[Start-up of CANON Process and Short-cut Nitrification in a Pilot-scale MBBR Reactor].

Using a 150 L moving bed biofilm reactor (MBBR), with the temperature controlled at 28℃ and high NH4+-N concentration (average concentration 350 mg·L-1), inorganic wastewater was used as an influent to start the completely autotrophic nitrogen removal over nitrite (CANON) process. Meanwhile, the flocculent sludge was taken into a 5 L sequencing batch reactor, and the influent NH4+-N concentration was maintained at 90-200 mg·L-1 for the recovery of short-cut nitrification. The results showed that in the MBBR reactor, when the average hydraulic retention time (HRT) was 12 h, short-cut nitrification and total nitrogen (TN) removal rate were mutually constrained, the average TN removal rate was 38.2%, and the average δNO3--N/TN value was 0.274; when the HRT dropped to 6 h, the δNO3--N/TN value decreased from 0.347 to 0.146. The sequencing batch reactor (SBR) maintained aeration and anoxic time for 30 min and 20 min, respectively, by intermittent aeration, while the dissolved oxygen concentration during the aerobic process was 0.5 mg·L-1 to 0.6 mg·L-1, the free nitrous acid concentration was higher than 0.18 mg·L-1 at the end of each cycle, NAR increased from 0 to 99.2% after 12 days, NUR decreased to 0 from an initial 24.8 mg·(g·h)-1, and the TN removal rate decreased from 13% to 3%; the system successfully converted to short-range nitrification. High-throughput sequencing results showed that the abundance of Candidatus Kuenenia in the flocculent sludge and biofilm in the MBBR reactor were 7.91% and 17.38% respectively, Nitrosomonas accounted for 27.43% and 2.55%, respectively, while Nitrospira accounted for 0.30% and 0.28%, respectively. After the recovery of short-cut nitrification in the SBR, the abundance of ammonia-oxidizing bacteria and anaerobic ammonia oxidation decreased to 1.18% and 0.01%, respectively, and the abundance of Nitrospira increased to 1.39%.

[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.

[Impact of C/N Ratio on Nitrogen Removal Performance and N2O Release of Granular Sludge CANON Reactor].

To Explore a suitable C/N ratio for efficient nitrogen removal and simultaneously achieving N2O release reduction, ammonia-rich wastewater with sodium acetate as an organic carbon source in a granular sludge completely autotrophic nitrogen removal over nitrite (CANON) reactor under different C/N water conditions were studied to determine the reactor's nitrogen removal performance and N2O release. The results showed that the total nitrogen (TN) removal rate and the removal load tended to increase gradually with the increase of C/N, ranging from 0 to 2.0. When C/N=0, the TN removal rate was 56.50 mg·L-1 in 7 h; the highest TN removal efficiency was 49%. When C/N=2.0, the highest TN removal rate was 71.42 mg·L-1 in 7 h; the highest TN removal efficiency was 59.52%, and the contribution of CANON to nitrogen removal gradually decreased, whereas the denitrification contribution gradually increased. When △NO3--N/△TN=0.086, the contribution of CANON nitrogen removal was only 51.48% and that of denitrification was 48.52%. The N2O release volume and release ratio decreased with increasing C/N. When C/N=0, the N2O release volume and rate were the highest, namely 3.60 mg and 2.13%, respectively. The lowest N2O release volume and rate were 1.61 mg and 0.75%, respectively, when C/N=2.0.

[Optimization of the Mainstream Anaerobic Ammonia Oxidation Process and Its Changes of the Microbial Community].

The completely autotrophic ammonium removal over nitrite(CANON)biofilm reactor acclimated by high-strength ammonia wastewater was used to treat low-strength ammonia wastewater. The treatment can be divided into three stages:① the nitrogen removal efficiency of anaerobic ammonia oxidation was low during the continuous aeration stage with inorganic wastewater as raw water (0-59 d) and with an aeration amount of 30 mL·min-1 and ammonia concentration of 80 mg·L-1 (until day 56), the TN removal load was only 0.13 kg·(m3·d)-1; ② during the continuous aeration stage with domestic wastewater as raw water (60-110 d), the addition of organic carbon improved the TN removal load to 0.22 kg·(m3·d)-1 on day 79; the removal rate of NH4+-N then reached 100% when the aeration volume improved to 100 mL·min-1 on day 103; however, the TN removal efficiency and TN removal load decreased to 42.36% and 0.14 kg·(m3·d)-1, respectively. ③ To increase both the NH4+-N and TN removal efficiency during the intermittent aeration stage with domestic wastewater as raw water (110-160 d), the aeration amount was increased to 50 mL·min-1, while aeration was continued for 30 min and was stopped for the next 30 min; on day 131, the NH4+-N removal efficiency increased to 86.34%, the TN removal efficiency and removal load reached 85.87% and 0.3 kg·(m3·d)-1 respectively; on day 141, the aeration was increased to 100 mL·min-1 and the removal efficiency of NH4+-N reached 100%, while the removal efficiency and removal load of TN were 64.28% and 0.22 kg·(m3·d)-1, respectively, indicating that the intermittent aeration strategy effectively improves the nitrogen removal performance of the CANON reactor. To analyze the variation of the microbial community during different stages, the samples of three stages (0, 56, and 152 d) were analyzed using high-throughput sequencing technology. The results show that:① Candidatus Brocadia is less affected than Candidatus Kuenenia during the low-strength ammonia stages with inorganic and domestic wastewater as raw water; ② Nitrosominas and Nitrospira were the dominant bacteria of AOB(ammonia oxidizing bacteria) and NOB (nitrite oxidizing bacteria), respectively. Domestic wastewater had a greater impact on Nitrosomonas than on Nitrospira; ③ Denitrifying bacteria were present during the whole stage; Pseudomonas and Paracoccus were the most adaptable, even though their relative abundances during each stage were below 0.5%.

[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.

[Analysis of Precipitation Formation in Biofilm CANUN Reactor and its effect on Nitrogen Removal].

A CANON reactor with polymeric sponge as carrier was started by incubating sludge from another CANON reactor using synthetic inorganic ammonia-rich wastewater as raw water, and was operated at 30 degrees C +/- 1 degree C, pH 6.92-8.52. The precipitation on the surface of carriers was studied in this paper, including influence on nitrogen removal efficiency, causes for formation and composition. The results showed that: (1) the precipitation could influence the distribution of substrate to undermine the performance of CANON reactors; (2) the precipitation was calcium carbohydrate; (3) the production of precipitation may be a common result of four effects that were the regulatory effect of microorganisms on pH value, stripping effect, the role of extracellular polymers, adsorption of sponge and simultaneous chemical, biological reactions; (4) once the precipitation formed, it was difficult to recover to normal. Therefore, some measures are necessary to avoid precipitation, including: (1) raw water pretreatment to reduce the concentrations of Ca2 and Mg2. (2) ensuring short-cut nitrification stable, which could avoid increase of pH because of reduction of DO; (3) we can choose other carriers to reduce precipitation, which must ensure the optimal total nitrogen removal performance and stable short-cut nitrification.

[Effects of Hydraulic Retention Time and Dissolved Oxygen on a CANON Reactor with Haydite as Carrier].

One Completely Autotrophic Nitrogen Removal Over Nitrite ( CANON) reactor with haydite as carrier was investigated to study the effects of different hydraulic retention time ( HRT) and dissolved oxygen (DO) on CANON reactors by seeding sludge from another mature CANON reactor and using synthetic inorganic ammonia-rich waste water as influent. During the experiment, the concentration of influent ammonia nitrogen was basically unchanged, the HRT of the reactor were 9, 7, 5 h in turn and the range of DO was 1.16-3.20 mg x L(-1). The results showed that: (1) When DO was 1.20-1.75 mg x L(-1), despite the increase of DO can improve AOB's activity and matrix mass transfer in the system, NH4(+) -N and TN removal efficiency were still fell with the shortening of HRT for the CANON reactor, especially when DO was higher than 2.50 mg x L(-1), TN removal efficiency dropped sharply; (2) Under the condition that DO was 1.20-1.75 mg x L(-1), with the shortening of HRT, partial nitritation tended to be stable in the CANON process, and when DO was higher than 1.75 mg x L(-1), even if HRT was shorter, partial nitritation was still severely damaged; (3) Under the condition that DO was 1.20-1.75 mg x L(-1) and HRT was 7 h, for the CANON reactor, partial nitritation and total nitrogen removal efficiency kept well. Hydraulic retention time and dissolved oxygen both are important operational parameters for biological wastewater treatment process, which could directly affect the effect of biological treatment and effluent quality, so to choose appropriate hydraulic retention time and dissolved oxygen coordinately is very important to improve the effect of treatment of ammonium-rich wastewater by CANON process.

[Start-up by inoculation and operation of a CANON reactor with haydite as the carrier].

A CANON reactor with haydite as the carrier was started by incubating sludge from another CANON reactor and using synthetic inorganic ammonia rich wastewater as the raw water. Both start-up and operation were studied. The result showed that haydite can be a suitable carrier for CANON reactor. With this carrier, start-up of CANON reactor can be completed in 60 days with total nitrogen removal load up to 0.79 kg x (m3 x d)(-1), when the reactor was equipped with a water jacket to maintain the water temperature at 30 degrees C +/- 1 degrees C, and pH at 7.00-8.08, hydraulic retention time of 9 hours. The critical range of dissolve oxygen for CANON reactor was 1.12-1.69 mg x L(-1), and both characteristics of short-cut nitrification and ANAMMOX were stable. However, the CANON reactor can be instable if dissolve oxygen concentration increased above this range. Although the ratio of nitrate variation to total nitrogen variation (deltaNO3(-) -N/deltaTN) was 0.150-0.204, which deviated a little from its theoretical value, 0.127. The performance of CANON reactor kept relatively stable. The total nitrogen removal efficiency was up to 75.56% while total nitrogen removal load was 0.97 kg x (m3 x d)(-1), which means the temperature for CANON reactor can be decreased to 25 degrees C at least.

[Performance stability of CANON reactor and temperature impact].

In order to study long-term effect of completely autotrophic nitrogen removal over nitrite (CANON) reactor, performance stability was investigated by using synthetic inorganic ammonia-rich wastewater as raw water with a continuous flow CANON reactor. Both performances of short-cut nitrification and ANAMMOX were stable for more than one year. Under the condition that inner temperature at 35 degrees C +/- 1 degrees C, pH 7.39 and 8.01, and hydraulic retention time 3.7-5.1 h, the average total nitrogen removal load was 1.8 kg x (m3 x d)(-1), and the average and maximum total nitrogen removal efficiency were 65.09% and 81.65% respectively. Under sudden low temperature conditions, both ANAMMOX bacteria and AOB were inhibited, however, the ANAMMOX bacteria were inhibited more, which caused highly accumulated nitrite. When temperature increased to 35 degrees C as normal, the performance of CANON reactor recovered soon, which means low temperature impact will have no significant influence on stability. When the temperature reached more than 50 degrees C, the activity of ANAMMOX bacteria was completely destroyed, so high temperature must be avoided, though AOB can recovered to normal in one week.

[Research on CANON process for municipal sewage in room temperature].

In the room temperature 14.7-24.7 degrees C, simultaneous nitrification-ANAMMOX (CANON) process for municipal sewage was tested by SBR while the DO was controlled between 0.05 and 0.30 mg/L. As a result, the research shows that CANON process can be applied to the nitrogen treatment of municipal wastewater in room temperature by SBR. DO can be regarded as the indication parameter of reaction terminal, and 1 mg/L has been confirmed in the experiment. In the exploring SBR experiments, the consumption velocity of NH4(+) -N was 0.164-0.218 kg/(m3 x d), the production velocity of NO3(-) -N was 0.026-0.036 kg/(m3 x d), the removal velocity and efficiency of TN were 0.124-0.194 kg/(m3 x d) and 65%-75% respectively. Additionally, in the improving SBR experiments, there were three methods for avoiding nitrite accumulation and increasing the nitrogen removal efficiency. They were improving temperature, adding non-aeration period of time and increasing the quantity of ANAMMOX bacteria. Therefore, the removal efficiency of TN was increased to 77%-88% through the three ways above. However, in view of the nitrogen removal velocity and the fact of engineering application condition, the third approach was the best to advance the general ability of ANAMMOX.

[Study of CANON process start-up under aerobic conditions].

The start-up of CANON process was studied to reveal adaptability and how to condense time of start-up with a lab-scale experiment. During start-up stage, temperature was controlled at 35 degrees C +/- 1 degrees C, pH was 7.39-8.01 and free ammonium was 2.89-12.37 mg x L(-1). Partial nitritation was first built up in 60th day and kept steady, nitrite accumulation rate (NO2(-) -N/NO(x) (-) -N) was up to 98%. In the 160th day, the reactor started to show effects of anaerobic ammonium oxidation, and in the 210th day, CANON process was started-up under aerobic conditions successfully, and total nitrogen removal load was 1.22 kg/(m3 x d) and 70% removal rate on average was attained. When using ammonium wastewater without organic carbon sources as influent, there are two signs to indicate the CANON start-up: first, nitrogen gas was produced in carriers; the other one was the ratio of total nitrogen loss and increased nitrate keep steady, and in this study average ratio was 8.61 compared to theoretical value 8.

[Effect of electron acceptors on anoxic phosphorus uptake of DPB].

The test of anoxic phosphate uptake of denitrifying phosphorous removal bacteria (DPB) which was cultivated during the anaerobic/ anoxic/aerobic processes was conducted at the various situations of electron acceptors. The various concentrations of nitrate or nitrite were added during the anoxic stage respectively. The conclusions stated that the anoxic phosphate uptake of DPB was rarely influenced by the concentration of nitrate with the adequate nitrate as electron acceptors. It takes 1 mg PO4(3-) -P when the consumption of NO3(-) -N is 1 mg. The nitrite could be regarded as the electron acceptor to participate into the activities of denitrifying phosphorous removal. Compared with the nitrate, the phosphorous uptake rate of DPB with nitrite was rather higher at a low concentration (NO2(-) -N with the concentration range of 5 - 20 mg/L). Furthermore, the rate of anoxic phosphorous uptake was increased with the decreased concentration of NO2(-) -N. The restraining effects related to the anoxic phosphors uptake of DPB was increased as the increase of nitrite concentration. Hence, the anoxic phosphorous uptake of DPB was entirely inhibited when the concentration of NO2(-) -N was higher than 35 mg/L.