Unchartered waters: the unintended impacts of residual chlorine on water quality and biofilms

Exploring water quality variations and biofilm growth in a drinking water distribution system via a biofilm annular reactor series system and predictive modelling of residual chlorine

The hydraulic conditions vary significantly across different segments of the drinking water distribution system (DWDS), leading to distinct variations in water quality throughout the system. Understanding these changes in water quality and biofilm development over time is crucial for enhancing drinking water management efficiency. This study focused on replicating the hydraulic conditions found in transmission and distribution pipelines within a specific pipeline path of the DWDS in Singapore using a biofilm annular reactor series system (BARSS). The BARSS experiment revealed that the total residual chlorine (TRC) concentration in water was greatly influenced by both flow velocity and the amount of biofilm present. TRC decay occurred more rapidly at higher flow velocity and was influenced by bacterial growth under fast flow conditions. Furthermore, UV254 levels in the water decreased with extended water age in the BARSS, due to the degradation of organic matters into smaller molecules. The study also found that higher TRC concentrations had a more pronounced inhibitory effect on biofilm formation and the proliferation of minor taxa. In the last part of the study, a predictive model for TRC concentration was developed using water quality parameters from preceding stages in the BARSS. This model demonstrated excellent prediction accuracy for TRC concentration, with a mean square error (MSE) of 0.0110 and R2 of 0.9893.

Deep generative modeling of annotated bacterial biofilm images

Biofilms are critical for understanding environmental processes, developing biotechnology applications, and progressing in medical treatments of various infections. Nowadays, a key limiting factor for biofilm analysis is the difficulty in obtaining large datasets with fully annotated images. This study introduces a versatile approach for creating synthetic datasets of annotated biofilm images with employing deep generative modeling techniques, including VAEs, GANs, diffusion models, and CycleGAN. Synthetic datasets can significantly improve the training of computer vision models for automated biofilm analysis, as demonstrated with the application of Mask R-CNN detection model. The approach represents a key advance in the field of biofilm research, offering a scalable solution for generating high-quality training data and working with different strains of microorganisms at different stages of formation. Terabyte-scale datasets can be easily generated on personal computers. A web application is provided for the on-demand generation of biofilm images.

Detection of extracellular antibiotic resistance genes in river water: Application of ultrafiltration-magnetic beads method

Antibiotic resistance genes (ARGs) are widespread contaminants that pose significant threats to public health. Rivers play a crucial role in the dissemination of ARGs within the aquatic environment. However, there are limitations in the current research on the differentiation of intracellular ARGs (iARGs) and extracellular ARGs (eARGs) in river water. In this study, we developed a method combining ultrafiltration and adsorption of silica-hydroxy magnetic beads for efficient extraction of extracellular DNA (eDNA) from river water. The conditions of adsorption, washing, desorption, and pretreatment were optimized to enhance eDNA recovery. By using only 90 mL of water sample, our method could collect sufficient eDNA for subsequent detection of eARGs through qPCR analysis. The eDNA recovery rate ranged from 51.4% to 69.8%. The occurrence of five prevalent ARGs (tetC, sulI, blaTEM, ermB, qnrS) as well as integrase gene intl1 were investigated in both iDNA and eDNA extracted from river water samples collected from two tributaries of the Pearl River. Our results revealed that the absolute abundance levels of eARGs ranged from 10-1 to 105 copies/mL, which were significantly higher than those observed for iARGs ranging from 10-1 to 104 copies/mL. Moreover, there was a significant difference in contamination profiles for ARGs between two tributaries. The ultrafiltration-magnetic beads method overcomes challenges associated with low efficiency extraction when working with water samples containing low nucleic acid concentrations. This approach provides an improved technique for extracting eARGs from river water while also generating valuable data supporting assessments related to eARG contamination in such environments.

Water chlorination increases the relative abundance of an antibiotic resistance marker in developing sourdough starters

Multiple factors explain the proper development of sourdough starters. Although the role of raw ingredients and geography, among other things, have been widely studied recently, the possible effect of air quality and water chlorination on the overall bacterial communities associated with sourdough remains to be explored. Here, using 16S rRNA amplicon sequencing, we show that clean, filtered-air severely limited the presence of lactic acid bacteria in sourdough starters, suggesting that surrounding air is an important source of microorganisms necessary for the development of sourdough starters. We also show that water chlorination at levels commonly found in drinking water systems has a limited impact on the overall bacterial communities developing in sourdough starters. However, using targeted sequencing, which offers a higher resolution, we found that the abundance of integron 1, a genetic mechanism responsible for the horizontal exchange of antibiotic-resistance genes in spoilage and pathogenic bacteria, increased significantly with the level of water chlorination. Although our results suggest that water chlorination might not impact sourdough starters at a deep phylogenetic level, they indicate that it can favor the spread of genetic elements associated with spoilage bacteria.

IMPORTANCE

Proper development of sourdough starters is critical for making tasty and healthy bread. Although many factors contributing to sourdough development have been studied, the effect of water chlorination on the bacterial communities in sourdough has been largely ignored. Researchers used sequencing techniques to investigate this effect and found that water chlorination at levels commonly found in drinking water systems has a limited impact on the overall bacterial communities developing in sourdough starters. However, they discovered that water chlorination could increase the abundance of integron 1, a genetic mechanism responsible for the horizontal exchange of antibiotic resistance genes in spoilage and pathogenic bacteria. This suggests that water chlorination could favor the growth of key spoilage bacteria and compromise the quality and safety of the bread. These findings emphasize the importance of considering water quality when developing sourdough starters for the best possible bread.

Exploring the use of clay pots as sustainable storage containers to improve water quality

BACKGROUND

Currently, tap water consumption is not highly preferred in Egypt and around the world. People prefer to consume bottled water because they believe that it is much safer and tastes better than tap water. Unfortunately, this preference can create an economic burden for many people, especially in developing countries. Clay pots can be used to provide cool, alkaline drinking water because of their porous micro-texture, which traps pollutants. This study aimed to investigate the use of clay pots to store tap water and its impact on the requirements for drinking water quality. This is done with the intent to decrease the need for bottled water as a means of offering a more sustainable and economical option.

METHODS

In this study, the efficiency of clay pots as sustainable storage containers for drinking water was tested by measuring physicochemical parameters (pH, TDS, EC, turbidity, DO, ammonia, chloride, total hardness, Ca hardness, Mg hardness, chlorine, Zn, and CaCO3) and biological parameters (TPC and Legionella).

RESULTS

After 7 days of storage, the quality of the water stored in clay pots met the standards set by the Egyptian law with a significant difference (p < 0.05) before and after the storage of water It was found that the dissolved oxygen increased from 6.17 ppm to 7.52 ppm after 7 days. As for total hardness, it declined from 195 to 178 ppm. There was also a significant drop in terms of TDS from 338 to 275 ppm. Furthermore, clay pots effectively filtered out both total viable bacteria and Legionella.

CONCLUSION

This study proved the efficiency of using these containers with respect to some indicator values for tap water and tank water analysis. Clay pots are an excellent, cost-effective, and sustainable alternative for storing water.

A review of research advances on disinfection strategies for biofilm control in drinking water distribution systems

The presence of biofilms in drinking water distribution systems (DWDS) is responsible for water quality deterioration and a possible source of public health risks. Different factors impact the biological stability of drinking water (DW) in the distribution networks, such as the presence and concentration of nutrients, water temperature, pipe material composition, hydrodynamic conditions, and levels of disinfectant residual. This review aimed to evaluate the current state of knowledge on strategies for DW biofilm disinfection through a qualitative and quantitative analysis of the literature published over the last decade. A systematic review method was performed on the 562 journal articles identified through database searching on Web of Science and Scopus, with 85 studies selected for detailed analysis. A variety of disinfectants were identified for DW biofilm control such as chlorine, chloramine, UV irradiation, hydrogen peroxide, chlorine dioxide, ozone, and others at a lower frequency, namely, electrolyzed water, bacteriophages, silver ions, and nanoparticles. The disinfectants can impact the microbial communities within biofilms, reduce the number of culturable cells and biofilm biomass, as well as interfere with the biofilm matrix components. The maintenance of an effective residual concentration in the water guarantees long-term prevention of biofilm formation and improves the inactivation of detached biofilm-associated opportunistic pathogens. Additionally, strategies based on multi-barrier processes by optimization of primary and secondary disinfection combined with other water treatment methods improve the control of opportunistic pathogens, reduce the chlorine-tolerance of biofilm-embedded cells, as well as decrease the corrosion rate in metal-based pipelines. Most of the studies used benchtop laboratory devices for biofilm research. Even though these devices mimic the conditions found in real DWDS, future investigations on strategies for DW biofilm control should include the validity of the promising strategies against biofilms formed in real DW networks.

Microbial ecology of drinking water from source to tap

As drinking water travels from its source, through various treatment processes, hundreds to thousands of kilometres of distribution network pipes, to the taps in private homes and public buildings, it is exposed to numerous environmental changes, as well as other microbes living in both water and on surfaces. This review aims to identify the key locations and factors that are associated with changes in the drinking water microbiome throughout conventional urban drinking water systems from the source to the tap water. Over the past 15 years, improvements in cultivation-independent methods have enabled studies that allow us to answer such questions. As a result, we are beginning to move towards predicting the impacts of disturbances and interventions resulting ultimately in management of drinking water systems and microbial communities rather than mere observation. Many challenges still exist to achieve effective management, particularly within the premise plumbing environment, which exhibits diverse and inconsistent conditions that may lead to alterations in the microbiota, potentially presenting public health risks. Finally, we recommend the establishment of global collaborative projects on the drinking water microbiome that will enhance our current knowledge and lead to tools for operators and researchers alike to improve global access to high-quality drinking water.

The Role of Chlorine in the Formation and Development of Tap Water Biofilms under Different Flow Regimes

Water companies make efforts to reduce the risk of microbial contamination in drinking water. A widely used strategy is to introduce chlorine into the drinking water distribution system (DWDS). A subtle potential risk is that non-lethal chlorine residuals may select for chlorine resistant species in the biofilms that reside in DWDS. Here, we quantify the thickness, density, and coverage of naturally occurring multi-species biofilms grown on slides in tap water with and without chlorine, using fluorescence microscopy. We then place the slides in an annular rotating reactor and expose them to fluid-wall shears, which are redolent of those on pipe walls in DWDS. We found that biofilms in chlorine experiment were thicker, denser and with higher coverage than in non-chlorine conditions under all flow regimes and during incubation. This suggests that the formation and development of biofilms was promoted by chlorine. Surprisingly, for both chlorinated and non-chlorinated conditions, biofilm thickness, density and coverage were all positively correlated with shear stress. More differences were detected in biofilms under the different flow regimes in non-chlorine than in chlorine experiments. This suggests a more robust biofilm under chlorine conditions. While this might imply less mobilization of biofilms in high shear events in pipe networks, it might also provide refuge from chlorine residuals for pathogens.

The impact of potassium peroxymonosulphate and chlorinated cyanurates on biofilms of Stenotrophomonas maltophilia: effects on biofilm control, regrowth, and mechanical properties

The activity of two chlorinated isocyanurates (NaDCC and TCCA) and peroxymonosulphate (OXONE) was evaluated against biofilms of Stenotrophomonas maltophilia, an emerging pathogen isolated from drinking water (DW), and for the prevention of biofilm regrowth. After disinfection of pre-formed 48 h-old biofilms, the culturability was reduced up to 7 log, with OXONE, TCCA, and NaDCC showing more efficiency than free chlorine against biofilms formed on stainless steel. The regrowth of biofilms previously exposed to OXONE was reduced by 5 and 4 log CFU cm-2 in comparison to the unexposed biofilms and biofilms exposed to free chlorine, respectively. Rheometry analysis showed that biofilms presented properties of viscoelastic solid materials, regardless of the treatment. OXONE reduced the cohesiveness of the biofilm, given the significant decrease in the complex shear modulus (G*). AFM analysis revealed that biofilms had a fractured appearance and smaller bacterial aggregates dispersed throughout the surface after OXONE exposure than the control sample. In general, OXONE has been demonstrated to be a promising disinfectant to control DW biofilms, with a higher activity than chlorine. The results also show the impact of the biofilm mechanical properties on the efficacy of the disinfectants in biofilm control.

Chlorine decay and disinfection by-products transformation under booster chlorination conditions: A pilot-scale study

Booster chlorination was usually employed in water distribution systems with a long hydraulic retention time. The free chlorine decay and disinfection by-products (DBPs) transformation under booster chlorination conditions were investigated within a pilot-scale water distribution system (WDS). Compared with the initial chlorination in water plants, the loss of chlorine was relatively slow and could be described with first-order kinetic model. The rate of chlorine decay and the generation of DBPs in WDS were much greater than those in beaker. High flow rate and the hydraulic transients both promoted chlorine decay and DBPs formation, especially for dichloroacetonitrile (DCAN). The formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was higher in the ductile iron pipe than in the steel pipe. After booster chlorination, THMs, HAAs, and DCAN all climbed up and then declined continuously, but the peak times were different during the reaction process. The results showed the generation period of DBPs followed the order: THMs (27 h) > HAAs (22 h) > DCAN (5 h). DCAN was not stable in WDS and could be decomposed for a long hydraulic retention time (HRT). The decrease of dichloroacetic acid (DCAA) and increase of trichloroacetic acid (TCAA) indicated that DCAA may turn into TCAA. Linear relationships between the free chlorine demand (FCD) and the generation of THMs that considered both buck water and the pipe wall, as well as the different hydraulic conditions, were established to predict the formation of DBPs in WDS after booster chlorination.

Flexible decision-making framework for developing operation protocol for water distribution systems

Past water distribution systems (WDS) management studies derived operation protocols to maximize WDS reliability by using residual chlorine as the sole surrogate parameter for water quality reliability. Albeit the advancement in mechanistic modeling to examine the WDS water quality, emerging water quality parameters of concern are not yet involved in solving WDS management problems. This paper attempts to overcome this limitation by developing a flexible decision-making framework -integrating EPANET-C, a mechanistic modeling tool for WDS water quality, with Analytic Hierarchy Process (AHP), a multi-criteria decision-making method - to rank the possible water quality parameter-based operating alternatives (organic matter and residual chlorine levels at the source points) for WDS. The uncertainty analysis was incorporated into the mechanistic modeling using the Monte Carlo method to realize insufficient knowledge about the complex biological and physicochemical interactions inside WDS. Six cases, each ranking the alternatives diversely, were applied to reflect the expert judgment impressions on the AHP outcomes. The consistency of the proposed decision-making framework was verified by deriving the operation protocol for two test networks by making trade-offs between the multiple and conflicting microbiological, chemical, and organoleptic quality criteria. The disinfection by-products formation control and taste and odor problems control emerged as the most critical water quality criteria determining the WDS performance under the operating alternatives examined. Altogether, the obtained results suggested the practicality of adopting a flexible operation protocol to maintain the water quality benchmarks over various plausible WDS performance scenarios, ranging from worst to best.

Hypochlorous Acid: From Innate Immune Factor and Environmental Toxicant to Chemopreventive Agent Targeting Solar UV-Induced Skin Cancer

A multitude of extrinsic environmental factors (referred to in their entirety as the 'skin exposome') impact structure and function of skin and its corresponding cellular components. The complex (i.e. additive, antagonistic, or synergistic) interactions between multiple extrinsic (exposome) and intrinsic (biological) factors are important determinants of skin health outcomes. Here, we review the role of hypochlorous acid (HOCl) as an emerging component of the skin exposome serving molecular functions as an innate immune factor, environmental toxicant, and topical chemopreventive agent targeting solar UV-induced skin cancer. HOCl [and its corresponding anion (OCl-; hypochlorite)], a weak halogen-based acid and powerful oxidant, serves two seemingly unrelated molecular roles: (i) as an innate immune factor [acting as a myeloperoxidase (MPO)-derived microbicidal factor] and (ii) as a chemical disinfectant used in freshwater processing on a global scale, both in the context of drinking water safety and recreational freshwater use. Physicochemical properties (including redox potential and photon absorptivity) determine chemical reactivity of HOCl towards select biochemical targets [i.e. proteins (e.g. IKK, GRP78, HSA, Keap1/NRF2), lipids, and nucleic acids], essential to its role in innate immunity, antimicrobial disinfection, and therapeutic anti-inflammatory use. Recent studies have explored the interaction between solar UV and HOCl-related environmental co-exposures identifying a heretofore unrecognized photo-chemopreventive activity of topical HOCl and chlorination stress that blocks tumorigenic inflammatory progression in UV-induced high-risk SKH-1 mouse skin, a finding with potential implications for the prevention of human nonmelanoma skin photocarcinogenesis.

Characterization of Scale Deposits in a Drinking Water Network in a Semi-Arid Region

The quantity and quality of the supply of fresh water to households, commercial areas, small industries, green spaces irrigation and public and private institutions in large cities face challenges from the supply sources availability and suitable distribution network performance to the full satisfaction of the established drinking water guidelines. In Mexico, the main source of water comes from groundwater. Most of the Mexican aquifers are located in arid and semi-arid weather conditions. The groundwater’s physical–chemical properties are closely related to geology. This study was carried out at the north-central part of the country in which igneous and sedimentary rocks predominate, with high calcium carbonate (CaCO₃) concentrations. The accumulation of CaCO₃ in the pipelines is also known as scale deposit that decreases the fluid flow, causing a deficiency in the water supply. The main objectives of this study were determining the physical–chemical groundwater parameters and saturation indexes injected into the drinking water networks and characterizing the scale deposits by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicate that the scale deposits are mainly calcium carbonate and silica oxide crystals, caused by the water aggressiveness according to the saturation indexes and the lack of control over the saturation pH.

Biofilms in Water Hoses of a Meat Processing Environment Harbor Complex Microbial Communities

Safe and hygienic water distribution is essential for maintaining product quality and safety. It is known that biofilms alter the appearance and microbial quality of water along the distribution chain. Yet, biofilms in water hoses throughout the food processing environment have not been investigated in detail. Here, microbial communities from water hoses and other environmental sites in contact with water, in addition to the source water itself, were studied in the meat processing environment. Biofilms were present in all water hoses as determined by the presence of bacterial DNA and biofilm matrix components (carbohydrates, extracellular DNA, and proteins). The microbial community of the biofilms was dominated by Proteobacteria, represented mainly by Comamonadaceae and Pseudoxanthomonas. Moreover, genera that are associated with an intracellular lifestyle (e.g., Neochlamydia and Legionella) were present. Overall, the microbial community of biofilms was less diverse than the water microbial community, while those from the different sample sites were distinct from each other. Indeed, only a few phyla were shared between the water hose biofilm and the source water or associated environmental samples. This study provides first insights towards understanding the microbiota of water hose biofilms in the food processing environment.

Non-invasive Biofouling Monitoring to Assess Drinking Water Distribution System Performance

Biofilms are endemic in drinking water distribution systems (DWDS), forming on all water and infrastructure interfaces. They can pose risks to water quality and hence consumers. Our understanding of these biofilms is limited, in a large part due to difficulties in sampling them without unacceptable disruption. A novel, non-destructive and non-disruptive biofilm monitoring device (BMD), which includes use of flow cytometry analysis, was developed to assess biofouling rates. Laboratory based experiments established optimal configurations and verified reliable cell enumeration. Deployment at three operational field sites validated assessment of different biofouling rates. These differences in fouling rates were not obvious from bulk water sampling and analysis, but did have a strong correlation with long-term performance data of the associated networks. The device offers the potential to assess DWDS performance in a few months, compared to the number of years required to infer findings from historical customer contact data. Such information is vital to improve the management of our vast, complex and uncertain drinking water supply systems; for example rapidly quantifying the benefits of improvements in water treatment works or changes to maintenance of the network.

Assimilable organic carbon cycling within drinking water distribution systems

A new conceptual model to describe and understand the role of assimilable organic carbon (AOC) within drinking water distribution systems is proposed. The impact of AOC on both drinking water biofilm and water quality was studied using bespoke pipe loop experimental facilities installed at three carefully selected operational water treatment works. Integrated physical, chemical and biological monitoring was undertaken that highlights the central role of biofilms in AOC cycling, forming the basis of the new conceptual model. Biofilms formed under high AOC conditions were found to pose the highest discoloration response, generating a turbidity (4.3 NTU) and iron (241.5 µg/l) response sufficient to have caused regulatory failures from only 20 m of pipe in only 12 months of operation. This new knowledge of the role of biofilms in AOC cycling, and ultimately impacts on water quality, can be used to inform management and help ensure the supply of high-quality, biostable drinking water.