Final


Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

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Al-khwarizmi  
Engineering   

Journal       
                      Al-Khwarizmi Engineering Journal, vol.1, no.1,pp 117-124, (2005)         

 
Removal of Oil From Wastewater Using  

Walnut-Shell  
 

Dr. Zainab Ziad Ismail 
 Environmental Engineering Dept/College of Engineering./University of Baghdad 

 
 
Abstract  
The ability of pulverized walnut-shell to remove oil from aqueous solutions has 
been studied. It involves two-phase process which consists of using walnut-shell as 
a filtering bed for the accumulation and adsorption of oil onto its surface. Up to 
96% oil removal from synthetic wastewater samples was achieved while tests 
results showed that 75% of oil can be removed from the actual wastewater 
discharged from Al- Duara refinery in the south of Baghdad. 
Keyword: Wastewater, Oil Removal, Walnut-Shell, Adsorption. 
 
Introduction 
 Fats, oils and greases (FOG) 
content of wastewater can cause many 
problems in both sewers and waste 
treatment plants. If oil or grease is not 
removed before discharge of the waste 
it can interfere with the biological life 
in the surface wasters and create 
unsightly floating matter and films [1]. 
The acute effects of oils on birds, fish 
and microorganism are reasonably well 
cataloged. The potentially more 
harmful is the subtle effect on other 
aquatic life [2].  
 The food industry seeks 
effective technologies to remove fats, 
oils and greases. Manufactures of oil-
containing foods face the problem of 
reducing the oil containment load to 
downstream wastewater systems. A 
large amount of water is used in the 
refinery processes and a big fraction of 
it comes out as waste after getting 
polluted by oil which enters into the 
wastewater from leaks, spills etc., at 
various stages [3]. 
 Methods of separating FOG 
from water include physical and/or  
 
 

 
chemical separation. In physical 
separation, free FOG is separated 
according to differences in specific 
gravity or in surface tension 
phenomena. In chemical separation, 
dispersed water droplets and solids are 
destabilized through the use of 
chemicals. 

Dissolved air flotation (DAF) is 
a well-accepted method of FOG 
removal in the meat and diary 
industries. Through the addition of 
coagulants and flocculants, very 
effective separation is achievable. 
However, the coagulants and 
flocculants are fairly expensive and 
alter the composition of retained fats 
and solids so that reuse as animal food 
is sometimes not possible. 
Ultrafilteration (UF) membranes work 
very well on filtering out FOG. Oil in 
water from can-washing operations 
also has been removed by membranes. 
Membrane configurations for FOG 
separation include flat sheet, tubular, 
hollow fiber, or spiral wound design 

[4].                                                     
 
 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

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           Other techniques have been 
attempted with less success, including 
combinations of lignin or halogen with 
natural or synthetic polymers; have 
been recently patented as agents to 
facilitate separation of FOG from food 
processing wastewater [5].                   

       A new pressurized thermal 
technology for separating oil/water 
emulsions can have application to food 
processing FOG. This technology uses 
the change in physical properties and 
surface tension of water and FOG at 
elevated temperature up to 3000C at 
pressures of 100 atmospheres to break 
the emulsion and allow recovery of 
separate oil and water streams for 
reuse or recycle [6]. One oxidation 
system, wet air oxidation, has already 
reported for olive mill wastewater 
treatment, but was found satisfactory 
only in combination with biotreatment. 
Electro-flotation seems to be an 
excellent method for obtaining high 
retention of FOG. In this method FOG 
emulsions are broken under the effect 
of electric field. 

Most refineries and many 
chemical plants use oil-water 
separation devices as API separators, 
corrugated plate interceptors (CPI), 
sometimes called titled plate 
interceptors (TPI). (CPIs) are widely 
used for oil-water separation in many 
industries, but have found only limited 
acceptance in refineries. The reason is 
that the units cannot take shock loads 
and high flows as well as a 
conservatively designed API separator 
[7]. 

Walnut-shells were originally 
developed for cleaning gasoline and 
diesel engines due to its lack of silicon 
and toughness. One of the most 
popular uses is the deflashing of 
molded plastic parts. A typical pH and 
moisture content values available for 
walnut-shells are as follows [8]: 
pH: 5.4 - 4.5 

 

Moisture: 4.5% 
Activated carbon can be 

prepared from walnut shell which is 
chemically activated by zinc chloride. 
It is observed that a the ratio of 
activating agent to raw material 
increases to 100%, a sharp 
enhancement of surface area and pore 
volume of activated carbon product 
results[9]. Walnut-shell filtration was 
developed as a more suitable method 
for filtering oil and suspended solids in 
the applications where sand filters 
were conventionally used. It is used to 
treat refinery wastewater, oil field 
produced water, steel mill direct spray 
and caster water, ethylene plant quench 
water, copper concentrate decant and 
oily water [10]. 
       The main objectives of this 
research are the following  
1-Improves the potential of 
using natural products in the 

environmental                             
applications to avoid side effects of 

using synthetic chemical materials. 
2-Study the efficiency and mechanism 
of oil removal from wastewater using 
walnut-shell. 

 
Experimental  
Materials  

Pulverized walnut-shell was 
used in this study. It was obtained from 
peeling the walnut fruits which was 
supplied from the local market. The 
hard external peels were milled and 
then sieved into different particle sizes 
with maximum diameter of 850 µm. 
The sieved pulverized walnut-shell 
was washed with distilled water for 
dust and fine removals, then  heated at 
1050C for 24 hours and stored in a 
desiccator until required for use. The 
effluent used in this work was obtained 
freshly from the discharge point of the 
API unit in the treatment plant of AL-
Duara refinery in Baghdad/Iraq. The 
quality of this effluent is presented in 
table 2. 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

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Another set of experiments 
were performed with oily aqueous 
solutions prepared by adding cooking 
oil (sun flower oil) in potable water to 
obtain synthetic oily aqueous samples 
of oil content 50 mg/l as a stock 
solution, subsequent concentrations of 
40, 30, 20, 10 mg/l were made by 
dilution. All the materials used in this 
research are supplied by Iraqi locally 
market. Oil specifications as 
represented the Turkish manufacturer 
(Trade mark cezer) of the sun flower 
oil are shown in table1. 

 
Table 1 Specifications of sun flower 

oil given  by the Turkish manufacturer 
 

constituents Average 
composition / 

100 grams 
Energy 884 Kcal 
Protein 0 g 

Unsaturated 87.5-91.3 g 
Saturated 8.7-12.5g 

Carbohydrate 0 g 
Cholesterol 0 g 

Sodium 0 g 
Vitamin 3 mg 

 
 

Analysis 
 

Table 2 represents the quality 
of the freshly collected actual samples. 
All measurements were carried out in 
accordance with the  quantitative 
analysis methods described in the 
Standard Methods for Examination of 
Water and Wastewater [11]. 

 
 

 
 

 
 
 
 
 

Table 2 Average composition 
of the freshly collected actual samples. 

 
Constituen

ts 
unit

s 
Concentrati

on range 
Aver
age 

conce
ntrat
ion 

pH - 7-7.5 7 
COD mg/

l 
200-600 400 

Suspended 
solids 

= 40-100 75 

Oil & 
grease 

= 8-12 10 

Phenol = 0.9-1.5 1 
 

pH and suspended solids 
measurements were done by the 
researcher, whereby COD and phenol 
analysis were carried out in the service 
laboratory / Department of chemistry / 
Faculty of science / University of 
Baghdad. Oil and grease contents were 
performed in the laboratories of 
ministry of Environment. Shimadzu 
Model UV-160 spectrophotometer was 
used to determine the concentrations of 
phenol which absorb ultraviolet 
radiation at λmax= 270 nm [12]. All 
reagents used in the analyses of 
wastewater samples were of analytical-
reagent grade. The pH of solutions was 
measured by a pH meter of Swiss 
made (type: Methrihm 605). 

 
Experimental procedure 

Three sets of batch tests were 
performed in this study with oily 
samples each of 100 ml volume. The 
first set of experiments were conducted 
with the laboratory prepared samples 
containing 10 mg/l initial 
concentration of cooking oil (sun 
flower oil) were introduced into Pyrex 
stoppered bottles containing accurately 
weighed amounts of pulverized 
walnut-shell ( 1, 2, 3, 4 and 5 g ). The 
bottles were shaken at room 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

 ١٢٠

temperature (25 ± 2º C) and allowed 
sufficient time up to 48 hours to reach 
equilibrium. By the end of each run, 
the reaction mixtures were filtered and 
the filtrate was analyzed for 
determination of equilibrium 
concentrations. Control solution was 
similarly treated, without walnut-shell 
as a blank solution. Residual 
concentration of the blank solution was 
taken as the initial one. Another set of 
experiments were conducted with 
freshly collected oily samples from Al-
Duara refinery effluent. The third set 
of the laboratory batch tests carried out 
by mixing and shaking the laboratory 
prepared samples of different initial 
concentrations of cooking oil (50, 40, 
30, 20 mg/l) with fixed amount (4 g) of 
pulverized walnut-shell and allowed to 
reach equilibrium.  

Adsorption isotherm was 
obtained by plotting the amount of oil 
adsorbed per mg pulverized walnut-
shell verses the corresponding 
equilibrium concentration. 
       
Results & discussion 
Quality of the treated  samples 

Table 3 represents the quality 
of the treated oily samples and 
percentage removal of the pollutants. It 
can be seen that the maximum 
percentage adsorption of oil in 
synthetic solution is 96%. This occurs 
when the initial concentration of oil is 
10 mg/l.  

  
 
 

 
 
 
 
 
 
 
 
 
 

Table 3 Specifications of the treated 
effluent samples 

Constituents Units Average concentration 

Percen
tage 

reduct
ion of 

polluta
nts % 

Prepared samples 
Oil & grease mg/l 0.4 96 

Actual samples 
pH - 7 - 

COD mg/l 75 81.25 
Suspended 

solids 
= 30 60 

Oil & grease = 2.5 75 
phenol = 0.1 90 

 
 

For the freshly collected actual 
samples of wastewater the percentage 
adsorption of oil decreased to 75%. 
This may be attributed to the existence 
of other pollutants like phenol rather 
than oil that could be adsorbed by the 
walnut-shell particles. As represented 
in this table the phenol, chemical 
oxygen demand (COD) and suspended 
solids show good percentage reduction 
in their concentrations of 90%,  
81.25% and 60% respectively. Oil 
molecules may be arrested due to 
physical adsorption represented by 
electrokinetic forces which seems to be 
the most governing mechanism in this 
process. The space between the 
walnut-shell grains act as a 
sedimentation tank in which the 
suspended matter settles upon the 
walnut-shell particle. 

 
Effect of walnut-shell doses on 
adsorption 
The percentage adsorption of 
oil at different walnut-shell doses is 
shown in figure 1. It can be seen from 
this  figure that the percentage 
adsorption of oil increases and reaches 
a maximum value of 96% at 4 g of 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

 ١٢١

walnut-shell particles and remains 
constant for synthetically prepared 
waste samples; whereas the percentage 
adsorption of oil in actual waste 
samples increases with the increase of 
adsorbent doses and reaches the 
maximum value of 75% since the 
initial oil concentration was 10 mg/l 
reduced by adsorption to 2.5 mg/l in 
the treated effluent samples as shown 
in table 3. The increase in percentage 
adsorption may be related to the fact 
that the number of available adsorption 
sites increases by increasing the 
adsorbent doses and that results in the 
increase of the oil removal 

efficiency.

Pulverized walnut-shell dose (g)

A
ds

or
pt

io
n 

%

50

60

70

80

90

100

0 1 2 3 4 5

Prepared samples
Actual samples

 
 

Figure 1. Percentage adsorption of oil 
in synthetic and actual waste samples 
of initial               oil concentration of 

10 mg/l with different pulverized 
walnut-shell doses 

 
Effect of time on adsorption 

Figure 2 represents the effect of 
time on the adsorption process for both 
synthetic and actual samples. As 
represented by these plots, adsorption 
at equilibrium conditions were attained 
after a contact time of 24 hours for 
both types of samples. 

 

Time (h)

X
 (m

g)

0

2

4

6

8

10

0 10 20 30 40 50

Actual samples
Prepared samples

 
 

Figure 2. Effect of time on the 
adsorption of oil in actual samples 

 
Adsorption isotherm 

Figures 3 and 4 represent the 
adsorption isotherm of oil on 
pulverized walnut-shell and the 
linearized plot of Langmuir isotherm 
respectively. 

 

Ce (mg/l)

C
s  

0.000

0.002

0.004

0.006

0.008

0.010

0 4 8 12 16

Figure 3. Adsorption isotherm of oil on 
pulverized walnut-shell at 25º C 

 

Ce (mg/l)

C
e/C

s (
m

g/
l)

0

400

800

1200

1600

2000

0 4 8 12 16

Ce/Cs=76.724+111.221Ce
R= 0.9949

Figure 4. Linearized plot of Langmuir 
isotherm 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

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As shown in figures 3 and 4, 

adsorption isotherm of oil particles 
shows a good agreement with the 
typical Langmuir isotherm plot and 
those encountered in the adsorption of 
most organic compounds from dilute 
aqueous solutions. This plot shows 
that, as the concentration of oil is 
increased in the liquid phase, 
proportionality more of the adsorbent 
surface is covered with oil at higher 
concentration of the material in the 
solution phase, the adsorbent is 
completely based on the assumption 
that a single monolayer  of oil 
accumulates at the solid phase. The 
Langmuir data demonstrates that 
walnut-shell is an effective adsorbent 
for oil. The results indicate a good 
positive applicability of the Langmuir 
model. The correlation coefficient was 
found to be 0.9949. The equation that 
describes the Langmuir system is 
represented by equation (1) and its 
linearized form equation (2) [13]. 

 

e

e
s bC1

abC
M
X

C
+

==                ……… (1) 

 

e
e C

a
1

ab
1

X/M
C

+=                 ……… (2) 

 
To obtain the sorption 

characteristics of the system, the 
laboratory study was followed by best-
fit analysis of the sorption isotherm 
model. The empirically determined 
Langmuir equation given by equation 
(3), was used to find the isotherm 
constant (a) and the saturation 
coefficient (b) of oil as a relevant 
adsorbate as follows: 

e
s

e 111.221C76.724
C
C

+=     …… (3) 

 
a = 0.009 

b = 1.45 l/mg 
 

The effect of  isotherm shape 
effect on whether the adsorption is 
favorable or not the following formula 
has been used [12]: 

 

oaC1
1

r
+

=                        ……… (4) 

 
It is a favorable adsorption for 

values of r less than 1. For values 
greater than 1 it is unfavorable. For 
this system including both synthetic 
and actual oily samples with initial oil 
concentration of 10 mg/l, the 
adsorption was found to be favorable 
since the separation constant r is equal 
to 0.9. 

 
Conclusion 

This study shows the potential 
of walnut-shell application for the oil 
removal from wastewater. The results 
revealed that during the filtration 
process, adsorption was taking place 
on the active surfaces of walnut-shell 
particles. The Langmuir constants and 
the constant separation factor have 
been determined. The percentage 
removal of oil from synthetic and 
actual wastewater was 96% and 75% 
respectively. The beauty of the walnut-
shell application for oil removal from 
wastewater is that it is ecologically 
sound and environmentally desirable 
treatment technique. In large scale 
application of this technique it is 
recommended to use a complementary 
scrubbing system to improve the 
backwashing process. Further work is 
recommended to study the column 
tests system.   

 
 
 
 
 
 
 
 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

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References  
  

1- Metcalf & Eddy, Inc. Wastewater 
Engineering. T M H Edition, TATA 
McGraw-Hill publishing Company 

ITD New Delhi, pp. 239-240, 1974. 
 

2- Vesilind, P.A.et.al. Environmental 
Pollution and Control.3rd Edition. 
Butterworth-Heinemann, A division of 
Reed Publishing (USA) Inc., pp. 18, 

1990. 
 

3- Rao, M.N. & Datta, A.K., 
Wastewater treatment, 2nd Edition, 
Oxford & IBH publishing 

CO.PVT.LTD, pp. 303, 1987. 
 

4- Shih, J.C.H. and Kozink, M.B., 
Ultrafilteration Treatment of Poultry 
Processing Wastewater and Recovery 
of a National of a Nutritional By- 
Product, Poultry Science, 59:247-252, 

1980. 
 

5- Miller, J.C., Process for Removing 
Proteinaceous Materials, Fats and Oils 
from Food Processing Wastewater and 
Recovering Same. U.S. patent 
5,413,720, May 9, 1995, and U.S. 

patent 5,543,058, August 6, 1996. 
 

6- Sealock, L.J., Treatment Methods 
for Breaking Certain Oil and Water 
Emulsions. U.S. patent 5,100,559, 

March 31, 1992.  
 

7- Stephenson, R.L. & Blackburn, J.B. 
The Industrial Wastewater Systems 
Handbook. LEWIS publishers, USA, 

pp. 130-137, 1998. 
 

8- Walnut Shell Abrasives, Carriers, & 
Media offer from Reade Advanced 

Materials, pp. 1-3, 1997.  
9- M. Abedinzadegan Abdi, M. 
Mahdyarfar, A. M. Raqshidi, A. 
Ahmadpourr, Preparation of  Activated 
Carbon from Chemical Activation of 

Walnut Shell, Jor. of Faculty of  

 
 

Engineering, Ferdowsi University of 
Mashhad, 14, (1), pp. 1-13,  2002.  

 
10- Special report. Environmental 
processes, 98, Hydrocarbon 

processing, 77, (8), pp.72-110, 1998. 
 

11- Standard Methods for the 
Examination of Water and Wastewater. 
15th Edition, American Public Health 

Association, 1980. 
 

12- Mckay, G., Bino, M.J. and 
Altamemi, A.R., The adsorption of 
various pollutants from aqueous 
solutions on to activated carbon, Water 

Research, 19, (4), pp. 491-495, 1985. 
 

13- Watts, R., J., Hazardous wastes, 
Sources, Pathways, Receptors, JOHN 
WILEY & SONS, INC, pp. 267-271, 

1997. 
 
Nomenclature 
Ce= equilibrium concentration of 
pollutant in solution after adsorption 
(mg/l) 
Co= initial concentration of pollutant 
(mg/l) 
X = adsorbed contaminant 
concentration 
Cs= X/M contaminant concentration 
adsorbed per unit weight of 
adsorbent(mg/mg)  
a = empirical constant 
b = saturation coefficient (l/mg) 
R = dimensionless constant 
separation factor  

 
 
 
 
 
 
 
 
 
 



Zainab Ziad Ismail / Al-khwarizmi Engineering Journal ,vol.1, no. 1,PP 117-124  (2005)    

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  ازالة الزيوت من المياه الملوثة بها باستخدام قشور ثمار الجوز
  

  زياد اسماعيل زينب.د
  جامعة بغداد /كلية الهندسة/قسم هندسة البيئة 

  
  

  :الخالصة
ة الزيوت من المياه الملوثة تم في هذا البحث دراسة قابلية مسحوق قشور ثمار الجوز في إزال

مسـحوق  (تتضمن عملية اإلزالة وجود طورين هما الطور  السائل الملوث بالزيت والطور الصلب . بها
تم استخدام مجموعتين من النماذج المائية الملوثة . الذي يتم تراكم وامتصاص الزيت عليه) قشور الجوز

ة مختبريا وقد بلغت نسبة إزالة الزيت مـن هـذه   األولى محضر المجموعة, بالزيت في التجارب العملية
أما المجموعة الثانية فهي نماذج حقيقية تم جمعها من مياه الصـرف الصـناعية فـي    %. ٩٦النماذج 

  %٧٥د بلغت نسبة إزالة الزيت منها مصافي الدورة جنوب بغداد وق