[Optimization of the Nitrogen Removal Performance on the CANON Process in a Biofilm Reactor: From FBBR to MBBR]

To optimize the performance of completely autotrophic nitrogen removal over nitrite (CANON), a CANON process with modified polyethylene as carriers was operated in a moving-bed biofilm reactor (MBBR), using synthetic inorganic ammonia-rich wastewater (NH₄⁺-N about 400 mg ·L^-1) as influent at 30℃±1℃. With an HRT of 6 h, pH at 7.8, and filling rate of 35%, the average removal rate of NH₄⁺-N and TN reached 74.28% and 87.93%, respectively, and the highest removals reached 84.68% and 98.82%, respectively, while the value of ΔNO₃^-/ΔTN was 0.12, which was close to the theoretical value of 0.127. This suggested that CANON sludge gradually adapted to the environment in the MBBR and began to enter the stable stage. Compared with a fixed-bed biofilm reactor (FBBR) under the same influent and operating conditions, the mean square error of MBBR and FBBR in terms of NH₄⁺-N removal rate, TN removal rate, and TN removal load were 8.31% and 14.06%, 7.09% and 1.79%, 0.17 kg ·(m³ ·d)^-1 and 0.27 kg ·(m³ ·d)^-1, respectively, the former are lower than the latter. Moreover, while DO concentrations of MBBR and FBBR were 1.96 mg·L^-1 and 3.09 mg ·L^-1, respectively, their TN removals of per liter carriers were 0.53 kg ·(m³ ·d)^-1 and 0.37 kg ·(m³ ·d)^-1. Therefore, it was concluded that:① MBBR had a more stable nitrogen removal performance than did of FBBR, and ② MBBR had a higher TN removals of per liter carriers than did FBBR in addition to the higher utilization rate of oxygen.