Legionella contamination control is crucial in healthcare settings where patients suffer an increased risk of disease and fatal outcome. To ensure an effective management of this health hazard, the accurate application of a hospital-specific Water Safety Plan (WSP), the choice of a suitable water disinfection system and an extensive monitoring program are required. Here, the ten-year experience of an Italian hospital is reported: since its commissioning, Legionellosis risk management has been entrusted to a multi-disciplinary Working Group, applying the principles of the World Health Organization\'s WSP. The disinfection strategy to prevent Legionella and other waterborne pathogens relies on the treatment of domestic hot water with a system ensuring the in situ production and dosage of monochloramine. An average of 250 samples/year were collected and analyzed to allow an accurate assessment of the microbiological status of water network. With the aim of increasing the monitoring sensitivity, in addition to the standard culture method, an optimized MALDI-ToF MS-based strategy was applied, allowing the identification of Legionella species and other relevant opportunistic pathogens. Data collected so far confirmed the effectiveness of this multidisciplinary approach: the fraction of positive samples never overcame 1% on a yearly basis and Legionnaires\' Disease cases never occurred.

Thirty-two short term (∼7.5 h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9), dissolved inorganic carbon (DIC, 10 or 50 mg C L-1) and phosphate (0 or 3 mg P L-1) concentrations and 4 mg Cl2 L-1 free chlorine or monochloramine. To quantify oxidant reactivity with the new metal coupons, microelectrodes were used to obtain oxidant (free chlorine or monochloramine and dissolved oxygen (DO)) concentration and pH microprofiles from the bulk water to near the metal coupon surface. From the microprofiles, apparent surface reaction rate constants (k) were determined for each oxidant. An ANOVA analysis evaluated if the five variables (Material, Oxidant, Phosphate, DIC, and pH) significantly affected estimates of k, finding that the Material and Oxidant variables and their interaction were statistically significant (p<0.05), but the effect of variables of Phosphate, DIC, and pH on k values were not significant in this study. In general, both ductile iron and copper coupons showed significant surface reactivity towards free chlorine and monochloramine. For ductile iron, DO consumption was greater than for copper, which showed minimal DO reactivity, and DO was less reactive towards the copper surface than either free chlorine or monochloramine. Furthermore, pH microprofiles provided insight into the complexity that might exist near corroding metal surfaces where the bulk water pH may be substantially different from that measured near metal surfaces which is significant as pH is a controlling variable in terms of scale formation and metal solubility. This study represents an important first step towards using microelectrodes to (1) understand and provide direct measurement of oxidant microprofiles from the bulk water to the metal surface; (2) determine pipe wall reactivity using the directly measured concentrations profiles versus estimated pipe wall reactivity from bulk water measurements, and (3) understand how variables measured by bulk water samples (e.g., pH) may be drastically different from what is occurring at and near the metal surface. Together, these insights will assist in understanding disinfectant residual maintenance, corrosion, and metal release.

To evaluate natural organic matter (NOM) processing impacts on preformed monochloramine (PM) reactivity and as a first step in creating concentrated disinfection byproduct (DBP) mixtures from PM, a rational methodology was developed to proportionally scale PM NOM-related demand in unconcentrated source waters to waters with concentrated NOM. Multiple NOM preparations were evaluated, including a liquid concentrate and reconstituted lyophilized solid material. Published kinetic models were evaluated and used to develop a focused reaction scheme (FRS) that was relatively simple to implement and focused on monochloramine loss, including considerations for inorganic chloramine stability (i.e., autodecomposition) and bromide and iodide impacts. The FRS included critical reaction pathways and accurately simulated (without modification) monochloramine experimental data with and without bromide and iodide present over a range of PM-dosed NOM-free waters. For NOM-containing waters, addition of two NOM reactions in the FRS allowed (i) apportioning monochloramine loss to either inorganic or NOM-related reactions and (ii) selecting experiment conditions to provide an equivalent monochloramine NOM-related demand in unconcentrated and concentrated waters. The methodology provides a framework for future experimentation to evaluate DBP scaling and their speciation in concentrated water matrices when providing an equivalent NOM-related monochloramine demand in unconcentrated and concentrated matrices.

Ammonia-oxidizing archaea (AOA) can oxidize ammonia to nitrite for energy gain. They have been detected in chloraminated drinking water distribution systems (DWDS) along with the more common ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). To date, no members of the AOA have been isolated or enriched from drinking water environments. To begin the investigation of the role of AOA in chloraminated DWDS, we developed a selective approach using biofilm samples from a full-scale operational network as inoculum. A Nitrososphaera viennensis-like AOA taxon was enriched from a mixed community that also included Nitrosomonas-like AOB while gradually scaling up the culture volume. Dimethylthiourea (DMTU) and pyruvate at 100 μM were added to promote the growth of AOA while inhibiting AOB. This resulted in the eventual washout of AOB, while NOB were absent after 2 or 3 rounds of amendment with 24 μM sodium azide. The relative abundance of AOA in the enrichment increased from 0.2% to 39.5% after adding DMTU and pyruvate, and further to 51.6% after filtration through a 0.45-μm pore size membrane, within a period of approximately 6 months. IMPORTANCE Chloramination has been known to increase the risk of nitrification episodes in DWDS due to the presence of ammonia-oxidizing microorganisms. Among them, AOB are more frequently detected than AOA. All publicly available cultures of AOA have been isolated from soil, marine or surface water environments, meaning they are allochthonous to DWDS. Hence, monochloramine exposure studies involving these strains may not accurately reflect their role in DWDS. The described method allows for the rapid enrichment of autochthonous AOA from drinking water nitrifying communities. The high relative abundance of AOA in the resulting enrichment culture reduces any confounding effects of co-existing heterotrophic bacteria when investigating the response of AOA to varied levels of monochloramine in drinking water.

Water-based opportunistic pathogens (OPs) are a leading cause of drinking-water-related disease outbreaks, especially in developed countries such as the United States (US). Physicochemical water quality parameters, especially disinfectant residuals, control the (re)growth, presence, colonization, and concentrations of OPs in drinking water distribution systems (DWDSs), while the relationship between OPs and those parameters remain unclear. This study aimed to quantify how physicochemical parameters, mainly monochloramine residual concentration, hydraulic residence time (HRT), and seasonality, affected the occurrence and concentrations of four common OPs (Legionella, Mycobacterium, Pseudomonas, and Vermamoeba vermiformis) in four full-scale DWDSs in the US. Legionella as a dominant OP occurred in 93.8% of the 64 sampling events and had a mean density of 4.27 × 105 genome copies per liter. Legionella positively correlated with Mycobacterium, Pseudomonas, and total bacteria. Multiple regression with data from the four DWDSs showed that Legionella had significant correlations with total chlorine residual level, free ammonia concentration, and trihalomethane concentration. Therefore, Legionella is a promising indicator of water-based OPs, reflecting microbial water quality in chloraminated DWDSs. The OP concentrations had strong seasonal variations and peaked in winter and/or spring possibly because of reduced water usage (i.e., increased water stagnation or HRT) during cold seasons. The OP concentrations generally increased with HRT presumably because of disinfectant residual decay, indicating the importance of well-maintaining disinfectant residuals in DWDSs for OP control. The concentrations of Mycobacterium, Pseudomonas, and V. vermiformis were significantly associated with total chlorine residual concentration, free ammonia concentration, and pH and trihalomethane concentration, respectively. Overall, this study demonstrates how the significant spatiotemporal variations of OP concentrations in chloraminated DWDSs correlated with critical physicochemical water quality parameters such as disinfectant residual levels. This work also indicates that Legionella is a promising indicator of OPs and microbial water quality in chloraminated DWDSs.

Chloramine is a secondary disinfectant used to maintain microbial control throughout public water distribution systems. This study investigated the relationship between chloramine concentration, heterotrophic bacteria, and specific Mycobacterium species. Sixty-four water samples were collected at four locations within the utility\'s distribution network on four occasions. Water samples were analyzed for total chlorine and monochloramine. Traditional culture methods were applied for heterotrophic bacteria and nontuberculous mycobacteria (NTM), and specific quantitative polymerase chain reaction (qPCR) assays were used to detect and quantify Mycobacterium avium, M. intracellulare, and M. abscessus. Total chlorine and monochloramine concentrations decreased between the distribution entry point (4.7 mg/L and 3.4 mg/L as Cl2, respectively) to the maximum residence time location (1.7 mg/L and 1.1 mg/L as Cl2, respectively). Results showed that heterotrophic bacteria and NTM counts increased by two logs as the water reached the average residence time (ART) location. Microbiological detection frequencies among all samples were: 86% NTMs, 66% heterotrophic bacteria, 64% M. abscessus, 48% M. intracellulare, and 2% M. avium. This study shows that heterotrophic bacteria and NTM are weakly correlated with disinfectant residual concentration, R2=0.18 and R2=0.04, respectively. Considering that specific NTMs have significant human health effects, these data fill a critical knowledge gap regarding chloramine\'s impact on heterotrophic bacteria and Mycobacterial species survival within public drinking water distribution systems.

Copper ion (Cu2+), a common corrosion product released from copper pipes, is widely present in water distribution system (WDS). Cu2+ was confirmed to be capable to catalyze the decay of monochloramine (NH2Cl), which is a commonly used disinfectant and need to maintain a minimum concentration in WDS. Cu2+ and NH2Cl form a system in WDS and their interaction with other substances in WDS is unclear. In this study, the performance of Cu2+/NH2Cl system on degradation of trace pollutants, taking carbamazepine (CBZ) as an example, in WDS was investigated, and significant promotion on CBZ degradation was observed. The acceleration was due to the generation of Cl, OH and other oxidants, which were identified by scavenge experiments. CBZ degradation in Cu2+/NH2Cl system was highly pH-dependent, because the catalytic effect of Cu2+ can only work at low pH (Cu2+ precipitating at pH > 6.0). The removal of CBZ increased with the concentration of Cu2+ increasing. Water matrix (NOM, HCO3- and Br-) can inhibit the removal of CBZ in Cu2+/NH2Cl system. Further, five disinfection byproducts (DBPs), namely, trichloromethane (TCM), dichloroacetonitrile (DCAN), dichloroacetone (DCP), trichloronitromethane (TCNM) and trichloroacetone (TCP), were detected in chloramination in the presence/absence of Cu2+. Compared with chloramination without Cu2+, the cytotoxicity and genotoxicity of formed DBPs increased significantly in the presence of Cu2+, indicating that the chemical safety in WDS deserves more attention.

Water quality management will be a priority issue in the near future. Indeed, due to scarcity and/or contamination of the water, regulatory frameworks will be increasingly strict to reduce environmental impacts of wastewater and to allow water to be reused. Moreover, drinking water quality standards must be improved in order to account for the emerging pollutants that are being detected in tap water. These tasks can only be achieved if new improved and sustainable water treatment technologies are developed. Nanomaterials are improving the ongoing research on advanced oxidation processes (AOPs). This work reviews the most important AOPs, namely: persulfate, chlorine and NH2Cl based processes, UV/H2O2, Fenton processes, ozone, and heterogeneous photocatalytic processes. A critical review of the current coupling of nanomaterials to some of these AOPs is presented. Besides the active role of the nanomaterials in the degradation of water contaminants/pollutants in the AOPs, the relevance of their adsorbent/absorbent function in these processes is also discussed.

Monochloramine (NH2Cl) is increasingly used as alternative disinfectant to free chlorine in industrial plants. After use in cooling systems, the waters are released to the environment and residual NH2Cl may be discharged into the receiving waters. As NH2Cl is suspected to exhibit toxicity towards aquatic organisms, a proper risk assessment of its occurrence in environmental waters is needed to prevent adverse effects on wildlife. For this purpose, a comprehensive model simulating monochloramine loss in natural riverine waters was developed. This model incorporates the following processes: (i) autodecomposition; (ii) reaction with nitrite and bromide; (iii) oxidation with Dissolved Organic Carbon (DOC); (iv) oxidation with organic fraction of Suspended Particulate Matter (SPM); (v) reactions in bottom sediments and (vi) volatilization. The model was also designed to conduct uncertainty and sensitivity analysis. It was tested on several French rivers submitted to discharges of monochloraminated effluents and on several seasonal conditions. Uncertainty analysis allowed evaluation of confidence intervals related to NH2Cl half-lives in natural waters. It was shown that simulation intervals are in good agreement with experimental data obtained on the same rivers. Sensitivity analysis using an EFAST variance decomposition approach allowed identification of the most influential parameters on half-life determination. It was shown that the kinetic rate describing rapid reaction of NH2Cl with DOC is by far the most sensitive parameter, demonstrating the predominance of such reactions in the loss process. Variables or parameters involved in temperature dependence (temperature and activation energy) can also significantly influence model results. To a lesser extent, wind velocity is the most sensitive parameter explaining uncertainty in the prediction of volatilization, with a high level of interactions with other parameters, showing that loss through volatilization can be essential in some specific conditions only. This study then identified the most important research priorities for improving the prediction of NH2Cl half-lives in natural rivers.

Although drinking water disinfection proved to be an effective strategy to eliminate many pathogens, bacteria can still show disinfection tolerance in drinking water distribution systems. To date, the molecular mechanisms on how environmental stress affects the tolerance of Pseudomonas aeruginosa to monochloramine are not well understood. Here, we investigated how three stress conditions, namely starvation, low temperature, and starvation combined with low temperature, affected the monochloramine tolerance of Pseudomonas aeruginosa, an opportunistic pathogen commonly found in drinking water distribution systems. All stress conditions significantly promoted monochloramine tolerance, among which starvation had the most drastic effects. Proteomic analyses suggested that the three conditions not only triggered a positive antioxidant defense against oxidative damages but also prepared the bacteria to employ a passive defense mechanism against disinfectants via dormancy. Moreover, the expression of antioxidant enzymes reached the maximum under the starvation condition and further low temperature treatment had little effect on bacterial response to oxidative stress. Instead, we found further treatment of the starved cells with low temperature decreased the osmotic stress response and the stringent response, which generally play pivotal roles in disinfection tolerance. Taken together, these findings shed light on how abiotic factors influence the bacterial disinfection tolerance and will aid design of efficient strategies to eliminate Pseudomonas aeruginosa from drinking water.