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.
Keywords: community structure; correlation analysis; influent nitrifiers; municipal sewage; nitrification performance.