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Bhaskar Sengupta1*,
Soumyadeep
Mukhopadhyay2,
Mohd. Ali Hashim2
1 SPACE, Queen’s University
Belfast, David Keir Building,
Belfast, BT9 5AG, UK
2 Department of Chemical
Engineering, University of
Malaya, 50603, Kuala Lumpur,
Malaysia
* Presenting Author
Adsorption
Adsorption, the binding of molecules or
particles to a surface. This process creates a
film of the adsorbate on the surface of
the adsorbent.
Coprecipitation
Coprecipitation is the carrying down of soluble
substances in a solution by a precipitate.
Langmuir isotherm
It relates the coverage or adsorption of molecules on a solid
surface to gas pressure or concentration of a medium above the
solid surface at a fixed temperature. The equation is stated as:
θ = fractional coverage of the surface, P = gas pressure or
concentration, α = constant (Langmuir adsorption constant)
Freundlich adsorption isotherm
It is an adsorption isotherm relating the concentration of
a solute on the surface of an adsorbent, to the concentration of
the solute in the liquid with which it is in contact. It is
mathematically expressed as:
x = mass of adsorbate; m = mass of adsorbent; p =
Equilibrium pressure of adsorbate; c = Equilibrium concentration of
adsorbate in solution. K and n are constants for a given adsorbate
and adsorbent at a particular temperature.
In-situ Arsenic Treatment
Permeable Reactive Barriers (PRBs)
Iron Based Technologies
Surfactant Flushing of Soil
In-situ Bioprecipitation Process (ISBP)
Biological Sulphate Reduction (BSR)
Immobilization of Radionuclides by Microorganisms
Biosorption of Heavy Metals
Membrane & Filtration Processes
Electrokinetic Treatment of Soil
Fe, As,
Mn,
SO42-,
NO3-
Advantage
No chemicals used
No waste produced
Low operating cost
Limitation
The recharge rate should be calculated carefully to support adsorption
of As(V) on Fe(III) over coprecipitation process
Recharge at regular interval of time is necessary to maintain the
oxidation zone
Fe, As,
Mn,
SO42-,
NO3-
A permanent, semi permanent or replaceable reactive media is placed in the
subsurface across the flow path of a plume of contaminated groundwater which
must move through it under its natural gradient, thereby creating a passive
treatment system.
Treatment walls remove contaminants from groundwater by degrading,
transforming, precipitating, adsorbing or adsorbing the target solutes as the
water flows through permeable reactive trenches.
Cd, Cu,
Ni, Cr,
As, Pb,
Zn, Cr,
As, Cr,
Ni, Pb,
Mn, Se,
Co, Ca,
Mg, Sr, Al
and AMD
Types of reactive cells in PRBs:
Sorption & precipitation process based cells with iron based materials
(ZVI, red mud, pyrite)
Activated Carbon & Peat
Zeolites (natural and fly-ash zeolites)
Denitrifying and Sulphate reducing bacteria
Mixing biotic components with ZVI
Alkaline complexing agents (Limestone, lime, calcium carbonate or
hydroxides)
Atomized slag containing composites of CaO, FeO, Fe2O3, SiO2, etc
Caustic Magnesia (mixture of MgO, CaO, SiO2, Fe2O3 and Al2O3)
Cd, Cu,
Ni, Cr,
As, Pb,
Zn, Cr,
As, Cr,
Ni, Pb,
Mn, Se,
Co, Ca,
Mg, Sr, Al
and AMD
Reduction of soil heavy metals by colloidal ZVI
ZVI is a strong chemical reductant and converted mobile oxyanions
(e.g., CrO42- and TcO4-) and oxycations (e.g. UO22+) into immobile
forms. Colloidal ZVI of micro-nanometer particle size can be injected
into natural aquifers.
Pollutant adsorption in iron based materials in PRB
ZVI, pyrite and red mud (fine particles of aluminum, iron, silica,
calcium and titanium oxides and hydroxides, derived from the
digestion of bauxite) can be used in PRB cells to trap HMs.
As(V),
Hg, Cr,
Ni, Pb,
Mn, Se,
Co, Cu,
Cd, Zn,
Ca, Mg,
Sr and Al
Use of ferrous materials as adsorbents
Fe oxides, oxyhydroxides and sulphides to sorb or immobilize heavy metals
from groundwater
Fe3O4 nanoparticles coated with humic acid
Combination of ferric and manganese binary oxides (FMBO) adsorption, sand
filtration, and ultra-filtration (UF) techniques
Mixed magnetite and maghemite nanoparticles
Ferrous salts as in-situ soil amendments
The soil amendments (e.g. goethite, ferrous sulphate, Fe grit, Fe(III)
hydroxide) immobilize the contaminants by reducing their leachability and
bioavailabilty through adsorption to mineral surfaces, surface precipitation,
formation of stable complexes with organic ligands and ion exchange processes
Some amendments may have detrimental effects on plant growth
As(V),
Hg, Cr,
Ni, Pb,
Mn, Se,
Co, Cu,
Cd, Zn,
Ca, Mg,
Sr and Al
In-situ Surfactant Flushing System
Cd, Pb,
Zn, As,
Cd, Cu,
Ni
Surfactants lower the surface tension of the liquid in which it is dissolved by virtue of
its hydrophilic and hydrophobic groups. Decrease in the surface tension of water
makes the heavy metals more available for remediation from contaminated soils.
Some typical processes helping in contaminant removal are solubility enhancement,
surface tension reduction, micellar solubilization, wettability and foaming capacity.
Inorganic surfactant flushing
Anionic (SDS) and nonionic (Triton X 100) are frequently experimentyed for their heavy
metal solubilizing capability.
Complexing agents e.g. EDTA can be alsoused with SDS or other surfactants for enhance
heavy metal extraction.
Biosurfactant flushing (Cd, Zn, Ni)
Biologically produced surfactants e.g. surfactin, rhamnolipids and sophorolipids could
remove Cu, Zn, Cd and Ni from a heavy metal contaminated soil.
Soapnut (Sapindus mukorossi) is also being experimented for its ability to solubilize the
heavy metals from aquifer.
Cd, Pb,
Zn, As,
Cd, Cu,
Ni
ISBP immobilizes the heavy metals in groundwater as solid phase
sulphide precipitates. Carbon sources e.g. molasses, lactate,
acetate and composts are injected in the aquifer, where they
undergo fermentation and trap the metal ions in an organic
matrix.
However, at later dates, heavy metal sulphides (e.g. Ni and Co)
may get remobilized with changing soil pH.
Cu, Zn,
Cd, Ni,
Co, Fe,
Cr, As
BSR is the process of reduction of sulphate to sulphide, catalyzed by the
activity of sulphate-reducing bacteria (SRB) using sulphate as electron
acceptor. Metal sulphides precipitate with metal ions already present in the
solution, due to their low solubility. BSR can be utilized for treatment of
AMD on-site in reactive barriers as well as off-site in anaerobic bioreactors
A wide range of electron donors such as
ethanol, lactate, hydrogen and economically
favorable waste products, pure substrates
are injected and is inoculated with media
(manure, sludge, soil) containing SRB to
start BSR process either in aquifer or in
anaerobic bioreactors.
Divalent
metal
cations
Biobarriers can be formed by subsurface injection of acetate (electron donor) to
stimulate the activity of dissimilatory metal-reducing microorganisms e.g.
Geobacteraceae species can reduce U(VI) & Tc.
Acidophilic chemolithotrophic bacteria and diluted sulphuric acid in the acidic
soil and various heterotrophs and soluble organics and bicarbonate in the
alkaline soil removed radionuclides (mainly U and Ra) and non-ferrous heavy
metals (mainly Cu, Zn, Cd and Pb) in situ from heavily contaminated plots.
In-situ biobarriers can be used to neutralize pH and remove nitrate and
radionuclides from groundwater contaminated with nitric acid, U, and Tc over a
longer time period (e.g. two years).
U, Ra,
Tc
Uptake by Organisms
Cr is removed upto 85-90% by adsorption in non-living R. arrhizus (fungus) biomass at acidic
pH of 2 in a stirred tank reactor.
Pseudomonas aeruginosa and Pseudomonas fluorescens (gram-negative, rod-shaped
bacterium can extract Pb from its carbonates to an exchangeable fraction.
Extractable Ni in soil increased upto 15 times by Microbacterium arabinogalactanolyticum
Spirulina (Arthrospira) platensis (cyanobacteria) removed low level Cd (>100 mg L-1) from
water and wastewater.
Calotropis procera, a wild perennial plant has high uptake capacity of Cd(II) at pH 5.0 to 8.0.
Single-stranded DNA aptamers can bind and remove As from groundwater.
The Trichoderma sp.(mycelial strain), Neocosmospora sp. and Rhizopus sp. (fungal strains)
are highly effective in biological uptake of As from soil.
Biosorption process in different materials can be utilized either inside in-situ
PRBs to treat groundwater or in ex-situ bioreactors to treat contaminated soils
Cd, Cr,
Zn, As,
Fe, Ni
Cellulosic Materials and agricultural wastes
The functional groups acetamido, alcoholic, carbonyl, phenolic, amido, amino and sulphydryl groups
present in agricultural waste biomass forms metal complexes or chelates with heavy metal ions. The
biosorption process occurrs by chemisorption, complexation, adsorption on surface, diffusion through
pores and ion exchange mechanisms.
Modified cellulose materials produced by esterification, etherification, halogenation and
oxidation e.g. Peanut hulls (Cu), Tree bark (Cu), Sugar cane bagasse (Pb), Orange peel (Ni), P.
Chrysosprium (Cu, Pb, Cd), P. Versicolor (Ni), Hazelnut shell (Ni), Trametes versicolor (Cu, Pb,
Zn), Sugar beet pulp (Pb), Grape stalk waste (Ni, Cu, Pb)
Rubber-wood ash adsorbs the Ni(II) cation from dilute solutions
Adsorbents prepared from cellulose grafted with calix[4]arene polymers can adsorb Co2+, Ni2+,
Cu2+, Cd2+, Hg2+ and Pb2+ and Cr2O72−/HCr2O7
−
Grape stalk, a by-product of wine production, can adsorb Pb and Cd from aqueous solutions
Untreated rice husk can remove both As(III) and As(V) from aqueous solutions
Activated rice husk reduced Pb and BOD upto 77.15% and 19.05%, respectively in a three phase
modified multi-stage bubble column reactor (MMBCR).
Walnut hull adsorbs Cr(VI) from solutions, reaching 97.3% removal at pH 1.0
Pb, Ni,
Cu,
Cd, Zn
Membranes can be of several types such as electrodialytic membrane, liquid
membrane, polymer membrane, ultrafiltration membrane and nanofibre membrane
An effective membrane method should reduce the volume of contaminated water to
be treated while producing clean water that meets the applicable effluent guidelines
Cation and anion exchange membrane barriers when coupled with electrokinetic
method to remove Cu, Cr, Hg, Pb, and Zn
Rochem Environmental's (Torrance, CA) high-pressure (1000 psig) Disk Tube™
technology employed reverse osmosis to remove organics and metal contaminants
from landfill leachates with an efficiency of more than 98%
Liquid membranes employing metal-complexing ligands can isolate U(VI), Tc(VII),
Cr(VI) and nitrates from groundwater in the presence of calcium and magnesium ions.
Cu, Cd,
Pb, Cr,
Hg, Pb,
Zn, U,
Tc, As
Electrokinetic Treatment of Soil Contaminants
As, Cd,
Cr, Co,
Hg, Ni,
Mn, Mo,
Zn, Sb,
Pb
When a direct current is applied across a wet mass of contaminated
soil, the migration of non-ionic pore fluids by electro-osmosis and the
ionic migration of dissolved ions towards the electrodes take place.
Combining these two removal mechanisms result in the electrokinetic
extraction of metal contaminants from soils
Electro migration rates in the subsurface is dependent upon the soil
pore, density of water current, grain size, ionic mobility, concentration
of contaminant and total ionic concentration
Electro-kinetic remediation techniques demonstrated 85-95% efficiency
in removing As, Cd, Cr, Co, Hg, Ni, Mn, Mb, Zn, Sb and Pb from low-
permeability soils such as clay, peat, kaolinite, high-purity fine quartz
and argillaceous sand
As, Cd,
Cr, Co,
Hg, Ni,
Mn, Mo,
Zn, Sb,
Pb
Selection of a suitable technology for groundwater contamination remediation is
an extremely challenging management issue due to uncertainty in assessment of
parameters such as soil permeability, groundwater flow pattern and complex
chemical processes taking place in the aquifer. No thumb-rule can be suggested
regarding this issue.
Detailed subsurface characterization data, capturing geochemical and
hydrogeologic variability including a flux-based analysis, is needed for successful
applications of different technologies.
Keeping the sustainability issues and environmental ethics in mind, the
technologies encompassing natural chemistry, bioremediation and biosorption
are recommended to be adopted in appropriate cases.
More than one technology can be combined to achieve synergistic effects and to
address different types of pollutants in a single aquifer.
Bhaskar Sengupta1*, Mohd. Ali Hashim2,
Soumyadeep Mukhopadhyay2
1 SPACE, Queen’s University Belfast, David Keir Building,
Belfast, BT9 5AG, UK2 Department of Chemical Engineering, University of Malaya,
50603, Kuala Lumpur, Malaysia* Presenting Author
Innovative Technologies for
Heavy Metal Contaminated
Groundwater Remediation