An Operational Definition of
Biostability
Water Research Foundation Project 4312
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
November 9, 2015
Southeast Florida Utility Council
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)
2
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
Case Study – Utility 23-MA
 Problem: Bacterial growth, unstable chlorine residual, nitrification
 65 violations of total coliform MCL from 1995-1997
 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
MWRA System-Wide TCR % Positive Rate and Chlorine Residual Trends
tracking
1.4
8%
1.0
6%
0.8
0.6
4%
0.4
2%
0.2
0.0
-9
5
Ap
r-9
5
Ju
l-9
Oc 5
t-9
5
Ja
n96
Ap
r-9
6
Ju
l-9
Oc 6
t-9
6
Ja
n97
Ap
r-9
7
Ju
l-9
Oc 7
t-9
7
Ja
n98
Ap
r-9
8
Ju
l-9
8
Oc
t-9
8
Ja
n99
Ap
r-9
9
0%
TCR % Positive Rate
Avg Cl2
Total Chlorine Residual, mg/L
TCR Regulatory Limit
1.2
TCR % Positives
• Chlorine:ammonia ratio
target: 4.5:1
• Average chlorine residual
increased to 0.9 mg/L in
1998
10%
1.6
Ja
n
• Solution: Add ammonia
downstream of regulatory
compliance point
12%
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
States with Participating Utilities
Users
Distribution System Characteristics
80%
60%
40%
20%
Brass
Galvinized Iron
PCCP
Polyethylene
Copper
Ductile Steel
Concrete
Transite Cement
Steel
0%
Cement-Lining
28% <50 yrs
36% 50-100 yrs
36% >100 yrs
Pipe Materials
PVC
Max Pipe Age
100%
Ductile Iron
19% < 0-3 days
25% < 3-6 days
44% < 6-9 days
13% 9-10 days
Cast Iron
Max Residence Time
Monitoring and Control Programs
Control Programs
Monitoring Programs
Storage Tank Cleaning
Turbidity
Total Dissolved Solids
None
Temperature
HPCs
Increase Flow
Nitrate/Nitrite
Replace Pipe
Ammoina
DBPs
Line Pipe
Coliforms
Disinfectant Residual
Flushing Program
0%
10%
20%
30%
40%
50%
60%
70%
60%
50%
40%
30%
20%
10%
0%
None
Historical Data Analysis – Identification of
Stability Issues
Number of Facilities
30
25
65% 75%
71% 82% 40% 44% 15% 40% 100% 50% 100% 4%
5%
20
15
10
5
0
No Response
Without Problem
With Problem
Statistical Evaluation – Preliminary Associations
• Goal: Identify parameters
associated with bacterial
growth, nitrification, DBP
formation, and disinfectant
residual stability.
• Method: Selected parameters
that were associated with all
four effects.
Potential Causes
- Bacterial Growth
- Nitrification
- DBP Formation
- Disinfectant
Residual Stability
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
10
Biofilm Measurements
 Installed mild steel corrosion coupons
 Replaced coupons on regular basis
 Scraped biofilm off coupons
 See LeChevallier et al. 2015 for details
 Measured ATP in scraped biofilm
 Determined Biofilm Formation Rate as
ATP/(coupon surface area x time installed)
11
Linear Polarization Resistance (LPR) Measurements
 In-Situ Corrosivity
Measurement
 Install mild steel electrodes
 Measurements collected in
~10 min
12
Factors Affecting Biostability
 Complex interactions
Biofilm Formation Rate (pg/mm2-d)
 No simple correlations – threshold values played a key role
 Utility specific
 Interplay of temperature, water quality, time, pipe materials, etc.
0.010
08-OK
13-VA
0.008
0.006
0.004
0.002
0.000
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
Temperature (°C)
13
Impact of Chlorine Residual on Biofilm
Accumulation Rate
1E+00
ATP (pg/mm2-d)
08-OK DS2
08-OK DS3
13-VA DS2
13-VA DS3
21-NJ DS2
21-NJ DS3
23-MA DS2
23-MA DS3
Combined Chlorine
1E+01
slope = 1
1E-01
1E-02
1E-03
1E-04
b.
1E+00
1E-02
1E-03
1E-04
1E-05
1E-06
1E-06
1
2
3
4
5
slope = 0.7
0.6
1E-01
1E-05
0
08-OK DS2
08-OK DS3
10-GA DS2
10-GA DS3
20-NJ DS2
20-NJ DS3
21-NJ DS2
Free Chlorine
1E+01
ATP (pg/mm2-d)
a.
0
1
Chlorine Residual (mg/L)
2
3
4
5
Chlorine Residual (mg/L)
Chloramines
(mg/L)
Free Chlorine
(mg/L)
2-log
~2.1
~1.5
3-log
~3.1
~2.1
14
Order of variables for minimizing ATP accumulation
Higher
Importance
Lower
Importance
Chloramines
Free chlorine
15
Order of variables for minimizing free chlorine variability
Higher
Importance
Lower
Importance
16
Order of variables for minimizing total chlorine variability
Higher
Importance
Lower
Importance
17
Order of variables for minimizing corrosion rate
Higher
Importance
Lower
Importance
18
Threshold values for explanatory variables
Measure of Water Stability
Biomass
Accumulation
Corrosion
Rate
Temperature (C)
15
Water Age (hr)
80
Free Chlorine (mg/L)
Chlorine Variability
Free
Chloramines
20
20
15
200
80
80
1.0
---
---
Combined Chlorine (mg/L)
1.8
---
---
Corrosion Rate (mpy)
4
4
4
DOC (mg/L)
1.8
1.8
1.8
AOC (mg acetate C/L)
120
120
220
0.025
---
Biofilm Formation Rate (pg/mm2-d)
0.028
0.134
Phosphate (mg/L)
1.4
0.8
pH
7.4
Most Important Variable
Second Variable
Third Variable
19
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
20
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
 http://www.waterrf.org/resources/pages/PublicWebTools-detail.aspx?ItemID=30
21
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 sitespecific data
Chloramine
(mg/L)
Free Chlorine
(mg/L)
2-log
~2.1
~1.5
3-log
~3.1
~2.1
22
Acknowledgements
• Water Research Foundation
– Project Manager, Dr. Hsiao-wen Chen
– USEPA, Grant No. EM83406801
– 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.
Useful Information
•
WRF Project 4312 website:
http://www.waterrf.org/Pages/Projects.aspx?PID=4312
•
Webcasts on Demand:
http://www.waterrf.org/resources/webcasts/Pages/ondemand.aspx
•
Source: Mark W. LeChevallier, Orren D. Schneider, Lauren A. Weinrich, Patrick K. Jjemba, Patrick J.
Evans, Jennifer L. Hooper, and Rick W. Chappell. 2015. An Operational Definition of Biostability in
Drinking Water. Water Research Foundation. Reproduced with Permission.
Contact Information
Jennifer Hooper, P.E.
[email protected]
24