Electrochemical arsenic remediation for rural Bangladesh

314 Pages·2008·3.74 MB·English

by  Susan Amrose Addy

Lawrence Berkeley National Laboratory
Lawrence Berkeley National Laboratory
Title
Electrochemical arsenic remediation for rural Bangladesh
Permalink
https://escholarship.org/uc/item/32n7d47w
Author
Addy, Susan Amrose
Publication Date
2009-01-26
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University of California
Electrochemical Arsenic Remediation for Rural Bangladesh
by
Susan Elizabeth Amrose Addy
B.S. (University of Michigan at Ann Arbor) 2000
M.A. (University of California at Berkeley) 2003
A dissertation submitted in partial satisfaction of the
requirements for the degree of
Doctor of Philosophy
in
Physics
in the
GRADUATE DIVISION
of the
UNIVERSITY OF CALIFORNIA, BERKELEY
Committee in charge:
Professor Ashok Gadgil, Co-Chair
Professor Robert Jacobsen, Co-Chair
Professor Richard Muller
Professor David Sedlak
Fall 2008
The dissertation of Susan Elizabeth Amrose Addy is approved:
Co-Chair Date
Co-Chair Date
Date
Date
University of California, Berkeley
Electrochemical Arsenic Remediation for Rural Bangladesh
Copyright 2008
by
Susan Elizabeth Amrose Addy
1
Abstract
Electrochemical Arsenic Remediation for Rural Bangladesh
by
Susan Elizabeth Amrose Addy
Doctor of Philosophy in Physics
University of California, Berkeley
Professor Ashok Gadgil, Co-Chair
Professor Robert Jacobsen, Co-Chair
Arsenic in drinking water is a major public health problem threatening the lives
of over 140 million people worldwide. In Bangladesh alone, up to 57 million people
drink arsenic-laden water from shallow wells. ElectroChemical Arsenic Remediation
(ECAR) overcomes many of the obstacles that plague current technologies and can be
used affordably and on a small-scale, allowing for rapid dissemination into Bangladesh
to address this arsenic crisis.
In this work, ECAR was shown to effectively reduce 550 - 580 µg/L arsenic (in-
cludingbothAs[III]andAs[V]ina1:1ratio)tobelowtheWHOrecommendedmaximum
limitof10µg/LinsyntheticBangladeshgroundwatercontainingrelevantconcentrations
of competitive ions such as phosphate, silicate, and bicarbonate. Arsenic removal ca-
pacity was found to be approximately constant within certain ranges of current density,
but was found to change substantially between ranges. In order of decreasing arsenic
2
removal capacity, the pattern was: 0.02 mA/cm2 > 0.07 mA/cm2 > 0.30 - 1.1 mA/cm2
> 5.0 - 100 mA/cm2. Current processing time was found to effect arsenic removal ca-
pacity independent of either charge density or current density. Electrode polarization
studies showed no passivation of the electrode in the tested range (up to current density
10 mA/cm2) and ruled out oxygen evolution as the cause of decreasing removal capacity
with current density. Simple settling and decantation required approximately 3 days to
achieve arsenic removal comparable to filtration with a 0.1 µm membrane.
X-ray Absorption Spectroscopy (XAS) showed that (1) there is no significant
difference in the arsenic removal mechanism of ECAR during operation at different cur-
rent densities and (2) the arsenic removal mechanism in ECAR is consistent with ar-
senate adsorption onto a homogenous Fe(III)oxyhydroxide similar in structure to 2-line
ferrihydrite.
ECAR effectively reduced high arsenic concentrations (100 - 500 µg/L) in real
Bangladesh tube well water collected from three regions to below the WHO limit of 10
µg/L. Prototypefabricationandfieldtestingarecurrentlyunderway.
Professor Ashok Gadgil
Dissertation Committee Co-Chair
Professor Robert Jacobsen
Dissertation Committee Co-Chair
i
This work is dedicated
to my husband,
Nathan Joseph Addy
my love, my heart, and my partner in all things,
to my father,
Fredrick James Amrose
who has encouraged me and supported me for my entire life,
and to the friend I will always admire most,
Maya Sophia James
who has saved my life and my sanity and helped shape my outlook on all things.
ii
Contents
List of Figures vi
List of Tables xii
1 Introduction 1
1.1 Arsenic contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Worldwide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Crisis in Bangladesh and West Bengal . . . . . . . . . . . . . . . . 4
1.2 Arsenic remediation and safe water sources . . . . . . . . . . . . . . . . . 6
1.3 A new implementation model for Bangladesh . . . . . . . . . . . . . . . . 7
1.4 ElectroChemical Arsenic Remediation (ECAR) . . . . . . . . . . . . . . . 10
1.4.1 ECAR operating parameters . . . . . . . . . . . . . . . . . . . . . 12
1.4.2 Other considerations - treatment time and cost . . . . . . . . . . . 13
1.4.3 Previous electrocoagulation research . . . . . . . . . . . . . . . . . 14
1.4.4 The need for parameter studies in Bangladesh groundwater . . . . 16
1.5 Thesis objectives and dissertation structure . . . . . . . . . . . . . . . . . 17
1.5.1 Chapter 2: Relevant Scientific Background . . . . . . . . . . . . . 18
1.5.2 Chapter 3: Chemical and Physical Analysis of Arsenic Complexa-
tion with Iron in ECAR . . . . . . . . . . . . . . . . . . . . . . . . 18
1.5.3 Chapter 4: Characterization of Reaction Products . . . . . . . . . 20
1.5.4 Chapter 5: ECAR Performance in Real Bangladesh Groundwater . 21
2 Relevant Scientific Background 23
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 Arsenic in Natural Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3 Iron (Hydr)oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4 Arsenic sorption onto iron (hydr)oxides . . . . . . . . . . . . . . . . . . . 30
2.4.1 Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.4.2 Review of arsenic adsorption literature . . . . . . . . . . . . . . . . 35
2.4.3 Arsenic removal via zero valent iron . . . . . . . . . . . . . . . . . 38
2.4.4 Effect of pH and speciation on arsenic sorption . . . . . . . . . . . 40
iii
2.4.5 Kinetics of arsenic sorption . . . . . . . . . . . . . . . . . . . . . . 43
2.4.6 Effects of co-occuring solutes . . . . . . . . . . . . . . . . . . . . . 48
2.5 Electrocoagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.5.1 Electrochemical cell theory . . . . . . . . . . . . . . . . . . . . . . 54
2.5.2 Electrocoagulation (EC) using iron . . . . . . . . . . . . . . . . . . 62
2.5.3 As[III] oxidation in EC . . . . . . . . . . . . . . . . . . . . . . . . 73
2.5.4 Arsenic removal mechanism using EC . . . . . . . . . . . . . . . . 75
2.5.5 Arsenic removal studies using EC . . . . . . . . . . . . . . . . . . . 75
2.5.6 Kinetics of EC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
2.5.7 Characterization of EC products . . . . . . . . . . . . . . . . . . . 79
2.6 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3 Chemical and Physical Analysis of Arsenic Complexation with Iron in
ECAR 84
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.1.1 Operating parameters in ECAR. . . . . . . . . . . . . . . . . . . . 84
3.1.2 Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
3.2.1 Arsenic analysis and arsenic speciation . . . . . . . . . . . . . . . . 90
3.2.2 pH, dissolved oxygen measurements . . . . . . . . . . . . . . . . . 92
3.2.3 Development of Synthetic Bangladesh Groundwater (SBGW) . . . 93
3.2.4 Electrochemical cell . . . . . . . . . . . . . . . . . . . . . . . . . . 101
3.2.5 Electrochemical Arsenic Remediation Procedure . . . . . . . . . . 105
3.2.6 ECAR batch experiments run 1 - Matrix 1 . . . . . . . . . . . . . 108
3.2.7 ECAR batch experiments run 2 - Matrix 2 . . . . . . . . . . . . . 117
3.2.8 Adsorption using post-synthesis ECAR-generated adsorbent . . . . 122
3.2.9 Polarization studies . . . . . . . . . . . . . . . . . . . . . . . . . . 124
3.2.10 Electrochemical Impedance Spectroscopy . . . . . . . . . . . . . . 128
3.2.11 Sedimentation tests . . . . . . . . . . . . . . . . . . . . . . . . . . 131
3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
3.3.1 Resistivity of synthetic Bangladesh water . . . . . . . . . . . . . . 133
3.3.2 Arsenic removal capability in synthetic Bangladesh water . . . . . 136
3.3.3 Effect of charge density . . . . . . . . . . . . . . . . . . . . . . . . 143
3.3.4 Effect of current density . . . . . . . . . . . . . . . . . . . . . . . . 146
3.3.5 Effect of current processing time . . . . . . . . . . . . . . . . . . . 152
3.3.6 Effect of phosphate and silicate on arsenic removal . . . . . . . . . 154
3.3.7 Parameter trends, tradeoffs, and implications for Bangladesh . . . 157
3.3.8 Adsorption using post-synthesis ECAR-generated adsorbent . . . . 158
3.3.9 As[III] removal in ECAR . . . . . . . . . . . . . . . . . . . . . . . 164
3.3.10 Polarization studies . . . . . . . . . . . . . . . . . . . . . . . . . . 169
3.3.11 Sedimentation versus 0.1µm vacuum filtration . . . . . . . . . . . . 175
3.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
iv
4 Characterization of Reaction Products 189
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
4.1.1 Research objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
4.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
4.2.1 Arsenic breakthrough as a function of membrane pore size . . . . . 194
4.2.2 Scanning Electron Microscopy (SEM) . . . . . . . . . . . . . . . . 194
4.2.3 Chemical analysis of EGA sludge . . . . . . . . . . . . . . . . . . . 195
4.2.4 X-ray Absorption Spectroscopy (XAS) . . . . . . . . . . . . . . . . 196
4.2.4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
4.2.4.2 Iron XANES and XRF-maps . . . . . . . . . . . . . . . . 198
4.2.4.3 Null arsenic EXAFS attempts . . . . . . . . . . . . . . . 202
4.2.4.4 Arsenic k-edge EXAFS . . . . . . . . . . . . . . . . . . . 204
4.2.4.5 Iron k-edge EXAFS . . . . . . . . . . . . . . . . . . . . . 206
4.2.4.6 Reference spectra. . . . . . . . . . . . . . . . . . . . . . . 207
4.2.4.7 XAS data analysis . . . . . . . . . . . . . . . . . . . . . . 208
4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
4.3.1 Limit on the average EGA cluster size . . . . . . . . . . . . . . . . 209
4.3.2 Scanning Electron Microscopy (SEM) . . . . . . . . . . . . . . . . 210
4.3.3 XRF Fe-As mapping of EGA sludge . . . . . . . . . . . . . . . . . 214
4.3.4 Chemical analysis of waste EGA sludge . . . . . . . . . . . . . . . 215
4.3.5 Iron oxidation state in EGA . . . . . . . . . . . . . . . . . . . . . . 218
4.3.6 EGA iron structure - comparison to known iron (hydr)oxides . . . 219
4.3.7 Arsenicbondingstructure-comparisontoknownarsenic-ironcom-
plexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
4.3.8 EGA iron structure - comparison between current densities . . . . 224
4.3.9 Arsenic bonding structure - comparison between current densities. 226
4.3.10 Arsenic capture in the bulk solution compared to the electrode
surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
4.4 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
5 ECAR Performance in Real Bangladesh Groundwater 231
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
5.1.1 Issues of groundwater transport and storage . . . . . . . . . . . . . 232
5.1.2 Research objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 234
5.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
5.2.1 Arsenic analysis and arsenic speciation . . . . . . . . . . . . . . . . 235
5.2.2 Tube well water sample collection and storage . . . . . . . . . . . . 235
5.2.3 Measurements of As[III]/As ratio over time . . . . . . . . . . . . 239
tot
5.2.4 Chemical analysis for co-occuring solutes . . . . . . . . . . . . . . 241
5.2.5 ECAR Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
5.3.1 As[III] monitoring in samples of real groundwater . . . . . . . . . . 245
5.3.2 ECAR performance in real groundwater . . . . . . . . . . . . . . . 249
5.3.3 Mixing time in real groundwater compared to synthetic groundwater252