Identifying Future Drinking Water Contaminants (1999) / Chapter Skim
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10 Biofilms in Drinking Water Distribution Systems: Significance and Control
10 Biofilms in Drinking Water Distribution Systems: Significance and Control
Pages 206-219
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From page 206... ...
BiofiIms can be responsible for loss of distribution system disinfectant residuals, increased bacterial levels, reduction of dissolved oxygen, taste and odor changes, red or black water problems due to iron or sulfate-reducing bacteria, microbial-influenced corrosion, hydraulic roughness, and reduced materials life (Characklis and Marshal, 1990~. Microorganisms in biofihns can include bacteria (including coccoid round, rod-shaped, filamentous, and appendaged bacteria)
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From page 207... ...
Systems that typically experienced cold water had increases in conform occurrences when water temperatures ranged near 10°C. The strains of coliform bacteria in these systems may be better adapted to grow at lower temperatures (psychrophiles)
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From page 209... ...
showed that free chlorine effectively did not penetrate aIginate beads containing bacterial cells but that chIoramines did penetrate into the aIginate material and reduced bacterial levels nearly ~ million-fold over a 60-minute interval (2.5 mg/L chioramines, pH 8.9~. The effectiveness of a chioramine residual for controlling conform occurrences suspected to be the result of biofiIm growth in distribution pipelines is shown in Figure 10-3.
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From page 210... ...
~_ ~x? :~-xS x~1 x: >1 ~0 ~.s .~.~0 1~.~0 ~~0 FIGURE 10-4 Relationship between AOC and distribution system disinfectant residuals.
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From page 211... ...
Figure 10-6 illustrates a decision tree that graphically depicts combinations of threshold values above which the probability of coliform occurrence is increased (Volk et al., 19961. As more of the threshold values are exceeded, the probability of coliform occurrences is increased.
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From page 212... ...
| Dlelafecte at >100 Chin, reeldual AOC ~Dlelafectent C100 cool reeldual lo,~7 1 h;~ O FIGURE 10-6 Decision tree for coliform occurrences in drinking water. 2I2 Identifying Future Drinking Water Contaminants :9 : ~ h h o d r -10< - 2 b he 1 x c .
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From page 213... ...
Studies have shown that biofihns developed more quickly on iron pipe surfaces than on plastic PVC pipes, despite the fact that adequate corrosion control was applied, He water was biologically treated to reduce AOC levels, and chlorine residuals were consistently maintained (Haas et al., 1983; Camper, 199Q This Bief lms in Drinking Water Distribution Systems 213
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A . ~ - ~m = ~ ~4 FIGURE 10-8 Microbial populations isolated from PVC (A)
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From page 215... ...
TABLE 10-2 Multiple Linear Regression Modela for Monochloramine Disinfection of Biof~lm Bacteria Log Reduction Coefficient Standard t-statistic Significance Viable Counts Error Level Intercept -1.0734 0.5685 -1.888 0.0816 Log Larson index -0.5808 0.1963 -2.958 0.0111 Log corrosion rate -0.4820 0.3205 -1.504 0.1566 Log 2.0086 0.9226 2.177 0.0485 monochioramine Phosphate level 0.1445 Corrosion in R- 0.746 squared 0.0336 4.295 0.0009 F test: 13.474 a Model is based on 18 observations. TABLE 10-3 Detection Frequency of Slow-Growing Mycobacteria in Water Samples Percent Samples Containing Slow-Growing Mycobacteria Raw PlandWell Midpoint Effluent O O O O o o 6 11 17 11 Free Free Disinfectant Nutrient Type Level O3/free High Free Medium Low Groundwater Deadend 24 6 11 NA Chloramine High 47 Chloramine Medium 39 Chloramine Medium/Iow 39 Chloramine Groundwater NA o 29 6 o 11 6 o 6 6 24 12 33 50 o Biers lms in Drinking Water Distribution' Systems 215
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From page 216... ...
Either free-chlorine or ozone treatment appeared to be sufficient to eliminate mycobacteria to below detectable levels in plant effluent levels. The conclusion that chIoramines provide a selective advantage for mycobacteria may be premature because of the higher rates of mycobacteria detection in raw water and possible elimination of bacteria that overgrow the selective medium.
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From page 217... ...
Even systems that do not experience coliform problems may want to more closely examine biofilm control strategies and a means of limiting the occurrence of opportunistic pathogens such as Mycobacterium avium complex in drinking water supplies. Biers lms ir' Drinking Water Distribution Systems
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From page 218... ...
1991. Mycobacterium avium complex infection in the acquired immunodeficiency syndrome.
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From page 219... ...
1995. PCR amplification and restriction endonuclease analysis of a 65-kilodalton heat shock protein gene sequence for taxonomic separation of rapidly growing mycobacteria.
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