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