Long-term study of nitrate, nitrite and pesticide removal from groundwater: A two-stage biological process

The simultaneous biological removal of nitrate, atrazine, deethylatrazine and metolachlor, chemicals frequently encountered in groundwater, in a two-stage continuous system, was studied. A primary denitrification step in a reactor packed with ceramic biofilm carrier was followed by passage through an aerobic expanded-bed reactor packed with Kaldnes™ carrier. This second step removes almost all NO2–N and up to 78% total organic carbon (TOC) residues passed by the denitrifying reactor. In spite of shock loads and other environmental changes, the two-stage process removes more than 99% of nitrate at the rate of 0.34 g l−1 NO3–N day, and up to 80% of deethylatrazine, 25% of atrazine, and 45% of metolachlor. However, the final effluent exceeded the maximum contaminant levels for pesticides and total organic carbon according to the EU Drinking Water Directive.

► Nitrate, nitrite are removed from groundwater with a two-stage biological system. ► Metolachlor, atrazine and its metabolites can be removed by this system too. ► Dissolved organic carbon is also removed by the system. ► The system is resistant to shock loads and environmental changes. ► Rates of denitrification and pesticide removal have been determined.