The objective of this study was to compare the effect of corrosion inhibitors on the level of
heterotrophic bacteria in bulk water and biofilm in 14 parallel pilot-scale water
distribution systems (PDSs). The study took one year with 12 PDSs receiving different
types and doses of corrosion inhibitors. Water and pipe coupon samples were taken and
examined during the experiments. There was a statistically significant increase relative
to the control lines (PDS 13-14) in bulk water bacterial densities (measured as
heterotrophic plate count, HPC) with the addition of any of the four inhibitors. For bulk
HPC this increase was relatively small, being 15.4% (0.42 log) when using phosphate
based inhibitors (PDS 1-9), and 11.0% (0.31 log) for the silica based inhibitor (PDS 10-
12). The data also showed a statistically significant increase of 0.34 log in biofilm
bacterial densities (measured as HPC) with the addition of any of the phosphate based
inhibitors (ortho-phosphorus, blended ortho-poly-phosphate, and zinc ortho-phosphate).
The silica based inhibitor resulted in an increase of 0.36 log. It was determined that
phosphorous stimulated growth in separate experiments, however the compound causing
the Si based inhibitors to increase bulk and biofilm density was never identified. Analysis
of all 14 PDSs showed that bulk HPC was affected most by temperature and residual. A
sensitivity test showed that maintaining higher residual levels can counteract the
relatively modest increases in bulk HPC due to inhibitors. Biofilm HPC was most
affected by pipe material, effluent residual and temperature in addition to the small
increase due to inhibitor. Biofilm density on polyvinyl chloride (PVC) pipes were
consistently much lower than the other materials (0.66, 0.92, and 1.22 log lower than
lined cast iron (LCI), unlined cast iron (UCI), and galvanized steel (G), respectively). Includes 14 references, tables, figure.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 810 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 17 |
| Published : | 11/01/2008 |
