Mechanism of Biofilm Formation on Installation Materials and Its Impact on the Quality of Tap Water

Abstract

In the conducted study, an attempt was made to verify and evaluate the impact of the biofilm formed on the surfaces of the installation material on the quality and sanitary safety of tap water reaching the consumer. For biofilm studies, fractal analysis and quantitative bacteriological analysis were used. The quality of tap water flowing through the experimental installation (semi-technical scale) was determined using physicochemical and microbiological parameters. The quantitative analysis of the biofilm showed that an increase in the number of microorganisms was observed in the initial phase of biofilm formation (reached 1.4 × 104 CFU/mL/cm2 on day 14). During this period, there was a chaotic build-up of bacterial cells, as evidenced by an increase in the roughness of the profile lines. Unstable elevations of the biofilm formed in this way could be easily detached from the structure of the material, which resulted in deterioration of the bacteriological quality of the water leaving the installation. The obtained results indicate that the biofilm completely and permanently covered the surface of the tested material after 25 days of testing (the surface roughness described by the fractal dimension decreased). Moreover, the favorable temperature (22.6 °C) and the recorded decrease in the content of inorganic nitrogen (by 15%), phosphorus (by 14%), and dissolved oxygen (by 15%) confirm the activity of microorganisms. The favorable environmental conditions in the installation (the presence of nutrients, low chlorine concentration, and high temperature) contributed to the secondary development of microorganisms, including pathogenic organisms in the tested waters.

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

“…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. Other modeling studies mimicking conditions in indoor networks (in buildings), taking into account periods of water stagnation, have also shown that the biofilm in PVC pipes does not contain mineral deposits and is based on densely dispersed, single cells of Pseudomonas aeruginosa bacteria.…”

“…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 (Biedro n 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) phthalates dibutyl phthalate, di-n-hexane phthalate, and di-(ethylhexyl) phthalate released from HDPE and PVC pipes during aging on Pseudomonas biofilm growth. The results showed that already at lower phthalate concentrations (1-5 μg/L), the formation of more biofilm matrix and an increase in biofilm density (increase in volume fraction from 27.1% to as much as 50.6%) is observed.…”

“…Its increase intensifies the migration of chemical compounds from the inner layers of the material into the water and also promotes bacterial proliferation. The effect of temperature may be particularly important for the distribution of treated waters extracted from surface waters characterized by elevated temperatures during summer periods (Papciak et al, 2022).…”

“…However, the conducted model tests showed that networks made of PE and PVC are also susceptible to biofilm formation, whose intensity depends on many factors. These include, among others: the pipe material (Biedroń et al, 2017; Eerkes‐Medrano et al, 2015; Goraj et al, 2021; Liu et al, 2017; Rożej et al, 2015; Zhang & Liu, 2014), the content of chemical compounds that are nutrients for microorganisms (Denberg et al, 2007; Dong et al, 2018; Papciak et al, 2022; Piringer & Baner, 2000; Zhao et al, 2022), the concentration of disinfectant (Papciak et al, 2022; Yang et al, 2022; Zhang & Liu, 2014), water flow rate (Fish et al, 2017; Zhang et al, 2014), hydraulic conditions (Fish et al, 2017) and temperature (Inkinen et al, 2014; Lee, 2013; Papciak et al, 2022; Zhu et al, 2014) (Figure 4). The number of literature reports on the subject is increasing year by year, but the vast majority of published results involve studies conducted in systems that simulate conditions in DWDNs or mimic indoor distribution networks in buildings.…”

“…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.…”