1.
[Effects of Environmental Factors on the Synergy of Functional Bacteria in Completely Autotrophic Granular Sludge].
Chen, X, Qian, FY, Wang, JF, Gao, JJ, Shen, YL, Jia, X
Huan jing ke xue= Huanjing kexue. 2018;(4):1756-1762
Abstract
To obtain experimental evidences for optimizing a completely autotrophic nitrogen removal process based on granules, the effects of dissolved oxygen (DO) concentration, temperature (t), initial ammonium (NH4+-N) concentration, and solution pH conditions on the synergy between the aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AMX) were investigated using a single factor batch experiment, while the analysis of the microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing. Results revealed that AOB (genus Nitrosomonas) and AMX (genus Candidatus Kuenenia) dominated in the granules, representing relative abundances of 32.9% and 9.8%, respectively. For the granules, the highest specific nitrogen removal rate of q(TN)=(17.7±1.0) mg·(g·h)-1 was obtained at a DO concentration of 2 mg·L-1, while the initial NH4+-N concentration was set at 100 mg·L-1. And a lower DO level resulted in partial nitritation became the rate-limiting step of process, otherwise, it would be the ANAMMOX reaction instead. According to the free energy of the reactions, the activity of AMX was more sensitive to low temperature than that of AOB. When the reaction temperature was lower than 30℃, nitrite accumulation could be observed in bulk liquid, with the significant decrease of q(TN) for the granules. Under the same oxygen supply conditions, an initial NH4+-N concentration lower than 100 mg·L-1 could inhibit the activity of AMX partly. However, with an initial NH4+-N concentration over 150 mg·L-1, either oxygen-limiting or high free ammonia concentration could lead to the dramatic decrease of q(TN). In addition, the effective synergy of the two types of ammonium oxidizers in granules was always achieved at solution pH in the range of 7.0-8.5.
2.
Nitrite accumulation inside sludge flocs significantly influencing nitrous oxide production by ammonium-oxidizing bacteria.
Chen, X, Yuan, Z, Ni, BJ
Water research. 2018;:99-108
Abstract
This work aims to clarify the role of potential nitrite (NO2-) accumulation inside sludge flocs in N2O production by ammonium-oxidizing bacteria (AOB) at different dissolved oxygen (DO) levels with focus on the conditions of no significant bulk NO2- accumulation (<0.2 mg N/L). To this end, an augmented nitrifying sludge with much higher abundance of nitrite-oxidizing bacteria (NOB) than AOB was enriched and then used for systematically designed batch tests, which targeted a range of DO levels from 0 to 3.0 mg O2/L at a fixed ammonium concentration of 10 mg N/L. A two-pathway N2O model was applied to facilitate the interpretation of batch experimental data, thus shedding light on the relationships between N2O production pathways and key process parameters (i.e., DO and NO2- accumulation inside sludge flocs). The results demonstrated (i) the biomass specific N2O production rate firstly increased and then decreased with DO, with the maximum value of 3.03 ± 0.05 mg N/h/g VSS obtained at DO level of 0.75 mg O2/L, (ii) the AOB denitrification pathway for N2O production was dominant (98.0%) at all DO levels tested even without significant bulk NO2- accumulation (<0.2 mg N/L) observed in the system, but its contribution decreased with DO, (iii) DO had a positive impact on the hydroxylamine pathway for N2O production which therefore increased with DO, and (iv) the nitrite accumulation existed inside the sludge flocs and induced significant N2O production from the AOB denitrification pathway.