Phosphate dosing is used by water utilities to prevent plumbosolvency in water supply networks. However, there is a lack of knowledge regarding biofilm formation on lead and plastic materials when phosphate concentrations are modified in drinking water systems. In this study, biofilms were grown over lead coupons and PVC tubes in bioreactors supplied with local drinking water treated to provide different phosphate doses (below 1, 1 and 2 mg/L) over a period of 28 days. A range of commercial iron pellets (GEH104 and WARP) were tested aiming to maintain phosphate levels below the average 1 mg/L found in drinking water. Changes in biofilm community structure in response to three different phosphate treatments were characterised by Illumina sequencing of the 16S rRNA gene for bacteria and the ITS2 gene for fungi. Scanning electron microscopy was used to visualise physical differences in biofilm development in two types of materials, lead and PVC. The experimental results from the kinetics of phosphate absorption showed that the GEH104 pellets were the best option to, in the long term, reduce phosphate levels while preventing undesirable turbidity increases in drinking water. Phosphate-enrichment promoted a reduction of bacterial diversity but increased that of fungi in biofilms. Overall, higher phosphate levels selected for microorganisms with enhanced capabilities related to phosphorus metabolism and heavy metal resistance. This research brings new insights regarding the influence of different phosphate concentrations on mixed-species biofilms formation and drinking water quality, which are relevant to inform best management practices in drinking water treatment.
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.
Phosphate is added to drinking water by UK water companies as a treatment to prevent the corrosion and metal leaching, like lead, in pipes. However, phosphate is a nutrient for microorganisms, and it can favour biofilm formation in Drinking Water Distribution Systems (DWDS), which can alter the water quality and safety. This study analyses the effect of phosphate addition on biofilm formation over different materials and its consequences for drinking water quality by i) using controlled experimental pipeline facility representative of a real-scale DWDS with high-density polyethylene coupons and ii) using a small-scale DWDS biofilm reactors with lead coupons. Biofilms developed over one month were exposed to the effect of different phosphate dosing and compare with UK normal water phosphate concentrations. During the experiment, physico-chemical analysis of water and microbial analysis of biofilms was carried out. Sequencing analysis of the 16s rRNA gene, from extracted DNA obtained from biofilms, provided information on any bacterial changes, and Scanning Electron Microscopy gave information about the biofilm organization. The results indicate that microorganisms find more difficult to establish and develop biofilms under high phosphate dosing, resulting in biofilms with less cells. Also, some physico-chemical parameter seems to be affected by phosphate dosing, like chlorine and lead. It is expected that differences in the biofilm community will be found depending on phosphate dosing. This study will provide information on the effect of phosphate on biofilm development in different pipes materials, which will facilitate to adjust an optimal phosphate dose to prevent plumbosolvency in DWDS.
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