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 (TM) 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. (c) 2013 Elsevier Ltd. All rights reserved.