investigation on the effect of nano-photo …environmental friendly. recently, reverse osmosis (ro)...

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INVESTIGATION ON THE EFFECT OF NANO-PHOTO CATALYSIS USING SOLAR

ENERGY AS A PRE-TREATMENT FOR REVERSE OSMOSIS DESALINATION

PROCESS

MUNA SALIM SAID ALFOORI1, SHAIK FEROZ2, VARGHESEM J3, MURTUZA ALISYED4

& NAGESWARA RAO LAKKIMSETTY5

1,3,4,5Department of Mechanical & Industrial Engineering, College of Engineering, National University of Science and

Technology, Sultanate of Oman

2Prince Mohammad Bin Fahd University, Al Khobar, Kingdom of Saudi Arabia

ABSTRACT

Sultanate of Oman is experiencing rapid increase in water demand due industrialization and population growth.

Desalination contributes nearly 35-40% of water demand in Sultanate and almost all desalination plants are based on

conventional energy sources. Due its abundance availability throughout the year in Sultanate of Oman use of solar

energy in desalination is a right choice. The efficiency of solar photocatalysis for the treatment of pollutants present in

saline water was investigated. Zinc oxide (ZnO), Nano photocatalyst in the presence of polyamide (PA) were used under

direct sunlight in batch process. The degradation of pollutants present in saline water was evaluated through various

parameters, total organic carbon (TOC), dissolved oxygen (DO), total dissolved solids (TDS), pH, and salinity.

KEYWORDS: Nano Photocatalysis, ZnO, Polyamide, Seawater Treatment & Solar Energy

Received: Jun 08, 2020; Accepted: Jun 29, 2020; Published: Sep 15, 2020; Paper Id.: IJMPERDJUN20201234

1. INTRODUCTION

Most of the countries in Middle East and North Africa (MENA) including Sultanate of Oman were having extensive

advantage to utilize sunlight in many industrial processes including reverse osmosis [Al Barwani et.al.,]. The

membrane reverse osmosis (RO) process is very sensitive to contaminations present in feed water, which makes the

pre-treatment step very significant to ensure maximum efficiency. In Reverse osmosis process, there is scope to use

photocatalysis as a pre-treatment step.The photocatalytic reaction is comparatively lesser in cost as it only needs

photons/light, catalyst, and air for the reaction to take place. Compared to the normal catalyst, Nano photocatalyst

has more photocatalytic activity due its larger surface area for contacting between the reactants.The Nano size of the

photocatalyst will decrease the time needed for the carrier diffusing out of the photocatalyst pours to the

photocatalyst surface [Adel Gastli].Photocatalysis has recently become a common word and different products using

photocatalytic functions have been commercialized due to high photo sensitivity, non-toxic in nature, low cost, and

environmental friendly. Recently, reverse osmosis (RO) become the most widely accepted method for desalting

seawater. It is the most economical method of removing 90% to 99% of contaminants, but it has disadvantage of

shortcoming including lack of ability on filtering substances that are less dense than water such as trace elements and

organic compounds.

Many studies have been conducted on different applications of metal oxide semiconductors for

environmental remediation such as wastewater treatment. When a photocatalyst exposed to the sunlight or

Orig

ina

l Article

International Journal of Mechanical and Production

Engineering Research and Development (IJMPERD)

ISSN (P): 2249–6890; ISSN (E): 2249–8001

Vol. 10, Issue 3, Jun 2020, 12933-12946

© TJPRC Pvt. Ltd

12934 Muna Salim Said Alfoori, Shaik Feroz, Varghesem J, Murtuza Alisyed

& Nageswara Rao Lakkimsetty

Impact Factor (JCC): 8.8746 SCOPUS Indexed Journal NAAS Rating: 3.11

illuminated light source like fluorescent lamps, it will absorbultraviolet (UV) radiation and produce pairs of electrons and

holes. The electron of the valence band of photocatalyst becomes excited. The excess energy of this excited electron

promoted the electron to the conduction band of photocatalysis therefore creating the negative-electron (e-) and positive-

hole (h+) pair. This stage is referred as the semiconductor's 'photo-excitation' state. The energy difference between the

valence band and the conduction band is known as the 'Band Gap'. The positive hole can oxidize the pollutant directly or

oxidize water to form (HO.) radicals. At the same time, the electron reduces the oxygen adsorbed to the photocatalyst,

which prevents the combination of electrons and the positive hole [R. Al-Rasheed et.al., D. Bahnemann et.al., and S. Feroz

et.al]. Equations 1 to 5 and Figure 1 represent the photocatalytic mechanism.

Photocatalyst e-+ p+ (1)

e- + O2O2- (2)

p++ Organics CO2 (3)

p++ H2O HO. + H+ (4)

HO. + Organics CO2 (5)

Photocatalytic reaction breaks down the pollutant molecules without any residue thereby eliminates the need of

the removing sludge to landfill. The other advantage is that the catalyst lasts for long time and there is no need for adding

chemicals in the process, which makes the operation simple and economical.

Figure 1: Mechanism of Photocatalysis.

Seawater consists predominantly of water with various materials dissolved within it. Major 5 groups of solutes in

seawater namely., constituents (the salts), nutrients, gases, trace elements and organic compounds. These substances

adversely affect and damage the membrane in reverse osmosis process, these has to be removed from the feed water before

they enter the membrane system. Several previous studies have been reported the oxidation of contaminants by the

integration of two or more AOPs (suchas ZnO/TiO2, ZnO/Fenton/sunlight and TiO2/Fenton). Anju et al., stated that the

removal % of phenol for thecombination of ZnO/TiO2 process was enhanced from 37to 46% at 1.5hrs in aqueous solutions

after using H2O2 with it. Tonyet al., presented that an COD removal by using ZnO/Fenton/UV in the diesel oil-water

mixture was 66%, while the CODremoval % was 84% by using TiO2/Fenton/UV under similar settings due to the surface

area of ZnO<TiO2. Zarei et al.,reported that the elimination % of phenol by using photo electro-Fenton/Mn2+/TiO2 at 150

min from aqueous solutions was 69.35%. Duran et al., investigated that TiO2 dosage and pH in the TiO2/Fenton/Solar

process were the keyelements that affected the blue 4 dye removal, while Nogueira et al., reported that TiO2 dosage were

Investigation on the Effect of Nano-Photo Catalysis Using Solar Energy 12935

as a Pre-Treatment for Reverse Osmosis Desalination Process


less significant than that of iron and H2O2 in DCA removal. Kim et al. investigated that the TiO2/Fe3+ /H2O2/UV process

increased organic matter removal at pH 6.5 to 7.5 and improved the reactivity of the oxidant.

Experimental investigations carried out by R. Al-Rasheed et.al., have proved that photocatalysis got the ability in

oxidizing the pollutants, which are present in seawater in a way that can improve the membrane life. The present study has

been carried out to investigate environmentally friendly and effective solution for the removal pollutants present in saline

water. By harnessing the solar energy through photocatalysis to degrade the contaminants present in seawater using ZnO

and polyamide was studied.

2. MATERIALS AND METHODS

Seawater was collected 1 km from Al Seeb beach, Oman. PA was obtained from from Carl Roth GmbH Company,

Germany and ZnO nano powder is obtained from mkNano, Japan.A transparent borosilicate glass cylindrical tube reactor

of dia 0.10 m, thickness 0.0025 m and a length 0.40 m was used as photocatalytic batch reactor. A magnetic stirrer also

used to ensure no settling of ZnO particles at the bottom of the reactor and provide a turbulence. Figure 2 shows the

schematic diagram of the experimental set-up. Shimadzu, Japan make TOC–LCPH/CPN total carbon analyzer was used for

TOC analysis of the samples. The COD was analyzed by using the Chemetrics COD HR 2200 Analyzer. TDS, and pH

were analyzed by Eutech make waterproof cyber scan PCD 650 water analysis kit.

Figure 2: The Schematic Diagram of Experiment Setup.

1.5 L of seawater was used for each experiment with different concentrations of ZnO (1.0 to 5.0g) and Polyamide

(0.5 to 2.0g). Table 1 shows a sample of seawater analysis data. However, for each trail of experiments the seawater was

analyzed and the data was recorded. The percentage reduction of parameters was estimated using equation 6 [Murtuza et

al].

Percentage removal efficiency = (𝐶𝑜− 𝐶𝑓)

𝐶𝑜𝑥100 (6)

Where, c0 and cf are the initial and final concentrations in mg/L respectively.




Table1: Seawater Analysis Data

Parameter Value

pH 7.96

Conductivity, mS 54.22

Salinity,ppm 34,200

Turbidity, NTU 1.60

Dissolved Oxygen, ppm 5.38

Total Dissolved Solids (TDS), ppm 53,200

Chemical Oxygen Demand, (COD), ppm 5.0

Biological Oxygen Demand (BOD), ppm 2.0

Total Organic Carbon, ppm 2.94

Total Inorganic Carbon, ppm 23.2

E-coli ND

The reason to choose polyamide along with photocatalyst zinc oxide was due the fact that most of the membranes

were manufactured using PA and pollutants struck to the membranes, thereby forms scaling.Hence, the research was made

to study the effect of photocatalyst degradation in the presence of PA. After a proper mixing of the chemicals and seawater

with initial sample and the reactor was exposed to the sun light as shown in figure 2. The entire experimental analysis was

conducted at National University campus from 10:00 am to 3:00 pm. In most parts of Oman, clear sunny weather is

experienced 250 to 300 days a year, this makes Oman a suitable site for the solar-based treatment processes. The solar

radiation intensity was 650 W/m2 and UV-index from 9 to 11 during maximum experimental runs.

3. RESULT AND DISCUSSIONS

3.1 Effect of Concentration of Photocatalyst

The samples collected for each experiment were analyzed, where the concentration of ZnO varies from 1.0 to 5.0g. Figure

3 shows the % reduction of TOC with time for various concentrations of ZnO. It was observed that with increase in the

ZnO concentration the TOC reduced appreciably, this may be due to the fact that more photocatalyst active sites are

available for the production of hydroxyl radicals, which in turn oxidizes the organic pollutants present in the seawater. A

maximum of 35% reduction in TOC was observed for 5 g dosage of ZnO.

Figure 3: % Reduction of TOC at Various Concentrations of ZnO.

The % reductions of COD at concentrations of ZnO (1.0 to 5.0g)were shown in figure 4. It was observed similar

trends as that of TOC and a maximum of 75% reduction in COD was achieved for higher dosage of ZnO. The maximum %




reduction was with respect to 4 hours of irradiation in the presence of direct sunlight.

Figure 4: % Reduction of COD at Various Concentrations of ZnO.

The variations of total dissolved solids (TDS) and pH with respect to reaction time are shown in Figure 5 and 6.

The % reduction of TDS increases with increase in exposure time for various concentrations of ZnO with marginal effect

on dosage of photocatalyst. pH decreases with increase in exposure time, which may be due to formation of mineral acid

by-products during the photocatalytic process.

Figure 5: % Reduction of TDS at Various Concentrations of ZnO.




Figure 6: Variation of pH at Various Concentrations of ZnO.

3.2 Effect of Various Concentration of Photocatalyst with PA

Another set of experiments were carried out by adding various concentrations of polyamide (PA) in the solution to test its

effect on photocatalytic degradation of pollutants. Three sets of experiments were carried out with 0.5g, 1.5g and 2.0g of

PA respectively.

Figure 7: % Reduction of TOC at Various Concentrations of ZnO and 0.5 g of PA.

The photocatalytic performance in the presence of PA slightly reduced when compare to the presence of

photocatalyst alone. This may be due to the fact that PA particles limit the mass transfer rate of pollutants towards

photocatalyst and also it might hinder the excitation of ZnO particles, thereby reducing the formation of oxidizing hydroxyl

radicals. Figure 7 shows the % reduction of TOC at concentrations of ZnO (0.5 to 5.0g) with 0.5 g of PA and a maximum

reduction of 30% was observed.





Figure 8 and 9 shows the percentage reduction of TOC for concentration of ZnO (1.0 to 5.0g) in the presence of

1.5g PA and 2.0g PA, respectively. A maximum reduction of 25% and 20% was observed in TOC, respectively.


Figure 10 to 12 shows the percentage removal of COD at various concentrations of ZnO and 0.5, 1.5 and 2.0g of

PA. The trends are similar to the TOC with lower percentage removal of COD in the presence of PA compare

photocatalyst alone.

0

5

10

15

20

25

0 1 2 3 4 5

% R

educt

ion o

f T

OC

Time, hr

1g ZnO + 2.0 PA

2g ZnO + 2.0 PA

3g ZnO + 2.0 PA

4g ZnO + 2.0 PA

5g ZnO + 2.0 PA




Figure 10:% Reduction of COD at Various Concentrations of ZnO and 0.5 g of PA.

Figure 11: % Reduction of COD at Various Concentrations of ZnO and 1.5 g of PA.




Figure 12: % Reduction of COD at Various Concentrations of ZnO and 2 g of PA.

Figures 13 to 15 shows the variation of pH with various concentrations of ZnO for the dosage of 0.5g,1.5g and 2g

of PA, respectively. The pH keeps on decreasing with reaction time as it was observed in ZnO alone, which may be due to

formation of mineral acids as by-product.

Figure 13: Variation of pH at Various Concentrations of ZnO and 0.5 g PA.

Figure 14: Variation of pH at Various Concentrations of ZnO and 1.5 g PA.




Figure 15: Variation of pH at Various Concentrations of ZnO and 2 g PA.

CONCLUSIONS

The results showed the ability of photocatalysis in the treatments of pollutants present in seawater.It was found that the

optimum exposure time of photocatalytic reaction under solar radiation was within 2 hours for the most experiments.The %

reduction of TOC and COD slightly decreased in the presence of PA when compared to ZnO alone. pH of the solution

dropped continuously during reaction time, which may be attributed to formation of mineral acids. The presence of

chloride ions leads to scavenging of hydroxyl radicals and hence overall efficiency of the process is on lower side. Also,

the ZnO photocatalyst is considered to be not stable in aqueous medium.

ACKNOWLEDGMENT

The authors would like to acknowledge the financial support received from The Research Council, Oman through grant

number 83 (ORG/EI/12/003).

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AUTHOR’S PROFILE

Muna Salim Said AL Foori1Completed M.Sc Process Engineering from National University of Science and Technology

in Mechanical and Industrial Engineering department

Prof. Dr. Shaik. Feroz is presently working as Professor at Prince Mohammad Bin Fahd University, Al Khobar, Kingdom

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https://www.researchgate.net/publication/342546376_Investigation_of_epoxy_resinnano-TiO_2_composites_in_photocatalytic_degradation_of_organics_present_in_oil-produced_water

https://www.researchgate.net/publication/342546376_Investigation_of_epoxy_resinnano-TiO_2_composites_in_photocatalytic_degradation_of_organics_present_in_oil-produced_water

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of Saudi Arabia. He has obtained his doctorate in the field of Chemical Engineering from Andhra University, India and

Post Doc Research Fellow from Leibniz University, Germany. He has worked with various organizations for about 25years

which includes 5 years of Industrial and 20 years of teaching and research experience. Professor Feroz has more than 150

publications to his credit in journals and conferences of international repute. He is a life member of Indian Institute of

Chemical Engineers and Institution of Engineers, India. He is also a member of Oman Society of Engineers and

Environmental Society of Oman. Professor Feroz is associated as the Principal Investigator/CO-Investigator to a number of

research projects and also involved as “Technology transfer agent” by Innovation Research Center, Sultanate of Oman. His

has a significant contribution as Editorial member and peer reviewer for various reputed international journals and

conferences. He was awarded “Best Researcher” by the Caledonian College of Engineering for the year 2014. Professor

Feroz developed research links with various international research centers and his research interest includes solar nano-

photocatalysis, solar desalination, solar photocatalytic hydrogen production and environmental engineering.

Mr. Varghese M J is presently working as Senior Research Assistant at Centre for Creativity and Innovation, College of

Engineering, National University of Science and Technology, Sultanate of Oman. He is having more than 15 years of

teaching and research experience in the field of Nano photocatalysis and Water and wastewater treatment area.

Dr. Syed Murtuza Ali S. K. is presently working as Assistant Professor in Department of Mechanical & Industrial

Engineering. He has authored and co-authored multiple peer-reviewed scientific papers and presented works at many

national and International conferences. Dr. Syed Murtuza Ali S.K. contributions have acclaimed recognition from

honorable subject experts around the world and actively associated with different societies and academies. Dr. Syed

Murtuza Ali S.K. research interests include Green Polymers and Composites, Interpenetrating Polymer Networks,

Biomaterials, Nanotechnology.

Dr. Lakkimsetty Nageswara Rao is presently working as Assistant Professor in Department of Mechanical & Industrial

Engineering (Chemical Engineering) & Programme Manager Masters- Chemical Process Engineering at College of

Engineering, National University of Science and Technology, Muscat, Sultanate of Oman. Dr. Rao has obtained his

doctorate in the field of Chemical Engineering from Sri Venkateshwara University, India in the year 2013. He has worked

with various organizations for 18 years which includes 6 years of research experience. Dr. Rao has 82 research




publications to his credit in journals and 65 conferences of International/ National repute. He is a life member of the

American Institute of Chemical Engineers, Indian Institute of Chemical Engineers, Institution of Engineers and I.S.T.E.

His has a significant contribution as a peer reviewer for various reputed journals. Dr Rao has interest includes advance

separation processes, Biochemical Engineering Nano-based treatment of wastewater & Environmental engineering

investigation on the effect of nano-photo …environmental friendly. recently, reverse osmosis (ro)...

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