Chapter ONE
Introduction
1.1 TREATMENT OF INDUSTRIAL EFFLUENTS
Contamination of H2O by industrial wastewaters is a serious job experienced by states throughout the developed and developing universe. Recently, rapid industrial enlargement particularly petrochemical, pharmaceutical, fabric, agricultural, nutrient and chemical industries all produce waste wastewater contaminated with organic compounds such as aromatics, haloaromatics and dyes has contributed to the taint of fresh H2O in the ecosystem ( Robertson et al. , 2005 ) . The released of untreated organic pollutants are of high precedence concern since they are harmful to the environment and even their taint in H2O at a few mg/L degrees are extremely carcinogenic to human and animate beings. In Malaysia, the figure of H2O pollution beginnings was reported to be increased by 26 % from 13992 beginnings in 2000 to 18956 beginnings in 2006 ( WHO, 2005 ; DOE, 2006 ) . In this respect, a stricter H2O quality control criterions and ordinances such as Environmental Quality Act have been implemented in Malaysia in an attempt to accomplish a end in environment protection direction policy. Therefore, the enforcement of the bing environmental Torahs is indispensable to guarantee the capableness of the industrial sector in destructing the potentially harmful compounds from the wastewater before safe disposal into the natural Waterss.
A assortment of conventional biological, chemical and physical methods are soon available to handle the harmful compounds in the wastewaters. However, these conventional effluent interventions have restrictions of their ain in order to make the grade of pureness required for concluding usage. Biological intervention ( aerophilic or anaerobiotic digestion ) normally is non effectual in the effluent intervention due to some of the toxic compounds present in the industrial wastewater are found non readily biodegradable and may kill the active bugs ( Sanrom & A ; aacute ; n et al. , 2004 ) . Chemical intervention ( chlorination and ozonation ) gave peculiar jobs where chlorinated organic compounds as byproduct after the chlorination intervention can be generated ( Moonsiri et al. , 2004 ) . Due to the instability and risky nature, the usage of ozone may be more harmful to the environment ( Bizani et al. , 2006 ) . Finally, physical intervention ( charcoal surface assimilation, rearward osmosis and ultrafiltration ) is non-destructive and normally comprises a simple transportation of organic pollutants from a spread stage to a concentrated stage ( Kabir et al. , 2006 ) , therefore doing secondary pollution.
In this manner, new and more efficient intervention engineerings to degrade the complex furnace lining molecules into simpler molecules must be considered to cut down the deteriorating H2O quality.
1.2 PHOTOCATALYSIS IN WASTEWATER TREATMENT
In recent old ages, heterogenous photocatalysis is one of the advanced oxidization procedures ( AOP ) that has been accepted as a promising new alternate method in the country of effluent intervention ( Chen and Ray, 1999 ; Bekkouche et al. , 2004 ; Cao et al. , 2005 ; Liu et al. , 2007 ; Merabet et al. , 2009a ) . Compared with conventional effluent interventions, heterogenous photocatalysis has such advantages as: ( 1 ) pollutants are non simply transferred from one stage to another, but they are chemically transformed and wholly mineralized to environmentally harmless compounds ( 2 ) this procedure is immune to organic toxicity to do it attractive for the debasement of toxic organic compounds and ( 3 ) this procedure has the possible to use sunshine or seeable visible radiation for irradiation, thereby will give advantage in economic economy particularly for large-scale operations ( Chang et al. , 2005 ; Yu et al. , 2007a ) .
By and large, three basic constituents must show in heterogenous photocatalysis in order for the reaction to take topographic point: an emitted photon ( in the appropriate wavelength ) , a accelerator surface ( normally TiO2 ) and O ( Lasa et al. , 2006 ) . Photocatalytic procedure is occurred when the accelerator is activated by UV visible radiation and followed by the excitement of an negatron from the valency set to conductivity set, go forthing a positive hole behind in the valency set. These positively charged holes will respond with H2O molecules taking to the formation of the hydroxyl groups ( & A ; bull ; OH ) , which are the strong oxidizers to degrade the organic molecules ( Zhang et al. , 2005a ) .
Two manners of TiO2 as photocatalyst: ( 1 ) suspended TiO2 pulverization and immobilized TiO2 are typically used in the photocatalytic debasement procedures. Both types of TiO2 offered assorted advantages and disadvantages. Suspended TiO2 pulverization has been the most normally used because of its simpleness and offers high surface country for reaction with about no mass transportation restriction. However, extra separation procedures are required to retrieve the TiO2 pulverization at the terminal of the intervention, either by filtration or centrifugation which is expensive in term of clip and cost. Another concern is suspended TiO2 pulverization tends to agglomerate into larger atoms at high concentration, which reduces the catalytic activity. Therefore, in footings of big scale application, immobilized TiO2 is preferred. However, there is another job that activity of immobilized TiO2 system may take down than slurry system due to the surface country decrease and mass transportation restriction ( Li et al. , 2005 ; Damodar et al. , 2008 ; Song et al. , 2008 ) .
1.3 PROBLEM STATEMENT
In recent old ages, increasing usage of immobilized photocatalyst in the heterogenous photocatalysis has witnessed its important application in the effluent intervention ( Kang, 2002 ; Zhang et al. , 2006 ; Zhu and Zou, 2009 ) . Even though immobilized TiO2 allows the easy uninterrupted usage of the photocatalyst by extinguishing the demand of extra separation processes in a slurry system, there are still proficient challenges that must be farther investigated and overcame. It is good established that the photocatalytic public presentation of TiO2 are strongly influenced by the physiochemical belongingss such as crystallinity, crystal size and surface country, which are governed by the readying method ( Jang et al. , 2001 ; Senthilkumaar et al. , 2006 ; Tian et al. , 2009 ) . Synthesis of immobilized nanosized TiO2 is of import to counterbalance for the decreased public presentations associated with the immobilisation procedure due to its big surface country and consistent with a high volume fraction of active sites available on the surface for substrate surface assimilation. Hence, cognition particularly in the synthesis of immobilized nanosized TiO2 still requires better apprehension.
As most normally known, sol-gel, chemical vapour deposition ( CVD ) and hydrothermal are outstanding methods for the synthesis of TiO2. Sol-gel and CVD normally generate a comparatively homogenous TiO2 coating but high calcination temperature above 450 & A ; # 730 ; C is normally required to bring on crystallisation. This is non economical and can do crystal growing ( Shang et al. , 2003 ; Sayilkan et al. , 2007 ) . To avoid these defects, hydrothermal has been considered as an alternate method for the readying of immobilized TiO2 in a nanocrystalline province, where low reaction temperature is available, and physiochemical belongingss such as crystal size, morphology and crystalline stage of the prepared photocatalyst can be controlled ( Kolen’ko et al. , 2003 ; Yu et al. , 2005 ; Zhao et al. , 2007 ) .
Besides, the choice of a proper substrate as a support for immobilized TiO2 is indispensable to increase the photocatalytic debasement activities. Early works chiefly focused on surfacing TiO2 on non-adsorbent supports such as glass, vitreous silica sand and unstained steel substrate ( Shang et al. , 2003 ; Sonawane et al. , 2004 ; Pozzo et al. , 2006 ) . The photocatalyst separation job is slightly can be solved, but no betterment in the photoefficiency is observed due to the diffusion restriction of pollutants to the surface of TiO2. To avoid this job, much attending is given to back up TiO2 on adsorbent stuffs such as zeolite, activated C ( AC ) and silica gel ( Zhang et al. , 2006 ; Mahalakshmi et al. , 2009 ; Sun et al. , 2009 ) . Among these supports, AC is used in this survey owing to its high quality of surface assimilation capacity, high surface country and lower cost ( Sun et al. , 2009 )
In add-on, an effectual reactor design is considered of import in the photocatalytic debasement reaction where confidant contact can be achieved between UV visible radiation, photocatalyst and reactants. In this sense, fluidized bed reactor is believed can increase the photocatalytic efficiency owing to its first-class reactant contact, high photocatalyst burden and efficient UV visible radiation exposure ( Nam et al. , 2002 ; Nelson et al. , 2007 ) . However, proficient development of fluidized bed reactor is still non widely studied in heterogenous photocatalysis engineering for effluent intervention. Therefore, it is imperative to carry on a thorough survey on the consequence of operating parametric quantities to look into the photocatalytic public presentation of the prepared photocatalyst in a fluidized bed reactor. The importance of the present work is to work the broad and ever-growing application of TiO2 photocatalysis to be more practical in the effluent intervention by analyzing the standards in the synthesis of immobilized TiO2 with its photocatalytic public presentation in a fluidized bed reactor.
1.4 RESEARCH OBJECTIVES
The purpose of this research is to develop an immobilized photocatalyst with high photoactivity, which is capable of degrading and mineralizing phenol under UV irradiation. The aims of this research include:
- To synthesise nanosized TiO2 immobilized on farinaceous activated C ( TiO2/GAC ) utilizing a hydrothermal method.
- To qualify the prepared TiO2/GAC based on its chemical and physical belongingss.
- To analyze the public presentation of TiO2/GAC on the photocatalytic debasement of phenol in a fluidized bed reactor.
- To analyze the consequence of runing parametric quantities such as TiO2 burden, inorganic anions, pH, air flow rate, H2O2 concentration and initial phenol concentration on photocatalytic debasement of phenol in a fluidized bed reactor.
- To obtain optimal runing parametric quantities by utilizing response surface methodological analysis.
- To analyze the kinetic of photocatalytic debasement of phenol over TiO2/GAC.
1.5 SCOPE OF STUDY
This research is focused on the development of extremely effectual immobilized TiO2 utilizing a hydrothermal method. The development of the photocatalyst includes analyzing the consequence of hydrothermal temperature ( 120oC – 200oC ) and GAC as a support on the TiO2 photocatalytic activity. The newly prepared immobilized photocatalyst are characterized utilizing X-ray diffraction ( XRD ) , transmittal negatron microscopy ( TEM ) , scanning negatron microscope ( SEM ) , energy diffusing X-ray spectrometry ( EDX ) and Brunauer-Emmett-Teller ( BET ) . Their photocatalytic activities are evaluated through phenol debasement in a fluidized bed reactor.
Assorted runing parametric quantities such as TiO2 burden ( 1 bed – 4 beds ) , pH ( 3.0 – 11.0 ) , inorganic anions ( Cl- , HCO3- , CO32- and SO42- ) , air flow rate ( 1.0 L/min – 3.0 L/min ) , H2O2 concentration ( 50 mg/L – 400 mg/L ) and initial phenol concentration ( 20 mg/L – 110 mg/L ) are studied to measure the photocatalytic public presentation of TiO2/GAC in a fluidized bed reactor. Data analysis is farther studied utilizing 23 factorial experimental design of response surface methodological analysis ( RSM ) to optimise and analyse the possible interaction between the procedure variables on phenol debasement. Finally, kinetic survey based on Langmuir-Hinshelwood dynamicss theoretical account is studied to find the rate of reaction in the phenol debasement.
1.6 ORGANIZATION OF THESIS
There are five chapters in this thesis. Chapter 1 ( Introduction ) provides a brief description of intervention of industrial wastewater and photocatalysis in effluent intervention. This chapter besides includes the job statement that describes the job faced and the demands of the current research. The aims and Scopess of this survey are so explained in this chapter. This is followed by the organisation of the thesis.
Chapter 2 ( Literature Review ) provides the past research works in the photocatalysis field. A brief account about advanced oxidization procedure is in the first portion and followed by the overview of photocatalysis. Subsequently, information sing with the TiO2 as a photocatalyst, the immobilisation onto the support and photocatalytic reactor are discussed in the 2nd portion. Following, the feature of phenol and inside informations of phenol debasement are described. The effects of assorted runing parametric quantities that affect the photocatalytic activity are included. Finally, the design of experiment ( DOE ) is discussed.
Chapter 3 ( Materials and Methods ) covers the experimental portion. Detailss of the stuffs and chemical reagents with a general description about the photocatalytic reactor that are used in the present survey are described in the first portion. This is followed by the treatment on the detailed of the photocatalyst readying and word picture techniques throughout this research. Last, procedure surveies and experimental design are described in this chapter.
Chapter 4 ( Results and Discussion ) presents the experimental findings together with the treatment. It is divided into eight parts: ( a ) word picture of TiO2/GAC, ( B ) Consequence of hydrothermal temperature on the photocatalytic public presentation, ( degree Celsius ) finding of factors impacting the photocatalytic activity, ( vitamin D ) public presentation comparing between immobilized TiO2 and suspended TiO2, ( vitamin E ) extraction surveies, ( degree Fahrenheit ) consequence of operating parametric quantities, ( g ) optimisation surveies and ( H ) dynamicss surveies.
Chapter 5 ( Conclusions and Recommendations ) summarizes the consequences reported in the chapter 4 and recommends the possible ways to better the present surveies for the future research in this field.
