1. An Operational Definition of Biostability
Jennifer Hooper, PE and Dr. Patrick Evans (co-PI), CDM Smith
Dr. Mark LeChevallier (PI), Dr. Orren Schneider, PE, Dr. Lauren Weinrich, Dr. Patrick Jjemba, American Water
An Operational Definition of Biostability
Water Research Foundation Project 4312
November 9, 2015
Southeast Florida Utility Council

2. Background
Biostability = potential for bacterial growth in the distribution system
Biologically stable water in Europe is <50 mg/L AOC
based on the ABSENCE OF CHLORINE
Some water treatment processes (e.g., aeration, ozonation, chlorination) can increase likelihood of regrowth by increasing biodegradable organic matter concentration or increasing the ability of microorganisms to degrade organic matter (rate of uptake)

3. Important Parameters to Consider
Regrowth in unlined cast-iron pipe
Pipe Material
Pipe Age
Hydraulic Residence Time
Temperature at the monitoring point
Flow rate at the monitoring point
Disinfectant residual at monitoring point
Finished water disinfectant dose
Finished water disinfectant residual

4. Case Study – Utility 23-MA
Problem: Bacterial growth, unstable chlorine residual, nitrification
65 violations of total coliform MCL from
Cause: 1989 free chlorine residual regulatory change to >0.25 mg/L 100 ft downstream of POE
Chlorine:ammonia ratio altered from 4:1-5:1 to 11:1.
Chlorine residual low ~ 0.17 mg/L
Maintenance (flushing, storage tanks, dead ends), communication, data tracking
Solution: Add ammonia downstream of regulatory compliance point
Chlorine:ammonia ratio target: 4.5:1
Average chlorine residual increased to 0.9 mg/L in 1998
TCR Regulatory Limit
Uses ozone, pH adjustment, chloramines for disinfection

5. WaterRF Project 4312: An Operational Definition of Biological Stability
Objective: develop an integrated decision support system that embodies the factors affecting biostability and practical indicators of biostability

6. Distribution System Characteristics
Max Residence Time
19% < 0-3 days
25% < 3-6 days
44% < 6-9 days
13% 9-10 days
Max Pipe Age
28% <50 yrs
36% yrs
36% >100 yrs

7. Monitoring and Control Programs

8. Historical Data Analysis – Identification of Stability Issues
Who has what problems, but want to know why

9. Statistical Evaluation – Preliminary Associations
Potential Causes
Goal: Identify parameters associated with bacterial growth, nitrification, DBP formation, and disinfectant residual stability.
Method: Selected parameters that were associated with all four effects.
- Bacterial Growth
- Nitrification
- DBP Formation
- Disinfectant Residual Stability

10. Long-term sampling Six systems June 2011 to September 2012
Examine changes through distribution system
POE (DS1), distribution system midpoint (DS2), endpoint (DS3)
20 sampling events, 6 locations, 3 sites = 360 data points
Biodegradable Carbon
TOC
AOC
BDOC
Disinfectant Stability
HAA5
Free/Total Chlorine
pH, Temperature
Corrosion/Biofilm Formation
ATP accumulation
Corrosivity
Inorganic Nutrients
Nitrate
Ammonia
Phosphate
Preliminary results from sampling and analysis program:
No clear regrowth problems despite some high AOC/BDOC values; No simple linear relationships found, multiple factors; multivariate statistical analysis for hierarchical data

11. Biofilm Measurements Installed mild steel corrosion coupons
Replaced coupons on regular basis
Scraped biofilm off coupons
See LeChevallier et al for details
Measured ATP in scraped biofilm
Determined Biofilm Formation Rate as
ATP/(coupon surface area x time installed)

12. Linear Polarization Resistance (LPR) Measurements
In-Situ Corrosivity Measurement
Install mild steel electrodes
Measurements collected in ~10 min

13. Factors Affecting Biostability
Complex interactions
No simple correlations – threshold values played a key role
Utility specific
Interplay of temperature, water quality, time, pipe materials, etc.

14. Impact of Chlorine Residual on Biofilm Accumulation Rate
0.7
Chloramines (mg/L)
Free Chlorine (mg/L)
2-log
~2.1
~1.5
3-log
~3.1

15. Order of variables for minimizing ATP accumulation
Higher Importance
Lower Importance
Chloramines
Free chlorine

16. Order of variables for minimizing free chlorine variability
Higher Importance
Lower Importance

17. Order of variables for minimizing total chlorine variability
Higher Importance
Lower Importance

18. Order of variables for minimizing corrosion rate
Higher Importance
Lower Importance

19. Threshold values for explanatory variables
Measure of Water Stability
Biomass Accumulation
Corrosion Rate
Chlorine Variability
Free
Chloramines
Temperature (C) 15 20
Water Age (hr) 80
200
Free Chlorine (mg/L)
1.0
---
Combined Chlorine (mg/L)
1.8
Corrosion Rate (mpy) 4
DOC (mg/L)
AOC (mg acetate C/L)
120
220
Biofilm Formation Rate (pg/mm2-d)
0.028
0.134
0.025
Phosphate (mg/L)
1.4
0.8 pH
7.4
Most Important Variable
Second Variable
Third Variable

20. Important Explanatory Variables
Biofilm Formation Rate
ATP Accumulation/(coupon area x installation period)
Corrosion Rate
Chlorine/Chloramine Coefficient of Variation (CV)
Standard deviation of residuals on given day
Average of residuals on same day

21. Biostability Analysis Tool (BSAT)
Excel-based macros data analysis tool
Performs multiple statistical analyses to evaluate site-specific data from a utility
Summary statistics (average, max, min)
Box plots
Trend plots
Correlations and liner regressions
Regression Tree analysis
Free! ..and available for download

22. Conclusions
Biofilm accumulation rate, chlorine CV, and corrosion rate are useful parameters for evaluating water stability
Water temperature has greatest impact on Biofilm Accumulation Rate, free chlorine variability, and corrosion rate
Water age has greatest impact on total chlorine variability
For control variables, chlorine residual has greatest impact on Biofilm Accumulation Rate. Reducing corrosion rate also has impact
Effective flushing to remove biofilms can have positive impact on chlorine stability and corrosion
Organic carbon (DOC/AOC) play lesser roles but can still be important control measures
BSAT is a useful tool for analyzing and tracking site- specific data
Chloramine (mg/L)
Free Chlorine (mg/L)
2-log
~2.1
~1.5
3-log
~3.1

23. Acknowledgements Water Research Foundation American Water
Project Manager, Dr. Hsiao-wen Chen
USEPA, Grant No. EM
Project Advisory Committee
Eric Irwin, Fort Worth Water Department, Texas
Chandra Mysore, Jacobs Engineering Group
Eva Nieminski, Utah Department of Environmental Quality
Youngwoo Seo, University of Toledo
American Water
26 Participating Utilities
CDM Smith gratefully acknowledges that the Water Research Foundation are funders of certain technical information upon which this presentation is based. CDM Smith thanks the Water Research Foundation, for their financial, technical, and administrative assistance in funding the project through which this information was discovered.

24. Useful Information
WRF Project 4312 website:
Webcasts on Demand: demand.aspx
Source: Mark W. LeChevallier, Orren D. Schneider, Lauren A. Weinrich, Patrick K. Jjemba, Patrick J. Evans, Jennifer L. Hooper, and Rick W. Chappell An Operational Definition of Biostability in Drinking Water. Water Research Foundation. Reproduced with Permission.
Contact Information
Thank you Karl, Harold, and James.
For more information about project 43-76, please visit the project webpage on Water Research Foundation's website.
You can also visit our website in a few days to watch today’s webcast again and download the presentation.
Jennifer Hooper, P.E.