Abstract
Advanced onsite wastewater treatment systems (OWTS) use biological nitrogen removal (BNR) to mitigate the threat that N-rich wastewater poses to coastal waterbodies and groundwater. These systems lower the N concentration of effluent via sequential microbial nitrification and denitrification. We used high-throughput sequencing to evaluate the structure and composition of nitrifying and denitrifying bacterial communities in advanced N-removal OWTS, targeting the genes encoding ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ) present in effluent from 44 advanced systems. We used QIIME2 and the phyloseq package in R to examine differences in taxonomy and alpha and beta diversity as a function of advanced OWTS technology, occupancy pattern (seasonal vs. year-round use), and season (June vs. September). Richness and Shannon’s diversity index for amoA were significantly influenced by season, whereas technology influenced nosZ diversity significantly. Season also had a strong influence on differences in beta diversity among amoA communities, and had less influence on nosZ communities, whereas technology had a stronger influence on nosZ communities. Nitrosospira and Nitrosomonas were the main genera of nitrifiers in advanced N-removal OWTS, and the predominant genera of denitrifiers included Zoogloea, Thauera, and Acidovorax. Differences in taxonomy for each gene generally mirrored those observed in diversity patterns, highlighting the possible importance of season and technology in shaping communities of amoA and nosZ, respectively. Knowledge gained from this study may be useful in understanding the connections between microbial communities and OWTS performance and may help manage systems in a way that maximizes N removal.
Highlights
Nitrogen pollution from wastewater poses a serious threat to surface and groundwater in coastal watersheds
Autotrophic microorganisms are primarily responsible for nitrification, in which ammonia is first oxidized to nitrite by ammonia-oxidizing bacteria (AOB), and nitrite is oxidized to nitrate by nitrite-oxidizing bacteria
Facultative anaerobic heterotrophic bacteria are thought to carry out denitrification [5]
Summary
Nitrogen pollution from wastewater poses a serious threat to surface and groundwater in coastal watersheds. N from wastewater—are often required in areas vulnerable to excess N inputs [1]. These technologies vary in their design, but they all have an oxic zone to facilitate nitrification and an anoxic/hypoxic zone. Autotrophic microorganisms are primarily responsible for nitrification, in which ammonia is first oxidized to nitrite by ammonia-oxidizing bacteria (AOB), and nitrite is oxidized to nitrate by nitrite-oxidizing bacteria. Several other pathways (e.g., anaerobic ammonia oxidation (anammox)), and groups of organisms (e.g., ammonia-oxidizing archaea (AOA)) may be involved in nitrification [2,3]. AOB are believed to be primarily responsible for ammonia oxidation in wastewater treatment settings [4]. Facultative anaerobic heterotrophic bacteria are thought to carry out denitrification [5]. The effluent is discharged to a soil treatment area (STA), which provides a final opportunity for treatment before it enters the surrounding environment
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