Biofilms occur throughout drinking water distribution systems, and their
composition is highly dependent on the water matrix as well as the material and condition
of the pipes. Many utilities are considering changes in their disinfection regimes to
improve the microbial quality of the water and to limit the formation of disinfection
byproducts in plant effluent. These changes often involve the addition of upstream ultraviolet (UV)
treatment and/or the use of monochloramine instead of chlorine to provide the
disinfectant residual. There is little information about what effect such changes in
disinfection regime will have on distribution biofilms.
Using a flow-through laboratory model, the study used molecular techniques to examine
the bacterial composition of biofilms formed from the same water source on different
pipe materials, under different disinfection regimes (chlorine and monochloramine at
appropriate concentrations) with and without upstream UV treatment. Source water was a
soft surface water source in Halifax, Canada. Controls were also included without any
additional disinfectant residual. Two substrates, cast iron and polycarbonate coupons in
annular reactors, were used to represent pipe materials.
The biofilm samples were removed from the coupons at defined intervals and
total DNA was extracted from the samples. The samples were also cultured on R2A
medium for heterotrophic plate count, and R2A plates were harvested to extract DNA
from cultivable bacteria. The DNA samples from both sources were then used to assess
the composition of the biofilm bacterial community by PCR-DGGE (denaturing gradient
gel electrophoresis). Primers for a variable region of the 16 S rRNA gene were used to
amplify bacterial DNA. These fragments were then separated on a DGGE gel which
separates same size fragments on the basis of their sequence. Identification is achieved by
carefully excising bands from the gel, cloning, sequencing and comparing sequences with
libraries from online databases (BLAST and Ribosomal Database Project II).
Differences were clearly seen in the gels for each of the treatments examined so
far; full characterization of the biofilms is ongoing and it is anticipated that definite
differences will emerge between different disinfectants as well as the coupon materials.
The significance of such differences remains to be determined. Includes figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 2.4 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 7 |
| Published : | 11/01/2005 |
