[Seasonal Effects of Influent Ammonia Oxidizing Bacteria of Municipal Wastewater Treatment Plants on Activated Sludge System].

The specific ammonia uptake rates (SAUR) and ammonia oxidizing bacteria (AOB) community of influent sewage and activated sludge in the 2nd wastewater treatment plant (WWTP) of Xi'an without the primary settling tank were analyzed over multiple years to explore the seasonal effects of the influent AOB on the activated sludge systems. During the experiment, the SAUR of the raw sewage and activated sludge were 0.48-3.02 mg·(g·h)-1 and 0.68-2.25 mg·(g·h)-1, respectively. Meanwhile, the correlation analysis indicated that the monthly SAUR of the raw sewage was highly correlated with that of the activated sludge of the following month (r=0.862,P<0.05), which indicated that influent nitrifiers had a significant effect on the nitrification performance of activated sludge. Considering that the estimated AOB seeding intensities based on the ammonia oxidizing activity were 0.21-0.92 g·(g·d)-1, the nitrifier immigration from the raw sewage should added to the design of WWTP and the activated sludge modeling. Moreover, the qPCR results revealed that the AOB abundance of activated sludge in winter decreased but remained at 1010 cells·g-1, indicating that the immigration of influent nitrifiers could partially compensate for the reduction of the AOB abundance in the activated sludge caused by decreasing temperatures. Finally, the Illumina MiSeq sequencing demonstrated that the shared dominant AOB between the raw sewage and activated sludge were Nitrosomonas sp. Nm58, Nitrosomonas sp. JL21, and bacterium CYCU-0253. These findings can provide theoretical support for the design and operation of a WWTP.

[Adaptability of Nitrifying Biofilm Systems to Low Temperature: MBBR and IFAS].

The long-term effects of a decreasing temperature on the nitrification performance, biofilm characteristics, and nitrifier community in a moving-bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS) system were investigated at various temperatures (20, 15, and 10℃) to explore the adaptability of nitrifying biofilm systems to low temperatures. During the experiment, the extracellular polymeric substances (EPS) in the biofilms increased with decreasing temperature, which resulted in an increased biofilm mass and thickness. As there was only a biofilm phase in the MBBR to remove ammonia, the part of the carriers in the MBBR at 10℃ became plugged, which partially led to a deterioration in the effluent water quality. This indicated that the IFAS system was more adaptable to low temperatures than was the MBBR. Meanwhile, the results for the nitrifier activities showed that, although the nitrification contribution rate of the suspended phase in the IFAS system always dominated during the experiment, that of the fixed phase with regards to the ammonia uptake rate (AUR) gradually increased from 30.72% at 20℃ to 39.85% at 10℃. This indicated that the biofilm played an enhanced role in nitrification in the IFAS system. Moreover, the qPCR results revealed that the nitrifier copies of the number of biofilms increased slightly with decreased temperature, and coincided with an increase in biomass, which partially compensated for the decreased nitrification activity. These findings provide a theoretical basis for the application of the biofilm systems to wastewater treatment.

[Effect of the Flow Patterns of Main-stream Reactors on the Efficiency of Nitrification Enhancement with Bioaugmentation].

A nitrifying sequencing batch reactor (SBR) and continuous stirred-tank reactor (CSTR) were operated at 15℃ under the same conditions to investigate the effect of two typical flow patterns (plug flow and complete mixing) on the efficiency of nitrification enhancement. The results show that, during bioaugmentation, the ammonia utilized rate(AUR)and nitrite utilized rate(NUR)in the SBR were 2.34 and 2.39 times of that before bioaugmentation, and after bioaugmentation ceased, the AUR and NUR slightly decreased to 2.01 and 1.78 times of that before bioaugmentation. Meanwhile, the AUR and NUR in the CSTR were 2.63 and 2.44 times that before bioaugmentation, and after bioaugmentation ceased, the AUR and NUR decreased to 1.48 and 1.31 times that before bioaugmentation. Fluorescence In-Situ Hybridization (FISH) results showed that during bioaugmentation, the ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in the SBR were 2.67 and 2.71 times of that before bioaugmentation, and after bioaugmentation ceased, the AUR and NUR slightly decreased to 2.14 and 1.95 times that before bioaugmentation. Meanwhile, the AUR and NUR in the CSTR were 2.91 and 1.77 times of that before bioaugmentation, and after bioaugmentation ceased, the AUR and NUR decreased to 1.25 and 1.50 times of that before bioaugmentation. Therefore, the efficiency of nitrification enhancement was similar between the two types of flow patterns during bioaugmentation, but the seeded nitrifiers were much more vulnerable to wash out in the CSTR than that in the SBR due to r/K selectivity of the flow patterns.