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Context. Changes in drinking water treatment can affect the biofilm in the drinking water distribution system (DWDS) and enhanced monitoring is recommended to guarantee drinking water safety after substantial process modifications. Ultrafiltration was introduced in 2016 to the drinking water treatment plant Kvarnagården in Varberg, Sweden, achieving total removal of bacteria cells. This improved treatment led to the decision to remove the disinfectant monochloramine in 2020. Gap. Several studies compare the bacteria in different DWDS with and without disinfectants. To minimize complicating variables, this study examined the effects of the removal of the disinfectant in a single full scale DWDS. Aim. This study describes flow cytometry (FCM) monitoring initiated to follow bacteria in the water of the DWDS during removal of monochloramine. Methods. Water samples from 15 points in the DWDS were analysed by standard FCM, with data analysis using custom scripts in R for data analysis. Findings. By comparing FCM data to baselines, distinct changes in the bacterial community were observed following removal of monochloramine. Percentages of high nucleic acid bacteria (HNA) decreased at all sampling points, from 55 – 90 % to 45 – 60 %. Total cell counts (TCC) increased only in parts of the DWDS that had been exposed to monochloramine before the removal. Principal component analysis visualized the changes (Figure 1). The bacterial community at DWDS locations that used to differ largely regarding TCC and %HNA started to become more homogenous, emphasizing the value of FCM monitoring, as these same changes were not observed with traditional heterotrophic plate counts. The bacterial communities stabilized in summer 2020 and began to follow previously observed seasonal trends. Utilization. This study demonstrated the application of FCM monitoring of the impact of monochloramine removal on bacterial water quality, and the importance of having robust baselines for multiple locations within a DWDS for comparison.

The financial support of the GenoMembran-project funded by The Swedish Water and Wastewater Association (Swedish Water Development, SVU), Norrvatten, and VIVAB is gratefully acknowledged. Pentair X-Flow is acknowledged for the provision of various test modules and general membrane investigations.

In the version of this Article originally published, the name of the author 'Mathew Robert Brown' was incorrectly written as 'Mathew Brown' in the main author list and as 'Matthew Brown' in the Global Water Microbiome Consortium list. In addition, in the Global Water Microbiome Consortium list, the names of the authors 'Kevin F. Boehnke', 'Janeth Sanabria' and 'Adalberto Noyola' were incorrectly written as 'Kevin Boehnke', 'Janeth Sanabria Gómez' and 'Adalberto Noyola Robles', respectively. The names have now been corrected and the author initials in the author contributions section updated accordingly.

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.

Anaerobic co-digestion (AcoD) allows for underutilised digesters to increase biomethane production. The organic fraction of municipal solid waste (OFMSW), e.g. food waste, is an abundant substrate with high degradability and gas potential. This paper focuses on the implementation of codigestion of mixed sludge from wastewater treatment and OFMSW through batch and continuous labscale experiments, modelling and microbial population analysis. The results show a rapid adaptation of the process and an increase of the biomethane production of 20 to 40% with 50% OFMSW and it has an impact on the microbial community. The methanogenic activity increases and changes towards acetate degradation while the community without co-substrate remains unaffected. The modelling results show that ammonium inhibition increases at elevated organic loads and that intermittent feeding causes fluctuations in digester performance due to varying inhibition. Modelling can be successfully used for designing feed strategies and experimental set-ups for anaerobic co-digestion.

Natural organic matter (NOM) is found in all surface, ground, and soil waters. During recent decades, reports worldwide show a continuing increase in the color and NOM of the surface water, which has an adverse effect on drinking water purification. For several practical and hygienic reasons, the presence of NOM is undesirable in drinking water. Various technologies have been proposed for NOM removal with varying degrees of success. Membranes are an exceptional barrier to particles, turbidity, microorganisms, and disinfectant by-product (DBP) precursors from drinking water. Significant improvements in membrane technology, design, and materials during the past three decades, has made the drinking water production processes nowadays more effective and environmentally friendly. Based on the research trend, it can be seen that membrane applications for NOM removal will play a more prominent role in the future.This dissertation presents results for selective NOM removal by ultrafiltration (UF) and nanofiltration (NF) membrane configurations at two Swedish surface water treatment plants (WTPs). Extensive field testing with several customized and fully-automated pilot plants were carried out for evaluation of different membrane concepts for NOM removal. Modelling of membrane performance and retention behavior of hollow-fiber (HF) NF membranes using a solution-diffusion approach and two-dimensional axisymmetric computational fluid dynamics (CFD), provided accurate prediction of NOM removal. For this reason, it was used for full-scale process design and feasibility studies. Direct NF filtration of surface water indicated stable membrane performance and high average NOM removal rates (UV254: 91.6–94.7 %; TOC: 82–92.2 %). The NF membrane retention was highest for biopolymers (>95% removal), followed by Humic Substances (HS) (>80% removal). Combined coagulation/UF processes removed approximately 30% of the DOC, and 50% of the HS and biopolymers. However, building blocks (BB) and low molecular weight acids (LMWacids) remained unchanged compared with the NOM composition of the feed and permeate. For optimization of hybrid membrane processes, an automatic coagulant dosing system based on online measurements was successfully applied.Autopsy results of HF-NF membranes after twelve months of continuous pilot operation with pretreated feed water (coagulation and rapid sand filtration), showed no substantial changes of the aged membranes from different module sections compared to virgin membranes. Rigorous analysis of the nanomechanical properties of HF-UF membranes harvested after 12–14 months pilot operation showed that the detected change in nanomechanical characteristics did not result in considerable impact on the macroscopic properties of the membranes. Comprehensive UF pilot trials resulted in improvements of the two-stage full-scale UF facility during the design phase and commissioning at Kvarnagården WTP.