat manure and industrial water by azeotropy (a distillation process), allows to recover phosphorus, nitrogen and potassium. These elements, available  in the form of of recycled fertilizers , enable an optimized use of fertilizers, and thus reduce the risk of eutrophication.

Sources :

http://www.environnement.gouv.qc.ca/eau/algues-bv/plan_intervention_2007-2017.pdf

http://www.environnement.gouv.qc.ca/eau/bassinversant/global-2004/Influence2004.htm

http://sagascience.cnrs.fr/doseau/decouv/ecosys/eutrophisat.html

http://www.environnement.gouv.qc.ca/eau/rsvl/methodes.htm

https://inee.cnrs.fr/fr/cnrsinfo/colloque-

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