title: Improved biostability assessment of drinking water with a suite of test methods at a water supply treating eutrophic lake water.
abstract: Assessment of drinking-water biostability is generally based on measuring bacterial growth in short-term batch tests. However, microbial growth in the distribution system is affected by multiple interactions between water, biofilms and sediments. Therefore a diversity of test methods was applied to characterize the biostability of drinking water distributed without disinfectant residual at a surface-water supply. This drinking water complied with the standards for the heterotrophic plate count and coliforms, but aeromonads periodically exceeded the regulatory limit (1000 CFU 100 mL(-1)). Compounds promoting growth of the biopolymer-utilizing Flavobacterium johnsoniae strain A3 accounted for c. 21% of the easily assimilable organic carbon (AOC) concentration (17 ± 2 μg C L(-1)) determined by growth of pure cultures in the water after granular activated-carbon filtration (GACF). Growth of the indigenous bacteria measured as adenosine tri-phosphate in water samples incubated at 25 °C confirmed the low AOC in the GACF but revealed the presence of compounds promoting growth after more than one week of incubation. Furthermore, the concentration of particulate organic carbon in the GACF (83 ± 42 μg C L(-1), including 65% carbohydrates) exceeded the AOC concentration. The increased biomass accumulation rate in the continuous biofouling monitor (CBM) at the distribution system reservoir demonstrated the presence of easily biodegradable by-products related to ClO2 dosage to the GACF and in the CBM at 42 km from the treatment plant an iron-associated biomass accumulation was observed. The various methods applied thus distinguished between easily assimilable compounds, biopolymers, slowly biodegradable compounds and biomass-accumulation potential, providing an improved assessment of the biostability of the water. Regrowth of aeromonads may be related to biomass-turnover processes in the distribution system, but establishment of quantitative relationships is needed for confirmation.
authors.affiliation: KWR Watercycle Research Institute, Post Box 1072, 3430 BB Nieuwegein, The Netherlands. Electronic address: dick.van.der.kooij@kwrwater.nl.
authors.forename: Dick
authors.initials: D
authors.lastname: van der Kooij
authors.affiliation: PWN Technologies, PO Box 2046, 1990 AA Velserbroek, The Netherlands. Electronic address: bram.martijn@pwntechnologies.nl.
authors.forename: Bram
authors.initials: B
authors.lastname: Martijn
authors.affiliation: Water Supply Company Noord-Holland PWN, Rijksweg 501, Velserbroek, The Netherlands. Electronic address: peter.schaap@pwn.nl.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Schaap
authors.affiliation: Het Waterlaboratorium, J.W. Lucasweg 2, 2031 BE Haarlem, The Netherlands. Electronic address: wim.hoogenboezem@hetwaterlaboratorium.nl.
authors.forename: Wim
authors.initials: W
authors.lastname: Hoogenboezem
authors.affiliation: KWR Watercycle Research Institute, Post Box 1072, 3430 BB Nieuwegein, The Netherlands.
authors.forename: Harm R
authors.initials: HR
authors.lastname: Veenendaal
authors.affiliation: KWR Watercycle Research Institute, Post Box 1072, 3430 BB Nieuwegein, The Netherlands. Electronic address: paul.van.der.wielen@kwrwater.nl.
authors.forename: Paul W J J
authors.initials: PW
authors.lastname: van der Wielen
mesh_terms: D060766:Drinking Water / Q000032:analysis* / Q000382:microbiology*; D005068:Eutrophication; D060106:Lakes / Q000382:microbiology; D018508:Water Purification / Q000379:methods*; D060753:Water Quality; D014881:Water Supply
chemical_list: D060766:Drinking Water
keywords: Aeromonas; Biomass-accumulation rate; Biostability; Easily assimilable organic carbon; Particulate organic carbon; Slowly-biodegradable organic compounds