AWWA WQTC69433

The objective of this study was to compare the effect of corrosion inhibitors on the level ofheterotrophic bacteria in bulk water and biofilm in 14 parallel pilot-scale waterdistribution systems (PDSs). The study took one year with 12 PDSs receiving differenttypes and doses of corrosion inhibitors. Water and pipe coupon samples were taken andexamined during the experiments. There was a statistically significant increase relativeto the control lines (PDS 13-14) in bulk water bacterial densities (measured asheterotrophic plate count, HPC) with the addition of any of the four inhibitors. For bulkHPC this increase was relatively small, being 15.4% (0.42 log) when using phosphatebased 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 biofilmbacterial densities (measured as HPC) with the addition of any of the phosphate basedinhibitors (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 thatphosphorous stimulated growth in separate experiments, however the compound causingthe Si based inhibitors to increase bulk and biofilm density was never identified. Analysisof all 14 PDSs showed that bulk HPC was affected most by temperature and residual. Asensitivity test showed that maintaining higher residual levels can counteract therelatively modest increases in bulk HPC due to inhibitors. Biofilm HPC was mostaffected by pipe material, effluent residual and temperature in addition to the smallincrease due to inhibitor. Biofilm density on polyvinyl chloride (PVC) pipes wereconsistently much lower than the other materials (0.66, 0.92, and 1.22 log lower thanlined cast iron (LCI), unlined cast iron (UCI), and galvanized steel (G), respectively). Includes 14 references, tables, figure.

Product Details

Edition:

Vol. - No.

Published:

11/01/2008

Number of Pages:

17

File Size:

1 file , 810 KB