[Operation Characteristics of the Biofilm CANON Reactor During the Temperature Reduction Process].

The focus of this paper, was low temperature, high ammonia nitrogen wastewater. The operation characteristics of the biofilm CANON process during the temperature reduction process were determined, by continuously adjusting different operating conditions. The aim was to explore the methods needed for the CANON process to obtain stable shortcut nitrification and a good nitrogen removal effect, when the influent NH4+-N concentration is high and the temperature low. The results showed that, ① compared with the biofilm CANON reactor temperature changing from medium to low temperature directly (30℃±1℃→19℃), it was more conducive to adapt the nitrogen-removing bacteria to the low-temperature environment, while the temperature was gradually lowered. Moreover, the extent of each reduction should be minimized. Besides, the operating conditions should be adjusted to ensure the nitrogen removal effect. ② The temperature was gradually reduced to about 19℃ after 25 d, and then decreased to about 15℃ after another 18 d. The NH4+-N and TN removal rates could be respectively stable at 90% and 70% over a long period of time. The TN removal rate and removal load could still reach 72.52% and 0.78 kg·(m3·d)-1, respectively, even when the temperature dropped to 12℃. ③ When adapting biological CANON sludge during the temperature reduction process, shortcut nitrification should be given priority. A stable shortcut nitrification effect should be obtained by maintaining a certain concentration of residual NH4+-N, and by strictly controlling the DO concentration to restrain NOB activity.

[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.

[Short-cut Nitrification Recovery and Its Transformation into CANON Process in a Biofilm Reactor].

A short-cut nitrification process with modified polyethylene as carrier was operated to investigate the biofilm short-cut nitrification recovery using synthetic inorganic ammonia-rich wastewater as influent at 30℃ ±1℃. The short-cut nitrification was destroyed first by excessive aeration, and it was not built in 83 days under the condition of continuous aeration with DO less than 0.5 mg·L-1 and free ammonia (FA) more than 1.5 mg·L-1, which are very beneficial to short-cut nitrification. However,short-cut nitrification was realized by changing continuous aeration to intermittent aeration on 84th day, and it was proved again on 142nd day. After that, biofilm system provided a living environment for ANAMMOX bacteria, anaerobic ammonia oxidation occurred, and the biofilm short-cut nitrification process was gradually transformed into CANON process. As the load of influent and aeration increased, the total nitrogen removal efficiency and removal load increased, and the total nitrogen removal load could reach up to 2.52 kg·(m3·d)-1. Finally, in the 3rd stage, ΔNO3--N/ΔTN was 0.10 on average, which means stabe short-cut nitrification in the CANON process. Therefore, once NOB was adapted to FA, it would be not very easy to recover short-cut nitrification, while intermittent aeration was an effective way, and the nitriation process would be finally transformed into CANON process, which would further improve the short-cut nitrification stability.

[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.