CHEMICAL DENITRIFICATION DURING EVAPORATION/DRYING OF LANDFILL LEACHATES / Kemisk denitrifikation vid avdunstning/torkning av lakvatten

A new treatment system has been proposed to remove nitrogen from landfill leachates with the combination of partial nitritation (biological oxidation of ammonium to nitrite) followed by chemical denitrification with oxidation of remaining ammonium with nitrite to nitrogen gas (Nikolic and Hultman, 2003 a). Chemical denitrification is much dependent on high concentrations of ammonium and nitrite and the use of evapora-tion/drying as a concentration method with temperatures at 60 and 90°C, respectively, was investigated in this paper. Small initial sample volumes (normally 20 ml) were used in the experiments due to possible safety risks as crystals of ammonium nitrite may explode when heated above 60-70°C. In the experiments nearly all nitrogen was transferred to the gas phase at initial neutral pH-values during the evaporation/drying process (somewhere between 75 and 100 % removal of liquid) both for a water solution and leachate with the same initial concentration of ammonium and nitrite nitrogen. Thus, from a technical standpoint a system with partial nitritation to the same amount of ammonium and nitrite nitrogen followed by chemical denitrification during evaporation/drying has a great potential. The removal of ammonium nitrite was very well correlated with the decrease of conductivity. Before the proposed system can be applied in full-scale, safety risks must be carefully studied and evaluated (for instance the use of evaporation technology that operates at low temperatures in combination with natural drying of the concentrate) as well as possible side reactions forming nitrogen oxides or release of ammonia