DOI 10.1002tqem.21536R E S E A R C H A R T I C L EEx

DOI: 10.1002/tqem.21536
R E S E A R C H A R T I C L E
Experimental investigation of adsorption capacity of anthill
in the removal of heavy metals from aqueous solution
Adeyinka Sikiru Yusuff Idowu Iyabo Olateju
Department of Chemical and Petroleum Engi-
neering, College of Engineering, Afe Babalola
University, Ado-Ekiti, Nigeria
Correspondence
Adeyinka Sikiru Yusuff, Department of Chemical
and Petroleum Engineering, College of Engineer-
ing, Afe Babalola University, Ado-Ekiti P.M.B.
5454, Nigeria.
Email: [email protected]
Abstract
In the present work, the adsorption capacity of anthill was
investigated as a low-cost adsorbent
to remove the heavy metal ions, lead (II) ion (Pb2+), and zinc
(II) ion (Zn2+) from an aqueous solu-

tion. The equilibrium adsorption isotherms of the heavy metal
ions were investigated under batch
process. For the study we examined the effect of the solution's
pH and the initial cations con-
centrations on the adsorption process under a fixed contact time
and temperature. The anthill
sample was characterized using a scanning electron microscope
(SEM), X-ray fluorescence (XRF),
and Fourier transform infrared (FTIR) techniques. From the
SEM analysis, structural change in the
adsorbent was a result of heavy metals adsorption. Based on the
XRF analysis, the main compo-
sition of the anthill sample was silica (SiO2 ), alumina (Al2 O3
), and zirconia (ZrO2 ). The change in
the peaks of the spectra before and after adsorption indicated
that there was active participation
of surface functional groups during the adsorption process. The
experimental data obtained were
analyzed using 2- and 3-parameter isotherm models. The
isotherm data fitted very well to the 3-
parameter Radke–Prausnitz model. It was noted that Pb2+ and
Zn2+ can be effectively removed
from aqueous solution using anthill as an adsorbent.

K E Y W O R D S
adsorption, anthill, characterization, equilibrium isotherm,
heavy metal
1 I N T R O D U C T I O N
Indiscriminate disposal of wastewater containing heavy metals
has
received considerable attention in recent years, primarily due to
the
fact that their presence in waste stream can be readily adsorbed
by
aquatic organisms and make them directly enter the human food
chain,
thus posing a serious health risk to consumers (Lin, MacLean, &
Zeng,
2000). Because of the ability of heavy metals to accumulate in
living
tissues and because they cause damage to these tissues over
time,
heavy metals are classified as carcinogens. For example,
exposure to
lead ions can cause anemia, kidney damage, and even untimely
death
(Mohammed-Ridha, Ahmed, & Raoof, 2017), while zinc ions at
elevated

concentration result in pancreas damage, osteoporosis, and even
death
(Wahi, Ngaini, & Jok, 2009). Water or wastewater containing
heavy
metals requires effective treatment techniques that can
completely
remove these toxic metals (Yusuff, 2017).
A number of treatment techniques for the removal of heavy
metals from waste solution have been reported. These
techniques
include chemical precipitation, ion exchange, membrane
separation,
the Fenton-biological method, ultrafiltration, electrochemical
degra-
dation, and adsorption. Among these methods, adsorption of
adsor-
bate from fluid onto porous solid material called adsorbent has
been
identified as a simple and economical technique (Yusuff, 2017).
Adsor-
bent plays an important role in the adsorption process as it
serves
as a site for the separation of adsorbate from the fluid.

However, the
unique feature of an adsorbent is its adsorption capacity, which
is
usually influenced by the material used and method adopted for
its
production (Hameed, Krishni, & Sata, 2009). This is because
the adsor-
bent source and its preparation conditions will influence its
physi-
cal, chemical, and morphological properties. Many adsorbents
derived
from different sources such as agricultural waste (Yusuff,
Olateju, &
Ekanem, 2017), naturally occurring materials (Mohamed,
Abdelka-
rim, Ziat, & Mohamed, 2016), and microorganism (Mohammed-
Ridha
et al., 2017) just to mention but a few that have been used for
the
removal of heavy metals from wastewater. In this present work
how-
ever, anthill, a form of siliceous fireclay, was used as a low -
cost adsor-
bent for the removal of heavy metals from aqueous solution due

to its
ready availability in Nigeria. According to Akinwekomi,
Omotoyinbo,
and Folorunso (2012), anthill sample contains metal oxides such
as sil-
ica (SiO2 ), alumina (SiO2 ), iron oxide (Fe2 O3 ), and the like.
However,
some of these metal oxides in their pure or composite forms
have been
used as adsorbents for the removal of contaminants from
wastewa-
ter (Eletta, Ajayi, Ogunleye, & Akpan, 2016; Fisli, Ridwan,
Krisnandi, &
Gunlazuardi, 2017). This is the main reason why anthill was
chosen as
Environ Qual Manage. 2018;27:53–59. c© 2018 Wiley
Periodicals, Inc. 53wileyonlinelibrary.com/journal/tqem
54 YUSUFF A N D OLATEJU
an adsorbent for the removal of cations from aqueous solution
for the
present study. Furthermore, to the best of our knowledge, no
literature

on the adsorption behavior of anthill for the removal of heavy
metals
from aqueous solution is reported. Thus, in this present study,
an anthill
sample was thermally activated, characterized, and employed as
adsor-
bent to remove lead (Pb2+) and zinc (Zn2+) ions from aqueous
solu-
tion. The effects of process parameters affecting the adsorption
pro-
cess, such as medium pH and initial heavy metal concentrations,
were
investigated. An equilibrium adsorption isotherms study was
also car-
ried out and discussed in details.
2 M AT E R I A L S A N D M E T H O D S
2.1 Materials
The anthill sample used in this study was harvested from a type
II
anthill situated behind the University's staff quarters, Afe
Babalola
University, Ado-Ekiti, Nigeria. All chemical reagents and
materials used

in this study were of analytical grade. About 1,000 milligrams
per liter
(mg/L) stock solutions of Pb2+ and Zn2+ were prepared
separately
by dissolving 3.09 grams (g) of lead nitrate (Pb(NO3 )2 ) and
4.43 g
of zinc sulfate (Zn(SO4 )) in 1 liter (L) of distilled water each.
From
this prepared stock solution, the desired initial concentrations
of each
heavy metal ion was prepared for each run, and the
concentration
was analyzed using atomic absorption spectrophotometer (AAS,
Buck
Scientific 210VGP, USA).
2.2 Adsorbent preparation and characterization
The harvested anthill sample was ground by a mechanical
grinder into
a fine powder. Thereafter, the fine anthill powder was passed
through a
sieve mesh of 0.5 millimeter to obtain an even finer powder.
The anthill
powder was then calcined in a muffle furnace at a temperature
of 900

degrees Celsius (◦C) for 2 hours. The adopted heating rate was
10◦C
per minute, and after the calcination time was attained, the
calcined
anthill sample was immediately removed from the furnace
before its
temperature dropped to room temperature. The activated anthill
sam-
ple was then kept in a sealed glass bottle to prevent
contamination
with atmospheric moisture. The morphology and topography of
the
adsorbent before and after adsorption was examined by scanning
elec-
tron microscope (SEM-JEOL-JSM 7600F). Fourier transform
infrared
(FTIR) analysis was carried out on both thermally treated and
used
adsorbents in order to identify various surface functional groups
and
compared, by using FTIR spectroscope (FTIR-IR Affinity-1S
Shimadzu,
Japan). Moreover, the chemical compositions of the anthill
samples

before and after adsorption were determined by X-ray
fluorescence
machine.
2.3 Batch equilibrium studies
The batch adsorption process was carried out by bringing into
con-
tact the thermally activated anthill adsorbent with an aqueous
solution
containing a mixture of Pb2+ and Zn2+ in a set of conical flasks
of 250
milliliters capacity each. The flasks were agitated in a
temperature-
controlled water bath shaker (SearchTech Instrument) operating
at a
constant stirring speed of 150 revolutions per minute. The
adsorp-
tion process was conducted under the following operating
condi-
tions: the pH of the aqueous solution was variously 3, 4, 5, 6, 7,
8,
and 9, and the initial Pb2+ and Zn2+ concentrations were 10,
20,
30, 40, 50, and 60 mg/L at a fixed temperature of 35◦C for 90

min-
utes equilibrium contact time. After equilibrium was attained,
each
sample was filtered to obtain solution containing un-adsorbed
Pb2+
and Zn2+ that was free of the adsorbent, and the concentration
of
each metal ion was analyzed by atomic absorption
spectrophotome-
ter (AAS, Buck Scientific 210VGP, USA). The removal
percentage,
EA (%), and the amount of metal ions adsorbed at equilibrium,
qe
in milligrams per gram (mg/g), of each metal ion were
calculated as
follows:
EA =
(
Co − Ce
)
Co
× 100% (1)
qe =
(

Co − Ce
)
V
W
(2)
where Co and Ce (mg/L) are the initial concentration and
concentration
at equilibrium, respectively. V (L) is the volume of the solution
and W (g)
is the mass of activated anthill adsorbent.
3 R E S U LT S A N D D I S C U S S I O N
3.1 Adsorbent characterization
The SEM images of the prepared activated anthill before and
after
adsorption of Pb2+ and Zn2+ are shown in Exhibit 1a and 1b,
respec-
tively. As can be seen in Exhibit 1a, it is obvious that the
thermally
treated anthill possesses different layers of pores on its surface,
which
paves the way for heavy metals to be adsorbed. However, some
of
the pores were blocked due to adsorption of cations on the

activated
anthill as can be seen in Exhibit 1b.
The chemical composition analysis of prepared activated anthill
before and after adsorption as shown in the table in Exhibit 2
revealed
that silica (SiO2 ) constitutes the largest percentage in the
anthill sam-
ple, followed by alumina (Al2 O3 ) and zirconia (ZrO2 ).
However, the
percentage of SiO2 and Al2 O3 decreased after the adsorption
pro-
cess, as can also be seen in Exhibit 2. This implies that SiO2
and Al2 O3
are identified adsorption sites in anthill, and their reduction in
total
composition after the adsorption process could also be
attributed to
the fact that the SiO2 surface contained silanoh (OH group),
which
can interact with Pb2+ and Zn2+ (Fisli et al., 2017). A similar
observa-
tion was reported for the adsorption of Pb2+, Cu2+, and Zn2+
on soil
(Lim & Lee, 2015). This is corroborated by the FTIR analysis.

Further-
more, the good adsorption capacity exhibited by the thermally
treated
anthill sample can also be attributed to the interaction among
the
metal oxides in the adsorbent as they create several adsorption
sites
for the adsorbates.
YUSUFF A N D OLATEJU 55
EXHIBIT 1 SEM images of prepared anthill adsorbent (a)
before and (b) after adsorption of Pb2+ and Zn2+ [Color figure
can be viewed at wiley-
onlinelibrary.com]
E X H I B I T 2 X-ray fluorescence results of prepared activated
anthill
before and after adsorption process
Chemical composition
(wt%)
Before
adsorption
After
adsorption
SiO2 58.2 51.0

Al2 O3 21.6 18.3
Fe2 O3 2.36 2.66
MgO 4.77 4.72
Na2 O 4.13 4.24
K2 O 0.95 3.91
CaO 0.64 1.10
ZrO2 6.99 12.4
Other 1.20 3.57
The functional groups present on the surface of the prepared
adsor-
bent before and after adsorption process were identified by
FTIR
analysis, and their spectra are shown in the table in Exhibit 3.
Upon
the adsorption process, some of the spectra in activated anthill
shifted,
vanished, and new peaks were formed. The difference in the
FTIR
spectrum obtained for the prepared activated anthill before and
after
adsorption is an indication that there was participation of the

surface
functional groups during adsorption process (Yusuff, 2017).
3.2 Effect of process parameters on heavy metals
removal
3.2.1 Effect of pH
The adsorption of Pb2+ and Zn2+ as a function of the hydrogen
ion
concentration contained in aqueous solution was examined over
a pH
range of 3 to 9 as shown in Exhibit 4. The removal percentage
of
both cations decreased with increased pH of the aqueous
solution. For
both Pb2+ and Zn2+, the maximum removal percentage was
attained
at a pH of 5. The result obtained herein indicates that the
adsorp-
tion by the anthill of Pb2+ and Zn2+ would be enhanced at a
low
pH. Similar observations were reported for Pb2+ onto low -cost
bio-
sorbent (Mohammed-Ridha et al., 2017) and for Zn2+ onto soil
(Lim

& Lee, 2015). The maximum removal percentage of the heavy
met-
als recorded for an acidic medium could be the result of
interaction
between cations in solution and functional groups on the
adsorption
sites of anthill (Chiban, Lehutu, Sinan, & Carja, 2009).
E X H I B I T 3 The major absorption band and assignment for
anthill adsorbent before and after adsorption
Wavenumber (cm−1 )
Infrared band Before adsorption After adsorption
Assignment/Vibration mode
1 3,747.69 – Si-OH (silanol) vibration mode
2 – 3,693.68 Si-Si-OH or Al-Al-OH stretching vibration
3 1,649.14 1,649.14 H-OH deformation vibration
4 1,085.92 1,105.21 -Si-O stretching
5 – 1,029.99 -Si-O stretching of clay vibration
6 – 914.26 Al-Al-OH deformation
7 785.03 786.96 Al-Mg-OH vibration of clay sheet or O-Si-O
deformation vibration
8 688.59 692.44 Coupled Al-O and Si-O out of the plane

9 – 538.14 -Al-O-Si deformation
10 468.70 462.92 Si-O-Al deformation vibration
EXHIBIT 4 Effect of pH on removal percentage of Pb2+ and
Zn2+
at fixed initial heavy metal concentration = 50 mg/L, adsorbent
dosage = 0.2 g, and temperature = 35◦C
EXHIBIT 5 Effect of initial concentration on removal
percentage
of Pb2+ and Zn2+ at fixed pH = 5, adsorbent dosage = 0.2 g,
and
temperature = 35◦C
3.2.2 Effect of initial concentration of heavy metals
The effects of the initial concentrations of Pb2+ and Zn2+ on
their
removal percentages by thermally treated anthill was studied by
considering various values of initial concentrations between 10
and
60 mg/L. It was noticed that the removal percentage of cations
decreased from 95% to 84.2% and from 93% to 70% for Pb2+
and

Zn2+, respectively, by increasing the initial concentrations from
10
to 60 mg/L as shown in Exhibit 5. This observation revealed
that
the adsorbent dosage of 0.2 g provided enough active bonding
sites
for the adhesion of metal ions when the initial concentration
was
10 mg/L. However, increasing the initial cations concentrations
cause
the active bonding sites to become saturated, and the adsorbent
capac-
ity becomes exhausted due to non-availability of adsorption
sites
(Wang & Wang, 2007).
3.2.3 Adsorption isotherm
In a bid to quantify the amount of adsorbed heavy metals onto
acti-
vated anthill at equilibrium conditions, two- and three-
parameter
isotherm models were employed. However, the parameters
contained
in the selected isotherm models are evaluated by non-linear
curve

fitting, using Excel Solver and the isotherm model that best
describes
the experimental results is chosen based on the correlation
coefficient
(R2 ). The experimental data are assumed to be well-predicted
by the
model the closer the R2 value comes to unity.
3.2.4 Two-parameter isotherm model
In this present work, the experimental data for Pb2+ and Zn2+
adsorp-
tion onto activated anthill were fitted to two-parameter isotherm
mod-
els, the Langmuir and the Freundlich models. The Langmuir and
Fre-
undlich isotherm models are given in Equations (3) and (4),
respec-
tively, as follows:
qe =
qmax bCe
(1 + bCe)
(3)
qe = kF C
1∕n

e (4)
where qe (mg/g) is the amount of metal ions adsorbed at
equilib-
rium; Ce (mg/L) is the equilibrium concentration of metal in
solu-
tion; qmax (mg/g) is the maximum adsorption capacity; b is the
Langmuir equilibrium constant; kF (mg/g (L/mg)
1/ n ) indicates the
adsorption capacity of the adsorbent; and n is an adsorption
intensity.
A dimensionless constant referred to as separation factor (RL )
is
applied to ascertain the nature of adsorption by using the
Langmuir
equilibrium constant (b) and the highest initial concentration of
Pb2+
and Zn2+ (Co , mg/L), as given in Equation (5).
RL =
1
(
1 + bCO
) (5)

The separation factor (RL ) can either indicate irreversible
adsorp-
tion (RL = 0), favorable adsorption (0 < RL < 1), linear
adsorption
(RL = 1), or unfavorable adsorption (RL > 1).
From the non-curve fitting analysis shown in Exhibit 6a and 6b,
the
parameters contained in both the Langmuir and the Freundlich
mod-
els were determined and are presented in the table in Exhibit 7.
Based
on the value of R2 , Freundlich isotherm provides the best fit to
the
adsorption equilibrium data of Pb2+, while the adsorption of
Zn2+ onto
activated anthill was best described by the Langmuir isotherm
model.
A similar observation was reported for adsorption of Pb2+,
Cd2+, and
Zn2+ onto NALCO plant sand (Mohapatra, Khatun, & Anand,
2009).
However, the values of separation factor (RL ) obtained for both
Pb
2+
and Zn2+ were less than 1 as can be seen in Exhibit 7, thus

suggesting
a favorable adsorption process. Furthermore, by comparing the
maxi-
mum adsorption capacities of Pb2+ and Zn2+ on different
adsorbents
as shown in the table in Exhibit 8, activated anthill is found to
pos-
sess relatively high adsorption capacity, and this implies that it
could
be regarded as an effective and low-cost adsorbent for the
removal
of heavy metals from aqueous solution, especially when
compared
with other forms of clay such as Agbani clay (0.65 mg/g)
(Dawodu,
Akpomie, & Ejikeme, 2012) and bentonite clay (5.07 mg/g)
(Oludotun,
2015).
3.2.5 Three-parameter isotherm model
For further analyses of the acquired experimental data, three-
parameter isotherm models, the Sip and Radke–Prausnitz, were

EXHIBIT 6 Two-parameter isotherm models for adsorption of
(a) Pb2+ and (b) Zn2+ onto activated anthill
E X H I B I T 7 Two-parameter isotherm parameters and
correlation
coefficients for adsorption of Pb2+ and Zn2+ onto activated
anthill
Isotherm Pb2+ Zn2+
Langmuir
qmax (mg/g) 11.44 8.39
b (L/mg) 0.119 0.09
R2 0.9807 0.9842
RL 0.123 0.156
Freundlich
kF (mg/g (L/mg)
1/ n ) 1.53 1.04
n 1.62 1.76
R2 0.9903 0.9783
employed. The Sip and Radke–Prausnitz models are given in
Equations (6) and (7), respectively. All of the parameters
contained in

these two models (evaluated by the non-linear analysis method)
and
correlation coefficient (R2 ) are presented in Exhibit 9.
However, the
plots of qe against Ce , which display the non-linear regression
of the
three-parameter isotherm models to the experimental results,
and
also provide solutions to those models, are depicted in Exhibit
10a and
10b. Based on the value of R2 , the Radke–Prausnitz isotherm
model
provides a better fit to the isotherm data than the Sip model.
qe =
q
Ms
max(KS Ce)
1 + (KS Ce)
(6)
qe =
qmax KRP Ce
(
1 + KRP Ce
)MRP

(7)
where qe (mg/g) is the amount of metal ions adsorbed at
equilib-
rium; Ce (mg/L) is the equilibrium concentration of metal in
solution;
qmax (mg/g) is the maximum adsorption capacity; KS and KRP
are the Sip
and the Radke–Prausnitz equilibrium constants, respectively;
and MS
and MRP are Sip and Radke–Prausnitz model exponents,
respectively.
E X H I B I T 8 Comparison of adsorption capacities of
different
adsorbents for Pb2+ and Zn2+
Adsorption
capacity (mg/g)
Adsorbent Pb2+ Zn2+ Reference
Anthill 11.44 8.39 Present work
Red mud – 14.51 Gupta and Sharma,
2002
Calcareous soil – 4.587 Mesquita and e Silva,
1996
Agbani clay 0.65 – Dawodu et al., 2012

Nalco plant sand 21.78 58.28 Mohapatra et al.,
2009
Acid soil – 6.004 Arias, Pérez-Novo,
López, and Soto,
2006
Waste beer yeast 2.34 – Parvathi, Nagendran,
and Nareshkumar,
2007
Bentonite clay 5.07 – Oludotun, 2015
E X H I B I T 9 Three-parameter isotherm parameters and
correlation
coefficients for adsorption of Pb2+ and Zn2+ onto activated
anthill
Isotherm Pb2+ Zn2+
Sip
qmax (mg/g) 222.05 126.44
KS 0.00035 0.00027
MS 0.626 0.583
R2 0.9927 0.9769
Radke–Prausnitz
qmax (mg/g) 242.71 153.73
KRP 0.051 0.059

MRP 0.381 0.431
R2 0.9932 0.9782
EXHIBIT 10 Three-parameter isotherm models for adsorption of
(a) Pb2+ and (b) Zn2+ onto activated anthill
4 C O N C L U S I O N
This study revealed that anthill, a naturally occurring material,
could be
used as a low-cost adsorbent to remove Pb2+ and Zn2+ from
aqueous
solution. The adsorption capacity of the cations from aqueous
solution
descended in order of Pb2+ > Zn2+. The maximum removal
percent-
age of the heavy metal ions was obtained at an optimum pH of
5. The
applicability of 2- and 3-parameter isotherm models for the
adsorption
of heavy metals onto activated anthill was also discussed in
detail. The
equilibrium adsorption isotherm study revealed that the
isotherm data

fitted very well to the 3-parameter Radke–Prausnitz model.
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A U T H O R S'B I O G R A P H I E S
Adeyinka Sikiru Yusuff obtained his PhD from the Federal
Univer-
sity of Technology, Minna, Nigeria, in 2017. He is a senior
lecturer at
the Department of Chemical & Petroleum Engineering, Afe
Babalola
University, Ado-Ekiti, Nigeria. His areas of research interests
are cen-
tered on catalysis, renewable energy, separation process, and
environ-
mental technologies.
Idowu Iyabo Olateju holds an MEng in chemical engineering
from
the University of Lagos, Akoka Lagos, Nigeria. She is a lecturer
at the
Department of Chemical & Petroleum Engineering, Afe
Babalola Uni-

versity, Ado-Ekiti, Nigeria. Her areas of research interests are
focused
on environmental management, biochemical engineering, and
process
development.
How to cite this article: Yusuff AS, Olateju II. Experimental
investigation of adsorption capacity of anthill in the removal
of heavy metals from aqueous solution. Environ Qual Manage.
2018;27:53–59. https://doi.org/10.1002/tqem.21536
001914
001914
https://doi.org/10.1002/tqem.21536
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ORIGINAL PAPER
Role of carbohydrases in minimizing use of harmful substances:
leather as a case study
Jayanthi Durga1 • Ramakrishnan Ramesh3 • Chellan Rose2 •
Chellappa Muralidharan3
Received: 10 August 2016 / Accepted: 10 December 2016 /
Published online: 9 January 2017
� Springer-Verlag Berlin Heidelberg 2017
Abstract Leather processing is an important industrial
activity. Globally about 2.0 billon sqmt of leather is pro-
duced annually. Conventional cleansing operations carried
out prior to tanning generate large amounts of waste.
Among them dehairing and fibre opening process (relim-
ing) generate large amount of effluent containing haz-
ardous substances and alkaline sludge, resulting in high
negative impact on the environment. In this study, both
these pre-tanning process steps have been combined using
a cocktail of carbohydrases along with optimum quantity of
chemicals to minimize the environmental concerns. Car-

bohydrate and proteoglycan removal were chosen as the
parameters of study for efficacy of unhairing and fibre
opening. The morphology features of skins were analysed
using scanning electron microscopy and histology. Pollu-
tion load of the enzyme aided process effluent was deter -
mined and compared with conventional process. Findings
of the study indicate complete elimination of reliming
process step is possible when both unhairing and fibre
opening is carried out simultaneously using carbohydrases
as an adjunct. Reduction in use of harmful sulphide and
lime up to 40% apart from substantial saving in time and
water input is the major outcome of the present work.
Keywords Carbohydrases � Single-step processing �
Leather making � Pollution reduction
Introduction
Tanneries are among the oldest manufacturing industries.
Tanneries are engaged in transformi ng the raw hides and
skins into leather through several unit operations. During
the last few decades, many new materials and technologies

are being studied and applied in manufacturing in order to
reduce the ecological impact of leather production (Jian
et al. 2011). Leather manufacturing has been, very often,
identified as one of the environmentally unfavourable
industrial activities. The non-substantive chemicals used in
the pre-tanning and tanning operations are predominantly
source for large amount of the harmful substances in tan-
ning effluents (Ludvik 1996).
Conventional pre-tanning involves use of chemicals
such as lime and sulphide, aimed at the removal of non-
leather making substances, which accounts for almost
80–90% of the total pollution load (Sivasubramanian et al.
2008). Besides this, sulphide in the effluent may librate
hydrogen sulphide under specific conditions, a toxic gas
that poses serious hazard for tannery workers. Many fatal
accidents have been reported due to generation of hydrogen
sulphide at high concentration, particularly at tannery
effluent treatment plants (Vijayaraghavan et al. 2015).

However, use of large amounts of lime (Ca(OH)2) and
sulphide (Na2S) for processing has remained unchanged
due to non-availability of viable cost-effective alternatives.
Unutilized lime contributes to significant quantity of sludge
Electronic supplementary material The online version of this
article (doi:10.1007/s10098-016-1321-x) contains
supplementary
material, which is available to authorized users.
& Chellappa Muralidharan
[email protected]
1
Academy of Scientific and Innovative Research (AcSIR),
AnusandhanBhawan, 2 Rafi Marg, New Delhi, 110 001, India
2
Department of Biotechnology, CSIR - Central Leather
Research Institute, Adyar, Chennai 600020, India
3
Leather Processing Division, CSIR - Central Leather
Research Institute, Adyar, Chennai 600020, India
123
Clean Techn Environ Policy (2017) 19:1567–1575
DOI 10.1007/s10098-016-1321-x

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generation which under specific conditions can become
hazardous (Schlosser et al. 1986). Several lime- and sul-
phide-free pre-tanning methods have been studied exten-
sively in last few decades (Rose et al. 2007). These include
unhairing methods based on proteolytic enzymes, ionic
liquids and lactobacillus to replace sulphide (Seggiani et al.
2014; Sandhya et al. 2005). In leather making, many
enzyme-based processes have been reported to be cost-
ineffective (Ludvik 2000).
Enzymes have been widely used in leather manufacture
in soaking, unhairing, bating and degreasing processes
(Kandasamy et al. 2012). Currently enzyme-assisted
dehairing is being used in many industries due to its better
environmental performance (Senthilvelan et al. 2012).

Recently, a cocktail of carbohydrases has been successfully
employed to facilitate rapid fibre opening of skins in about
30 min compared to 72-h duration required in conventional
process replacing lime (Durga et al. 2015). In the present
study, an attempt has been made to carry out unhairing and
fibre opening process in a single step with a view to opti-
mize chemicals and time and to facilitate cleaner leather
production. The results of the study indicate substantial
benefits to leather making could be achieved by combining
process steps through use of the carbohydrases in pre-
tanning operation.
Materials and methods
Cocktail of carbohydrase enzymes produced by solid-state
fermentation (SSF) of Aspergillus terreus was used for
integrated dehairing and fibre opening along with optimum
quantities of sodium sulphide and lime. The enzyme
activity of carbohydrase was found to be 40,000 U/g of
substrate using a method of Dey and Pridham (1972) and

Miller (1972). The stability of the enzyme used in this
study was in the temperature range of 25–40 �C and pH
range of 6–13. All the chemicals used for leather making
were of commercial grade.
Experimental
Goat skins were used as substrate in this study. Wet salted
goat skins were vertically cut into left (L) and right
(R) pieces, and were marked accordingly. The left pieces
were processed by conventional unhairing and fibre open-
ing (reliming) process by pasting method using 10% lime
20% water and 2.5% sodium sulphide. The paste was
applied on flesh side of the skin and left over night. Next d
the skins were unhaired and relimed with 5% lime and
100% water for a d in drum.
The respective right pieces were processed by employ-
ing different concentrations of sodium sulphide and lime in
the form of paste containing 20% water and 1% fibre
opening enzyme (carbohydrase). Next d the skins were
washed with 100% water for a period of 30 min. The pelts

thus obtained from both control and experiments were
assessed at this stage for fibre opening.
Optimization of sulphide concentration
Experiments were carried out to optimize the quantity of
sulphide for complete removal of hair in the presence of
carbohydrase and reduced lime quantity. The right pieces
were pasted on the flesh side with varying concentrations
Conventional process Experimental process
Soaking
Liming(unhairing)
Lime 10%; Sodium sulfide 2.5%; Water 10%
Re-liming (Fiber opening)
Lime 5% ; Water 100%
Tanning after flesh removal
Liming(unhairing) & Re-liming (Fiber opening)
Lime 5% ;Sodium sulfide 1.5%
Water 20%; carbohydrase 1.0%
Soaking

Re-liming (Fiber opening)
Tanning after flesh removal
1568 J. Durga et al.
123
of sodium sulphide, i.e. 0.5, 1.0, 1.5, 2.0 and 2.5% with 5%
lime, 1% cocktail of carbohydrases and 20% water and left
overnight. Skins were unhaired the next d and assessed
visually. Removal of sugar and glycosaminoglycan were
assayed by using standard procedures.
Optimization of lime concentration
Second set of experiments was carried out to determine the
optimum concentration of lime required for this combined
process employing reduced sulphide in the presence of
carbohydrase. The sulphide of optimized concentration
along with 1% cocktail of carbohydrases and 20% water
was used for different lime concentrations, viz. 1.0, 2.0,
3.0, 4.0, 5.0, 6.0 and 7.0 without changing other parame-

ters. The skins were assessed visually and the carbohydrate
and proteoglycan levels in the pelt samples were quantified
spectrophotometrically to determine the optimum lime
concentration required for maximum removal of interfib-
rillarly materials. All the skins were converted into wet
blue leathers using standard chrome tanning process (given
as ‘‘Appendix 1’’). Chromium content of both the leathers
was analysed adopting IUC method.
Tanned leathers (wet blue) were then shaved to a uni-
form thickness and were converted into crust leather as per
the process given in ‘‘Appendix 2’’. The crust leathers were
assessed and evaluated as per standard test methods and
assessment procedures.
Carbohydrate assay
Total carbohydrate content of the pelt samples, both the
experimental and control, was determined by phenol–sul-
phuric acid method using D-glucose as standard (Dubolis
et al. 1956). Soaked skin sample was used as blank to

compare the remaining sugar content of the both conven-
tional and experimental samples. Sample for assay was
prepared by hydrolysing 100 mg each of lyophilized
sample with 0.5 N sulphuric acid solution at 100 �C in
sealed tube for 4 h. Assay was carried out by using 1 ml of
hydrolysed aliquot of pelt sample mixed with 5% (v/v)
phenol. And then the tubes were cooled in ice for 10 min
and 5 ml of concentrated sulphuric acid was added through
the sides of tubes. The contents were thoroughly mixed,
and the tubes were heated in a water bath at 80 �C for
20 min. After cooling the tubes to room temperature, the
absorbance was noted at 490 nm using a spectrophotome-
ter. A reagent blank was prepared in the same manner
using distilled water. The amount of carbohydrate
remained in the pelt samples was calculated as glucose
from the standard curve drawn using glucose solution of
known concentration.
Estimation of proteoglycan
In order to estimate the amount of proteoglycan in the pelt

sample, both the experimental and conventional samples
were assayed by Schiff’s colorimetric method (Mantle and
Allen 1978). Initially, 100 mg of sample was hydrolysed
using 0.5 N sulphuric acid solution at 100 �C in sealed tube
for 16–18 h and allowed to cool to room temperature. To
1 ml of hydrolysed sample, 100 ll of decolorized Schiff
reagent was added and incubated at 37 �C for 2 h. After-
wards the reaction mixture was allowed to remain at room
temperature for 30 min for colour development. Absor-
bance of the reaction product was measured at 555 nm
using UV–Vis spectrophotometer and the total amount of
proteoglycan present in the sample was calculated using
mucin as standard.
Scanning electron microscopic analysis
Samples from conventional and experimental pelts were
cut, washed and fixed in formalin solution. Then the
samples were dehydrated using a graded ethanol series and
were finally freeze-dried. The dried samples were cut into
approximately 5 mm thickness and examined by scanning
electron microscopy. The samples were mounted both

vertically and horizontally on aluminium stubs. The stubs
were coated with gold using an Edwards E-306 sputter
coater and introduced into the specimen chamber of a FEI-
Quanta 200 scanning electron microscope. The micro-
graphs for the cross section were obtained by operating the
microscope at higher voltage.
Histological studies
Conventional and experimental limed skins were cut and
preserved in 10% formalin for 48 h. The samples of both
experimental and conventional trials were fixed using for -
malin (10%) in phosphate-buffered saline (PBS), cassetted
and blocked in paraffin wax. Sample sections of 4–5 lm
thickness were cut using microtome (Leica) and mounted
on glass slide. The tissue specimens thus obtained were
dehydrated using series of alcohol (30, 60 and 100%) and
stained using haematoxylin and eosin and visualized in
bright-field microscope, to assess the extent of removal of
epidermis and opening of fibre bundles of collagen and

distribution in the sample.
Analysis of chrome content
Chromium content of leathers was determined by follow-
ing the official procedure (IUP 2 2000). A known quantity
(*1 g) of the sample was weighed, and the percentage of
chromium was estimated as per standard procedures.
leather as a case study 1569
123
Initially the samples were analysed for moisture content;
chrome content was expressed on dry weight basis of
leather.
Evaluation of strength characteristics and visual
assessment of leathers
Various physical properties such as tensile strength, per -
centage elongation at break, tear strength and grain crack
strength of leather samples of experimental and conven-
tional processes were examined as per the standard pro-

cedure (IUP 6 2000; IUP 8 2000). Samples were
conditioned to the required relative humidity of 60 ± 4%
at 20 ± 2 �C for 48 h as per standard procedures. The crust
leathers were assessed for softness, grain tightness and
general appearance by hand and visual examination.
Analysis of spent liquor
Spent liquor from both conventional and experimental
processes were collected and analysed for pollution
parameters such as biochemical oxygen demand (BOD),
chemical oxygen demand (COD) and total dissolved solids
(TDS) according to the method followed by Thangam et al.
(2001) and Eaton et al. (1995). The results are expressed in
parts per million (ppm).
Results and discussion
Initially, trials were performed to optimize concentrations
of sulphide and lime matching the requireme nts of the
conventional process. Trials with different concentrations
of sodium sulphide (0.5–2.5%), lime (1.0–7.0%) along
with 1% carbohydrases were carried out in the study. The

experimental skin was white in colour; it had cleaned grain
surface compared to its control (processed by traditional
method). Enzymatic fibre opening assisted the depilation of
hair at its roots. On the contrary, the hairs in the control
were removed by solubilization. The hair roots were still
present in the deep dermis regions, leading to unclean
appearance.
Breaking of O-glycosidic linkages of the lysyl residue of
collagen enables the loosening of the collagenous fibrillar
bundles which in turn facilitated the depilation of hair that
has been already discussed in our earlier report (Durga
et al. 2016).
Sodium sulphide optimization
Skins subjected to combined unhairing and fibre opening
process using 1% (v/w) enzyme dosage varying at varied
concentrations of sodium sulphide (0.5–2.5% w/w)
exhibited different degrees of unhairing. At 0.5–1.0%
sodium sulphide levels, unhairing was found not satisfac-

tory. Sulphide concentration of 1.5% along with 1%
enzyme was found to be optimum requirement for com-
plete unhairing. Visual assessment of unhaired skins indi -
cated that experimental pelts were comparable or
marginally better than the conventional pelts, and the data
obtained are presented in Table 1 on a 10-point scale. The
carbohydrase enzyme also was found to exhibit better
functionality at this sulphide concentration (1.5%), as
observed from the results of carbohydrate and proteoglycan
removal given in Table 2. The removal of sugars and
glycosaminoglycan at this optimum quantity is remarkably
high compared to other concentrations employed. While a
minimum of 1.5% sodium sulphide was found necessary
for dehairing, increasing sodium sulphide concentration
beyond was found not to be useful apart from adding to
harmful pollution. Higher concentration of sodium sul-
phide beyond 1.5% also was found to adversely affect the
fibre opening efficiency of carbohydrases.

Table 1 Visual assessment of unhaired pelt
Properties Conventional process Enzyme-assisted process
Sulphide 2.5% (w/w),
Lime 10%(w/w)
Optimized concentration
Sulphide 1.5% (w/w),
Lime 5% (w/w) ?
Enzyme 0.5%
Unhairing
efficiency
9.5 ± 0.2 9.5 ± 0.2
Grain pattern 9.6 ± 0.2 9.7 ± 0.2
substance 9.4 ± 0.2 9.8 ± 0.1
Smoothness 9.3 ± 0.2 9.5 ± 0.2
Pelt colour 9.2 ± 0.2 9.7 ± 0.2
Scale of 1–10; 1—poor; 10—best
Average value of 3 experts
Table 2 Extent of carbohydrate and proteoglycan removal

Sample Sugar removal (%)* GAG removal (%)*
Control 67.0 ± 0.5 71.6 ± 1.0
0.5% sulphide ? EL 73.5 ± 1.0 77.0 ± 1.0
1.0% sulphide ? EL 74.0 ± 0.9 83.0 ± 1.0
1.5% sulphide ? EL 88.0 ± 1.0 86.4 ± 1.5
2.0% sulphide ? EL 78.0 ± 1.0 84.0 ± 1.5
2.5% sulphide ? EL 79.5 ± 0.5 85.0 ± 0.5
EL enzyme 1%; Lime 5.0%, GAG Glycosaminoglycan
* Average value of 3 determinations
123
Optimization of lime
The process was carried out with different concentrations
[1.0–7.0% (w/w)] of lime along with standardized con-
centration of 1.5% sodium sulphide and 1% carbohydrase.
Compared to conventional processes employing 10% lime,
lime quantity of 5% was found sufficient for combined

process of unhairing and fibre opening. Visual assessment
of fibre opened experimental pelts indicated comparable or
marginally better features as presented in Table 3. The
results of carbohydrate and proteoglycan removal are pre-
sented in Table 4. This provides clear understanding that
the enzyme-assisted combined process is superior in
function compared to that of the conventional chemical
only process. Higher concentrations of lime beyond 7%
were found to be adversely affecting the enzyme activity.
Chromium content
The percentage of chromium oxide content in wet blue lea-
ther from conventional and experimental processes were
found to be 4.0 ± 0.3 and 4.9 ± 0.2 (w/w), respectively.
Experimental leather showed a marginal increase in chro-
mium uptake compared to conventionally processed leather.
The increased level of chromium uptake in the enzyme-
treated wet blue sample may be attributed to possible
availability of chromium binding functional groups on the

microfibrillar surface, due to the carbohydrase mediated
deglycosylating fibre opening process, although not con-
firmed experimentally.
Physical testing and visual assessment data
The strength properties such as tensile, tear and grain crack
strength values were determined by following standard
procedures. After dehairing, visual assessment of enzymatic
pelt from goat skin revealed that there was complete and
uniform removal of hair showing white clean pelt with the
complete absence of hair root. The strength properties of
control and experimental crust leathers are given in Table 5.
It is obvious from the results that the strength properties of
experimental crust leathers are comparable to that of con-
ventionally processed crust leathers. The visual assessment
and the hand evaluation of crust leathers revealed that the
enzyme-assisted process led to improve the organoleptic
properties such as grain pattern appearance, smoothness and
fullness (Fig. 1). Both the visual and feel tests suggested that

the crust leathers made out of enzyme-treated skins were
fuller probably due to improved diffusion of tanning and
post-tanning chemicals in to the skins because of better
opening up and removal of interfibrillary materials.
Environmental benefits
The spent liquors have been collected from conventional
and experimental processes, and analysed for pollution
parameters such as biochemical oxygen demand, chemical
oxygen demand and total dissolved solids. The values are
presented in Table 6. It is seen that the BOD, COD, TDS in
the experimental process is much lower than the control
process. This is mainly due to the partial replacement of
lime and sulphide with the help of fibre opening enzyme.
This method appreciably decreases the usage of chemicals,
reduces pollution load and eliminates intermediate process,
reliming. Moreover, the remarkable decrease in the BOD
level indicates the decreased solubilization of hair due to
judicious usage of sulphide (1.5% w/w) in the combined

process as against conventional two-stage chemical process
where sulphide is used to the extent of 2.5% (w/w) along
with lime 5% in reliming.
Economic benefits of integrated process
The combination of unhairing–fibre opening by using a
cocktail of carbohydrase has been developed to enhance
economic benefits of leather processing. The total cost
consumption of chemicals and enzyme used in
Table 3 Visual assessment of defleshed pelt
Properties Conventional process Enzymatic process
Lime 5.0% (w/w) with
100% water (v/w)
Unhaired pelt with 100%
water (v/w)
Grain
pattern
9.6 ± 0.1 9.7 ± 0.1
substance 9.4 ± 0.1 9.8 ± 0.1

Smoothness 9.3 ± 0.1 9.5 ± 0.1
Pelt colour 9.2 ± 0.1 9.7 ± 0.1
Scale of 1–10; 1—poor; 10—best
Average value of 3 experts
Table 4 Extent of carbohydrate and proteoglycan removal with
conventional and experiment
Sample Sugar removal (%)* GAG removal (%)*
Control 65.0 ± 0.5 73.5 ± 0.5
1.0% lime ? ES 72.4 ± 1.0 76.2 ± 0.5
2.0% lime ? ES 75.0 ± 1.0 77.0 ± 0.5
3.0% lime ? ES 81.0 ± 1.0 84.2 ± 1.0
4.0% lime ? ES 84.0 ± 1.0 86.0 ± 1.5
5.0% lime ? ES 87.0 ± 1.5 87.5 ± 1.5
6.0% lime ? ES 85.2 ± 1.5 86.3 ± 1.5
7.0% lime ? ES 84.1 ± 1.5 85.4 ± 1.0
ES enzyme 1%; sulphide 1.5%, GAG glycosaminoglycan

123
conventional and experimental method are given in
Table 7. The enzymatic formulation of carbohydrase has
effectively used to remove the hair and interfibrillary
materials such as glycosami noglycan and proteoglycan.
Reduction in usage of lime and sodium sulphide in
experimental process provides cost reduction to an extent
of US$ 40/ton of skins. The experimental process would
lead to saving in chemical cost due to 40–50% reduction in
lime and sulphide process. In this work, a single-step
process leads way to a cleaner technology. This new
technology will result in increased productivity with the
existing methods due to substantial time saving.
Evaluation using scanning electron microscopy
The pelt sample processed by both conventional and
experimental (enzyme-assisted) methods was examined
through scanning electron microscope, and the details are

shown in Fig. 2. According to the micrographs, the cross-
sectional study of the experimental sample indicated
smooth and opened fibre bundles compared to that of
conventionally produced pelt specimen. The micrographs
confirm that the enzyme was able to bring out a conspic-
uous complete removal of hair and opening up of fibre
structure compared to conventional process. Efficacy of
enzyme-assisted and chemical-driven unhairing and fibre
opening process was corroborated with the results of his-
tological studies. Harish et al. (2015) also reported
enzyme-dehaired skins exhibit better characteristics, com-
pared to conventional process.
Histology
Haematoxylin- and eosin-stained sections of both the
samples of chemical- and enzyme-assisted processes were
analysed for extent of removal of epidermis, glandular
structures and hair root. The absence of the keratinous
structural features was observed in pelts obtained by

enzyme-assisted single-stage treatment, whereas removal
of such components was incomplete in the conventional
pelts. Haematoxylin and eosin staining clearly distin-
guished the removal of residues of interfibrillary materials
through histological studies of both conventional and
experimental pelts as shown in Fig. 3. It is seen that cross
section of control samples exhibited moderate opening of
collagen fibre bundles, while the experimental pelts
showed distinct fibres with good orientation. Complete
removal of epidermal layer from skin was observed when
dehairing was performed using carbohydrase.
Conclusion
The present work deals with combining the unhairing and
fibre opening by using a cocktail of enzyme in the presence of
judicious concentration of lime, and sulphide has been
developed to enhance economic and environmental benefits
of leather making. Only 1.5% sulphide and 5% lime were
found to be sufficient for unhairing when simultaneously

treated with 1.0% carbohydrases for fibre opening leading to
saving in 40–50% chemicals usage. Graphical representation
of the process is given in Supplementary Figure. This present
8.4
8.6
8.8
9
9.2
9.4
9.6
9.8
10
10.2
A
ss
es
sm
en
t

R
at
in
g
Control
Experiment
Fig. 1 Visual assessment of wet blue leathers
Table 6 Environmental benefits
Process BOD (ppm)* COD (ppm)* TDS (ppm)*
C 5780 ± 10 7560 ± 10 15,320 ± 10
E 2264 ± 10 5040 ± 10 8330 ± 10
Table 5 Physical testing results of conventional and
experimental leathers
Experiment Tensile strength (Kg/cm
2
)* % Elongation at break* Tear strength (Kg/cm)* Grain crack
strength*
Load (Kg) Distension (mm)
C 242.8 ± 0.2 68.8 ± 0.5 45.0 ± 0.2 41.6 ± 0.2 9.5 ± 0.2
E 248.0 ± 0.2 57.8 ± 0.5 41.9 ± 0.2 46.6 ± 0.2 8.9 ± 0.2

123
Fig. 2 Scanning electron microscopy images of control and
experimental goat skins. a Control, b experiment
Table 7 Cost of chemicals for processing one ton of raw skins to
tanned leather
Chemicals Conventional method Experimental method
Quantity required (%) Cost (US $/ton) Quantity required (%)
Cost (US $/ton)
Lime (Ca(OH)2) 10 15.04 5.0 7.52
Sodium sulphide (Na2S) 2.5 13.54 1.5 7.9
Enzyme – – 1.0 3.01
Lime (Ca(OH)2) 10 15.04 – –
Ammonium chloride (NH4Cl) 3.0 2.71 2.1 1.89
Alkali Bate 1.0 13.54 1.0 –
Salt (NaCl) 10 6.02 10 6.02
Formic acid (HCOOH) 0.5 0.23 0.5 0.23
Sulphuric acid (H2SO4) 1.0 0.3 1.0 0.3

Basic chromium sulphate (BCS) 4.0 42.11 4.0 42.11
Basic chromium sulphate (BCS) 4.0 42.11 4.0 42.11
Sodium formate 0.7 4.74 0.7 4.74
Sodium bicarbonate 1.0 13.54 1.0 13.54
Total 47.7 168.92 31.8 129.37
Fig. 3 Photomicrographs of H-
and E-stained control- and
experiment-treated goat skins.
a Control, b experiment
123
invention also resulted in significant removal of interfibrillar
substances without damage to collagen structure. The partial
reduction in sulphide and lime lowers sulphide toxicity, hair
solubilization, BOD and sludge formation. This study
therefore provides an important solution to one of the long-
pending problems of leather processing.

Acknowledgements The authors gratefully acknowledge the
Council
of Scientific and Industrial Research (CSIR), New Delhi, for
funding
this research. Authors thank ‘‘Science and Technology
Revolution in
Leather with a Green Touch’’ (STRAIT)—1190.
Appendix 1
The pelts were washed with 200% water for 10 min.
Subsequently, the pelts were delimed by adding 100%
water and 1% (w/w) ammonium chloride for 45 min in a
drum. Deliming was ascertained by checking the cross
section of the delimed pelts for colourlessness due to
phenolphthalein indicator. After deliming, bating process
were carried out in the same bath for 30 min by the addi -
tion of bating enzyme. The pelts were washed with 100%
water for 10 min. Pickling was carried out. 1% sulphuric
acid (w/w) was added in 4 feeds at 10-min interval and
tumbled in a drum for 60 min to obtain pickled skin at pH
of 2.8. The pickled skins were tanned using 8% (w/w) basic

chromium sulphate (BCS) in 50% pickle water for 90 min.
Then 50% (w/w) water was added and the drum was run
further for 30 min. To the running drum, 1% (v/w) sodium
formate (mixed with 10% w/v water) was added. After
30 min, 1% (w/w) sodium bicarbonate (mixed with 10%
w/v water) was added in 3 feeds at 10-min interval and
continued the tumbling for 60 more min to bring the pH to
3.8.
Appendix 2
Post-tanning operations comprise of rechroming of semi-
finished wet blue leather, neutralization, dyeing, fat
liquoring and finishing. The wet blue leathers obtained by
the procedure under Appendix 1 to were shaved to 1.0 mm
thickness. All the samples were washed in 100% (w/v)
water in a drum for 10 min. After draining, the wet blue
leathers were treated with 1.0% (w/w) neutralizing syntan
with 100% water for 20 min. Sodium formate 0.5% (w/w)
and sodium bicarbonate were then added to the drum in 3

feeds at 10-min interval, while the drum was in running
mode. After ensuring the pH of the cross sections at 5.0, the
leather samples were washing twice with 200% (w/v) water
for 10 min. The neutralized skins were washed with water
followed by treatment with resin syntan (3% w/w) and
allowed to run in the drum for 20 min. After this, dying
(2% w/w acid dye) and fat liquoring (4% w/w synthetic fat
liquor) were carried out by drumming for 30 min. Subse-
quently melamine- and naphthalene-based retanning syn-
tans 4% (w/w) was added and run for 40 min followed by
the addition of synthetic fat liquor 4% (w/w), polymeric fat
liquor 3% (w/w) and natural fat liquor oil 4% (w/w) and
further running the drum for 40 min. Finally the auxiliaries
were fixed using 2% (v/w) formic acid diluted with 20% (v/
w) water and added at 3 feeds at every 10-min interval and
the drum was further run for 30 min and piled overnight.
The leathers were set, conditioned, again set with rever-
sible setting machine and hooked for drying. After drying,

leather was staked and buffed using 400-grit emery paper.
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(2015)
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chemical free process. J Am Leather Chem Assoc 110:07–12
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123
Reproduced with permission of copyright owner.
Further reproduction prohibited without permission.
leather as a case studyAbstractIntroductionMaterials and
methodsExperimentalOptimization of sulphide

concentrationOptimization of lime concentrationCar bohydrate
assayEstimation of proteoglycanScanning electron microscopic
analysisHistological studiesAnalysis of chrome
contentEvaluation of strength characteristics and visual
assessment of leathersAnalysis of spent liquorResults and
discussionSodium sulphide optimizationOptimization of
limeChromium contentPhysical testing and visual assessment
dataEnvironmental benefitsEconomic benefits of integrated
processEvaluation using scanning electron
microscopyHistologyConclusionAcknowledgementsAppendix
1Appendix 2References
This unit has assessed engineering principles applicable to
industrial and hazardous waste management. Steps were
evaluated for an adsorption system design using engineering
principles and presenting engineering calculations for waste
treatment.
The steps in the lesson were accomplished by the required
reading of an article describing laboratory adsorption tests for
lead and zinc removal. The lesson used the article's data
combined with engineering principles to design a prototype lead
treatment system, and a required article presented a novel
method for reducing leather tanning waste.
For this assignment, prepare a PowerPoint presentation that
assesses engineering principles applicable to industrial and
hazardous waste management by evaluating steps for an
adsorption system design using engineering principles and
presenting engineering calculations for waste treatment.
Specifically address the following items in your PowerPoint
presentation.
· Provide a title and introduction.
· Summarize the Durga, Ramesh, Rose, and Muralidharan
Required Unit Resources article.
· List the steps required for design of a prototype adsorption
system.

· From Required Unit Resources, use the Yusuff and Olateju
article's equation (7) for the Radke-Prausnitz isotherm to
evaluate qe for a Ce lead concentration of 10 mg/L. Show your
calculation.
· Explain how your value of qe determined from the equation
compares to the value in Yusuff and Olateju’s article exhibit
10a. Do you think there is an error in the equation? Explain.
· In the unit lesson, if the prototype's wastewater flow is 500
gpd instead of 100 gpd and the influent lead concentration is
still 10 mg/L, what would be the lead inflow rate in units of
grams per day? Show your calculation.
· Provide a summary of your PowerPoint information.
Your PowerPoint presentation must be at least 15 slides in
length with a title slide and reference slide (title and reference
slides do not count toward the minimum slide count). You
should utilize at least the two Required Unit Resources: the
Durga et al. and the Yusuff and Olateju articles. Ensure you
refer to the unit lesson as you are creating your PowerPoint
presentation.
Please adhere to APA Style when creating citations and
references for this assignment. Do not include slide notes in
your presentation. Be sure to use fonts that are large enough to
view from a distance. This includes any fonts within images that
you use. Be sure to cite and reference all information and
images.

DOI 10.1002tqem.21536R E S E A R C H A R T I C L EEx

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