• Whitby, Corinne
• Tang, Lone
• Søborg, Ditte Andreasen
• Skovhus, Torben Lund

Abstract

Summary<br/>There is increased use of polyethylene (PE) pipes in household installations and water distribution networks in Denmark. The leaching of organic compounds from PE pipes is significant during commissioning of the pipes in the distribution system, due to degassing of the often newly produced pipes. For the non-chlorinated water network in Denmark, biofilm is deemed an essential part of what makes up a healthy drinking water distribution system. <br/>In this pilot study, biofilms found in the Danish water distribution system were investigated for their ability to biodegrade three specific compounds that were found to leach from PE pipes into drinking water. <br/>Two biofilm sample types were studied: PE pipe biofilm samples collected in proximity to consumers, and PE pipe biofilm samples collected close to the groundwater source. Enrichment cultures were set up with each of the biofilm sample types incubated in minimal salts medium containing the PE pipe leached substrates as the sole carbon and energy source. Growth of both bacteria and archaea from drinking water biofilm was shown on selected organic compounds leaching from new PE pipes.<br/><br/>Keywords: Polyethylene pipes, drinking water, biodegradation, water quality, biofilm, microbiome.<br/> <br/>Introduction<br/>There is increased use of polyethylene (PE) pipes in household installations and water distribution networks in Denmark since the 1960s (Coron, 2008). This increased use is largely due to their enhanced flexibility, long durability and corrosion resistance that benefit the manufacturer through decreased installation costs; compared to traditional polyvinylchloride (PVC), ductile steel or copper pipes. However, PE pipes leach organic compounds including phenol, quinone and ketone into drinking water, in sufficient quantity to affect water quality (Brocca et al., 2002). <br/>The leaching of organic compounds from PE pipes is significant during commissioning of the pipes in the distribution system, due to degassing of the often newly produced pipes. In the long-term, like most industrial materials, as PE ages, they lose their physical properties. This happens due to chain breaking reactions that occur in the presence of oxygen. Sources of instigation for PE degradation are known to be caused by parameters such as light (high energy radiation), catalytic residues, heat, reaction with impurities and mechanical stress. As this degradation takes place, research has shown the migration of complex organic compounds into water distribution networks (Denberg, 2009). <br/>For the non-chlorinated water network in Denmark, biofilm is deemed an essential part of what makes up a healthy drinking water distribution system. For instance, a healthy mature biofilm has been shown to increase the microbiological stability of the water (Skovhus et al., 2018). The role of biofilm in degradation of complex organic compounds leaching from PE pipes, however, is still unknown.<br/><br/>Materials and methods<br/>In this pilot study, biofilms found in the Danish water distribution system were investigated for their ability to biodegrade three specific compounds that were found to leach from PE pipes into drinking water. The compounds tested were as follows: 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione; 2,4-di-tert-butylphenol; and 2,6-Di-tert-butyl-1,4 benzoquinone (10 mg/ml final concentration). Figure 1 shows the molecular structure of the 3 compounds. <br/>Two biofilm sample types were studied: PE pipe biofilm samples collected in proximity to consumers, and PE pipe biofilm samples collected close to the groundwater source. Figure 2 shows the biofilm rigs located in the water works near the ground water source. <br/>Enrichment cultures were set up with each of the biofilm sample types incubated in minimal salts medium containing the PE pipe leached substrates as the sole carbon and energy source. Cultures were incubated in the dark with shaking (110 rpm) for 45 days at either 12ºC or 20ºC. Abiotic controls were also prepared without any biofilm inoculum, to determine whether any abiotic losses had occurred. Biodegradation was monitored by GC-MS analysis. Changes in the bacterial and archaeal communities during biodegradation were also quantified by qPCR analysis of the 16S rRNA genes.<br/><br/>Results and discussion<br/>Growth of both bacteria and archaea from drinking water biofilm collected at two locations in the Danish drinking water distribution system was shown on selected organic compounds leaching from new PE pipes, with higher growth rates found when cultures were incubated at 20ºC compared to 12ºC. Although in Denmark, the temperature rarely reaches 20°C, it can be speculated that a higher degradation potential will be found during the summer months. Biofilm close to the consumer resulted in the highest growth on 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione, followed by 2,4-di-tert-butylphenol, and 2,6-Di-tert-butyl-1,4...

Topics

• impedance spectroscopy
• compound
• Carbon
• corrosion
• Oxygen
• steel
• copper
• leaching
• durability
• gas chromatography
• ketone
• degassing
• molecular structure
• gas chromatography-mass spectrometry