Abstract
A sequencing batch reactor (SBR) with an intermittent aeration mode was established to achieve partial nitrification (PN) and the short-term effects of C/N ratios were investigated. Stable nitrite accumulation was achieved after 107 cycles, about 56d, with the average ammonia nitrogen removal efficiency (ARE) and nitrite accumulation rate (NAR) of 96.92% and 82.49%, respectively. When the C/N ratios decreased from 4.64 to 3.87 and 2.32, ARE and NAR still kept a stable and high level. However, when the C/N ratio further decreased to 0.77, nitrite accumulation became fluctuation, and ARE, total nitrogen (TN), and chemical oxygen demand (COD) removal performance declined obviously. Except for four common phyla (Proteobacteria, Bacteroidetes, Chloroflexi, and Actinobacteria) in the wastewater treatment system, Patescibacteria, the newly defined superphylum, was found and became the most dominant phylum in the PN sludge for their ultra-small cell size. The only ammonia oxidation bacteria (AOB), Nitrosomonas, and nitrite oxidation bacteria (NOB), Nitrospira, were detected. The relative abundance of NOB was low at different C/N ratios, showing the stable and effective inhibition effects of intermittent aeration on NOB growth.
Highlights
In the trend of increasingly stringent nitrogen discharge standards, conventional biological nitrogen removal (BNR) technologies are gradually unable to meet demands due to the insufficient carbon sources and great energy consumption [1,2]
Increased to 64.50% (Figure 2b), indicating that the intermittent aeration promoted a rapid start of partial nitrification (PN)
The lower limit of the C/N ratio of wastewater was supposed to exist for a PN system
Summary
In the trend of increasingly stringent nitrogen discharge standards, conventional biological nitrogen removal (BNR) technologies are gradually unable to meet demands due to the insufficient carbon sources and great energy consumption [1,2]. Partial nitrification, as a novel BNR process, can reduce oxygen consumption during the aeration phase by 25% and save the organic carbon requirement by 40% during the denitrification phase [3]. PN only completes the process of converting ammonia nitrogen into nitrite nitrogen, the intermediate product Other processes such as partial denitrification or anaerobic ammonia oxidation (anammox) are required to further remove nitrite nitrogen. In contrast with conventional BNR technologies, the novel combined processes can significantly save the carbon sources cost and energy consumption, and reduce the sludge production. Both practicality and the economy can be realized, they became promising technologies in the wastewater treatment filed. The achievement of PN to accumulate nitrite is critical for those processes based on nitrite removal
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