Biofilm formation and multiplication of Legionella in a model warm water system with pipes of copper, stainless steel and cross-linked polyethylene.
Legionella pneumophila was grown in a model warm water system with pipes of copper (Cu), stainless steel (SS) and cross-linked polyethylene (PEX) during recirculation of tap water at 25--35 degrees C. Subsequently, domestic use of warm (37 degrees C) water was simulated using tap water with a low AOC concentration (<10 microg C/L). Two times each week the temperature of the water in the electric heaters (not in the pipes) was elevated to 70 degrees C for 30 min. ATP concentrations in the water sampled from the pipes over a 2-year period were significantly different for the pipe materials, with median values of 2.1 ng/l (Cu), 2.5 ng/l (SS) and 4.5 ng/l (PEX), respectively. Median values of the biofilm concentration were similar on Cu and SS (about 630 pg ATP/cm(2)) and 1870 pg ATP/cm(2) on PEX. Legionella multiplied in these biofilms and median values of Legionella concentrations in water were 1500 CFU/l (Cu) and about 4300 CFU/l for SS and PEX. Legionella to ATP ratios in water had median values of about 0.8 CFU/pg. Hot water flushing (70 degrees C) of the pipes on day 552, followed by 2 weeks of recirculation at 37 degrees C, caused strongly increased concentrations of ATP (up to 300 ng/l) and Legionella (>10(7)CFU/l), with about 100 CFU/pg ATP. Concentrations declined to original levels within 1 week of domestic water use, etc. Legionella concentrations in water and biofilms were at the same levels for all materials after 2 years. Hence, copper temporarily limited the growth of Legionella under the applied conditions and a rapid biomass development strongly increased the Legionella to ATP ratio.
van der Kooij
Dick
D
Kiwa Water Research, Groningenhaven 7, P.O. Box 1074, 3430 BB NIEUWEGEIN, The Netherlands. dick.van.der.kooj@kiwa.nl
Veenendaal
Harm R
HR
Scheffer
Will J H
WJ
D000255:Adenosine Triphosphate / Q000032:analysis; D018441:Biofilms / Q000254:growth & development*; D018533:Biomass; D015169:Colony Count, Microbial; D003300:Copper / Q000032:analysis; D006358:Hot Temperature; D007501:Iron / Q000032:analysis; D016952:Legionella pneumophila / Q000502:physiology*; D008345:Manganese / Q000032:analysis; D020959:Polyethylene / Q000737:chemistry; D013193:Stainless Steel / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014871:Water Microbiology; D014881:Water Supply
D014867:Water; D013193:Stainless Steel; D008345:Manganese; D003300:Copper; D000255:Adenosine Triphosphate; D020959:Polyethylene; D007501:Iron