Assessment of industrial byproducts as permeable reactive barriers for landfill leachate management

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 03 | March-2014, Available @ http://www.ijret.org 637
ASSESSMENT OF INDUSTRIAL BYPRODUCTS AS PERMEABLE
REACTIVE BARRIERS FOR LANDFILL LEACHATE MANAGEMENT
Barjinder Bhalla1
, M.S. Saini2
, M.K. Jha3
1
Scientist C, Pushpa Gujral Science City, Kapurthala- 144601, Punjab, India
2
Director, Guru Nanak Dev Engineering College, Ludhiana-141006, Punjab, India
3
Professor and Dean Academics, Department of Chemical Engineering, Dr.B.R.Ambedkar National Institute of
Technology (NIT), Jalandhar-144011, Punjab, India
Abstract
Laboratory scale studies were conducted to investigate the feasibility of Industrial by-products as potential alternative medium to
conventional gravel in the drainage layer of leachate collection system as permeable reactive barriers (PRBs) for landfill leachate
treatment. Industrial by-products were used to treat effectively the landfill leachate, which is an innovative in-situ remediation
technology. This study will open a tremendous scope of using industrial byproducts as potential medium for treating leachate and this
would reduce the magnitude of the current industrial waste disposal problem and convert one waste into a beneficial material.
Industrial waste, such as Steel plant by-product (Waste slag), Tire industry by-product (scrap-tire-shreds) and Rice Sheller by-product
(Rice husks) were studied. The availability and the cost are important criteria in selecting a reactive material. These Industrial waste
materials are inexpensive and abundant, and are, therefore, ideal for low cost leachate treatment. Leachate treatment efficiency was
evaluated on the basis of percentage reduction in concentration of leachate parameters before and after treatment by passing through
Test Cells 1 to 11 having different combinations of conventional gravel and various Industrial by-products with total thickness 500
mm of PRBs (multibarrier). Treated leachate samples were collected from Test Cells 1 to 11 at the interval of 30, 60 and 90 days. The
percentage reduction in various leachate parameters was maximum with Test Cell-11 having combination of rice husk (125 mm),
waste slag (125 mm), scrap-tire-shreds (125 mm) and gravel layer (125 mm) in equal proportion as PRBs (multibarrier). It has been
observed that leachate sample after passing through combined beds of Industrial by-products and conventional gravel gave better
results in comparison to Test Cell-1 containing conventional gravel bed singly. This performance trend can be attributed due to
combined effect of conventional gravel and Industrial by-products bed on adsorption, ion exchange reactions, filtration, precipitation
and biological uptake. The percentage reduction in BOD5, COD, Chloride (Cl−
), Nitrate (NO3
−
), Phosphorus (P), Sulphate (SO4
2-
)
value was maximum upto 76.5%, 83.5%, 64.4%, 81.2%, 73.5% respectively. For reliable expectation on the longevity of PRBs
(multibarrier), column test has to be performed for longer periods of time and the changes in material reactivity need to be observed.
Keywords: Permeable reactive barriers, Landfill, Leachate, Industrial byproducts, Test Cells
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1. INTRODUCTION
Rapid growth of population and industrialization and other
development activities during the past few decades have been
responsible for environment pollution and resources
degradation. Rapid urbanization has seriously enhances the
problem of waste disposal and management. Industrial
byproducts disposal remains a problematic issue in
industrialized nations around the world. Huge quantity of
Industrial byproducts are being generated every year and
results in major environmental hazards worldwide. The present
recycling techniques of the industrial byproducts may only
consume a very small amount of the unwanted scrap. The
percentage of industrial byproducts recycled is not compatible
with the growth of unwanted scrap. This has become a serious
problem in many countries. A large number of industrial
byproducts are landfilled, stockpiled and illegally dumped. In
order to avoid the continual addition of industrial byproducts to
these unsightly and unhealthy stockpiles, innovative methods
of recycling and reuse of industrial byproducts needs to be
developed. Emphasis should be given on sound waste
management strategy which includes waste minimization,
recovery, recycling and reuse.
During the last decade of the 19th century, as well as during
initial years of 20th century, millions of people died due to
Bubonic Plague in India, which had linkages to poor
management of solid waste. Solid waste management includes
the control of generation, storage, collection, transfer and
disposal of solid waste in an environmentally acceptable
manner. The disposal of solid waste currently relies principally
on landfilling. In India most landfills are usually open
dumps/unlined landfills. Only a fraction can be regarded as
engineered landfills (designed and constructed according to
engineering specifications). Engineered landfills are
constructed to include containment system and structure

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designed to protect the environment. These measures include
lining systems, gas pipes, rain water collection control and
monitoring boreholes. Landfilling continues to be the most
common form of waste disposal despite the fact that leachate
seriously contaminates water sources. Leachate is the liquid
residue resulting from the various physical, chemical and
biological processes taking place within the landfill. Landfill
leachate is generated by excess rainwater percolating through
the waste layers in a landfill. This liquid contains large number
of organic and inorganic compounds. The leachate accumulates
at the bottom of the landfill and percolates through the soil.
Areas near landfills have a greater possibility of groundwater
contamination because of the potential pollution source of
leachate originating from the nearby site. Such contamination
of groundwater resource poses a serious threat to the natural
environment and human health [1,2]. The extensive size of
many of these leachate contaminated groundwater plumes,
covering several to hundreds of hectares [3], renders
conventional ex-situ groundwater remediation techniques
economically and technically unfeasible, due to the long
treatment duration and huge costs in soil excavation,
groundwater pumping and processing of the contaminated
substances.
1.1 Permeable Reactive Barriers (PRBs)
The PRBs technology has generated a significant interest
among researches. This is to due to the perceived cost/benefit
ratio and the potential of PRBs to mitigate the spread of
contaminants that have proven difficult and expensive to
manage with other cleanup methods [4]. PRB is a continuous,
permeable treatment zone designed to intercept and remediate
a contaminant. The treatment zone may be created directly
using reactive materials such as iron or indirectly using
materials designed to stimulate secondary processes, such as
by adding carbon substrate and nutrients to enhance microbial
activity. In this way, contaminant treatment may occur through
physical, chemical and biological processes. The phenomena,
which help in remediation within PRBs, are
adsorption/sorption, precipitation, oxidation/reduction and
biodegradation. Recently, many researchers have introduced
the PRBs system as an alternative technology to control
leachate [5,6,7,8,9,10,11,12,13,14,15,16]. Multifunctional
PRBs (multibarrier) was recently reported by Van Nooten et al.
[17] as a semi-passive and innovative in-situ remediation
technology to treat landfill leachate contamination. Fig. 1
shows schematic overview of the Multibarrier concept that was
successfully designed for the semi-passive removal of
ammonium, AOX, COD and toxicity from landfill leachate. A
multibarrier combines different reactive materials and
contaminant removal processes, which is necessary to remove
a complex pollutant mixture such as landfill leachate
contamination. PRBs which is an emplacement of reactive
materials in the subsurface designed to intercept a contaminant
plume, provides a flow path through the reactive media, and
transform the contaminants into environmentally acceptable
forms to attain remediation concentration goals down gradient
of barrier [4]. They are considered a low cost, effective
alternative for remediating contaminated sites. The technology
of PRBs could potentially allow many more contaminated sites
to be remediated effectively, thus greatly enhancing natural
groundwater protection. Groundwater remediation using PRBs
is an in situ method with low energy demand and therefore
more cost-effective than standard remediation techniques [18].
It is a passive, in situ technology that has a high potential to
treat shallow aquifers at a lower cost than traditional pump-
and-treat methods, but due to a lack of long-term data, its cost-
effectiveness has not been proven [19,20]. However, Schad
and Gratwohl [21] found that the remediation costs can be up
to 50 percent less than pump-and-treat methods based on data
collected at several sites. In addition, using PRBs reduces
contaminant exposure to humans and allows the overlying land
to be actively used during remediation. A wide variety of
pollutants are degraded, precipitated, sorbed or exchanged in
the reactive zone, including chlorinated solvents, heavy metals,
radio nuclides and other organic and inorganic species [22,23].
Therefore, making PRBs cost-effective is imperative. In order
to achieve this, experiments on low-cost reactive media is of
utmost importance. The main engineering challenge is
determination of suitable type and amount of reactive materials
in a permeable wall and proper placement techniques. The
availability and the cost are important criteria in selecting a
reactive material. Continuing controlled column experiments
for prolonged periods of time provides an opportunity to derive
the treatment system [24].
Fig-1: Schematic overview of the permeable reactive barriers
(multibarrier) concept

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Several researchers have devoted their attention to the use of
industrial byproducts for civil and environmental engineering
applications. However, alternative materials are being explored
that facilitate sustainability, are less expensive and may be less
prone to fouling by mineral precipitates. Some industrial
byproducts appear to have significant potential as low cost and
effective reactive materials for PRBs used to treat number of
contaminants. Large scale uses of shredded tires have been
identified by several researchers for civil engineering
applications, such as highway embankments, pavements,
retaining structures and lightweight fill material. Economically
and environmentally feasible alternatives have been
investigated for recycling of waste scrap tires. One of these
applications is the use of shredded scrap tires as drainage
material in landfill system. Tire shreds can be used as an
alternative to crushed stones (gravel) as drainage media in
landfill leachate collection systems was supported by number
of workers [25,26,27,28,29,30,31,32]. The use of shredded
scrap tires as drainage material has the potential for the
utilization of large quantities of scrap tires. Such use offers an
economic advantage over conventional materials without
compromising engineering performance in addition; this
implementation utilizes the scrap tires as a valuable resource
material and helps to alleviate the growing problems currently
associated with the management and disposal of scrap tires.
PRBs (multibarrier) is a sustainable technology for cleaning
contaminated groundwater. PRBs with zero-valent iron as a
reactive material could be one of the most promising
technologies to remediate the contaminated groundwater
[33,34,35]. Removal of contaminants in leachate from landfill
by waste steel scrap and converter slag is the first investigation
of it kind related to potential benefits of recycling industrial
waste in controlling contaminants in leachate [36]. Feasibility
studies related to other industrial byproducts as effective
reactive materials for PRBs (multibarrier) and scope of Multi-
Permeable Reactive Barriers for leachate treatment needs to be
investigated.
1.2 Leachate Collection Layer (Drainage Layer)
Leachate management can be achieved through effective
control of leachate generation, its treatment and subsequent
recycling. In India most landfills are open dumps/unlined
landfills. Engineered landfill sites are provided with
impermeable liner and drainage system at the base of the
landfill, which will not allow leachate to percolate into subsoil.
Optimal leachate treatment, in order to reduce the negative
impact on the environment, is today's challenge.
Landfill design generally consists of three layers: the cover soil
layer, the drainage layer and the barrier layer. Fig. 2 shows
leachate drainage layer in MSW landfills [37]. The current
practice of landfill design is to use granular soil ranging from
fine sands to coarse gravels as the drainage material (also
known as leachate collection layer) which is supported by
number of studies [25,26,27,29,37,38,39,40].
As per Ontario Ministry of Environment (MoE) [41] report of
landfill standards a minimum thickness of 0.3 m (300 mm) of
granular drainage material is usually recommended for the
drainage layer with a minimum of 0.5 m (500 mm) at the
location of perforated leachate collection pipes. In the present
study, various industrial byproducts were introduced as
potential alternative medium to conventional gravel in the
drainage layer of leachate collection system as permeable
reactive barriers for leachate treatment either singly or in
combination.
Fig- 2: Leachate drainage layer in MSW landfills
1.3 Objective of the Study
The present study is an effort to explore the potential benefits
of recycling industrial waste in controlling contaminants in
leachate. The aim of this study was to conduct laboratory scale
investigations to study the feasibility of PRBs (multibarrier)
with low-cost, locally and readily available Industrial by-
products to be used as a reactive material to treat effectively
the landfill leachate, which is an innovative in-situ remediation
technology to treat landfill leachate contamination. Industrial
waste, such as Steel plant by-product (waste slag), Tire
industry by-product (scrap-tire-shreds) and Rice Sheller by-
product (rice husks) were studied. These industrial waste
materials are inexpensive and abundant, and are, therefore,
ideal for low cost leachate treatment. Thus, the present study
will open a tremendous scope of using industrial byproducts as
potential medium for treating leachate and this would reduce
the magnitude of the current industrial waste disposal problem
and convert one waste into a beneficial material. Leachate
treatment efficiency was evaluated on the basis of percentage
reduction in concentration of leachate contaminants before and
after treatment by passing through PRBs (multibarrier). In
summary, there is perhaps no systemic study on the Industrial
by-products as potential alternative medium to conventional
gravel in the drainage layer of leachate collection system as
permeable reactive barrier for leachate treatment.

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2. MATERIALS AND METHODS
2.1 Study Location
Ludhiana is the largest city in Punjab, both in terms of area and
population. It lies between latitude 300
55' N and longitude
750
54' E. The Municipal Corporation limit of city is spread
over an area of 141sq.km. The population of the city within the
Municipal Corporation area is estimated at 34,87,882 in 2011
[42]. The climate of Ludhiana is semi arid with maximum
mean temperature reaching upto 42.80
C and minimum mean
temperature is as below as 11.80
C. Total rainfall during the
year is 600-700 cm; 70% of total rainfall occurs from July to
September. The altitude varies from 230 m to 273 m from
mean sea level [43]. Leachate sample for the present study was
collected from Jamalpur landfill site of Ludhiana City, Punjab
(Table1). Fig. 2 shows municipal solid waste heaps at Jamalpur
landfill site. No cover of any description is placed over the
spread waste to inhabit the ingress of surface water or to
minimize litter blow and odours or to reduce the presence of
vermin and insects. Rag pickers regularly set fire to waste to
separate non-combustible materials for recovery. Since, there
are no specific arrangements to prevent flow of water into and
out of landfill site, the diffusion of contaminants released
during degradation of landfill wastes, may proceed uninhibited.
No proper compaction is done to compress the waste into the
site.
Table- 1: Details of Jamalpur landfill site of Ludhiana City,
Punjab (India)
Fig- 3: Municipal solid waste heaps at Jamalpur landfill site of
Ludhiana City, Punjab (January, 2012)
2.2 Leachate Sampling
Leachate sample was collected from landfill site on Tajpur
Road at Jamalpur Village having 25 acres of low lying land
area. This site is non-engineered low lying open dump. It has
neither any bottom liner nor any leachate collection and
treatment system. Therefore, all the leachate generated finds its
paths into the surrounding environment. The landfill site is not
equipped with any leachate collectors. To determine the quality
of leachate, integrated samples were collected from different
landfill locations. Leachate samples were collected from the
base of solid waste heaps where the leachate was drained out
by gravity. Leachate samples were collected in January end,
2012. Monitoring parameters were selected based on relative
importance in municipal landfill leachate composition and their
pollution potential on groundwater resources as per Municipal
Solid Waste (Management and Handling) Rules, 2000 under
the Environment Protection Act (EPA), 1986 by Ministry of
Environment and Forests (MoEF), Govt. of India. Various
leachate parameters viz Biological Oxygen Demand (BOD5),
Chemical Oxygen Demand (COD), Chloride (Cl−
), Nitrate
(NO3
−)
, Phosphorus (P), Sulphate (SO4
2-
) and heavy metals
were analyzed to determine pollution potential of leachate
discharge from municipal solid waste landfill site to estimate
its pollution potential.
2.3 Analytical Work
Analytical methods were according to Standard methods for
examination of water and wastewater specified by American
Public Health Association [44]. Biological Oxygen Demand
(BOD)-Winkler’s method was used for estimating initial and
final DO in the sample and BOD was determined (5210-B of
Standard methods). Chemical Oxygen Demand (COD) was
determined by refluxion of sample followed by titration with
Ferrous Ammonium Sulphate (FAS) was adopted (5220.C:
Standard Methods). Argentometric volumetric titration method
in the presence of Potassium chromate was adopted for
chloride (4500-Cl-.B of Standard Methods). Nitrate was
analyzed by HACH Portable Spectrophotometer (DR 2800) by
Cadmium Reduction Method (8039) adapted from Standard
Methods at a wavelength of 450 nm [45]. Total Phosphorus
was analyzed by HACH Portable Spectrophotometer (DR2800)
by Molybdovanadate Method (10127) with Acid Persulfate
digestion adapted from Standard Methods at a wavelength of
420 nm [45]. Sulphate was analyzed by HACH Portable
Spectrophotometer (DR 2800) by SulfaVer 4 Method (8051)
adapted from Standard Methods at a wavelength of 520 nm
[45]. Heavy metals like Iron, Lead, Chromium, Cadmium,
Copper, Zinc, Nickel and Arsenic were analyzed using ELICO
double beam SL 210 UV-VIS Spectrophotometer [46].
Land area
(acres)
Average depth
(in ft.)
Future life
(years)
25 8 to 10 25

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2.4 Laboratory Experimental Setup
Test Cells 1 to 11
11 nos of Test Cells consisting of polyvinyl chloride cylinders
(PVC) of height 1524 mm and diameter 152.3 mm were used
in the laboratory for experimental work. Taps were drilled at
the base of the Test Cells to collect treated leachate samples.
Test Cells 1 to 11 were consisted of conventional gravel and
various Industrial by-products beds of different combinations
with total thickness 500 mm [41] in the drainage layer of
leachate collection system as PRBs (multibarrier). Collected
landfill leachate samples were passed through 11 nos of
laboratory Test Cells having combined beds of Industrial by-
products (waste slag, scrap-tire-shreds and rice husks) and
conventional gravel with this objective to find out the efficacy
of Industrial by-products as potential alternative medium to
conventional gravel in the drainage layer of leachate collection
system as PRBs (multibarrier) for leachate treatment. The
treatment was conducted without applying any stress on PRBs
(multibarrier). The details of different combinations of
conventional gravel and various Industrial by-products used in
Test Cells were shown in Table 2.
Table-2: Details of Test Cells 1 to 11
The schematic representations of each Test Cells from 1 to 11
were shown in Fig. 4. There was a perforated plate over the
media at the top of the Test Cells to distribute leachate evenly
throughout the column and to prevent by-passing of water. All
the reactive materials were washed and then dried before
loading. The leachate was loaded into Test Cells with the help
of shower. 15 litres of leachate sample was passed through
each of the 11 laboratory Test Cells. Treated leachate samples
were collected from taps at the base of the Test Cells. Leachate
samples were collected from Test Cells 1 to 11 at the interval
of 30, 60 and 90 days. Unsaturated conditions prevailed in all
the Test Cells, the treatment mechanism was expected to be
greatly similar to natural attenuation in the unsaturated zone of
soil. However, these Test Cells differed from the unsaturated
zone due to the presence of reactive media. Bagchi [47]
identified following mechanisms of leachate attenuation in
soil: adsorption, ion exchange reactions, dilution, filtration,
precipitation and biological uptake. It was expected that these
conditions would improve the attenuation of some parameters.
Test Cells were opened at the top. Therefore at the upper

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layers, aerobic biodegradation was possible and at the middle
and bottom layers both aerobic and anaerobic conditions exist.
3. RESULTS AND DISCUSSION
Laboratory studies were conducted to investigate Industrial by-
products (waste slag, scrap-tire-shreds and rice husks) as a
potential alternative to conventional gravel in the drainage
layer of leachate collection system at the base of landfill as
PRBs (multibarrier) by comparative performance study of Test
Cells consisting of different combination of conventional
gravel and Industrial by-products (waste slag, scrap-tire-shreds
and rice husks) as leachate collection layer. Best combination
in terms of reduction in various leachate parameters after
passing through Test Cells 1 to 11 has been identified.
Leachate samples were analyzed for various parameters viz
Biological Oxygen Demand (BOD5), Chemical Oxygen
Demand (COD), Chloride (Cl−
), Nitrate (NO3
−
), Phosphorus
(P), Sulphate (SO4
2-
) and the results indicated that all the
parameters were beyond USEPA permissible limits. Heavy
metals viz Iron, Lead, Chromium, Cadmium, Copper, Zinc,
Nickel and Arsenic values for leachate were in trace amount as
the waste is domestic in nature.
The comparative performance study of Test Cells- 1 to 11 has
been expressed in terms of percentage reduction of various
parameters. Fig.5 (a-f) showed percentage reduction in various
leachate parameters after passing through Test Cells-1 to 11
having bed of different combinations of conventional gravel
and Industrial by-products (waste slag, scrap-tire-shreds and
rice husk). The percentage reduction in various leachate
parameters was maximum with Test Cell-11 having
combination of rice husks (125 mm), waste slag (125 mm),
scrap-tire-shreds (125 mm) and conventional gravel layer (125
mm) in equal proportion as PRBs (multibarrier) followed by
Test Cell-7 having combination of rice husks (375 mm) and
conventional gravel layer (125 mm) followed by Test Cell-6
having combination of waste slag (125 mm) and conventional
gravel layer (125 mm) followed by Test Cell-5 having
combination of scrap-tire-shreds (375 mm) and conventional
gravel layer (125 mm) followed by Test Cell-4 having
combination of rice husks (250 mm) and conventional gravel
layer (250 mm) in equal proportion followed by Test Cell-3
having combination of waste slag (250 mm) and conventional
gravel layer (250 mm) in equal proportion followed by Test
Cell-2 having combination of scrap-tire-shreds (250 mm) and
conventional gravel layer (250 mm) in equal proportion
followed by Test Cell-10 having combination of rice husks
(125 mm) and conventional gravel layer (375 mm) followed by
Test Cell-9 having combination of waste slag (125 mm) and
conventional gravel layer (375 mm) followed by Test Cell-8
having combination of scrap-tire-shreds (125 mm) and
conventional gravel layer (375 mm) and followed by Test Cell-
1 containing conventional gravel layer singly (500 mm). The
data presented in this study indicated that with the passage of
time at the interval of 30, 60 and 90 days percentage reduction
in various parameters of leachate samples values increased.
This performance trend can be attributed due to combined
effect of conventional gravel and Industrial by-products bed
(waste slag, scrap-tire-shreds and rice husks) on adsorption, ion
exchange reactions, filtration, precipitation and biological
uptake. It is hypothesized that introduction of Industrial by-
products in gravel layer enhances the uniformity of the
permeating leachate and thus increases both the amount of
surface area and contact time available for sorption. Industrial
by-products (waste slag, scrap-tire-shreds and rice husks)
provide greater surface area for the sorption of various waste
constituents from the leachate. Test Cell-1 with only
conventional gravel layer contains fewer interconnecting voids
for fluid movements; flow is limited and restricted to only a
few flow channels in comparison to Industrial by-products
layer as a result less surface area for sorption is available.
Sorption refers to the exchange of molecules and ions between
the solid phase and the liquid phase [48]. Hence, vacant sites
for adsorption decrease with time leading to lesser sites for
adsorption to take place. Biodegradation takes some time to
execute because it needs the synthesis of microorganisms. It
implies that the dominant treatment mechanism of
biodegradable portion of organic matter could be biological
uptake. In fact the percentage removal increased with time
confirms that the major mechanism of removal could be
biodegradation since the rate of removal by adsorption is rapid
at the beginning and decreases with time. Leachate sample
after passing through combined beds of gravel and Industrial
by-products (waste slag, scrap-tire-shreds and rice husks) gave
better results in comparison to Test Cell-1 containing gravel
bed when used singly. The present study indicates that
Industrial by-products (waste slag, scrap-tire-shreds and rice
husks) can be used as a potential alternative to conventional
gravel in the drainage layer of leachate collection system as
PRBs (multibarrier) by improving upon the reduction in the
various leachate parameters of environmental concern. The
following sub sections show the status of percentage reduction
in the various leachate parameters viz Biological Oxygen
Demand (BOD5), Chemical Oxygen Demand (COD), Chloride
(Cl−
), Nitrate (NO3
−
), Phosphorus (P), Sulphate (SO4
2-
) by
laboratory scale Test Cells with reactive media.
3.1 Removal of BOD5
BOD5 value of the leachate sample collected from landfill site
was 495 mg/l. The measured BOD5 value of leachate sample
was considerably higher than the standard limit. BOD5 is the
measure of biodegradable organic mass of leachate and that
indicates the maturity of the landfill which typically decreases
with time [49]. Adsorption and biological uptake could be the
dominant treatment mechanisms of organic matter. Percentage
reduction in BOD5 value of the treated leachate samples
collected from Test Cells-1 to 11 after 30 days were 10.5%,
16.8%, 19.8%, 22.6%, 27.8%, 30.7%, 36.9%, 12.1%, 13.7%,

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14.3 % and 40.5%, after 60 days were 15.9%, 23.6%, 27.3%,
31.4%, 36.2%, 42.4%, 48.2%, 16.6%, 18.1%, 21.8 % and
53.9% and after 90 days were 25.4%, 35.6%, 39.2%, 47.8%,
50.9%, 55.7%, 65.1%, 27.8%, 30.3%, 33.8 % and 76.5% as
shown in Fig. 5(a). Percentage reduction in BOD5 value after
passing through Test Cell-11 having combine bed of rice husks
(125 mm), waste slag (125 mm), scrap-tire-shreds (125 mm)
and conventional gravel layer (125 mm) in equal proportion as
PRBs (multibarrier) gave better results in comparison to others.
The percentage reduction in BOD5 value was 40.5% after 30
days, 53.9% after 60 days and 76.5% after 90 days. The
percentage reduction in BOD5 values increased rapidly with
time.
3.2 Removal of COD
COD value of the leachate sample collected from landfill site
was 2535 mg/l. The measured COD value of leachate sample
was considerably higher than the standard limit. Bagchi [47]
stated that the most important mechanism of COD attenuation
in soil is biological uptake and filtration is a minor mechanism.
According to the same author, the surfaces of organic matter
provide some adsorption sites; in addition they may serve as
energy source for microorganisms. Activated carbon is used to
remove a portion of the remaining dissolved organic matter
after secondary treatments [48]. Therefore, adsorption can also
be considered a potential removal mechanism of organic
materials in the columns with organic reactive media.
Percentage reduction in COD value of the treated leachate
samples collected from Test Cells-1 to 11 after 30 days were
11.2%, 21.4%, 25.5%, 28.1%, 33.5%, 40.7%, 49.5%, 13.4%,
14.5%, 18.2 % and 55.8% after 60 days were 16.8%, 28.6%,
32.1%, 39.8%, 46.1%, 53.2%, 61.3%, 18.8%, 20.9%, 24.2 %
and 69.2% and after 90 days were 28.6%, 49.2%, 54.6%,
60.2%, 65.3%, 70.4%, 75.2%, 32.7%, 39.3%, 43.6 % and
83.5% as shown in Fig. 5(b). Percentage reduction in COD
value after passing through Test Cell-11 having combine bed
of rice husks (125 mm), waste slag (125 mm), scrap-tire-shreds
(125 mm) and conventional gravel layer (125 mm) in equal
proportion as PRBs (multibarrier) gave better results in
comparison to others. The percentage reduction in COD value
was 55.8% after 30 days, 69.2% after 60 days and 83.5 % after
90 days. The percentage reduction in COD values increased
rapidly with time.
3.3 Removal of Chloride
Chloride value of the leachate sample collected from landfill
site was 1836 mg/l. The measured chloride value of the
leachate sample was considerably higher than the standard
limit. Chloride is not attenuated by any soil type and is highly
mobile under all conditions [49]. Dilution is the only
mechanism for of attenuation of chloride in soil [47]. However
the opposite of above statements happened in these columns
because they had organic matter that increased the adsorption.
Percentage reduction in chloride value of the treated leachate
11.4%,16.5%, 18.4%, 20.1%, 22.6%, 28.1%, 31.6%, 12.7%,
13.8%, 15.5 % and 37.9% then after 60 days were 14.1%,
20.9%, 22.5%, 25.2%, 30.3%, 36.8%, 42.1%, 15.2%, 16.3%,
18.7 % and 50.3% and after 90 days were 20.5%, 32.6%,
35.7%, 39.4%, 42.6%, 48.4%, 53.9%, 23.9%, 27.5%, 30.2 %
and 64.4% as shown in Fig. 5(c). Percentage reduction in
chloride value after passing through Test Cell-11 having
combine bed of rice husks (125 mm), waste slag (125 mm),
scrap-tire-shreds (125 mm) and conventional gravel layer (125
mm) in equal proportion as PRBs (multibarrier) gave better
results in comparison to others. The percentage reduction in
chloride value was 37.9% after 30 days, 50.3% after 60 days
and 64.4% after 90 days. The percentage reduction in chloride
values increased rapidly with time.
3.4 Removal of Nitrate
Nitrate value of the leachate sample collected from landfill site
was 18.6 mg/l. The measured nitrate value of leachate sample
was considerably higher than the standard limit. According to
Bagchi [47], the major attenuation mechanism of nitrate is
biological uptake. Microbial decomposition of organic carbon
influences on many processes of the nitrogen cycle. With time,
nitrogen concentration decreased due to microbial utilization of
nitrate compounds and denitrifying as ammonia gas. Nitrate is
the primary contaminant that leaches into groundwater.
Percentage reduction in nitrate value of the treated leachate
20.1%, 34.5%, 38.6%, 40.8%, 44.6%, 50.5%, 54.5%, 22.3%,
25.1%, 30.2 % and 63.4% after 60 days were 27.2%, 42.9%,
45.2%, 49.9%, 56.5%, 61.2%, 66.8%, 32.8%, 30.4%, 38.5%
and 76.8% and after 90 days were 40.6%, 53.8%, 56.8%,
61.5%, 67.1%, 72.4%, 75.2%, 45.9%, 48.5%, 50.6 % and
81.2% as shown in Fig. 5(d). Percentage reduction in nitrate
value after passing through Test Cell-11 having combine bed
of rice husks (125 mm), waste slag (125 mm), scrap-tire-shreds
(125 mm) and conventional gravel layer (125 mm) in equal
proportion as PRBs (multibarrier) gave better results in
comparison to others. The percentage reduction in nitrate value
was 63.4% after 30 days, 76.8% after 60 days and 81.2% after
90 days. The percentage reduction in nitrate values increased
rapidly with time.
3.5 Removal of Phosphorus
Phosphorus value of the leachate sample collected from landfill
site was 83.5 mg/l. The measured phosphorus value of the
limit. Phosphorus is one of the key elements necessary for
growth of plants and animals and is a backbone of the Kreb's
Cycle and Deoxyribonucleic acid (DNA). Phosphorus
transported from agricultural lands to surface water can
promote eutrophication, which is one of the leading water
quality issues in lakes and reservoirs. Percentage reduction in
phosphorus value of the treated leachate samples collected
from Test Cells-1 to 11 after 30 days were 18.6%, 29.1%,
33.8%, 35.5%, 37.8%, 42.3%, 49.7%, 20.9%, 23.7%, 27.3 %

__________________________________________________________________________________________
and 53.2% after 60 days were 23.3%, 36.9%, 40.2%, 43.8%,
48.1%, 53.4%, 57.5%, 26.8%, 30.3%, 32.6 % and 65.6% and
after 90 days were 35.2%, 52.2%, 55.7%, 58.3%, 63.4%,
68.6%, 72.1%, 33.6%, 40.3%, 46.8 % and 79.8% as shown in
Fig.5(e). Percentage reduction in phosphorus value after
The percentage reduction in phosphorus value was 53.2% after
30 days, 65.6% after 60 days and 79.8% after 90 days. The
percentage reduction in phosphorus values increased rapidly
with time.
3.6 Removal of Sulphate
Sulphate value of the leachate sample collected from landfill
site was 65.1 mg/l. The measured sulphate value of the
limit. The sulphate content of leachate mainly depends on the
decomposition of organic matter present in the solid wastes. It
is expected to decrease with refuse age. This decrease is caused
by the reduction of sulphate to sulphide coincident with the
initiation of anaerobic conditions in the landfill [48]. Thus, the
sulphate concentration in leachate can also be used as an
indicator of waste stabilization within landfill. Percentage
reduction in sulphate value of the treated leachate samples
collected from Test Cells-1 to 11 after 30 days were 16.3%,
30.2%, 32.8%, 36.4%, 40.3%, 44.9%, 48.7%, 20.2%, 23.6%,
61.7 % and 56.5% after 60 days were 21.2%, 38.9%, 40.6%,
43.9%, 48.8%,52.6%, 55.2%, 28.3%, 31.4%, 35.4 % and
62.3% and after 90 days were 33.1%, 50.8%, 53.9%, 57.7%,
60.5%, 63.4%, 69.1%, 39.6%, 42.1%, 47.5 % and 73.5% as
shown in Fig. 5(f). Percentage reduction in sulphate value after
The percentage reduction in sulphate value was 56.5% after 30
days, 62.3% after 60 days and 73.5% after 90 days. The
percentage reduction in sulphate values increased rapidly with
time.
4. CONCLUSIONS
The following conclusions were drawn from the present study;
 In the laboratory scale column experiment, different
degrees of contaminant removal were shown by different
Test Cells-1 to 11 having different combination of
reactive media, Industrial by-products (waste slag, scrap-
tire-shreds and rice husks). The percentage reduction in
BOD5, COD, Chloride (Cl−
), Nitrate (NO3
−
), Phosphorus
(P), Sulphate (SO4
2-
) value was maximum upto 76.5 %,
83.5%, 64.4 %, 81.2%, 73.5% respectively.
 Unsaturated conditions prevailed in all the Test Cells, the
treatment mechanism was expected to be greatly similar
to natural attenuation in the unsaturated zone of soil.
However, these Test Cells differed from the unsaturated
zone due to the presence of reactive media. Bagchi [47]
identified following mechanisms of leachate attenuation
in soil: adsorption, cation and anion exchange reactions,
dilution, filtration, precipitation and biological uptake.
 The percentage reduction in various leachate parameters
was maximum with Test Cell-11 having combination of
rice husks (125 mm), waste slag (125 mm), scrap-tire-
shreds (125 mm) and conventional gravel layer (125 mm)
in equal proportion as PRBs (multibarrier) followed by
Test Cell-7 having combination of rice husks (375 mm)
and conventional gravel layer (125 mm) followed by Test
Cell-6 having combination of waste slag (125 mm) and
conventional gravel layer (125 mm) followed by Test
Cell-5 having combination of scrap-tire-shreds (375 mm)
and conventional gravel layer (125 mm) followed by Test
Cell-4 having combination of rice husks (250 mm) and
followed by Test Cell-3 having combination of waste slag
(250 mm) and conventional gravel layer (250 mm) in
equal proportion followed by Test Cell-2 having
combination of scrap-tire-shreds (250 mm) and
followed by Test Cell-10 having combination of rice
husks (125 mm) and conventional gravel layer (375 mm)
followed by Test Cell-9 having combination of waste slag
(125 mm) and conventional gravel layer (375 mm)
followed by Test Cell-8 having combination of scrap-tire-
shreds (125 mm) and conventional gravel layer (375 mm)
and Test Cell-1 containing conventional gravel layer
singly (500 mm).
 This performance trend can be attributed due to combined
effect of conventional gravel and Industrial by-products
bed (waste slag, scrap-tire-shreds and rice husks) on
adsorption, cation and anion exchange reactions,
filtration, precipitation and biological uptake. It is
hypothesized that introduction of Industrial by-products
in conventional gravel layer enhances the uniformity of
the permeating leachate and thus increases both the
amount of surface area and contact time available for
sorption. Industrial by-products (waste slag, scrap-tire-
shreds and rice husks) provide greater surface area for the
sorption of various waste constituents from the leachate.
Test Cell-1 with only gravel layer contains fewer
interconnecting voids for fluid movements; flow is
limited and restricted to only a few flow channels in
comparison to Industrial by-products layer as a result less
surface area for sorption is available. Sorption refers to
the exchange of molecules and ions between the solid
phase and the liquid phase [48]. Hence vacant sites for
adsorption decrease with time leading to lesser sites for
adsorption to take place. Biodegradation takes some time
to execute because it needs the synthesis of
microorganisms. It implies that the dominant treatment
mechanism of biodegradable portion of organic matter
could be biological uptake. The percentage removal

__________________________________________________________________________________________
increased with time confirms that the major mechanism of
removal could be biodegradation. The rate of removal by
adsorption is rapid at the beginning and decreases with
time. Leachate sample after passing through combined
beds of conventional gravel and Industrial by-products
(waste slag, scrap-tire-shreds and rice husks) gave better
results in percentage reduction in various leachate
parameters in comparison to Test Cell containing
conventional gravel bed when used singly.
 The reactivity of the organic materials depends on the
ability or availability of the contained carbon and
according to the study of Waybrant et al. [50], the
combination of more than one organic source is more
successful than the use of solely one material. This is due
to the fact that a mixture of organic materials contains
compounds with varying complexity, some of them
decomposing fast and others in a long time period, thus
achieving long term reactivity of the barrier.
 For reliable expectation on the longevity of PRBs,
column test has to be performed for longer periods of
time and the changes in material reactivity need to be
observed.
 In summary, there is perhaps no systemic study on the
Industrial by-products as potential alternative medium to
conventional gravel in the drainage layer of leachate
collection system as permeable reactive barriers for
leachate treatment. The present study is an effort to
explore the potential benefits of recycling industrial waste
in controlling contaminants in leachate.
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Fig- 4: Schematic representation of the experimental setup of Test Cells 1 to 11

__________________________________________________________________________________________
(a) (b)
(c) (d)
(e) (f)
Fig- 5 (a-f): Percent reduction in leachate parameters vs Test Cells-1 to 11 after 30, 60 and 90 days

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