Nitrogen removal via nitrite in a sequencing batch reactor treating leachate: evaluation under uncontrolled pH, dissolved oxygen, and temperature values

ABSTRACT In recent years, various processes have been studied for removing nitrogen from high-ammonia wastewater, particularly those that use nitrite as the main oxidant in denitrification. In this study, a sequencing batch reactor treating landfill leachates was monitored for 277 days, 53 days for biomass acclimation, 106 and 118 days operating in 48 and 72 h cycles, respectively (48 h: 24 h of aerobic, 23 h of anoxic, and 1.0 h for sedimentation, discharge and new loading, and 72 h: 48h of aerobic, 22.5 h of anoxic, 1.0 h for sedimentation, and 0.5 h for discharge and new loading). Nitrite accumulation was observed without controlling the dissolved oxygen (DO) concentration, pH and temperature (80% for 48 h cycle and 39.5% for 72 h cycle). The quality of raw leachate, such as the high pH (8.2 to 9.5) and high-ammonia nitrogen (495–1,302 mgNH4+−N/L), favored nitrite accumulation. The combination of raw leachate quality with temperature, pH, and DO conditions resulted in 39.7% savings of an external carbon source. The average nitrogen removal rate was 75% (48-h cycle) and 82% (72-h cycle). Hence, the findings of this study confirm the biological removal of nitrogen under uncontrolled conditions for temperature, DO, and pH.