Core activated sludge communities are influenced little by immigration: Case study of a membrane bioreactor plant

Microbial immigrants arriving with influent wastewater may influence activated sludge (AS) ecosystems. However, the extent to which immigration impacts AS communities is still debated. To explore the intensity of immigration impact, we used sequencing technology to track the raw wastewater and AS communities from a membrane bioreactor plant over a 12-month period. We first distinguished core populations from peripheral ones in both raw wastewater and AS based on their occurrence frequency and abundance. The results showed that core OTUs (≥ 80% occurrence frequency) made up a large fraction (> 90%) of total sequences, while peripheral OTUs composed the majority of all detected OTUs but merely occupied a few sequences. A significant difference in core communities between the influent and AS was found, as well as between the compositions of core and peripheral populations. Additionally, the persistent functional bacteria of AS, although not numerically dominant, accounted for 96.24% of the total sequences related to nutrient turnover, suggesting the presence of a small number of longstanding and core functional bacteria in the AS ecosystem. Importantly, 64% of the 5188 OTUs in AS, which accounted for 91.51% of the sequences, exhibited positive growth rates, which suggested that their apparent abundances were due to growth within the plant, not from immigration. Taken together, these results demonstrated that the impact of influent populations on core AS communities was limited. Overall, this work provides quantitative insights into the impact of immigration, which is expected to advance our understanding of the AS community assembly.

Coupling growth kinetics modeling with machine learning reveals microbial immigration impacts and identifies key environmental parameters in a biological wastewater treatment process

BACKGROUND

Ubiquitous in natural and engineered ecosystems, microbial immigration is one of the mechanisms shaping community assemblage. However, quantifying immigration impact remains challenging especially at individual population level. The activities of immigrants in the receiving community are often inadequately considered, leading to potential bias in identifying the relationship between community composition and environmental parameters.

RESULTS

This study quantified microbial immigration from an upstream full-scale anaerobic reactor to downstream activated sludge reactors. A mass balance was applied to 16S rRNA gene amplicon sequencing data to calculate the net growth rates of individual populations in the activated sludge reactors. Among the 1178 observed operational taxonomic units (OTUs), 582 had a positive growth rate, including all the populations with abundance > 0.1%. These active populations collectively accounted for 99% of the total sequences in activated sludge. The remaining 596 OTUs with a growth rate ≤ 0 were classified as inactive populations. All the abundant populations in the upstream anaerobic reactor were inactive in the activated sludge process, indicating a negligible immigration impact. We used a supervised learning regressor to predict environmental parameters based on community composition and compared the prediction accuracy based on either the entire community or the active populations. Temperature was the most predictable parameter, and the prediction accuracy was improved when only active populations were used to train the regressor.

CONCLUSIONS

Calculating growth rate of individual microbial populations in the downstream system provides an effective approach to determine microbial activity and quantify immigration impact. For the studied biological process, a marginal immigration impact was observed, likely due to the significant differences in the growth environments between the upstream and downstream processes. Excluding inactive populations as a result of immigration further enhanced the prediction of key environmental parameters affecting process performance.

Comparison of bioenergetics of walking during a multistage incremental shuttle walk test and a 6-min walk test in active older adults

The goal of the present research was to compare the bioenergetics variability of walking, during the 6-min walk test (6-MWT) and a multistage incremental shuttle walk test (MISWT) in an active older population. Twenty-two healthy physically active older adults with a group mean age of 70.4 ± 5.8 years completed the 6-MWT and the MISWT. Heart rate (HR), walking speed and walking [Formula: see text]O₂ were measured throughout each test with a portable metabolic cart. Strong correlations were found for the [Formula: see text]O₂ peak and the walking speed (r = 0.91 and r = 0.89 respectively for 6-MWT and MISWT). Differences in [Formula: see text]O₂ peak values were analysed with a paired Student's t test. Repeated measures ANOVA were conducted to detect differences between tests. The Bland and Altman plot indicates that the average difference between both tests was 2.5 ml kg^-1 min^-1. MISWT [Formula: see text]O₂ peak means were significantly greater than the 6-MWT [Formula: see text]O₂ peak mean values (21.6 ± 5.3 vs. 18.9 ± 4.5 ml kg^-1 min^-1) which indicate bioenergetics differences between the two walking tests. Thus, the MISWT and 6-MWT elicited different walking [Formula: see text]O₂ peak and HR suggesting that the MISWT field test challenge the participants to a higher level of cardiovascular and respiratory stress. The walking [Formula: see text]O₂ peak recorded for the MISWT was significantly greater than the 6-MWT. Consequently, both tests seem to measure different facets of the aerobic capacity. MISWT seems to be a better indicator of maximal aerobic power whereas the 6-MWT provides more relevant information regarding aerobic endurance in aging population.

Reliability and validity of an accelerometry based measure of static and dynamic postural stability in healthy and active individuals

Postural stability is an important measure in both research and clinical practice. A portable, easy to use device that can provide higher resolution than current clinical tests may allow for better identification of patients or athletes with postural stability deficits. The purpose of this study was to evaluate the ability of a tri-axial accelerometer to quantify postural stability in a healthy athletic population. Ten subjects were recruited to determine the reliability of the accelerometer to measure dynamic postural stability and thirteen were recruited to compare the accelerometer measures across tasks of varying difficulty. Subjects were asked to complete four static postural stability tasks with eyes open and eyes closed and two dynamic postural stability tasks for a total of ten tasks. During each task postural stability was measured using a tri-axial accelerometer and force platform. Differences between postural stability scores between tasks and the correlation between the two measures were assessed. The accelerometer demonstrated moderate to good test-retest reliability (ICC=0.732 to 0.899). Only the medial-lateral axis of the accelerometer showed significant differences between static tasks but all directions were able to show significant differences between static and dynamic tasks. Additionally, Spearman's ranked correlations showed little to no correlation between the accelerometer and force platform scores. Accelerometers are a reliability tool for postural stability that measure low difficulty tasks best in the medial-lateral direction. Low correlation between the accelerometer and force platform suggest that these two methods are not measuring the same components of postural stability.