EPA/600/2-91/011
April 1991
ARSENIC(III) AND ARSENIC(V) REMOVAL FROM
DRINKING WATER IN SAN YSIDRO, NEW MEXICO
by
Dennis Clifford and Chieh-Chien Lin
Department of Civil and Environmental Engineering
University of Houston
Houston, Texas 77004-4791
Cooperative Agreement No. CR-807939
Project Officer
Thomas J. Sorg
Drinking Water Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
The information is this document has been funded in pan by the United States
Environmental Protection Agency under Cooperative Research Agreement Number 807939 to
the University of Houston. It has been subjected to the Agency's peer and administrative
review and has been approved for publication as an EPA document. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
11
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if improperly
dealt with, can threaten both public health and the environment. The U.S. Environmental
Protection Agency is charged by Congress with protecting the Nation's land, air, and water
resources. Under a mandate of national environmental laws, the agency strives to
formulate and implement actions leading to a compatible balance between human activities
and the ability of natural systems to support and nurture life. These laws direct the EPA to
perform research to define our environmental problems, measure the impacts, and search
for solutions.
The Risk Reduction Engineering Laboratory is responsible for the planning,
implementing, and managing of research, development, and implementation programs to
provide an authoritative, defensible engineering basis in support of the policies, programs,
and regulations of the EPA with respect to drinking water, wastewater, pesticides, toxic
substances, solid and hazardous wastes, and Superfund-related activities. This publication
is one of the products of that research and provides a vital communication link between the
researcher and the user community.
Toxic arsenic in the forms of arsenite and arsenate is occasionally found in
groundwater used for drinking water supply. This report describes research on the
methods of removing arsenic from a community water supply to protect the public health.
Successful central treatment processes for combined arsenite and arsenate removal include
adsorption onto activated alumina, and reverse osmosis hyperfiltration. In-home treatment
devices utilizing reverse osmosis hyperfiltration were also tested and found to be effective.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
iii
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ABSTRACT
The removal of a natural mixture of As(III) (25-39 ^ig/L) and As(V) (49-65 ^ig/L)
from groundwater high in total dissolved solids (TDS), and also containing fluoride (2.0
mg/L) was studied in San Ysidro, New Mexico using the University of Houston/U.S. EPA
Mobile Drinking Water Treatment Research Facility. The raw water in this study was
deliberately unchlorinated so as not to oxidize the As(ni) present. The mean concentration
of total arsenic in the San Ysidro water during this study was 89 ^ig/L.
This is a companion study to two other EPA-funded arsenic removal pilot studies--
Fallon, Nevada and Hanford, California where As(V) removal was studied following
chlorination of the raw water. The original objectives of this study were to establish cost-
effective means of removing As(III), As(V) and fluoride from this and similar waters.
When Maximum contaminant level (MCL) for fluoride was set at 4.0 mg/L, the fluoride-
removal objective was dropped.
Arsenic adsorption onto fine-mesh (28 x 48) activated alumina gave better-than-
expected results in view of the knowledge that As(IIl) is known to be poorly retained on
alumina. Approximately 9000 bed volumes (BV) could be treated at pH 6 before the
arsenic MCL (0.05 mg/L) was reached. At the natural pH of 7.2, however, only 1900 BV
could be treated before exceeding the MCL of 0.05 mg/L. Approximately 70% of the
adsorbed arsenic was recoverable by cocurrent regeneration with 6.5 BV of 4% NaOH, but
after two regenerations, the column capacity was reduced to 72% of its virgin performance.
Coarser, 12 x 28 mesh, alumina did not perform as well in adsorption or regeneration. The
spent alumina regenerant was treated by lowering its pH to 8,5 and quantitatively
coprecipitating the arsenic with the bulk Al(OH)3 precipitate. The sludge produced was not
hazardous as determined by the EP toxicity test. Analyses of the spent regenerant solution
showed that unavoidable oxidation of the As(lII) to As(V) occurred on the alumina which
helps to explain its better-than-expected column performance.
Reverse Osmosis (RO) treatment with either a cellulose triacetate or polyamide
hollow fiber membrane resulted in >97% arsenic removal and >94% TDS removal.
Electrodialysis (ED) removed 73% of the arsenic and was able to meet the arsenic MCL on
the City Water containing 89 ^ig/L total arsenic but only removed 28% of the As(III) from a
new well containing 100% As(III) at a level of 230 mg/L.
Chloride-form anion exchange also performed better-than-expected but not well
enough for it to be considered seriously for treatment. About 200 BV could be treated
before the arsenic MCL was reached. Point-of-use RO treatment with a thin film composite
membrane was effective in removing >91% of the arsenic and >94% of the TDS at low (3-
12%) water recovery.
Due to the small size (70 dwellings) of the community, the difficulty of central
treatment, and the poor water quality, San Ysidro was chosen by EPA as a test community
for point-of-use RO treatment. That study showed point-of-use RO treatment to be a viable
alternative to central treatment.
This report was submitted in fulfillment of cooperative research agreement number
807939 by the University of Houston under the partial sponsorship of the U. S.
Environmental Protection Agency. The report covers the period from March, 1984 to
October, 1984, and work was completed as of December, 1984.
iv
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CONTENTS
Disclaimer ii
Forward iii
Abstract iv
Contents v
Figures vi
Tables ix
Abbreviations and Symbols xi
Acknowledgement xiii
1. Introduction 1
The San Ysidro arsenic problem ; 1
Lime softening tests on Well No. 4 3
Mobile inorganics pilot plant 4
Hazardous waste disposal considerations 4
2. Conclusions 7
3. Recommendations 10
4. Experimental Details 11
Overview of arsenic removal experiments 11
Analytical Methods 14
Quality Assurance 16
Electrodialysis apparatus and procedures 16
Reverse Osmosis appararus and procedures 18
Alumina apparatus and procedures 18
Ion exchange appararus and procedures 20
Ferric ion precipitation tests 20
Arsenic sludge disposal tests 20
EP Toxicity test procedure for Al(OH)3 sludge ,23
5. Results and Discussion 24
San Ysidro water quality 24
Arsenic(UI) oxidation 25
Desalting process results 27
Cellulose triacetate membrane RO results 29
Polyarrude membrane RO results 29
Activated alumina results 33
Ion exchange results 53
Point-of-Use RO Treatment 57
6. References 60
7. Appendices 62
Appendix A—Analytical Procedures 62
Appendix B--Equipment Specifications 67
Appendix C--Activated Alumina Runs 80
Appendix D—Ion Exchange Runs 93
Appendix E—Correspondence 98
v
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LIST OF FIGURES
No. Page
1 Mobile research concept including transportable pilot
plant/laboratory, travel trailer, and pickup truck 5
2 Interior layout of UH/EPA drinking water treatment research facility 6
3 Flow diagram for the reversible electrodialysis (ED) system 17
4 Flow diagram for the reverse osmosis (RO) system 19
5 Flow schematic for the activated alumina (AA1) system 21
6 Flow schematic for the ion exchange (IX) system 22
7 Results of EDR Run No. 1 28
8 Results of RO Run No. 1, DOW HF CTA 30
9 Results of RO Run No. 2, DuPont HF PA 31
10 Breakthrough curves for fluoride and arsenic from 28 x 48 mesh
activated alumina columns, Run No. 2 34
11 Comparison of As(lII) and As(V) breakthrough curves on
synthetic water 38
12 Comparison of arsenic breakthrough curves for coarse- and fine-
mesh aluminas 39
13 Comparison of fluoride breakthrough curves for coarse- and fine-
mesh aluminas 40
14 Fluoride and arsenic elulion curves during Run 2 R, regeneration of fine-mesh
alumina following exhaustion Run No. 2 43
15 Relative % arsenic or fluoride recovery as a function of quantity
of NaOH regenerant 44
16 Comparison of arsenic recovery efficiencies of 1% and 4% NaOH
for regeneration of fine- and coarse-mesh aluminas 46
17 Effect of cocurrent regenerations on fluoride breakthrough curves
for fine-mesh aluminas 48
18 Effect of cocurrent regenerations on the arsenic breakthrough curves
for coarse-mesh aluminas 49
19 Effect of cocurrent regeneration on the arsenic breakthrough curves
for fine-mesh aluminas 50
v i
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LIST OF FIGURES (Continued)
No. Page
20 Results of IX Run No. 2, effluent concentration histories for arsenic,
fluoride, bicarbonate and pH from a chloride-form strong-based
anion resin, Dowex 11 54
21 Arsenic and fluoride elution during a typical ion exchange
regeneration with 6% (1.0 N) NaCl 58
APPENDIX FIGURES
B1 Interna] flow schematic for the Ionics Aquamite 1 EDR unit 67
CI Fluoride and arsenic breakthrough curves for alumina Run No. 1 80
C2 Fluoride and arsenic elution curves for regeneration Run No. 1R 81
C3 Fluoride and arsenic breakthrough curves for Run No. 3 82
C4 Fluoride and arsenic elution curves for regeneration Run No. 3R 83
C5 Fluoride and arsenic breakthrough curves for alumina Run No. 4 84
C6 Fluoride and arsenic elution curves for regeneration Run No. 4R 85
C7 Fluoride and arsenic breakthrough curves for alumina Run No. 5 86
C8 Fluoride and arsenic elution curves for regeneration Run No. 5R 87
C9 Fluoride and arsenic breakthrough curves for alumina Run No. 6 88
CIO Fluoride and arsenic elution curves for regeneration Run No. 6R 89
CI 1 Fluoride and arsenic breakthrough curves for alumina Run No. 7 90
C12 Fluoride and arsenic elution curves for regeneration Run No. 7R 91
CI3 Breakthrough curve for arsenic during Run No. 8 92
D1 Breakthrough curves for ion-exchange Run No. 1 93
D2 Ion exchange Run No. 1-expanded 94
D3 Fluoride and arsenic elution curves for Run No. 2 95
D4 Breakthrough curves for ion-exchange Run No. 3 96
D5 Ion exchange Run No. 3--expanded 97
v ii
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LIST OF TABLES
No. Page
1 Historical arsenic and fluoride data for city water 1
2 Chemical analyses of test wells in San Ysidro, N"M 3
3 Chronological list of San Ysidro experiments 11
4 List of analytical methods used in the San Ysidro arsenic study. 15
5 Quality assurance results 16
6 Raw water analyses in San Ysidro, NM 24
7 Arsenic(III) and Arsenic(V) concentrations in San Ysidro city water 26
8 Electrodialysis (ED) performance data on City Water 27
9 Dow HF CTA RO performance data 29 ..
10 DuPont HF PA RO performance data 32-
11 Summary of EDR and RO results on San Ysidro City Water 32
12 Summary of activated alumina results 35
13 Comparison of fluoride and arsenic run lengths using alumina 35
14 Background water analyses for Figures 11 and 12 36
15 Comparison of laboratory and Field data for fluoride and arsenic
removal 36
16 Changes in adsorption capacity as a function of pH and arsenic
concentration 41
17 Activated alumina regeneration summary 41
18 Relative percent recoveries of fluoride and arsenic using 3.0 equiv.
NaOH/L alumina 45
19 Reduction in alumina's arsenic removal capacity with regeneration 51
20 Arsenic coprecipitation with Al(OH)3 52
21 Arsenic coprecipitation with Fe(OH)3 from natural Fe present 53
22 Summary of chloride-form anion exchange results in San Ysidro, NM 55
23 Arsenic composition of effluent and feed for ion exchange Run No. 2 56
Vlll
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LIST OF TABLES (Continued)
No. Page
24 Results of point-of-use reverse osmosis pilot test 59
APPENDIX
A1 Laboratory experimental analysis -- Twining Laboratories 64
A2 On-Site analysis--Twining Laboratories 65
B1 Reversible electrodialysis system specifications 68
B2 Reverse osmosis system specifications 69
B3 DuPont RO projections for City Water 70
B4 DuPont RO projections for Well No. 4 water 72
B5 Dow RO projections for City Water 74
B6 Dow Ro projections for Well No. 4 water 77
IX
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ABBREVIATIONS AND SYMBOLS
AA1 — activated alumina, Alcoa F-l in this study
As — arsenic, also referred to as As(Tot), i.e., totaJ arsenic including As(III) and As(V)
As(ffl) -- crivalent arsenic, i.e., arsenite (HjAsO^ or arsenious acid (H3As03) with
pKa = 9.2
As(V) — pentavalent arsenic, i.e., arsenate (HjAsOj, HAsO^or AsO^") or
arsenic acid with pKa values of 2.2, 7.1 and 11.5
BV — bed volume, i.e., the volume including voids occupied by an adsorbent in a
column, or an equal volume of solution passed through the column
C -- concentration, mg/L, meq/L or |ig/L
CQ -- initial concentration or conc. at process inlet
C-l — column No. 1
CTA -- cellulose triacetate
d — days
EBCT -- empty bed contact time, min.
ED — electrodialysis, the general process description
EDR — electrodialysis with current reversal, all ED in this study was EDR
EDTA -- ethylenediaminetetraacetate, a chelating agent
eff — effluent
EP - Extraction Procedure, the standard EPA test procedure to establish lo toxicity of a
sludge
EPA — U.S. Environmental Protection Agency
F' — fluoride ion
F-1 — the grade or designation of the Alcoa activated alumina used in these tests
g -- grams
GAC -- granular activated carbon
GFAAS -- graphite furnace atomic absorption spectroscopy
HF -- hollow fiber, in reference to an RO membrane
HPIC -- high pressure ion chromatography
hr -- hours
IC -- ion chromatography
ICP AES -- inductively coupled plasma atomic emission spectroscopy
IX -- ion exchange
kPa -- kilopascals
kg - kilogram
L -- liters
x
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m -- molar, one gram mol/L
m3 — cubic meters
MCL - maximum contaminant level
mg — milligrams
meq — milliequivalents
mL — milliliters
min — minutes
mol — mole, one gram molecular weight
N -- normal, one gram equiv/L
P -- pressure, psig or kPa
PA — polyamide, in reference to an RO membrane
P-E — Perkin Elmer
mg/L — parts per million or mg/kg, a concentration unit equivalent to mg/L when the
solution density is 1.00
jig/L - parts per billion or Hg/kg, a concentration unit equivalent to ng/L when the
solution density is 1.00
ppt — precipitation or precipitate
P-l — pump No. 1
Qi - volumetric flow of i-th stream, LVmin
R — suffix designating a regeneration, Run No. 1R
regen — regeneration or regenerated
RO -- reverse osmosis
RO-1 -- RO module No. 1. DuPont HF PA
RO-2 — RO module No. 2, Dow HF CTA
SDI — silt density index
T-Alk — total alkalinity, mg/L as CaC03
TDS - total dissolved solids, mg/L
T-Hard -- total hardness, mg/L as CaC03
T-l -- tank No. 1
V-l — valve No. 1
V -- volume, m3 or L
p. — micro
(ig — micrograms
jiS — microSiemens, conductivity unit equivalent to ^.mho/cm
jimho -- micromho, 10"6 reciprocal ohms
XI
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ACKNOWLEDGEMENTS
We arc sincerely grateful to Mr. Tom Sorg, the U.S. EPA project officer, for his many
helpful suggestions regarding this study, and his continuing support during this and related
studies.
We appreciate and gratefully acknowledge the cooperation given to us by Mayor Robert
Garcia and Ms. Barbara Trujillo of the city of San Ysidro, and Mr. Walter Webster and his co-
workers at Leedshill-Herkenhoff Inc.--the city of San Ysidro's engineering consultants.
We thank the many persons in the state of New Mexico Environmental Improvement
Division who cooperated with this study by providing historical analytical data and information
on discharge permits and hazardous waste disposal.
We acknowledge the skillful typing of this report by Ms. LanChi Tram, Ms. Tam Ngo
and Ms. Linda Faircloth.
xii
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INTRODUCTION
THE SAN YSIDRO ARSENIC PROBLEM
San Ysidro, NM is a small community of 67 dwellings located 50 miles northwest of
Albuquerque. The current water supply, a 12 ft deep infiltration gallery, is inadequate in
quantity during the summer months and exceeds, year around, the U.S. EPA maximum
contaminant level (MCL) of 0.05 mg/L for arsenic. It also contains 2.0 mg/L of fluoride which
at the rime of this study also exceeded the old 1.4 mg/L MCL. Additionally, this "City Water"
has high levels of total dissolved solids (TDS = 810 mg/L), hardness (282 mg/L) and alkalinity
(468 mg/L). Historical arsenic and fluoride data from the State of New Mexico files are
presented in Table 1 along with values foT the inorganic contaminants which do not exceed
their MCL's. During the six-year period summarized, the mean arsenic concentration was
0.074 mg/L while fluoride ranged from 1.56 to 3.04 mg/L.
In an effort to obtain an adequate quantity of arsenic-free wateT, three test wells,
ranging in depth from 44 to 128 ft, were drilled in 1982. Unfortunately, these new wells
contained much higher levels of arsenic, fluoride, dissolved solids, iron, sulfate, chloride and
manganese :han the existing City Water from the shallow infiltration gallery. The State of New
Mexico anaiyses for these test wells are summarized in Table 2. As can be seen in the table,
the water quality deteriorated with depth. Therefore, what little research we did on these wells
was done on the shallowest (44 ft) one.
Not only do the new wells contain two to four times the arsenic levels found in the City
Water, but also our subsequent arsenic speciation tests revealed that they contain 100%
trivalent arsenic while the City WateT is more aerobic in nature and contains only 40% trivalent
arsenic. The significance of the speciation is that trivalent arsenic, i.e., arsenite or As(III), is
considered to be as much as 60 times as toxic as pentavalent arsenic, i.e., arsenate or As(V)
[1].
TABLE I. HISTORICAL ARSENIC AND FLUORIDE DATA
FOR SAN YSIDRO CITY WATER
Collection Arsenic Fluoride Others
Date mg/L mg/L mg/L
9-08-75
0.084
1.56
4-08-76
0.10
Boron 1.36
8-05-76
0.06
Boron 0.44
2-07-77
0.025
Se 0.006
3-21-77
0.02
8-05-77
0.06
2-28-78
0.08
1.55
Ba 0.28, Cd <0.001, Pb <0.005, Hg 0.002,
Cr <0.005, Ag <0.001, and Se <0.001
5-16-78
0.082
5-26-78
0.092
(continued)
1
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TABLE 1. (continued)
Collection Arsenic Fluoride Others
Date rog/L mg/L
5-31-78 0.083
6-27-78 0.041
11-14-78 0.101 Pb 0.039
1-29-79 0.054
6-21-79 0.095
8-02-79 0.067
1-03-80 0.081
1-08-80 0.087
1-29-80 0.088
12-11-80 0.069 (repeat analysis with identical results)
12-11-80 0.017 (repeat analysis with identical results)
12-21-80 0.092
2-03-81 0.078
2-03-81 0.103
6-29-81 0.075 3.04 N03-N 0.25, Ba <0.10, Cd <0.001, Cr <0.005,
Pb <0.005, Hg <0.0005, Se <0.005, and
Ag <0.001
8-10-81 3.14 (no arsenic analysis)
10-07-81 2.59 (no arsenic analysis)
11-11-8 1 2.35 (no arsenic analysis)
* All analyses by State of New Mexico ELA Laboratory.
t For arsenic: mean = 0.074 mg/L, std dev = 0.023 mg/L.
§ Samples are from various locations in the distribution system.
i The City Water source is a 12-ft deep infiltration gallery.
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TABLE 2. CHEMICAL ANALYSES OF TEST WELLS IN SAN YSIDRO,
NEW MEXICO
Contaminant
Well No. 4
Well No. 2
Well No. 1
44 ft
100 ft
128 ft
Arsenic
0.163
0.235
0.235
Fluoride
5.22
6.60
5.18
Iron
2.50
7.2
8.9
Sulfate
120.0
367.0
371.0
Chloride
289.0
864.0
1257.0
Manganese
0.32
0.68
* All values in mg/L
t All analyses by State of New Mexico EIA Laboratory
§ All ihree wells were drilled within a 5 foot radius, and are located behind the San Ysidro
City Hall.
LIME SOFTENING TESTS ON WELL NO. 4
Neptune Microfloc Corp. of Corvallis, Oregon performed a pilot study of arsenic and
fluoride removal from Well No. 4 water in San Ysidro in July,'1983. In the study they used a
combined lime-softening, crossflow filtration device called a HYDROPERM unit. The theory
behind the operation of the unit is that: (a) lime ((CaOH)2) is added to precipitate CaC03,
thereby reducing hardness and alkalinity; (b) lime and magnesium sulfate are added to
precipitate both magnesium hydroxide (Mg(OH)2) and CaC03; and (c) the gelatinous
Mg(OH)2 floe adsorbs both fluoride and arsenate. Thus, if the arsenite is first oxidized to
arsenate using chlorine, the HYDROPERM process should theoretically reduce the TDS,
hardness, alkalinity, arsenic, fluoride, iron, and manganese levels.
Their tests indicated that reductions in all these contaminants did indeed occur. However, to
reduce the arsenic from 0.22 mg/L to 0.03 mg/L required enormous chemical dosages: 900
mg/L MgS04*H2O, 750 mg/L Ca(OH)2 and 3 mg/L Cl2. Fluoride was still relatively high at
2.8 mg/L, and the TDS reduction was only slight. Even without reducing the product water
pH down from 10.4, the capital plus operating costs were estimated at $1.74/1000 gallons.
These costs were for a 100 gpm unit operated 8 hours/day, and arsenic sludge disposal costs
were not included. Clearly the HYDROPERM was not a feasible treatment alternative. In this
range of treatment costs, reverse osmosis (RO) and (ED) electrodialysis would be economically
competitive and yield a much superior product water.
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MOBILE INORGANICS PILOT PLANT
Part of our original plan in moving the UH/EPA Mobile Drinking Water Treatment
Research Facility to San Ysidro was to attempt treatment of both the City Water and the best of
the new test wells, Well No. 4, because of their differing levels of arsenic, fluoride and iron.
This unit, also called the Mobile Inorganics Removal Pilot Plant, is shown in Figures 1 and 2.
After much consideration, however, a decision was made to work almost exclusively with the
existing City Water supply. Any feasible treatment scheme for Well No. 4 would have been
too complicated and too expensive to be operated successfully in such a small community
where money and skilled labor are in short supply.
HAZARDOUS WASTE DISPOSAL CONSIDERATIONS
The alumina adsorption, electrodialysis, reverse osmosis, and ion exchange processes
were studied in San Ysidro without oxidative pretreatment of the raw water, i.e., the treatment
processes were fed the natural mixture of As(III) and As(IV). We chose to perform the
alumina adsorption and ion exchange tests in lab scale (1-inch diameter) columns rather than in
the 8- or 10-inch diameter pilot-scale columns. Use of these smaller columns, several of which
could be run simultaneously, was begun in Scottsdale, Arizona where an ion-exchange run
could last as long as 120 days. Therefore, running one large column at a time, which is all the
pilot-scale design allows, would have taken several years to complete all the required tests.
The high quality of the Scottsdale 1-inch column data in terms of its contaminant leakage and
breakthrough curves compared to the 10-inch diameter columns prompted their use in San
Ysidro but for different reasons. Here the small columns were required so as to minimize the
production of arsenic-contaminated sludges from alumina and ion-exchange regeneration. This
was done to avoid having to stockpile 55-gallon drums of spent regenerant solutions for later
treatment to precipitate the arsenic with Al(OH)3(s) followed by filtration and subsequent
disposal of filtrate and sludge.
The ion-exchange regeneration in San Ysidro yielded spent regenerant salt solutions
containing less than 2.0 mg/L arsenic and therefore were also considered non-hazardous
wastes since they were below 5.0 mg/L arsenic.
Prior to the determination that we would not be producing hazardous wastes in San
Ysidro, we corresponded with State of New Mexico officials who in tum made inquiries of
Federal officials regarding our need to obtain hazardous waste permits to operate in San
Ysidro. In the final analysis no permits or discharge plans were required because we did not
create significant quantities of arsenic-contaminated sludges. One hundred and seventy grams
of arsenic-containing Al(OH)3 sludges were eventually filtered, dried and stored for future
study in the pilot plant. Also, because the desalting processes simply separate groundwater
into product and brine streams which were recombined for surface discharge into a nearby
arroyo, no discharge permits were required. Sanitary wastes from the living trailer were
disposed of in the septic-tank, tile-field system.
4
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WASTEWATER-
TELEPHONE —
RAN WATER-
220V, 100 A-
r
L
FIELD RESEARCHER
LIVING QUARTERS
Located adjacent to the research trailer in
San Ysidro, New Mexico
II
31' TRAVEL TRAILER
a
I TON PICK-UP TRUCK
WATER TREATMENT PILOT PLANT
RO, IX, EOR, AAJ, PUMPS, CONTROL PANEL,
CHEM STORAGE AND PREP., WATER a
WASTEWATER TANKS, PRETREATMENT SYS.,
WORKSHOP, TOOLS, SPARE PARTS, SAFETY
SHOWER, EYE WASH, FIRE EXT.
OFFICE
AND
ANALYTICAL LAB
pH, ^.mho, TDS, JTU
SOI, F", NOj ,CT , AS
TH, Alk, SOj", Si02
10*40'
RESEARCH TRAILER
Figure 1. . Mobile research concept including transportable pilot plant/
laboratory, travel trailer, and pickup truck.
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AIR- CONDITIONING
AND
DRYING RACK ABOVE SINK
LABORATORY BENCHES
FILE CABINET
EXHAUST MOOD
H ADJUST TANK
MIOUL N)
ELCCTRODlAl YSlS UNIT
DEFP BED FILTER
AUTO SAMPl FH
yL OW ME T ERS
sampling vessel
DISTILLATION
UNIT
ACK) TANK
CONTROL PANfc I
BOV
STORAGE
CARINE T
PH ADJUST
PUMP
KCASE
NOOW
f
s
STORAGE
CABINE T
STORAGE SHFlVES
TRfcATED WATER PUMI
AND
WASTEWATER PUMP
WORK BENCHES
UTILITY SINK
STORAGE
CABINE T
ACID PUMP
AND
BASE PUMP
LAB ENTRANCE
DESK
STORAGE COMPARTMENT
TREATED WATER
AND
WASTEWATER TANKS
(300 GAL EACH)
REAR DOOR
FEED WATER PUMP
PILOT plant entrance
POWER PANELS
EIFCTRICAL SERVICE
Figure 2. Interior layout of the UH/EPA Drinking Water Treatment Research
Facility. While in San Ysidro, NM and ilanford, CA, the graphite
furnace atomic absorption spect rophotoinerer (GFAA) was located
under the exhaust hood.
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CONCLUSIONS
The existing San Ysidro city water containing 810 mg/L TDS, 282 mg/L CaC03
hardness, 190 mg/L sodium and contaminated with 57 ^g/L As(V), 31 \ig!L As(III) and
2.0 mg/L fluoride can be successfully treated for arsenic removal by means of activated
alumina adsorption, reverse osmosis and possibly electrodialysis. The first two treatment
methods can be applied either in central treatment or at the point of use. Pre-oxidation using
chlorine to convert As(III) to As(V) will definitely aid in the removal of arsenic but is not
essential. Since the MCL for fluoride has been set at 4.0 mg/L, fluoride removal is no longer a
problem.
The best new San Ysidro well (No. 4) has water of such poor quality that its treatment
should not be considered. Its major troublesome contaminants are 1400 mg/L TDS, 230 |ig/L
As(III), 6.6 mg/L F" and 2.0 mg/L Fe. Desalting using ED or RO preceded by extensive
pretreatment would be technically feasible but too costly.
Although one objective of the San Ysidro experiments was to avoid raw water
oxidation and study the removal of both As(IlI) and As(V), significant oxidation appears to
have occurred in aJl the processes tested and consequently beter-than-expected removal of
arsenic occurred in all cases.
Electrodialysis with no pretreatment except cartridge filtration reduced the city water
arsenic by 73% from 85 down to 23 tig/L while reducing the TDS by 72%. Electrodialysis-
was not effective, however, in removing As(III) from the anaerobic Well No. 4 water. There
arsenic was only reduced by 28%, from 188 Hg/L down to 136 |ig/L. Any installation of ED
for arsenic removal should include chlorine (or equivalent) oxidation of As(III) to As(V).
Calcium carbonate scaling of the reversible ED membranes did occur but was easily removed
by acid cleaning.
Both the cellulose triacetate (CTA) and the polyamide (PA) hollow fiber RO membranes
did an excellent job, 99% and >99% removal, respectively, in removing arsenic from the city
water without prechlorination to convert As(Ill) to As(V). Greater than 94% TDS and fluoride
removal were also obtained. For all contaminants, the PA membrane performance was
superior. Thus, RO with pretreatment consisting of sodium hexamethaphosphate addition,
cartridge filtration and possible pH adjustment to 6.0 is a technically effective, but costly,
means of creating the San Ysidro city water. About 25% of the raw water could be bypassed
and then blended with the RO product water to provide a stable water for distribution thereby
reducing the treatment costs.
About 8800 bed volumes of pH 6, unchlorinated San Ysidro city water could be
continuously passed through a virgin fine mesh (28 x 48) activated alumina column before the
arsenic MCL was reached. This is intermediate between the short run of 300 BV obtained
from laboratory studies on a simulated water containing 100 ng/L As(III) and the long (23,400
BV) run for a simulated water containing 100 ug/L As(V). Coarse (14 x 28) mesh alumina did
not perform as well on the San Ysidro water. Under similar conditions a run length of 6800
BV was obtained for the coarse alumina.
In all the activated alumina tests, fluoride broke through long before arsenic. For
example, using the fine-mesh alumina at pH 6, fluoride reached the interim MCL of 1.4 mg/L
at 2500 BV while arsenic did not reach its 0.05 mg/L MCL until 8800 BV. Even though
fluoride was driven off the alumina by the more-preferred arsenic, the fluoride elution peak
was not large. The highest fluoride concentration observed in the alumina column effluent was
7
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2.4 mg/L while the feed was 1.9 mg/L. Therefore, the revised fluoride MCL of 4.0 mg/L
would not be exceeded during an alumina run to the arsenic MCL.
Feedwater pH was the most significant variable in activated alumina treatment for
arsenic removal. At the natural pH of 7.3, only 1900 BV could be treated prior to the arsenic
MCL compared to 8800 BV at pH 6.
Partial regeneration of the arsenic spent alumina is possible. When using a
considerable excess, 6.7 BV of 4% (1.0 N) NaOH, 63% of the adsorbed arsenic was eluted
during a cocurrent (downflow) regeneration of spent, fine-mesh alumina. A larger volume of
more dilute NaOH was also effective in partially regenerating the alumina. Cocurrent
regeneration with 15-19 BV of 1% (0.25 N) NaOH recovered 67-70% of the adsorbed arsenic.
Countercurrent upflow regenerations were not attempted in San Ysidro but would probably
have been more effective assuming that channeling was avoided and adequate flow distribution
was achieved. Also, in practice, lesser volumes of regenerant could be used followed by a
displacement rinse with raw water to conserve regenerant.
Even with these excessive regenerations, a maximum of 70% of the adsorbed arsenic
was recovered, and subsequent runs to arsenic breakthrough were shorter than with virgin
alumina. During the third exhaustion cycle the run lengths were reduced to 72% and 66% of
the virgin capacity respectively for the fine- and coarse-mesh aluminas.
A material balance on the arsenic adsorbed and eluted from the alumina indicated that
34% of the As(III) fed to the column was adsorbed, and 65% of the As(III) adsorbed was
eventually oxidized to As(V) on the alumina. Only a small percentage (8.6%) of the arsenic in
the spent regenerant solution was As(lll).
99.8% of the As(V) and 36% of the As(III) in the spent NaOH regenerant solution
were removed by coprecipitation with the Al(OH)3 produced when the spent regenerant
solution was acidified to pH 6.5 using HC1. The total arsenic remaining in solution after
precipitation was 0.92 mg/L consisting of 97% As(III).
The arsenic-contaminated A](OH)3 sludge resulting from the pH 6.5 precipitation
procedure on the dilute (1% NaOH) regenerant was 12% of the solution volume after 24-hr
settling. The dried sludge (7.8 g/L of spent regenerant) was subjected to the U.S. EPA
extraction procedure (EP) toxicity test and easily passed. Even though the sludge contained
As(IIl), the final leachate arsenic concentration was 0.6 mg/L, i.e., far below the 5.0 mg/L
limit for classification as a toxic waste.
Attempts were made to coprecipitate the arsenic from the city water with the Fe(OH)3(s)
resulting from chlorine oxidation of the Fe(II) originally present. This failed because of the
low (0.06 mg/L) iron content of the city water. The arsenic content (200 Mg/L) of the Well No.
4, containing 2.0 mg/L Fe(II), was, however, reduced 69% by this procedure.
Even though the city water contained 40% As(III) which is non-ionic at the natural pH
of 7.2, ion-exchange with chloride-form strong-base resins worked reasonably well in
reducing the total arsenic concentration. 160-220 BV could be treated before the arsenic MCL
was reached. Arsenic leakage, primarily As(III), was substantial, however, and the runs were
too short to seriously consider ion exchange as a treatment method. (Chlorine oxidation of the
As(IlI) would probably increase the run lengths to 500 BV.) Fortunately, due to the high TDS
of the raw water, the effluent arsenic concentration did not exceed the influent concentration
when it broke through. Finally, fluoride broke through almost immediately (4-18 BV) but was
also subject to significant peaking.
8
-------
A point-of-use (POU) reverse osmosis (RO) system containing a thin-film-composite
(TFC) membrane achieved 91% removal of arsenic and 95% reduction in TDS. The arsenic
removal appeared to increase with time.
Although coarse-mesh alumina is nearly as good as the fine-mesh variety for fluoride
removal, it is particularly important to use a fine-mesh (28 x 48) activated alumina for arsenic
removal. The coarse-mesh alumina was exhausted much sooner and was much more difficult
to regenerate.
9
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RECOMMENDATIONS
Although these results for activated alumina indicate a beter-than-expected removal of a
natural mixture of As(HI) and As(V), future pilot studies and central municipal arsenic removal
installation should always include chlorine or alternative means of oxidarion of As(III) to
As(V).
San Ysidro, a small, Temote community of 67 families should be considered as a test
site for evaluation of point-of-use (POU) treatment using reverse osmosis and possibly
activated alumina adsorption. In this case no cental pretreatment needs to be provided and the
water need not be chlorinated to oxidize As(IH). The objecdves of the POU RO study would
be to determine the actual operating costs and evaluate the long term (e.g., 2 years)
effectiveness of treatment by monitoring all the units installed forTDS (conductivity), arsenic,
product water flow rate, and membrane life. Occasional samples are also recommended for
bacterial monitoring, and all system maintenance requirements should be carefully recorded.
Point-of-use testing of activated alumina at San Ysidro or a similar community with a
natural mixture of As(III)/As(V) and moderate, i.e., <4 mg/L fluoride contamination is
recommended now that the fluoride MCL has been set at 4.0 mg/L. Even without chlorinarion
of the feedwater, POU devices should operate much longer than was observed in these studies,
before the arsenic MCL is reached. This is because of the intermittent nature of operation of
POU systems. The "off' (no flow) periods will provide time for oxidation of As(III) and
relaxation of the solid-phase concentration gradient which will result in improved adsorption
during the "on" periods.
Countercurrent (upflow) regeneration of arsenic-spent alumina should be studied on a
pilot or full-scale using a relatively concentrated (e.g., 4%) NaOH solution. The objective of
such a study would be to determine if countercurrent regeneration alone (i.e., not
countercurrent followed by cocurrent) can eliminate or reduce the earlier leakage which was
observed following cocurrent regeneration.
10
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EXPERIMENTAL DETAILS
OVERVIEW OF THE SAN YSIDRO ARSENIC REMOVAL EXPERIMENTS
The basic objective of the San Ysidro arsenic removal experiments was to develop a
simple cost-effective way to remove the arsenic from the city water, after having decided that
the new wells were too difficult to treat. A few experiments were, however, performed using;
Well No. 4 for comparison. Because an extensive study of Arsenic(ni) oxidation was planned
in Hanford, CA, oxidative pretxeatment using chlorine was not studied in San Ysidro. A
chronological list of the San Ysidro experiments is presented in Table 3.
Arsenic(V) is easily removed from water even in the presence of high TDS and strongly
competitive ions like fluoride [Singh and Clifford, 1981; Rosenblum and Clifford, 1984], It
was of particular interest to study the removal of natural mixtures of As(III) and As(V) by
activated alumina since this had not been studied previously. Also of interest was any
unplanned oxidation of arsenic(III) which might occur in the adsorption columns. The
optimum pH for the adsorption of arsenic and fluoride is known to occur in the 5.5 to 6.0
range, therefore a pH of 6.0 was fixed for most of the alumina runs. Because adsorption onto
alumina is known to be a kinetically controlled process, the two common mesh sizes (14 x 28
and 28 x 48) of Alcoa F1 alumina were used for comparison. Finally, two concentrations of
the NaOH regenerant were used to determine which was most economical in terms of the mass
of arsenic removed/mass of NaOH applied.
Fox [19791 and Sorg [19811 have shown that arsenic is well removed by RO
membranes, but the percent removals of arsenite, a non-ionic species at neutral and acidic pH,
varied widely (43-81%). Arsenate, on the other hand, typically showed greater that 97%
rejection. This is not unexpected since arsenate exists predominantly as a large anion at pH's
above about 3.0. Thus, it was of interest to study the removal of a mixture of As(III) and
As(V) using polyamide (PA), cellulose triacetate (CTA) and thin-film composite (TFC)
membranes. TFC membrane performance was studied using a Culligan Point of Use RO
system. Reverse osmosis was of particular interest because of the high TDS of the water and
the presence of multiple contaminants.
TABLE 3. CHRONOLOGICAL LIST OF SAN YSIDRO
EXPERIMENTS
Run/(Date)
(1984) Description
EDR Run
(Preliminary)
(March, 1984)
EDR Run 1
(March 12-17)
RO Run 1
(April 1-9)
Well No. 4 feed, no chemical pretreatment, feed pH 7.1, product flow
1450 L/day, 80% recovery. Preliminary run to determine As(III) passage
(it passes-90%).
City water, no chemical pretreatment, feed pH 7.1, product flow 1450
L/day, 81 % recovery. Objectives: to determine % rejections and fouling.
DOW HF CTA, pH 6.3, 10 mg/L SHMP, product flow 11700 L/day,
50% recovery. Objectives: to determine % rejections and fouling.
(continued)
11
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TABLE 3. (continued)
Run /(Date) Description
(1984)
AA1 Run 1 12 x 28 mesh, pH 6.0, EBCT 5 min. Objectives: to determine F" and As
(4/12-5/3) breakthroughs.
AA1 Run 2 28 x 48 mesh, pH 6.0, EBCT 5 min. Objectives: to compare
(4/12 - 5/8) breakthroughs for fine and coarse mesh alumina.
AAlRunlR 6 BV 1.0 N (4.0 %)NaOH, EBCT 15.4 min. Objective: to determine F"
(May 14) and As recoveries and regeneration efficiency.
AA1 Run 2R g gv 1.0 N (4.0 %)NaOH, EBCT 15.4 min. Objective: to determine F"
(May 14) As recoveries and regeneration efficiency.
AAJ Run 3 12 x 28 mesh, used, pH 6.0. EBCT 5 min. Objective: to determine F"
(5/16 - 6/3) and As capacities compared to Run 1.
AA1 Run 4 28 x 48 mesh, used, pH 6.0, EBCT 5 min. Objective: to compare F" and
(5/16-6/11) As capacity to Run 2.
AA1 Run 3R 16 BV 0.25 X (1.0 %) NaOH, EBCT 15.4 min. Objective: to compare
(June 15) 1.0 N to 0.25 N regenerants on coarse mesh.
AA1 Run 4R 16 BV 0.25 N (1.0 %) NaOH, EBCT 15.4 min. Objective: to compare
(June 18) 1.0 N to 0.25 N regenerants on fine mesh.
AA1 Run 5 12 x 28 mesh, used, pH 6.0, EBCT 5 min. Objective: to compare F" and
(6/19-7/7) As capacities to Run 3.
AA1 Run 6 28 x 48 mesh, used. pH 6.0, EBCT 5 min. Objective: to compare F" and
(6/19-7/12) As capacities to Run 4.
AA1 Run 5R 15 BV 0.25 N (1.0 %) NaOH, EBCT 12 min. Objective: to compare F"
(July 23) As recoveries to regeneration 3R.
AA] Run 6R 14 BV 0.25 N (1.0 %) NaOH, EBCT 12.4 min. Objective: to compare
(July 23) p As recoveries to regeneration 4R.
AAl Run 7 28 x 48 mesh, new, pH 7.3 (no adjustment), EBCT 5 min. Objective: to
(7/16 - 7/23) determine F and As run lengths at natural pH.
AAJ Run 1 12 x 28 mesh, pH 6.0, EBCT 5 min. Objective: to determine F'and As
(4/12-5/3) breakthroughs.
(continued)
12
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TABLE 3. (continued)
Run/(Date)
(1984)
Description
RO Run 2 DuPont HF PA, pH 7.6 (natural), 10 mg/L SHMP, product flow 4500
(8/2 - 8/7) L/day, 50% recovery. Objective: to determine % rejections and fouling.
IX Run 1 Dowex 11, used, pH 7.2. Objective: to determine if As(III) breaks
(8/14 - 8/15) through immediately as expected.
IX Run 2 Dowex 11, new, pH 7.3. Objective: to verify unusual results of IX Run
(8/23 - 8/25) 1 using fresh resin.
IX Run 1R 5 BV 1.0 N (6 %) NaCl, 4.5 BV/hr. Objective: to establish amount of
(Sept. 4) NaCl required and F' and As recoveries.
IX Run 2R 4 BV 1.0 N (6 %) NaCl, 4.7 BV/hr. Objective: to compare to
(Sept. 4) regeneration Run 1R.
AA1 Run 8 Well No. 4, 12 x 28 mesh, new, pH 7.1 (no adjustment), EBCT 5 min.
(9/20 - 9/21) Objective: to determine As run length at natural pH on high As(IH) source ,
water.
Al(OH)3 Reduce pH of spent regenerant solution to 6.5 to precipitate Al(OH)3 and
precipitation coprecipitate As. Objective: to determine if As can be removed from
regenerant solution.
EP Toxicity Leach Al(OH)3 sludge at pH 5. Objective: to determine if As leaches
from sludge to yield a hazardous waste.
Fe(OH)3 Increase pH of raw water to 8.5 after oxidizing As(III) and Fe(II) with
precipitation Cl2. Objective: to determine if As can be removed from city water and
Well No. 4 by coprecipitation with Fe(OHb.
The electrodialysis (ED) desalting process is usually considered as direct competition to
RO for brackish water treatment. Removal of individual nonionic contaminants by ED,
however, may not be competitive. Such is the case with the nonionic arsenite which is not
expected to be removed by ED because it does not transport a charge across the membrane.
Arsenate anions such as H2As04 or HAsO^" transport one or two changes depending on pH.
In this regard, it was of interest to study the ED process on both the mixed As(III)/As(V) city
water and the pure As(III) Well No. 4 water. The published ED literature contains no data on
arsenic rejection and there was some speculation that the potential and current generated in the
ED stack might oxidize and thereby remove arsenite.
Attempts were made to verify the expectation of very short ion exchange runs because
of: (a) the presence of nonionic arsenite, (b) high TDS, and (c) high sulfate in the feedwater.
Previous studies by Homg [1983] showed arsenic(V) to be well removed by ion exchange, but-
inherent danger of an eiution peak of high arsenic exists if the column runs beyond
breakthrough. These considerations, in addition to the interesting possibility of a
13
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sulfate/arsenate selectivity reversal due to the high TDS, prompted a study of strong-base anion
resins in the chloride form for the treatment of the San Ysidro city water.
Although precipitation processes are not included in the pilot scale equipment, bench
scale tests were performed because arsenate has been found to be removed from water by
coprecipitation with Fe(OH)3 [Buswell, 1943; Rosehart and Lee, 1972; Gullege and
O'Connor, 1973]. The removal of arsenic from Well No. 4 water containing 2.0 mg/L of iron,
and city water containing 0.06 mg/L of iron by the precipitation of the naturally occurring iron
was tried after oxidizing the arsenite to arsenate using chlorine.
Finally, wastewater disposal studies were performed on the spent regenerant solutions
from the alumina column regenerations. It was of particular interest in these experiments to
determine if the results of Rubel and Hathaway [1985] from their Fallon, Nevada arsenic
removal studies could be duplicated. They found that, by simply neutralizing the alumina
regenerant solution, the resulting aluminum hydroxide precipitate would adsorb the arsenate
yielding a supernatant water with less than 0.10 mg/L total arsenic. Their filtered, Al(OH)3(s)
sludge passed the EPA Extraction Procedure (EP) test as a non-hazardous waste. (The
difference between our study and Rubel's was the presence of a significant amount of
arsenic(lll) which might have been poorly adsorbed on the alumina, thus causing the
Al(OH)3(s) sludge to fail the EP toxicity test. Fortunately, most of the As(IH) retained by the
alumina was unintentionally oxidized to As(V), and our sludges also passed the EP test.)
ANALYTICAL METHODS
Summary of Methods
With the exceptions of metals analyses done using a Perkin Elmer Model 5500
Inductively Coupled Plasma (ICP) Spectrometer at the University of Houston, and a check
sample of the city water run by Water Test Corporation of New London, NH, all analyses
were done with equipment in the Mobile research facility. The methods used are summarized
in Table 4 with their respective references.
Arsenic Determinations
The method used for arsenic speciation was developed by Clifford, Chow and Ceber
[1983] especially for use in field situations. The method makes use of the fact that in the pH
range of 3.0 to 8.4, As(V) exists as monovalent H2As04 or divalent HAsO^" whereas As(III)
exists as the uncharged arsenous acid, H3As03. When chloride-form strong-base anion resins
are used for the separation, As(III) passes through the column unhindered while As(V) is
completely retained by the resin. In the simplest determination, 100 mL of sample are passed
at 10 mL/min through a small column containing 5 mL of resin beads with a depth of 10 cm.
GFAAS is used to determine total arsenic (As(IIl) + As(V)) on the untreated sample
and As(III) on the column filtrate. Arsenic(V) is determined by difference, and it can be
14
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TABLE 4, LIST OF ANALYTICAL METHODS USED IN THE
SAN YSIDRO ARSENIC STUDY
Test Method Reference
Total Arsenic
GFAAS, P-E 372 with HGA-2200
Appendix A
Arsenic(III)
IX separation then GFAAS
Appendix A
Arsenic(IV)
EX separation then GFAAS
Appendix A
pH
Orion 231 Digital pH meter with
combination glass electrode and ATC
Orion Research Manual
TSS
Glass Fiber Filtration
Reeve Angel-934 AH, 4.25 cm
TDS
Evaporation at 105® C
Conductivity
Hach Conductivity Meter-16300
Hach Manual
SDI
Filtration with Millipore-FIA, 0.45 }im
DuPont RO Manual
Turbidity
Hach Turbidimeter-2100A
Hach Manual
Silica
Molybdosilicate
Standard Method
14th Ed., p 487, 1975
Total Hardness, TH
EDTA Titration
Standard Method
14* Ed., p 487, 1975
Total Alkalinity, T. alk
Hach Digital Titrator-AL-DT
Hach Manual
Sulfide
Methylene Blue
Standard Method
14th Ed., p 503, 1975
Bicarbonate
Hach Digital Titrator-AL-DT
Hach Manual
Fluoride
Electrode, Orion-96-09-00
Orion Research Manual
Chloride, Bromide,
Dionex HPIC-2010i
Dionex Manual
Sulfate, Nitrate
Na, Ba, K, Mn, Fe,
ICP AES at UH
P-E Manual
Ca, Sr
Magnesium
Difference of TH and Ca
checked by elution of the column with 50 mL of 0.5 N HC1 followed by GFAAS analysis of
the As(V) in the eluate.
Ferric iron interferes by adsorbing As(III) if the pH is above 3.1. Fortunately, the
interference due to the presence of up to 1.0 mg/L Fe3+ may be completely eliminated by
adjusting the sample pH into the 2.8 to 3.1 range. Distilled water could not be used for reagent
preparation, rinsing and dilution because it contained traces of chlorine carryover from the tap
water from which it was distilled. These traces of Cl2 completely oxidized any As(III) present.
Deionized water, i.e., water from a standard mixed bed demineralizer preceded by an activated
carbon adsorber, was found to be satisfactory, however, for reagent preparation and dilution.
15
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Complete details of the As(lII)/As(V) ion-exchange separation method can be found in
"Arsenic(W)/Arsenic(V) Separation by Chloride-Form Ion-Exchange Resins" (Clifford et. al.,
1983). Although it is not a "standard method", it has been used successfully over a period of
three years on hundreds of As(IlI)/As(V) samples in the University of Houston Laboratories
and in San Ysidro. Furthermore, the method has been validated by an independent testing
laboratory in Fresno, California-Twining Laboratories. In evaluating the method for
determination of the arsenic speciation of Hanford, CA groundwaters, they found the
procedure to be "very good" as evidenced by the average recovery of As(IIl) of 99±1%, and
As(V) of 100±2%. Their 4-page evaluation report including analysis of Hanford's Well No.
31 is included in Appendix A.
QUALITY ASSURANCE
The basic quality assurance procedure used was participation in the EPA's Quality
Assurance Surveys. Regarding arsenic, fluoride and nitrate analyses, the field researcher has
achieved acceptable results for these parameters while using the analytical equipment in the
UH/EPA trailer during three years of research prior to the San Ysidro study. This indicates
that our standards and analytical procedures are of acceptable accuracy.
While in San Ysidro, the field researcher determined arsenic, fluoride and nitrate with
the results in Table 5. All UH analysis values were within the acceptable range as determined
by the EPA Quality Assurance Officer. Appropriate blanks and standards were run at least
once each day when the analytical tests were performed.
TABLE 5. QUALITY ASSURANCE RESULTS
Survey No. Analysis Sample #1 Sample #2
(Date) UH True Value UH True Value
WS 014
(5/18/84)
Arsenic, |ig/L
Fluoride, mg/L
Nitrate, mg/L
Chromium, ng/L
22.0
1.0
9.87
37.0
73.0
0.41
0.66
67.0
WS 013
(11/18/843
Arsenic, |ig/L
Fluoride, mg/L
Nitrate, mg/L
12.5
2.17
6.05
104.0
0.223
0.404
WS 012
(5/23/83)
Arsenic, ug/L
Fluoride, ^g/L
Nitrate, mg/L
Chromium, ng/L
19.0
1.51
2.12
13.8
18.0
1.50
2.1
14.3
51.0
0.89
1.13
81.7
48.1
0.86
1.13
78.6
ELECTRODIALYSIS APPARATUS AND PROCEDURES
The pilot-scale electrodialysis (ED) unit used in San Ysidro is an Ionics Inc. Aquamite I
unit with automatic current reversal (EDR) to prevent fouling. It was operated to produce 1790
L/day (475 gpd) of product water at 81% recovery utilizing internal brine recycle. The flow
16
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ft
RAW WATER FEED
(NO PRETREATMENT)
C
V-2 TF-2
WATER
AGH R-l y
-O—'-0
P-4 >-<1.
TREATED
WATER
FROM T-6
CONTROLLER
AG-2
T-2
ACID
P-2
AG-3
T-3
P-3
SV-24
CAUSTIC OR
CLEANING SOLUTION
SV-II
BACKWASH
R-2
PRODUCT
WATER
EDR
UNIT
I u
I n
OVERFLOW
VESSEL
. AUTOMATIC
SAMPLER
MEASUREMENT
T-4, PRODUCT STORAGE
OR
T-5, WATER TANK
LEGEND
REJECT WATER
TO T-5
TRAY DRAIN
TO WASTE
V ¦ Manual valve
SV» Solenoid valve
P ¦ Pump
T ¦ Tank
EDR ¦ Reversible Eleclrodialysis
R ¦ Rotameter
TF ¦ Totalizing Flowmeter
C * Common
CVa Check valve
AG* Agitator
ELECTRODIALYSIS FLOW SYSTEM
Figure 3, Process and instrumentation flow diagram for the reversible electrodialysis system.
An internal flow schematic can he found in Appendix B—Figure 15 1.
-------
scheme is shown in Figure 3. Further details, including an internal flow schematic for the unit
and a list of specifications, are presented in Appendix B as Figure B1 and Table Bl,
respectively.
Raw water without pH adjustment or antiscalant addition was fed directly through valve
V-l to the unit. This lack of pretreatment was done at the manufacturer's suggestion and to
verify their claim that pretreatment is not required. Actually, since the internal flow schematic
(Figure Bl) contains a 10-micion cartridge filter and a granular activated carbon column (for
dechlorination), some pretreatment does occur.
Prior to the tests in San Ysidro, the ED unit had been operated intermittently for four
years in three previous locations. However, the membrane stack had to be replaced
approximately six months prior to its use in San Ysidro because it was improperly stored and
allowed to dry out. Thus, it was effectively a relatively new unit
The ED unit was severely challenged in San Ysidro by operating it without pretreatment
on both the city water and Well No. 4. The result was that membranes did scale up and needed
to be acid cleaned prior to use in Hanford, California, the subsequent field location. The
cleaning procedure is outlined in Appendix B following the EDR specifications.
REVERSE OSMOSIS APPARATUS AND PROCEDURES
The RO system flow schematic is given in Figure 4 and the list of specifications are
presented in Appendix B, Table B2. Two different modules were used in the study-a Dow,
hollow-fiber, cellulose triacetate-membrane type and a DuPont hollow-fiber, polyamide-
membrane type. Each was operated separately as single module at approximately 50%
recovery. The Dow module (RO-1) was larger, producing 11,700 L/day compared to 4500
L/day of product for the DuPont module (RO-2). Based on the recommendations from each
manufacturer, the feed to the Dow unit was acidified to pH = 6.3 while no acid was added to
the DuPont module feed. Their respective computer projections and pretreatment requirements
are reproduced in Appendix Tables B3 through B6 following the RO system details.
For both the Dow and Dupont systems, the deep-bed AG-media filter was used ahead
of ihe 10-|j.m cartridge filter. Also, an antiscalant, 10 mg/L sodium hexametaphosphate
(SHMP), was added continuously during each run by pumping from tank T-3 into the
recirculating feed tank T-l.
During the EDR and RO runs, product water samples were taken automatically from the
overflow vessel by the 1SCO automatic sampler at predetermined volumes and time intervals.
Feed and brine samples were taken manually at least once per day. No preservatives were used
in the sample bottles.
ALUMINA APPARATUS AND PROCEDURES
As previously discussed, 1-inch diameter columns rather than the 8- or 10-inch
diameter pilot columns were used for all the alumina and ion exchange runs to minimize the
production of arsenic wastes in San Ysidro. The flow schematic for the alumina system is
given in Figure 5. The 100-L pilot-scale feed tank T-l was used to adjust the pH of the
incoming raw water, however, most of the tank effluent was bypassed to waste to minimize
mixing, aeration and detention time in T-l. This was done to prevent oxidation of the As(III),
and to represent more closely, the actual feedwater which would exist in a full-scale treatment
process.
18
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vO
|SV 36
TO COLUMNS AND
EDR UNIT
LEGEND
Agitotor
Common
Check Votve
Filler
Pressure gage
Pump
Rotameter
Reverse Osmosis Unit
Tank
Manual Valve
Pressure switch
Totalizing Flowmeter
PROOUCT
WATER
V-30
V-2 TF 2
BACKWASH TO
WASTE OR T-5
WATER
PG-15
TO
AUTOMATIC
SAMPLER
P-4
"(^/CONTROLLER
AG-2
PGI6
CV-5
PG-17
PG-10
-OPS-3
PC 19
P-8 PRETREATMENT PUMP
CLEANING
SOLUTION
CLEANING SOLN RETURNS
T-3
CLEANING
SOLUTION OR
PRETREATMENT
CHEMICALS
OVERFLOW
VESSEL
MEASUREMENT
T-4, PRODUCT STORAGE
OR
T-5,WASTE TANK
RO FLOW SYSTEM
REJECT BRINE
TO T -5
Figure 4. Process and instrumentation flow diagram for the reverse osmosis (RO) system.
-------
For all the alumina experiments, the feedwater pH was adjusted to 6.0 with 2% H2S04 added
from T-2 using an Ecodyne model 2500C metering pump, P-3. The feedwater metering
pumps, P-Cl and P-C2, which fed the alumina columns, operated at a flow rate of 80±3
mL/min for an EBCT of 5 minutes—typical of full-scale operations. Two different mesh sizes
of alumina were used, but the bed volumes were always 400 mL resulting in a bed depth of
81.5 cm (32 in).
Generally, the alumina runs were continued until the MCL for arsenic (0.05 mg/L) was
achieved in the effluent. This meant that the runs were continued far beyond fluoride
exhaustion. This was not considered a serious violation of the fluoride MCL (1.4 mg/L in
1984) because the feed fluoride level was only 2.0 mg/L. Now that the MCL for fluoride is
4.0 mg/L, potential fluoride violations are not a problem with the San Ysidro city water. In
these experiments, the alumina runs lasted from 20-25 days. Only total arsenic was determined
on the column effluents, i.e., there was no speciation of As(III) or As(V).
ION EXCHANGE APPARATUS AND PROCEDURES
The ion exchange runs were done to verify that immediate arsenic(III) breakthrough
would result because of the molecular (nonionic) nature of arsenious acid. To insure that
oxidation would not occur, the holding time in the feedwater tank T-l was reduced to 6
seconds by replacing T-l (100 L) with a 2-L beaker to receive the raw feed. This is shown in
Figure 6—the ion exchange system schematic. In these experiments, the pH of the feedwater
was not adjusted. The resin bed consisted of 400 mL of chloride-form, strong-base anion
resin. Two different resins were used: lonac ASB-1, a type 1 gel resin with microporosity,
and Dowex-11, an isoporous "improved porosity" type 1 resin.
Following each exhaustion run, the resin was regenerated with'5 BV of 1.0 N (6 %)
NaCl solution, i.e., approximately 4-5 times the stoichiometric requirement based on total resin
capacity. During each regeneration the elution curves for fluoride and arsenic were monitored.
Arsenic was speciated occasionally during the exhaustions and regenerations.
FERRIC IRON PRECIPITATION TESTS
Batch oxidation/precipitation tests were run on 500-mL samples of city water and Well
No. 4 water. These consisted of adding an excess of chlorine (bleach) to the raw water,
adjusting the pH of one half of the chlorinated water to 8.5 and filtering the samples prior to the
determination of arsenic in the filtrate. This was done to determine the amount of arsenic
which was adsorbed onto any precipitate that was formed at the adjusted pH of 8.5 and the
unadjusted precipitation pH of approximately 7.2 for both the city water and Well No. 4.
Diluted Purex® bleach was used for the oxidation, and a fine, quantitative-analysis filter paper
was used for the filtration step.
ARSENIC SLUDGE DISPOSAL TESTS
In a typical Al(OH)3 precipitation test, 500 mL of spent alkaline regenerant solution
(pH 13) was placed into a 1-L beaker and acidified to pH 6.5 using about 7 mL of concentrated
reagent-grade HC1. In order to maintain the pH < 6.5 and to prevent redissolution of Al(OH)3,
a small amount of acid was added at 1/2 to 4 hour intervals during the next 14-hour period.
The solution was allowed to stand overnight (10 hours) prior to filtration. The precipitate with
its absorbed arsenic was then filtered through a quantitative, paper filter which was later dried
20
-------
Raw
water
V-2
N>
pump-C2
—g1-
pump-C 1
80 ml/min
80 ml/min
pH pump P- 3
2%
h,so4
sol'n
T-1
(100 L)
T-2
(100 L)
EBCT ¦ 1 hrf)pH=6.0
manual
sampling
T-3
00 CM
£P—
pump-1
waste
Bypass flow 1.7 L/mln
overflow
vessel
(1.4 L)
<
to waste
Figure 3.
Flow schematic for the activated aJumina system.
-------
Raw V 2
water—[><}
pump-C 1
IX Column
2-L beaker
EBCT-6 sec
400 mL
resin
tank-1
manual
sampling
V-9
-cJch
tank-3
tank-7 and waste
to
tank-
Figure 6. Flow schematic for rlie ion-exchange (IX) .system.
-------
for 12 hours at ambient temperature (22® C) and stored for the future studies including the
Extraction Procedure (EP Toxicity) Test (U.S. EPA 1980). Total arsenic, As(III) and
Arsenic(V) were determined on the spent regenerant prior to precipitation and on the filtrate
after filtration. This procedure was used as a screening test only, i.e., to quantify the amount
of As(in) and As(V) coprecipitated with the Al(OH)3 near its pH of minimum solubility, i.e.,
6.5.
EP TOXICITY TEST PROCEDURE FOR Al(OH)3 SLUDGE
The Al(OH)3 sludge dried for 12 hours at ambient temperature was subjected to the
Extraction Procedure (EP Toxicity) test (Appendix A). Briefly, the procedure consists of
extracting the sludge with 16 times its weight of distilled water after adjusting the pH to 5 using
acetic acid. If, at the end of the first 24-hour extraction period, the pH is greater than 5.2,
more acid is added and the extraction is continued. Subsequent to the extraction step, the
sludge is filtered and the arsenic measured in the filtrate. If the total arsenic concentration
exceeds 5.0 mg/L, the sludge is considered a hazardous waste and must be disposed of in a
hazardous waste landfill. Although the sludge passed the EP test, there were no such landfills
in the State of New Mexico. So, the results of the test had important disposal-cost
implications.
23
-------
RESULTS AND DISCUSSION
SAN YSIDRO WATER QUALITY
The compositions of the city water and Well No. 4 are shown in Table 6. Most values
are single-point determinations while others, notably the As(III) and As(V) and total arsenic
values are the averages of several determinations. Table 7 lists the separate As(III) and As(V)
values for the city water which were used to compute the averages. The mean As(III) value
was 31 ±8.6 ng/L while As(V) was 57±8.2 ng/L, and the total As concentration was 89±8.3
yg/L. The total arsenic value, 89 ng/L, was slightly higher than the sum of As(III) + As(V)
(31 + 57 = 88) because more samples were included in the As(total) average. Finally, the data
indicate that the total arsenic concentration appeared to be increasing during the course of the
study.
Other particularly troublesome constituents of the city water are TDS (810 mg/L),
hardness (282 mg/L), total alkalinity (468 mg/L) and sodium (190 mg/L). To achieve the U.S.
EPA secondary MCL's would require desalting, e.g., with EDR or RO. With desalting,
however, problems also exist, depending on the concentration factor encountered in the reject
brine and the amount of precipitation inhibitor, SHMP, used for scale control. Both the Dow
and DuPont RO computer projections indicate that the City Water is supersaturated with respect
to BaS04 and CaF2. For Well No. 4 water, these same two compounds were computed to be
at supersaturation. Further elaboration of the scaling problem can be found in the discussion of
EDR and RO performance.
TABLE 6. RAW WATER ANALYSES IN SAN YSIDRO, NM
Contaminant City Water * f § Well No. 4
Arsenic(III), ng/L 31 230
Arsenic(V), ng/L 57 0
Arsenic Total, \igfL 88 230
pH 7 7.2
Dissolved solids, TDS 810 1393
Suspended solids, TSS 0.05 0.05
Conductivity,^ 1530 2860
Silt Density Index, SDI 1.13 0.7
Turbidity, NTU 0.11 4.4
Silica, Si02 60 66
T. Hardness as CaC03 282 126
T. Alkalinity as CaC03 468 642
Sulfide 0 0.032
(continued)
24
-------
Contaminant City Water
Well No. 4
Bicarbonate
571
783
Fluoride
2.0
6.6
Chloride
123
300
Nitrate as N
0.22
0
Sulfate
37
101
Bromide
0.35
0.83
Strontium
0.85
0.56
Calcium
85
38
Magnesium
17
7.5
Iron
0.06
2
Manganese
0.02
016
Potassium
12
15
Barium
0.2
0.06
Sodium
190
510
* All concentration are mg/L unless otherwise specified.
+ See Table 5 for analytical methods used.
§ Values shown are averages of several samples taken during the course of the
study, 1/84 through 9/84.
ARSENIC(III) OXIDATION
As Table 7 indicates, the As(III) concentration was quite variable (22-44 \ig[L) during
the course of the study. If the raw water sample was allowed to sit for several hours or more,
prior to speciation, some or all of the As(III) was occasionally found to oxidize to As(V).
Consequently, concern existed that the water in the raw water recirculation tank, T-l, with a
typical retention time of one hour, would be subject to air oxidation of As(III). There was,
however, no clear indication that oxidation took place in this tank. Comparing the As(UI)
values of samples taken directly from the tap (24, 24, 34 and 28 ng/L) to the samples from T-l
shows the tap samples on the average to be lower in As(III) than those from T-l. This is
probably due to the fact that the tap samples were all taken in the earlier pan of the study when
both the As(HI) and As(V) values were somewhat lower than they were near the end of the
study.
The variability of As(III) oxidation presents a problem with treatment to remove total
arsenic. As previously discussed, As(III> is known to be poorly removed by alumina,
chloride-form ion-exchange, and ED -- especially ED. Nevertheless, to assess the direct
applicability of these processes, they were all tried in San Ysidro without chlorine pretreatment,
i.e., on the natural water as it came from the ground. Tt was suspected early in the study that
point-of-use (POU) treatment using RO might be the only feasible alternative in the small
25
-------
community of San Ysidro. This is because POU RO devices are operated at such low water
recovery (10-20%) that membrane scaling and fouling are minimal compared to central RO
treatment with 50-80% recovery. The reduced scaling at lower water recovery is, of course,
due to the reduced brine concentration factor.
TABLE 7. ARSENIC(III) AND ARSENIC(V) CONCENTRATIONS IN THE
SAN YSIDRO CITY WATER
No.
Date (1984)
As(IU)
Ug/L
As(IV)
Hg/L
Total As
Hg/L
% As(m)
1 *
3-12
24
59
83
29
2 »
3-13
24
59
83
29
3 ~
3-15
34
51
85
40
4
4-4
44
47
91
48
5
4-5
38
6
4-6
44
47
91
48
7 •
4-19
28
46
74
38
8
4-20
75
9
4-22
36
50
86
42
10
5-8
85
11
5-22
22
62
84
26
12
5-28
26
60
86
30
13
6-2
28
63
91
31
14
6-4
26
74
90
18
15
6-5
40
56
96
42
16
6-7
98
17
6-27
28
62
90
31
18
7-20
107
19
7-23
101
X , mean
31
57
89
35
n, samples
14
13
18
s, std dev.
8.58
8.16
8.33
* Samples 1, 2, 3 and 7 were taken directly from the tap; all others were from tank T- 1 where
feedwater was exposed to air.
26
-------
DESALTING PROCESS RESULTS
PrQcssfi PsrfQrnisiit? on Well ^fti 4
Immediately after the research trailer moved into San Ysidro and before the speciation
tests, Well No. 4 water was treated using EDR to produce drinking water for Lin's family.
EDR was used because it required no pretreatment and could simply be "turned on" to produce
potable water. The product water was low in TDS and tasted good. Use of this water for.
drinking was stopped immediately, however, when arsenic analysis revealed 136 ug/L
As(total) in the EDR product from a 188 jj.g/L As(total) feedwater. The supposition is that,
although not yet speciated, the feed contained primarily molecular As(III) which was not
removed by electrodialysis. Later, it was determined that the arsenic in Well No. 4 was 100%.
As(DI). Thus, in retrospect, only 28% of the As(III) was removed by the EDR unit possibly
by means of oxidation or adsorption/precipitation onto the membranes.
Electrodialvsis Process Performance on Citv Water
The Ionics EDR unit was run for five days on city water with the results shown in
Figure 7. The only pretreatment was the standard 10-micron cartridge filter and the granular
activated carbon (GAC) filter for dechlorination (which was unnecessary since there was no
Cl2 in the feed). Averaging the effluent concentration histories in Figure 7, the EDR
performance data in Table 8 were generated.
The overall removal of arsenic was 73%, which was higher than expected. No As(IH)
was found in the ED product water; when speciated, it was 100% As(V) even when analyzed
within 30 minutes after sampling. The arsenic in the product water was probably As(III) that
remained in the ED feedwater as it became product water during its passage through the
membrane stack. The mechanism by which this As(III) was oxidized to As(V) in the product
water was not determined in this study. Assuming 90% rejection of As(V), the calculated
rejection of As(III) was 60% whereas we expected only 30% As(III) rejection based on the
performance of ED on Well No. 4.
TABLE 8. ELECTRODIALYSIS PERFORMANCE
DATA ON CITY WATER*
Constituent Feed Brine Product % Removal
pH
7.1
--
6.8
--
TDS, mg/L
810
--
227
72
As(total), |ig/L
85
200
23
73
Fluoride, mg/L
2.4
8.0
0.43
82
Sulfate, mg/L
36
125
-3.6
90
Bicarbonate, mg/L
552
1300
99
82
Chloride, mg/L
142
475
17
88
* Water recovery was 81%; run length was 5 days, and feed temperature was 12fi C.
Feedwater As(III) concentration was 34 ng/L.
27
-------
Time, hours
18
8
16
_i
_j
- DJ
-
o>
£
- E_14
-
_ u
c
o _
o _
S 6
- O 12
-
O
- i
o
1
o
" *10
- 100 •
X
_ i»
o
-
cr
- £ 8
1
o
00
T
1
i -
" o"
U)
CM *
A
o
- x 6
- .60 -
to
i
ci
- u.
- c
o
2
4
- ° 40 -
«
- <
2
- 20 -
0
0
o
Oi 1
Figure 7.
Results of EDR
anions
during t
12
"" i
36
60
—i—
84
—i—
i 1 1
Ban Yildro EDR Hun No. 1
City Water
March 12-17, 1884
Feed pH ¦ 7.11 0.1
0Fsad> 1790 L/day <473 gpd)
Oprod ¦ 1453 <-/day (384 gpd)
Recovery "81*
Tamp. - 12 S 2 *C
HCOj, C0« 652 ppm.
108
-I—
•fine m PPm
SOT, C« ¦ 38 ppm
Effluent pH
2.4 ppm,
ppm
85 ppb
¦ 200 ppb
Time, days
run no. 1, effluent concentration histories for
he EDR run with City Water feed and 81 % reccverv.
28
-------
Close examination of the effluent concentration histories in Figure 7 reveals that the data during
hours 86 through 96 were not plotted. During this time the stack becomes fouled due to
membrane scaling by calcium carbonate, and the scale was removed using 10% HC1 recycled
through the unit. This acid cleaning procedure successfully regenerated the unit.
CELLULOSE TRIACETATE MEMBRANE RO RESULTS
Effluent concentration history data from an 8-day run of the Dow hollow fiber,
cellulose triacetate (CTA) membrane module are plotted in Figure 8. The average performance
of the system during the last 5 days of the run after the unit stabilized are shown in Table 9.
Although 20-50% As(III) passage was expected with the CTA membrane, it averaged
less than 5%. In fact, nearly half the product water samples tested exhibited total arsenic
values below the detection limit. During the last 5 days of the run, arsenic never exceed 4
Mg/L. Because this Dow module had been used in four previous desalting studies, some
residue or scale may have developed on the membrane and aided in the arsenic removal.
However, based on the generally good overall performance of the Dow module (and the
DuPont RO module) this excellent arsenic removal performance is expected from typical
commercial installation of these units.
TABLE 9. DOW HF CTA RO PERFORMANCE DATA
Constituent
Feed
Brine
Product
% Removal
pH
6.3
--
5.0
--
TDS, mg/L
922
1785
57.0
94
As(total), p.g/L
91
168
1.0
99
Fluoride, mg/L
2.4
4.8
0.15
94
Sulfate, mg/L
286
543
6.5
98
Bicarbonate, mg/L
256
487
18.0
93
Chloride, mg/L
138
267
9.0
93
* Sulfuric acid was added for pH adjustment, water recovery was 50% and feed temperature
was I29C. Feedwater As(EII) was 42 |ig/L.
POLYAMIDE MEMBRANE RO RESULTS
The performance of the DuPont hollow fiber polyamide (PA) RO module is shown in
Figure 9 and summarized in Table 10. The DuPont polyamide membrane clearly performed
better than the other desalting processes for all contaminants, especially arsenic which was
undetectable in the product water. Again, this essentially complete removal of arsenic,
including As(III), was not expected. The high arsenic rejection agreed with the results
obtained with the Dow module and the Culligan point-of-use RO system. The better
performance of the PA membrane compared to CTA may have been due to the higher pH of the
feedwater for PA (pH = 7.6) compared to CTA (pH = 6.3).
29
-------
Time, hours
90 r 1-8 r 180
CT)
E
o
c
o
0
1 m
O
O
X
t
0
1
CM*
o
(0
80
70
60
50
40
30
20
10
0
1.6
1.4
=! 12
D>
E. 1.0
6
c
o
0 0.8
1
u.
0.6
0.4
0.2
0
160
140
120
-D)
h f 100
I-
.<
60
40
20
0
20
*"1—
60
—i—
Aa*3
Aa*
Feed
42
48
Prod
0
0
100 140 180
—i 1 1 1 1—
San Yildro RO Run No. 1
City Water
Dow HF CTa Module
April 1-9, 1084
Feed pH«fl.3t0.1 (Acid Added)
Q(Feed)" 23,380 L/d <6180 qpd)
CKProd) - 11,658 L/d <3080 <*>d)
Recovery — 50%
Temp - 12± 1*C
P(FMd) ~ 200 ~230 palg
Effluent pH
-O—
-CI-, C0"138 ppm. Cr,| - 267 ppm
. 80j , C0 ~ 286 ppm, CrS| ™ 643 ppm
HCOj . C0 - 266 ppm, Cf#| - 467 |
-A-
" f . C0 - 2.4 ppm
Cr#J - 4.8 ppm
Aa, C0 - B1 f4>6, Cra) - 168 ppO
6
Time, days
Figure 8.
Results ot DOW:R0 Kun, effluent, concentration histories for the DOW HF
CTA K0 system operated at 50% recovery on San Ysidro City Water.
-------
Time. Hours
-1
o>
E
d
c
o
O
_i
o
o>
X
n.
¦ *
-
O
o
CO
c
o
-
- O
- o 4
- " 40
<
- X
-
- ^ 2
i •
- 20
<5
-
L o
L o
Figure 9.
20 40 60 80 100 120
T I | I I I
II I | I I I I | II I I | I I II | I
ppb ppb ppb
As*3
As
TotAs
Feed
36
6 1
97
Prod
0
0
0
Rei
X
X
169
M
San Yaidro RO Run No.2
City Water
OoPont HF PA Module
Auouet 2-7. 1084
Feed pH - 7.6 ± 0.1(No Acid Feed)
Q(Feed) ' 0235 L/d(2440 gpd)
Q(Prod) = 4542 L/d(1200 Qpd)
Recovery * 60%
Temp < 3211 *C
P(Feed) > 340 -3S0 pals
O Effluent pH
F~ Co i 1.8 ppm. Cl(| > 2.8 ppm
CI-. Co s 142 ppm. Cr«|*272 ppm
HCOj , Co 3 604 ppm, Craj *1156 ppm
. Co = 42 ppm. Cr#, = 81 ppm
, ! ! ! [ As, Co 187 ppm. C„) - 160 ppm
8
7
6
0 1 2 3 4 5
Time, Days
Results of DuPonl R0 run iio. 2, effluent concentration histories for the DuPont
HF PA R0 system operaLed aL 50% recovery on San Ysidro City Water.
-------
TABLE 10. DUPONT HF PA RO PERFORMANCE DATA
Constituent
Feed
Brine
Product
% Removal
pH
7.6
—
6.0
...
TDS, mg/L
924
1841
27.0
97
As(total), |ig/L
87
169
nd
>99
Fluoride, mg/L
1.8
2.6
0.04
98
Sulfate, mg/L
42
81
0.15
>99
Bicarbonate, mg/L
594
1156
12.0
98
Chloride, mg/L
142
272
3.5
98
* nd = not detected. Run length was 5 days. No acid was added, feed temperature was
23SC, and feedwater As(IIl) was 36 ng/L.
A Comnarison of the Desalting Processes
Table 11 summarizes and compares the performance of the EDR and RO units. Based
on percent removal of contaminants, the polyamide membrane was clearly the best giving 97%
TDS removal and greater than 99% arsenic removal at 50% recovery with a single pass. As
predicted, electrodialysis gave the poorest removal of arsenic-presumably because molecular
As(III) could not be transported out of the feedwater using electrical current. The lower TDS
removal by the ED process is in pan attributed to the higher (80%) water recovery compared to
the RO unit (50%). Electrodialysis cannot be recommended if As(III) removal is a major
criterion. This conclusion is in contrast to those made using ED for fluoride, nitrate or
chromate removal in previous studies where ED performed equal to or better than RO for
contaminant rejection. If ED is to be used for As(III) removal, preoxidation with chlorine, for
example, is required to convert molecular As(ITI) to ionic As(V).
TABLE 11. SUMMARY OF EDR AND RO RESULTS ON
SAN YSIDRO CITY WATER
Parameter
ED §
Dow RO HF t
Cellulose Triacetate
Dow RO HF
Polyamide
Run Length, days
5
8
5
Pretreatment *
Filt
pH, SHMP, Filt.
SHMP, Filt.
Water Recovery, %
81
50
50
TDS Removal, % t
72
94
97
Arsenic Removal, %
73
>97
>99
(continued)
32
-------
TABLE 11.
(continued)
Parameter
ED §
Dow RO HF +
Cellulose Triacetate
Dow RO HF
Polyamide
Fluoride Removal, %
82
94
98
Sulfate Removal, %
90
98
>99
Bicarbonate Removal, %
82
93
98
Chloride Removal, %
88
93
98
Conductivity Reduction, %
80
94
97
Feed pH
7.2
6.3
7.6
Product pH
6.8
5.0
5.9
Temperature, ®C
12.0
12.0
23.0
* For pretreatment, pH means pH reduction using sulfuric acid; SHMP means
addition of 10 mg/L sodium hexametaphosphate; Filt is 10 micron cartridge
filtration.
t removal shown are based on average product concentration after the run
stabilized.
§ ED is electrodialysis with intermittent current reversal.
t HF is Hollow Fiber.
ACTIVATED ALUMINA RESULTS
Curves 3t pH dil?
Figure 10 presents the typical breakthrough curves for fluoride and arsenic in the
effluent from the activated alumina column during Run No. 2, one of eight alumina runs made.
Fluoride broke through first and reached a maximum level of 1.4 mg/L long before arsenic
reached its 0.05 mg/L MCL. If activated alumina is used in this fashion, i.e., without
oxidative pretreatment, the time to reach the arsenic MCL will be typically two to three times as
long as the time to reach a fluoride level of 1.4 mg/L for this particular water. This may be
seen in Table 12 -- the summary of the alumina results, and in Table 13 — a comparison of the
fluoride and arsenic run lengths.
Complete effluent concentration histories (breakthrough curves) of all the alumina runs
are presented in chronological order in Appendix C, where exhaustion runs are the even-
numbered figures and regenerations are the odd-numbered figures in the C1-C15 series.
33
-------
<
Time, Hours
200 400
-p—j-
Time, Days
10 15 20
600
1 r
600
n—i—
3.2
2.8
2.4
ra
n
o
8 40
5
-T"
15
!
30
—i—
35
1 1 1
Bin Yaldro Alumina Run No. 2
20x48 maah, F-1 Alumina
April 12-May 8. 1984
Bed Volume ¦ 400 mL
Flow Rat* ¦ BO mLfmln, City Water
EBCT ¦ 6 min
pH Feed ¦ 6.0 - 0.1
" Total As Adaorbad > 210 mg(or 230 mg to 60 ppb Ae)
_ Total F~ Adaorbad ¦ 2025 mg(or 1663 mg to 1.4 ppm F ) /
30
20
10
0 u
-O 1.6
2644
^ 8760 BV
/^To 50 ppb As
Aa. C0 >60 ppb [40% Aa(lll)]
2000
4000 6000 6000
Bed Volumes, BV
Figure 10. Breakthrough curves for fluoride anc arsenic from 28 x 48
mesh activated alumina columns, Run No. 2.
34
-------
TABLE 12. SUMMARY OF ACTIVATED ALUMINA RESULTS
Run No.
1
2
3
4
5
6
7
8
Mesh Size
1428
Coarse
28-48
Fine
14-28
Coarse
28-48
Fine
14-28
Coarce
28-48
Fine
28-48
Fine
14-28
Coarse
Condition §
new
new
lxReg.
2xReg.
2xReg.
2xReg.
New
New
Fcedwater * t
CW
CW
CW
CW
CW
CW
CW
No. 4
Feed pH $
6.0
6.0
6.0
6.0
6.0
6.0
7.3
7.1
BV to 1.4 mg/L F"
3084
2544
2376
2376
1740
2040
547
-
3 .
g/m F Adsorbed
to 1.4 mg/L F~
3870
4160
3063
3870
2260
3130
925
-
BV to 50 ^g/L As
6840
8760
5880
8040
4500
6300
1944
252
g/'m"' As
Adsorbed to
50 ug/L As
390
575
380
575
305
493
175
53
* For runs 1 through 7, San Ysidro city water (CW) with 92±10 |ig/L As was pH
adjusted to 6.0 before using.
t For Run 8, Well No. 4 water with 230 ug/L As was fed.
§ 1 x Reg. = once regenerated; 2 x Reg. = twice regenerated.
$ No pH adjustment was made for runs 7 and 8.
TABLE 13. COMPARISON OF FLUORIDE AND ARSENIC RUN LENGTHS
USING ACTIVATED ALUMINA
Days to Days to
Run Mesh Condition j 4 mg/L f~ 50 |ig/L As
1 Coarse New 10.8 23.8
3 Coarse 1 x Regenerated 8.1 20.4
5 Coarse 2 x Regenerated 6.0 15.6
2 Fine New 9.0 30.4
4 Fine 1 x Regenerated 8.1 27.9
6 Fine 2 x Regenerated 7.1 21.9
35
-------
Expected Breakthrough Curves for AsfTIH and AsfVl
In a related study [Frank and Clifford, 1986] laboratory alumina-run simulations were
made using synthetic waters similar to the San Ysidro city water except that the synthetic
waters contained either 100% As(III) or 100% As(V). In this way it was possible to compare
the arsenic and fluoride removal performances among three runs to quantify the effect of
oxidizing the San Ysidro As(III) to As(V). This comparison is presented in Figure 11, and a
list of the potentially competing anions in the various feedwaters is given in Table 14. Finally,
the bed volumes (BV) to fluoride and arsenic breakthrough for the As(III) and As(V)
laboratory waters and the San Ysidro City Water are summarized in Table 15.
TABLE 14. BACKGROUND WATER ANALYSES FOR
FIGURES 11 AND 12
Simulated Groundwaters San Ysidro
Constituent As(TII) As(V) City Water
As(III), Hg/L
100
0
32
As(V), ng/L
0
100
57
As(total), ng/L
100
100
89
Fluoride, mg/L
3.0
3.0
2.0
Sulfate, mg/L
384
384
365
Chloride, mg/L
71
71
123
PH
6
6
6
* Sulfate was measured after pH adjustment to 6.0 using sulfuric acid.
TABLE 15. COMPARISON OF LABORATORY AND FIELD DATA
FOR FLUORIDE AND ARSENIC REMOVAL
UH Laboratory Tests Field Test
Simulated Groundwaters San Ysidro
As(in) As(V) City Water
BV to 0.05 mg/L As
300
23,400
8,760
Arsenic capacity, g/m"
18
1,610
575
BV to 1.4 mg/L F'
1,600
1,550
2,520
¦y
Fluoride capacity, g/m
4,190
4,280
4,160
* The anionic composition of the waters is given in Table 14.
From the above comparison, the arsenic breakthrough curve for a mixture of As(III)
and As(V) falls between that of pure As(III) and pure As(V). Furthermore, oxidizing the San
36
-------
Ysidro city water to 100% As(V) will approximately triple the alumina run length to about
24,000 BV at pH 6.0.
The shape of the San Ysidro arsenic breakthrough curve (Figure 10) was delayed and
surprisingly sharp. A much earlier As(III) breakthrough was expected based on the lab
simulation data—Figure 11, As(III), Run No. 1. By way of explanation, some oxidation of
As(13I) to As(V) occurred in the field column, as proven later by regeneration studies of eluted.
As(III) and As(V). Also, the trivalent arsenic concentration of the field study was only 32:
Mg/L, i.e., one-third the concentration in the lab study. Furthermore, in the lab study the
pentavalent arsenic breakthrough curve (Figure 11, As(V), Run No. 2) showed early leakage
of As(V). This was probably due to the lab column's shorter EBCT (3 min compared to 5 min
in the field), its shallow bed depth (15.8 cm) and the fact that its adsorption zone was a large
fraction of the bed depth.
The fluoride capacities of the various columns were remarkably similar at 4160-4280
g/cm3. This is in spite of the fact that the San Ysidro water contained only 2 mg/L F whereas
the laboratory waters contained 3.0 mg/L F". Finally, in these column tests, the presence of
As(lII) and As(V), at a level of 100 mg/L total arsenic, did not seem to influence the fluoride
capacity of the alumina.
Effect of Mesh Size on Arsenic 8nd Fluoride Removal
Figure 12, representing the arsenic breakthrough curves for San Ysidro Runs 1 and 2
illustrates that the mesh size of the alumina has a dramatic effect on its performance for arsenic
removal. The summary data are listed in Table 12 where it can be seen that the coarse mesh
grade treats 6840 BV to the arsenic MCL while the fine mesh can treat 8760 BV with resulting
arsenic capacities of 390 g/m for the coarse and 575 g/m for the fine-mesh adsorbent. Such
large differences between coarse and fine were not noted during fluoride removal, however.
Figure 13 compares the fluoride breakthrough curves for coarse- and fine-mesh
aluminas. Considering the entire run, i.e., up to about 6000 BV, the coarse and fine-mesh
aluminas adsorbed almost exactly the same amount of fluoride—4830 g/m3 and 5060 g/m3
respectively. The adsorption kinetics of the fine mesh alumina are better, of course, so less
fluoride leakage resulted during the first 2000 BV compared to the coarse variety. This
improved fluoride removal by the fine-mesh alumina early in the run is, however, compensated
for by a slightly superior performance of the coarse alumina during the later portion of the run.
Similar behavior might have been observed for arsenic had we run the columns far beyond the
MCL of 0.05 mg/L. In theory, the mesh size of the alumina should not significantly affect the
equilibrium adsorption capacity.
F.ffect of dH on Alumina's Adsorption Capacity
Not reducing the pH of the feedwater to the optimum range of 5-6 results in a drastic
loss in both the arsenic and fluoride removal capacity of alumina. This loss is evident in Table
16 and in the arsenic breakthrough curves for City Water (Figure Cl 1) and Well No. 4 water
(Figure C13) at their natural pH's of 7.3 and 7.1, respectively.
37
-------
20
Days
30
40
t
50
T
As(lll). Arsanite, Run No. 1
¦— MCL. 50 ppb—^
As(v), Arsenate, Run No. 2
10 15 20
«
1000 Bed Volumes
25
Figure 11. Comparison of pure As(III) or pure As(V) breakthrough curves
from minicclurnns of activated alumina being fed synthetic
waters containing ICO jJg/L arsenic and 3 Tig/1, rlucride.
38
-------
o> 60
o 30
2000 4000 6000
Bed Volumes, BV
8000
Figure 12. Comparison of arsenic breakthrough curves ror
coarse (14 x 23) and fine (28 x £8) mesh aluminas.
39
-------
2.4 -
o
=»¦ 2.0 -
c
o
CO
c
0)
o
Fluoride MCL 1.4 mg/L
C
o
O
Mesh
(Run 1),
•S 0.B
28 * 48 Mesh
(Run 2)
k-
O
3
^ 0.4
8000
6000
2000
4000
Bed Volumes, BV
Figure 13. Comparison o£ fluoride breakthrough curves for
coarse (14 x 28) and fine (28 x 48) mesh aluminas.
40
-------
TABLE 16. CHANGES IN ADSORPTION CAPACITY AS A FUNCTION OF
pH AND ARSENIC CONCENTRATION
Run
Mesh
Feed Condition
BV to
BV to
No.
|ig/L As
pH
50 |ig/L As
1.4 mg/L F*
2
Fine
90
6.0
8760
2544
7
Fine
90
7.3
1944 (22%)
547 (22%)
1
Coarse
90
6.0
6840
8*
Coarse
250
7.1
252 (4%)
* Run No. 8 was made with Well No. 4 water (100% As(III); Runs 2, 7 and 1 were
with City Water (40% As(III)).
(%) Values in parentheses are % of optimum BV at pH 6.0.
The effect of varying both arsenic concentration (from 90 to 250 |ig/L) and pH (from
6.0 to 7.1) are seen by comparing Runs 1 and 8 in Table 16. The high, crivalent arsenic
concentration and unadjusted feedwater pH during Run 8 resulted in a run length (252 BV)
which was only 4% of that using city water at pH 6.0. These unadjusted-pH runs were made
to illustrate the short run lengths which would occur in the simplest point-of-use treatment
systems compared to a pH-optimized system.
The Regeneration of Spent Alumina
Fluoride is more easily and completely eluted from the exhausted alumina during NaOH
regeneration than is arsenic. This is evident in Figure 14 containing typical regeneration elution
curves and in the series of exhaustion-followed-by-regeneration figures in Appendix C. The
fluoride elution curve always begins slightly ahead of the arsenic curve and the arsenic elution
curve has a much longer tail. The alumina regeneration conditions are summarized in Table 17
where the percent arsenic recoveries are also summarized.
TABLE 17. ACTIVATED ALUMINA REGENERATION SUMMARY § # @
Run
NaOH Cone.
N
BV
NaOH
Equiv.NaOH
L Alumina
Arsenic
Adsorbed
mg
Arsenic
Recovered
mg
Arsenic
Recovered
%
1.0
6.5
6.5
146
85
58
3*
0.25
18.0
4.5
142
92
65
5*
0.25
16.0
4.0
136
91
67
2tt
1.0
6.7
6.7
210
132
63
4t
0.25
19.0
4.8
212
148
70
61
0.25
15.3
3.8
198
133
67
41
-------
* Coarse activated aJumina (14 x 28 mesh) was used for the sequence of runs 1, 3 and 5.
t Fine activated alumina (28 x 48 mesh) was used for the sequence of runs 2,4
and 6.
§ All regenerations were cocurrent (downflow) at a rate of 0.5 gal/minft3(EBCT=15.4min).
% The regeneration times were 100 minutes for runs 1 and 2 and 240 minutes for the others.
@ All regenerations were excessive in order to remove as much arsenic as possible
and to provide the data to establish Figures 15a-d and 16a-b.
# All regenerations were followed by neutralization with 2% HjSC^ (0.41 N) until effluent
pH was 5.0 or less.
To convert equiv. NaOH/L alumina to lbs NaOH/ft3 alumina, multiply by 2.50.
The higher efficiency of fluoride compared to arsenic recovery is more clearly
illustrated in Figures 15a-d. Where, at any give dose of NaOH (on the x-axis) a higher
percentage of fluoride is eluted compared to arsenic. In these figures, fluoride or arsenic
recovered is plotted as a function of the equivalents of NaOH added per liter of spent alumina.
Figures 15a and 15b are for 4% (1.0 N) NaOH regenerant while Figures 15c and 15d are for
1 % (0.25 N) NaOH. The weaker regenerant (1% NaOH) is usually recommended for fluoride
removal [Rubel, 1984] because higher concentrations are considered wasteful and
unnecessariily corrosive. The higher (4% NaOH) concentration was used because, although
more corrosive to the alumina, it had been found to be more effective than 1% NaOH for
arsenic(V) recovery from alumina [Clifford and Chou, 1987],
In all the Figures (15a-d), the percent recovery is based on what was eluted during the
entire regeneration not on what was adsorbed during the exhaustion. This approach is not
unreasonable because, as can be seen in the Appendix C regeneration curves (even-numbered
figures in the CI-CI 5 series), the amounts of regenerant used were always in excess of that
which was considered necessary. Thus, we expect that nearly all the fluoride or arsenic
"reasonably" recoverable was, in fact, recovered during these excess regenerations. Fluoride
was always more efficiently eluted than arsenic, i.e., less NaOH was invariably required to
elute fluoride compared to arsenic. With the coarse alumina, for example, it can be seen in
Figure 15a that 3 BV of 4% NaOH elute 94% of the recoverable fluoride but only 11% of the
arsenic. Note that in Figures 15a-d the BV of regenerant is measured from the time of first
appearance of fluoride or arsenic.
A comparison of the fluoride and arsenic recovery efficiencies is presented in Table 18.
For both fluoride and arsenic removal, 3.0 equiv. of the dilute (1%) NaOH/L alumina eluted
more arsenic than the concentrated (4%) NaOH. The fine-mesh alumina permitted higher
arsenic recoveries with both the 1% and 4% NaOH solutions.
42
-------
Time, Minutes
20 40 60 80 100
8000 -
6000 -
o>
E
v
c
o
O
4000 -
2000
1 360
San Ysidro Alumina Run No. 2R
May 14, 1984
AA Regeneration Data(Mesh 28x48)
Regenerant = 4%( 1 N) NaOH
Regeneration Rate = 26.7 mli'min =4 BV/HR
EBCT = 1 5 min, BV = 400 mL
Total F~Cesorbed During Regeneration « 1645 mg(8 1%)
Total F" Adsorbed During Exhaustions 2025 mg
Total As Desorbed During Regeneration =132 mg(63%)
.Total As Adsorbed During Exhaustion = 210 mg
320
280
240
Bed Volume, BV
Figure 14. Arsenic and fluoride eluti.cn during a regeneration of fine-mesh
alumina using i.% NaOH. Run 1R—regeneration following exhaustion
Run No. 2 .
43
-------
BV of NaOH
BV of NaOH
100
0)
<
o
©
>
o
a
©
QC
Run 1 R
Run 2R
14x28 Mesh
1 .ON NaOH
(4% NaOH)
28x48 Mesh
1 .ON NaOH
(4% NaOH)
15-b
1 5-a
0 1 2 3 4 5
Equiv. NaOH/L Alumina
0 1 2 3 4 5
Equiv. NaOH/L Alumina
100
BV of NaOH
0 4 8 12 16
100
BV of NaOH
0 4 8 12 16
in
<
o
>
©
>
o
©
IE
Run 3R
14x18 Mesh
0.25N NaOH
(1% NaOH)
Run 4R
(1% NaOH)
15-d
28x48 Mesh
0.25N NaOH
0 12 3 4
Equiv. NaOH/L Alumina
Figure 15. Relative % arsenic cr
of quantity cf NaOH r
0 12 3 4
Equiv. NaOH/L Alumina
fluoride recovery as a function
eger.erant.
44
-------
TABLE 18. RELATIVE PERCENT RECOVERIES OF FLUORIDE AND
ARSENIC USING 3.0 EQUIV. NaOH/L ALUMINA
Relative % Recoveries for
Relative % Recoveries for
Species Eluted
fine alumina
coarse
alumina
1 % NaOH
4% NaOH
1% NaOH
4% NaOH
Fluoride
97
93
96
94
Arsenic
93
87
89
77
* 3.0 equiv. NaOH/L media represents 3 BV of 4% (1.0 N) NaOH and 12 BV of 1% (0.25
N) NaOH. % recoveries are relative to the recovery of As or F at a maximum regeneration
level of 5 equiv. NaOH/L alumina.
It is useful to compare the slopes of the fluoride and arsenic recovery curves at 100%
relative recovery in Figures 15a-d. In all cases, the fluoride slope is flatter than that for
arsenic, indicating a small percent increase in fluoride recovery with the last increment of
regenerant applies. The percent increase in arsenic recovery, on the other hand, is quite large
for the last increment of regenerant added especially with the coarse alumina (Figure 15a).
An interpretation of the data in Figure 15d, fine-mesh alumina regenerated with 1%
NaOH, lends support to the regeneration recommendations of Rubel [1984] in his fluoride
removal design manual. Rubel recommends 4 BV of 1% NaOH (i.e., 1.0 equiv. NaOH/L
alumina) for fluoride elution in a procedure consisting of:
2 BV 1% NaOH, upflow
4 BV water slow rinse, upflow
2 BV 1% NaOH, downflow
24 BV pH 2.5 HjSO^ neutralization downflow
Assuming that the NaOH is still effectively regenerating the alumina during the slow
rinses as suggested by Clifford and Chou 11987], about 8 BV of "effective regenerant" are
being applied during Rubel's procedure. In Figure 15d it may be seen that 8 BV of \% NaOH
elutes a respectable 93% of the recoverable fluoride in agreement with his recommendation.
We do not believe, however, that upflow regeneration is necessary for fluoride removal
systems. This complicated procedure is generally used only to eliminate contaminant leakage
during the subsequent exhaustion run--an unnecessary consideration in fluoride removal where
fluoride leakage is tolerable due to the high MCL, and is unavoidable due to alumina's poor
adsorption kinetics. Upflow regeneration may, however, be of some use in arsenic removal
applications but that is yet to be proven, and it is doubtful that the upflow-then-downflow
sequence is necessary even for arsenic removal.
The debate as to whether \% ot 4% NaOH is preferred for regeneration of arsenic-
spent alumina is at least partially resolved by examining Figures 16a and 16b. For the fine
mesh alumina (Figure 16a), the percent recoveries of arsenic for 1% and 4% NaOH were the
same as a function of the equivalents of NaOH added per liter of alumina. However, for the
coarse alumina (Figure 16b) the dilute NaOH was a slightly more efficient regenerant
45
-------
100
.
Ir»
©
>
o
o
©
ae
*
©
>
iS
©
DC
0.25N (1 %)
NaOH
1 .ON (4%)
NaOH
Fine Mesh Alumina
(28x48)
2 3 4
Equiv. NaOH/L Alumina
cfl
<
•#—
O
>
L.
©
>
o
u
©
'IX
©
>
©
tr
100
so
60
40
20
0.25N (1%)
NaOH
1.0N (4%)
NaOH
Coarse Mesh Alumina
(14x28)
Equiv. NaOH/L Alumina
Figure 16. Comparison of arsenic recovery efficiencies of 1% and 4% NaCH
regeneration c:
:ine-
(16-a) and coarse-mesh ( 16—b ) alurr.inas.
46
-------
Dilute 1% NaOH (0.25 N) is less hazardous and less corrosive to the alumina; these are.
further reasons to prefer it to the 4% (1.0 N) NaOH for regeneration. It was, however, found
in a previous laboratory study of alumina regeneration [Clifford and Chou, 1987] that the
dissolution of alumina by NaOH (and H2S04) is a function of exposure time and
concentration. Thus, dilute regenerants can be just as corrosive as concentrated ones at
correspondingly longer regeneration times. For example, using equal regenerant flow rates
and equivalents of NaOH/L alumina, the 1% solution would take four times longer to apply
than a 4% solution, and nearly the same degredation (dissolution) of the media would result.
Furthermore, a dilute regenerant yields a proportionately larger volume of spent regenerant,
and this can be a critical, negative factor in application where spent regenerants are difficult to
dispose of.
In summary, both 1% and 4% regenerants are feasible for regeneration. The 1%
solution is probably somewhat less corrosive and hazardous, although one has to deal with it,
100% NaOH (flakes or pellets) or concentrated (40-50%) NaOH liquid when preparing either
solution. The advantage of 4% NaOH is that regeneration time and spent regenerant volume
are reduced. Rubel and Hathaway [1985] used 4% NaOH to successfully regenerate As(V)
spent alumina in their Fallon, Nevada pilot study. Of course, regenerant concentrations are not
limited to 1% and 4% NaOH.
The comments regarding the strength of NaOH also apply to the F^SO,} used for
neutralization following regeneration. Neutralization of the NaOH-laden column with a
relatively concentrated 2% H^SO^ (0.4 N) solution applied at the same flow rate (3.9 BV/hr) as
the regenerant immediately following regeneration is preferred. This procedure is believed to
be simpler than the procedure recommended above by Rubel [1984] for fluoride removal
applications.
Effect of Regeneration on Adsorption Capacity
The breakthrough curves for fluoride adsorption on fine alumina are only slightly
affected by one or two regenerations as shown in Figure 17. A single curve has been drawn
through the fluoride effluent data points for fresh, once- and twice-regenerated alumina. It
appears that very little change in fluoride capacity has occurred due to the regeneration
procedure. However, a slight but clear tendency exists toward earlier fluoride breakthrough
w ith subsequent regenerations.
Regenerations have a clearly negative effect, however, on the arsenic breakthrough
curves as shown in Figures 18 and 19. After two regenerations, the BV to 50 ^g/L As for the
coarse-mesh alumina (Figure 18) dropped to 4500 from 6840, i.e., a 34% reduction. A
summary of the reduction in arsenic capacity is presented in Table 19 where the reduction in
arsenic capacity was smaller for the fine- as compared to the coarse-mesh alumina. The data in
Table 19 shows the reduction due to the first regeneration (7 BV of 4% NaOH) were smaller
than those for the second regeneration (18 BV of 1% NaOH) for both the coarse and fine
aluminas. This observation suggests that a shorter regeneration (100 minutes) with stronger
caustic (4%) is preferred to the longer regeneration (240 minutes) with dilute (1%) caustic.
However, this suggestion is based on using little data. Furthermore, the decay of arsenic
capacity upon regeneration may simply be nonlinear. More work on this area was done during
the arsenic removal study in Hanford, California [Clifford and Lin, 1987],
47
-------
2.4
O)
E 2.0
c
o
"5 1-6
b_
c
wit-.h 1^ NaOH.
(1% NaOH)
~ ~
(4% NaOH)
Fluoride
1.4 mg/L
O ¦ Freah Alumina (Run 2)
A * One* Regenerated Alumina (Run 4)
~ " Twice Regenerated Alumina (Rune)
48
-------
eo
70
Once Regenerated Alunina
(Run 3)
O) 60
Arsenic MCI 0.05 mg/L
Twice Regenerated Alumina
(Run 5)
- Freeh Alumina
(Run 1)
2000
4000
6000
8000
Bed Volumes, BV
Figure 18. Effect of cocurrent regenerations on the arsenic
breakthrough curves for coarse-Tncsh (14 x 28)
al'^riina. First regeneration was made with 4%
while the second was r.ade with II NaCH.
49
-------
80
70
o> 60
=L
50
40
30
20
10
1 x Raganaratad Alumina
(Run 4)
Aa MCL ¦ 0.05 mfl/L
2 * Raganaratad Alumina
(Run 6)
Fraah Alumliia
(Rtai 2)
2000
4000
6000
8000
Bed Volumes, BV
Figure 19. Effecc of cocurrent regenerations on the arsenic
breakthrough curves for fine-mesh (14 x 28}
alumina. First reoe.ne ration was made with 4%
while the second was made with ll. NaCH.
50
-------
TABLE 19. REDUCTION IN ALUMINA'S ARSENIC REMOVAL
CAPACITY WITH REGENERATION
Run No.
Mesh
Condition
BV to
50 (lg/L As *
Percent of
Original BV
1
Coarse t
Fresh
6840
100
3
Coarse
After first (4%) regen.
5880
86
5
Coarse
After second (1%) regen.
4500
66
2
-Fine t
Fresh
8760
100
4
Fine
After first (4%) regen.
8040
92
6
Fine
After second (1%) regen.
6300
72
* BV to 50 ^g/L As are based on the data in Table 12.
t For each series, i.e., coarse or fine alumina, the first regeneration was made with 4% while
the second was made with 1% NaOH.
Rubel and Hathaway [1985J, in their recently completed As(V) removal study in
Fallon, Nevada, used 4-5% NaOH upflow followed by downflow for regeneration of arsenic-"
spent alumina. Although the regeneration time and amount of regenerant were undisclosed,
they reported 80% recovery of arsenic (all As(V)) and no significant loss of arsenic removal
capacity upon two subsequent arsenic removal runs at pH 5.5. Their reported better
performance with regenerated alumina may have been due to one of several differences: (a) the
initial upflow step in the regeneration sequence, (b) the absence of As(IIl) from the feedwater,
(c) the amount of regenerant used or, (d) the exhaustion pH-5.5 compared to our value of 6.0.
In any case, their results suggest that an As(V)-spent alumina column can be restored to
essentially its virgin capacity for As(V) even though only 80% of the As(V) is recovered during
a presumably intense regeneration with 4-5% NaOH.
Results of AI(OH)3 Precipitation from Spent Regenerant
The spent-regenerant solutions from regeneration runs 5R and 6R (Figures C8 and
CIO) were combined, acidified to pH 6.5 with HC1, settled for 24 hours and filtered prior to
analysis of the arsenic remaining. The results are presented in Table 20.
The coprecipitatioo/filtration procedure removes essentially all of the As(V) but only
36% of the As(in), and 97% of the arsenic remaining after precipitation is As(III). Therefore,
if this procedure is to be used in a full-scale application, any As(III) in the regenerant should be
oxidized to As(V). Using the results of Frank and Clifford [1986], chlorine should be added
after the pH has been reduced to 6.5 to take advantage of the much faster As(III) oxidation in
the 6-10 pH range.
51
-------
TABLE 20. ARSENIC COPRECIPITATION WITH AL(OH)3
Sample
Total As
mg/L
As(V)
mg/L
As(HI)
mg/L
As(DI)
Percent
Combined Regenerants from
Runs 5R and 6R
16.2
14.8
1.4
8.6
Filtrate after Al(OH)3
Precipitation
0.92
0.03
0.89
97.0
Arsenic Removal (%)
94.0
99.8
36.0
The arsenic-contaminated alum sludge produced in this manner amounted to
approximately 12% of the total initial solution volume. Rubel [1982], using a similar
precipitation procedure on a 4% NaOH spent regenerant (more concentrated), found the settled
sludge to be 25% and the filtered sludge solids to be less than 1% of the original wastewater
volume.
Results of Extraction Procedure (EP) Toxicity Test
The details of the Al(OH)3 precipitation of arsenic and a summary of the EPA
Extraction Procedure Toxicity test are given in Appendix A. After drying at room temperature,
the Al(OH)3 sludge solids amounted to 7.8 g/L of regenerant solution (which was originally
1% NaOH). Following the 24-hour extraction procedure, the arsenic (total) concentration in
the filtrate was 0.6 mg/L, i.e., far below the 5.0 mg/L limit for classification as a toxic waste.
Rubel and Hathaway [1985] found even less arsenic (0.036 mg/L) in their EP toxicity test
filtrate from an As(V)-contaminated Al(OH)3 sludge which they derived by adjusting the pH
(to 6.5) of a spent alumina regenerant solution (originally 4% NaOH). The higher, but
nevertheless acceptable, total arsenic concentration was presumably due to the presence of
As(III), in the original regenerant solution and in the Al(OH)3 sludge. Furthermore, both
studies resulted in a low-volume non-toxic arsenic sludge from the regenerant wastewater.
Arsenic Cgprecipitation from Raw Water
Iron hydroxide floe and hydrous iron oxide solids can be used to remove arsenic from
water by a mechanism of coprecipitation or adsorption [Buswell, 1943]. Moreover, As(V) is
much more effectively removed by ferric hydroxide than is As(lII) [Pierce and Moore, 1982].
Based on this knowledge an attempt was made to remove at least part of the arsenic from San
Ysidro city water and Well No. 4 water by oxidation and precipitation of the natural iron
present. The results of these tests are summarized in Table 21. A relatively high dosage, 10
mg/L, of free chlorine from household bleach (5.25% NaOCl, equivalent to 50,000 mg/L Cl2)
was used to assure oxidation of all chlorine demanding substances present, viz., ferrous iron,
sulfides and arsenite. The unadjusted pH following chlorination was 7.1. In one test the pH
was adjusted to 8.5 corresponding to the minimum solubility of Fe(OH)3(s).
52
-------
TABLE 21. ARSENIC COPRECIPITATION WITH Fe(OH)3 FROM
NATURAL Fe PRESENT
Sample
Raw Water
Fe(II)
mg/L
Percent Arsenic Removal
pH 7.1
pH 8.5
City Water *
City Water + C^
Well No. 4 t
Well No. 4 + Cl2
0.06
0.06
2.0
2.0
0
0
0
60
0
0
0
52
* City water samples contained 86 jig/L As(total).
t Well No. 4 water samples contained 200 ng/L As(total).
The City Water did not contain enough iron to give a visible precipitate, and no arsenic
was removed by chlorination and filtration at either pH. Well No. 4 water containing 2.0 mg/L
Fe(II) is partially treatable by this arsenic removal method. Sixty percent arsenic removal was
achieved at pH 7.1 while somewhat less, 52%, removal was observed at pH 8.5. The lower^
removal at the higher pH, 8.5, is in accord with the observations of Pierce and Moore [1982]~
who suggest that the optimal pH for As(V) removal by ferric hydroxide is 4.0, and that As(V)'
is removed by specific adsorption rather than electrostatic attraction. No further tests were
done at lower pH's, however, because the Well No. 4 water was of such poor quality.
ION EXCHANGE RESULTS
Performance of the Anion Exchange Columns
Chloride-form strong-base anion exchange tests were conducted to a limited extent (3
experimental runs) to verify the prediction that anion exchange is not effective for the removal
of nonionic As(III) in the raw water. Based on prior laboratory studies, immediate
breakthrough of essentially all the As(III) was expected, but did not occur. The typical
breakthrough curves for arsenic, fluoride, bicarbonate and pH from a 76-cm (30-in) deep bed
of Dowex-11 resin are presented in Figure 20. The performance of all three runs is
summarized in Table 22 and the breakthrough curves for the remaining runs are presented in
Appendix D--Figures D1 (Run 1), D2 (Run 2, expanded), D4 (Run 3), and D5 (Run 3,
expanded).
53
-------
900 r 3.6
800
700
600
o
E
J 500
5 400
I CO
0
1 300
200
100
0 L
3.2
2.8
d 24
O)
E
: 20
d
c
o
h o 1.6
I
1.2
0.8
0.4
Time, hours
20 30 40
As. C0= 93 ng/L
° 40
Effluent pH
60
200 400
Bed Volume, BV
San Ysidro, New Mexico
DOWEX-1 1. IX Run No. 2
Bed Depth ™ 77 cm
Bed Volume - 388 mL
Flow Rate ¦ 78 mL/min.
EBCT = 5 min.
Feed pH = 7.3 ± 0.1
HC03 , CQ= 561 mg/L
OF", CQ = 1.58 mg/L
600
8
I
a
6
5
Figure 20.
Results of IX Run No. 2, effluent' conciMiLrat ion histories for arsenic, fluoride, bicarbonate
and pll f rotn a ch 1 or i de-f or m strong-base anion resin, Dowex-I I.
-------
TABLE 22. SUMMARY OF CHLORIDE-FORM ANION
EXCHANGE
RESULTS IN SAN YSIDRO, NEW MEXICO
IX Run No.
Resin Type
Condition
BV to 1.4 mg/L F-
BV to 50 \igfL As
1
Dowex-11 §
New
—
223
2
Dowex-11 §
Regenerated
3.6
223
3
ASB-1 t
New
18.0
156
* No pH adjustment was made for the IX runs.
t San Ysidro City Water with 92 ng/L As was fed (33% As(III), 67% As(V)) in all
runs.
§ Dowex-11 is an improved porosity strong-base, Type-1 resin with an exchange
capacity of 1.3 meq/mL.
+ Ionac ASB-1 is a gel, strong-base, Type-1 resin with an exchange capacity of 1.1
meq/mL.
Referring to Figure 20 it is clear that immediate breakthrough of the 25-36 ng/L As(EQ)
present in the feedwater did not occur. Rather, about 200 BV was passed before a level of 30
Hg/L total arsenic was reached in the column effluent. The 93 ng/L total arsenic level in the
feed was not reached in the effluent until 570 BV passed through the bed. Most importantly,
the arsenic concentration in the effluent never exceeded that of the influent. Thus,
chromatographic peaking did not occur due to sulfate driving arsenic off the column as has
been regularly observed in laboratory studies fHorng, 1983]. We are not, however,
completely ruling out the possibility of an arsenic peak much later in the run.
Neither the sulfate nor the chloride breakthrough curves are shown in the figures
because their effluent concentrations as analyzed by ion chromatography did not make sense.
Sulfate appeared to be breaking through before chloride (the presaturant), and the sulfate that
apparently eluted during the first 200 BV was nearly five times the sulfate fed to the column
during that period. No reason existed to believe that there was sulfate on the column due to
regeneration because reagent grade NaCl was used to put the resin in the chloride form. The
analytical problem was never resolved, but it seems safe to assume that sulfate eluted from the
column prior to arsenic elution. The early sulfate elution was undoubtedly due to a selectivity
reversal of the usual preference for sulfate over chloride. This reversal is expected for such a
high TDS (810 mg/L) high ionic-strength (I = 0.017 M) water.
For both the Dowex-11 runs, the 50 ng/L arsenic MCL was not reached until 220 BV.
For Run 3, Ionac ASB-1 the run was shorter, 156 BV, before the MCL was reached. In spite
of the better-than-expected performance of these resins, they did not perform well enough to be
considered seriously as a viable treatment alternative (400 BV+). Also, in spite of the fact that
arsenic did not peak, its breakthrough was not sharp; an ever increasing level of arsenic leaked
from the column right from the start of the run.
AsCIH) Leakape During Ion Exchange
Table 23 summarizes the As(TII) and As(total) in the feedwater and the column effluent
during Run 2 (Figure 20). The early leakage was nearly all (93%) As(IU), and later dropped to
a value (26%) near that of the feed (33%). Oxidation of As(III) to As(V) within the bed
55
-------
appears to have occurred because there was 31 ug/L As(III) in the feed and only 8-20 ^g/L
AsQII) in the effluent during the first 400 BV.
TABLE 23. ARSENIC COMPOSITION OF EFFLUENT AND FEED FOR
ION EXCHANGE RUN NO.2
Effluent As(IH) Effluent As(total) Effluent As(ITl)
Run Time Hours BV .lan ,.an Percent
3.0 36 7.8 8.4 93
6.0 72 9.6 12.3 78
33.5 402 18.9 72.0 26
Feedwater 31.0 (As(III)) 93,0 (As(total)) 33 %(As(III))
dH Reduction in Ion Exchange Effluent
At the beginning of all the ion exchange runs, the effluent pH was quite acidic-pH 5.5
for Runs 1 and 2, and pH 4.3 for Run 3. After about 20 BV, however, the pH rose to near its
influent value of 7.2. It is believed that this low initial pH is a verification of the previously
observed [Horng, 1983] conversion of bicarbonate to carbonate within the resin according to
the following reaction:
2 RC1 + HC03 = R2C03 + 2Cr + H+ (1)
where RC1 is resin in the chloride form, and R2CO3 is resin in the caibonate form.
A strong acid, HC1, is produced which both lowers the pH and reacts with any bicarbonate
remaining in the aqueous phase according to reaction (2):
HC1 + HCO3 = H2C03 + CI" (2)
The aqueous C02, i.e., carbonic acid (H2C03) generated passes unhindered through the
remainder of the bed. To the extent that reactions (1) and (2) proceed, and HCOj is
exchanged for chloride, the alkalinity of the column effluent is reduced. Initially the effluent
alkalinity is zero, but eventually it rises to the influent value when the column is completely
exhausted.
This rise in effluent alkalinity to the influent value, indicating equilibrium between the
feedwater and the resin, did not occur in any of the runs, i.e., the columns were not completely
exhausted even at 600 BV throughput. The implication of this observation is that, at complete
exhaustion when the carbonate wave reaches the end of the bed, an arsenic peak might occur as
carbonate displaces arsenic. This is, however, merely a possibility to be considered in the
event ion exchange is used to treat the San Ysidro water.
56
-------
Fluoride Removal bv Ion Exchange
In all the ion-exchange runs (Figures 20, Dl, D2 and D3) fluoride was not removed to
any significant extent by the chloride-form anion resins. In Figure D2, an expanded plot of the
first 80 BV of Run 2, fluoride is seen to reach 1.4 mg/L (the old MCL) at approximately 4 BV.
Such an early breakthrough is expected due to the very low affinity of fluoride for the usual
strong-base anion resins. Further data on fluoride removal are presented in Table 22 where
one can observe that, although the performance of ASB-1 was poor for arsenic removal, it
performed better than Dowex-11 for fluoride removal. Neither resin could be used for
municipal defluoridation, however. Their fluoride capacities are simply too low.
The exhausted ion exchange columns were completely and easily regenerated using
approximately 3 BV of 1.0 N (6%) NaCl in a cocurrent (downflow) mode. Figure 21 presents
the arsenic and fluoride elution curves during regeneration Run 1R following the first
exhaustion of Dowex-11 resin during Ran No. 1. The arsenic elution curve is particularly
sharp and denotes the ease with which the adsorbed arsenic is eluted from the exhausted resin.
The ease with which anion exchange columns were regenerated in this study and the
fact that arsenic did not peak after breakthrough suggests that ion exchange should be further
studied. These and previous results with strong-base anion exchange resins [Horng, 1983]
indicate a real potential for chloride-form anion exchange for As(V) removal. Results from this
study suggest that approximately 400-500 BV could be attained prior to the arsenic MCL if the
As(DI) had been oxidized to As(V) prior to anion exchange.
POINT-OF-USE TREATMENT
In August 1984, 6 months after the San Ysidro project started, the test results
suggested no easy solution to the combined arsenic/fluoride contamination problem. Even if
the water was chlorinated to produce As(V) which would yield alumina runs in excess of
20.000 BV, the fluoride present would force termination of the alumina runs at 2,000 BV so as
not to exceed the existing MGL of 1.4 mg/L. (Now the MCL is 4.0 mg/L [U.S. EPA, 1986]
and fluoride is no longer a problem in San Ysidro.)
The anticipated short alumina runs due to fluoride, the complexity of the alumina
adsorption/regeneration cycle for a small community and the anticipated sludge disposal
problem led to the consideration of point-of-use treatment using reverse osmosis. A Culligan
Model No. H-82 was installed and tested in San Ysidro. The system used had a nominal
capacity of 8 gal/day product water and contained a thin-film-composite RO membrane. The
entire H-82 system comprises a 10 |im cartridge filter, a granular activated carbon (GAC) filter,
a TFC RO membrane; a second, smaller GAC filter, and finally, a pressurized storage tank.
Other manufacturers supply similar equipment, and no endorsement is implied.
A salient feature of POU-RO units is their low percent water recovery-typically 10-
15%. This is both an advantage and a disadvantage. With such low recovery there is no
significant concentration of the brine, and membrane scaling and fouling problems are minimal
compared to central treatment with the typical 70-80% recovery. The disadvantage is that only
10-15% of the feedwater is available for drinking.
57
-------
Time, minutes
20 40
San Ysidro, New Mexico
DOWEX-11 Regeneration Data
Regeneration No. 1R
Column = C 1
Regenerant ¦ 1 N NaCI
Regeneration Rate 3 29.4 mL/min
4.5 BV/hr
EBCT » 13.2 min.
Figure 21.
Bed Volume, BV
Arsenic and fluoride elution during a typical ior. excnange
regeneration witn 6.t (1.0 N) NaCI.
58
-------
The initial results of the POU-RO pilot test are presented in Table 24. Subsequent
arsenic analyses on the product water from this unit yielded undetectable arsenic levels, i.e.,
<0.2 ng/L.
TABLE 24. RESULTS OF POINT-OF-LSE REVERSE
OSMOSIS PILOT TEST
Parameter Feed Product Percent Removal
pH 7.2 5.5
Water flow, gal/day 50 6
Conductivity, |iS 1430 120 92
IDS, mg/L 750 35 95
Arsenic, ug/L 90 8 91
59
-------
REFERENCES
Buswell, A.M. et al, "Water Problems in Analysis and Treatment," JAWWA. October, 1943.
Clifford, D.A. and M.R. Bilimoria, "A Mobile Water Treatment Research Facility for
Removing Inorganic Contaminants: Design Construction and Operation," EPA-600/S2-84-
018, March, 1984. U.S. EPA Cincinnati, also NTIS No. PB 84-145507, Springfield,
VA.
Clifford, D., L. Ceber and S. Chou, "Arsenic(III)/Arsenic(V) Separation by Choride Forms
Ion-exchange Resins," Proc. XI AWWA WQTC Conference, Norfolk, VA, December,
1983.
Clifford, D.A. and L. Chou. "The Regeneration of Activated Alumina," University of
Houston, Dept. Civil/Environmental Eng., Houston, TX, 1984.
Clifford, D.A. and C.C. Lin, "Arsenic Removal from Drinking Water in Hanford, California -
a preliminary report." University of Houston, Dept. Civil/Environmental Eng., Houston,
TX, 1986.
Fox, K.R., "Removal of Arsenic and Selenium from Drinking Water by Reverse Osmosis,"
M.S. Thesis. University of Cincinnati, 1981.
Frank, P. and D. Clifford, "Arsenic(III) Oxidation and Removal from Drinking Water,"
EPA/600/S2-86/021, U.S. EPA, Cincinnati, OH, April, 1986.
Gullege, J.H. and J. O'Connor, "Removal of As(V) from Water by Adsorption on Alumina
and Ferric Hydroxides," JAWWA. pp. 548-552, August, 1973.
Gupta, S. and K. Chen, "Arsenic Removal by Adsorption," JWPCF. March, 1978, pp. 493-
506.
Horng, L.L., "Reaction Mechanisms and Chromatographic Behavior of Polyprotic Acid
Anions in Multicomponent Ion Exchange," Ph.D. Dissertation, University of Houston,
1983.
Pierce, M.L. and C. Moore, "Adsorption of Arsenite and Arsenate on Amorphous Iron
Oxide." Water Research. 16:1247-1253, 1982.
Rosehart, R. and J. Lee, "Effective Methods of Arsenic Removal from Gold Mine Wastes,"
Canadian Mining Journal, pp. 53-57, June, 1972.
Rosenblum, E. and D. Clifford, "The Equilibrium Arsenic Capacity of Activated Alumina,"
EPA-600/S2-83-107, February, 1984, U.S. EPA, Cincinnati, Ohio; also, NTIS No. PB
84-110 5277, Springfield, VA.
Rubel, F., Jr., "Design Manual-Removal of Fluoride from Drinking Water Supplies by
Activated Alumina," EPA-600/2-84-134, U.S. EPA, Cincinnati, OH, August, 1984.
Rubel, F., Letter Report to Marvin Tebeau of the State of Nevada, Division of Environmental
Protection, Rubel and Hager Inc., Tucson, AZ, November 19, 1982.
60
-------
Rubel, F., Jr. and S.W. Hathaway, "Pilot Study for Removal of Arsenic from Drinking Water
at the Fallon, Nevada, Naval Air Station," EPA/600/52-85/094, U.S. EPA, Cincinnati,
OH, September, 1985.
Singh, G. and D. Clifford, "The Equilibrium Fluoride Capacity of Activated Alumina," EPA-
600/S2-81-082, July 1981, U.S. EPA, Cincinnati, OH; also, NTIS No. PB 81-204075,
Springfield, VA.
Sorg, T. and W. B. Williams; "Arsenic Removal from Drinking Water by a Household
Reverse Osmosis System," Internal Report, EPA, Cincinnati, OH, August 1979.
Sorg, T.J. and G. Logsdon, "Treatment Technology to Meet the Interim Primary Drinking
Water Regulations," JAWWA. July 1978, pp. 379-393.
U.S. EPA, (EP Toxicity Test) Federal Register. Vol. 45, No. 98, May 19, 1980, pp. 33127-
28.
U.S. Environmental Protection Agency, "National Primary Drinking Water Regulation:
Fluoride," Federal Register. Vol. 50, No. 220, November 14, 1985, pp. 47165-71.
61
-------
r«fMi5*s • iHGits.tes
March 16, 1984
For:
Sample:
umin
lJ2lbiJ£6,^—/ric.
j,-c.
?5?* P'n^o Si'eet
»i"e Sv'e '
SC?5 A-t . Sj'le 206
940i w Cfi^i
*ft i^o C> 93-i'
Mccej:o.C* 9535'
Sl©c*'
-------
City of Hanford
Examination
Page 2
84-017C5
Results: The precision and accuracy of the prccedure for arsenic
1. The average As(111) recovery is 99 ± 1%. The average As (V)
recovery is 100 ± 2%.
From Table 2, the average % As(111) in. well 31 is 98 ± 2 and
the average % As(V) is 1 i 2. The arsenic in well 31 is predom-
inately trivaient arsenic [As (111)].
Re ference 5:
I • 5 Ir. , "Arsenic 1111 //Arsenic .(V) Separation by chloride-
form icn-exchar.ge resins", University of Houston, 1983 .
2.) 3uchet, J. P., et. al., "Comparison of the urinary excretion of
arsenic", Int. Arch. Cccup, Environmental Health 48, 71-79, 1981.
3.) EPA, "Methods for Chemical Analysis of Water and Wastes", Method
206.3 , 600/4-79-020 , March 1979.
speciation is very good as evidenced by the % recovery from Table
THE TWINING LABOP.ATORIES , INC.
DD/n
2c: wfel «'.>"i Lii
^u!xftalb\
Ffei-iQ v-ams Sloewten Pa*eM?ieic
63
-------
Table A-l. Laboratory Experimental Analysis
Sample
mgAs(111)/I
found
%As(111)
recovered
rr.gAs (V) /I
fcur.c
%As(V)
recovered
1. Deionized Water
None
None
2. O.OSmgAs (11U/1
0.050
100
Ncr.e
3. 0.05mgAs(111)/I
0 . C49
98
None
4. 0.05mgAs(V)/l
None
0 .051
102
0-05mgAs(V)/I
None
0 . C 4 9
0.C 5ngAs(111) &
0.C5ngAs(V)/I
0.050
100
0.049
98
0.05ngAs(111) &
0.05ngAs(V)/I
0.049
98
0 . 051
102
64
fit^uLoviZbxiei. &nc.
Premo Moceito SIDCktor Vi»lia
-------
Table A-2 , On Sits Analysis
samoie
mgAs(111)/I
found
%AS (111)IN
Well 31
mgAs(V)/I
found
%As (V) IN*
Well 31
Deionized Water
None
None
2. Well 31
0 . G36
ICC
None
3. Well 31
n . 0 7 5
:. C C1
4. 0.05-cAs(111)/:
0.050
None
5. 0 . OSir.gAs (V) / I
None
0 . C5C
6. Well 31 + 0.05
rr.cAs (111) /I
0 . 085
97
Ncr.e
None
7. We 11 31 + C.05
rr.g As (V) / I
0.036
100
C .050
None
NOTE: Total arsenic concentration for well '31: 0.035 ng/1
Ja&yia&tics.
Frey-.o M^sero S'.ecMon v/isn.i
65
-------
Fp TmHcitv Procedure (U.S. EPA, 19B0)
A 100-g sample (wet weight) ol centrifuged or filtered sludge was placed in a 4-
Uter Ehrienmeyer flask with 16 times its weight of denionized water. The sludge +
water mixture was stirred on a magnetic stirrer with sufficient mixing to keep the
sludge particulates In solution. The initial pH of the mixture was measured, and if it was
greater than 5.0 + 0.2, 0.5 N acetic acid was added to lower the pH to 5. The pH of the
solution was checked at intervals of 0.25, 0.5, 1, 2, 3, 4, 5 and 6 hours after the start
of the test. If necessary, 0.5 N acetic acid was added to lower the pH to 5; however, the
maximum limit for total acid addition was 4 mL per gram of solids. The sludge-water
mixture was stirred for 24 hours at 25°C. At the end of 24 hours, the solution pH was
checked, and if the pH was not below 5.2 and the maximum amount of acid had not been
added, the solution pH was again adjusted into the range of 5.0-5.2 and the extraction
was continued for 4 more hours with pH adjustment every hour.
At the end of the 24-hour (or 28-hour) extraction period, deionized water was
added to Ihe extractor in an amount determined by:
V = 20W - 16W - A
where: V = ml deionized water to be added.
W = weight in grams of the solid being extracted.
A = ml of 0.5 N acetic acid added during the extraction.
The supernatant was then filtered through a 0.45 |im membrane filter, acidified
lo a pH < 2 with 1:1 HNO3, and stored in a plastic bottle at 4°C for later GFAAS analysis
of total arsenic.
66
-------
On
-J
PRODUCT
FLUS
WATER
m
.q
c
¦5'
i >
3 -O
-*¦ ~o
try ®
£ 3
(D —•
O X
55 oj
o
w
o'
3
RV-IE'P
v-oh*-
V-3E ii
&
PIE
BRINE
RECIRCULATION
PUMP
BRINE
REJECT
PRODUCT
WATER
ST-2E
^FEED
R-2E
BRINE
El E2
MEMBRANE
E4
' E 3
SV-3E
STACK
ST-3E
PRODUCT V 1§J '
-\lr
SV-4E
±
Figure B1 .
Internal. [Low .schematic for the Ionics AquamiLe I 12 DK un i t --elect rod i al ys is with current
r ever sa 1 .
-------
TABLE Bl. REVERSIBLE ELECTRODIALYSIS SYSTEM SPECIFICATIONS
Manufacturer: Ionics, Inc., Aquamite I
Pairs of Membranes: 200
Kumber of Hydraulic Stages: 6 in series
Stack Dimensions: 40.6 cm long x 24.1 cm wide x 30.5 cm high
(16 in long x 9.5 in wide x 12 in high)
Product Flow: 1.9 m^/day (500 gal/day at 2500 mg/L TDS feed)
Typical Product TDS: 100 mg/L at 50% recovery, 2500 mg/L
TDS feed
X Recovery: 5C percent without brine recycle
6C percent with brine recycle
Polarity Reversal: Once each 15 rainu te s
Power Characteristics: 120V, Single Phase
Power Consumption: 8 kWhr/1000 gal
Temperaure Range: 0-45°C (32-110cF)
Operating Pressure: 311 k?a (45 psig)
Stack Pressure Drop: 173 kPa (25 psig)
pH Range: 1-13
Chlorine Tolerance: CI2 must be removed
Filter: One 10 cartridge type
68
-------
TABLE B2. REVERSE OSMOSIS SYSTEM SPECIFICATIONS
Number of Modules: Two in parallel
Mode of Operation: Module 1 0£ Module 2
Module 1: duPont Model No. 0420-21
Menbrane Type: B-9 Aramid
Menbrane Configuration: Hollow Fiber
Shell Dimensions: 13.3 cm OD x 63.5 cm long
(5.25 in OD x 25 in long)
Product Water Capacity: 7.95 m"^/day (2,100 gpd at 1500 ppm TDS)
Operating Pressure: 0-2760 kPa (0-400 psig)
Operating Temperature: 0-35sC (32-95°F)
pH Range, Continuous: 4-11
Minimum Brine Rate: 4.2 L/tain (1.11 gpra)
Chlorine Tolerance: CI2 must be removed
5i11 Density Index, SDI: 2 3.0
Module 2: Dow Model Dowex 4K
Membrane Type: Cellulose Triacetate
Menrane Configuration: Hollow Fiber
Shell Dimensions: 15.88 cm OD x 122 cm long
(6.25 in OD x 48 in long)
Produce Water Capacity: 15.14 day (4,000 gpd at 1500 ppm TDS)
Operating Pressure: 0-2760 kPa (0-400 psig)
Operating Temperature: 0-30°C (32-86°F)
pH Range, Continuous: 4.0 - 7.5
Minimum Brine Rate: 1.9 L/min (0.5 gpm)
Chlorine Tolerance: £ 1.0 mg/L
Silt Density Index, SDI: - 4.0
R0 Pucip: Moyno SP3, 316 ss Rotor
Maximum Punp Pressure; 5520 kPa (800 psig)
Puip Operaing Pressure; 2760 kPa (400 psig)
Puitip Motor: 3 hp, 220 v, Single Phase
;Lig'n Pressure Cutoff: 3105 kPa (450 psig)
High Pressure Relief: 3105 kPa (450 psig)
Low Pressure Cutoff: 2070 kPa (300 psig)
RO Pre treacraent Filters: Two Provided—One Deep Bed,
One 10 Cartridge
Deep Bed Filter: 35.6 cm OD x 165 cm height
(14 in OD x 65 in height)
Filter Media: 76.2 era AG over 10 cia flint gravel
(30 in AG over 4 in fiint gravel)
Filtration Rate: 117-293 m/day
(2-5 gal/min ft^)
69
-------
TABLE B3. Du Pont RO Projections for City Water
Du Pont Co. PERMASEP Projection GLA
SAN YSIDRO NM • Cltv Water
APRIL 2, 1984
Design Temp = 59.0 F {15.0 C)
Feed Pressure = 400.0 psig
Overall Conversion = 45.0%
Plant Capacity = not specified
Permeator Model - 0420-021
LSI = .78 pH ; A.FD. - 7.20
H2SO4 Added (AS 100%) = 0.0
Ionic Strength Acid Feed = .0177
Max. Allow. Conv.:
CaS04
BaSC>4
SrS04
CaF2
Max. Allow. Conv.:
Si02
Staging Ratio: 2.0
Stage Permeators Percent
£& Per Stage Conversion
1 2.0 45.0
Max Temp = 59.0 F (15.0 C)
Product Pressure = 10.0 psig
Term = 10,000 hrs.
Bal. Tube « 20 psig
Salt Passage = 10.0%
pH Brine - 7.44 ; pH sat.- 6.67
PPM = 0.0 Ibs/kgals. Product
Brine = .0321
Without NaHVIP With NaHMP
95.5% 96.9%
-88.7% 87.1%
97.8% 99.4%
-2.3% 77.9%
Lit. Dst3 QpfiTi Dstci
0% 52.4%
Perm Press ---Flow/Perm (gpm)---
Prop (psi) Efisd Brine Product
3.4 2.2 1.2 1.0
Stage
Nq- mfrc
1 .868
TOTAL
---Feed---
psig kgpd
400.0 6.4
---Brine---
psig kgpd
396.6 3.5
---Product---
psig kgpd
10.0 2J1
2.9
70
-------
TABLE B3.
(Continued)
Raw Feed as ppm Acid Feed As ppm
Cations Ions Ions CaCGi
Brine as ppm
Ions CaCQq
Product as ppm
Ifioa CaCCh
Ca
85.00
85.00 21 2.1 0
153.10
381.90
1 .80
4.50
Mg
17.00
17.00 69.90
80.60
125.90
.40
1 .50
Na
190.00
1 90.00 413.30
330.90
719.70
1 7.80
38.70
K
1 1.70
11.70 15.00
20.80
26.60
.60
.80
Sr
.90
.90 1.03
1.62
1 .85
.02
.02
Ba
.18
.18 .13
.32
.24
.00
.00
Fe
.02
.02 .04
.04
.06
.00
.00
TOTAL
304.80
304.80 71 1.40
537.30
1256.20
20.60
45.50
Anions
HCQj
571 .00
571.00 467.60
1 003.70
822.00
42.20
34.50
SO4
60.50
60.50 63.00
1 09.00
1 13.50
1 .30
1.30
a
123.00
123.00 173.40
21 8.80
307.80
6.50
9.20
F
2.70
2.70 7.10
4.80
12.60
.20
.40
NO3
.20
.20 .20
.40
.30
.00
.00
TOTAL
757.50
757.50 71 1.40
1336.20
1 256.20
50.20
45.50
TDS ION
1 122.30
1 122.30
1978.70
75.60
Si02 ppm
60.00
60.00
1 05.20
4.80
CO2 ppm
58.90
58.90
58.90
58.90
pH
7.20
7.20
7.44
6.07
Osmotic Pressure, PSI
8.60
1 4.90
.60
Equiv. NaCl, PPM
771.00
1341 .00
57.00
71
-------
TABLE B4. Du Pont RO Projections for Well No. 4 Water
Du Pont Co. PERMASEP Projection GLA
SAN YSIDRO NM - WELL #4
APRIL 2, 1984
Design Temp = 59.0 F (15.0 C)
Feed Pressure = 400.0 psig
Overall Conversion = 45.0%
Plant Capacity not specified
Permeator Model = 0420-021
Max Temp * 59.0 F (15.0 C)
Product Pressure - 10.0 psig
Term = 10,000 hrs.
Bal. Tube = 20 psig
Salt Passage = 10.0%
LSI = .36 pH; A.FD. . 7.02
H2S04 added (As 100%) = 0.0
Ionic Strength Acid Feed = .0283
pH Brine = 7.26 ; pH Sat. = 6.90
PPM = 0.0 Ibs/kgals Product
Brine = .0512
Max. Alfow. Conv.
CaS04
BaS04
SrS04
CaF2
Max. Allow. Conv.
Si02
Without NaHMP
96.1%
¦60.5%
97.3%
-41.8%
Lit- Data
-10.0%
With NaHMP
97.2%
91.8%
99.2%
69.4%
47.6%
Staging Ratio: 2.0
Stage Permeators
Ni Per Staoe
1
2.0
Percent
Conversion
45.0
Perm Press
Droo (osH
3.3
Flow/Perm (gpm) ---
Brine Product
2.2
1 .2
1 .0
Stage
fcjQ.
1
TOTAL
Feed
MFRC psio kgpd
.868 400.0 6.2
Brine
psia kgpd
396.7 3.4
Product
psig kood
1 0.0
ZJ.
2.8
72
-------
TABLE B4. (Continued)
Raw Feed as ppm Arid Feed As ppm
Cations Ions Ions CaCO»
Brine as ppm
Ions CsCCn
Product as ppm
Ions CaCCh
ca
38.00
38.00 94.80
68.40
170.70
.80
2.1 0
Mg
7.50
7.50 30.80
1 3.50
55.50
.20
.70
Na
510.00
510.00 1 109.30
895.30
1947.40
39.00
84.90
K
15.00
15.00 19.20
26.60
34.00
.30
1 .00
Sr
.56
.56 .64
1 .01
1.15
.01
.01
Ba
.06
.06 .04
.1 1
CD
O
.00
.00
Fe
2.00
2.00 3.58
3.60
6.45
.04
.08
TOTAL
573.10
573.10 1258.30
1008.60
221 5.30
40.90
88.80
Anions
HCO3
783.00
783.00 641.30
1363.10
11 1 6.40
74.00
60.60
SO4
169.80
169.80 176.70
305.60
31 8.20
3.70
3.90
a
300.00
300.00 423.00
532.10
750.20
16.40
23.10
F
6.60
6.60 17.30
1 1 .60
30.50
.50
1.30
TOTAL 1
259.40
1259.40 1258.30
221 2.40
221 5.30
94.50
88.80
TDS ION
1898.50
1 898.50
3336.60
140.80
SIO2 ppm
66.00
66.00
11 5.60
5.40
CO2 ppm
122.20
1 22.20
122.20
122.20
pH
7.02
7.02
7.26
6.00
Osmotic Pressure, psi
15.90
27.70
1 .20
Equiv. NaCI, ppm
1434.00
2493.00
1 10.00
73
-------
TABLE B5. Dow RO Projections for City Water
Dowe X* R.O. Permeator System Design
Project: City Water Analysis
Date: Mar 23, 1984 9:50:10
This is the design of a 1 stage reverse osmosis system with 1 permeator type SP9605
(initial standard test performance of 5000. GPD, 96.0% salt rejection.) The system is
operating at a recovery of 54.%, feed pressure of 400. psi and interstage pressure drops of:
Stage 1 - 2 = 50. psi
The feed water temperature range is 15.0 C to 15.0 C.
Acidification ion for carbonate scale Ctrl: 1.96 lbs H2SO4 (100 pct)/kgal feed.
The design results below reflect system performance after 3.0 years.
WATER ANALYSIS
ION
PPM ION IN
RAW FEED
PPM ION IN
TREATED
FEED
PPM CaC03
IN
TREATED
FEED
PPM ION IN
PERMEATE
PPM ION IN
CONCEN-
TRATE
Ca++
85.00
85.00
212.24
2.44
179.99
Na+
190.00
190.00
413.63
7.13
400.40
Mg++
17.00
17.00
69.99
0.40
36.10
Fe++
0.02
0.02
0.04
0.00 "
0.04
Mn++
0.02
0.02
0.04
0.00
0.04
K+
11.70
11.70
14.98
0.58
24.50
Ba++
0.18
0.18
0.13
0.00
0.38
Sr++
0.85
0.85
0.97
0.02
1.81
Total +
304.77
304.77
712.07
10.56
643.27
cr
140.24
140.24
198.02
4.10
296.88
F"
2.67
2.67
7.03
0.09
5.64
SO4--
37.00
271.52
282.92
5.78
577.25
NO3-
0.22
0.22
0.18
0.03
0.44
Si02
60.00
60.00
99.96
4.29
124.10
PO4-' *
0.00
0.00
0.00
0.00
0.00
HCCV
570.60
279.02
228.80
14.53
583.33
CO3--
0.19
0.01
0.02
0.00
0.02
Total -
810.93
693.68
716.97
24.53
1463.56
TOTAL
1115.70
1058.45
814.48
39.38
2230.93
pH
7.17
6.22
5.41
6.49
C02
273.14
310.60
204.85
351.70
Langelier
Index
-0.20
74
-------
OPTIMIZED DESIGN CONFIGURATION AND RATINGS
STAGE MODULES FEED MODULE PIGTAIL INTER-
NO PER STAGE PRESSURE DELTA P DELTA P STAGE
PSI PSI PSI DELTA P
PS I
TOTAL TOTAL
PRODUCT BRINE
FLOW FLOW
GPD GPD
400.
2.
48.
50.
3443.
2992.
STAGE
AVGPROD
FLOW (GPD)
AVG BRINE
FLOW
(GPM)
PRODUCT
QUAL (PPM)
EXIT
BRINE
CONC
(PPM)
PERCENT
RECOVERY
PERCENT
NaCL
3443.
3.27
39.
2231.
53.50
96.28
Maximum recovery to avoid saturation with:
Gypsum
Anhydrite
BaSOa
SrS04
S1O2
CaF2
93.3%
96.5%
0.0%
95.57c
53.9%
0.07c
These maximum recoveries assume the addition of a scale inhibitor.
** A pigtail is an artificial pressure drop consisting of nylon or stainless steel tubing which
allows all permeators in a given stage to operate at approximately the same recovery.
Notes:
A. The Dowex* RO System should be operated in such a manner as to prevent the
precipitation of any salts within the permeator.
Specifically we recommend:
1) Acid addition for carbonate scale control
2) Scale inhibitor addition for sulfate scale control
3) An automatic flush of the permeators at low pressure (50-100 psi) with permeate
water on system shut down for silica and other scales.
B. Iron should be maintained at less than 0.1 ppm at all times, including start up and shut
down.
C. Barium and strontium should be analyzed at the 0.01 and 0.1 ppm level of detection
respectively. If an accurate analysis was not available at the time of this design, please
note that it may be neccesary to lower the overall system recovery to prevent barium
and strontium sulfate scale formation.
D. The maximum level of free chlorine which can be tolerated in the RO feedwater varies
with temperature as follows: 1 ppm at 4-25 degrees C, 0.5 ppm at 26-30 degrees C,
0 ppm at 31-35 degrees C.
75
-------
E. The feedwater should be sterile.
F. The feedwater should be pretreated to a silt density index < 4.
This estimate of an appropriate design configuration and expected performance of Dowex*
RO permeators is based upon the particular feedwater analysis submitted to the Dow
Chemical Co. The design and expected performance are presented in good faith, but no
warranty is expressed or implied. Although these criteria should assure proper
performance of the Dowex* RO permeators, the ultimate success of any RO facility
depends upon an adequately engineered system that is properly operated and maintained.
* Trademark of the Dow Chemical Company
76
-------
TABLE B6. Dow RO Projections for Well No. 4 Water
Dowe X* R.O. Permeator System Design
Project: Well #4 Analysis
Date: Mar 23, 1984 9:41:08
This is the design of a 1 stage reverse osmosis system with 1 permeator, type SP9605
(initial standard test performance of 5000. gpd, 96.0% salt rejection.) The system is
operating at a recovery of 48.%, feed pressure of 400. psi and interstage pressue drops of:
Stage 1-2 = 50. psi
The feedwater temperature range is 15.0 C to 15.0 C.
Acidification for carbonate scale Ctrl: 1.76 lbs H2SO4 (100 pet) /Kgal feed the design
results below reflect system performance after 3.0 years.
WATER ANALYSIS
Q PPM ION IN PPM ION IN PPM CaCOj PPM I0N IN PPM ION IN
iUN RAW FEED TREATED IN pfrv^atf roNPFV
FEED TREATED
FEED TRATE
Ca^*
38.00
38.00
94.89
1.12
72.04
Na+
510.00
510.00.
1110.27
19.14
963.10
Mg++
7.50
7.50
30.88
0.17
14.27
Fe++
0.10
0.10
0.18
0.00
0.19
Mn++
0.16
0.16
0.29
0.01
0.30
K+
15.00
15.00
19.20
0.72
28.19
Ba+_t"
0.06
0.06
0.04
0.00
0.11
Sr++
0.56
0.56
0.64
0.01
1.07
Total +
571.38
571.38
1256.42
21.17
1079.27
ci-
348.25
348.25
491.73
13.62
657.14
F"
6.59
6.59
17.36
0.21
12.48
SO4--
101.00
311.48
324.57
5.67
593.77
NO3-
0.00
0.00
0.00
0.00
0.00
Si02
66.00
66.00
109.96
4.58
122.70
PO4-""
0.00
0.00
0.00
0.00
0.00
HCO3-
782.62
520.90
427.14
24.88
978.76
CO3"
0.19
0.03
0.05
0.00
0.06
Total -
1304.64
1187.25
1260.84
44.39
2242.20
TOTAL
1876.02
1824.63
1368.59
70.14
3444.16
pH
7.02
6.44
5.60
6.68
C02
310.23
352.77
232.67
381.82
Langelier
Index
-0.20
77
-------
OPTIMIZED DESIGN CONFIGURATION AND RATINGS
STAGE MODULES FEED MODULE PIGTAIL INTER- TOTAL TOTAL
NO PER STAGE PRESSURE DELTA P DELTA P STAGE PRODUCT BRINE
PSI PSI PSI DELTA P FLOW FLOW
PSIGPD GPD
1 1 400. 3. 47. 50. 3334. 3612.
STAGE AVG PROD AVG BRINE PRODUCT EXIT PERCENT PERCENT
FLOW (GPD) FLOW QUAL (PPM) BRINE RECOVERY NaCL
(GPM) CONC
(PPM)
1 3334. 3.67 70. 3444. 48.00 96.16
Maximum recovery to avoid saturation with:
Gypsum 97.1%
Anhydrite 98.3%
BaS04 22.6%
SrS04 97.4%
Si02 48.4%
CaF2 0.0%
These maximum recoveries assume the addition of a scale inhibitor.
** A pigtail is an artificial pressure drop consisting of nylon or stainless steel tubing which
allows all permeators in a given stage to operate at approximately the same recovery.
Notes:
A. The Dowex* RO System should be operated in such a manner as to prevent the
precipitation of any salts within the permeator.
Specifically we recommend:
1) Acid addition for carbonate scale control
2) Scale inhibitor addition for sulfate scale control
3) An automatic flush of the permeators at low pressure (50-100 psi) with permeate
water on system shut down for silica and other scales.
B. Iron should he maintained at less than 0.1 ppm at all times, including start up and shut
down.
C. Barium and strontium should be analyzed at the 0.01 and 0.1 ppm level of detection
respectively. If an accurate analysis was not available at the time of this design, please
note that it may be neccesary to lower the overall system recovery to prevent barium
and strontium sulfate scale formation.
D. The maximum level of free chlorine which can be tolerated in the RO feedwater varies
with temperature as follows: 1 ppm at 4-25 degrees C, 0.5 ppm at 26-30 degrees C,
0 ppm at 31-35 degrees C.
78
-------
E. The feedwaier should be sterile.
F. The feedwater should be pretreated to a silt density index < 4.
This estimate of an appropriate design configuration and expected performance of Dowex*
RO permeators is based upon the particular feedwater analysis submitted to the Dow
Chemical Co. The design and expected performance are presented in good faith, but no
warranty is expressed or implied. Although these criteria should assure proper
performance of the Dowex* RO permeators, the ultimate success of any RO facility
depends upon an adequately engineered system that is properly operated and maintained.
* Trademark of the Dow Chemical Company
79
-------
San Ysidro Arsenic Removal Report
Appendix C
Activated Alumina Runs
o
r~
200
Time, Hours
400
600
t—i 1 1 1 1 1—i 1—i r
~i 1 r
Time , Days
10 15 20
25
30
T
T
M Yildro Alumina Run No. 1
14x2B mesh, F-1 Alumina
April 1 2-May 3, 1 9B4
Bed Volume = 400 mL
Flow Rale =80 mL/min, City Water
EBCT = 5 mln
pH = 6.0 - 0.1
Total As Adsorbed =146 mg(or 156 mg to 50 ppb As)
Total F~Adsorbed * 1932 mg(or 154B mg to 1.4 ppm F )
+
F , Cq = 2.0 ppm
O 40
Effluent pH
As, C0 = BO ppb [40% As(iri)]
10
a
2000 4000 6000 8000
Bed Volumes, BV
I
a
Figure CI. BreaAtnrough curves for fluoride anc arseni
new, coarse-nesh alumina.
curing Run No
80
\
-------
Time, minutes
20
8000
6000
a
o
0
1
u.
4000
2000
40
—i—
60
—i—
60
—]—
100
—I—
n—~i—i—i—i—i—i—r
6an Yaldro Alumina Run No. 1R
May 14, 1064
AA Regeneration Data(Mesh 12x28)
Regenersnt «4% (1N> NaOH
Regeneration Rate *26 ml/min • 3.9 BV/hr
EBCT >16.4 mln. BV >400 mL
Total F'Desorbed During Regeneration "1478 mg(78U)
Total F~ Adsorbed During Exhaustion" 1832 mg
Total As Desorbed During Regeneration ¦ 85 mg(9B%)
Total As Adsorbed During Exhaustion* 148 mg
360
320
260
240
200
oi
E
. o
: c
160 5
03
<
120
80
40
Bed Volumes, BV
Figure C2. Arsenic and fluoride elution during a regeneration cf fine
ir.esh alumina using U% NaOH. Run 1R — regeneration following
exhaustion run No. 1.
81
-------
90
80
70
60
D>
3.
r 50
o
c
o
u 40
bj
<
30
20
10
0
Time, Hours
0 200 400 600
, , , j__j , j 1 1 1 , 1 ,
Time, Days
5 10 15 20 25
ui
3.2
2.8
2.4
2.0
i r i i n
&mn Yiidfo Alumina Run No. 3
14x28 mash, F-1 Alumina
May 16-June 3, 1084
Bed Voluma = 400 mL
Flow Rat# = 80 ml/min, City Water
EBCT = 5 min
PH Feed - e,0±0.1
Total As Adsorbed = 142 mg(or 152 mg to SO ppb As)
Total F~ Adsorbed = 1890 mg(or 1225 mg to 1.4 ppm F~)
F~ C0 = 2.07 ppm
o 1.6
O
1.2
0.8
0.4
0
+
As. C, - 08 ppb [28* AsCSD]
10
9
8
7
6
5
X
a
2000 4000 6000
Bed Volumes, BV
8000
Figure 03. Fluoride and arsenic breakthrough curves for Hun No. 3--once-
regenerated, coarse-nesh alumina.
82
-------
Time, minutes
20 40
—I 1 1 1 r
60 80 100 120 140 160 180 200 220 240
—i 1 1 1 1 1 1 1 r
r
~r
-i r
T"
t
San Ysidro Alumina Run No. 3R
June IS, 1084
AA Regeneration Data(Mesh 12x28)
Regenerant = 1% (0.25 N) NaOH
Regeneration Rate = 28.6 m/min = 4.3 BV/hr
EBCT = 14 min. BV = 400 ml
Total F" Oesorbed During Regeneration - 1390 mg(82%)
Total F~ Adsorbed During Exhaustion ¦ 1890 mg
Total As Desorbed During Regeneration = 92 mg(65%)
Total Aa Adsorbed During Exhauatlon » 142 mg
oo
D>
E
o
c
o
O
1000
800
600
400
200
0
50
6 8 10 12
Bed Volumes, BV
Figure C4. Fluoride and arsenic elulion during II NaOH rrKc>ne ra t ion of coarse-mesh alumina following
exhaustion Run No. 3.
-------
0
r
Time, Hours
200 400
600
CT
E
90
80
70
60
50
3.2 -
-i 1 1 1 1 1 1 1 1 1 r
Time, Days
5 10 15 20
! j ! !
San Ysidro Alumina Run No. 4
25
—i—
30
o
c
o
O 40
V)
<
CT>
E 2
o
o 1
o
I
30
20
10
0
.8
.4
.0
.6
.2
.8
.4
0
28x48 mesh, F-1 Alumina
May 16-June 1 1, 1984
Bed Volume " 400 mL
Flow Rate »80 mL/min, City Water
EBCT - 5 min
pH Feed * 8.0 ±0.1
-Total As Adsorbed = 212 mg(or 230 mg to 50 ppb As)
Total F~Adsorbed = 2245 mgtor 1548 mg to 1.4 ppb As)
2.07 ppm
Effluent pH
+
As, Go " 88 ppb
[26% AsUII)]
10
9
8
7
6
5
2000 4000 6000
Bed Volumes, BV
8000
r
Q.
Figure C5. Breakthrough cf fluoride and arsenic during Run No. i—once-
reeeneracted fir.e-~.esh alumina
84
-------
Time, minutes
OO
0 20 40 60
1800 1 1 1 1 1 r
1600 -
100 120 140 160 180 200 220 240
cr
£
o
c
o
o
1400
1200
1000
800
600 -
400
200
i—i i i i i i—i
San Ysldro Alumina Run No. 4R
June 18, 1984
AA Regeneration Data (Mesh 28 x 48)
Regenorant = 1% NaOH
Regeneration Rate = 30 mL/mln = 4.5 BV/hr
EBCT = 13 mln. BV = 400 mL
Total F Desorbed During Regeneration " 1360 mg(81%)
Total F Adsorbed During Exhaustion => 2245 mg
Total As Desorbed During Regeneration = 148 mg(70%)
Total As Adsorbed During Exhaustion =212 mg
40 o
8 10 12
Bed Volumes, BV
Figure; C6,
Fluoride and arsenic, elution curves during regeneration of spent, Cine-mesh alumina
loll owing exhaustion Hun No. U.
-------
Time, hours
200 400
600
2.8-
i—i—i—i—i—i—i—i—i—i—i—i—i—i
Time, days
5 10 15 20 25 30
1 1 1 1 1
San Ytldro Alumina Run No. 5
14x28 Mesh, F-1 Alumlne
June 18 - July 7. 1884
Bed Volume » 400 mL
Flow Rate • 80 mL/mln, City Water
EBCT " S mln
pH Feed - 6.0 t 0.1
Total As Adsorbed " 136 mg
(or 122 mg to 50 ppb As)
Total F~ Adsorbed ¦ 802 mg
(or 804 mg to 1.4 ppm F~)
c 50
84 ppb
O 1.2
Effluent pH
2000 4000 6000
Bed Volumes, BV
8000
Figure C7. Breakthrough curves for fluoride and arsenic during Ru
twice-regenerated coarse-mesh alumina.
86
-------
Time, minutes
OO
¦—I
O)
o
c
o
o
1800
1600 -
1400
1200
1000
800
20
—i—
40
—T
60
—i—
80
T~
100
T 1
120 140 160
t 1 1 1 1 1 r
San Ysldro Alumina Run No. 5R
180 200
90
July 23. 1984
AA Regeneration Data (Mesh 14x28)
Regonerant = 1% NaOH
Regeneration Rate= 33.3 m/mln = 5 BV/hr*
EBCT = 12 mln. BV = 400 mL
Total F~ D«sorbed During Regeneration - 1200 mg(1B0%).
Total F~ Adsorbed During Exhautlon ¦= 802 mg
Total As Desorbed During Regeneration = 91 mg(87%)
Total As Adsorbed During Exhaustion = 136 mg
80
70
60
- 50
- 40
- 30
- 20
- 10
6 8 10 12
Bed Volumes, BV
o
E
o
c
o
O
0)
Figure C8, Fluoride anrl arsenic elution during 17, NaOII regeneration of coarse-mesh alumina following
exhaustion Run No. .
-------
Time, Hours
o>
o
c
o
O
V)
<
0 200
i—i 1 r
i—r
400
1 1 r
600
t—i—i—r
90
80
70
60
50
40
30
20
10
0
Time, Days
10 15 20
25
3.
3
2.
i
2.
1 1 i 1 1
Ban Ysidro Alumina Run No. 6
28*46 mash, F-1 Alumina
June 19-July 12, 1984
Bed Volume • 400 mL
Flow Rate • 60 mL/min, City Water
EBCT • 6 min
pH Feed = 6.0 - 0.1
Total As Adsorbed 1 198 mg(or 1B7 mg to 50 ppb As)
" Total F~ Adsorbed = 1220 mg(or 1251 mg to 1.4.ppm
30
—r
F~)
C0 = 94 ppb[36% AsCSd}
Eflluenl pH
8
X
Q
2000 4000 6000
Bed Volumes, BV
6000
Figure C9. Breakthrough curves for fluoride and arsenic during exhaustion
Run No. 6--twice-rcgenerated fine-mesh alumina.
88
-------
OO
vO
0 20 40
1800 —i 1 1—i r
1600 -
o
E 1000
d
° 800
Time, minutes
80 100 120 140 160 180 200
3an Yaldro Alumina Run No. 6R
July 23. 1984
AA Regeneration Data (Mesh 28x48)
Regenerant * 1% NaOH
Regeneration Rate = 32.3 m/mln = 4.8 BV/hr
EBCT = 12.4 mln. BV = 400 ml
1400
Total F~ Desorbod During Regeneration 11300 mg(112%)
Total F~ Adsorbed During Exhaustion = 1220 mg
Total As Desorbed During Regeneration = 133 mg(67%)
Total As Adsorbed During Exhaustion = 108 mg
1200
6 8 10
Bed Volumes. BV
o>
E
o
c
o
O
(0
<
Figure CIO.
Iluoritle ami arsenic eluLion during \7. NaOII regeneration ol fintr-niesh alumina following
exhaust ion Kun No. ft.
-------
Time, Hours
200
400
600
——i—
90 r
60 - 3.2
70 - 2.8 -
o>
o
c
o
O
CO
<
60
50
40
30 -
20
10
0 L
2.4 -
5
~T
Time, Days
10 15
1 1
San Yaidro, New Mexico
AA, 28x48, Run No. 7{Fresh Media)
July 16-23, 1984
Bed Volume ¦ 400 mL
Flow Rate *81 mL/min. City Water
EBCT « 5 min
PHi«ed 1 7 3 °-1tNo Acid Added)
Total As Adsorbed = 73 6 mg(or 70 mg to 50 ppb As)
Total F~ Adsorbed i 364 ma(or 370 mg toi.4 ppm F-)
1944 BV
To 50 ppb AS
547 BV Tol.4 ppm F"
Effluent pH
As, Co - 104 ppb(40% AS(111))
9
6
7
6
5
I
Q.
1 2 3
Bed Volume, x 1000 BV
Figure Cll. Break through curves for fluoride and arsenic during exhaustion
Run No. 7_.f ir.e-nesh alur.ir.a and unadjusted feed pH .*
90
-------
Time, minutes
VO
o>
E
o
120 140 160
, , ,—,—
San Ysldro Alumina Run No. 7R
July 25, 1884
AA Regeneration Data (Mesh 26x48)
Rageneranl =1% NaOH
Regeneration Rate = 32,3 mL/mln = 4,8 BV/hr -
EBCT =12.4 min. BV=400 mL
Total F~ Oeaoroed During Regeneration - 281 mo(77%)
Total F" Adsorbed During Exhaustion = 364 mg
Total As Desorbed During Regeneration = 41 mg(56%)
Total As Adsorbed During Exhaustion = 74 mg
6 8 10
Bed Volumes, BV
O)
E
d
c
o
Q
m
<
Figure C12. fluoride and arsenic eluiion during IX NaOII regeneration of fine-mesh aJumina foJ lowing
exhaust. i on Kun No. '/,
-------
TECHNICAL REPORT DATA
(Pttait read Instruction: on the reverse before comple'
1. REPORT NO.
EPA/600/2-91/011
4. TITLE AND SUBTITLE
ARSENIC (III) AND ARSENIC (II) REMOVAL, FROM
DRINKING WATER IN SAN YSIDRO, NEW MEXICO
S. REPORT DATE
April 1991
6. performing organization code
7. AUTHORIS)
Dennis Clifford
Chieh-Chieh Lin
8 PERFORMING organization report no.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Civil and Environmental Engineering
University of Houston
Houston, Texas 77004-4791
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
CR 807939
12. SPONSORING AGENCY NAVE AND AOORESS
Risk Reduction Engineering Laboratory—Cincinnati, OH
Office of Research and Development
U. S. Environmental Protection Agency
Cincinnati, OH 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
1«. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
PROJECT OFFICER - Thomas J. Sorg (513)569-7370, FTS 684-7370.
16 ABfKeACremoval of a natural mixture of As (III) (31 ug/L) and As (V) (57 ug/L) from a
groundwater high in total dissolved solids (TDS), and also containing fluoride (2.0
mg/L), was studied in San Vsidro, NM using the University of Houston (UH)/U.S.
Environmental Protection Agency (EPA) Mobile Drinking Water Treatment Research
Facility. The objective of the study was to establish a cost-effective means of
removing AS(III), As(V), and fluoride from this and similar waters.
Arsenic adsorption into fine-mesh activated alumina gave better-than-expected
results. Approximately 9000 bed volumes (BV) could be treated at pH 6 before the
arsenic maximum contaminant level (MCL) (0.05 mg/L) was reached. At the natural pH
of 7.2. however, only 1900 BV could be treated before exceeding the MCL.
Reverse Osmosis (R0) treatment resulted in >97% arsenic removal and >94% TDS removal.
Electrodialysis (ED) removed 73% of the arsenic and was able to meet the arsenic MCL
on the City Water containing 89 ug/L total arsenic; however, ED removed only 28% of
the As(III) from a new well containing 100% As(III) at a level of 230 ug/L.
Chloride-form anion exchange also performed better-than-expected (200 BV) but not
well enough for it to be considered seriously for treatment. Point-of-use (P0U) R0
treatment was effected in removing >91% of the arsenic and >94% of the TDS at low
(<15") water recovery.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS C. COSATi Field/Group
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
EPA Form 2220-1 (Rav. 4-77) previous edition is obsolete
19. SECURITY C'-ASS (This Report}
T^TT A^TFT»n
21 NC CP PAGES
118
20. SECURITY C-A5S (This pag?)
UNCLASSIFIED
22. PRICE
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