40
Reduction/Coagulation/Filtration for Hexavalent Chromium Removal from Drinking Water Nicole Blute, PhD, PE Ying Wu, DEnv, PE Ramon Abueg, PE
Reduction/Coagulation/Filtration for
Hexavalent Chromium Removal from
Drinking Water
Nicole Blute, PhD, PE
Ying Wu, DEnv, PE
Ramon Abueg, PE
Agenda
• Introduction
• Key Deciding Factors in Process Selection
• RCF Treatment Performance
• Cost Estimates
• Conclusions
2
Chromium 6, Chromium 3, and Total Chromium
Cr 6
Cr(VI)
Cr 3
Cr(III)
Total Cr
Hexavalent
ChromiumTrivalent
Chromium
Parts per billion (ppb) equal micrograms per liter (ug/L)
Cr 3 may be converted to Cr 6 if not removed 4
0
20
40
60
80
100
0 2 4 6 8
Cr
6 C
on
cen
trat
ion
(p
pb
)
Days after Chloramine Addition
0 mg/L
0.5 mg/L
1.0 mg/L
2 mg/L
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
5
Extensive, full-scale treatment testing in
Glendale, California
6
Chromium Research Program 7
• 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
Bench Scale Testing
Pilot Testing
Demonstration
Scale Testing
Treatment technologies
Four treatment strategies emerged as leading options
– All can achieve the draft MCL of 10 ppb
8
8
Reduction/
Coagulation
/Filtration
Weak-Base
Anion
Exchange
Reverse
Osmosis
Strong-Base
Anion
Exchange
with
Residuals
Treatment
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
Key deciding factors in technology selection10
Reduction/Coagulation/Filtration
• Similar to
conventional water
treatment with
coagulation and
filtration
• Different in the
addition of upstream
reduction using
ferrous iron
11
Reduction/Coagulation/Filtration12
FeIISO4 FeIII(OH)3
Cr(VI) Cr(III)
Reduction Coagulation Filtration
Reduction/Coagulation/Filtration13
Ferrous
iron
ReductionOxidation
of ferrous
with air or
chlorine
Treated
WaterRaw
Water
Filtration
(Polymer
if
granular
media)Backwash
Backwash
waste
RCF treatment demonstration14
City of Glendale, California
• 100 gpm
• Influent of 5 to 80 ppb
• Recycle or direct
disposal of backwash
water
• Variables:
reduction time
aeration
chlorination
filtration
Iterative New Technology Testing
Bench and Pilot of RCF
Demonstration of RCF
• 45 min. reduction
• Aeration
• 45 min. reduction
• Aeration
• Granular media
Demonstration of RCMF
• 45 min. reduction
• Aeration with chlorination
• Microfiltration
WaterRF 4450
• 10 min. reduction
• Higher Fe Dose
• Use of ACH
• Chlorination
Jar Testing
WaterRF 4423
• 5 min. reduction
• Higher Fe dose
• Chlorination
WaterRF 4445
• 5 min. reduction
• Higher Fe dose
• Chlorination
Reduction of Cr 6 to Cr 3
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
Ferrous
iron
ReductionOxidation
Treated
WaterRaw
Water
Filtration
(Polymer ) Backwash
Backwash
waste
Initial tests of less reduction time
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
0
1
2
3
4
5
6
7
8
9
10C
r(V
I) C
on
cen
trat
ion
(p
pb
)
Fe:Cr(VI) = 25:1w/ aeration45 min reduction
Fe:Cr(VI) = 25:1w/ aeration30 min reduction
Fe:Cr(VI) = 25:1w/ aeration15 min reduction
45 min 30 min 15 min
Reduction time
Ferrous
iron
ReductionOxidation
Treated
WaterRaw
Water
Filtration
(Polymer ) Backwash
Backwash
waste
Lower reduction time may be possible with higher
iron dose
Ferrous Dose, mg/L 1 2 1 2 1 2Cr(VI) reduction Time prior to Cl addition, min 1 1 5 5 15 15Cr(VI) 20 20 20 20 20 20
Jar 1 Jar 2 Jar 3 Jar 4 Jar 5 Jar 6Raw water
Cr(VI) 20 20 20 20 20 20Total Cr 20 20 20 20 20 20Iniitial pH 7.94 7.94 7.94 7.94 7.94 7.94adj. pH 7.71 7.71 7.72 7.72 7.72 7.72
Settled WaterTurbidity 1.21 1.61 1.36 2.33 0.99 1.47pH 7.65 7.69 7.43 7.48 7.62 7.62Ferrous residual 0.03 0.03 0.03 0.02 0.02 0.03Total Fe 1.04 1.41 1.02 1.33 0.95 0.97Chlorine 0.11 0.78 0.36 0.85 0.61 1.26After Reduction Cr(VI) 4 <0.05 2.1 <0.05 3.1 <0.05
0.8 um FilteredCr(VI) 5 0.39 2.2 <0.05 3.1 <0.05Total Cr 6.8 <0.5 3 <0.5 3.4 <0.5
0.1 um FilteredCr(VI) 5 0.46 2.2 0.06 3.1 <0.05Total Cr 5.8 <0.5 2.5 <0.5 3.9 <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
0
1
2
3
4
5
6
1 2 3 4 5 6
Cr6
Co
nce
ntr
atio
n (p
pb
)After Reduction
0.8 um Filtered
0.1 um Filtered
1 min 5 min 15 min
Ferrous = 1 mg/L
1 min 5 min 15 min
Ferrous = 2 mg/L
ND ND ND ND ND ND
Granular media filtration was demonstration tested
Ferrous
iron
ReductionOxidation
Treated
WaterRaw
Water
Filtration
(Polymer ) Backwash
Backwash
waste
Cr(VI) reduction and removal is reliable with RCF
Ferrous
iron
ReductionOxidation
Treated
WaterRaw
Water
Filtration
(Polymer ) Backwash
Backwash
waste
0
1
2
3
4
5
6
7
8
9
10
Chro
miu
m C
on
cen
trat
ion
(p
pb
)
Cr 6 Results
Low ppb levels of Cr 3 may get through granular
filters
Ferrous
iron
ReductionOxidation
Treated
WaterRaw
Water
Filtration
(Polymer ) Backwash
Backwash
waste
0
1
2
3
4
5
6
7
8
9
10Ch
rom
ium
Con
cent
rati
on (
ppb)
Total Cr Results
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
22
Chlorine can effectively oxidize ferrous iron without
significantly impacting Cr 3 conversion to Cr 6
0.1
2
0.0
92
0.0
76
0.0
93
0.0
94
0.0
25
0.1
7
0.0
35
0.0
54
0.0
23
<0.0
2
0.0
56
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
2.5 min2 mg/L iron
5 min2 mg/L iron
5 min2 mg/L iron (repeat)
10 min2 mg/L iron
15 min2 mg/L iron
5 min3 mg/L iron
Ch
lori
ne
Re
sid
ual
(m
g/L)
Hex
aval
en
t C
hro
miu
m (
pp
b)
Cr 6 Reduction by Ferrous Iron at Various Reduction Times with Chlorination (Bench-Scale Testing Results)
Cr(VI) in Reduced Water
Cr(VI) in Chlorinated Water
Free Chlorine Residual (after 3 min)
RCF – microfiltration testing24
24
Ferrous
iron
ReductionOxidation
Treated
WaterRaw
Water
Filtration
(Polymer ) Backwash
Backwash
waste
Microfiltration: Submerged and
Pressure
Microfiltration results25
0.2
0.2
<0.2
<0.2
<0.2
<0.2
<0.2
0.2
<0.2
<0.2
<0.2
<0.2
<0.2
0.7
0.3
<1 0.2
<0.2
<0.2
<0.2
0.2
0.2
<0.2
<0.2
<0.2
<0.2
<0.2
<0.2
0
20
40
60
80
100
0
10
20
30
40
50
606
/1
6/4
6/6
6/8
6/1
1
6/1
3
6/1
5
6/1
8
6/2
0
6/2
2
6/2
5
6/2
7
6/2
9
7/2
MF
Flu
x (g
fd)
Tota
l Ch
rom
ium
(pp
b)
SP-602 PALL Effluent
SP-604 GE Effluent
PALL Flux
GE Flux
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)
Cr(VI) Total Cr
Spiked TOC = 2.3 mg/L
Ambient TOC = 0.61 mg/L
PI: Issam Najm, Co-PI: Nicole Blute
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
RCF – residuals
Backwash water
• Disposal to sewer if possible
• Solids thickening and dewatering would yield
non-RCRA, California hazardous waste
• Potential for recycle
29
Spent Filter
Backwash
Water
Equali-
zation
Solids to
landfillThicken-
ing
De-
watering
Super-
natent
RCF – operational considerations
• Multiple chemical feeds
• Backwashing and possibly dewatering
• 3 to 5% of process flow
30
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%)
31
Estimated capital cost of treatment32
$0
$2,000,000
$4,000,000
$6,000,000
$8,000,000
$10,000,000
10 100 500 2,000
System Size (gpm)
RCF with recycle
RCF without recycle
WBA
Estimated O&M cost of treatment to achieve
a target of 10 ppb
33
$0.0
$0.4
$0.8
$1.2
$1.6
$2.0
10 100 500 2,000
O&
M C
ost
($ M
illio
ns)
System Size (gpm)
RCF with recycle
RCF without recycle
WBA
Estimated costs of treatment to achieve a target of
10 ppb in $/AF
a34
$0
$500
$1,000
$1,500
$2,000
$2,500
$3,000
$3,500
$4,000
10 100 500 2,000
An
nu
aliz
ed
Co
st ($
/AF)
System Size (gpm)
RCF with recycle
RCF without recycle
WBA
$13,493
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
Cost Estimating Tool
• As part of project #4450, a Cost Estimation Tool for
Cr(VI) Removal from Groundwater was developed
36
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
37
Acknowledgments38
Reference Materials
City of Glendale Final Report
(February 28, 2013)
Available on City website
39
Water Research Foundation
sponsored study – Guidelines for
Hexavalent Chromium Treatment
Studies, #4418
Available on WaterRF website
