[Effect of Initial pH on Nitrogen Removal Performance and N₂O Emission of a Sequencing Batch CANON Reactor]

A completely autotrophic nitrogen removal over nitrite (CANON) reactor with haydite as carrier was operated in a sequencing batch biofilm reactor. The effect of different initial pH on nitrogen removal performance and N₂O emission was investigated using synthetic inorganic ammonia-rich wastewater as influent at 30℃±1℃. During the experiment, the pH of influent was controlled at 6.64, 6.98, 7.15, 7.88 and 7.95 under the same influent ammonia concentration condition, with hydraulic retention time of 5 hours and aeration rate of 6 m³·(m³·h)^-1. The results showed that, when the initial pH was between 6.64 and 7.95, the performance of autotrophic nitrogen removal over nitrite was basically stable. The total nitrogen removal efficiencies were 81.38%, 87.32%, 92.12%, 88.21% and 86.84%, respectively. And the total nitrogen removal loads were all higher than 1.56 kg·(m³·d)^-1. Initial N₂O emission rates were basically equal and decreased after rising to a peak value. Besides, the lower the initial pH was, the higher the maximum N₂O emission rate was. In addition, N₂O emissions and ratios decreased with rising initial pH. Initial pH between 6.64 and 7.95 had little influence on nitrogen removal but N₂O emissions. Initial pH should be kept at about 7.90 to achieve high efficient nitrogen removal and reduction of N₂O emission synchronously.