Organic Pollutants Removal from Petroleum Refinery Wastewater with Nanotitania Photo-catalyst and...

Journal of Innovative Engineering Dheeaa al deen A. Aljuboury et al., Journal of Innovative Engineering 2014, 2(3):5

Journal of Innovative Engineering ISSN: 2347-7504

Article Type: Research Article

Organic Pollutants Removal from Petroleum Refinery Wastewater with

Nanotitania Photo-catalyst and solar irradiation in Sohar Oil Refinery

Dheeaa al deen A Aljuboury1*

, Puganeshwary Palaniandy1, Hamidi Bin Abdul Aziz

1 and Shaik

Feroz2

1School of Civil Engineering, Universiti Sains Malaysia, Malaysia

2Caledonian College of Engineering, Oman

*Corresponding author: Dheeaa al deen A Aljuboury, School of Civil Engineering, Universiti Sains Malaysia,

14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia, Email: [email protected]

Received September 01, 2014; Accepted October 20, 2014; Published November 04, 2014

Citation: Dheeaa al deen A Aljuboury, Puganeshwary Palaniandy, Hamidi Bin Abdul Aziz and Shaik Feroz (2014)

Organic Pollutants Removal from Petroleum Refinery Wastewater with Nanotitania Photo-catalyst and solar

irradiation in Sohar Oil Refinery. Journal of Innovative Engineering 2(3): 5

Copyright: © 2014 Dheeaa al deen A Aljuboury et al. This is an open-access article distributed under the terms of

the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any

medium, provided the original author and source are credited.

Abstract

Nowadays, there are increasingly stringent regulations requiring more and more treatment of industrial effluents to

generate product waters which could be easily reused or disposed to the environment without any harmful effects. In

the present study, Photo-catalytic activities of Titanium dioxide (TiO2 P25) under sunlight processes are

investigated through laboratory experiments as an alternative to conventional secondary treatment for the organic

content reduction of high Chemical Oxygen Demand (COD) wastewater from Petroleum Refinery Wastewater plant

in Sohar Oil Refinery and develop a batch photo-catalytic reactor and continuous reactor under same condition and

evaluate their efficiency. This research addresses the photo degradation efficiency of Chemical Oxygen Demand

(COD) and Total Organic Carbon (TOC) and the generation of hydroxyl radicals using the Sunlight/TiO2 system.

All experiments are conducted to investigate the effects of parameters such as, catalyst dosage, initial concentration

of COD and TOC, initial pH and irradiation time under sunlight and also the industrial effluent is characterized.

Experimental results revealed that the photo-catalytic activity of the TiO2 for the COD removal efficiency is highest

with using 1gm/l TiO2 dosage. Optimization of catalyst dose, pH and COD concentration has been done. A

maximum COD removal of 85% from the effluent is achieved in 240 min. The percentage removal of TOC reaches

to a maximum for a catalyst loading of 1.5gm/L which is 18% in 300 minutes of reaction time period. It can be used

as a treatment step in the high organic wastewater treatment during the primary stage.

Keywords: Photo-catalysis; Sunlight; Hydroxyl radical; TiO2; COD degradation; TOC degradation

mailto:[email protected]



1. Introduction

Industrial wastes, sewage and a wide array of synthetic chemicals, pollute considerable parts of water resources. The

elimination of toxic chemicals from wastewater is presently one of the most important aspects of pollution control.

Recently, considerable attention has been focused on complete oxidation of organic compounds to harmless

products of CO2 and H2O by the advanced oxidation processes. Photo-catalysis is a promising technique for the

treatment of contaminated water and groundwater, which has been widely studied in recent years because it was fast,

effective, eco-friendly, economically viable and able to completely oxidize organic molecules at a low energy cost

[3]. In fact, many studies on photo-catalytic degradation of pollutants by TiO2 upon illumination with sunlight have

been reported. The solar photo-catalytic wastewater treatment is based on reactive free potent chemical oxidants

such as the hydroxyl radical [1]. Upon absorption of light energy that is equal to or greater than band gap energy, the

electrons in the valence band of the semiconductors such as TiO2 can be excited to those in the conduction band,

leaving a positive hole in the valence band [1]. The positive hole is a strong oxidant, which can oxidize compound

directly or react with the electron donors in the environment such as water or hydroxide ions to form hydroxyl

radicals (OH) that are also potent oxidants [1].

The aim of this paper is to develop a method of solar photo-catalytic oxidation of synthetic high organic waste water

in Sohar Oil Refinery, Oman by TiO2/Sunlight which it is investigated in batch reactor and continuous reactor under

same condition. Wastewater with a high COD of the order of more than 1000 mg/L is treated. The effects of

parameters like optimum catalyst doses, pH and actual initial concentration of COD have also been investigated. A

wide range of organic compounds are detected in high organic wastewater in Sohar Oil Refinery, so, the study will

lead to a possibility of implementation of solar photo-catalytic process as a treatment step for high organic

wastewater in Sohar Oil Refinery, Oman.

2. Experimental Procedure:

2.1 Materials and Methods

The laboratory tests are performed using the pretreated refinery wastewater samples (after coagulationand flotation

units) from Sohar Oil Refinery. The samples of raw effluent are collected from the point that the wastewater is just

leaving the dissolved air flotation (DAF) and just into the biological treatment unit in wastewater treatment plant at

Sohar petroleum refinery. The catalyst is TiO2 Aeroxide P-25 (manufactured by Evonik Industries Co in Germany),

and it is used for the photo-catalytic degradation and 150-ml beakers are used as batch reactors. A magnetic plate is

used to stir the TiO2-wastewater solution. All the photo-reaction experiments are performed under ambient

conditions on Caledonian College of Engineering campus, located in Sultanate of Oman. 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 during maximum experimental runs. All the

experiments are carried out in a concentrating solar collector with a parabolic trough reflector. The photo-reactor

used is two transparent borosilicate glass tubes with 38 mm internal diameter, 0.5 m length. The system is shown in

Figure 1. It maintains the turbulent conditions and there is no mass transfer limitation. It is a nearly closed system no

vaporization of volatile compounds takes place. The initial simulated volume of wastewater is 2 L for photo-



catalytic experiments. The reactor volume was 1 L. TiO2 is added in the form of a suspension with an initial sample

of the wastewater. The time period of experiments is up to 360 minutes.

Figure 1: Schematic diagram of photo-reactor model (Continuous reactor) used for Sunlight/TiO2 in Organic

Pollutants Removal from Petroleum Refinery Wastewater

Figure 2: Schematic diagram of photo-reactor model (Batch reactor) used for Sunlight/TiO2 in Organic

Pollutants Removal from Petroleum Refinery Wastewater



2.2 Analytical procedure and characterization of the industrial effluent

The physicochemical characteristics of pretreated refinery wastewater samples (after coagulation and flotation units)

from Sohar Oil Refinery used for the study are given in Table (1). A Shimadzu TOC analyzer (LCSH/CSN) is used

to measure the TOC for each sample. Chemical oxygen demand (COD) is measured by COD photometer. pH is

monitored regularly throughout the experiment. pH levels are monitored by using a digital pH meter. COD is

estimated before and after treatment.

Table 1: Simulated influent concentration in the pretreated refinery wastewater samples (after coagulation

and flotation units) from Sohar Oil Refinery

No. Parameter Unit Concentration in row

wastewater

1 pH --- 6.5 -9.5

2 Conductivity mg/l 2.60 - 2.95

3 TDS ppt 1.2 – 1.5

4 D.O. mg/l 0.6 – 4.9

5 COD ppm (mg/l) 550 - 1600

6 TOC ppm 220- 265

2.3 Photo-catalytic reaction process

The photo catalytic degradation of COD and TOC in an industrial effluent is studied in a glass reactor. It is placed

outside in order to display to sunlight.

2.4 Batch Process

In a batch reactor, the reactants are charged into a container, well mixed, and are left to react for a certain period

(Figure 2). The effects of the pH, initial COD concentration and amount of catalyst on photo-degradation of COD

are investigated and optimal conditions are found out. Experiments on photo-degradation of COD using TiO2 under

sunlight are carried out.

2.5 Continuous Process

Continuous experiments (Figure 1) are carried out by taking the optimum parameters such as pH and dosage of

catalyst obtained from batch experiments. The flow rate of 5 L/min and 3 L/min are tried and dosage of catalyst

1g/L is used for period of 6 hr. the efficiency of COD degradation is analyzed.

3. Results and Discussion

3.1 Batch Process

3.1.1 Effect of TiO2 loading on photo-catalytic degradation of COD using solar irradiation: Photo-catalytic

degradation of COD in industrial waste water effluent from Sohar Oil Refinery is studied by varying the catalyst

loading from 0.1gm/L to 1.5gm/L. A set of experiments are conducted under sun light with the industrial effluent

and samples are filtered before the analysis. The catalyst concentration (TiO2) is varied as 0.1, 0.25, 0.5, 1, and 1.5



g/L to obtain an optimum concentration to be used for further experiments. Based on the COD values, the photo

catalytic degradation efficiency is calculated by using the equation:

Where:

X; photo-catalytic degradation of COD

[COD]0 and [COD]t stand the initial and after any irradiation time, COD values.

Figure 3: Effect of TiO2 loading on photo-catalytic degradation of COD using Solar Irradiation in industrial

waste water effluent from Sohar Oil Refinery

The results are shown in Figures (3,4). Generally, an increase in catalyst concentration results in a very rapid

increase in degradation, which confirms to a heterogeneous regime [10]. The low photo-catalytic reaction rate at

catalyst loading of 0.1gm/L is due to less availability of active sites. The photo-catalytic degradation is observed to

increase as the catalyst loading increases. At a catalyst concentration (TiO2) of 0.5 g/L under sunlight, the photo-

catalytic degradation of COD is 46% in 240 minutes of reaction time and On increasing the concentration of catalyst

to 1 g/L, 48% COD removal is observed in same time. The percentage removal of COD reaches to a maximum for a

catalyst loading of 1gm/L. This rise in percentage of COD removal may be explained by increase in concentration of

TiO2 increases the number of active sites on the photo-catalyst surface, which in turn increases the number of OH°

radicals [6].

However, a reverse effect occurs when the TiO2 concentration increases to higher than the optimum value, the

degradation rate declines due to the interference of the light by the suspension [8,9]. The large number of active sites

is with the increase of catalyst loading upto1gm/L, the rate of radical formation in the aqueous solution increases.



For to high catalyst loading beyond 1.0 upto1.5gm/L, No significant increase is observed for 1.5g/L of TiO2. It may

be due to light scattering effect and reduction in light penetration through the effluent due to the obstruction of large

number of solid particles [6,7].

3.1.2 Effect of TiO2 loading on photo-catalytic degradation of TOC using solar irradiation (Batch reactor).

Photo-catalytic degradation of TOC in industrial waste water effluent from Sohar Oil Refinery is studied by varying

the catalyst loading from 0.5gm/L to 1.5gm/L. A set of experiments are conducted under sun light with the industrial

effluent and samples are filtered before the analysis. The catalyst concentration (TiO2) is varied as 0.1, 0.25, 0.5, 1,

and 1.5 g/L to obtain an optimum concentration to be used for further experiments.

Based on the TOC values, the photo catalytic degradation efficiency of TOC is calculated by using the equation:

Where:

X; photo-catalytic degradation of TOC

[TOC]0 and [TOC]t; stand the initial and after any irradiation time, TOC values.

The results are shown in Figures (5 and 6). Generally, it is observed in this study that the catalyst loads have a

positive effect on the adsorption. This is because of the larger catalyst surface available for adsorption. the photo-

catalytic degradation is observed to increase as the catalyst loading increases and The results of photo-catalytic

degradation efficiency of TOC at 5 hours are from 12, 14 and 18% for the catalyst (TiO2) concentrations 0.5, 1, and

1.5 g/L respectively as shown in figure 5.

The percentage removal of TOC reaches to a maximum for a catalyst loading of 1.5gm/L which was 18% in 300

minutes of reaction time period. This rise in percentage of TOC removal may be explained by increase in

concentration of TiO2 increases the number of active sites on the photo-catalyst surface, which in turn increases the

number of OH° radicals [6]. After that, The TiO2 adsorption capability show a decrease of 4 % at 60 minutes

because The TOC concentrations increasing trend indicate desorption of cationic species from the catalyst surface.

Higher TiO2 load has a negative effect on the photo-catalytic degradation due to the higher slurry turbidity, which

did not allow the penetration photons of the reactor inner zones [11].



Figure 5: Effect of TiO2 loading on photo-catalytic degradation of TOC using Solar Irradiation in industrial

waste water effluent from Sohar Oil Refinery

Figure 6: Effect of TiO2 loading on TOC concentration using solar irradiation in industrial waste water

effluent from Sohar Oil Refinery (Batch reactor)

3.2 Continuous Process

3.2.1 Effect of TiO2 loading on photo-catalytic degradation of COD using solar irradiation: Photo-catalytic

degradation of COD in industrial waste water effluent from Sohar Oil Refinery is studied by varying the catalyst

loading from 0.1gm/L to 1.5gm/L. A set of experiments are conducted under sun light with the industrial effluent



and samples are filtered before the analysis. The catalyst concentration (TiO2) is varied as 0.1, 0.25, 0.5, 1, and 1.5

g/L to obtain an optimum concentration to be used for further experiments.

The results are shown in Figure (7), the photo-catalytic degradation is observed to increase as the catalyst loading

increases. At a catalyst concentration (TiO2) of 0.5 g/L under sunlight, the photo-catalytic degradation of COD is

48% in 240 minutes of reaction time and On increasing the concentration of catalyst to 1 g/L, 85% COD removal is

observed in same time. The percentage removal of COD reaches to a maximum for a catalyst loading of 1gm/L. This

rise in percentage of COD removal may be explained by increase in concentration of TiO2 increases the number of

active sites on the photo-catalyst surface, which in turn increases the number of OH° radicals [6]. Beyond 1gm/L,

the degradation further decreases (shown in Figure 7). No significant increase is observed for 1.5 g/L of TiO2.

Figure 7: Effect of TiO2 loading on photo-catalytic degradation of COD using Solar Irradiation in industrial

waste water effluent from Sohar Oil Refinery (continuous reactor)

By comparing photo-degradation efficiency with TiO2 / Sunlight method in batch reactor and continuous reactor

under same condition, it was noted that the photo-degradation efficiency (%) of COD using batch reactor is 48% in

240 minutes of reaction time while is 87% in 240 minutes of reaction time using continuous mode of study because

the mechanism of degradation can be achievable under prolonged exposures to sunlight irradiation. Therefore

continuous process is better since handling of feed liquid is more compared to batch method.

3.2.2 Effect of pH on degradation of COD using solar irradiation: pH has important influence on pollutant

molecules, catalyst surface charge, and also on the mechanism and the rate of hydroxyl radical generation [13].

Photo catalytic experiments are performed under sunlight at the actual pH value of the wastewater without any pH

alteration in row industrial waste water effluent from Sohar Oil Refinery with the optimum dosage of TiO2 (1 gm/l)

at 3h. The actual pH values are 6.7, 8, 8.5, 8.7 and 9. The results are depicted Maximum and fastest reaction and



better removal efficiency of COD in row industrial waste water effluent from Sohar Oil Refinery at pH value of 8.7

which is found 78%, and it is considered as the optimal pH for this study as shown in Figure (8). No further decrease

is observed on performing the reaction after 180 minutes till 300 minutes. As compared to pH values, the decrease

was more in the alkaline pH range. In 180 minutes, photo catalytic degradation of COD values are 15%, 24%, 60%

and 47% at pH values 6.7, 8, 8.5 and 9 respectively. The pH affects the surface charge for the photo-catalyst as well

as the organic pollutants [6]. The decrease in adsorption values may be due to the abundance of OH- ions, causing

increased hindrance to diffusion of organics [12].

Figure 8: Effect of pH on degradation of COD using solar irradiation (1 gm/l TiO2 at 3h.) in row industrial

waste water effluent from Sohar Oil Refinery.

3.2.3 Effect of initial concentration of COD: Experiments are carried out at 4 hr with sunlight irradiation for

different initial concentrations of COD (850 ppm, 1125 ppm, 1200 ppm and 1600ppm) in row industrial waste water

effluent from Sohar Oil Refinery using 1.0 gm/l of catalyst (TiO2). The COD of solution is estimated before and

after the reactions. Based on the COD values, the photo catalytic degradation efficiency is calculated by using the

equation:

Degradation efficiency = [(Initial COD – Final COD) / Initial COD) ×100] % (3)

The results for the effect of initial concentration on COD removal at various effluent concentrations are shown in

Figure 9. It is observed that the percentage removals of COD become 48%, 52%, 70% and 49% respectively. It is

found that the degradation of COD increased with increasing the initial concentration of COD. The reason for this

can be explained by considering the formation of hydroxyl radicals in water by the irradiation [6]. The maximum

efficiency for degradation of COD is 70 % at the initial concentration of COD (1200 ppm) at 240 min. But it is

noted that the percentage removal of COD decreases as the initial concentration of COD increases after this value.

The current study reveals that the reason for the smaller degradation rate at the latter stage of the process (after 1200

ppm) is likely due to the decrease in the formation of hydroxyl radicals on the catalyst surface with the increase in

pollutants concentration and at the same time the available active sites decrease by the increase of adsorbed



pollutants on the catalyst surface (the coverage of active sites by reaction intermediates), which inhibits the direct

contact between pollutants and hydroxyl radicals [3].

Figure 9: Efficiency of degradation of COD for various initial concentrations of CODin row industrial waste

water effluent from Sohar Oil Refineryusing 1 gm/l TiO2 under solar irradiation at 4h.

3.2.4 Effect of irradiation time on the removal of COD: The required duration for the complete photo-

catalytic reaction is also observed. The reaction irradiation time is varied from 1 h to 6 h under the Sunlight source

by loading of 0.1 g/L catalyst into 1.5 g/L TiO2. Results represented that COD removal efficiency increases with

time as shown in Figure 7 and photo-catalytic reaction of the industrial effluent needs longer irradiation time due to

the fact that these effluents commonly contain high molecular weight and complex structured organic pollutants [6].

The difference is very small between 2 hr and 6 hr contact time. Therefore it is concluded that 4 hr operation is

suggested as optimum reaction time and it reduces the cost of pumping.

4. Conclusions

The performance of the photo-degradation of COD and TOC for row industrial waste water effluent from Sohar Oil

Refinery in presence of TiO2 is found to be the best method and has good efficiency for the removal of COD and

TOC from row industrial waste water. Several parameters have been studied, it appear that dose of TiO2 and

concentration of COD, initial pH and irradiation time of the reaction medium mainly controls the rate of



degradation. The efficiency of the process depends strongly on the experimental conditions. pH 8.7 is the optimum

value for the rapid generation of OH radicals. This gives the TiO2 a positive charge which attracts the negatively

charged pollutants onto the surface of the catalyst resulting in efficient degradation. At low loading from 0.1 to 1 g/l

TiO2, the degradation of COD increases with increase TiO2 concentration and at loading over 1 g/l TiO2,

degradation of COD is a bit or constant with increase TiO2 concentration. The COD degradation efficiency

increased as the initial COD concentration increased until COD level of row industrial waste water samples from

Sohar Oil Refinery were more than 1200 mg/L but after that the COD degradation efficiency start by decreased. So,

a catalyst (TiO2) concentration of 1g/l under pH of 8.7 and the initial COD concentration under 1200 mg/L can be

introduced as the optimum operating conditions. The time of exposure increases the degradation efficiency; the

difference is very small between 2 hr and 6 hr contact time. Therefore it is concluded that 4 hr operation is suggested

as it reduces the cost of pumping. Under these conditions, a degradation efficiency of COD more than 78% of the

organic pollutants is achieved when applying near 240 min irradiation and significant removal can still be obtained

in much shorter times, after about 120 min. By comparing photo-degradation efficiency with TiO2/Sunlight method

in batch reactor and continuous reactor under same condition, it is noted that the photo-degradation efficiency (%) of

COD using batch reactor is 48% in 240 minutes of reaction time while is 87% in same time using continuous mode

of study because the mechanism of degradation can be achievable under prolonged exposures to sunlight irradiation

therefore continuous process is better since handling of feed liquid is more compared to batch method. The

percentage removal of TOC reaches to a maximum for a catalyst loading of 1.5gm/L which is 18% in 300 minutes

of reaction time period.

Solar detoxification of high COD wastewater is a unique treatment process utilizing renewable solar energy and

treating the wastewater with minimum chemical input. The photo-degradation by titanium dioxide (TiO2) has low

operation cost and a very high probability of COD degradation. This advanced oxidation process offers an

environmental alternative for the treatment of row industrial waste water effluent from Sohar Oil Refinery.

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