Study on Stability and Influencing Factors of Nitrite Accumulation in Biological Aerated Filter

Study was made on stability and influencing factors of nitrite accumulation in Biological Aerated Filter (BAF) treating simulated municipal wastewater. The possibility of shortcut nitrification-denitrification in low ammonia wastewater treatment was discussed. The mode of natural start-up was favorable to the nitrite accumulation in BAF and the highest nitrite accumulation rate was over 80%. By adjusting pH, nitrite accumulation can take place in BAF. When the influent pH value was 6.5 to 7, the highest nitrite accumulation rate was 57%. But long-term stable nitrite accumulation cannot be obtained only through changing influent pH value. The lower concentration of DO was of advantage to the formation of the nitrite accumulation. When the concentration of DO was controlled to less than 0.5 mg/L, the nitrite accumulation rate can improved significantly to the maximum over 80%. The increasing of hydraulic loading can contribute to nitrite accumulation. When the hydraulic loading was enhanced to 10 m³/(m²·h) , the average nitrite accumulation rate can be increased by 52.5 times. The increasing of influent ammonia loading cannot improve nitrite accumulation notably. When influent pH was 6.5 to 7, concentration of DO was 1.0 to 1.5 and the filtration rate was 5 m/h, the nitrite accumulation of BAF reactor was of good stability. During 60 days´ running, the nitrite accumulation can keep at 65% to 75% stably and obvious shortcut nitrification-denitrification was found.