Abstract
A new conceptual model to describe and understand the role of assimilable organic carbon (AOC) within drinking water distribution systems is proposed. The impact of AOC on both drinking water biofilm and water quality was studied using bespoke pipe loop experimental facilities installed at three carefully selected operational water treatment works. Integrated physical, chemical and biological monitoring was undertaken that highlights the central role of biofilms in AOC cycling, forming the basis of the new conceptual model. Biofilms formed under high AOC conditions were found to pose the highest discoloration response, generating a turbidity (4.3 NTU) and iron (241.5 µg/l) response sufficient to have caused regulatory failures from only 20 m of pipe in only 12 months of operation. This new knowledge of the role of biofilms in AOC cycling, and ultimately impacts on water quality, can be used to inform management and help ensure the supply of high-quality, biostable drinking water.
Highlights
The supply of microbially safe, high quality drinking water is one of the most fundamental requirements and functions of every water utility
The current study focuses on the interactions between Assimilable organic carbon (AOC) and microbial cells, further research is required to understand the interaction between additional biofilm characteristics and AOC cycling within drinking water distribution systems (DWDS)
This paper presents the first use of full-scale DWDS simulation experimental facilities at the outlet of water treatment works (WTW) to study the impact of different AOC concentrations on biofilm and bulk water quality
Summary
The supply of microbially safe, high quality drinking water is one of the most fundamental requirements and functions of every water utility. The term regrowth has been used to describe the recovery of disinfectant-injured cells, whereas aftergrowth has been used to describe microbial growth in a distribution system (Characklis, 1988; van der Kooij, 2003). In this study, (re)growth includes both the recovery of disinfection damaged cells which have passed through the treatment works and the multiplication of organisms within the DWDS itself. Low concentrations of AOC have been demonstrated to limit microbial growth, and constitute biostable water, at concentrations spanning ≤10 – 100 μg C/L in DWDS field studies (Van der Kooij, 1992; LeChevallier et al, 1996) and ≤10 – 110 μg C/L within laboratory studies (Ohkouchi et al, 2013; Wang et al, 2014; LeChevallier et al, 2015). It is critical to consider interactions between AOC and a disinfectant residual when assessing drinking water biostability
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