The structure of microbial communities of activated sludge of large-scale wastewater treatment plants in the city of Moscow

www.nature.com/scientificreports OPEN The structure of microbial communities of activated sludge of large‑scale wastewater treatment plants in the city of Moscow Shahjahon Begmatov1, Alexander G. Dorofeev2, Vitaly V. Kadnikov1, Alexey V. Beletsky1, Nikolai V. Pimenov2, Nikolai V. Ravin1* & Andrey V. Mardanov1* Microbial communities in wastewater treatment plants (WWTPs) play a key role in water purification. Microbial communities of activated sludge (AS) vary extensively based on plant operating technology, influent characteristics and WWTP capacity. In this study we performed 16S rRNA gene profiling of AS at nine large-scale WWTPs responsible for the treatment of municipal sewage from the city of Moscow, Russia. Two plants employed conventional aerobic process, one plant—nitrification/ denitrification technology, and six plants were operated with the University of Cape Town (UCT) anaerobic/anoxic/oxic process. Microbial communities were impacted by the technology and dominated by the Proteobacteria, Bacteroidota and Actinobacteriota. WWTPs employing the UCT process enabled efficient removal of not only organic matter, but also nitrogen and phosphorus, consistently with the high content of ammonia-oxidizing Nitrosomonas sp. and phosphateaccumulating bacteria. The latter group was represented by Candidatus Accumulibacter, Tetrasphaera sp. and denitrifiers. Co-occurrence network analysis provided information on key hub microorganisms in AS, which may be targeted for manipulating the AS stability and performance. Comparison of AS communities from WWTPs in Moscow and worldwide revealed that Moscow samples clustered together indicating that influent characteristics, related to social, cultural and environmental factors, could be more important than a plant operating technology. The removal of numerous pollutants produced by agriculture, industry, and households is important for the protection of natural ecosystems and human health. Wastewater treatment plants (WWTPs) employ a series of mechanical and biological processes that convert contaminated water into a sufficiently clean state through a series of steps removing different types of organic and inorganic p ollutants1,2. Typically, wastewater treatment in large facilities takes place in three stages. The first stage includes physical methods of water purification, the second stage—chemical and/or biological treatment in bioreactors with suspended or attached activated sludge (AS). The third stage is the final treatment of water and its disinfection. At the second stage, a consortium of microorganisms of AS transforms pollutants into harmless products or into products less hazardous to the environment and humans than the original c omponents3. AS is a taxonomically and metabolically diverse microbial community with complex trophic relationships between its m embers4. It is the largest managed artificial ecosystem, continuously functioning in many cases for decades. The composition of the microbial community, which is shaped by both operating conditions and influent characteristics5,6, determines the main biochemical processes of wastewater treatment, and its change, for example, the massive development of filamentous forms of bacteria, can lead to a decrease in the efficiency of treatment and the occurrence of emergency s ituations7. 1 Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Leninsky Prosp, bld. 33‑2, Moscow, Russia 119071. 2Winogradsky Institute of Microbiology, Research Center of Biotechnology of the Russian Academy of Sciences, Leninsky Prosp, bld. 33‑2, Moscow, Russia 119071. *email: ; Scientific Reports | (2022) 12:3458 | https://doi.org/10.1038/s41598-022-07132-4 1 Vol.:(0123456789) www.nature.com/scientificreports/ In municipal wastewater treatment plants, microbial consortia of AS are often developed under similar conditions, since the content of the main components of wastewater is limited to a rather narrow range of concentrations (except in some extreme cases of highly diluted or concentrated wastewater), pH is usually 7–8, temperatures vary from 10 to 30 °C8. In addition, in modern technologies certain biologically determined rules are followed: maintaining the minimum aerobic age of sludge necessary for the development of nitrification (the retention time of solid matter), ensuring the optimal retention time of the sludge in the anaerobic zone for effective enhanced biological phosphorus removal, optimizing the ratio of biochemical oxygen demand, nitrogen and phosphorus, etc.3. Therefore, it can be expected that the composition of microbial communities of activated sludge will contain a common component, which was confirmed by the results of studies comparing the composition of AS communities of various W WTPs6,9,10. At the same time a high diversity and differences of microbial communities of AS were noted, which was associated with climatic factors and the specificity of certain treatment plants: the share of the industrial component in the total influent, the temperature regime, the peculiarity of the used technologies and the exploitation of plants9. It has been shown that there is a relationship between the diversity and composition of the microbial community and the performance of treatment f acilities2, although the authors noted that the real effect is not the performance itself, but the variation of indicators such as chemical oxygen demand, the retention time of suspended matter etc. Despite the extensive application of traditional and modern molecular methods for studying microbial consortia of AS, their ecophysiology, population dynamics and diversity are far from being comprehensively understood. Most microorganisms of activated sludge are not cultivated, and the role of many typical inhabitants is not clearly known11,12. Recently, using a systematic worldwide sampling, a Global Water Microbiome Consortium (GWMC) analysed the 16S ribosomal RNA gene sequences from ~ 1,200 AS samples taken from 269 W WTPs10. This study revealed that although the global AS bacterial communities contain ~ 1 billion phylotypes, ASs has a small, global core bacterial community of 28 phylotypes that is strongly linked to WWTP p erformance10. This study showed that although the type of treatment process exerted significant effects on microbial community structures, it was overwhelmed by geographical separation, and the compositions of AS microbial communities were significantly different between any two continents10. Although the GWMC study included WWTPs from 23 countries on 6 continents, the distribution of samples was geographically biased and covered mostly North America, Western and Central Europe, Eastern Asia (mostly China), Australasia, and several cities in South America and South Africa10. Another large-scale initiative, the MiDAS project, analyzed samples (mostly AS) from 740 WWTPs using different types of treatment technologies, and rep (...truncated)