Biological stability of drinking water refers to the concept of providing consumers with drinking water of same microbial quality at the tap as produced at the water treatment facility. However, uncontrolled growth of bacteria can occur during distribution in water mains and premise plumbing, and can lead to hygienic (e.g., development of opportunistic pathogens), aesthetic (e.g., deterioration of taste, odor, color) or operational (e.g., fouling or biocorrosion of pipes) problems. Drinking water contains diverse microorganisms competing for limited available nutrients for growth. Bacterial growth and interactions are regulated by factors, such as (i) type and concentration of available organic and inorganic nutrients, (ii) type and concentration of residual disinfectant, (iii) presence of predators, such as protozoa and invertebrates, (iv) environmental conditions, such as water temperature, and (v) spatial location of microorganisms (bulk water, sediment, or biofilm). Water treatment and distribution conditions in water mains and premise plumbing affect each of these factors and shape bacterial community characteristics (abundance, composition, viability) in distribution systems. Improved understanding of bacterial interactions in distribution systems and of environmental conditions impact is needed for better control of bacterial communities during drinking water production and distribution. This article reviews (i) existing knowledge on biological stability controlling factors and (ii) how these factors are affected by drinking water production and distribution conditions. In addition, (iii) the concept of biological stability is discussed in light of experience with well-established and new analytical methods, enabling high throughput analysis and in-depth characterization of bacterial communities in drinking water. We discussed, how knowledge gained from novel techniques will improve design and monitoring of water treatment and distribution systems in order to maintain good drinking water microbial quality up to consumer’s tap. A new definition and methodological approach for biological stability is proposed.

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Biological Stability of Drinking Water: Controlling Factors, Methods, and Challenges

A water demand end-use model was developed to predict water demand patterns with a small time scale (1 s) and small spatial scale (residence level). The end-use model is based on statistical inform...

Simulating Residential Water Demand with a Stochastic End-Use Model

The effects of changing water flow velocity on the formation of biofilms and water quality in pilot distribution system consisting of copper or polyethylene pipes.

Potential impacts of changing supply-water quality on drinking water distribution: A review

A drinking water distribution system (DWDS) is the final and essential step to supply safe and high-quality drinking water to customers. Biological processes, such as biofilm formation and detachment, microbial growth in bulk water, and the formation of loose deposits, may occur. These processes will lead to deterioration of the water quality during distribution. In extreme conditions, pathogens and opportunistic pathogens may proliferate and pose a health risk to consumers. It is, therefore, necessary to understand the bacteriology of DWDSs to develop effective strategies that can ensure the water quality at consumers' taps. The bacteriology of DWDSs, both the quantitative growth and the qualitative bacterial community, has attracted considerable research attention. However, the researchers have focused mainly on the pipe wall biofilm. In this review, DWDS bacteriology has been reviewed multidimensionally, including both the bacterial quantification and identification. For the first time, the available literature was reviewed with an emphasis on the subdivision of DWDS into four phases: bulk water, suspended solids, loose deposits, and pipe wall biofilm. Special concentration has been given to potential contribution of particulate matter: suspended particles and loose deposits. Two highlighted questions were reviewed and discussed: (1) where does most of the growth occur? And (2) what is the contribution of particle-associated bacteria to DWDS bacteriology and ecology? At the end of this review, recommendations were given based on the conclusion of this review to better understand the integral DWDS bacteriology.

Bacteriology of drinking water distribution systems: an integral and multidimensional review

Water discolouration in networks results from increased turbidity due to high levels of suspended particles. Hydraulic incidents such as pipe burst or hydrant use impose extra shear stresses on sediment layers in the network, leading to particle resuspension. The mass balance over a network or parts of the network may be used to analyse the different sources and accumulation processes; this article focuses on the contribution of the “mass in” from the pumping station as particles. Three analysis methods have been developed within the joint research program of the Dutch water companies (BTO-program): the continuous monitoring of turbidity, the Mass Settling Potential Method and the Resuspension Potential Method. The continuous monitoring of turbidity and particle counting enable an analysis of the relative contribution of sources for particles, e.g. corrosion of cast iron. The Mass Settling Potential and Resuspension Potential methods add insight into actual sediment load and actual discolouration risk. Further development of these methods will enhance knowledge of the origin and fate of particles in a network, enabling the formulation of effective measures against discolouration and associated water quality problems.

Particles in the drinking water system: from source to discolouration

The Dutch drinking water companies are constructing velocity based self-cleaning residential drinking water distribution systems (DWDS). Field studies with particle counters have shown that these DWDS indeed do not foul. Laboratory studies have shown the settlement and re-suspension of particles in water mains under constant flow conditions. However, the relation between mains fouling and hydraulic conditions under realistic (variable) flows has not been determined. In the presented study, the effect of variable flow velocities on particles in a real residential DWDS was studied through a detailed analysis of turbidity measurements during flushing in combination with a detailed EPANET network model. Firstly, each pipe stretch was flushed with 1.5 m/s for three turnovers and most of the pipes appeared to be clean after the first turnover. This means that it was possible to link the measured turbidity to the location in the pipe from where it was re-suspended. Secondly, an all-pipes EPANET network model was filled with realistic demand patterns from the end-use model SIMDEUM; a small hydraulic time step (0.01 h) was used. This allowed for determining the maximum daily velocity occurring in each pipe stretch. The combination of the first and second step led to a graph of resuspended turbidity against maximum daily velocity. The study showed that in this residential DWDS there is a threshold value for the maximum velocity of 0.2 to 0.25 m/s above which the pipes remain clean. Thus, the existence of the self-cleaning velocity was demonstrated. This study helps in understanding particle behavior in DWDS.

The self-cleaning velocity in practice

Measuring discoloration risk: resuspension potential method

Sediment formation in drinking water distribution systems can lead to brown water at customer taps. Previous studies have shown that sediment formation is closely linked with (micro)biological processes in the distribution system, however the mechanism is not fully understood. Most available studies on discoloration or sediment formation mechanism are based on modeling, pilot-scale experiments, or low frequency data collected during pipe flushing. In this study, long-term sediment development in a large-scale drinking water distribution system was studied at one location over 11 years and at several locations along a known water trajectory during one year. Particulate material was collected at several locations using built-in and mobile filters that were connected to transport and distribution pipes in a semi-continuous manner. The volume of the collected material varied seasonally and the highest volumes were collected in the summer season. The material followed similar variations as temperature, invertebrates biomass and concentration of Aeromonas. The results showed that particulate matter of the sediment at downstream distribution locations was not released by the treatment works but instead forms along the distribution network, with increasing particle/floc size, biomass and Fe and Mn content. The large crustacean, Asellus, contributed to material production through feces excretion and formation of detritus by degradation of exoskeletons of dead animals. Detailed chemical characterization of the collected material showed the presence of proteins, calcium carbonate and iron precipitates. A similar sediment composition in a reference distribution system where customer complaints about brown water are experienced less frequently suggests that the sediment formation mechanism is the same but that water quality of the treatment effluent impacts the extent of material formation and growth of invertebrates. Overall, the results indicate that sediment formation in the distribution system is the result of complex combinations of (micro)biological and bio-chemical processes, including aggregation of particles with organic and inorganic matter, microbial growth on particles and biofilm, biomineralization, and growth of invertebrates. The determining factors to limit sediment formation, however, could not be identified. Further research is required to focus on the impact of treatment on shaping the distribution system ecosystem.

https://www.mdpi.com/2073-4441/15/2/214/pdf?version=1672812422

(Micro)Biological Sediment Formation in a Non-Chlorinated Drinking Water Distribution System

Discolouration incidents in the drinking water distribution networks are caused by the resuspension of loose particles. Removing particles will consequently reduce the discolouration risk. Unidirectional water flushing can be an effective method when strict boundary conditions are met like a minimum velocity of 1.5 m/s, flushed volume 2 to 3 times the content of the pipe and using a clear water front. Supposedly adverse effects of cleaning of cast iron pipes are that the protective layer of corrosion products can be damaged leading to increased particle production post cleaning. The Resuspension Potential Measurement gives unbiased and reproducible information on the discolouration risk. This methodology is used to assess the efficacy of the flushing program of the Water Company of Limburg in the Netherlands (WML). The program is followed with an extensive measuring campaign involving 701 RPM measurements at more than 120 locations. The adverse effects of cleaning of ferrous pipes were observed in the period immediately following the cleaning. This effect was neutralized within a year which led to the conclusion that water flushing is practically as effective in ferrous pipes as it is in non-ferrous pipes provided that the operational boundaries are met on velocity, volume and order of flushing.

P. G. Schaap

Papers

Particles in the drinking water system: from source to discolouration

The self-cleaning velocity in practice

Measuring discoloration risk: resuspension potential method

(Micro)Biological Sediment Formation in a Non-Chlorinated Drinking Water Distribution System

How effective is flushing of cast iron pipes