Effect of biofilm, temperature and type of source water on the formation of haloanisoles in a pilot drinking water distribution system.

Taste and odor deviations in tap water affect many consumers and cause a preference for bottled water. However, since tap water is more sustainable than bottled water, these issues should be solved and prevented rapidly. Haloanisoles (HAs) have a very low odor threshold concentration (sub ng.L-1) and are of considerable concern since they are mainly formed in drinking water distribution systems (DWDS). Understanding their formation and influencing factors is a crucial aspect of addressing these odor problems. Therefore, this study uses a DWDS pilot to closely mimic the complex situation in real DWDS and investigates the (microbial) formation of six HAs regarding biofilm cell density and composition, temperature, and type of source water. Ten to thirty times higher formation was observed when a stable biofilm (5 months, 10 times more biomass) was present, compared to a young biofilm (2 weeks). With a spiked halophenol (HP) concentration of 0.1 mg.L-1, the HA concentrations produced by a young biofilm were already within the OTC range. The mature biofilm contained a higher variety of HA-producing microorganisms and more O-methyltransferase genes to convert the precursors (HPs) into HAs. Higher temperatures (24 °C instead of 16 °C) increased the formation of each HA by a factor of 2 to 4, although still low HP-HA conversion ratios were observed (0.2 %). Regardless of the temperature and the type of source water, a clear pattern is observed in the type of HAs formed, with 2,3,4-trichloroanisole being the most abundant. This study finally investigated the effectiveness of flushing to mitigate these odorous compounds in DWDS and concludes that their partitioning between the biofilm and water phase affects the performance of flushing procedures.