Is flushing necessary during building closures? A study of water quality and bacterial communities during extended reductions in building occupancy

Drinking water stagnation can lead to degradation of chlorine residual, bacterial growth (including of opportunistic pathogens and nitrifiers), and metals release from plumbing materials;however, few studies have characterized building water quality and bacterial communities during the extended stagnation periods that occurred during COVID-19 pandemic-related building closures. Additionally, despite a lack of evidence-based guidance, flushing fixtures has been recommended to restore building water quality. We aimed to evaluate the impacts of reduced building occupancy (>2 months) and weekly restorative flushing on drinking water quality, bacterial communities, and the occurrence of undesirable microorganisms in three university buildings. Reduced occupancy led to diminished chloramine and elevated intact cell counts, but values remained stable after additional weeks of limited water use. Flushing temporarily improved water quality, with chlorine and cell counts remaining stable for at least 1 day but returning to levels measured prior to flushing within 1 week. Alpha diversity was lower under more stagnant conditions, and fixture identity, not flushing, was the most influential factor on bacterial community composition, suggesting a strong influence from local biofilm. Although Mycobacterium, Legionella, Pseudomonas, Nitrosomonas, and Nitrospira were detected in samples via amplicon sequencing, concentrations measured via qPCR of M. avium complex, L. pneumophila, P. aeruginosa, and ammonia-oxidizing bacteria were very low or were undetected, supporting that stagnation alone did not lead to high occurrence of undesirable microorganisms. Findings from this study contribute to our understanding of the effects of stagnation on building water microbiomes and the efficacy of flushing to improve water quality. Under the conditions of this case study, repeated flushing on a weekly timescale during low occupancy periods was not sufficient to maintain chlorine residual and prevent bacterial growth in fixtures. Building managers need to weigh the temporary water quality benefits of flushing against the labor and water resources required considering local context.

Biological Activated Sludge from Wastewater Treatment Plant before and during the COVID-19 Pandemic.

The COVID-19 pandemic and the related measures brought a change in daily life that affected the characteristics of the municipal wastewater and further, of the biological activated sludge. The activated sludge process is the most widely used biological wastewater treatment process in developed areas. In this paper, we aim to show the situation of specific investigations concerning the variation of the physicochemical parameters and biological composition of the activated sludge from one conventional wastewater treatment plant from a metropolitan area. The investigations were carried out for three years: 2019, 2020 and 2021. The results showed the most representative taxa of microorganisms: Microtrix, Aspidisca cicada, Vorticella convallaria, Ciliata free of the unknown and Epistylis and Rotifers. Even if other microorganisms were found in the sludge flocs, their small presence did not influence in any way the quality of the activated sludge and of the wastewater treatment process. That is why we conclude that protozoa (especially Flagellates and Ciliates) and rotifers were the most important. Together with the values and variation of the physicochemical parameters, they indicated a good, healthy, and stable activated sludge, along with an efficient purifying treatment process, no matter the loading conditions.

A Review and Discussion of Wastewater Process Inhibitions Observed in the U.S. as a Result of COVID-19 Countermeasures

This paper provides a summary of case studies from water resource recovery facilities (WRRFs) in the United States that have experienced wastewater process inhibitions as a result of COVID-19 countermeasures. Anecdotal feedback from staff operating impacted WRRFs and preliminary influent toxicity screening data point to quaternary ammonium compounds (QAC) in the influent as the possible cause for the inhibition events. As such, a high-level overview of QACs, and a synopsis of their fate and potential impacts in WRRFs, are summarized in this paper. Empirical evidence from full-scale facilities is presented, demonstrating that high concentrations of disinfectants used during the pandemic caused nitrification inhibition. This paper also highlights the potential of disinfectants to inhibit enhanced biological phosphorus removal (EBPR), a treatment phenomenon not yet reported on in literature to our knowledge. Finally, the authors provide recommendations for best management operational practices to mitigate inhibitory impacts at WRRFs in the future. Copyright © 2021 Water Environment Federation

Family Sphingomonadaceae as the key executor of triclosan degradation in both nitrification and denitrification systems

The usage of triclosan (TCS) has increased with the COVID-19 virus outbreak, causing more TCS were released into wastewater treatment systems. However, the difference in TCS removal pathway and TCS degrading bacteria between nitrification and denitrification systems was still unknown. In this study, batch tests of TCS biodegradation mechanism and DNA stable isotope probing (DNA-SIP) technique were applied to decrypt the different TCS removal pathway and the corresponding degrading taxon between two nitrification and two denitrification systems. The main TCS degradation pathway in both nitrification and denitrification systems were the metabolism of heterotrophic bacteria, only a little TCS was degraded by the co-metabolism of heterotrophic or nitrifying bacteria, and higher NH4+-N or NO3--N concentration contributed to more TCS degradation. Moreover, denitrification system had stronger TCS removal capacity (0.11 and 0.65 mg TCS/g SS) than nitrification system (0.83 and 1.12 mg TCS/g SS). DNA-SIP assay further revealed that active TCS degrading bacteria in both systems belonged to Sphingomonadaceae family. Furthermore, the oligotype TATGCC, TAATCA and GCCCCG of Sphingomonadaceae played important roles in degrading TCS in both systems. Moreover, reactor performance and mixed liquor suspended solids might play important roles in shaping the ecotypes of Sphingomonadaceae, which caused the difference in degrading TCS between nitrification and denitrification systems. This lab-scale research might provide meaningful opportunities for evaluating the scale-up applications, and the TCS degrading bacteria identified in present study might be recommended to be used as bioaugmentation strains in practical engineering.

Triclosan weakens the nitrification process of activated sludge and increases the risk of the spread of antibiotic resistance genes.

The usage of triclosan (TCS) may rise rapidly due to the COVID-19 pandemic. TCS usually sinks in the activated sludge. However, the effects of TCS in activated sludge remain largely unknown. The changes in nitrogen cycles and the abundances of antibiotic resistance genes (ARGs) caused by TCS were investigated in this study. The addition of 1000 µg/L TCS significantly inhibited nitrification since the ammonia conversion rate and the abundance of nitrification functional genes decreased by 12.14%. The other nitrogen cycle genes involved in nitrogen fixation and denitrification were also suppressed. The microbial community shifted towards tolerance and degradation of phenols. The addition of 100 µg/L TCS remarkably increased the total abundance of ARGs and mobile genetic elements by 33.1%, and notably, the tetracycline and multidrug resistance genes increased by 54.75% and 103.42%, respectively. The co-occurrence network revealed that Flavobacterium might have played a key role in the spread of ARGs. The abundance of this genus increased 92-fold under the addition of 1000 µg/L TCS, indicating that Flavobacterium is potent in the tolerance and degradation of TCS. This work would help to better understand the effects of TCS in activated sludge and provide comprehensive insight into TCS management during the pandemic era.