1. Using Biological Activity Reaction Tests (BART) to Monitor Microbially-Influenced Corrosion in Cast Iron Pipes
Darlyce Simpson1, Steve Craik1 and Rasha Maal-Bared2
1Analytical Operations, Quality Assurance and Environment, EPCOR Water Services, Edmonton, Alberta, Canada.
2Scientific Services, Quality Assurance and Environment, EPCOR Water Services, Edmonton, Alberta, Canada.
Introduction
Results and Discussion
Results and Discussion (continued)
In 2015, EPCOR Water Services received complaints of water discoloration and the formation of an orange film on surfaces that come in contact with tap water from residents of an Edmonton neighborhood. It was determined that the likely cause was the corrosion of aging cast iron pipes used in that section of the water distribution system. Microbially- influenced corrosion (MIC) is corrosion caused by the presence and metabolic activity of microorganisms on a metal surface. Iron-related bacteria (IRB), sulfate-reducing bacteria (SRB) and biofilm forming bacteria are considered to be the main types of bacteria associated with MIC in cast iron pipes (1). IRB oxidize dissolved ferrous iron to form ferric oxide resulting in an insoluble reddish precipitate. Hydrogen sulfide gas produced by the break down of sulfur compounds by SRB also contributes to corrosion. Biofilm forming bacteria facilitate the creation of biofilms, which provide an environment for IRB and SRB to grow. Biological activity reaction tests (BART) can be used for the semi-quantitative evaluation of nuisance bacteria such as IRB and SRB.
Chemical Analyses
SRB and biofilm bacteria were detected in swab samples taken from a water meter in an adjacent affected house and from the removed section of the water main prior to replacement (Table 1). The toilet tank swab showed the presence of biofilm bacteria but no SRB. It is likely that the water meter and the cast iron pipe provided a more suitable environment to culture populations of SRB. Indications of the presence of IRB were seen in all of the samples but were more difficult to determine with certainty as the observed reaction time exceeded the standard length of the test. This may be due to very low populations or a low level of bacterial activity from environmental stressors (2).
During the connection to the temporary water supply, IRB, SRB and biofilm bacteria were not detected suggesting that the premise plumbing may not have been colonized by significant populations possibly due to the lack of suitable materials that support these bacteria.
After the water main replacement, SRB were not detected in either water or swab samples. Biofilm bacteria were detected in water samples indicating that these bacteria are still present in the water main upstream of the repair area. The observed IRB levels were similar to those seen in the initial samples collected prior to replacement.
Figure 1. Changes in iron concentrations prior to, during and post water main replacement from one of the homes in the affected area.
As expected, samples collected prior to the water main replacement showed elevated iron concentrations with a marked decrease in concentrations after residents were connected to the temporary water supply (Figure 1). A slight increase in iron concentrations was observed again after the replacement, which gradually decreased with water usage over time. Manganese and aluminum concentrations did not fluctuate.
Objectives
Providing high quality and reliable drinking water to the public is a priority for EPCOR Water Services.
This study aimed to:
Evaluate if BART can be used to determine if IRB and SRB influence water quality changes;
Identify the long-term changes in IRB and SRB after a section of the cast-iron water main suspected to have undergone MIC was replaced.
Bacteriological Analyses
Conclusions and Limitations
Test
Sample Date
Sample Point
IRB
SRB
Biofilm
Prior to Replacement
October 8, 2015
Water Meter Swab +
+++ ++
Toilet Tank Swab -
October 20, 2015
Water Main Swab (West)
Water Main Swab (East)
Connected to Temporary
October 28, 2016
Tap Water Sample
Post Replacement
November 5, 2015
December 14, 2015
February 5, 2016
March 29, 2016
- Absent
+ Not Aggressive
++ Moderately Aggressive
+++ Aggressive
It is important to develop a method for identifying and forecasting MIC in order to better manage and prioritize cast iron water main replacements.
More studies may be needed to determine the effectiveness of this method on biofilm samples as it is difficult to obtain a representative sample and therefore difficult to standardize and quantify these results.
Results from these tests are semi-quantitative thus any numbers produced by BART need to be evaluated and explained to customers with caution.
IRB and SRB have no known effects on human health but they can impact the aesthetic quality of water delivered to customers.
Materials and Methods
Water grab samples and biofilm swabs were collected from three homes in the affected area for chemical and/or bacteriological analyses: a) prior to water main replacement; b) during the main replacement while the homes were connected to a temporary water supply; and c) for five months after the replacement was completed. Chemical analyses included, but were not limited to: turbidity, chlorine, color, and metals (iron, manganese and aluminum). BART were used for IRB, SRB and biofilm bacteria.
Table 1. Summary of BART results prior to, during and post water main replacement from one of the homes in the affected area.
References
Beimeng, Q., Chongwei, C., Yixing, Y Int. J. Electrochem. Sci. 10:
Droycon Bioconcepts Inc. 2004, Biological Activity Reaction Test BART User Manual. Retrieved from
Contact
 For more information, please contact Darlyce Simpson at
Figure 2. BART Biodetectors