Biofilm Formation and Multiplication of Legionella in a Model Warm Water System With Pipes of Copper, Stainless Steel and Cross-Linked Polyethylene

Water Res. 2005 Aug;39(13):2789-98. doi: 10.1016/j.watres.2005.04.075.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / analysis
  • Biofilms / growth & development*
  • Biomass
  • Colony Count, Microbial
  • Copper / analysis
  • Hot Temperature
  • Iron / analysis
  • Legionella pneumophila / physiology*
  • Manganese / analysis
  • Polyethylene / chemistry
  • Stainless Steel / chemistry
  • Water / chemistry
  • Water Microbiology*
  • Water Supply*

Substances

  • Water
  • Stainless Steel
  • Manganese
  • Copper
  • Adenosine Triphosphate
  • Polyethylene
  • Iron