Planning a Chlorine Decay Test - WordPress.com · 2017. 2. 10. · Microsoft PowerPoint - 3 -...
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Planning a Chlorine Decay Test
Brian CarolanCwMAG Autumn Conference 2015
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Introduction
• The various stages in planning a chlorine decay test will be discussed
• This will be done in the context of a fictitious case study
Planning a Chlorine Decay Test
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Network
Service Res & WBS
ServiceRes
DMA1
DMA2
DMA3
N
• 3 DMAs, two supplies
• DMA 2 & 3 are gravity fed
• DMA 1 is pumped
• Low flows throughout the system
• Flushing required to maintain water quality
Planning a Chlorine Decay Test
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Network Water Quality
Service Res & WBS
ServiceRes
N
• Chlorine residuals are lower than desired upon entry to the DMAs from the two sources
• Critical to water company that no water quality failures occur in this area
• Chlorine decay model required, to examine if water quality issues are within the network
Planning a Chlorine Decay Test
DMA1
DMA2
DMA3
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Overview of Chlorination
Planning a Chlorine Decay Test
Toxic by-products possible
1.0 mg/l
Effective Disinfection
0.2mg/lIneffective Disinfection
• Chlorine decay occurs within the distribution system due to chemical reactions with– Materials in water (Bulk decay)– Materials along pipe surfaces (Wall decay)
WHO Guidelines
• Chlorine is added to water as a disinfectant to:– Inhibit bacterial growth– Prevent algal growth
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Chlorine Decay Theory
1st Order Bulk Decay Equation (kb)
Arrhenius Equation
[Cl2] = chlorine concentration (mg/l)[Cl2] 0 = initial chlorine concentration (mg/l)t = time (days)A = Arrhenius pre-exponential factor (takes same units as kb)n = Order NumberEa = Activation energy (J/mol)kw = wall coefficientkf = mass transfer coefficientR = Gas constant (8.3144621 J/mol.K)T = Temperature (K)
Where:
Wall Decay Equation (kw)
Planning a Chlorine Decay Test
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Chlorine Modelling
• Modelling is dependent on the accuracy of the following inputs to the model:– Initial chlorine concentration– Organic matter soluble in water (its concentration & nature)– Hydrodynamic conditions– Temperature
Planning a Chlorine Decay Test
• 1.9 – 5.0 fold increase in decay coefficient when temperature increases from 10 to 20oC (L.Monteiro et al.2015)
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Chlorine Monitoring SoftwareInfoWorks
Maximum Velocity Age of Water
Planning a Chlorine Decay Test
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Location Selection• Hydraulic modelling identified
locations with issues such as:
– Age of water
– Low velocities
• Monitoring also required at:– Sites
– Outlying locations (for good coverage)Service Res & WBS
ServiceRes
N
Planning a Chlorine Decay Test
DMA1
DMA2
DMA3
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Chlorine Monitoring Equipment
Planning a Chlorine Decay Test
Hardware
Chloroclam chlorine monitor, courtesy of Evoqua Water TechnologiesATi chlorine monitor
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Conclusions
Calibrated Hydraulic
Model
Location Selection for Monitoring
Points
Investigative Site Visit
Installation of Chlorine Monitors
Calibrate Chlorine Decay Model
Planning a Chlorine Decay Test
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Thank you
Questions Welcome
Planning a Chlorine Decay Test 12