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www.processinstruments.co.uk
Process Instruments (UK) Ltd.
Dr Rob Paramore- Process Instruments (UK) Ltd.
Coagulation Control Using UV254– the
Theory and the Reality
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Discussion points
• What is coagulation?
• Why do we want to automate this process and how can this be done?
• How do UV254 instruments work?
• How UV254 is used to automate the coagulation process?
• What are the issues with using UV254 to control coagulation?
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The use of chemicals to make very fine particulates gather or clump together so they will settle out of the water and be of a more filterable size.
Coagulation
Alum- -
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Types of Coagulant
Sweep Flocculation – Turbidity removal- Organics removal
Charge Neutralisation (Enhanced Coagulation)- Turbidity removal - Organics removal
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Charge neutralisation– pH is key
Floc …little charge left
Best …highest charge
Terrible …soluble
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Manual Adjustment
Coagulant Pumped
Manual Pump AdjustmentsCoagulant Demand
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Chemical Feed Automatically Controlled
Coagulant Demand
Coagulant Pumped
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Parameters That Impact Coagulation
Changes in:• Coagulant Dose/Makeup• Turbidity• Organics• Disinfection/Oxidation• pH• Temperature• Physical (e.g. mixing)
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Possible Control Parameters
• Single Parameter• pH (Raw)
• pH (Post Coagulation)
• Turbidity (Raw)
• Turbidity (Settled)
• Streaming Current (Post Coagulation)
• Colour/UV254 (Raw)
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Using Light Absorption (Colour/UV254)
• Many chemical compounds have specific absorbance characteristics at different wavelengths of light
• By measuring the light absorbed by a water sample at particular wavelengths, the concentration of a contaminant can be determined
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Sample
UV254 Instruments
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Sample
UV254 Instruments
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Sample
UV254 Instruments
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UV254 Instruments
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Sample
UV254 Instruments
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Sample
UV254 Instruments
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Sample
UV254 Instruments
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Sample
UV254 Instruments
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Use the amount of UV254 light that passes through a sample to calculate the level of dissolved organics
Challenges-Keeping them cleanTurbidity increases errorLongevity of light source
Summary UV254 Instruments
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Conventional WTP
MIXING FLOC BASIN SEDIMENTATION FILTRATION FINISHED
UV254SCM
pH/TempUV254 Cond..
Coag
pHAdj
Poly
Cl
NTU
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UV254 Correlation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
UVA
mg/l Coagulant
UVA against Coagulant Dose (mg/l)
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Parameters That Impact Coagulation
Changes in:• Coagulant Dose/Makeup• Turbidity• Organics• Disinfection/Oxidation• pH• Temperature• Physical (e.g. mixing)
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UV254 Feed Forward Control – Plant B
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UV254 Feed Forward Control – Plant B
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UV254 Feed Forward Control
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14/2/19 – 21/2/19 Plant N
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14/2/19 – 21/2/19 Plant N
R² = 0.7295
0
10
20
30
40
50
60
0 5 10 15 20 25 30 35
14/2/19 - 21/2/19
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21/3/19 – 28/3/19 Plant N
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Conventional WTP
MIXING FLOC BASIN SEDIMENTATION FILTRATION FINISHED
UV254SCM
pH/TempUV254 Cond..
Coag
pHAdj
Poly
Cl
NTU
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Conclusions
• UV254 measures organics, a big driver of coagulation demand, but doesn’t measure all the other things that affect coagulation.
• UV254 can only be used as a feed forward control.
• UV254 control is only as good as the correlation.
• UV254 will struggle to control a highly variable source particularly variable turbidity.
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Process Instruments (UK) Ltd.
Thank you!
Any Questions?