Pilot-scale drinking water distribution system to study water quality changes during transport

Abstract

Drinking water (DW) can undergo quality changes during transport through the distribution network. Physical-chemical and/or microbial changes can lead to the development of taste and odor events, and/or regrowth of pathogens. To understand the root causes and study in depth how these changes arise, the use of pilot plants that emulate drinking water distribution networks is essential. Here we describe the design and functionality of a new pilot plant for this purpose. First, we describe the choice of piping material, sensors and instrumentation. Secondly, we show evidence of how the three independent loops (100 m each) of the pilot behave identically when tested for physical-chemical and microbial changes over time. This pilot plant thus allows to test three conditions simultaneously, and to monitor 1) the formation of taste and odor compounds, 2) the regrowth of microorganisms, and 3) changes in dissolved organic carbon composition. Additionally, online measurements of both physical and biological parameters enable real-time follow-up of the pilot, and inner pipe biofilm sampling is possible using coupons. To reproduce different network conditions, temperature, flow rate and pressure are modulable. The temperature control feature presents an opportunity for studying the effect of climate change on drinking water quality, and its modularity and flexibility allows to study the impact of different piping material and source waters on DW quality changes in the distribution network.

Chemical and microbiological safety of drinking water in distribution networks made of plastic pipes

“…PVC, in addition to releasing volatile organic compounds such as aldehydes (e.g., hexanal, octanal, etc.) into water, can also be a source of organotin compounds (Biedroń et al, 2017; García‐Timermans et al, 2023; Skjevrak et al, 2003; Skjevrak et al, 2005) (Table 2). Tin‐stabilized PVC is used when contact with drinking water can occur in pipes (Sixsmith & Hanselka, 1997).…”

“…Most commonly, these are flocs and aggregates of bacteria forming populations that have the ability to cover both the surface of pipe materials and the pores or microcracks present in their structure (Costerton et al, 1995; Yang et al, 2022). The average number of bacterial cells in a biofilm is assumed to be 10 4 –10 8 cells/cm 2 (García‐Timermans et al, 2023; Liu et al, 2013; Makris et al, 2014; Proctor & Hammes, 2015), representing approximately 10%–25% of the dry weight (Costerton et al, 1995; Flemming & Wingender, 2010; Liu, Gunawan, et al, 2016; Yang et al, 2022). The microorganisms are further protected from adverse environmental conditions, including the presence of disinfectants, by an extracellular polymeric substance (EPS) (Liu, Ling, et al, 2016) which in turn can account for up to 75%–90% of dry weight (Costerton et al, 1995; Flemming & Wingender, 2010; Liu, Ling, et al, 2016; Yang et al, 2022).…”

“…Among the key factors for the formation and growth rate of biofilms in water mains, the pipe material plays an important role. Due to surface properties, such as roughness increasing with material degradation, and additives used in production (adhesives, plasticizers, stabilizers), which can be an important source of nutrients for bacteria (Biedroń et al, 2017; García‐Timermans et al, 2023; Manuel et al, 2007; Momba & Makala, 2004; Papciak et al, 2022; Parizzi et al, 2004; Sitarska & Traczewska, 2009; Zhao et al, 2022), thermoplastics provide an excellent substrate for biofilm growth. Literature data cited in earlier chapters indicate that PE and PVC can release numerous organic compounds, which become a medium for microorganisms both present in the transferred water and attached to the inner wall of the pipes.…”

“…The results of studies published so far on the composition and growth rate of bacterial biofilms on plastic pipes have shown that bacteria bind very easily to the PE and PVC surface and start building biofilms very quickly. García‐Timermans et al (2023) noted that after just 8 days of running the model system, the number of bacteria in the water leaving the model increased by an order of magnitude, from 10 5 cells/mL at the feed to 10 6 cells/mL at the exit of the system. Similar results have been obtained by other authors (Papciak et al, 2022; Skovhus et al, 2022; Zhao et al, 2022), but Skovhus et al (2022) showed that initially the number of bacterial cells determined in the water at the exit of the test system increases and then decreases, which correlates with an increase in the number of biofilm‐building cells associated with the pipe surface.…”