Reduction/Coagulation/Filtration for
Hexavalent Chromium Removal from
Drinking Water
Nicole Blute, PhD, PE
Ying Wu, DEnv, PE
Ramon Abueg, PE
2
Agenda
•
•
•
•
•
Introduction
Key Deciding Factors in Process Selection
RCF Treatment Performance
Cost Estimates
Conclusions
Chromium 6, Chromium 3, and Total Chromium
Cr 6
Cr 3
Cr(VI)
Cr(III)
Hexavalent
Chromium
Trivalent
Chromium
Total
Cr
Parts per billion (ppb) equal micrograms per liter (ug/L)
4
Cr 3 may be converted to Cr 6 if not removed
Cr 6 Concentration (ppb)
100
80
60
0 mg/L
0.5 mg/L
40
1.0 mg/L
2 mg/L
20
0
0
2
4
Days after Chloramine Addition
6
8
5
Summary of draft California Cr 6 MCL
•
•
•
•
Cr 6 concentration of 10 ppb
Regulated at points of entry
Quarterly running annual average
Best available technologies include:
– Ion exchange
– Coagulation/filtration (with reduction upstream)
– Reverse osmosis
• CDPH can require chromium speciation study if
monitoring results exceed 10 ppb and
disinfection is used
Extensive, full-scale treatment testing in
Glendale, California
6
7
Chromium Research Program
• Technologies tested include: ion exchange, reduction
and filtration, high pressure membranes, and adsorption
• Results from each step were used to circle back to
earlier steps and adjust for further testing
Pilot Testing
Bench Scale Testing
Demonstration
Scale Testing
8
Treatment technologies
Four treatment strategies emerged as leading options
– All can achieve the draft MCL of 10 ppb
Weak-Base
Anion
Exchange
Reduction/
Coagulation
/Filtration
Strong-Base
Anion
Exchange
with
Residuals
Treatment
Reverse
Osmosis
8
Operational experience with WBA and RCF
serving customers
• Glendale chose to design and construct WBA and RCF
removal facilities to treat their groundwater
• SBA not selected by Glendale due to concerns about
long-term brine disposal – however, experience in Cr6
treatment by SBA is proven elsewhere
9
10
Key deciding factors in technology selection
11
Reduction/Coagulation/Filtration
• Similar to
conventional water
treatment with
coagulation and
filtration
• Different in the
addition of upstream
reduction using
ferrous iron
12
Reduction/Coagulation/Filtration
FeIISO4
FeIII(OH)3
Cr(VI)
Reduction
Cr(III)
Coagulation
Filtration
13
Reduction/Coagulation/Filtration
Backwash
waste
Treated
Water
Raw
Water
Reduction
Ferrous
iron
Oxidation
of ferrous
with air or
chlorine
Filtration
(Polymer
if
granular
media) Backwash
14
RCF treatment demonstration
• 100 gpm
• Influent of 5 to 80 ppb
• Recycle or direct
disposal of backwash
water
• Variables:
 reduction time
 aeration
 chlorination
 filtration
City of Glendale, California
Iterative New Technology Testing
Bench and Pilot
of RCF
• 45 min. reduction
• Aeration
Demonstration
of RCF
• 45 min. reduction
• Aeration
• Granular media
Demonstration
of RCMF
• 45 min. reduction
• Aeration with chlorination
• Microfiltration
Jar Testing
WaterRF 4450
• 10 min. reduction
• Higher Fe Dose
• Use of ACH
• Chlorination
WaterRF 4445
• 5 min. reduction
• Higher Fe dose
• Chlorination
WaterRF 4423
• 5 min. reduction
• Higher Fe dose
• Chlorination
Reduction of Cr 6 to Cr 3
Backwash
waste
Treated
Water
Raw
Water
Reduction
Ferrous
iron
Oxidation
Filtration
(Polymer )
Backwash
Iron Dose
• Small iron doses compared with
conventional treatment (e.g. 2- 3 mg/L Fe for
80 ppb Cr 6)
• Sufficient iron needed to enable effective
particle removal for lower Cr 6 concentrations
Initial tests of less reduction time
Backwash
waste
Treated
Water
Raw
Water
Oxidation
Ferrous
iron
(Polymer )
Filtration
Fe:Cr(VI) = 25:1
w/ aeration
Backwash
45 min reduction
Fe:Cr(VI) = 25:1
w/ aeration
30 min reduction
Fe:Cr(VI) = 25:1
w/ aeration
15 min reduction
9
8
Reduction time
7
6
5
4
3
2
45 min
ND
ND
ND
ND
ND
ND
0
ND
1
ND
ND
ND
Cr(VI) Concentration (ppb)
10
ND
ND
ND
Reduction
30 min
15 min
Lower reduction time may be possible with higher
iron dose
6
After Reduction
5
Cr6 Concentration (ppb)
Ferrous Dose, mg/L
Cr(VI) reduction Time
prior to Cl addition, min
Cr(VI)4
Raw water
Cr(VI)
Total3Cr
Iniitial pH
adj. pH
Settled Water
Turbidity
2
pH
Ferrous residual
Total Fe
Chlorine
1
After Reduction Cr(VI)
0.8 um Filtered
Cr(VI)
Total0Cr
0.1 um Filtered 1 min
1
Cr(VI)
Total Cr
1
2
1
2
1
20
Jar 1
1
20
Jar 2
5
20
Jar 3
5
20
Jar 4
20
20
7.94
7.71
20
20
7.94
7.71
20
20
7.94
7.72
1.21
7.65
0.03
1.04
0.11
4
1.61
7.69
0.03
1.41
0.78
<0.05
1.36
7.43
0.03
1.02
0.36
2.1
5
6.8
0.39
<0.5
2.2
3
5
5.8
5 min
2
0.46
<0.5
Ferrous = 1 mg/L
15 min
3
2.2
2.5
2
15
20
Jar 6
20
20
7.94
7.72
20
20
7.94
7.72
20
20
7.94
7.72
2.33
7.48
0.02
1.33
0.85
<0.05
0.99
7.62
0.02
0.95
0.61
3.1
1.47
7.62
0.03
0.97
1.26
<0.05
1 min
4
1
0.1 um Filtered
15
20
Jar 5
<0.05
<0.5
ND
0.8 um Filtered
0.06
<0.5
ND ND
3.1
3.4
5 min
5
3.1
3.9
Ferrous = 2 mg/L
ND
<0.05
ND ND
<0.5
15 min
6
<0.05
<0.5
Bench-scale Testing Results for RCF
Development of a Uniform Approach to Prepare Drinking Water Hexavalent Chromium Compliance Plans (WaterRF 4445)
PI: Zaid Chowdhury, Co-PIs: Steve Bigley and Nicole Blute
Granular media filtration was demonstration tested
Backwash
waste
Treated
Water
Raw
Water
Reduction
Ferrous
iron
Oxidation
Filtration
(Polymer )
Backwash
Cr(VI) reduction and removal is reliable with RCF
Backwash
waste
Treated
Water
Raw
Water
Reduction
Oxidation
Ferrous
iron
Filtration
(Polymer )
10
Chromium Concentration (ppb)
9
8
7
6
5
4
3
2
1
0
Backwash
Cr 6 Results
Low ppb levels of Cr 3 may get through granular
filters
Backwash
waste
Treated
Water
Raw
Water
Ferrous
iron
Oxidation
Filtration
(Polymer )
10
Chromium Concentration (ppb)
Reduction
9
8
7
6
5
4
3
2
1
0
Backwash
Total Cr Results
22
Enhancements to the RCF process
• Better particle removal with microfiltration
• Oxidation of remaining ferrous iron with chlorination
• Potential for decreasing reduction time and footprint –
testing underway
Chlorine can effectively oxidize ferrous iron without
significantly impacting Cr 3 conversion to Cr 6
Cr(VI) in Reduced Water
1.0
0.90
Cr(VI) in Chlorinated Water
0.9
0.80
Free Chlorine Residual (after 3 min)
0.8
0.10
0.056
0.20
0.025
0.3
<0.02
0.30
0.094
0.4
0.023
0.40
0.093
0.5
0.054
0.50
0.076
0.6
0.035
0.60
0.092
0.7
0.17
0.70
0.00
0.2
0.1
0.0
2.5 min
2 mg/L iron
5 min
5 min
10 min
2 mg/L iron
2 mg/L iron (repeat)
2 mg/L iron
15 min
2 mg/L iron
5 min
3 mg/L iron
Chlorine Residual (mg/L)
1.00
0.12
Hexavalent Chromium (ppb)
Cr 6 Reduction by Ferrous Iron at Various Reduction Times with Chlorination
(Bench-Scale Testing Results)
24
RCF – microfiltration testing
Backwash
waste
Treated
Water
Raw
Water
Reduction
Ferrous
iron
Oxidation
Filtration
(Polymer )
Backwash
Microfiltration:
Submerged and
Pressure
24
0.2
0.3
6/4 0.2
<1
0
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
6/8
6/11
6/13
7/2
6/27
0.7
<0.2
<0.2
<0.2
6/29 <0.2
<0.2
<0.2
6/25 <0.2
6/20
<0.2
<0.2
6/22 <0.2
<0.2
6/15
<0.2
0.2
6/18 0.2
0.2
<0.2
0.2
60
PALL Flux
GE Flux
40
60
30
40
20
10
20
0
MF Flux (gfd)
50
6/6
6/1
Total Chromium (ppb)
25
Microfiltration results
100
SP-602 PALL Effluent
SP-604 GE Effluent
80
RCF – impacts of water quality
• Systems may require pH adjustment if greater
than pH 8 for effective
– May be overcome with higher iron
• Effectiveness of coagulation can be affected by:
– TOC
– Silica
26
Impact of Higher TOC (WaterRF 4450)
PI: Issam Najm, Co-PI: Nicole Blute
Cr(VI)
Ambient TOC = 0.61 mg/L
Spiked TOC = 2.3 mg/L
Total Cr
Impact of Higher Silica (WaterRF 4445)
• Lower ferrous dose (1 mg/L) resulted in lower Cr6 removal
• Silica impacted coagulation/floc formation step
• Improved removal with 0.1 um filter except at very high silica
Bench-scale Testing Results for RCF
Development of a Uniform Approach to Prepare Drinking Water Hexavalent Chromium Compliance Plans (WaterRF 4445)
PI: Zaid Chowdhury, Co-PIs: Steve Bigley and Nicole Blute
29
RCF – residuals
Backwash water
• Disposal to sewer if possible
• Solids thickening and dewatering would yield
non-RCRA, California hazardous waste
• Potential for recycle
Supernatent
Spent Filter
Backwash
Water
Equalization
Thickening
Dewatering
Solids to
landfill
RCF – operational considerations
• Multiple chemical feeds
• Backwashing and possibly dewatering
• 3 to 5% of process flow
30
31
Cost estimates - assumptions
• 100% utilization rate
• No blending
• Treatment objective equal to 10 ppb for WBA, 1 ppb for
RCF (as Cr 6)
• Facility capital costs amortized over 20 years
• Class 5 estimate (+50%, -30%)
32
Estimated capital cost of treatment
$10,000,000
RCF with recycle
$8,000,000
RCF without recycle
WBA
$6,000,000
$4,000,000
$2,000,000
$0
10
100
500
System Size (gpm)
2,000
Estimated O&M cost of treatment to achieve
a target of 10 ppb
$2.0
O&M Cost ($ Millions)
RCF with recycle
$1.6
RCF without recycle
WBA
$1.2
$0.8
$0.4
$0.0
10
100
500
System Size (gpm)
2,000
33
Estimated costs of treatment to achieve a target of a34
10 ppb in $/AF
Annualized Cost ($/AF)
$4,000
$13,493
RCF with recycle
$3,500
RCF without recycle
$3,000
WBA
$2,500
$2,000
$1,500
$1,000
$500
$0
10
100
500
System Size (gpm)
2,000
SBA and RO costs
• SBA and RO costs were not developed in the
Glendale work
• Estimated cost curves are available in a recent
Journal of AWWA article:
National and California treatment costs to comply with
potential hexavalent chromium MCLs. June 2013.
And in the WaterRF Cost Estimating Tool
36
Cost Estimating Tool
• As part of project #4450, a Cost Estimation Tool for
Cr(VI) Removal from Groundwater was developed
37
Summary
• RCF and RCMF are effective at removing Cr6
• Key drivers for technology selection include water quality
(TOC and silica), residuals disposal options, operational
preferences, and cost
• RCF/RCMF is most attractive when sewer disposal of
backwash water is possible
38
Acknowledgments
39
Reference Materials
City of Glendale Final Report
(February 28, 2013)
Available on City website
Water Research Foundation
sponsored study – Guidelines for
Hexavalent Chromium Treatment
Studies, #4418
Available on WaterRF website
40
Questions?
• Nicole Blute
[email protected]
310-266-6212