online monitoring practices for manganese control …€¦ · • raw water monitoring: manganese...
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ONLINE MONITORING PRACTICES FOR MANGANESE CONTROL IN DRINKING WATER TREATMENT Vadim B. Malkov , Hach Company Water Systems Optimization, 10/30/2015
INTRODUCTION
• Manganese in US source water – why is it a problem?
• Reservoir inversion and its consequences • Case Studies
– Dissolved Oxygen (LDO®) • Soldier Canyon DWTP, Ft. Collins, CO • Sherard DWTP, Cheyenne, WY
– Control of manganese treatment with permanganate • Permanganate only • Mixed oxidants
• Conclusions and Recommendations
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INTRODUCTION
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– Manganese in US source water (WHO) • Surface water (>90%) –1 to 200 ppb (median = 16 ppb) • Ground water (~70%) – up to single ppm, median = 10 ppb
– Locations and concentrations/occurrences of manganese in water (USGS)
RESERVOIR INVERSION – WHAT IS NEXT?
• Seasonal changes in shallow reservoirs – Thermal stratification – Anaerobic conditions = dissolved iron and manganese (Mn2+) – Water “turnover”
• Consequences of the inversion – Aesthetic issues (staining) – Bad taste and odor
• Control the situation – Analysis for manganese – Other indicative parameters (e.g. pH/ORP, turbidity, DO)
• Chemical treatment
– Permanganate – Chlorine, etc.
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LDO CASE STUDIES AT A GLANCE
Soldier Canyon DWTP, 50MGD • Source water
– Primary: Horsetooth Reservoir – Secondary: Cache La Poudre
River • Conventional treatment • Raw water monitoring:
manganese (lab), turbidity, pH/ORP, DO
• Pre-oxidation: chlorine dioxide feed after the intake (reactive approach)
• Post-disinfection: free chlorine
Sherard DWTP, 35 MGD • Source water
– Primary: Crystal Lake Reservoir – Secondary: Granit Springs
Reservoir (upstream) • Conventional treatment • Raw water monitoring:
manganese (lab), turbidity, pH/ORP, DO
• Pre-oxidation: oxygen feed at the bottom of reservoir (proactive approach)
• Post-disinfection: free chlorine
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LDO CASE STUDY – SOLDIER CANYON
• DO sampling point – Horsetooth reservoir raw water – Poudre river raw water – Online DO analysis
• Manganese analysis - laboratory
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SOLDIER CANYON – HISTORICAL LAB DATA
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0
0.05
0.1
0.15
0.2
0.25
0.3
0
2
4
6
8
10
12
14
16
18
20
2/22/08 9/9/08 3/28/09 10/14/09 5/2/10 11/18/10 6/6/11 12/23/11 7/10/12 1/26/13 8/14/13 3/2/14 9/18/14 4/6/15
Mn
conc
, ppm
DO (p
pm) &
Tem
p, C
Temp, C
DO, ppm (Lab)
Mn, ppm
Some annual cyclical pattern can be seen
SOLDIER CANYON – LAB AND ONLINE DATA
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Clear correlation between DO, water Temperature and Mn concentration
SOLDIER CANYON – DETAILED DATA ANALYSIS
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Trigger point
Mn Event
SOLDIER CANYON – EVENT PREDICTION (TRIGGER POINT)
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LDO CASE STUDY – SHERARD PLANT
Crystal Lake reservoir Plant Intake (Vault)
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SHERARD – SOURCE WATER MONITORING
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1 2 3 4 5
SHERARD – ONLINE MONITORING DATA ANALYSIS
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Turnover event Trigger point
SENSOR MAINTENANCE Crystal Lake LDO preventive maintenance Inlet strainer (monthly filter wash) Monthly sensor wiping Monthly flow cell cleaning (brush)
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Before cleaning, 9:54AM
After cleaning, 10:03 AM
MAIN TAKEAWAYS
Online DO and temperature monitoring of raw water (at the same sampling point) provides valuable results allowing to determine a trigger point before the reservoir water inversion.
The trigger point indicates the time frame (4-8 weeks) before elevated manganese levels appear in the treatment process, therefore allows for enough time to prepare for the event.
The closer monitoring point to the intake, the more accurate prediction.
If pre-oxidation is employed, the online monitoring of DO/Temperature allows for better treatment optimization (managing cost of pre-oxidants, i.e. chlorine dioxide, oxygen, permanganate).
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TREATMENT FOR MANGANESE REMOVAL
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US EPA - Secondary DW Regulations for iron and manganese
– Aesthetic, cosmetic, technical effects • Taste and Odor • Color • Corrosion and Scaling
– Secondary MCL • Iron: 0.3 ppm • Manganese: 0.05 ppm
– DW industry goals • Iron – 0.1 ppm • Manganese – 0.01 ppm
– Manganese removal and control • Oxidation with permanganate • Measure to maintain the balance • Use of process analysis
Manganese stains
Iron in water
MANGANESE REMOVAL PROCESS CONTROL – FIELD TEST
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• Field test at Hummelstown DWTP (near Harrisburg, PA) – Surface water of variable quality – Pre-oxidation with permanganate (DBP reduction, manganese) followed by chlorine – Membrane filtration followed by post-chlorination
• Facility goals – Maintain balance for permanganate feed to avoid “pink water” and T&O issues – Need to discern free chlorine residual before filters to control post-chlorination
CL17 FOR MANGANESE REMOVAL CONTROL – TEST RESULTS
18 Correlation between KMnO4 dose and its residual, as well as for Total Dose and TRO
CONCLUSIONS AND RECOMMENDATIONS
Raw water intake monitoring for DO and temperature (at the same point) with process sensors provides early notification of elevated manganese levels and therefore allows for better treatment optimization.
Process of manganese removal with permanganate can be efficiently controlled and optimized with the use of simple and reliable process analyzer.
Application of full suite of online monitoring instrumentation (e.g. LDO and two CL17 analyzers sequentially measuring permanganate and TRO concentration) provides a good tool for control and optimization of challenging water treatment processes.
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