Iraqi Journal of Chemical and Petroleum Engineering

Vol.17 No.3 (September 2016) 109- 116

ISSN: 1997-4884

Sorption of Nitrate Salts from Wastewater without and with

Modification Orange Peel

Zainab Abdulrazak N.

Environmental Engineering Department–College of Engineeringـــ University of Al-

Mustansiriyah

Abstract

This investigation deals with the use of orange peel (OP) waste as adsorbent for

removal of nitrate (NO3) from simulated wastewater. Orange peel prepared in two

conditions dried at 60C° (OPD) and burning at 500 °C (OPB). The effect of pH: 2-10,

contact time: 30- 180 min, sorbent weight: 0.5- 3.0 g were considered. The optimal

pH value for NO3 adsorption was found to be 2.0 for both adsorbents. The equilibrium

data were analyzed using Langmuir and Freundlich isotherm models. Freundlich

model was found to fit the equilibrium data very well with high-correlation coefficient

(R
2
). The adsorption kinetics was found to follow pseudo-second-order rate kinetic

model, with a good correlation (R
2
> 0.95 and 0.94) for the orange peel adsorbent at

500 °C (OPB) and at 60 °C (OPD), respectively. The results showed that the orange

peel was found to be an attractive low cost adsorbent for the treatment of wastewater.

Keywords: Orange peel (OP); Nitrate; Sorption; Isotherms; Kinetics; Wastewater.

Introduction

Nitrate contamination in surface and

ground water has become an

increasingly important problem for all

over the world. Although nitrate is

found in moderate concentrations in

most of the natural waters, higher

levels in ground water mainly result

from human and animal waste, and

excessive use of chemical fertilizers.

The other most common sources of

nitrate are uncontrolled land discharges

of municipal and industrial waste

waters, overflowing septic tanks,

processed food, dairy and meat

products, and decomposition of

Decaying organic matters buried in the

ground [1,2]. The high concentration

of nitrate in drinking water leads to the

formation of nitrosoamine, which is

related to cancer and increases the risk

of diseases such as methanoglobinemia

in newborn infants [3,4]. Nitrate is

more toxic than nitrite and can cause

human health problems such as liver

damage and even cancers. Nitrate can

also bind with hemoglobin and create a

situation of oxygen deficiency in

infant’s body called

methemoglobinemia. Nitrite, however,

can react with amines chemically or

enzymatically to form nitrosamines

that are very strong carcinogens [5].
For removal nitrate from

wastewater, adsorption has become

one of the most economic and effective

method. The process is superior to

many other methods of water reuse by

virtue of its low initial cost, low energy

requirements, simplicity of design and

University of Baghdad

College of Engineering

Iraqi Journal of Chemical and

Petroleum Engineering

Sorption of Nitrate Salts from Wastewater without and with Modification Orange Peel

www.iasj.netAvailable online at: - 6) 201 September( 3No. 7IJCPE Vol.1 111

possibility of reusing the spent carbon

via regeneration [9]. Adsorption in

general, is the process of collecting

soluble substances that are in solution

on a suitable interface. In the past, the

adsorption process has not yet been

used extensively in wastewater

purification but demands for a better

quality of treated wastewater effluent

have led to an intensive examination

and use of the process of adsorption on

adsorbents. Adsorbent is a very

expensive adsorbent for the removal of

pollutant so other inexpensive

adsorbents must be investigated

[10,11].

In recent years, agricultural by-

products have been widely studied for

NO3 salts removal from water. These

include peat, wood, pine bark, banana

pith, soybean and cottonseed hulls,

peanut, shells, hazelnut shell, rice

husk, sawdust, wool, pomegranate rind

and compost and leaves [6]. The use of

orange peel as a biosorbent material

presents strong potential due to its high

content of cellulose, pectin

(galacturonic acid), hemicellulose and

lignin. As a low cost, orange peel is an

attractive and inexpensive option for

the biosorption removal of dissolved

metals. Ajmal et al. employed orange

peel for metal ions removal from

simulated wastewater [7,8].

Therefore, the present study was

undertaken to produce adsorbent by

thermal and physical activation process

utilizing orange pe as abundant local

raw material for application in efficient

nitrate removal. The effects of various

operating conditions, namely, pH of

solution, initial concentration of

anions, contact time, and temperature,

were investigated. used sulfur and

limestone for nitrate removal from

potable water in a batch study.

Materials and Methods

1. Sorbent Preparation
Orange peel adsorbent (OP

adsorbent) was collected from a local

juice manufacturing industry. OP was

cut into small pieces, dried in an oven

at 60 °C for 24 h and crushed. The

powdered orange peel was washed

with hot water and dried in an oven at

60 (OPD) and burning in the furnace

at 500 °C for 12 h (OPB). After drying

they were sieved to particle size 0.5

mm, and used as an adsorbent.

2. Chemicals
NO3 solutions were prepared by

diluting 1000 ppm of KNO3 Potassium

Nitrate (Scharlau (30 % wt/wt)) stock

solution with demonized water to a

desired concentration range between

25 and 200 mg/L. Before mixing the

adsorbent, the pH of each test solution

was adjusted to the required value with

diluted and concentrated HCL and

NaOH solutions, respectively.

Insignificant decreases in the final

equilibrium pH were recorded, so

during the uptake pH was assumed

constant.

3. Adsorption Procedure
Batch adsorption experiments

were carried out by agitating 1 g of

the orange peel with 100 ml of NO3

solutions of desired concentrations

and pH at room temperature using an

orbital shaker operating at 200 rpm.

The effect of pH was studied by

adjusting the pH of the solutions

using (1N) HCL or (1N) NaOH

solution.

The effect of initial salts

concentrations was carried out by

shaking 100 ml NO3 solutions of

desired concentrations (25, 50, 75,

100, 150 and 200 mg L
−1

) with 1 g of

the adsorbent. All the samples were

adjusted to the optimum pH prior to

the addition of the adsorbent. The

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Zainab Abdulrazak N.

111 )6201September ( 3No. 17IJCPE Vol. www.iasj.netonline at: Available -

samples were withdrawn from the

shaker at pre-determined time

intervals and NO3 solution was

separated from the adsorbent by

centrifugation at 4000 rpm for 20

min. Blank runs, with only the

adsorbents in 100 ml of double-

distilled water, were conducted

simultaneously at similar conditions

to account for any color leached by

the adsorbents and adsorbed by glass

containers.

All the investigations were carried

out in duplicate to avoid any

discrepancy in experimental results

and salts solution controls were kept

throughout the experiment to

maintain quality control. The

percentage of salts adsorption by the

adsorbents was computed using the

equation [2]:

( )

…(1)

Where,

= initial NO3concentration in
sample (mg/L)

= equilibrium NO3 concentration in
sample (mg/L).

Result and Discussion

1. Characteristics of the Adsorbents
The chemical structure of this

orange peel adsorbent is shown in

Table 1.

Table 1: Chemical composition of the (OP) by

X-ray fluorescence analysis

Characteristic Values

CaO

K2O

SO3

MgO

Fe2O3

SiO2

P2O5

BaO

SrO

Al2O3

NiO

Organic matter

1.43%

0.17%

0.15%

0.11%

0.12%

0.09%

0.06%

0.01%

0.02%

0.01%

97.83%

2. Effect of pH
The effect of pH on removal

efficiency of nitrate by OP is shown in

Figure 1. The removal efficiency of OP

prepared at 60 °C (OPD) and OP

burned at 500 °C (OPB) was

decreased from 90 to 20 % and 95 to

71 %, respectively, when the initial pH

of the aqueous solution was increased

from pH 2 to 10. The nitrate content

was decrease in the pH range of 2–6.

However, removal efficiency for both

OP adsorbents was increased to 88%

for OPD and 95% for OPB adsorbent,

when the pH remained constant at pH

2. Though there is increase in OH
–

concentration at increased pH, yet

removal efficiency of NO3 decrease.

This may probably due to the

preferential adsorption of Nitrate.

Among OH
-
and NO3, affinity of OP

adsorbent 500 °C for NO3 is greater

than (OH
-
) [13].

Fig. 1: Removal of NO3 by OPD and OPB at

dosage 1% (W/V), initial concentration 50

mg/L, temp. 25
o
C, pH 2, agitation speed 200

rpm and contact time 3 h

3. Fourier-Transform Infrared
Analysis (FTIR)

Infrared spectra of Orange peel (OP)

samples before and after nitrate ions

binding were examined using

(Shimadzu FTIR 8000 series

spectrophotometer). The functional

groups have been identified in Figure 2

(a-c). As seen in these figures the

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Sorption of Nitrate Salts from Wastewater without and with Modification Orange Peel

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spectrum pattern of loaded OP showed

changes in the peak absorption as

compared to unloaded OP which result

from adsorption process. Contribution

of each functional group in this process

is summarized in Tables 2 and 3.

Fig. 2: Functional groups (a) before OP loaded

without NO3 salts (b) after OPD loaded with

NO3 salts (C) after OPB loaded with NO3 salts

Table 2: FTIR functional groups for OPD

Wave

number

(cm
-1

)

Assignment

Groups

After

adsorption

of NO3

3398.57
Carboxylic

acid, Amides
3402.43

1627.92
Amines,

Alkenes
1631.78

1435.04
Carboxylic

acid, Alkenes
1438.90

1161.15

Ketones,

Amines, Alkyl

halides

1165.00

725.23
Alkyl halides,

Aromatic
756.10

609.51
Alkyl halides,

Alkyanes
628.79

586.36 Alkyl halides 597.93

Table 3: FTIR functional groups for OPB

Wave

number

(cm
-1

)

Assignment

Groups

After

adsorption

of NO3

3398.57
Carboxylic

acid, Amides
3410.15

2927.94
Carboxylic

acid, Alkanes
2935.66

1033.85
Carboxylic

acid
1064.71

894.97 Alkenes 898.83

756.10 Aromatic 759.95

667.37 Aromatic 671.23

559.36 Alkyl halides 590.22

4. Effect of Sorbent Dose
The sorbent amount is one of the

important parameters used to obtain

the quantities uptake of NO3 salt .The

sorbent amount was studied by varying

the quantity of OP adsorbent (0.5, 1,

1.5, 2, 2.5, 3) g in 100 mL of 50 mg/L

of NO3 solution. Sorption of NO3 was

increased as the sorbent amount

increased. The results were expected

because for a fixed initial NO3

concentration, increasing adsorbent

amount provides greater surface area

or sorption site, this result agreement

with those obtained by other

researchers [12]. The higher removal

efficiency was achieved by using 2

g/100 ml sorbent dosages. The removal

efficiency of OPD adsorbent and OPB

adsorbent was increase from 89 to 97%

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Zainab Abdulrazak N.

111 )6201September ( 3No. 17IJCPE Vol. www.iasj.netonline at: Available -

and 85 to 91%, respectively, as show

in Figure 3.

Fig. 3: Removal of nitrate by OPD and OPB

with different contact time, initial

concentration 50 mg/L, adsorbent dosage:

2% w/v temperature 25°C, pH= 2; agitation

200 rpm

5. Effect of Contact Time
The effect of contact time on the

removal of nitrate by OPD and OPB

was observed to increase as contact

time increased as shown in Figure 4

The concentration of nitrate using

ODB was decreased substantially

from initial concentration of 50–

17mg/L within 1h of treatment where

the removal efficiency was around

66% . For OP adsorbent, the

percentage removal during the first

hour was 58% , the initial

concentration of 50mg/L was

decreased to 21 mg/L. The final

concentration of nitrate adsorbed by

both samples reached equilibrium

point within 2h of operation.

Fig. 4: Removal of nitrate by OP adsorbents

with different contact time, initial

concentration 50 mg/L, adsorbent dosage: 2%

w/v temperature 25°C, pH= 2; agitation 200

rpm and pH= 2

6. Adsorption Isotherms
In order to find an equation which

suitable for the results and can be

used for design purposes; Langmuir

and Freundlich isotherm equations

have been used for the equilibrium

modeling of adsorption systems. The

form of Langmuir (linear form) is:

…(2)

Where Ce is the equilibrium

concentration of the metal in solution

(mg/L), qe is the amount absorbed at

equilibrium (mg/g), Qo (mg/g) and K

(L/mg) are Langmuir constants

related to sorption capacity and

sorption energy, respectively.

Maximum sorption capacity (Qo)

represents monolayer coverage of

sorbent with sorbate and b represents

the enthalpy of sorption and should

vary with temperature. A linear plot

was obtained when Ce/qe was plotted

against Ce over the entire

concentration range of metal ions

investigated.

The Freundlich adsorption form

(linear form) is:

…(3)

Where qe is the amount of metal ion

adsorbed at equilibrium per gram of

adsorbent (mg/g), Ce is the

equilibrium concentration of metal

ion in the solution (mg/L), kf and n

are the Freundlich model constants

[13]. Freundlich parameters, kf and n,

were determined by plotting log qe

versus log Ce. The Langmuir and

Freundlich adsorption isotherms of

nitrate ions are given in Figures 5, 6

and Table 4.

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Fig. 5: Langmuir plots of NO3 sorption on (a)

OPD (b) OPB

Fig. 6: Freundlich plot of NO3 sorption on (a)

OPD (b) OPB

Table 4: Langmuir and Freundlich constants

for adsorption of NO3 onto OP

Adsorbent

Isotherm Models

Langmuir

R² a b

OPD 0.114 26.31579 0.017707

OPB 0.612 16.12903 0.087694

Freundlich

Adsorbent R² 1/n K

OPD 0.829 0.838 0.572796

OPB 0.918 0.702 1.503142

These results showed that in both

case (OPD or OPB) the best model is

Freundlich.

7. Kinetic Modeling
Two kinetic models namely

pseudo-first-order, and pseudo-second-

order models have been discussed to

identify the rate and kinetics of

adsorption of nitrate on prepared

orange peel adsorbent. The linear form

of pseudo-first-order (Lagergren rate

equation) equation is given in Eq. 4

[14]:

( ) …(4)

And the linear pseudo-second-order

model is given as:

(

) …(5)

Where qeq is the amount of metal

sorbed at equilibrium (mg/g); qt is the

amount of metal sorbed at time t

(mg/g); and k1; k2 is the equilibrium rate

constant of pseudo first sorption

(1/min).

Figure 7 (a, b) show a plot of pseudo-

first and second-order kinetic model of

nitrate adsorption on prepared

adsorbent (for unmodified and

modified), compiled in Table 3 along

with correlation coefficient (R
2
) values.

It is seen from Table 5 that the

theoretical qe (cal) values calculated

from the pseudo-first-order model did

(b)

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Zainab Abdulrazak N.

111 )6201September ( 3No. 17IJCPE Vol. www.iasj.netonline at: Available -

not give reasonable values with regard

to the experimental uptake ones, qe

(exp). Further, the correlation

coefficient (R
2
) is less than 0.99

suggesting that the present adsorption

system does not follow pseudo-first-

order process (in both case), while

pseudo-second-order model is the best

to describe our study.

Table 5: Comparison of sorption rate constants, experimental and calculated qe values for the pseudo-

first and second-order reaction kinetics for component systems

Adsorbent

Pseudo-first-order

qe exp.
k1 1/min

calculated R
2

mg/g mg/g

OPD 2.275 -0.025 1.8022 0.825

OPB 2.425 -0.021 1.4903 0.857

Adsorbent

Pseudo-second-order

k2 g/mg.min

calculated R
2

mg/g

OPD 0.01825 0.954

OPB 0.03185 0.972

Fig. 7a: Pseudo-first order kinetic for

adsorption of NO3 on OP

Fig. 7b: Pseudo-second order kinetic for

adsorption of NO3 onto OP

Conclusion
The results show that the adsorption

of nitrate using orange peel occurred

at wide range of concentrations. The

time required for utilizing nitrate

varies between 30-180 min depending

on the initial concentration nitrate.

The time of utilization increases as

the initial concentration of nitrate

increase.. The isotherm equilibrium

studies confirmed that the Freundlich

form and generalized models were the

highest fitted models for the both

adsorption process. Orange peel

adsorbent which is dried at 500 °C

was the best fitted than orange peel

adsorbent which is dried at 60 °C.

The maximum adsorption potential of

orange peel adsorbent for NO3 salts

removal was 2.532 mg/g. Pseudo-

second-order reaction kinetic has

provided a realistic description of

removal of NO3 salts with closer

experimental and calculated values of

uptake capacity. Also correlation

coefficients are higher in pseudo-

second-order kinetics.

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