Abstract
Microbial communities in activated sludge (AS) are the core of sanitation in wastewater treatment plants (WWTPs). Microbial communities in AS have shown seasonal changes, however, long-term experiments (>2 years) are rarely conducted, limiting our understanding of the true seasonal dynamics in WWTPs. In this study, we resolved the microbial seasonal dynamics at the species level in four municipal full-scale WWTPs, sampled every 7–10 days, during 3–5 consecutive years. By applying a new time-series analysis approach, we revealed that the seasonal pattern was species-specific, where species belonging to the same functional guild or genus may show different seasonal dynamics. Species could be grouped into cohorts according to their seasonal patterns, where seasonal cohorts showed repeatable annual dynamics across years and plants. Species were also grouped according to their net growth rate in the AS (i.e., growing species and disappearing species). Growing species were more prevailing in spring and autumn cohorts, while disappearing species, which were only present due to the continuous immigration from influent wastewater, were mostly associated with winter and spring cohorts. Most known process-critical species, such as nitrifiers, polyphosphate accumulating organisms and filamentous organisms, showed distinct species-specific patterns. Overall, our study showed that overarching seasonal patterns affected microbial species in full-scale AS plants, with similar seasonal patterns across plants for many dominant species. These recurrent seasonal variations should be taken into account in the operation, understanding and management of the WWTPs.
Highlights
Microbial communities in activated sludge (AS) are the core of wastewater treatment plants (WWTPs) worldwide, where organic pollutants and nutrients are transformed by the action of diverse microbial groups to produce clean water, and in more advanced configurations, recover resources such as phosphorus
Microbial composition and time-series dynamics of growth groups in full-scale WWTPs Species were classified according to their growth group to evaluate: (i) the relative contribution of each growth group to the total read abundance, (ii) the identity and relative read abundance of species in each growth group, and (iii) their temporal dynamics in each WWTP
This can be explained by the fact that disappearing species in AS are only present as a consequence of mass immigration of bacteria with the influent wastewater [4]
Summary
Microbial communities in activated sludge (AS) are the core of wastewater treatment plants (WWTPs) worldwide, where organic pollutants and nutrients are transformed by the action of diverse microbial groups to produce clean water, and in more advanced configurations, recover resources such as phosphorus. The understanding of the microbial communities in WWTPs is being continuously resolved and improving [1], and a good understanding of the factors determining AS community assembly and dynamics is important for informed management of the WWTPs. The microbial community assembly is determined by a variety of factors, with the relative importance of different factors varying across WWTPs with different process design and operation. The controlling factors can be deterministic, such as environmental factors (e.g., wastewater temperature, the chemical composition of the influent wastewater), process design, operation (e.g., solid retention time (SRT), aeration time, chemicals dosage [2, 3]), and neutral, such as dispersal (i.e., microbial immigration from influent wastewater) [4, 5]. Given the multiple factors affecting the AS, it is clear that the composition and assembly of the microbial community are exposed to a variety of temporal responses that can alter its dynamics. The few published longitudinal AS studies with good temporal resolution (e.g., ≥1 sample/month) have shown seasonal variations in community composition and abundance over the calendar year in different climate zones [6,7,8,9,10,11,12,13]
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