Hunting down micropollutants in Lake Geneva
Even following treatment, wastewater continues to carry trace amounts of a variety of micropollutants, ranging from hormones, pharmaceuticals, and pesticides to anti-corrosive agents used in dishwashing detergents.
Lausanne’s treated wastewater is released into Lake Geneva at a discharge site 700 m from shore, 30 m below the water surface. PhD student Florence Bonvin sampled the lake water above and around the discharge site over a period of ten months. Her results demonstrated the presence of a micropollutant plume and showed that thermal stratification of the lake water during the warmer months traps the plume at a depth where its density matches that of the surrounding water. As a result, the concentration of certain micropollutants, mainly antibiotics, can reach levels that pose a risk to the environment. In an ongoing follow-up study, data obtained using a submarine from the elemo field campaign are being evaluated to delineate the plume’s boundaries.