Heavy metal pollution of waste water is a common environmental hazard, since the toxic metal ions dissolved can ultimately reach the top of the food chain and thus become a risk factor for human health. Chromium is present in waste water as trivalent and hexavalent. Trivalent chromium is relatively less toxic and less mobile while hexavalent chromium is toxic, carcinogenic, and mutagenic to animals as well as humans. Therefore, the removal of Cr (VI) from industrial waste water has been a research topic of great interest. In the present study carried out the comparative study of removal of the chromium (VI) from waste water by adsorption method. The search for new technologies involving the removal of toxic metals from wastewaters has directed attention to adsorption, based on metal binding capacities of various materials.

1. Reduction of toxicity from aqueous solution by low cost adsorbent: RSM methodology
JPAR
Reduction of toxicity from aqueous solution by low
cost adsorbent: RSM methodology
Abhishek Sao1
and Omprakash Sahu2*
1
Department of Chemical Engineering, IT Guru Ghashi University, Bilaspur (CG), India.
2*
Department of Chemical Engineering, KIOT, Wollo University, Kombolcha (SW), Ethiopia
Heavy metal pollution of waste water is a common environmental hazard, since the toxic metal
ions dissolved can ultimately reach the top of the food chain and thus become a risk factor for
human health. Chromium is present in waste water as trivalent and hexavalent. Trivalent
chromium is relatively less toxic and less mobile while hexavalent chromium is toxic,
carcinogenic, and mutagenic to animals as well as humans. Therefore, the removal of Cr (VI)
from industrial waste water has been a research topic of great interest. In the present study
carried out the comparative study of removal of the chromium (VI) from waste water by
adsorption method. The search for new technologies involving the removal of toxic metals from
wastewaters has directed attention to adsorption, based on metal binding capacities of various
materials.
Keywords: Adsorption, biomass, concentration, efficiency, heavy metal
INTRODUCTION
Industrialization is one of the major reasons for the
dramatic increase of environmental pollution. Chromium
is the toxic heavy metal which occurs mainly in trivalent
and hexavalent states widely used in various industries
where the crude effluents are discharged in the
environment which affects the human health and the
living biota in the habitat (Krishna and Siva Krishna,
2013). Due to the discharge of untreated / partially
treated effluents, soil and ground water contamination
had occurred which leads to various detrimental
diseases26 like skin allergies, throat infections and
cancers etc. Especially in tanneries24 and electroplating
industries19, hexavalent chromium was extensively used
and was acutely toxic, mutagenic, teratogenic and
carcinogenic. These elements, or some form of them, are
commonly found naturally in foodstuffs, in fruits and
vegetables, and in commercially available multivitamin
product (Rafatullah et al., 2010). Diagnostic medical
applications include direct injection of gallium during
radiological procedures, dosing with chromium in
parenteral nutrition mixtures, and the use of lead as a
radiation shield around x-ray equipment. Heavy metals
are also common in industrial applications such as in the
manufacture of pesticides, batteries, alloys, electroplated
metal parts, textile dyes, steel, and so forth. Many of
these products are in our homes and actually add to our
quality of life when properly used. Heavy metals become
toxic when they are not metabolized by the body and
accumulate in the soft tissues (Hameed, 2009).
Heavy metals may enter the human body through food,
water, air, or absorption through the skin when they come
in contact with humans in agriculture and in
manufacturing, pharmaceutical, industrial, or residential
settings.
*Correspondence author: Omprakash Sahu,
Department of Chemical Engineering, KIOT, Wollo
University, Kombolcha (SW), Ethiopia.
Email:ops0121@gmail.com; Tel: +251933520653
International Journal of Toxicology and Environmental Health
Vol. 1(1), pp. 002-006, December, 2014. © www.premierpublishers.org, ISSN: 1822-424X
Research Article

2. Reduction of toxicity from aqueous solution by low cost adsorbent: RSM methodology
Sahu and Sao 002
Industrial exposure accounts for a common route of
exposure for adults. Ingestion is the most common route
of exposure in children (Gupta and Babu, 2009). Children
may develop toxic levels from the normal hand-to-mouth
activity of small children who come in contact with
contaminated soil or by actually eating objects that are
not food (dirt or paint chips). Less common routes of
exposure are during a radiological procedure, from
inappropriate dosing or monitoring during intravenous
nutrition, from a broken thermometer, or from a suicide or
homicide attempt. The human body contains
approximately 0.03 ppm of chromium (Mohan and
Pittman, 2006). Daily intake strongly depends upon feed
levels, and is usually approximately 15-200 μg, but may
be as high as 1 mg. Chromium uptake is 0.5-1%, in other
words very small. The placenta is the organ with the
highest chromium amounts. Trivalent chromium is an
essential trace element for humans. Together with insulin
it removes glucose from blood, and it also plays a vital
role in fat metabolism. Chromium deficits may enhance
diabetes symptoms (Gomez and Callo, 2006). Chromium
can also be found in RNA. Chromium deficits are very
rare, and chromium feed supplements are not often
applied. Chromium (III) toxicity is unlikely, at least when it
is taken up through food and drinking water. It may even
improve health, and cure neuropathy and
encephalopathy. Hexavalent chromium is known for its
negative health and environmental impact, and its
extreme toxicity. It causes allergic and asthmatic
reactions, is carcinogenic and is 1000 times as toxic as
trivalent chromium. Health effects related to hexavalent
chromium exposure include diarrhea, stomach and
intestinal bleedings, cramps, and liver and kidney
damage. Hexavalent chromium is mutagenic (Sikaily et
al., 2007). Toxic effects may be passed on to children
through the placenta. Chromium (VI) oxide is a strong
oxidant. Upon dissolution chromium acid is formed, which
corrodes the organs. It may cause cramps and paralysis.
The lethal dose is approximately 1-2 g. Most countries
apply a legal limit of 50 ppb chromium in drinking water
(WHO, 2004). A professional illness in chromium
industries is chromium sores upon skin contact with
chromates. Chromium trioxide dust uptake in the
workplace may cause cancer, and damage the
respiration tract.
The removal of poisonous Cr (VI) from industrial
wastewater by different low-cost abundant adsorbents
was investigated. Wool, olive cake, sawdust, pine
needles, almond shells, cactus leaves and charcoal were
used at different adsorbent / metal ion ratios (Rane et al.,
2010). The influence of pH, contact metal concentration,
adsorbent nature and concentration on the selectivity and
sensitivity of removal process was investigated. The main
aim of this work is to reduced the percentage of
chromium by low cost adsorbent at optimal condition.
Response surface methodology (RSM) and Central
composite design (CCD) which is an efficient statistical
technique for optimization of multiple variables is applied
to predict best performance conditions with minimum
number of experiments.
MATERIAL AND METHODS
Material
The synethic waste water was generated in chemical lab
and preserved in 20
o
C. Analytical grade K2Cr2O7 (Merk
Chemicals Ltd., Mumbai India) was used to make all
chromium standard solutions used in the experiments. A
stock solution of 1000 mg/L was prepared by dissolving
the powder in reagent grade water. Working standards
ranging from 10 mg/L to 100 mg/L were then prepared by
appropriately diluting the stock solution. Adsorbent which
has been used for experiment was arranged from the
local area.
Methods
Preparation of Adsorbent
The sawdust, used as an adsorbent, was obtained from a
local timber industry. The treated sawdust was used as
an adsorbent in the bench-scale studies. Typically, 1to 5g
sawdust was added in separate flasks each containing
100 ml of the test solution of Cr. The mixture of the test
solution and sawdust was stirred in a shaker at 80 rpm.
Aliquots were drawn after and the suspension was
centrifuged for 5 minutes at 3000 rpm. Then, the metal
concentration was analyzed by spectrophotometer. The
pH of the suspension in one set of experiments was
adjusted with 0.1M NaOH and 0.1N HCl. The adsorption
experiment was carried out at room temperature. The
effect of pH, effects of initial Cr concentration, and the
consumption of sawdust was observed.
Determination of chromium
A jar test procedure was followed to carry out the
chromium precipitation experiment. The Jar test
apparatus is a rotor with six paddles. Speed control is
attached to get variable agitation. Six glass beakers of
one litre volume are filled with tannery wastewater. The
stirring continued for 2 minutes with rapid mixing of 100
rpm, and a slow mixing for 5 minutes at 40 rpm. Then
stirring stopped, put off paddle and settling time for 5
minutes extended before taking samples from the
supernatant for analysis. Then, the supernatant was
separated from the solid phase by whatman paper. The
precipitate obtained was analyzed by spectrophotometer
to know the chromium concentration. Calculated has
been done by mass balance equation Eq. (1) as follows:
(1)
0( )( )
,
( )
e
e
C C Vmgof adsorbate
amount adsorbed q
gof adsorbent m
 


3. Reduction of toxicity from aqueous solution by low cost adsorbent: RSM methodology
Int. J. Toxicol. Environ. Health 003
Where C0 is the initial concentration (mg/L), Ce, the
equilibrium chromium concentration (mg/L), V is the
volume of the solution (mL) and m is the mass of the
adsorbent (g).
Response variable
Design Expert software was used for regression analysis
of the experimental data to fit the equations developed.
This method is suitable for fitting a quadratic surface and
it helps to optimize the effective parameters with a
minimum number of experiments, and also to analyze the
interaction between the parameters. Generally, the CCD
consists of a 2
n
factorial runs with 2n axial runs and nc
center runs (six replicates). For each numerical variable,
a 2
3
full factorial central composite design for the three
variables, consisting of 8 factorial points, 6 axial points
and 6 replicates at the centre points were employed,
indicating that altogether 20 experiments were required,
as calculated from Eq. (2) (Tan et al., 2008):
N = 2n + 2n + nc = 2
3
+ 2 × 3 + 6 = 20 (2)
Where N is the total number of experiments required and
n is the number of factors. The central composite design
has been mostly used for fitting a second order model.
Modeling can be done by doing only a minimum number
of experiments. In the modeling, it is not required to know
the detailed reaction mechanism. The response and the
corresponding parameters are modeled and optimized
using analysis of variance (ANOVA). It is used to
calculate the statistical parameters by means of response
surface methods. Basically this optimization process
involves three major steps, which are, performing the
statistically designed experiments, determining the
coefficients in a mathematical model and predicting the
response and checking the accuracy of the model
(Cronje et al., 2011). The response can be represented
as function of variables as in Eq. (3):
(3)
Where Y is the response of the system, and xi is the
variables of action called factors. The aim is to optimize
the response variable (Y), here in our case adsorption
capacity. It is assumed that the independent variables are
continuous and controllable by experiments with
negligible errors (Cronje et al., 2011). If the variance
analysis indicates that overall curvature effect is
significant, further experiments are carried out to develop
a second order model. The second order model is
defined as follows so as to facilitate calculations:
(4)
Where Y is the predicted response, b0 the constant
coefficient, bi the linear coefficients, bii the quadratic
coefficients, bij the interaction coefficients, and xi, xj are
the coded values of the adsorption variables (Tan et al.,
2008)
RESULT AND DISCUSSION
Effect of pH on initial concentration of Cr(IV): The
effect of pH on the removal of Cr (VI) by modified holly
sawdust was studied by changing the initial pH between
2 and 10. The relation between the initial pH of the
solution and the initial pH from 2 to 10. The favorable
removal of Cr (VI) at a lower pH was related to both the
anionic-type adsorption of Cr (VI) onto holly sawdust.
Various concentrations (20, 25, 30, 35, and 40 mg/L) of
Cr (VI) were used to investigate the effect of the initial Cr
(VI) concentration on its removal by modified holly
sawdust. The relationship between the initial Cr (VI)
concentration of the solution and the percentage of Cr
(VI) removed is shown in Fig. 1. Cr (VI) adsorption was
significantly affected by the initial concentration of Cr (VI)
in the aqueous solutions. The percentage of Cr (VI)
removed decreased from 56.37 to 22.34% on increasing
the initial Cr (VI) concentration from 20 to 40 mg/L. It
might be due to large surface area of the adsorbent. The
decrease in the percentage removal can be explained by
the fact the adsorbent had a limited number of active
sites, which would have become saturated above a
certain concentration (Sahu et al., 2009).
Effect of dose on initial concentration of Cr(IV)
The effect of the adsorbent dose on the removal of Cr
(VI) by modified holly sawdust was studied by varying the
adsorbent dose (1.25, 1.55, 1.85, 2.15, 2.45 and 2.75
g/100ml). The relationship between the adsorbent dose
and the percentage removal of Cr (VI) is shown in Fig. 2.
The percentage removal of Cr (VI) increased from 14.65
to 79.99% on increasing the adsorbent dose from 1.25 to
2.75 g/100ml. The increased Cr (VI) removal on
increasing the amount of sawdust was due to the
increased surface area and adsorption sites available for
adsorption (Hasan et al., 2008). Similar observations
have also been reported (Krishna and Padma Sree,
2012).
Effect of contact time on initial concentration of Cr
(IV)
The effect of the contact time on the removal of Cr (VI) by
modified holly sawdust was studied by varying the
contact time (30 to 75min) for different initial Cr (VI)
concentrations. It was evident from Fig. 3 that time is an
important adsorption parameter for the adsorption of Cr
(VI) by the sawdust. On increasing the Cr (VI)
concentration from 20 to 40 mg/L, the percentage
removal decreased from 69 to 18% during the initial 15
1 2 3( , , ......... )nY f x x x x
2
0
1 1 1 1
n n n n
i i ii i ij i j
i i i j
Y b b x b x b x x
   
     

4. Reduction of toxicity from aqueous solution by low cost adsorbent: RSM methodology
Sahu and Sao 004
Figure 1. Effect of pH on initial concentration of chromium (IV)
Figure 2. Effect of dosing on initial concentration of chromium (IV)
min of contact time. Thereafter, the percentage removal
of Cr (VI) slowly reached 99 and 97% for initial Cr (VI)
concentrations of 20 and 40 mg/L, respectively, until 75
min. A further increase in the contact time had a
negligible effect on the amount of Cr (VI) adsorbed. The
percentage removal of Cr (VI) increased from 48.53 to
69.76% on increasing the contact time from 30 to 75min
for an initial Cr (VI) concentration of 20 mg/L. Fig. 3
shows that the optimal removal efficiency was reached
within about 90 min. This probably resulted from the
saturation of the adsorbent surfaces with Cr (VI), followed
by the adsorption and desorption processes that occur

5. Reduction of toxicity from aqueous solution by low cost adsorbent: RSM methodology
Int. J. Toxicol. Environ. Health 005
Figure 3. Effect of contact time on initial concentration of chromium (IV)
after saturation. The rate of adsorption was decreased
during later stages of the Cr (VI) adsorption, probably due
to the slow pore diffusion of the solute ions into the bulk
of the adsorbent. Similar observations have also been
reported in another investigation (Kiran et al., 2007).
Below graph shows the results for the treatment of a real
wastewater. A removal efficiency of around 50% was
reached after 45 min of contact time. In this case, since
the concentration of total chromium was 295 mg/L, and
other components also existing in the solution, the
removal efficiency was high, as high as that of a unary
system.
Cost Estimation
The price of saw dust in local market is 16.65$ /Tone
Therefore for 1Kg= 0.166$
Than 1gram= 0.0001665$
To treat the 100ml of 2.75g/100ml of adsorbent required
Therefore, for 1liter= 27.5 gram/litre
To treat the 1 litre of chromium containing wastewater =
0.004578$ will required
As compared to other absorbent it’s very economical.
CONCLUSION
Hence by considering all the aspects of requirements
like, the time which can be spent for particular volumes of
effluent treatment, efficiency required, the initial
chromium concentration, the economic aspect, quality of
effluent regarding its pH, an industry can choose the
adsorbent, saw dust. The study has demonstrated the
use of a central composite design by determining the
conditions leading to the optimum percentage of
chromium removal. The maximum percentage of
chromium removal was found to be 71.05. This
methodology could therefore be successfully employed to
any process, where an analysis of the effects and
interactions of many experimental factors are referred.
Response surface plots are very helpful in visualizing the
main effects and interaction of its factors. Thus, smaller
and less time consuming experimental designs could
generally suffice the optimization of many fermentation
processes.
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Accepted 17 December, 2014.
Citation: Sahu O, Sao A (2014). Reduction of Toxicity
from Aqueous Solution by Low Cost Adsorbent: RSM
Methodology. International Journal of Toxicology and
Environmental Health, 1(1): 002-006.
Copyright: © 2014. Sahu and Sao. This is an open-
access article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium,
provided the original author and source are cited.