Adsorptive Remediation of Crude Oil Contaminated Marine Water Using Chemically and Thermally Modified Coconut (Cocos nucifera) Husks

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Adsorptive Remediation of Crude Oil Contaminated

Marine Water Using Chemically and Thermally

Modified Coconut (Cocos nucifera) Husks

Samuel E. Agarry , Kigho M. Oghenejoboh , Ewomazino. O. Oghenejoboh , Chiedu N. Owabor ,

Oladipupo O. Ogunleye¹

Biochemical and Bioenvironmental Engineering Laboratory, Department of Chemical Engineering, Ladoke Akintola University of Technology, P. M. B.

000, Ogbomoso, NIGERIA.

Biochemical and Bioenvironmental Engineering Laboratory, Department of Chemical Engineering, Delta State University, Abraka, P. M. B. 22, Oleh

Campus, NIGERIA.

Department of Chemical Engineering, Federal University of Petroleum Resources, Effurun, NIGERIA

Received: 17/01/2020

Accepted: 04/04/2020

Published: 20/05/2020

Abstract

This study evaluated the potential of a chemically and thermally modified coconut husk as oil-spill sorbents in the remediation of crude

oil contaminated marine water under varying physical factors of sorption time, initial oil concentration, temperature, sorbent dosage and oil

weathering number of days. Coconut husk (CH) was chemically activated with zinc chloride and then pyrolyzed at a different combination

of temperatures-retention times of 400 -800 C and 30 – 60 minutes to produce un-activated and activated coconut husk-derived biochar

(CHB and ACHB), while acetylated-coconut husk (ACCH) was produced using acetic anhydride. The results revealed that the sorption

potential of coconut husk can be enhanced by chemical, thermal (pyrolysis) and chemo-thermal treatments (chemical/pyrolysis). The oil

sorption capacities and oil removal efficiencies of raw CH, ACCH, CHB800-60, and ACHB800-60 were a function of the physical factors. The

rate of oil sorption by raw CH, ACCH, and CHB800-60 follows pseudo-second-order kinetics while that of ACHB800-60 follows pseudo-first-

order kinetics. The oil sorption by raw CH, ACCH, CHB800-60 and ACHB800-60 occurs via both surface and intraparticle diffusion mechanism.

Freundlich isotherm best describe the oil sorption behaviour of ACCH, CHB800-60, and ACHB800-60, respectively, while Langmuir isotherm

best describes the sorption of raw CH. The maximum monolayer sorption capacities were 12.11 g/g, 15.06 g/g, 16.10 g/g, and 16.84 g/g for

the raw CH, ACCH, CHB800-60 and ACHB800-60, respectively, and hence the performance of the sorbents was in the following order: ACHB800-

> CHB800-60 > ACCH > raw CH.

Keywords: Adsorptive remediation; Isotherms; Kinetics; Modified coconut husk; Oil spill

inorganic mineral, organic synthetic and organic vegetable [4-6].

Among the various commercial oil sorbents that have been

deployed for oil spill removal, synthetic sorbent made up of

polypropylene, polyethylene, and polyurethanes, and several

cross-linked polymeric materials are the most commonly

employed due to their good oleophilic and hydrophobic

characteristics [6-9]. However, the major disadvantages of these

sorbents are that they are not biodegradable [6, 8, 10], sometimes

have low sorption capacity and are often expensive [6, 8, 11].

Therefore, there is a renewed attention and interest in the usage

of natural sorbents as one of the most attractive options for oil

spill remediation due to their low cost, eco- friendliness,

effectiveness, low water pickup, high buoyancy, good reusability

and high sorption capacity [12-13].

Introduction¹

Small and massive scale of oil spills occurs yearly on land,

sea and marine water systems throughout the world as a result of

human mistakes and carelessness, deliberate acts of pipeline

vandalism, earthquakes, natural disaster [1], offshore drilling and

production activities, crude oil transports by ships, cargos,

vessels, tankers, rail and trucks, untreated oily waste disposal

from petroleum refineries, factories and industrial facilities [2].

For the cleanup strategies of oil in the coastal or marine

environment, several oil spill removal methods have been used,

such as the use of solidifiers, dispersants and controlled in-situ

burning, bioremediation, booms, skimmers and sorbent/adsorbent

[3].

Adsorption technology has been observed to be one of the

A wide variety of natural sorbents employed for oil spill

remediation in water have been reported in the literature. These

most effective method for oil spill removal or treatment. The

sorbents that are used for oil spill removal are classified as

Corresponding author: Samuel E. Agarry, Biochemical and Bioenvironmental Engineering Laboratory, Department of Chemical

Engineering, Ladoke Akintola University of Technology, P. M. B. 4000, Ogbomoso, NIGERIA. E-mail: sam_agarry@yahoo.com.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

include banana peels [6], modified pomelo peels [14], human hair

engineering aspects of the removal or sorption mechanism such

as kinetics and equilibrium of the crude oil sorption onto the

sorbents.

[15], corncob [9], luffa fibre [16], rice husk [5], coconut coir [17],

barley straw [18], and sugarcane baggase [4]. However, the major

draw-back of these agricultural plant-derived sorbents when

present in saturated oil-water environments is their tendency to

adsorb both water as well as oil, causing them to sink [17] as a

result of low hydrophobicity and poor buoyancy when compared

to synthetic sorbents such as poly-propylene [9, 11]. That is, when

agricultural plant-derived sorbents are applied to saturated oil-

water environments, water sorption is preferentially favoured

over oil sorption because of the typical hydrophilic (due to

abundant associated hydroxyl functional groups in the cellulose,

hemicelluloses and lignin) nature of the sorbent [17].

Hydrophobicity or oleophilicity is one of the major advantages of

sorbent characteristics that influences oil sorption effectiveness in

the presence of water [19]. The sorbents effectiveness in saturated

oil-water environments would be enhanced when the amount of

hydroxyl functional group present is reduced (i.e. hydrophilicity

is reduced) and hydrophobicity is increased [19]. The amount of

hydroxyl functional group of these sorbents can be reduced by

chemical modification, such as acetylation, acylation, acrylation,

benzoylation, cyanoethylation, and methylation [20] and as well

as by thermal modification (pyrolysis) in the production of

biochar. This chemical reactions involves the replacement of the

hydroxyl functional group in the cellulose, hemicelluloses, and

lignin present at the polymeric backbone with more hydrophobic

groups [17].

Materials and Methods

Simulated marine water was used for the remediation studies.

Chemicals and reagents used for the studies were of analytical

grade (Sigma-Aldrich, Germany). De-ionized water was made

used of throughout the experiments. Raw coconut husks (CH)

used for the studies were obtained from a small scale coconut

chips factory.

.1 Preparation of simulated marine water

The preparation of simulated marine water for this study was

carried out according to the recipe of Kester et al. [30] and

Nwadiogbu et al. [9]. Ten (10) litres of de-ionized water was

measured into a 20-L plastic container and the following

quantities of salts (chemicals) were weighed and added into it as

follows: Sodium chloride (NaCl) 23.926 g, Sodium sulphate

(

NaSO

bicarbonate (NaHCO

g and Boric acid (H

mixture was then stirred vigorously with a stirring rod.

) 4.008 g, Potassium chloride (KCl) 0.667 g, Sodium

) 0.196 g, Potassium bromide (KBr) 0.098

BO ) 0.026 g. For thorough mixing, the

.2 Preparation of chemically modified coconut husk

(acetylated coconut husks)

The raw coconut husks (CH) were chemically modified by

The use of biochar as a potential eco-friendly adsorbent for

wastewater and water purification has of recent received

increasing attention [21-23]. Biochar can be produced from a

myriad of discarded organic and biologically-based materials,

including agricultural by-products or wastes. Several biochar

derived from pyrolysis of agricultural wastes have been explored

for a variety of applications including their adsorption potential

for heavy metal removal from contaminated water [21-23], while

very few works involving their use as oil adsorbents (such as rice

husk biochar, corncob biochar, cornstalk biochar) in the removal

of oil have been reported in the literatures [24-27]. Thus, a study

for the implementation of biochar as sorbent for oil sorption needs

to be fully developed. According to Camilli et al. [28] and Reddy

et al. [29] there is the need to develop an effective, fast and cheap

methods to minimize or mitigate the negative consequences of oil

spill. However, report or information on the use of thermally and

chemically modified coconut husk (a commonly available low-

cost fibrous layer of lignocellulosic waste material found outside

the coconut shell) as oil sorbents is seldom scarce.

acetylation reaction. Raw CH were sorted out so that sand

impurities can be removed. The sorted coconut husks were sun-

dried and then comminuted into samples of uniform size. Prior to

acetylation of the raw CH, the influence of the CH fibre on

acetylation was reduced. This was done by weighing 20 g of the

sieved comminuted samples of the CH and then extracted in a

Soxhlet apparatus for 5 h with a mixture of n-hexane and acetone

(

1:4, v/v). The residue CH were then oven-dried at 60 C for 16

h. The extracted content was calculated as a percentage of the

oven-dried coconut husks. The oven-dried CH were then

acetylated using the method of Sun et al. [20]. This method of

acetylation was carried out in a solvent-free system using acetic

anhydride in the presence of N-bromosuccinimide (NBS) as

catalyst. Ten (10) grams of dried-extracted CH were put into a

round-bottom flask and thereafter 200 mL of acetic anhydride as

well as 1% NBS catalyst were added. The round-bottom flask was

fitted to a condenser and then placed in an oil bath that is on top

of a thermostat- controlled heating device set at a temperature of

00 C and the reaction was left for 1 h.

Since coconut husk tends to also adsorb water, its oil sorption

capacity may be reduced. Thus, acetylation reaction and pyrolysis

are introduced to increase the hydrophobicity of the husks.

Therefore, the major focus of this work are to (1) chemo-

thermally modify the coconut husk through chemical activation

using zinc chloride as agent and pyrolysis to produce activated

coconut husk-biochar, (2) chemically modify the coconut husk

through acetylation to produce acetylated-coconut husk and (3)

evaluate and compare the potentials and efficiencies of the raw

coconut husks and the resulting modified coconut husks (coconut

husk derived-biochar, activated coconut husk-derived biochar and

acetylated-coconut husk) as oil sorbents in the remediation of

crude oil contaminated marine water under varying conditions of

sorption time, temperature, oil concentration, oil weathering and

sorbent dosage. Attempts have also been made to study the

Thereafter, the round-bottom flask was taken out from the oil

bath and the hot reagent was decanted. The CH were then washed

thoroughly with acetone and ethanol. This was done to remove

any unreacted acetic anhydride and the acetic acid by-products.

The washed acetylated-CH (ACCH) obtained were then oven-

dried at 60 C for 16 h and stored in the desiccator prior to use.

.3 Preparation of thermally and chemo-thermally modified

coconut husks

The raw CH was thermally modified by the action of pyrolysis

as well as chemo-thermally modified by the action of chemical

activation and pyrolysis to produce un-activated and activated

coconut husk-derived biochar (CHB and ACHB). The preparation

of ACHB was carried out according to the method of Subha and

Namasivayam [31]. The comminuted CH samples were

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

impregnated with zinc chloride (ZnCl

g of the sample was added to 100 g of anhydrous ZnCl

boiled deionized water and the mixture stirred for 1 h to form a

) in a ratio 2:1. That is, 200

in 1 L of

the sorbent transferred to the non-polar (organic) liquid phase was

determined by filtration and then followed by drying and

weighing. The degree of hydrophobicity of the sorbent was

estimated based on Eq. (1) [38]:

paste, after which the remaining solution was decanted and then

oven-dried at 110 C for 1 h. The ZnCl

-impregnated CH samples

were then packed inside a steel container with a tight lid. The steel

container was then placed inside another larger steel container

with tight lid. The inner space of this larger container was filled

with sand consolidated layer by layer to the brim of the container

so as to achieve a near total absence of the sample’s exposure to

air except for the limited oxygen already trapped in the voids of

the sample. The whole setup was thereafter placed in a muffle

furnace after attaining the required temperature in the furnace.



W 

(1)

HD(%) 

100









where W_Hand W_Oare the weight of sorbent in hexane (g) and

original weight of sorbent (g), respectively.

.6 Remediation protocol

2.6.1 Screening of activated biochar for oil removal

The eight (8) activated biochar samples (ACHB400-30

ACHB400-45, ACHB400-60, ACHB600-30, ACHB600-45, ACHB600-60

The ZnCl -impregnated CH samples were pyrolyzed at 400, 600

and 800 C for different heating or retention time of 30, 45 and 60

min, respectively.

The activated biochar (activated coconut husk-carbon)

produced from the pyrolysis or carbonization was allowed to cool

to room temperature. After cooling, 100 mL of 1.0 M

hydrochloric acid (HCl) was added to each of the activated CH

derived-biochar (ACHB) in 500 mL beaker and the samples were

ACHB800-30, ACHB800-45 and ACHB800-60) prepared at different

pyrolysis temperature and retention time were first screened to

identify the best candidate for oil removal. One hundred (100)

millilitre of the simulated marine water was placed in a 500 mL

beaker and 5 g of crude oil was weighed and added. A weighed

sample (0.5 g) of each ACHB was sprinkled over the crude oil-

water system. The beaker was then placed on a temperature

controlled water bath shaker and agitated continuously at a speed

of 120 rpm for 15 min. At the end of 15 min, the wetted sorbent

was taken out and allowed to drain for 5 minutes on a filter paper

after which the saturated sorbent was weighed. The adsorbed

water in the sample was measured using the Karl Fischer

technique as well described in ASTM D1533 [39]. The quantity

left for one day so as remove or leach out excess ZnCl present in

the biochar. After that, the samples were filtered and washed

thoroughly with deionized water after which 50 mL of 1.0 M

NaOH was added to neutralize the acidic effects of the acid on the

activated biochar. The activated CH derived-biochar (ACHB)

was washed several times with deionized water until the pH of the

wash water was neutral. Each of the ACHB was then filtered and

oven-dried at 150 C for 3 hours till constant weight was achieved.

The ACHB were allowed to cool to room temperature and

thereafter stored in an air tight containers to avoid humidity

adsorption, prior to use. The ACHB produced at 400, 600 and 800

of sorbed oil at time, t (q ) (i.e. oil sorption capacity) was

calculated according to Eq. (2) [40] by taking into account the

weight of the sorbent, the weight of the sorbent, oil and water and

the weight of water:

C with retention time of 30, 45 and 60 min was respectively

labelled according to its pyrolysis temperature-retention time (i.e.

ACHB temperature-time) as: ACHB400-30, ACHB400-45, ACHB400-

M  (M  M )

, ACHB600-30, ACHB600-45, ACHB600-60, ACHB800-30, ACHB800-

and ACHB800-60. Preparation of the un-activated coconut husk

(2)

q 

M_i

derived-biochar (CHB) was carried with the same above

procedure, however, without the use of ZnCl (i.e. no chemical

activation)

where, M_iis the initial mass of sorbent (g), M_wis the mass of

wetted sorbent after draining (g) and MWC is the mass of water

content in wetted sorbent (g). All experiments were carried out in

triplicate and the mean values were used for calculations.

Following these preliminary sorption studies, the best performing

ACHB was selected for further studies. The effects of sorption

.4 Characterization of sorbents

The raw CH, ACCH, ACHB400-30, ACHB400-45, ACHB400-60

ACHB600-30, ACHB600-45, ACHB600-60, ACHB800-30, ACHB800-45

and ACHB800-60 samples were characterized for surface area using

the iodine number method, volatile matter, ash content, fixed

carbon, moisture content, bulk density and pH, using ASTM-

D4607-94, ASTM-D1762-84 and ASTM 3172-75 standard

methods [32] and functional groups using Fourier infra-red

spectroscopy (FT-IR), respectively.

time (1- 30 min), initial oil concentration (5 – 9 g/L), temperature

(

15 – 35 C), sorbent dosage (0.5 – 25 g) and oil weathering

number of days (3, 7 and 10 days) using the raw CH, ACCH,

CHB800-60 and ACHB800-60 were investigated.

.7 Data analysis

Correlations between biochar adsorption of crude oil as

.5 Determination of the degree of hydrophobicity

function of pyrolysis temperature and retention time was done

using the regression analysis tool of SPSS (ver. 10) software

package. Also, one-way ANOVA and Tukey Post-hoc (HSD)

tests were conducted to ascertain the significant difference

between the sorption capacities of the activated biochars prepared

at different pyrolysis temperatures and retention times and other

adsorbents used in the study.

The degree of hydrophobicity ( HD ) of the sorbents were

defined as the tendency of the materials to be removed from the

polar aqueous phase into a non-polar liquid phase [38]. In this

experiment, 1.0 g of sorbent was added into a beaker that

contained 20 mL of water and was sufficiently agitated. After this,

0 mL of hexane solvent (i.e. the same volume of water) was

added into the beaker and then the mixture was agitated for 3 min.

Thereafter, the mixture was then left to stand for 5 min to allow

for the separation of the two immiscible phases. The amount of

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

Table 1: Characterization properties of sorbents

ACHB

400 C

ACHB

600 C

ACHB

800 C

Parameter

N (mg/g)

Raw CH

CHB800-60 ACCH

2.684

3.88

80.74

6.05

9.33

0.084

6.8

160.7 167.2 180.4 250.1 257.5 266.8 278.0 310.6 342.2

30.44 31.76 32.72 33.52 34.96 35.66 36.58 37.82 38.64

29.20 27.80 26.50 25.94 24.42 23.24 18.52 16.82 14.93

176.4

46.26

23.45

2.76

12.89

5.95

70.82

AC (%)

VM (%)

MC (%)

FC (%)

5.96

5.90

5.86

5.67

5.65

5.60

5.55

5.44

5.40

5.88

34.40 34.54 34.92 34.87 34.97 35.50 39.35 39.92 41.03

0.324 0.310 0.284 0.266 0.242 0.226 0.210 0.197 0.183

27.53

0.743

8.20

17.35

0.137

6.2

BD (g/cm )

9.5

9.8

10.0

10.4

10.6

10.8

11.2

11.3

11.4

It is seen that the raw CH has a volatile matter (VM) content

of 80.74% which is very high with low ash content (AC) of 3.88%

palm kernel shell, safflower seed cake, sugar beet tailings,

sugarcane bagasse at high temperature [34, 42, 43, 45, 46].

The iodine number of a sorbent or material correlates with

surface area and porosity or pore development [42, 44, 47]. The

observed increase in iodine number with respect to increased

temperature implies that the surface area and porosity of the

activated biochars also increases with respect to increasing

temperature and retention time. Suman and Gautam [43] have

reported that the surface area and porosity of carbon produced

from coconut husk increased with increase in pyrolysis

temperature. Table 1 shows that high pyrolysis temperature and

longer retention time would result in the release of great amount

of volatile compounds from the raw material and consequently

influences the iodine adsorption. The highest iodine adsorption

was achieved with activated biochar produced at a pyrolysis

temperature of 800°C and retention time of 60 min (ACHB800-60

with iodine number of 342.2 mg/g). It is clearly shown in Table 1

that as the volatile matter content of the biochars decreased, the

iodine adsorption of these biochars increased. Lower pyrolysis

temperature and shorter retention time causes lower amount of

volatile compounds to be released and thus produces biochar with

underdeveloped carbon structures and reduced surface area ().

The iodine number of raw CH and ACCH are lower than the

values obtained for the biochars.

and a fixed carbon (FC) of 9.33%. The BD, I N, and pH values

for raw CH are 0.084 g/cm , 2.684 mg/g and 6.8, respectively.

However, when the raw CH was modified through acetylation

reaction with acetic anhydride to produce ACCH, variations in

these observed values occurred as presented for ACCH in Table

1. As it can be seen, the VM, AC, FC, BD, I N, and pH values of

ACCH are 70.82%, 5.95%, 17.35%, 0.137 g/cm , 12.89 mg/g and

.2, respectively.

In addition, when the raw CH was further modified through

thermo-chemical method using zinc chloride and pyrolysis at

different temperature and retention time to produce activated

biochar (ACHB400-30, ACHB400-45, ACHB400-60, ACHB600-30

ACHB600-45, ACHB600-60, ACHB800-30, ACHB800-45 and ACHB800-

), there are wide variations in the physical properties in

comparison with the raw CH as shown in Table 1. As it can be

seen, VM, AC, FC, BD, I N, and pH ranged from 29.20-14.93%,

0.44 – 38.64%, 34.40 – 41.03%, 0.324-0.183 g/cm , 160.7-342.2

mg/g, and 9.5-11.4, respectively. These values indicated that the

VM and BD gradually decreased with increasing pyrolysis

temperature (400 – 800 C) and retention time (30 – 60 min) while

AC, FC, I N and pH respectively increased with increases in the

pyrolysis temperature and retention time. Chen et al. [41], Angin

34] and Lee et al. [42] have reported similar observation of an

[

increase in ash content and fixed carbon as well as a decrease in

volatile matter as pyrolysis temperature increases. Suman and

Gautam [43] have reported a decrease in ash content with respect

to increasing temperature in the pyrolysis of coconut husk. Lee et

al. [42] and Olafadehan et al. [44] have reported similar

observation of a decrease in bulk density with respect to increase

in pyrolysis temperature and time.

3.2 FT-IR characterization

Result of the FTIR spectra carried out on raw CH, ACCH,

CHB800-60 and ACHB800-60 are presented in Table 2. The spectra

of the untreated raw CH precursor reveals the following peaks :

3560.25 – 3620.30 cm (-OH stretching of hydroxyl group that

occur in cellulose, and N-H stretch), 2850.10 – 2965.15 cm (C-

H asymmetric stretching of CH and CH of aliphatic), 1455.15 –

1652.05 cm (C-H deformation of CH , -C=C- stretching of

aromatic), 1715.04 – 1840.30 cm (carbonyl (C=O) group of

Bulk density measures the flow ability of a material. A good

sorbent or adsorbent is indicated by a lower bulk density [42]. The

lowest bulk density was achieved for activated biochar produced

ester (ascribed to hemicellulose), 1170.11 – 1325.20 cm (-C-O-

C stretching in cellulose, hemicellulose), (Nguyen et al., 2016).

For ACCH, the FTIR spectra revealed a peak band at 3500.11

at a temperature of 800 C and retention time of 60 min (ACHB800-

). The VM, AC, FC, BD, I

biochar (CHB800-60) are 23.45%, 46.26%, 27.53%, 0.743 g/cm ,

76.4 mg/g and 8.2, respectively. The pH of the sorbent

N, and pH values of the un-activated

-1

– 3540.45 cm indicating the presence of OH stretching of

hydroxyl group. The decrease in the OH peak intensity showed

that some of the OH groups were substituted by the acetyl group

and this substitution reduces the degree of hydrogen bonding [9].

constitutes a useful indicator of the nature of the functional groups

present on the sorbent surface. As shown in Table 1, the pH values

of raw CH and ACCH are slightly acidic while that of the un-

activated and activated biochars are alkaline. The alkaline nature

of the un-activated and activated biochars may be attributed to the

presence of relative larger concentration of inorganic material in

the form of mineral ash. Similar values of alkaline pH have been

reported for carbons or biochars produced from coconut shell,

The higher peak at 2900.15 – 2970.35 cm reveals the presence

of C-H stretching of alkane (CH and CH ). This indicates an

increase in the CH and CH (alkyl group) in ACCH and thus

increase in the hydrophobicity and oleophilicity of the acetylated

coconut husk.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

Table 2: FT-IR spectrum analyses of raw CH, ACCH, CHB800-60 and ACHB800-60

ACCH

Absorption Peak Number (cm )

OH (stretching), OH (non-bonding),3500.11 – 3540.45

N-H (stretching)

2 3

C-H, CH and CH C-H, CH and CH (aliphatic),

COOH (carboxylic group)

C-H (aliphatic), C=C, C=O1695.20 – 1820.40

stretching), N-H

Raw CH

Absorption Peak Number (cm ) Functional Groups

-1

Functional Groups

OH (stretching), OH (non-

bonding), N-H (stretching)

560.25 – 3620.30

850.10 – 2965.15

715.04 – 1840.30

455.15 - 1652.05

170.11 – 1325.20

(aliphatic),2900.15 – 2970.35

COOH (carboxylic group)

C-H (aliphatic), C=C, C=O

(stretching), N-H

(

C-H (deformation), N-H (bending),1430.23 - 1640.15

C=C (aromatic)

C-H N-H

(bending), C=C (aromatic)

(deformation),

C-O (stretching of alcohol, ether),1140.18 – 1295.25

C-N (stretching of amine)

C-O (stretching of alcohol,

ether), C-N (stretching of amine)

CHB800-60

ACHB800-60

488.05 - 3786.60

688.25 – 1810.11

410.10 - 1548.60

088.05 - 1190.20

OH (stretching), OH (non-bonding),3446.79 - 3751.55

N-H (stretching)

OH (stretching), OH (non-

bonding), N-H (stretching)

C-H (aliphatic), C=C, C=O

(stretching), N-H

C=C (aromatic), C-H (bending

in aliphatic)

C-H

(alkane),

C=C,

C=O1685.79 - 1799.59

(stretching), N-H

C=C (aromatic), C-H (bending in1400.32 - 1516.05

aliphatic)

C-O (stretching of alcohol, ether),1072.42 – 1147.55

C-N (stretching of amine)

C-O (stretching of alcohol,

ether), C-N (stretching of amine)

This hypothesis was confirmed by the presence of carbonyl

modifications. This could be the result of hemicellulose and

cellulose degradation in temperature of 800 C [25]. That is, high

(

C=O) group of ester or amides at the peak intensity of 1695.20 –

820.40 cm observed in ACCH which indicates that acetylation

carbonizing or pyrolysis temperature leads to high reduction of

surface functional group diversity and abundance [25, 48].

Pyrolysis of lignocellulosic biomass majorly leads to

dehydroxylation or dehydrogenation reactions which results in

polyaromatization of any left-over carbon. It is the presence of

this polyaromaticity that contributes to the hydrophobicity and

enough oleophilicity of biochar [27].

had occurred. This observation is in good agreement with the

increased degree of hydrophobicity of the raw CH from 19.4% to

5.6% after the modification. Thus, it is suggested that the

increased hydrophobicity of raw CH after modification with

acetic anhydride will increase the affinity of ACCH to absorb or

remove more crude oil. The FTIR spectrum of ACHB800-60

showed the presence of N-H stretch and O-H stretching (both free

-1

and H-bonded) at 3446.79 cm and 3751.55 cm , confirming the

presence of amine and OH groups from residual

hemicellulose/cellulose. The presence of C-H stretching of

3.3 Selection of activated biochar

Figure 1 shows the oil sorption capacity of the eight types of

activated biochar produced at different pyrolysis temperature of

aliphatic or alkane at the peak region of 2850.10-2965.15 cm as

seen in raw CH has completely disappeared in ACHB800-60 (i.e.

peak not observed) as well as in CHB800-60 [48]. The absence of

this C-H aliphatic peak positively correlates with increased

400 – 800 C and retention time of 30 – 60 min. At the respective

temperatures of 400, 600 and 800 C, the oil removal efficiency

of each ACHB increased with increase in pyrolysis retention time

(30 – 60 min). At the same pyrolysis retention time of 30-60 min,

the oil sorption capacity of ACHB increased with increase in

hydrophobicity in biochar. The band from 1685.79 cm to

799.59 cm indicates the presence of carbonyl (C=O) group of

pyrolysis temperature (400 – 800 C). Across all the activated

ester or amides, however, a relatively higher intensity or peak

(

biochars used for the treatment, the oil removal efficiency ranged

from 55.2 ± 0.5 to 76.8 ± 0.5%. This suggests that a considerable

percentage of oil was removed over the 15 min remediation

period. Indeed, there was statistically significant difference in the

oil removal efficiencies of the ACHB obtained at the different

-1

1688.25 – 1810.11 cm ) is observed in CHB800-60. The C=C

-1

stretching of aromatic at the band region of 1400.32 cm to

-1

516.05 cm was observed in ACHB800-60. While an increased

-1

band region of 1410.10 - 1548.60 cm was observed in CHB800-

as compared to ACHB800-60. The peak observed from 1072.42–

pyrolysis temperature and retention time (ANOVA: P = 4.3 × 10

147.55 cm was assigned to -C-O stretching (ascribed to

cellulose and hemicellulose). However, the peaks representing C-

H of aliphatic, C=C- of aromatic, C=O and OH of hydroxyl group

in ACHB800-60 and CHB800-60 are lower as compared to the

precursor which implied reduction of the functional group

diversity and abundance and thus indicating increased

hydrophobicity and oleophilicity of the biochar [48] which is in

good agreement with the increased degree of hydrophobicity of

the raw CH from 19.4% to 94.8% after the thermal and chemical

Furthermore, post hoc comparisons between the oil removal

efficiencies of different pairs of ACHB (36 pairs) using Tukey’s

(HSD) test at 5% probability level showed that there are

significant differences between the oil removal efficiencies of the

different pairs with the P-value ranging between 0.001 and 0.018.

Maximum oil removal efficiency of 76.84% was achieved with

ACHB obtained at pyrolysis temperature of 800 C and retention

time of 60 min (ACHB800-60).

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

400

350

300

250

200

150

100

Adsorbent

Oil Removal Efficiency

Iodine Number (Surface Area)

Figure 1: Oil removal efficiency of activated coconut husk derived-biochar (ACHB) produced at different temperature-time combinations

Sorption Time (min)

Raw CH

ACCH

CHB-800-60

ACHB-800-60

Figure 2: Effect of sorption time on oil sorption capacity of modified coconut husk (raw CH, ACCH, CHB800-60 and ACHB800-60

)

This was followed by ACHB600-60 and ACHB400-60 with oil

removal efficiencies of 68.2% and 60.2%, respectively. This

observation suggest that oil removal efficiency of ACHB

correlates positively with the pyrolysis temperature and retention

time as well as with the surface area of the biochar [21, 49]. These

observations are consistent with the observations reported for

biochar prepared from date seed used for heavy metal removal

performance, it was then selected for the remaining subsequent

experiments.

3.4 Effect of sorption time

The results for the effect of sorption time on oil removal is

shown in Figure 2. It can be seen that the oil sorption capacity of

raw CH, ACCH, CHB800-60 and ACHB800-60 respectively

increased with the increase in sorption time. The oil sorption

rapidly increase in the first 3 min and after which, it proceeded at

[

21] as well as for activated rubber particles used for oil removal

49]. The reason for this observation can be attributed to the

effects of pyrolysis temperature on the physiochemical

characteristics of the biochar including surface functional groups,

structure of the pores and surface area. Sorption is a combination

a slow rate until the 12 minute when there was no more

significant oil sorption and a maximum oil sorption capacity of 5

± 0.13 g/g, 8.42 ± 0.01 g/g, 8.75 ± 0.02 g/g and 9.35 ± 0.01 g/g

of adsorption and absorption. Adsorption is

surface

was attained by raw CH, ACCH, CHB800-60 and ACHB800-60,

phenomenon that has direct relationship with surface area. Thus,

increasing the surface area will result in increased adsorption.

More so, surface area indirectly affects the absorption of the

material to a large extent. This is because, as the surface area

increases, it increases the capillaries formed and so increases the

absorption [50]. Since ACHB800-60 displayed the best

respectively. The initial high rate of oil sorption may be attributed

to the presence of active sites (microscopic voids) on the sorbent

surfaces which was rapidly occupied with the oil molecules while

slower rate of sorption at the later stage may probably be due to

the active site saturation with oil molecules where there was no

more significant oil sorption and as well as the equilibrium

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

between the sorption and desorption processes that occurred after

saturation [15, 51, 52]. Similar observations regarding the use of

sorbents for oil removal have been reported [15]. The results in

Figure 2 also revealed that ACHB800-60 relatively demonstrated a

higher oil sorption capacity and thus a higher oil removal

efficiency than CHB800-60 (un-activated biochar), ACCH and raw

further showed that there is a significant difference in the sorption

capacity of CHB800-60 and ACHB800-60. The reason for these

observations may be due to difference in the proportions of

hydrophobic and hydrophilic functional groups in the sorbents

[53]. In addition, the higher surface area and pore volume as

indicated by the higher iodine numbers and as well as the swelling

and pores filling may also have been responsible for the high oil

sorption capacity and oil removal efficiency of the activated

biochar [24]. Al Zubaidy [54] has reported that the oil sorption

capacity of activated carbonized date palm kernel powder was

higher than the un-activated carbonized date palm kernel powder

while Nwadiogbu et al. [9] have reported that the oil adsorption

capacity of acetylated corncob was higher than that of the raw

corncob. Yusof et al. [17] have also observed and reported that

esterified coconut coir had a higher oil sorption capacity than the

raw coconut coir.

CH. This performance was closely followed by that of CHB800-60

ACCH and raw CH, respectively. Overall, there was statistically

significant difference in the sorption capacities of these sorbents

(

ANOVA: P = 1.11 × 10 ).

Post hoc comparisons using Tukey’s (HSD) test at 5%

probability level were carried out to basically determine the

significant difference in sorption capacity between any of the

sorbents. The difference in the mean sorption capacity between

pairs of sorbents were greater than the Tukey HSD value. Thus,

the Tukey’s test revealed that there are significant differences in

the sorption capacity between the raw CH and ACCH; between

the raw CH and CHB800-60 as well between raw CH and ACHB800-

3.5 Effect of initial oil concentration

, respectively. It also indicates that there are significant

difference in the sorption capacity between the ACCH and

CHB800-60 as well as between ACCH and ACHB800-60 while it

The changes in the oil sorption capacity and oil removal

efficiency at different initial oil concentration of 5 to 9 g are

illustrated in Figure 3.

Oil Concentration (g/L)

Raw CH

ACCH

CHB-800-60

ACHB-800-60

ACCH

CHB-800-60

Figure 3: Effect of initial oil concentration on oil sorption capacity and oil removal efficiency of modified coconut husk

Temperature ( C)

Raw CH

ACCH

CHB-800-60

ACHB-800-60

ACCH

CHB-800-60

Figure 4: Effect of temperature on oil sorption capacity and oil removal efficiency of modified coconut husk

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

It is seen that the oil sorption capacity of raw CH, ACCH,

CHB800-60 and ACHB800-60 respectively increased with increase in

the initial oil concentration while their oil removal efficiency

decreased with increase in initial oil concentration. Similar

observation has been reported for esterified coconut coir in its use

for oil removal from seawater with initial oil concentration of 0.05

to 0.2% mL/mL [17] as well as for bentonite/activated carbon in

its use for oil removal with initial concentration of 863 to 1613

ppm [55]. Maximum oil sorption capacity of 5 g/g, 8.42 g/g, 8.75

g/g and 9.35 g/g as well as a corresponding maximum oil removal

efficiency of 50%, 84.2%, 87.5% and 93.5% was attained by raw

CH, ACCH, CHB800-60 and ACHB800-60 respectively, with the use

of initial oil concentration of 5 g.

ACHB800-60 at different temperature of 15 to 35 C. The results in

Figure 4 demonstrated that the oil sorption capacity and oil

removal efficiency of raw CH, ACCH, CHB800-60 and ACHB800-

60 increases with increasing temperature. A similar observation

depicting an increase in the quantity of oil removed or sorbed with

increase in temperature was reported by Abdelwahab [16] in his

investigation of the effect of temperature on the oil sorption

capacity of raw luffa fibres. Hussein et al. [18] using barley straw

as well as Toyoda et al. [56] using exfoliated graphite have also

reported similar observation for the adsorption of heavy crude oil.

This increase in sorption may probably be due to decrease in the

viscosity of the oil as temperature increases making it suitable to

penetrate pores and be trapped between surface roughness until

maximum oil removal is attained at 35 ºC. Nevertheless, at lower

temperature, the viscosity of oil is high and this may cause the oil

to plug the pores and thus resulting in lower oil removal. On the

other hand, decrease in oil sorption capacity with increasing

temperature had been reported for the use of banana peel [13],

human hair [15] and modified pomelo peel [14] in crude oil

adsorption or removal.

.6 Effect of temperature

The effect of marine water temperature on the oil sorption

capacity and oil removal efficiency was investigated since the

temperature of marine water varies normally with seasonal

change and location. Figure 4 shows the oil sorption capacity and

oil removal efficiency of raw CH, ACCH, CHB800-60 and

1.5

2.5

0.5

1.5

2.5

Sorbent Dosage (g)

Raw CH

ACCH

CHB-800-60

ACHB-800-60

Figure 5: Effect of sorbent dosage on oil sorption capacity and oil removal efficiency of modified coconut husk

un-

3-day

7-day

10-day

un-

3-day

7-day

10-day

weathered weathered weathered weathered

oil

Raw CH

ACCH

CHB-800-60

ACHB-800-60

Raw CH

ACCH

CHB-800-60

ACHB-800-60

Figure 6: Effect of number of oil weathering days on oil sorption capacity and oil removal efficiency of modified coconut husk

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

.7. Effect of sorbent dosage

provided a good fit to the remediation kinetic data based on the

high values of the regression coefficient (R ) which were close to

Figure 5 shows the effect of sorbent dosage on the oil sorption

capacity and oil removal efficiency. The results in Figure. 5

revealed that as the mass of the sorbents (raw CH, ACCH,

CHB800-60 and ACHB800-60) increased from 0.5 g to 2.5 g, the oil

sorption capacity decreased with a corresponding increase in oil

removal efficiency. The reason for the observed decrease in oil

sorption capacity may be due to the overlapping or aggregation of

active adsorption sites while the observed increase in oil removal

efficiency may primarily be attributed to an increased surface area

and the availability of more active adsorption sites [9]. Yusof et

al. [17] and Nwadiogbu et al. [9] have correspondingly reported

similar observation for the use of esterified coconut coir (0.2 – 1

g) and acetylated corncob (0.5 – 2 g) in oil spill removal.

1. From Table 3, it can be seen that ACHB800-60 relatively

displayed the highest rate of sorption with a higher rate constant

(k) of 0.256 min . This was closely followed by that of CHB800-

-1

60 (k = 0.249 min ), ACCH (k= 0.231 min ) and raw CH (k =

0.201 min ), respectively. Similarly, the pseudo-second-order

kinetic model can be expressed as presented in Eq. (4) [58]:

q_tk₂q_eq_e



(4)



-1

where k is the pseudo-second-order rate constant (g/g.min ) and

is the theoretical equilibrium sorption capacity (g/g) both of

which can be calculated from the slope and intercept of the linear

plot of t/q versus t (plot not shown). The values of the constants

.8 Effect of oil weathering number of days

Oil weathering is the sum of the physical and biological

-1

are presented in Table 3. The initial sorption rate h (g g min )

processes acting on oil, which change the chemical composition

and physical properties, such as viscosity, over time [57]. The

quantity of oil respectively adsorbed by raw CH, ACCH, CHB800-

was calculated from the following equation:

^h^^k^qe

(5)

and ACHB800-60 as a function of the number of days of oil

subjection to weathering effect is presented in Figure 6.

It can be seen that the oil sorption capacity as well as the oil

removal efficiency relatively decreases with increase in the

number of days that the oil was subjected to weathering effect.

That is, the sorption capacity and removal efficiency displayed by

all the sorbents (raw CH, ACCH, CHB800-60 and ACHB800-60) was

higher for un-weathered crude oil than for the weathered oil. This

observation may be attributed to increase in the viscosity of oil as

the number of days for oil weathering increases. This observation

is in agreement with the observation reported by Sidik et al. [38]

for the use of lauric acid-modified oil palm leaves in the removal

of oil not exposed to air (un-weathered oil) and the one exposed

to air for 7 days (i.e. 7-days weathered oil). Nguyen and Pignatello

Table 3 shows that the pseudo-second-order kinetic model

equation provided a good fit to the remediation kinetics data

based on the high values of the regression coefficient (R ) which

were close to 1. The R values of the pseudo-second-order kinetic

model equation obtained for raw CH, ACCH, CHB800-60 and

ACHB800-60 were 0.9577, 0.9805, 0.9872 and 0.9946,

respectively. The results in Table 3 revealed that ACHB800-60

exhibited the highest initial sorption rate of oil with

.568 g/g.min and a faster rate of sorption with k value of 0.078

g/(g.min) than the other sorbents. This was relatively followed by

that of CHB800-60 (h = 4.812; k = 0.055), ACCH (h = 3.797; k =

.044) and raw CH (h = 1.336; k

value of

= 0.038), respectively. The R

[24] have also reported similar observation that weathered crude

value of pseudo-second-order kinetic equation obtained for raw

CH, ACCH and CHB800-60 was higher than that of its pseudo-first-

order kinetic equation (i.e., 0.9427, 0.9641 and 0.9807) and there

oil (chocolate mousse) was less absorbed by maple wood biochars

and commercial biochars when compared with un-weathered

crude oil. However, Hussein et al. [18] using barley straw and

Alaa Eldin et al. [13] using banana peels have respectively

reported increased sorption for 1-day and 7-days weathered heavy

crude oil.

e e

exist a very good agreement between q (theoretical) and q

experimental) which suggest that the pseudo-second-order

(

kinetic model provided a better fit to the oil remediation kinetic

data of raw CH, ACCH and CHB800-60, respectively.

Thus, the removal of oil spill by raw CH, ACCH and CHB800-

follows a pseudo-second-order kinetics. This is in agreement

with the observation made for the use of fatty acid-modified

banana trunk fiber [59], esterified coconut coir [17], human hair

15], fatty acid-modified pomelo peel [14] and lauric acid-

.9 Adsorptive remediation (sorption) kinetic studies

Sorption kinetics helps in predicting the rate at which sorption

takes place as well as assist in designing and optimising full-scale

applications [15]. Sorption kinetic models of Lagergren pseudo-

first-order, pseudo-second-order and intraparticle diffusion

models were applied to the remediation kinetics data to analyze

the rate and mechanism of crude oil sorption by raw CH, ACCH,

CHB800-60 and ACHB800-60. The Lagergren pseudo-first-order

kinetic model is expressed as given in Eq. (3) [58]:

[

modified oil palm leaves [38] in the removal of oil spill. While

the R value of pseudo-first-order kinetic equation (i.e., 0.9976)

obtained for ACHB800-60 is relatively higher than its pseudo-

second-order kinetic model equation (i.e., 0.9946) and there also

exist a very good agreement between q (theoretical) and q

e e

experimental) which indicates that pseudo-first-order kinetic

model provided a better fit to the kinetic data. Therefore, the

removal of oil spill by ACHB800-60 follows a pseudo-first-order

kinetics. This is in agreement with the observation of Nwadiogbu

et al. [9] for the use of raw and acetylated corncob. The transport

of oil from the aqueous phase to the sorbent surface and then its

diffusion into the interior of porous particles can be described by

Weber-Morris intraparticle diffusion model.

(

ln(q  q )  lnq  kt

(3)

where q

and q

are the quantities of crude oil sorbed at time

(s)

and at equilibrium, respectively, in g/g. is the pseudo-first-order

rate constant (min ) which can be determined from the slope of

the linear plots of ln(q -q ) versus t (plot not shown). The values

of the constants are presented in Table 3. The results presented in

Table 3 shows that the pseudo-first-order kinetic model equation

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

Table 3: Pseudo first-order, pseudo second-order, intra-particle and correlation coefficients obtained for the removal of crude oil from

marine water by raw CH, ACCH, CHB800-60 and ACHB800-60

Kinetic Model

Pseudo first-order

Parameter

Raw CH

0.201

ACCH

0.231

CHB800-60

0.249

ACHB800-60

0.256

_m_i_n-1₎

(

q_e

5.71

5.0

9.43

9.63

9.31

theo.) (mg/g)

exp)

8.42

8.75

9.35

0.9427

0.9641

0.9807

0.9974

Pseudo second-order

.038/0.049 0.044

0.055

0.078

k₂

q_e

(

g/(g.min))

5.74

5.00

1.336

9.29

8.42

9.45

8.75

9.85

(

theo.) (mg/g)

exp)

(

3.797

4.912

0.9872

7.568

0.9946

.9577

0.9805

Weber-Morris Intraparticle diffusion

(

mg/(g min⁰^.⁵))

1.45

2.43

2.59

2.74

K_p

0.3514

0.2942

0.9891

0.1677

0.9943

0.2091

0.9946

.9555

Weber-Morris Intraparticle Diffusion

t (min)

Raw CH Experimental Data

ACCH Experimental Data

ACHB-800-60 Experimental Data

CHB-800-60 Experimental Data

Figure 7: Application of Weber-Morris intraparticle diffusion to the sorption kinetic data of modified coconut husk

The model can be expressed as presented in Eq. (6) [58]:

intraparticle diffusion begins to decrease due to the extremely low

sorbate concentrations in the aqueous phase [60, 61]. This

q  K t C

(6)

observation is confirmed by the high

and a non-zero intercept

results obtained for raw CH, ACCH and CHB800-60 and ACHB800-

₆₀, respectively, as presented in Table 3. The high regression

suggest the existence of an intraparticle diffusion mechanism for

the sorption of crude oil by raw CH, ACCH and CHB800-60 and

ACHB800-60. Also, the presence of the intercept C (boundary layer

effect) confirmed the existence of film or surface sorption and

thus indicating that intraparticle diffusion was not the only rate-

controlling or determining step.

where K

is the intra particle diffusion rate constant (mg/g min )

is the intercept. The intercept of the plot indicates the

boundary layer effect and its magnitude determines the degree of

the surface sorption contribution in the rate determining step. K

and

can be determined from the slope of the plot of q

vs. t

Intraparticle diffusion becomes the sole rate determining step if

the plot passes through the origin [58]. In fact, the linear plots did

not pass through the origin and given the multilinearity of these

plots for oil removal by raw CH, ACCH and CHB800-60 and

ACHB800-60, this suggests that oil removal occurred in three

phases as shown in Figure 7.

The first steeper linear phase represents film or surface

diffusion, the second linear phase represents intraparticle or pore

diffusion and the third phase is final equilibrium stage where

.10 Sorption isotherms

The fundamental requirements for the design of adsorption

systems are the sorption isotherms. Sorption isotherm depicts at

constant temperature the equilibrium correlation or relationship

that exist between the quantity of sorbate in the liquid phase and

that on the surface of the sorbent [61]. A number of two, three or

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

four–parameter sorption isotherm models have been developed to

describe equilibrium relationships in adsorption systems. In this

present study, two-parameter models of Langmuir, Freundlich,

and Temkin were used to analyze the equilibrium data. The linear

form of Langmuir isotherm model is as given in Eq. (7):

The Freundlich isotherm model is normally applied to non-

ideal sorption on heterogeneous surfaces where binding sites are

not equivalent or independent [61]. The linear form of this

isotherm model can be expressed as presented in Eq. (8) [58]:

(

lnq  ln K 1 nlnC_e

(



^^qmax

q b C

^qe

max

where K

and n are Freundlich constants that roughly gives an

indicator of the adsorption capacity (mg/g) and the intensity of

sorption. The constants can be estimated from the slope and

intercept of the linear plot of lnq versus lnC .

where qmax and b are Langmuir isotherm constants. (mg/g) is the

maximum monolayer sorption capacity of the sorbent (mg/g), b

(L/mg) is related to energy of adsorption, which quantitatively

The values of the constants are presented in Table 4. The

obtained for raw CH, ACCH, CHB800-60 and ACHB800-60 are

.9806, 0.9896, 0.9966 and 9972, respectively and these values

represents the binding affinity between the sorbent and the

sorbate. The qmax and b can be determined from the linear plot of

^qe vs. ¹^Ce . The determined values of the Langmuir constants

indicates that the Freundlich isotherm provided a good fit to the

sorption equilibrium data. Values 1 < n < 10 or 1/n < 1 indicates

favourable sorption [61]. In this study, the values 1/n for raw CH,

ACCH, CHB800-60 and ACHB800-60 are 0.468, 0.318, 0,325 and

0.293, respectively, which indicates a favourable sorption of oil

are presented in Table 4.

As seen in Table 4, the R values are 0.9950, 0.9805, 0.9850

and 0.9868 for raw CH, ACCH, CHB800-60 and ACHB800-60

respectively, indicating that the Langmuir isotherm provided a

good fit to the sorbents equilibrium data. It can apparently be said

that when b > 0, sorption system is favorable [58]. In this study,

b was found to be 0.286, 4.33, 1.86 and 3.74 L/mg for raw CH,

ACCH, CHB800-60 and ACHB800-60, respectively. The value of qmax

obtained for ACHB800-60 (16.84 g/g) was found to be relatively

higher than the other sorbents used in this study. This was closely

followed by that of CHB800-60 (16.10 g/g), ACCH (15.06 g/g) and

raw CH (12.11 g/g), respectively. The qmax values obtained in this

study are relatively comparable with the values obtained for the

use of other adsorbents. Sathasivan and Mas Haris [59], Okiel et

al. [55], Uzoije et al. [62], Sidik et al. [38], Asadpour et al. [63],

Ifelebuegu et al. [15], Yusof et al. [17] and Elkady et al. [64]

correspondingly obtained qmax values of 0.149-0.476 g/g; 0.00712

g/g; 0.0014 g/g, 0.00172 g/g; 3.33 g/g, 4.226 g/g; 15.3 g/g; and

and their corresponding K

(g/g) (L/g). Smaller the values of 1/n, the higher the affinity

between sorbate and sorbent [55]. The K values which roughly

values are 3.32, 9.11, 10.24 and 13.10

indicates the sorption capacity revealed that ACHB800-60 had a

higher performance or sorption in comparison with the other

sorbents. This was relatively followed by CHB800-60, ACCH and

raw CH, respectively. The K : 1/n values obtained in this study

are relatively comparable with the values obtained for the use

other adsorbents. Sathasivan and Mas Haris [59], Okiel et al. [55],

Uzoije et al. [62], Sidik et al. [38], Asadpour et al. [63], Ifelebuegu

et al. [15] and Elkady et al. [64] correspondingly obtained K : 1/n

values of 0.028-0.25 g/g:0.385-0.779; 10.37 mg/g:0.658; 0.0055

g/g:0.641; 1.72 mg/g: 0.719; 0.0224-0.0340 g/g:, 1.477 g/g:

0.420; and 0.2751 g/g:0.926 for the use of fatty acid-modified

banana trunk fiber, powdered activated carbon, groundnut shell-

activated carbon, lauric acid-modified oil palm leaves, fatty acid-

modified mangrove bark, human hair and water hyacinth-derived

Nano-activated carbon in the removal of oil from water

respectively.

6.4 g/g for the use of fatty acid-modified banana trunk fiber,

powdered activated carbon, groundnut shell-activated carbon,

lauric acid-modified oil palm leaves, fatty acid-modified

mangrove bark, human hair, esterified coconut coir and water

hyacinth-derived Nano-activated carbon in the removal of oil

from water respectively.

Table 4: Adsorption isotherm parameters and correlation coefficients for the adsorption of crude oil by raw CH, ACCH, CHB800-60 and

ACHB800-60

Isotherm Model

Langmuir

Parameter

Raw CH

12.11

ACCH

15.06

CHB800-60

16.10

ACHB800-60

16.84

q_m_a_x(g/g)

b₂(L/g)

0.286

0.9950

4.33

0.9805

1.86

0.9850

3.74

0.9868

Freundlich

Temkin

(

g/g)(L/g

3.32

9.11

10.24

0.325

13.10

0.293

K _f

.468

0.318

0.9806

0.9896

0.9966

0.9972

.379

.846

.8851

16.08

3.291

0.766

18.51

3.546

0.7104

44.49

3.478

0.7243

(L/g)

b_T(kJ/mol)

0.9885

0.9816

0.9925

0.9972

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 694-707

Temkin isotherm can be represented in its linear form as [58]:

sorbent dosage and oil weathering. The rate of oil sorption by raw

CH, ACCH and un-activated CHB800-60 respectively follows a

pseudo-second order kinetics while activated CHB800-60 follows a

pseudo-first order kinetics. The sorption of oil by occurs via

surface and pore diffusion mechanisms. Freundlich isotherm can

be used to best describe the sorption behavior of ACCH, CHB800-

q  Bln A  BlnC_e

(

B A

where is related to the heat of sorption, is the equilibrium

binding constant (L/min) which corresponds to the maximum

and ACHB800-60 while Langmuir isotherm best describes the

sorption behavior of raw CH. The degree of oil removal

performance by these sorbents follows this order: ACHB800-60

binding energy. C

equilibrium (g/L), q

equilibrium (g/g),

degree Kelvin and R, the ideal gas constant (8.314×10 KJ mol^-¹

is concentration of the adsorbate at

is the amount of sorbate sorbed at

= ^R^T^bT where T is the temperature in

CHB800-60 > ACCH > raw CH. Coconut husk and its modified

forms has very strong potential for utilization as effective, low-

cost and eco-friendly alternative sorbents for oil spill remediation.

K ) and, b

from the linear plot of q

ACCH, CHB800-60 and ACHB800-60 are 0.9885, 0.9816, 0.9925 and

972, respectively and these values indicates that the Temkin

isotherm also provided a good fit to the sorption equilibrium data.

The values of and b are given in Table 4. As presented in

and

are constants.

and

can be determined

vs. lnCe. The R

obtained for raw CH,

Acknowledgment

The authors sincerely thanked the technical staff of

Thermosteel Laboratories, Warri, Delta State of Nigeria for the

provision of the facilities that were used for the physical and

chemical and analyses carried out on the contaminated marine

water and adsorbent.

Table 4, it is seen that the constant A value for ACHB800-60 (44.49

L/g) is higher than the values obtained for other sorbents. This

shows that ACHB800-60 had greater binding to the oil and greater

oil removal than other sorbents. This was followed by that of

CHB800-60 (18.51 L/g), ACCH (16.08 L/g) and raw CH (2.379

Ethical issue

Authors are aware of, and have complied with the best

practice in publication ethics specifically with regard to

authorship, dual submission, and manipulation of figures,

competing interests and compliance with policies on research

ethics. Authors have adhered to publication requirements that this

submitted work is original and has not been published elsewhere

in any form of language.

L/g), respectively. The lower values of b (< 8 KJ/mol) indicate

that the interaction between crude oil and each of the sorbent (raw

CH, ACCH, CHB800-60 and ACHB800-60) was weak. Hence, the

sorption process of crude oil onto raw CH, ACCH, CHB800-60 and

ACHB800-60 can respectively be expressed as physical sorption as

indicated by the value of b .

As shown in Table 4, it is observed that the R values obtained

for the application of Freundlich isotherm to the sorption

equilibrium data of ACCH, CHB800-60 and ACHB800-60 is

relatively higher than the corresponding values obtained for

Langmuir and Temkin isotherms. Thus, the results revealed that

the Freundlich isotherm model is more suitable for describing the

sorption of crude oil by ACCH, CHB800-60 and ACHB800-60,

respectively, than the Langmuir isotherm model. That is, the

sorption of crude oil onto ACCH, CHB800-60 and ACHB800-60

occurred on heterogeneous binding sites with non-uniform

distribution of energy. This observation is in agreement with the

results reported for the use of fatty acid-modified banana trunk

fibers [59], lauric acid-modified oil palm leaves [38], leaves and

root of Pistia stratiotes [65], acetylated kapok fibers [66] and

human hair [15] in the removal of oil from aqueous phase,

Competing interests

The authors wish to declare that there is no conflict of interest

in this research work.

Authors’ contribution

All the authors of this study have completely contributed to

the data collection, data analyses and manuscript writing.

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