Bilan de Metaux Lourds dans le Bassin Versant D’Une Station D’Epuration

Summary

Waste water of Switzerland are treated in approximatively 763 treatment plants. Sewage sludges which have been anaerobically or aerobically stabilized are, due to their amount of fertilizing elements, used as much as possible as agricultural manure or composted with garbage.

Nowadays, about 70 % of the producted sewage sludges, that is to say 1 680 000 m³/year are spread in agriculture.

Controls made by the FAC (Forschungsanstalt für Agrikulturchemie und Umwelthygiene - Liebefeld) showed that the concentration of heavy metals in these sewage sludges can sometimes be considered as alarming.

In order to collect more information on the importance, the distribution and the causes of the heavy metal pollution of waste water, a study has been carried out on the drainage basin of a middle-size treatment plant (25 000 eq).

Industrial and waste water as well as rain water have been analyzed during one year in order to determine the amount of Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn and Hg. The concentration of Zn has been in particular pointed out. The different parameters which have been analyzed as well as the measured or estimated fluxes made it possible to establish a balance of heavy metals in the drainage basin of a treatment plant. This balance has been controled through analyses of the sewage water arriving in the treatment plant as well as through the digested sludges.