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International audience; Microorganisms in wastewater treatment plants (WWTPs) are essential for water purification to protect public and environmental health. However, the diversity of microorganisms and the factors that control it are poorly understood. Using a systematic global-sampling effort, we analysed the 16S ribosomal RNA gene sequences from ~1,200 activated sludge samples taken from 269 WWTPs in 23 countries on 6 continents. Our analyses revealed that the global activated sludge bacterial communities contain ~1 billion bacterial phylotypes with a Poisson lognormal diversity distribution. Despite this high diversity, activated sludge has a small, global core bacterial community (n = 28 operational taxonomic units) that is strongly linked to activated sludge performance. Meta-analyses with global datasets associate the activated sludge microbiomes most closely to freshwater populations. In contrast to macroorganism diversity, activated sludge bacterial communities show no latitudinal gradient. Furthermore, their spatial turnover is scale-dependent and appears to be largely driven by stochastic processes (dispersal and drift), although deterministic factors (temperature and organic input) are also important. Our findings enhance our mechanistic understanding of the global diversity and biogeography of activated sludge bacterial communities within a theoretical ecology framework and have important implications for microbial ecology and wastewater treatment processes.

Numerous studies have shown that the continuous increase of atmosphere CO2 concentrations may have profound effects on the forest ecosystem and its functions. However, little is known about the response of belowground soil microbial communities under elevated atmospheric CO2 (eCO2) at different soil depth profiles in forest ecosystems. Here, we examined soil microbial communities at two soil depths (0 to 5 cm and 5 to 15 cm) after a 10-year eCO2 exposure using a high-throughput functional gene microarray (GeoChip). The results showed that eCO2 significantly shifted the compositions, including phylogenetic and functional gene structures, of soil microbial communities at both soil depths. Key functional genes, including those involved in carbon degradation and fixation, methane metabolism, denitrification, ammonification, and nitrogen fixation, were stimulated under eCO2 at both soil depths, although the stimulation effect of eCO2 on these functional markers was greater at the soil depth of 0 to 5 cm than of 5 to 15 cm. Moreover, a canonical correspondence analysis suggested that NO3-N, total nitrogen (TN), total carbon (TC), and leaf litter were significantly correlated with the composition of the whole microbial community. This study revealed a positive feedback of eCO2 in forest soil microbial communities, which may provide new insight for a further understanding of forest ecosystem responses to global CO2 increases.IMPORTANCE The concentration of atmospheric carbon dioxide (CO2) has continuously been increasing since the industrial revolution. Understanding the response of soil microbial communities to elevated atmospheric CO2 (eCO2) is important for predicting the contribution of the forest ecosystem to global atmospheric change. This study analyzed the effect of eCO2 on microbial communities at two soil depths (0 to 5 cm and 5 to 15 cm) in a forest ecosystem. Our findings suggest that the compositional and functional structures of microbial communities shifted under eCO2 at both soil depths. More functional genes involved in carbon, nitrogen, and phosphorus cycling were stimulated under eCO2 at the soil depth of 0 to 5 cm than at the depth of 5 to 15 cm.

Waste activated sludge (WAS), which is rich in organic substances, provides an energy resource. To recover hydrogen from the organic wastes, microbial electrolysis cell may be used as an efficient device. Since different extra applied voltages have significant effects on the efficiency of microbial electrolysis cell, this paper explores different extra applied voltages (0.6 V–1.2 V) affecting the utilization of sludge fermentation liquid (SFL) that is treated with synchronous double-frequency (28 + 40 kHz) and alkali coupling 72-bacth mesothermal anaerobic fermentation (35 °C). It is found that 0.8 V was the optimum extra applied voltage. With this voltage, the highest energy recovery efficiency will be 169 ± 1% and the peak of soluble chemical oxygen demand (SCOD) removal efficiency can be found at 51.4 ± 0.6%; Coulombic efficiency is 98.9 ± 1.0%. The order of complex matter consumption is found to be HAc > HPr > n HBu > n HVa > total carbohydrates > protein. The processing methods of synchronous double-frequency, alkaline, coupling with anaerobic fermentation are feasible for microbial electrolysis cell to transform large amount of waste activated sludge into energy.

In order to investigate microbial community structures in different wastewater treatment processes and understand the relationship between the structures and the status of processes, the microbial community diversity, variety and distribution in five wastewater treatment processes were studied by a culture-independent genetic fingerprinting technique single-strand conformation polymorphism (SSCP). The five processes included denitrifying and phosphate-removal system (diminished N), Chinese traditional medicine wastewater treatment system (P), beer wastewater treatment system (W), fermentative biohydrogen-producing system (H), and sulfate-reduction system (S). The results indicated that the microbial community profiles in the wastewater bioreactors with the uniform status were very similar. The diversity of microbial populations was correlated with the complexity of organic contaminants in wastewater. Chinese traditional medicine wastewater contained more complex organic components; hence, the population diversity was higher than that of simple nutrient bioreactors fed with molasses wastewater. Compared with the strain bands in a simulated community, the relative proportion of some functional microbial populations in bioreactors was not dominant. Fermentative biohydrogen producer Ethanoligenens harbinense in the better condition bioreactor had only a 5% band density, and the Desulfovibrio sp. in the sulfate-reducing bioreactor had less than 1.5% band density. The SSCP profiles could identify the difference in microbial community structures in wastewater treatment processes, monitor some of the functional microbes in these processes, and consequently provide useful guidance for improving their efficiency.