november 9, 2015 an operational definition of biostability water research foundation project 4312...
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November 9, 2015
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
Southeast Florida Utility Council
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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)
Important Parameters to Consider
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
Regrowth in unlined cast-iron pipe
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
tracking MWRA System-Wide TCR % Positive Rate and Chlorine Residual Trends
0%
2%
4%
6%
8%
10%
12%
TCR
% P
ositiv
es
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Tota
l Chl
orin
e R
esid
ual,
mg/
L
TCR % Positive Rate Avg Cl2
TCR Regulatory Limit• 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
WaterRF Project 4312: An Operational Definition of Biological Stability
States with Participating Utilities Users
Objective: develop an integrated decision support system that embodies the factors affecting biostability and practical indicators of biostability
Max Residence Time19% < 0-3 days25% < 3-6 days44% < 6-9 days13% 9-10 days
Max Pipe Age28% <50 yrs36% 50-100 yrs36% >100 yrs
Distribution System Characteristics
0%
20%
40%
60%
80%
100% Pipe Materials
Monitoring and Control Programs
None
Disinfectant Residual
Coliforms
DBPs
Ammoina
Nitrate/Nitrite
HPCs
Temperature
Total Dissolved Solids
Turbidity
-10% 0% 10
%
20%
30%
40%
50%
60%
Monitoring Programs
Flushing Program
Line Pipe
Replace Pipe
Increase Flow
None
Storage Tank
Cleaning
0% 10%
20%
30%
40%
50%
60%
70%
Control Programs
Historical Data Analysis – Identification of Stability Issues
0
5
10
15
20
25
3065% 75% 71% 82% 40% 44% 15% 40% 100% 50% 100% 4% 5%
No Response Without Problem With Problem
Num
ber o
f Fac
ilitie
s
Statistical Evaluation – Preliminary Associations
Potential Causes
- Bacterial Growth- Nitrification- DBP Formation- Disinfectant Residual Stability
• Goal: Identify parameters associated with bacterial growth, nitrification, DBP formation, and disinfectant residual stability.
• Method: Selected parameters that were associated with all four effects.
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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
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 asATP/(coupon surface area x time installed)
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Linear Polarization Resistance (LPR) Measurements
In-Situ Corrosivity Measurement
Install mild steel electrodes Measurements collected in
~10 min
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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.
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5.0 10.0 15.0 20.0 25.0 30.0 35.00.000
0.002
0.004
0.006
0.008
0.010
08-OK13-VA
Temperature (°C)
Bio
film
Fo
rma
tion
Ra
te (
pg
/mm
2-d
)
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Impact of Chlorine Residual on Biofilm Accumulation Rate
1E-06
1E-05
1E-04
1E-03
1E-02
1E-01
1E+00
1E+01
0 1 2 3 4 5
ATP
(pg/
mm
2 -d)
Chlorine Residual (mg/L)
Combined Chlorine 08-OK DS208-OK DS313-VA DS213-VA DS321-NJ DS221-NJ DS323-MA DS223-MA DS3
slope = 1
1E-06
1E-05
1E-04
1E-03
1E-02
1E-01
1E+00
1E+01
0 1 2 3 4 5AT
P (p
g/m
m2 -
d)Chlorine Residual (mg/L)
Free Chlorine 08-OK DS208-OK DS310-GA DS210-GA DS320-NJ DS220-NJ DS321-NJ DS2
slope = 0.6
a. b.
Chloramines (mg/L)
Free Chlorine (mg/L)
2-log ~2.1 ~1.5
3-log ~3.1 ~2.1
0.7
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
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Threshold values for explanatory variables
Most Important Variable Second Variable Third Variable
Measure of Water Stability
Biomass Accumulation
Corrosion Rate
Chlorine Variability
Free Chloramines
Temperature (C) 15 20 20 15
Water Age (hr) 80 200 80 80
Free Chlorine (mg/L) 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
Biofilm Formation Rate (pg/mm2-d) 0.028 0.134 0.025
Phosphate (mg/L) 1.4 0.8
pH 7.4
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 dayAverage of residuals on same day
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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
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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 ~2.1
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.
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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/on-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. 2015. An Operational Definition of Biostability in Drinking Water. Water Research Foundation. Reproduced with Permission.
Contact Information
Jennifer Hooper, [email protected]