Treatment of Dye Wastewater by Functionalization of Bentonite-Methylene Blue with Sodium Persulfate

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 2, Pages: 229-233

J. Environ. Treat. Tech.

ISSN: 2309-1185

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

Treatment of Dye Wastewater by

Functionalization of Bentonite-Methylene

Blue with Sodium Persulfate

&4*

2 3

, Parveen Fatemeh Rupani , Loh Kar Woon , Mohd Hafiz

4 2 2 3

Asha Embrandiri

Jamaludin , Mohd Azrul Naim , Jianzhong Sun , Weilan Shao and Suzy Ismail

- Faculty of Agro-Based Industry, University Malaysia Kelantan, Jeli Campus, Kelantan, Malaysia

- Biofuels Institute, School of Environment and Safety Engineering, Jiangsu University, Zhenjiang, China

- School of Chemical Engineering, Universiti Sains Malaysia, Nibong Tebal, Malaysia.

- Department of Biotechnology, Kulliyyah of Science, International Islamic University Malaysia, Kuantan, Malaysia.

Received: 21/02/2019

Accepted: 02/05/2019

Published: 01/06/2019

Abstract

Bentonite has been effectively used in many studies for the removal of methylene blue (MB) laden waste waters. This is

due to its high swelling ratio, good adsorptive properties and environmentally friendly characteristics. In spite of this,

prolonged use renders the BMB non-functional and cause for discard. Sodium persulfate (SPS), has been reported to be an

excellent flocculating agent for the functionalization of spent adsorbent due to some of its unique properties. In this study,

the functionalization of spent bentonite-methylene blue (BMB) adsorbent in dye wastewater treatment was carried out using

SPS at varying temperature conditions. Results revealed that the addition of SPS to MB-loaded adsorbent demonstrated

efficient adsorption, high flocculation efficiency as well as faster equilibrium (60 min). The BMB loaded adsorbent showed

5% removal efficiency up to three cycles. A plausible mechanism was proposed and discussed on the basis of the results.

Thus, exhausted BMB was found to be effectively used for treatment of coloured wastewater on an industrial scale.

Keywords: Bentonite; Methylene blue; Sodium persulfate; Dye wastewater; Functionalization.

of other industrial applications as well (9).

Introduction¹

Triarylmethane is also very useful in the laboratories for

staining purposes in microbiology and histo-pathological

techniques.

The textile industry utilises enormous volumes of

water as a medium range mill uses about 1.6 million

litres of water per day (1). Textile wastewater has

become a major cause of water pollution due to the

increasing the demand of textile products as well as the

utilization of synthetic dyes (2). Owing to the high

stability and extreme conditions, huge quantities of dyes

are not eliminated during conventional wastewater

treatment processes and remain in the ecosystem (3). Azo

dyes from the textile industry are reported to be

recalcitrant during their biodegradation and often

perceived as xenobiotic (4). In spite of this,

environmental legislation has made it mandatory for

industries to eliminate colour from their dye effluents

before discharge (5). Therefore, the textile industries

have received considerable attention in the recent years

In recent times low-cost adsorbents are being sought

after as the alternative for activated carbon in waste

water treatment (8, 10). These adsorbents are most often

natural materials, biosorbents and agricultural or

industrial waste materials. Amongst all other natural

materials, clay occupies a prominent position due to low

costs, easy availability, good sorption properties and

environmentally safe (10, 11). Adsorbents of clay origin

(diatomite, kaolinite, bentonite and fullers earth) are

utilized because of the presence of organic and inorganic

molecules (12). Bentonite, composed of montmorillonite

clay of the aluminum phyllosilicates group is a well-

known adsorbent used in wastewater treatment due to its

unique properties such as high porosity, surface area and

of high adsorption capacity (13, 14). The adsorption of

methylene blue on clay is controlled by the ion-exchange

processes. This implies that the adsorbing capacity

fluctuates with pH variation (15).

Removal of organic pollutants, phenol and dyes is

already an extensively studied area of waste water

research (16-18). However, investigation on regeneration

and recovery of adsorbed molecules on the adsorbent

surface is an area which needs to be explored. The reuse

of adsorbent is paramount to ensure an economical and

environmentally friendly process (19). Adsorbents can be

(6) with regards to effective removal methods.

Triarylmethane (triphenylmethane) a universally used

textile dye, makes up approximately 30%–40 % of the

overall dye consumption (7) and have been extensively

applied on wool, cotton, silk and nylon (8). It is used for

coloring food, paper, leather, plastics, waxes and a host

Corresponding author: Asha Embrandiri, Faculty of

Agro-Based Industry, University Malaysia Kelantan, Jeli

Campus, E-mail:

ashanty66@gmail.com. ORCID: 0000-0001-5038-3538.

Kelantan,

Malaysia.

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 2, Pages: 229-233

regenerated by chemical, thermal, solvent, and biological

methods (20). Regeneration is a method of adsorbent

recovery that ensures sustainable re-use of the bentonite

for at least 4 cycles. Regeneration or recyclability of low-

cost adsorbents is still not well-developed. Organic dyes

that are strongly adsorbed onto the adsorbent (bentonite)

is unfavourable for desorption. Sodium persulfate

of dye solution. Particle size of the flocs were determined

by a Zetasizer Nano Series (Malvern Instruments Ltd,

UK) and Hach pH meter for the pH measurements.

2.1 Preparation of solutions

Commercial grade cationic dye Methylene Blue

(MB) was used to prepare the stock solution ( 1.0 g of

MB in 1 L distilled water) and diluted to the required

concentrations at room temperature (27±2ºC).

Absorbance curve for different concentrations (0-

15mg/L) of dye were calibrated at 664 nm using UV-Vis

Spectrophotometer.

2 2 8

(Na S O ) (SPS), has been recently found to be a

potential remedy for regenerating the adsorbents in

textile effluents (21). It dissociates in water to form

persulfate anion (S

). The persulfate (PS) anion has a

redox potential ( E = 2.01 V) and is chemically

thermally activated to the sulfate radical (SO •), with a

stronger oxidant with redox potential, E = 2.4 V (22).

Persulfate has the potential to degrade organic

contaminants (ethylene blue) and the recovery of

bentonite to ensure its reusability and long term usage.

Most treatment processes involve advanced oxidation

processes (AOP) however, this study employed the

thermal activation of sodium persulfate to remove the

coloured pollutant (MB). Pollutants attached to bentonite

are expected to be fully degraded by this method which is

a significant contribution in the realm of coloured waste

water treatment.

2.2 Decolourisation of Methylene blue in aqueous

solution

100mL of phosphate buffer (PBS) was prepared by

mixing Na

HPO

2 4 2

(3.2025 g) and NaH PO ·2H O

(5.3038g) to obtain a neutral pH. 100 ppm MB was

thereafter added to PBS (5 mL each) to attain the desired

concentration of each reactant at 70 °C. The

decolourisation of MB in the aqueous solution was

observed in 75 min.

2.3 Decolourisation of MBloaded bentonite

After adsorption of MB (1h), the MB-loaded

bentonite was centrifuged at 4000 rpm and transferred

into a beaker (250 mL). To 50 mL of PB stock solution,

Materials and methods

Figure 1 gives an annotated description of the

00ppm sodium persulfate (SPS) was added and

proposed method to be used in this experiment. The

chemicals used in this study were Methylene

immersed into a water bath at 70 °C. The decolourisation

of MB and regeneration ability of bentonite was tested at

four different conditions:

Blue[adsorbate], Bentonite[adsorbent], Sodium

persulfate (SPS) oxidant (Na ) of [99% purity],

Sodium dihydrogen phosphate dihydrate

NaH PO ·2H O) [>99% purity] and Di-sodium

hydrogen phosphate anhydrous (Na HPO ). The UV

2 2 8

S O

(

1) heated for 6 hours (#A1),

2) heated for 24 hours (#A2),

3) not heated (at room temperature) (#A3), and

4) as a control (without SPS into the bentonite loaded

(

visible spectrophotometer (HACH DR-5000 Hach,

Colorado, USA) was utilized to measure the absorbance

with MB at room temperature) (#A4).

Figure 1: A proposed Scheme for the adsorption of MB and coagulation on bentonite by the addition of SPS.

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 2, Pages: 229-233

.4 Modification of Bentonite with sodium persulfate

The same procedures were followed as above without

Initially, there was a reduction in the concentration of

MB (100 % at 0 min.) to 2.25 % (at 5 min.) which

gradually decreased. Up to 97.8%, color removal

the adsorption prior to the addition of SPS to identify

whether SPS can modify or activate raw bentonite to

efficiency of MB was attained in

5 min which

improve its performance on MB removal.

conditions were tested with raw bentonite: (1) heated

upto 70 °C (#B1) and (2) at room temperature (#B2) for

Two

corroborates other studies on the efficiency of adsorption

of MB onto bentonite. This is owing to the basic

structure of bentonite montmorillonite consisting of two

tetrahedrically aligned sheets of silicon ions surrounded

by an octahedrically synchronized sheet of aluminum

ions (13). This permits the isomorphous substitutions of

h. Then, the modified raw bentonite was put into MB

solutions (100 ppm).

3+ 4+ 2+ 2+

Al for Si in the tetrahedral sheet and Mg /Fe for

.5 Reusability of bentonite

The reusability study was carried out using 100 ppm

MB solution. The procedures were repeated for three

cycles.

Al in the octahedral sheet resulting in the negatively

charged surface of bentonite. Thus, MB is a cationic dye

that is adsorbed onto bentonite demonstrating a strong

affinity towards heteroaromatic dyes (24). Electrostatic

attraction between cations (dye molecules) and

negatively charged monmorillonite (anions) surfaces

result in the adsorption of MB onto bentonite. It also

occurs via cation exchange. (25). In the study, adsorption

of MB onto bentonite decreased over time, with the same

initial MB concentration (100 ppm) (Fig. 4). For all

samples the percentage removal of MB up to 99.9 % was

achieved after an hour. Interestingly, flocculation of MB

was observed instead and only adsorption for #A1, #A2,

and #A3. The bentonite and MB coalescence resulted in

the formation of flocs. After 10 min of stirring and 1h

settling, a colour was obtained. A clear solution was

obtained for each sample.

Results and Discussion

Degradation of methylene blue (MB) was examined

using thermally activated (SPS) and PBS at pH 7. The

results revealed complete decolourization of MB at 70°C

in 60 min. Decline in color efficiency of MB aqueous

solution with time (as shown in Fig. 2) demonstrated

almost 99.99 % removal capacity was achieved in 60

min. Concentration of MB from 60 to 75 min also

remained the same (99.99 % removal). As a result,

complete decolourisation took place in 1 h. Change in

colour of MB solutions during oxidation with SPS (100

ppm) at different times is shown in Fig. 3. The colour

variation covered trend as: dark blue > dark green > pale

green > yellow > colorless.

Figure 4: Adsorption of MB onto bentonite with respect to time.

On the other hand, no observable formation of flocs

was found for #A4. The bentonite and MB agglomerated

and settled down together, however, still remained in

powdery form. Figure 5 shows the transparent colour

solution when the flocs formed settled down at the

bottom of beaker for #A1, #A2, and #A3 whereas a

relatively bluish-clear solution for #A4 when powdery

bentonite and MB had settled down. There is aggregation

of MB and bentonite after the regeneration with SPS

which implies that the addition of SPS to bentonite led to

flocculation. Thus, the regeneration process with SPS

promotes the flocculation of bentonite and MB which is

explained by the high adsorptive capacity of bentonite

Figure 2: Concentration of MB in the aqueous solution with

respect to time. At time = 60 min, the concentration of MB is

almost equal to zero.

(13). Regeneration of bentonite with SPS occurs

superficially within the interlayers of bentonite (26). This

increases the quantity of MB adsorbed which results in

formation of bigger flocs-molecules. In addition, it also

involves charge neutralization among the individual

molecules which further enhances bonding between MB

and bentonite (27).

Figure 3: Change in colour of MB solution (100 ppm) by the

oxidation of SPS (100 mM) with respect to different times

showing complete decolourisation inr 60 min. Experimental

condition: pH ~ 7.0, Temperature = 70 °C.

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 2, Pages: 229-233

#A1

#A3

#A2

#A4

Figure 5: Treatments heated for 6 h

In the control (#4), the aggregation of the particles is

achieved by the swelling behaviour of bentonite, since

the surface is hydrophilic, large uptake of water between

The percentage removal for all cases was found

relatively same after (99.9 %) which is an

achievement in comparison with 85% after first cycle to

platelets can be explained (24, 27). Organic cation (MB )

47% after 4 cycle in Pandey’s study (15) using

has more affinity to attract negatively charged surfaces as

compared to water (26). The inorganic cations are

eliminated as a result of the substitution of the interlayer

bentonite beads. MB removal was still effective by using

the bentonite with SPS as the regenerating agent,

irrespective of the regenerating conditions (Fig. 6).

However, the control shows a drastic decrease in

percentage removal of MB from 99.9 % in the first cycle,

drops to 32.7 % in the second cycle and lastly to 12.4 %

in the third cycle. This proved that the SPS plays

significant role to enhance flocculation of MB and

bentonite until optimum dye adsorption.

cations with MB thus simultaneously removing the

water molecules. As a result, bentonite and MB were

weakly attracted and there was no formation of floc in

the control sample. They remained in powder form and

settled down at the bottom of beaker, giving a relatively

bluish-clear solution.

It can be inferred from Table 1 that bentonite and

MB in #A1 has the biggest floc size (5993±0.01nm)

among all whereas the size of particles in #A4 were the

smallest (2450 ± 0.06nm) owing to the formation of

powdery agglomerates instead of flocs. This indicates

that flocculation occurs only in MB-loaded bentonite

with SPS. However, based on the result obtained the floc

size in #A1, #A2, and #A3 ranges from 3000 – 6000 nm.

Conclusion

This is a preliminary study that highlighted the

regeneration ability of MB-loaded bentonite using SPS.

Regenerated bentonite has been effectively used for MB

removal in MB solutions. Flocculation of bentonite and

MB was observed instead of degradation of dye using

oxidation process. The process of adsorption and

flocculation was found to be very fast and equilibrium

was reached in 1 hour with 99% removal efficiency.

However, by last cycle the efficiency reduced to 12.4%.

This study proved that SPS has great potential in

extending the life of the bentonite loaded with MB.

Therefore, more studies need to be carried out to validate

all possible errors in the process. The study would go a

long way in reutilizing the MB-bentonite, thereby

ensuring sustainability in the textile waste water

treatment process.

Conflict of Interest

The authors have declared no conflict of interest.

Figure 6: Percentage removal of MB with SPS after three cycles

Acknowledgments

Mr Woon is grateful to Universiti Sains Malaysia

(USM) for the research facilities during his study period.

Table 1: Floc size of all samples (#A1- 4).

#A2

Sample

Floc Size (nm)

A1: heated for 6 hours

#A1

5993± 0.02

#A3

3678±0.08

A#4

2450±0.06

3084±0.01

A2: heated for 24 hours

A3: not heated (at room temperature)

A4: SPS not added (at room temperature) [serves as control]

Journal of Environmental Treatment Techniques

2019, Volume 7, Issue 2, Pages: 229-233

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