The anaerobic treatment of nitrite containing wastewater using an expanded granular sludge bed (EGSB) reactor

The integration of denitrification from nitrite with methanogenesis was studied in this work. Experimental results from the continuous treatment of wastewater containing nitrite, which lasted for 144 days, demonstrated that wastewater containing nitrite could be anaerobically treated in an expanded granular sludge bed (EGSB) reactor. From 92% to 97% of COD was removed at organic COD volumetric loading rates up to 6.5 g COD l(-1) d(-1). Nitrite was denitrified for 97% to 100% at nitrite volumetric loading rates up to 0.9 g NO2--N l(-1) d'. Batch tests of 15 days with sludge from the reactor showed that 100% of nitrite and 93 to 95% of COD were removed. Nitrite was denitrified for 92 to 96% to N-2. The remaining nitrite might be converted to NO and N2O. The ratio of COD to NO2--N for the denitrification was varied from 2.49 to 5.64. Denitrification from nitrite preceded methanogenesis. Methanogenesis recovered rapidly after the denitrification from nitrite was completed. No dissimilatory reduction of nitrite to ammonium occurred. Some small losses of ammonium could not be accounted for in the process.