age of potable water impacts on dbp’s and disinfection residuals
TRANSCRIPT
Age of Potable WaterAge of Potable Water
Impacts on DBP’s and Impacts on DBP’s and Disinfection ResidualsDisinfection Residuals
Two Basic StrategiesTwo Basic Strategies
• Keep Your Water Young Strategy– Manage residence time in the system
• Preserve Your Water Quality Strategy– Manage water properties to extend the
storage life
Water Ageing FactorsWater Ageing Factors
• System Demands– Water conservation programs– Water rates– Seasonal fluctuations
• System Storage– Reservoir capacity– Pipeline capacity– Local demands
Manage System DemandsManage System Demands
• Water Conservation Programs– Often required by situations beyond your
control. These could be:• Supply shortage• Funding requirements• Political
– Evaluate the down side– Strike a balance
Manage System DemandsManage System Demands
• Water rates– Higher rates = Lower usage– Evaluate the down side of rate increase
• Seasonal rate structure
– Strike a balance
Manage System DemandsManage System Demands
Laramie Summer vs Winter
0.00
50.00
100.00
150.00
200.00
250.00
300.00
350.00
400.00
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
Year
MG
20000
22000
24000
26000
28000
30000
32000
Jul
Dec
Storage
Population
Manage Reservoir StorageManage Reservoir Storage
• Set Seasonal Operating Levels – Maintain minimum
levels in winter• Fire capacity• Average use
• Manage Fill and Drain Cycles– Fluctuate Levels– Manage fill rates
Manage Reservoir StorageManage Reservoir Storage
– Higher fill rates promote mixing
– Mixing reduces dead storage
– Down side is higher demand charge for power utility
– Pump during low consumption times of the day
– Consider you reservoir design
Manage Reservoir StorageManage Reservoir Storage
Mixing systemsSolar Bee Tideflex
Manage Pipeline StorageManage Pipeline Storage
• Fire flow normally determines the pipe size
• Reduce dead ends
• Monitor and actively manage the system– Mainline flows– Disinfectant levels– Flush as necessary– Use EPS model– Identify and manage problem areas
Manage Pipeline StorageManage Pipeline Storage
• Identify and Manage Problem Areas– Dead ends– Stagnate loops– Pressure zone breaks– Long transmission lines– Pipe condition
• Age• Material• Lining
Extend Useful Pipe Life GoalsExtend Useful Pipe Life Goals
• Protect customers from acute illness– Maintain disinfection residual levels– Prevent microbiological contamination
• Protect customers from chronic illness– Inhibit disinfection by product formation– Nitrification
• Maintain aesthetic quality– Taste & Odor– Color
Manage pHManage pH
Bulk Water Disinfection
Lower pH Higher pH
Biofilm Disinfection
Corrosion
BioFilm Stability
Disinfectant Decay Rate
Persistent Combine Chlorine residuals
DBP formation
Nitrification
Manage pHManage pH
Chlorine Break point and pHChlorine Break point and pHChlorine Break point
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2 2.5 3
Applied Dose
Res
idua
l
Free Residual
Combined pH 8
Combined pH 7
Combined pH 6
Total
Manage DBP’sManage DBP’s
• Remove precursor materials– TOC removal– Color– UV 254 abs– Source water
• Minimum Chlorine Levels– Microbes– Distribution system
Manage DBP’sManage DBP’s
• TOC Removal– Enhanced Coagulation– Absorption
• PAC• GAC
– Reduce Chlorine Demand
Manage Disinfectant DemandManage Disinfectant DemandChlorine Break point
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2 2.5 3
Applied Dose
Res
idua
l
Free Residual
Combined pH 8
Combined pH 7
Combined pH 6
Total
Manage DBP’sManage DBP’s
• Reduce Disinfectant
• Aeration
• Inhibit Formation– Ozone– Oxygen
Laramie’s ExperienceLaramie’s Experience
• Starting Conditions– Raw Water TTHMFP
350 – 500 ppb– Distribution THM 80-
100 ppb– Chlorine level 0.7- ND– pH not managed– Coagulation not
enhanced– Pressure zone flow not
managed
• Current Conditions– Raw Water TTHMFP
unknown new source– Distribution THM 10-
40 ppb– Chlorine Level 1.0 -0.3– pH managed at 7.6– Enhanced coagulation– Active pressure zone
flow management
Laramie’s Treatment Strategies Laramie’s Treatment Strategies
• Remove precursor material
• Inhibit formation
• Monitor removal by– Color removal– Chlorine demand– TOC removal– Chlorine decay rate
• Monitor inhibition by– UV 254 abs
Chlorine Decay RateChlorine Decay Rate
• Place sample in a series of non reacting glass bottles
• Analyze residual over time
• Plot Ln(Ct/Co) Should be a straight line. Slope of the line is the decay rate.
Chlorine Decay
y = -0.0137x + 560.77
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
12/3/20110:00
12/8/20110:00
12/13/20110:00
12/18/20110:00
12/23/20110:00
12/28/20110:00
1/2/2012 0:00
Date and Time
ln(C
t/Co)
Laramie’s Distribution StrategiesLaramie’s Distribution Strategies
• Minimize residence time
• Remove precursors
– Reservoir operating levels– Eliminate dead ends– Redesign Low Level reservoir
inlet
– Color removal– Chlorine demand– TOC removal– Chlorine decay rate– Pressure zone circulation– Take advantage of large
irrigation flows– Flush where necessary– Identify and correct problem
areas
Laramie’s Distribution StrategiesLaramie’s Distribution Strategies
• Stabilize Bio-Film
• Extend usable water age
– Manage pH– Maintain alkalinity– Manage corrosion– Maintain consistent
chlorine residuals– Maintain consistent TOC
removal
– Lower chlorine decay rate– Promote circulation and
mixing– Identify problem areas
Distribution System ModelingDistribution System Modeling
• Long term process requires many iterations
• Requires regular maintenance
• Calibrate using systematic field measurements– SCADA– Grab