Groundwater Arsenic Remediation: Treatment Technology and Scale UP

316 Pages·2015·12.17 MB·English

by  Parimal Pal

GROUNDWATER
ARSENIC
REMEDIATION
Treatment Technology
and Scale UP
GROUNDWATER
ARSENIC
REMEDIATION
Treatment Technology
and Scale UP
By
PARIMAL PAL
ProfessorinChemicalEngineering,
NationalInstituteof Technology, Durgapur
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ISBN:978-0-12-801281-9
DEDICATION
Dedicated to the memories of my late parents
v
ACKNOWLEDGEMENTS
Theideaofwriting thisbookwasplantedwhenKennethP.McCombs,at
Elsevier Science approached me for the same. Thanks to his very informal
and helpful approach that made the subsequent steps towards publication
simple and easy to follow. It has been my great pleasure to collaborate
and work with Peter Jardim, Anusha Sambamoorthy, and other editorial
staffmembersofElsevierSciencewhoworkedsosincerelytogivethefinal
shapetothebook.Roleofmydoctoralandpost-doctoralscholarsspecially
Ramesh, Sankha, and Jayato is very much appreciated for maintaining the
systemwheretheworkwasdoneandforcheckingthelonglistofreferences.
Special thanks to Sankha Chakrabortty and my other doctoral scholars for
tracing many figures and preparing many tables. Thanks are also due to
all authors and their publishers for kind permission for use of quite a few
illustrations. My sincere thanks are also due to my colleague, Dr. Mrinal.
K.Mandalforvaluablesupport.IamthankfultoProf.T.Kumar,Director
N.I.T. Durgapur for doing his best despite hindrances towards my work
placepeaceforthefirsttimeinmycareer.Withoutinspirationofthegreat
departed soulswho shaped mylife, thisbookcouldnot seethelight ofthe
day.Patience,toleranceandsupportofmydearandnearonesincludingmy
brothers, sisters, wife and daughter deserve special mention.
P. Pal
xi
PREFACE
Since the seventies of the 20th century, problems of contamination of
groundwaterbyleachedoutarsenicstartedmanifestingitself.Inthenineties
ofthelastcentury,reportspouredoverfromseveralpartsoftheworldsuch
as South West USA to the Far East on acute arsenic poisoning cases. Fifty
five million people in the Bengal-Delta Basin spreading over Bangladesh
and India alone became victims of arsenic-contaminated groundwater.
Considering widespread occurrence of arsenic and its huge carcinogenic
potential,theWorldHealthOrganizationset10ppbasthesafelimitofcon-
centrationlevelofarsenicindrinkingwaterinthebackdropofoccurrenceof
as high 3000ppb of arsenic in groundwater in many areas. Bringing down
concentration of arsenic from such a high level to 10ppb level became a
challenging task to the scientific community as well as the concerned gov-
ernments,andpolicymakers.Becauseoftheveryinsidiousnatureofarsenic
contamination problem, it takes long years for manifestation of the related
diseaseswhenthevictimalmostreachesapointofnoreturn.Earlygovern-
ment policies were mostly directed at arranging alternate sources of water
such as river water by laying hundreds of kilometers of pipelines involving
huge capital cost and inviting other water-borne diseases as river water
sources were in many cases heavily polluted by pathogens, chemical and
xenobiotic materials.
As a college student, I came across hundreds of newspaper reports and
journal papers on occurrence, causes and adverse health effects of arsenic
poisoninginthosedays.Suchreportsfrustratedmeatonepointasverylittle
onthesolutionfrontwasreallybeingtalkedof.Istartedworkingonthevery
well-known methods like adsorption and physico-chemical separation to
get first-hand knowledge of the hurdles that were standing in the way of
commissioningtreatmentplantsforarsenic-bearingwater.Withtheadvent
ofmembranes,particularlytailor-mademembranes,newavenuesopenedup
to the chemical engineering profession in the major task of separation and
purification. Gradually we as a team moved into the areas of separation of
arsenic by membrane-based modern techniques. We discovered that
scale-up confidence in commissioning a modern arsenic treatment plant is
extremelylimitedandthisstandsinabigwayinimplementationofmodern
arsenicabatementtechnologies.Idecidedtocompileallourworkonarsenic
abatementspanningoverthelasttwodecadesintoasinglecomprehensive
xiii
xiv Preface
booktoserveasaguidelineinplanning,developing,commissioning,oper-
atingandmaintainingonasustainablebasisamodern,efficientarsenictreat-
mentplant.Existingbooksonarsenicareeitheronaspecificareaonlysuch
asoccurrenceorhealtheffectsorongeologicalexplanationsoratthemostan
edited volume containing a review of the problem and at the most partial
solutions.Therearenowagoodnumberoftextsonmembranesandmem-
brane technology. Though these books, reviews and journal papers have
enlightened us enough with which we could see better, there is hardly
any book that integrates knowledge of occurrence of arsenic with the
knowledge of abatement by membrane technology. That scale-up confi-
dence is extremely limited is evident from practically non-existence of a
membrane-based treatment plant in the world’s most severely affected
region. This book fills this gap embracing the basic understanding of the
problem of occurrence of arsenic and the major technology options with
theirassociatedmeritsanddemerits.Thenovelmembranedistillationtech-
niquehasbeenelaboratedinthelightofdetailedmassandheattransferphe-
nomena as low flux is the major hurdle in application of membrane
distillationandthesamecanbeovercomeonlybyimprovingmassandheat
transferefficiency.Asstandardtraditionalmethods,adsorptionandchemical
coagulation have been most widely studied. Therefore, the basics and the
associated merits and demerits have been discussed along with new devel-
opments. The major emphasis has however, been put on nanofiltration-
based hybrid treatment that appears to the best solution being a sustainable
one from the points of ecological integrity, economic efficiency and social
equity.Thecomplexissueoftransportofionicspeciesthroughnanomem-
brane, thechange ofchemical speciationof arsenicthroughpriorchemical
conversion eventually producing safe potable water from arsenic-
contaminated groundwater, stabilization of arsenic rejects paving the way
forsafedisposalneedtobemathematicallycapturedformodellingthetotal
system for successful scale-up. This is what was absent in arsenic removal
literature in a comprehensive way and has been extensively covered only
inthisbook.Forsustainedoperationunderoptimumconditionswithfacil-
ity for continuous visual monitoring, user-friendly Visual Basic software
developed by the author and his team for physico-chemical as well as
nanomembrane-integrated hybrid processes is indeed new addition to the
literature of arsenic abatement technology through this book. However,
to help select a technology for a particular situation, understanding other
majortechnologyoptionsisalsoessential.Thisbookdealswithallthebroad
optionsoftreatmentofarsenic-bearingwater.Eachmajorchapterdealswith
Preface xv
onetechnology.Afterthefoundationhasbeenlaidoutwiththedissemina-
tionofknowledgeonoccurrence,causes,healtheffects,regulationsandthe
desiredlevelofpurification,therehasbeenlogicalprogressionofthesechap-
tersstartingfromtheverybasicsofthescienceandtechnologytoitsgradual
development towards practical solution involving modelling, simulation,
optimization,control,economicanalysisandscale-up.Thegreateststrength
of this book lies in the firsthand experience of an author belonging to the
world’s worst affected arsenic zone who investigated with real arsenic-
contaminated groundwater, experimentally collected data on the possible
bestsolutionsforarsenic-affectedareas,designedandfabricatednewdevices
fortreatmentofarsenic-bearingwaterandenrichedhimselfwithknowledge
fromthefindingsofthetirelessresearchcarriedoutbythescientistsallover
the world. Findings of the research activities on arsenic separation carried
out in the Environment and Membrane Technology Laboratory of the
Department of Chemical Engineering, National Institute of Technology
Durgapur have been acknowledged by the scientific community of the
world through several publications of the reputed publishers like Elsevier
Science, Springer, Taylor and Francis, American Chemical Society, Water
EnvironmentFederation,USAandInternationalWaterWorksAssociation
(IWA).Possibleschemesoftreatmenthavebeeninvestigatedandhavebeen
analyzed chemically, mathematically and socio-economically before sug-
gestingasolution.Comparisonshavebeenmadeintermsofseparationeffi-
ciency,complexityandcostofoperationandsustainablemanagement.The
bookshouldbeabletohelppeoplearriveataquicksolutioninselectingthe
bestschemeandinscalingup,settingupandsuccessfullyoperatinganeffi-
cientarsenicremovalplantdependingonthegroundrealitiesencompassing
geo-politico and socio-economic conditions. Even the issues of final dis-
posal of concentrated arsenic rejects have received attention. Integration
ofsomanynovelideasfromdiversepointsofviewinthecontextofremoval
of arsenic from contaminated water into a single book makes this volume
unique.
Scholarsfromundergraduateleveltoresearchlevelarelikelytofindthe
bookusefulalongwithmembranesuppliers,planners,governments,public
health engineers, managers and policy makers entrusted with the great
responsibility of providing safe potable water to the people in the affected
regions.
Parimal Pal
1st January, 2015.
CHAPTER 1
Introduction to the Arsenic
Contamination Problem
Contents
1.1 Arsenicchemistry 2
1.2 Occurrenceandcausesofarsenicingroundwater 6
1.3 Regulationsandmaximumcontaminantlevelofarsenic 10
1.4 Toxicityandhealthhazards 11
1.5 Introductiontomethodsofarsenicremoval 15
1.5.1 Chemicalprecipitation 15
1.5.1.1 Alumprecipitation 15
1.5.1.2 Ironprecipitation 16
1.5.1.3 Limesoftening 16
1.5.1.4 Coprecipitation 16
1.5.2 Adsorption 16
1.5.3 Ionexchange 16
1.5.4 Membranefiltration 18
1.5.4.1 Pressure-drivenmembranefiltration 18
1.5.5 Electrodialysis 19
1.5.6 Temperature-drivenmembranefiltration 19
1.5.7 Hybridmethodsofarsenicremoval 20
References 20
Contamination of groundwater by leached out arsenic results in a serious
human health problem when underground aquifers are used as a source
ofdrinkingwater.Millionsofpeopleinover20countriesacrosstheworld
such as Argentina, Bangladesh, China, India, Mexico, Mongolia, Nepal,
Taiwan, Thailand, theUnited States,Canada, Vietnam, among othersface
this arsenic contamination problem [1–25]. In some places in Bangladesh,
concentrationofarsenicingroundwaterisashighas1000μg/L.Thelargest
populationatriskamongthecountriesaffectedbyarseniccontaminationof
groundwaterisinBangladesh,followedbyWestBengalinIndia.Inoffering
relief to the suffering populations, region-specific policy formulation that
considers the huge variation of socioeconomic conditions and availability
of technology is essential. Despite extensive research on the occurrence
of arsenic and on mitigation methods, implementation of arsenic removal
GroundwaterArsenicRemediation ©2015ElsevierInc.
http://dx.doi.org/10.1016/B978-0-12-801281-9.00001-1 Allrightsreserved. 1
2 GroundwaterArsenicRemediation
technologyisverylimitedinthebackdropoflimitedscale-upconfidence.In
most cases, arsenic-free surface water from an alternate source is arranged
instead of using effective arsenic removal technology for making the con-
taminated water free from arsenic. But in areas where a source of alternate
safewaterisnotavailable,technologyfortheseparationofarsenicfromcon-
taminated water remains the only option. This necessitates adoption of a
new approach toward solving this problem, one that meets the scientific
challenge ofremoving arsenicfrom waterinsteadofignoringtheproblem.
Itisthusofparamountimportancetounderstandthechemistryofarsenicin
thewaterenvironment,thecausesofitsoccurrenceingroundwater,adverse
health effects, and possible technological mitigation approaches.
1.1 ARSENIC CHEMISTRY
Arsenicwithatomicnumber33islocatedingroupVAoftheperiodictable
directly below phosphorous. Because of the physico-chemical similarity
with phosphorus, often ingested arsenic in the human body disrupts the
ATPcycleandhencethemetabolismsystembyreplacingphosphorus.Arse-
nicisthe20thmostabundantelementintheearth’scrust,14thinseawater,
and the 12th most abundant element in the human body. Arsenic forms
inorganicandorganiccompoundsandmayoccurintheenvironmentinvar-
iousoxidationstates(–3,0,+3,+5).Innaturalwater,arsenicoccursmainly
in inorganic forms as oxyanions of trivalent (+3) arsenite or as pentavalent
(+5) arsenate. Inorganic compounds of arsenic include hydrides (e.g.,
arsine), halides, oxides, acids, and sulfides. Examples of inorganic arsenic
oxide compounds include As O , As O , and arsenic sulfides such as
2 3 2 5
As S , HAsS , and HAsS 3(cid:1). The two oxidation states predominant in
2 3 2 3
ground and surface waters are arsenate (V) and arsenite (III) and are part
ofthearsenic(H AsO )andarseneous(H AsO )acidsystems,respectively.
3 4 3 3
Inorganicarsenicspeciesthatarestableinoxygenatedwatersincludearsenic
acidandAs(V)speciessuchasH AsO ,H AsO (cid:1),HAsO 2(cid:1),andAsO 3(cid:1).
3 4 2 4 4 4
Arseneousacid(As(III))isalsostableasH AsO ,H AsO (cid:1),andHAsO 2(cid:1)
3 3 2 3 3
under slightly reducing aqueous conditions. These two forms of arsenic
depend upon oxidation–reduction potential and pH of the water [26].
Different structures of arsenic compounds are presented in Figure 1.1. At
a typical pH of 5.0 to 8.0 of natural water, the predominant pentavalent
arsenatespeciesareH AsO (cid:1) and HAsO 2(cid:1) andthetrivalentarsenite spe-
2 4 4
cies is H AsO . The ratio of As(v) to As (III) in natural water is about 4:1.
3 3
Arsenates are stable under aerobic or oxidizing conditions, while arsenite