Micro pollutants in drinking water

Micro pollutants, present at concentrations in the order of micrograms or even nanograms per liter, are found in drinking water and include substances such as pesticides, pesticide metabolites, drug residues, cleaning products, cosmetics, and PFAS. These substances are of concern due to their potential health and environmental impacts, even at very low concentrations.

Sources of micro pollutants

These substances reach groundwater and watercourses through runoff, especially from agricultural areas, but also through wastewater and sewage networks. This highlights the complexity of managing water quality in both urban and rural settings.

Current treatment methods and their limits

Some French factories already use treatments, notably activated carbon in granules, to reduce the presence of pollutants. However, the new generations of pesticides and certain particularly soluble or very small molecules highlight the limitations of these treatments. Activated carbon eliminates up to 90% of conventional pesticides but is ineffective on the R471811 metabolite of chlorothalonil or on TFA, a PFAS with an ultra-short chain, and reaches a maximum of 35-45% on regulated PFAS.

SEDIF's new approach

SEDIF, a public establishment that has supplied water to 4 million Ile-de-France residents since 1923, is implementing a new approach to combat these micro pollutants. Richard Dell'Agnola, president of SEDIF, states that inaction would be guilty given the regular appearance of new chemical molecules in rivers and streams.

Technology used by SEDIF

SEDIF has chosen to associate nanofiltration membranes, which retain particles of the size of a nanometer, with low-pressure reverse osmosis membranes, a million times finer than a hair, stopping particles ten times smaller. This combination treats 100% of the flow, stopping micro pollutants while preserving minerals.

How the process works

The process involves passing water under pressure through a wall with extremely small pores. In the device planned by SEDIF, the previously clarified water is propelled at a pressure of 4 to 7 bars. The membranes allow water molecules to pass through but retain some micro pollutants and lime.

Separating the treated water

The process then separates the flow into two. About 85% corresponds to the "permeate," that is, the water that passes through the membrane. SEDIF aims for an elimination of more than 90% of PFAS, pesticides, and drug residues, while preserving some essential minerals such as calcium and magnesium.

Handling the rejected flow

The remaining 15% constitute the membrane reject, which concentrates the pollutants and lime retained before a specific phosphorus treatment and then a discharge into the watercourse from which they originate. This ensures that the pollutants are not reintroduced into the environment.

Implementation timeline

A five-year project to transform three plants is underway. The first new generation membrane was installed on October 2, 2026, in the Méry-sur-Oise plant. Eight membrane lines must be replaced until the end of 2027.

Future plans

SEDIF plans a gradual deployment in the Choisy-le-Roi and Neuilly-sur-Marne plants by 2031. This episode is from the Source Sûre podcast series, which explores the behind-the-scenes of the production of drinking water.