TY - CONF
T1 - Microbial Degradation of Complex Organic Compounds in a Danish Drinking Water Pipeline Distribution System
AU - Skovhus, Torben Lund
AU - Tang, Lone
AU - Søborg, Ditte Andreasen
AU - Whitby, Corinne
PY - 2022/12/5
Y1 - 2022/12/5
N2 - SummaryThere 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. 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. 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.Keywords: Polyethylene pipes, drinking water, biodegradation, water quality, biofilm, microbiome. IntroductionThere 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). 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). 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.Materials and methodsIn 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. 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. 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.Results and discussionGrowth 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 benzoquinone. For the biofilm collected close to the groundwater source, the highest growth was seen for 2,4-di-tert-butylphenol, followed by 2,6-Di-tert-butyl-1,4 benzoquinone and 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione. No growth was observed in abiotic controls, as expected. A statistically higher growth activity and thereby biodegradation potential was seen for the biofilm in proximity to the consumer as compared to the one close to the groundwater source. In general, bacteria were in higher abundances compared to archaea across all substrates tested.Previous research has indicated that biodegradation rates are influenced by factors such as the molecular weight and chemical structure of the compound, (Johnson et al., 2011; Smith et al., 2008). In summary, of the three target compounds, 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione is likely to be more readily degraded followed by 2,4-di-tert-butylphenol, and 2,6-Di-tert-butyl-1,4 benzoquinone. However, increased rates at higher temperatures reach the conclusion that summer temperatures present more ideal conditions for biodegradation. An area of further study would be to investigate the effect of leaching compounds on community shifts in the biofilm especially those communities that more readily biodegrade these target compounds and the consequences of biodegradation upon older pipes within the water distribution system, in terms of biofilm present and water quality. Also tests with additional types of organic compounds is planned.
AB - SummaryThere 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. 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. 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.Keywords: Polyethylene pipes, drinking water, biodegradation, water quality, biofilm, microbiome. IntroductionThere 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). 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). 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.Materials and methodsIn 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. 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. 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.Results and discussionGrowth 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 benzoquinone. For the biofilm collected close to the groundwater source, the highest growth was seen for 2,4-di-tert-butylphenol, followed by 2,6-Di-tert-butyl-1,4 benzoquinone and 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione. No growth was observed in abiotic controls, as expected. A statistically higher growth activity and thereby biodegradation potential was seen for the biofilm in proximity to the consumer as compared to the one close to the groundwater source. In general, bacteria were in higher abundances compared to archaea across all substrates tested.Previous research has indicated that biodegradation rates are influenced by factors such as the molecular weight and chemical structure of the compound, (Johnson et al., 2011; Smith et al., 2008). In summary, of the three target compounds, 7,9-di-tert-Butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione is likely to be more readily degraded followed by 2,4-di-tert-butylphenol, and 2,6-Di-tert-butyl-1,4 benzoquinone. However, increased rates at higher temperatures reach the conclusion that summer temperatures present more ideal conditions for biodegradation. An area of further study would be to investigate the effect of leaching compounds on community shifts in the biofilm especially those communities that more readily biodegrade these target compounds and the consequences of biodegradation upon older pipes within the water distribution system, in terms of biofilm present and water quality. Also tests with additional types of organic compounds is planned.
KW - construction, environment and energy
KW - biofilm
KW - drinking water
KW - water quality
M3 - Poster
T2 - IWA Biofilms 2022<br/>
Y2 - 6 December 2022 through 8 December 2022
ER -