Effects of chlorine level on the growth of biofilm in water pipes

Three analogous laboratory-scale water pipe systems were constructed to study the effects of three chlorine levels of finished water on the growth of biofilm. The experimental results indicated that the heterotrophic plate counts (HPCs) of biofilm for chlorine-free water were approximately 2 and 3 orders of magnitude higher than those for low-chlorine water (0.3-0.5mg Cl-2/L) and high-chlorine water (1.2-1.5mg Cl-2/L). The difference in 14PC levels between low-chlorine water and high-chlorine water was below I order. Average biofilm formation rates are 325 ATP pg/cm(2) -day for chlorine-free water, 159 ATP pg/cm(2)-day for low-chlorine water and 118 ATPpg/cm(2)-day for high-chlorine water. The scanning electron microscope (SEM) observation showed that bacterial species separated from the biofilm were more complex than from the finished water. The Gram-negative bacteria were dominant in these species.