Removal of Nitrate from Ground Water Using Activated Carbon Prepared from Rice Husk and Sludge of Paper Industry Wastewater Treatment

Abstract

Nitrate found in ground waters over the past decades has aroused serious concerns to associated administrators. Among different methods of removing nitrate, using adsorption technique has drawn attention due to its high efficiency as well as economic considerations. In this study, the effectiveness of activated carbon absorbents obtained from pyrolysis of rice husk on nitrate adsorption is explored, and the results of the adsorption by carbon prepared from primary sludge of wastewater treatment of paper industry have been compared. The results of experiments for both absorbers indicated that the maximum adsorption occurred in pH equal 4, as the system has reached equilibrium during 4 hour contact time. The maximum removal of nitrate for activated carbon obtained from rice husk was 93.5 (mg/gr), and for the sludge obtained from paper industry was 79.5 (mg/gr). The result of tests for both adsorbents suggests a direct relationship between the level of adsorption run by Zncl2 used to activate adsorbents and the level of adsorbent. Moreover, the results of adsorption tests for adsorbents were adapted with Langmuir isotherm, and also the kinetics of adsorption was well fitted into pseudosecond-order model.

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VOL. 10, NO. 17, SEPTEMBER 2015 ISSN 1819-6608
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REMOVAL OF NITRATE FROM GROUND WATER USING ACTIVATED
CARBON PREPARED FROM RICE HUSK AND SLUDGE OF PAPER
INDUSTRY WASTEWATER TREATMENT
Mohammad Hassan Shahmoradi1, Behnoush Amin Zade, Ali Torabian and Mahdi Seyed Salehi2
1Department of Environmental Engineering, University of Tehran, Tehran, Iran
2Department of Environmental Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
E-Mail:m.s.salehi1365@gmail.com
ABSTRACT
Nitrate found in ground waters over the past decades has aroused serious concerns to associated administrators.
Among different methods of removing nitrate, using adsorption technique has drawn attention due to its high efficiency as
well as economic considerations. In this study, the effectiveness of activated carbon absorbents obtained from pyrolysis of
rice husk on nitrate adsorption is explored, and the results of the adsorption by carbon prepared from primary sludge of
wastewater treatment of paper industry have been compared. The results of experiments for both absorbers indicated that
the maximum adsorption occurred in pH equal 4, as the system has reached equilibrium during 4 hour contact time. The
maximum removal of nitrate for activated carbon obtained from rice husk was 93.5 (mg/gr), and for the sludge obtained
from paper industry was 79.5 (mg/gr). The result of tests for both adsorbents suggests a direct relationship between the
level of adsorption run by Zncl2 used to activate adsorbents and the level of adsorbent. Moreover, the results of adsorption
tests for adsorbents were adapted with Langmuir isotherm, and also the kinetics of adsorption was well fitted into pseudo -
second-order model.
Keywords: nitrate, adsorption, activated carbon, rice husk, sludge, paper industry.
1. INTRODUCTION
Nitrate contamination in ground and drinking
water caused concerns on a global scale. In the last
decade, nitrate concentration has increased both in ground
and surface water at a rapid rate. The increasing use of
nitrogen fertilizers in agriculture sector is the reason for
the contamination caused by nitrate. Other factors such as
sewage, urban and agricultural runoffs, untreated
wastewater disposal, industrial wastewater, septic system
leachate, waste disposal site leachate, agricultural
fertilizer, and nitrogen compounds added to the air through
industry and cars also give rise to the pollutants in waters
(Dong-Wan Cho et al. 2011). Due to its high solubility,
nitrate is the most likely cause of the contamination in
ground waters across the globe, and a potential threat to
water resource, as well as increasing eutrophication (A.A.
Hekmatzadeh et al. 2012).
Nitrate concentration increase in water would
cause negative effects on human health: Blue baby
Syndrome (Met Hemoglobin) especially in infants and the
carcinogenic potential for nitrosamine (Sudipta Chatterjee
et al. 2011). Recent studies indicated that increase in the
amount of nitrate in drinking water would likely cause a
variety of cancers in humans (P.C. Mishra et al. 2009).
Because of serious health problems associated with nitrate
in drinking water, the Environmental Protection Agency
(US EPA) has announced the maximum ensured nitrogen
concentration to be 10 milligrams per liter in water (Amit
Bhatnagar et al. 2010). So it is necessary to announce the
concentration of the purified water nitrate to be below the
permissible limit in order to supply water.
Due to its high solubility and sustainability, removal of
nitrate from drinking water has turned into a challenging
duty to researchers. There are physical, chemical, and
biological methods used to remove nitrate from drinking
water, namely chemical denitrification process using zero
capacity iron, zero capacity magnesium, ion exchange,
reverse osmosis, electro dialysis, and biologic
denitrification (Jae-Hee Ahn et al. 2008).
Nonetheless, the available technology applied to
remove nitrate include shortcomings and limitations,
expensiveness, low-impact, and side products can be
regarded as its other deficiencies. Therefore, the direction
of research has gone into the development of effective and
low-cost technologies (Yunfei Xi et al. 2010).
Among other technologies used for water
treatment, the adsorption process is in general low-cost,
simply designed, as it is identified as an easy applicable
technique (Sachin N. Milmile et al. 2011). Activated
carbon has been ameliorated to remove various pollutants
from aqueous solutions. At the present moment, research
has grown to modify carbon level in order to increase the
potentiality for its adsorption (Abbas Afkhami et al.
2007). Modification on carbon level may be a path to
novel applications of activated carbon in order to remove
specific pollutants.
2. MATERIAL AND METHODS
a) Water sample
For all experiments, the water ground of District
6 of Tehran was used, the specifications of which are
given in Table-1.

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Table-1.Water specifications of the water ground used.
Considering the fact that nitrate adsorption for different
concentrations was studied in this paper, NaNo3 was used
to increase nitrate concentration in other experiments.
b) Absorbents and their preparation
In this paper, two different types of absorbents
were used for nitrate adsorption, and their results were
compared in the same condition. To prepare absorbent,
rice husk and sludge of primary settling basin of sewage
treatment of pulp and paper factories located in Gillan
Province, Iran, were used.
The preparation of absorbents is much the same.
In order to prepare activated carbon, the sludge of paper
factory sewage is placed in an oven at 110 ° C for 24
hours, after partially dried by sunlight, so that it will be
completely dried as it is done to avoid weight loss because
of dryness. Moreover, rice husk was put into the oven after
being washed in the same condition. Having been ground
into powder and passed through a sieve of 600 microns,
the absorbents were chemically activated in the course of
Zncl2 mixture with different mass ratios for 8 hours (at
ambient temperature). They were then kept in the oven at
110 ° C for 24 hours in order to be completely dry. The
product was ground into powder by pounder. The powder
was put in a furnace under 70 ml per minute nitrogen flow.
The rate of furnace temperature increase was 10 ° C per
minute, as the final temperature was 800 ° C and the
duration for this temperature was 2 hours (pyrolysis
operation was performed in Material and Energy Research
Center in Meshkinshahr, Alborz Province). The
pyrolysised powder was washed in 500 ml of molar ½
hydrochloric acid solution. Thus, it was washed several
times with distilled water, so that its pH reached a constant
value. It was then dried in the oven at 100 ° C for 24
hours. Finally, the activated carbon was stored in sealed
glasses to be used for adsorption experiments
(U.S.Orlando et al. 2002).
Moreover, to increase the efficiency of
adsorption, all the absorbents were activated by Zncl2 with
various concentrations, the results of which were
compared with one another.
In order to chemically activate all the absorbents,
Hcl was used and kept in a mixing scenario along with the
absorbents for 2 hours with respect to the level of
activation.
c) Testing method
DR5000 spectrophotometer and spectroscopic
method were used to read nitrate concentration in the
solution. In order to investigate the effect of pH on
samples, they were adjusted prior to adding adsorbents to
the solution. PH adjustment in the samples is conducted
using hydrochloric acid solution and normal soda. Each
test was performed twice in a specific condition, and the
result of adsorption would be called acceptable in case the
differences between these scenarios were less than 2%.
d) Adsorption isotherm
An equilibrium ratio of the quantity of adsorbed
substance to mass unit of absorbent and its equilibrium
state concentration in the liquid phase at constant
temperature is called adsorption isotherm. It is one of the
most important parameters to realize the mechanism of
adsorption. Langmuir and Freundlich isotherms are the
most applicable isotherms, for which equations 1 and 2
respectively show their relationships.
e) Kinetics of adsorption
It is one of the most important characteristics
when dealing with the efficiency of adsorption. Several
kinetic models have been proposed by researchers until
now. In this paper, two models, pseudo-first-order and
pseudo-second-order, were assessed for two activated
carbons, one obtained from rice husk and the other from
the sludge of paper industry. In order to obtain kinetic of
adsorption, we need to plot adsorption graph of proposed
equations and build a kinetic model based on whether or
not data correspond. Pseudo-first-order and pseudo-
second-order are respectively shown in equations 1 and 2.

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3. RESULTS AND DISCUSSIONS
In this section, the results of nitrate adsorption
were compared by carbon adsorbents (activated carbon
obtained from rice husk and the other one from the sludge
of the treatment of paper industry), and the effects of
parameters such as contact time, pH, activation with Zncl2,
and the level of adsorbent concentration were examined.
a) The effect of pH and contact time
Figure-1 represents the ratio of nitrate adsorption
level (ratio of the nitrate adsorbed in term of (mg) to the
level of adsorbent in term of (gr)), to contact time (hr) for
the activated carbon obtained from rice husk which was
modified in a 1 to 1 ratio by Zncl2.
For this figure, pH=4 is the best possible pH for
this absorbent and 4 hour contact time was obtained as an
equilibrium time for it. The level of nitrate adsorption in
the condition equals to 80/9 (mg/gr)Experiments
performed with lower pH indicated that as pH drops due to
Hcl interaction added to the solution and nitrate ion with
negative charge, so decreases adsorption level. The result
of adsorption experiment by sugar beet pulp modified by
Zncl2 indicates optimal pH=4 and equilibrium time, 24
hours, and adsorption level as much as 63(mg/gr) (M.L.
Hassan et al. 2010). Therefore, the results of the activated
carbon obtained from rice husk seem very effective and
appropriate with respect to a short time contact.
Moreover, Figure-2 shows the relationship between nitrate
adsorption rate (mg/gr) and contact time (hr) for activated
carbon by the sludge of paper industry, which was
modified in 1 to 1 ratio by Zncl2. This figure demonstrates
that optimal pH is equal to 4 and equilibrium contact time
is equal to 6 for this absorbent.
Given the fact that the nitrate ion has a negative
charge, experiments on pH less than 4 revealed that
adsorption level rises due to electrostatic interactions
between positive surface charge and onions, as it will
decline for higher pH. However, the difference of
adsorption level between the pH of various acid or base
solution scenarios is partially low, and given the nitrate
concentration level of primary sample and the level of
essential removal in order to reach a standard level, it is
possible for us to reach a desired result with the same
natural pH of water by consuming little energy.
The high velocity of adsorption level is due to the
capacities available for adsorption for both adsorbents in
early minutes. Filling these capacities, the rate of
adsorption is reduced (Yuh-Shan Ho, 2005).
Figure-1. Nitrate adsorption versus contact time for activated carbon obtained from rice husk
activated by Zncl2 with 1 to 1 ratio.

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Figure-2. Nitrate adsorption versus contact time for
activated carbon obtained from the sludge of paper
industry activated by Zncl2 in a 1 to 1 ratio.
Given the fact that the maxim quantity of adsorption
occurs at pH=4 for both adsorbents, following experiments
were performed at the same condition.
b) The comparison of nitrate adsorption by activated
carbon obtained from rice husk and sludge of
paper industry
Figure-3 shows how two absorbents work
concerning nitrate adsorption at pH=4 in the same
condition for activation by Zncl2 in a 1 to 1 ratio. As for
all carbon absorbents at 4 hour contact time, the system
reached equilibrium and the level of adsorption was equal
to 93.5 and 74.5(mg/gr) respectively for husk activated
carbon and sludge activated carbon.
In a similar study on nitrate adsorption,
conventional rice husk was used as absorbent and the level
of adsorption was obtained 81.8 (mg/gr) at 48 hour contact
time (U.S. Orlando et al. 2002). Another study on coconut
shell activated by Zncl2 indicated that removal of nitrate
was performed as much as 10.2 (mg/gr) at a 2 hour contact
time (A. Bhatnagar et al. 2008). Additionally, the result of
a study into three absorbents, pulp of bagasse, pure
cellulose, and rice husk, indicated nitrate adsorption was
obtained 87.4, 83.1, and 81.8 (mg/gr) at a 48 hour contact
time ( U.S.Orlando et al.2002). In this study, the effect of
pH on removal of nitrate was not examined.
Therefore, converting rice husk into activated
carbon and using it as absorbent increases nitrate
adsorption significantly.
Figure-3. The comparison of carbon absorbent
performance with rice husk source and sludge of paper
industry with respect to removal of nitrate at the same
condition, pH=4, and activation by Zncl2 in a 1 to 2 ratio.
c) Effect of using Zncl2
The comparison of the results of nitrate
adsorption for rice husk activated carbon indicted that as
for activated state by Zncl2 in a 1 to 2 ratio the adsorption
level is about 15% greater than the one active in a 1 to 1
ratio.
The result of the study of this sort on coconut
shell concerning nitrate adsorption indicated that using
Zncl2 in 1 to 1 ratio would make the level of adsorption 5
times as much bigger. However, the activation was
performed in two stages (before coconut shell conversion
into activated carbon, and after that) at 80 °c, and the final
amount of nitrate adsorption was 11.7(mg/gr) (Amit
Bhatnagar et al. 2010). Meanwhile, concerning rice husk
activated carbon absorbent, the activation by Zncl2 in 1 to
1 ratio increased adsorption level by 85% in comparison to
non-activated absorbent. The activation was performed
just in one stage (i.e. before rice husk conversion into
activated carbon) at ambient temperature. Therefore, the
effect of activation by Zncl2 in this case is acceptable and
justifiable economically. Figure-4 shows the analogy for
pH=4 and primary concentration of nitrate 100(mg/lit).
Figure-4. The analogy of the effect of Zncl2 activation on
the level of nitrate adsorption by activated carbon of rice
husk.

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In addition, Figure-5 represents the analogy of the results
of nitrate adsorption for sludge activated carbon of paper
industry by Zncl2 for two activated cases in 1 to 1 and 1 to
2 ratios (the ratios of absorbent mass to Zncl2), and non-
activated case. As for the Zncl2 activated case in a 1 to 2
ratio, the adsorption level was about 18% more than the
activated case in 1 to 1 ratio. However, the activation of
sludge activated carbon of paper industry by Zncl2 in a 1 to
1 ratio would increase adsorption level by 110% in
proportion to non-activated paper industry sludge.
Considering the fact that the activation for this adsorbent
was conducted just in one stage at ambient temperature, it
seems economical and its results can be acceptable as
against the results of other researchers.
Figure-5. The analogy of the effect of Zncl2 activation on
nitrate adsorption level by activated carbon obtained from
sludge of paper industry.
It is worth noting that adsorption level increase in
the condition for activating absorbent by Zncl2 is due to an
increase in micropore cavities. Moreover, in activating,
Zncl2 itself plays a role as an adsorbent in mesopore
cavities, helping nitrate adsorption process (A. Bhatnagar
et al. 2008).
d) The effect of adsorbent concentration level
Figure-6 and Figure-7 respectively compare the
level of nitrate adsorption by rice husk activated carbon
and paper industry sludge activated carbon at different
adsorbent concentration. The results of the study indicated
that as adsorbent concentration rises, so does adsorption
level. The results of other studies also uphold the theory
that as adsorbent level increases, so does the entire
available surface as well as adsorption capacity (C.
Namasivayam et al. 2005). It is evident that such
adsorption increase is limited, because nitrate
concentration exists in low quantity in water.
Figure-6. The analogy of nitrate adsorption by rice husk
carbon activated by Zncl2 in a 1 to 2 ratio in pH=4 at
various adsorbent concentrations.
Figure-7. The analogy of nitrate adsorption by paper
industry sludge carbon activated by Zncl2 in a 1 to 2 ratio
in pH=4 at various adsorbent concentrations.
e) Examining an isotherm for nitrate adsorption
Figures-8 and Figure-9 respectively show
Langmuir isotherm and Freundlich isotherm graphs
representing nitrate adsorption by carbons activated by
rice husk and sludge of paper industry at Zncl2 activation
state.
Figure-8. Langmuir isotherm for rice husk activated
carbon and paper industry sludge activated carbon in
pH=4.

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Figure-9.Freundlich isotherm for rice husk activated
carbon and paper industry sludge activated carbon in
pH=4.
Furthermore, Table-2 shows coefficients of the isotherms
for both the adsorbents. The results indicated that the
results of adsorption correspond more with Langmuir
isotherm.
Table-2. Coefficients of Langmuir and Freundlich isotherms and the regression coefficient of rice husk activated carbon
and paper industry sludge activated carbon at a modified state by Zncl2 in a 1 to 2 ratio in pH=4.
f) Examining kinetics of adsorption
Table-3 and 4 show fixed values and regression
coefficients of pseudo-first and second-order kinetic
models for rice husk activated carbon and paper industry
sludge activated carbon respectively at three different
concentrations, 100, 150, 200, (mg/lit).
Table-3. Fixed values and regression coefficients of the adsorption kinetics of pseudo- first and second- order model for
nitrate adsorption by activated carbon activated by Zncl2 in a 1 to 2 ratio obtained from rice husk at various nitrate
concentrations.
In order to explore the consistency of kinetic adsorption
model, we need to consider regression coefficient factor
(R2) and difference in nitrate adsorption level at
equilibrium state qe(real) and concentration obtained based
on qe(real).

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In a study conducted on nitrate adsorption by activated
carbon obtained from coconut shell at two activated and
non-activated states, the maximum difference between
qe(cal) and qe(real) for pseudo-second-order model was
20%, while it was less than 14% in this paper, which truly
confirm that the result of the experiments correspond with
pseudo-second-order adsorption level.
Table-4. Fixed values and regression coefficients of the adsorption kinetics of pseudo- first and second- order model for
nitrate adsorption by paper industry sludge activated carbon activated by Zncl2 in a 1 to 2 ratio at various nitrate
concentrations.
As can be noticed from the above table, as for the
absorbent, the results of the experiments correspond more
with pseudo-second-order adsorption model.
The results of the tests performed by other
researchers also indicate that pseudo-second-order
adsorption level can finely interpret adsorption process in
the most tests (Amit Bhatnagar et al. 2008).
4. CONCLUSIONS
The results of the studies demonstrated that both
activated carbon adsorbents, obtained from rice husk and
sludge of paper industry wastewater treatment, have high
efficiency in adsorbing nitrate. Given a partially low
equilibrium contact time and partially high adsorption
level as against other relevant studies, both adsorbents
exhibited quite reasonable functionality for removal of
nitrate.
The use of Zncl2 has a positive effect on nitrate
adsorption level. As adsorbent concentration rises, so does
nitrate adsorption; however, this is limited.
The results of adsorption by both adsorbent
correspond with Langmuir adsorption isotherm, and
pseudo-second-order kinetic model could reasonably
delineate adsorption speed run by both adsorbents.
However, as for each groundwater sample which requires
decreasing nitrate concentration and bringing it to the
permissible level, it is imperative to choose the best
adsorbent, pH, and economical contact time with respect
to primary concentration, and essential adsorption level, as
well as economic considerations.
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