Application of Chlorine Dioxide to
Improve Treatment Plant Performance
John Civardi
Hatch Mott MacDonald
Presentation Agenda
• Project Background
• Chlorine Dioxide Fundamentals
• Bench and Demonstration Studies
• Design and Permitting
• Startup
• Questions
PROJECT BACKGROUND
Shenango Water Treatment Plant (16 MGD)
Aerial Imagery ©
2014 DigitalGlobe;
State of Ohio / OSIP;
USDA Farm Service
Agency; Landsat
Plant Location
Aerial Imagery ©
2014 DigitalGlobe;
Landsat; State of
Ohio / OSIP; USDA
Farm Service
Agency; Cnes / Spot
Image
Shenango River Lake
Shenango River Dam*
* Operated by the
Army Corps of
Engineers
Shenango
WTP
1 mi
River is fed by a Lake which can contribute elevated manganese and taste and odor
• Multiple Chemicals and multiple
application points
• Limited detention between raw
water pump station and Actiflo
• Limited detention time in Actiflo
• Chloramination is practiced to
minimize DBP formation
Raw and Point of Entry Water Quality
Averages
Turbidity
(NTU)
TOC
(mg/l)
Algae
(Counts/ml)
Geosmin
(ppt)
MIB (ppt)
Manganese (ppm)
Raw
9.6
5.67
16535
12
30
0.11
Limited
removal
0.03
Filter Influent
0.85
3.46
880
Limited
removal
Treated
0.08
3.12
11
Limited
removal
Limited
removal
0
Maximums
Turbidity
(NTU)
TOC (mg/l)
Algae
(Counts/ml)
Geosmin
(ppt)
MIB (ppt)
Manganese (ppm)
Raw
54
7.1
37,440
159
157
0.33
Filter Influent
3.39
6.4
2480
Limited
removal
Limited
removal
0.08
Treated
0.16
4.1
36
Limited
removal
Limited
removal
0.08
Water Quality Objectives
• Point of Entry Manganese Reduction
• Removal of Geosmin and MIB – 2 log needed 3003
– UV-AOP: 1 + log but more removal needed
• Reduce Point of Entry Disinfection By-Products
• Improve Distribution System Water Quality
• Reducing HPC
• Reducing Nitrification
Project Approach
• Treatability Study
• Bench Testing
• Pilot Testing
• Demonstration Study
• Full Scale Installation
Treatability Study Findings
• Chlorine dioxide in conjunction with UV-AOP enhances T&O removal
• Chlorine dioxide pre-oxidation could oxidize Mn and allow reduction of
filter top chlorine dose which would reduce POE DBPs
• Chlorine dioxide and residual chlorite could potentially reduce
distribution system nitrification
• No plants use chlorine dioxide in this regulatory jurisdiction of PA and
only a limited number of chlorine dioxide systems exist in all of PA
• Next steps: Bench Testing Pilot Test Demonstration Test Full Scale
CHLORINE DIOXIDE
FUNDAMENTALS
Chlorine Dioxide
•
Chlorine Dioxide,ClO2, is very different from chlorine
• Must be produced onsite as a gas
e.g. NaOCl + chlorite  ClO2
• Chlorine speciation is affected by pH, ClO2 is not
• Very volatile – causes a pungent chlorine-like odor at higher concentrations
•
Similarities to Chlorine
• Decays in bright light
• Stability in water similar to chlorine
• Color: yellow - green <3000ppm
• Odor: Similar to Chlorine
• Density: about 2.4 times that of air
Chlorine Dioxide Acceptance
• Potable Water Treatment
• 1944 City of Niagara Falls – Taste & Odor
• Approximately 500 installations in North
America
100%
• Approximately 13% of US population
80%
receives water treated by chlorine
60%
dioxide today
40%
• Continuing to grow
20%
• Used as a disinfectant in several hundred 0%
European utilities
HOCl
HOBr
ClO2
6
7
8
Solution pH
9
10
Disinfection Strategies
• Chlorine Dioxide
• Low Capital Cost
• Good Residual
• Fast Reaction Speed
• No THM or HAA Generation
• Effective on Crypto, Zebra
Mussels, & Biofilm
• Good Oxidizer of Fe, Mn, Taste
& Odor
• No Reaction w/ Ammonia
• Nitrification Control
•
•
•
•
Odors on new carpets
Needs to be Generated On-site
Analytical
Requires Routine Service
Chlorine Dioxide Generation Methods
Chlorite & Chlorine Gas
NaClO2 + 1/2Cl2

Chlorite, Bleach & Acid
2NaClO2 + HOCl + HCl
ClO2 + NaCl

2ClO2 + H2O + 2NaCl
Other Methods
Chlorite & Acid
5NaClO2 + 4HCl

4ClO2 + 5NaCl + 2H2O
• 80% Theoretical Conversion of Chlorite to Chlorine Dioxide
Monitoring
•
Chlorite ion
MCLG
MCL
0.8 mg/L
1.0 mg/L
Monitoring Requirement: One sample daily at entrance to distribution and
Three sample sets monthly
• One as close as possible to first customer
• One at location representative of average residence time
• One at location of maximum residence time
•
Chlorine Dioxide
MRDLG
MRDL
0.8 mg/L
0.8 mg/L (as ClO2)
Monitoring Requirement: Daily (one sample at entrance to distribution)
BENCH & DEMONSTRATION
TESTING
Bench testing with ClO2
2.00
2.0 mg/L
1.75
1.5 mg/L
1.0 mg/L
ClO2 (mg/L)
1.50
1.25
1.00
0.75
0.50
0.25
0.00
0
1
2
3
4
5
6
Time (min)
Chlorine dioxide demand/decay in Shenango raw water.
Temp. = 20˚C, pH = 6.2, Mn2+ = 0.25 mg/L, TOC = 6.58 mg/L.
7
8
9
10
Bench Testing Chlorine Dioxide
10 minutes of detention
Dissolved Mn Residual (mg/L)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.0
0.5
1.0
1.5
Chlorine dioxide dose (mg/L)
2.0
2.5
Pilot Study
•
Bench testing allowed us to evaluate dosages and was inexpensive
•
As part of the plant evaluation, DAF was pilot tested and chlorine dioxide
was added as a pre-oxidant to the DAF. DAF operated at a flowrate of 135
gpm. Chlorine dioxide was fed from a 330 gallon tote with a concentration
of 0.3% and the tote contains 8.2 lbs of chlorine dioxide.
•
CDG SOLUTION 3000™ was used and it has a concentration of 0.3%
•
Product is EPA-registered pure chlorine dioxide. CDG SOLUTION 3000™
liquid concentrate it requires no mixing or “activation”, which simplifies
chlorine dioxide application for small-volume users.
•
Pilot test provided Owner with experience using chlorine dioxide and preoxidation demonstrated successful oxidation of manganese
Demonstration Testing
The purpose of this full scale test was to evaluate the effectiveness of chlorine
dioxide as a pre-oxidant to improve the following:
1.
Manganese removal in the ballasted flocculation system.
2.
Reduction in filter top chlorine dose while still achieving similar pathogen
inactivation. Pre-oxidation with chlorine dioxide was expected to reduce
the chlorine demand and allow a reduction in the applied disinfection
chlorine dose while still maintaining the same effluent chlorine residual.
3.
Reduction in formation of DBPs in the combined filter effluent.
Demonstration Test
• The CLO2 system delivered 15 to 150 ppd .
• Siemens Millennium III™ C-150 Auto two chemical flow-pacing chlorine
gas/sodium chlorite chlorine dioxide generator; maximum of 150 ppd of
ClO2 with a 10:1 turn-down.
• Chlorine gas supplied using the plant’s existing pre-chlorinator.
• Sodium chlorite at a strength of 25% was delivered in 250 gallon totes.
• At the max CLO2 usage of 150 ppd, 84 gallons of sodium chlorite was used
and 79 pounds of chlorine was used.
Demonstration Unit
Findings
Disinfection Byproducts (µg/L)
2012 Chlorine Dioxide Study
2011 Weekly Data (Aug-Nov)
Parameter Value
1
2
CFE
Tap
CFE1
Tap2
Max
28.1
49.8
49.9
85.1
TTHMs
Mean
12.5
26.0
28.7
53.7
Min
5.6
12.2
14.8
34.5
Max
37.7
61.5
103.8
97.7
HAAs
Mean
22.2
41.6
71.7
70.5
Min
9.2
29.9
47.7
53.7
1. CFE is the combined filter effluent
2. Tap is the plant effluent tap.
Chlorite Levels
Distribution System Chlorite (mg/L)
Location
8/27/2012
9/12/2012
10/29/2012
11/7/2012
Chlorine Dioxide Dose
0.75
1.00
1.00
1.00
Near Entry Point
0.344
0.501
0.617
0.536
Average Residence Time
0.324
0.494
0.561
0.538
Maximum Residence Time
0.164
0.278
0.337
0.438
Full Scale
•
Bench, pilot and demonstration testing were successful
•
Permanent Installation needed
•
Project Delivery:
• Owner bid the equipment: prequalified Evoqua and Chemours formerly Dupont
• Chemours, formerly Dupont (International Dioxide) provided the lowest lifecycle cost
• Contract Documents developed for building modifications and installation; bidders prequalified by Owner
• Significant scrutiny by regulators
• System placed into service in September 2014
• Equipment Cost
• Total Construction cost (equipment plus installation)
Design Layout Demolition
Caustic Room Re-Purposed
Actual Facility
Distribution System Results from 2014
• Mercer Courthouse: suspected area of nitrification, highest ATP, HPC,
and Nitrite levels throughout sampling window
• Pre ClO2 10/2 : 5300 HPC result day after startup, ATP of 22.16, Nitrite
of 0.3, Chlorine < 1.0 ppm
• Post ClO2, 11/20 : 83 HPC, 1.88 ATP, Total Chlorine of 2.3 ppm.
• Some of the impact could be temperature related, testing is on going
Summary
• Chlorine Dioxide is a cost effective pre-oxidant and can overcome issues
associated with pre-chlorine
• Bench and demonstration testing can be performed
• Dosage is generally limited by the chlorite MCL
• Evaluate generation methods (2 and 3 chemical systems)
• Design standards are well developed
• Potential benefits in nitrification reduction
31
Acknowledgements
Aqua
Marc Lucca, VP Production
Zach Martin, Plant Manager
Bill Young, Water Quality Specialist
Hatch Mott MacDonald
Mark Tompeck and Margie Gray
Chemours Dupont
Rick Sutherland and Mike Morris