Safeguarding the microbial water quality from source to tap

Anthropogenic activities and climate change can deteriorate the freshwater quality and stress its availability. This stress can, in turn, have an impact on the biostability of drinking water. Up to now, the microbiological quality of drinking water has been maintained through the selection of high-quality water sources allied to the use of disinfectants and the removal of organic carbon. But as freshwater becomes richer in other nutrients, strategies used so far may not suffice to keep a steady and high-quality supply of drinking water in the future. This article readdresses the discussion on drinking water biostability. We need to reframe the concept as a dynamic equilibrium that considers the available nutrients and energy sources (potential for growth) relative to the abundance and composition of the bacterial community (potential to consume the available resources)

Flow cytometric fingerprinting to assess the microbial community response to changing water quality and additives

Water is used for a very broad range of industrial applications with different water quality requirements. In all cases, the microbial water quality remains of importance as the microbial community can cause biofouling, microbial induced corrosion, odor problems, or health hazards. A close and accurate monitoring of the microbial water quality is therefore relevant for all water types used in industrial applications. Flow cytometry and additionally flow cytometric fingerprinting have been proposed before as methods to monitor the aquatic microbial communities but it remains unclear on how sensitive the fingerprinting method is for detecting quality changes in practice for different types of water. In this paper, we compared the microbial dynamics of coarsely filtered surface water, tap water, and demineralized water by challenging these waters with different concentrations and types of nutrients (C, N, and P) and additives such as corrosion inhibitors and biocides. We demonstrated that the cytometric fingerprints of the aquatic microbial communities differed in function of the type and concentration of product added, but that these differences are dependent on the type of water. Flow cytometry proved to be sensitive enough to detect subtle changes in microbial communities and to measure bacterial regrowth in different types of water. As a result, we conclude that cytometric fingerprints can be considered as indirect indicators of the physical-chemical composition of the water and a tool to monitor water biostability, as a tell-tale for minor environmental changes

Biostability of drinking water systems : from online monitoring to microbial quality management

Safeguarding the microbial drinking water quality remains a worldwide challenge. With a growing world population, increased urbanization and climate change, the quality and availability of freshwater sources are decreasing. This, in turn, can stress the production and distribution of high-quality drinking water. Up to now, the microbiological quality of drinking water at the tap is guaranteed through the addition of chemical disinfectants that supress microbial growth in the drinking water distribution network (DWDS), such as chlorine. However, these chemicals may form potentially carcinogenic disinfection by-products, and can result in a deviating water taste and odour. Alternatively, the production of biostable water (biostability) could serve as a more sustainable approach to produce and maintain microbially safe water. In the last 40 years, researches have attempted to define and regulate biostability in different ways, which were either too complex to bring into practice, or were lacking scientific value. In Chapter 1 of this dissertation we first redefined biostability of drinking water systems as a dynamic stability of both the total microbial abundance and community composition during distribution, and we proposed a new framework for managing biostability as a balance between complexity (research) and feasibility (practice). When producing and distributing biostable drinking water, high-frequency monitoring of the microbial water quality becomes of utmost importance. In Chapter 2, we explored the use of online flow cytometry (FCM) and flow cytometric fingerprinting to monitor the biostability of drinking water systems within a full-scale water tower. We observed that events of biological instability occurred even though the water quality was legally compliant. Based on quantifying the difference between cytometric fingerprints, the Bray-Curtis dissimilarity was further developed as unambiguous parameter to indicate changes in the microbial drinking water quality during operational events. The results of Chapter 2 showed the added value of online FCM and fingerprinting as a tool for microbial water quality monitoring. In Chapter 3, we explored the applicability of a range of different online microbial monitoring techniques at a full-scale drinking water production facility. We compared their response towards operational changes and contaminations, as well as their detection limit. Enzymatic analysis, ATP measurement, and flow cytometric fingerprinting showed to be the most sensitive towards contaminations. On the other hand, optical classification and flow cytometric cell counts were more robust techniques that provide direct information about the cell concentration. These results showed that the choice for a certain technology will depend on the type of application, and will be a balance between sensitivity and maintenance. Biostability of a drinking water system implies stability of the community throughout production, the DWDS and in the household plumbing. In this regard, monitoring the microbial dynamics of domestic hot water (DHW) systems is important, as they form a potential source for the outgrowth of pathogens such as Legionella pneumophila. In Chapter 4, we investigated the dynamics of the DHW microbial abundance and community structure, and Legionella spp. in a controlled pilot system. We observed that daily hot water usage patterns and heat shock disinfection affect the microbial abundance and viability at hot water household taps and at the hot water supply. Furthermore, the results showed that Legionella spp. was not fully eradicated nor selectively enriched through heat shock disinfection. We hypothesized that selecting for heat-resistant species in the microbiome may be an alternative approach to maintain a biostable microbiome within DHW environments. Based on the theoretical framework developed in Chapter 1, the hypothesis was formulated that biostability can be accomplished through the creation of an environment that is oligotrophic in all available nutrients but eutrophic in energy. More specifically, the water can be “energized” through addition of hydrogen gas (H2) and oxygen gas (O2) as electron donor and acceptor, respectively. This way, autotrophic growth of hydrogen-oxidizing bacteria (HOB) is stimulated. In Chapter 5, we explored the potential of HOB for the production of biostable drinking water in a continuous trickling filter supplied with hydrogen gas. The bacterial regrowth, invasion potential, and nutrient composition of the water were determined. Treatment showed to improve the biostability significantly, and it is hypothesized that nutrient limitation, especially phosphorous, was a driving force. As a result, the regrowth and invasion potential were lowered, as shown with specific biostability bioassays. Overall, these results demonstrated the effectiveness of HOB for producing biostable drinking water through nutrient limitation. In conclusion, understanding of microbial (re)growth and its driving factors during production, storage, in the DWDS and household plumbing remain of utmost importance to ensure the microbial water quality from source to tap. In this respect, producing biostable drinking water, combined with online monitoring of the microbial dynamics, implemented within a network-specific microbial water quality management framework are the way forward for safeguarding the drinking water quality. In Chapter 6 of this dissertation, the insights gained from the research performed as a part of this dissertation are combined and discussed within a broader context of practical applications, future research challenges and the legislative framework

Online microbial monitoring of drinking water : how do different techniques respond to contaminations in practice?

Safeguarding the microbial water quality remains a challenge for drinking water utilities, and because of population growth and climate change, new issues arise regularly. To overcome these problems, biostable drinking water production and water reuse will become increasingly important. In this respect, high-resolution online microbial monitoring during treatment and distribution could prove essential. Here, we present the first scientific and practical comparison of multiple online microbial monitoring techniques in which six commercially available devices were set up in a full-scale drinking water production plant. Both the devices' response towards operational changes and contaminations, as well as their detection limit for different contaminations were evaluated and compared. During normal operation, all devices were able to detect abrupt operational changes such as backwashing of activated carbon filters and interruption of the production process in a fast and sensitive way. To benchmark their response to contaminations, the calculation of a dynamic baseline for sensitive separation between noise and events is proposed. In order of sensitivity, enzymatic analysis, ATP measurement, and flow cytometric fingerprinting were the most performant for detection of rain- and groundwater contaminations (0.01 - 0.1 v%). On the other hand, optical classification and flow cytometric cell counts showed to be more robust techniques, requiring less maintenance and providing direct information about the cell concentration, even though they were still more sensitive than plate counting. The choice for a certain technology will thus depend on the type of application and is a balance between sensitivity, price and maintenance. All things considered, a combination of several devices and use of advanced data analysis such as fingerprinting may be of added value. In general, the strategic implementation of online microbial monitoring as early-warning system will allow for intensive quality control by high-frequency sampling as well as a short event response timeframe

A combined culture-independent and simulation reactor approach to assess the microbial community of an operational denitrifying bioreactor treating As-bearing metallurgical wastewater

The biological treatment of metal(loid) bearing wastewater can be impacted by a multitude of biological and physicochemical parameters, providing challenges for in situ process optimisations. This study uses a combination of cultivation-independent sequencing, multivariate analysis and simulation reactors to characterise the microbial community in an operational bioreactor treating As- and nitrate-bearing wastewaters, and evaluate its response to higher arsenic concentrations. Over one year, whilst the denitrification performance was relatively stable (96%), time, sampling depth, pH, nitrate and arsenic all impacted the microbial community, which was dominated by nitrogen and sulfur cycling representatives. To identify the arsenic tolerance of the microbial community, down scaled simulation reactors were seeded from the operational bioreactor and treated with As(V) and As(III), however, no impact on denitrification was observed up to 1 g L−1 As(III). Overall, this study provides a framework of analyses and ex situ methods, which has wider implications for bioreactor process control

Production of biostable drinking water using a lab-scale biological trickling filter enriched with hydrogen-oxidizing bacteria

Abstract Safeguarding the drinking water quality remains a challenge from the production site to the tap. Alternatively to chemical disinfection, biostable drinking water could serve as a more sustainable approach to produce microbially safe drinking water and to maintain the microbial quality in the drinking water distribution system (DWDS). In this study, the potential of hydrogen-oxidizing bacteria (HOB) for the production of biostable drinking water was examined in a continuous trickling filter supplied with hydrogen gas. A biofilm was naturally enriched for 5 months and the bacterial regrowth, invasion potential, and nutrient composition of the water were determined. Treatment improved the biostability significantly, and it is hypothesized that nutrient limitation, especially phosphorous, was a driving force. As a result, the regrowth and invasion potential were lowered, as shown with specific biostability bioassays. Overall, this study demonstrates the effectiveness of HOB for producing biostable drinking water through nutrient limitation.</jats:p