Full Description

Biofilms occur throughout drinking water distribution systems, and theircomposition is highly dependent on the water matrix as well as the material and conditionof the pipes. Many utilities are considering changes in their disinfection regimes toimprove the microbial quality of the water and to limit the formation of disinfectionbyproducts 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 thedisinfectant residual. There is little information about what effect such changes indisinfection regime will have on distribution biofilms.Using a flow-through laboratory model, the study used molecular techniques to examinethe bacterial composition of biofilms formed from the same water source on differentpipe materials, under different disinfection regimes (chlorine and monochloramine atappropriate concentrations) with and without upstream UV treatment. Source water was asoft surface water source in Halifax, Canada. Controls were also included without anyadditional disinfectant residual. Two substrates, cast iron and polycarbonate coupons inannular reactors, were used to represent pipe materials.The biofilm samples were removed from the coupons at defined intervals andtotal DNA was extracted from the samples. The samples were also cultured on R2Amedium for heterotrophic plate count, and R2A plates were harvested to extract DNAfrom cultivable bacteria. The DNA samples from both sources were then used to assessthe composition of the biofilm bacterial community by PCR-DGGE (denaturing gradientgel electrophoresis). Primers for a variable region of the 16 S rRNA gene were used toamplify bacterial DNA. These fragments were then separated on a DGGE gel whichseparates same size fragments on the basis of their sequence. Identification is achieved bycarefully excising bands from the gel, cloning, sequencing and comparing sequences withlibraries from online databases (BLAST and Ribosomal Database Project II).Differences were clearly seen in the gels for each of the treatments examined sofar; full characterization of the biofilms is ongoing and it is anticipated that definitedifferences will emerge between different disinfectants as well as the coupon materials.The significance of such differences remains to be determined. Includes figures.

Product Details

Edition: Vol. - No. Published: 11/01/2005 Number of Pages: 7File Size: 1 file , 2.4 MB