Abstract
Water utilities treat drinking water by adding phosphate to prevent metal dissolution from water pipe work systems and particularly lead poisoning. Phosphate can be a limiting nutrient for microbial biofilms in DWDS, yet its effects on these microbial consortia are not well understood. This research presents results from phosphate dosing experiments using a real scale chlorinated DWDS, comparing standard phosphate concentrations of United Kingdom drinking water (1 mgP/L) with a double dose (2 mgP/L) commonly used in plumbosolvency treatment. Biofilm development during phosphate treatment experiments was monitored using a holistic approach by combining metagenomics analysis, flow cytometry and SEM characterisation. The increase of phosphate levels in drinking water, reduced biofilm cell numbers and promoted the presence of poorly distributed biofilms on inner pipe surfaces. Metagenomics analysis using genetic markers (16S rRNA and ITS2) showed that phosphate influenced biofilm community structure, particularly fungal composition. Whole metagenome sequencing showed that phosphate enrichment favoured the presence of sequencing reads associated to ATPases, ion transporters and DNA-interacting proteins, whilst reads associated to nitrogen metabolism were predominant in control samples. This research brings new knowledge regarding the influence of phosphate treatment on the composition and structure of biofilms within DWDS, and the implications that this might have for the management of these systems.
Highlights
Metal leaching from water pipes, mostly lead dissolution, is the main cause of drinking water contamination in many countries, endangering public health (Gordon and Hutchinson, 1994; Edwards, 2014)
Biofilms are diverse microbial consortia composed of bacteria, fungi, archaea, viruses, and protists (Hull et al, 2019; Mathieu et al, 2019), which are embedded in a matrix of extracellular polymeric substances (EPS) (Donlan and Costerton, 2002)
Orthophosphate dosing was effective at keeping stable phosphate levels in the water at 1.05– 1.17 mg/L in control condition and 2.4–2.9 mg/L in phosphate treatment over the studied period
Summary
Metal leaching from water pipes, mostly lead dissolution, is the main cause of drinking water contamination in many countries, endangering public health (Gordon and Hutchinson, 1994; Edwards, 2014). The affinity of orthophosphate ions for hydrated oxide particles leads to interactions between pipe surface metals and phosphate anions These interactions prevent corroded particles such as iron or lead from dissolving in the drinking water and limit the corrosion process in pipes (Persson et al, 1996; Gooddy et al, 2015). Biofilms are diverse microbial consortia composed of bacteria, fungi, archaea, viruses, and protists (Hull et al, 2019; Mathieu et al, 2019), which are embedded in a matrix of extracellular polymeric substances (EPS) (Donlan and Costerton, 2002) These organisms had complex interactions with the pipe environment and between them and are responsible for causing several problems in DWDS. Biofilms in DWDS have been associated with metal bio-corrosion (Szewzyk et al, 2000; Bremer et al, 2001; Beech and Sunner, 2004; Douterelo et al, 2013), water discolouration events (Lau and Ashbolt, 2009; Douterelo et al, 2013) and pathogens appearance (Lau and Ashbolt, 2009)
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