Development of Recirculating Photocatalytic Reactor for Wastewater Remediation Final Draft
1. The Robert Gordon University, Aberdeen
School of Engineering
BEng (Hons) in Mechanical Engineering
Development of a Recirculating Photocatalytic
Reactor for Wastewater Remediation
Mokanlasanya Akinyinka Johnson
1217611
April 2016
2. Development of a Recirculating
Photocatalytic Reactor for Wastewater
Remediation
Mokanlasanya Akinyinka Johnson
1217611
This report is submitted as part of the requirements for the BEng degree in
Mechanical Engineering at The Robert Gordon University, Aberdeen
3. Declaration
I declare that this report, except where otherwise stated, is based on my work alone,
and carried out in the School of Engineering of The Robert Gordon University,
between September 2015 and April 2016. To the best of my knowledge and belief,
this report contains no material previously published or written by another person,
except where due reference has been made.
Signed…………………………………………….. Date.………………………..
4. iv
Abstract
As the world population rises, availability of clean water supplies diminish. Demand
for effective water treatment methods are now rising, therefore improvements on
current wastewater remediation processes are necessary. Current technologies are
capable of meeting general treatment requirements although as the concern over
the global environment grows, so will standards rise. Photocatalysis shows Potential
of being the ideal solution for improvements upon current tertiary wastewater
treatment practices. The use of a non-harmful and unreactive catalyst prevent the
introduction of harmful substances into effluents and the ability to employ light
energy for activation presents a sense of versatility as it would be deployable in both
rural and urban areas.
Development of Photocatalytic reactors is central to photocatalysis, as they are
central to the development of the photocatalysis process. Many factors are
considered in reactor design like photocatalyst loading and the amount of incident
light, mass transport, agitation etc. such parameters determine the speed and
effectiveness of photocatalytic degradation and are important considerations for
every design.
Most photocatalytic reactors are developed for lab scale testing as implementing
photocatalysis for wastewater remediation at an industrial scale still presents
various difficulties. Most prominent being reactor design at an industrial scale
involves the use of large areas of space to cope with industrial wastewater volumes.
In this report, a recirculating photocatalytic reactor was developed at lab scale to
determine larger scale suitability. Various parameters considered where
incorporated into 4 design ideas and 1 selected for further analysis. Using
Methylene blue as a model compound, the developed design was able to effect 37%
degradation of the methylene blue solution over 60 minutes. Analysis of results
showed that the developed reactor at larger scale would present various problems
and through consideration of successes and drawbacks of the design an improved
concept was recommended for further development.
5. v
Acknowledgements
As the author, I would like to thank the following:
CRE+E labs for the provision of the site of my experimental and
developmental process.
Mr. David Allen for Assistance with Design considerations regarding the
Reactor.
Mr. Alan McClean for Assistance and support with risk assessments
Dr. Cathy McCullagh for research assistance and supervision of testing
phases.
6. vi
Table of Contents
Declaration ............................................................................................................. iii
Abstract ..................................................................................................................iv
Acknowledgements .................................................................................................v
List of Figures....................................................................................................... viii
Nomenclature..........................................................................................................x
Abbreviations..........................................................................................................xi
1 Introduction...................................................................................................... 1
1.1 Project Aim................................................................................................ 2
1.2 Objectives ................................................................................................. 2
2 Literature Review............................................................................................. 3
2.1 Introduction ............................................................................................... 3
2.2 Semiconductor Photocatalysis Fundamentals........................................... 3
2.2.1 Semi-Conductor Photocatalyst ........................................................... 5
2.3 Mechanism of TiO2 Photocatalysis............................................................ 6
2.4 Photoreactors and Types of Configurations .............................................. 7
2.4.1 Multi Tubular reactors......................................................................... 8
2.4.2 Suspended Liquid Reactors................................................................ 9
2.4.3 Flat Plate Reactors. .......................................................................... 10
3 Design Development...................................................................................... 14
3.1.1 Design Criteria.................................................................................. 14
3.1.2 Recirculation Mechanism.................................................................. 14
3.1.3 Design Development ........................................................................ 14
3.2 Developed Design................................................................................... 18
3.2.1 Build Procedure ................................................................................ 19
3.2.2 Design Calculations.......................................................................... 20
4 Testing........................................................................................................... 22
7. vii
4.1 Experimental setup.................................................................................. 22
4.1.1 Methylene blue ................................................................................. 22
4.1.2 Catalyst loading ................................................................................ 22
4.1.3 Pump ................................................................................................ 23
4.1.4 UV Light Containment Reactor (illumination source) ........................ 23
4.2 Experimental Procedure.......................................................................... 24
4.3 Results .................................................................................................... 25
5 Discussion ..................................................................................................... 29
5.1 General Overview.................................................................................... 29
5.2 Test Results ............................................................................................ 30
5.3 Improved Design ..................................................................................... 32
6 Conclusion..................................................................................................... 34
7 Further Development ..................................................................................... 35
References........................................................................................................... 36
8 Appendices.................................................................................................... 40
Appendix A – Technical drawings ..................................................................... 40
Appendix B – Pump Specifications ................................................................... 44
Appendix C – Unit Conversions ........................................................................ 45
8. viii
List of Figures
Figure 2.1 Generation of electron hole pairs .......................................................... 4
Figure 2.2 Photo excitation of Titanium Dioxide ..................................................... 7
Figure 2.3 Thin filmed multi tubular photoreactor and illumination box (M. Adams, et
al. 2012) ................................................................................................................. 8
Figure 2.4 Drum reactor finished model and schematic (C. McCullagh, et al., 2011)
............................................................................................................................... 9
Figure 2.5 Fixed bed Reactor schematic (Nogueira and Jardim, 1994) ............... 11
Figure 2.6 Flat plate reactor prototype (M. Adams, et al., 2008) .......................... 12
Figure 2.7 Comparison of substrate with angle at optimum TiO2 loading (M. Adams,
et al., 2008) .......................................................................................................... 13
Figure 2.8 Multiple thin film plate reactor stack, Lab unit (left) concept design (right)
(M. Adams, et al., 2008) ....................................................................................... 13
Figure 3.1 Paddle concept design........................................................................ 15
Figure 3.2 Glass Bead concept design................................................................. 16
Figure 3.3 Internal drum concept design .............................................................. 17
Figure 3.4 Reactor Model..................................................................................... 18
Figure 3.5 Reactor parts and assembled prototype.............................................. 20
Figure 4.1 Methylene blue Calibration curve ........................................................ 22
Figure 4.2 Ultraviolet Light Containment Reactor (UVLCR) ................................. 23
Figure 4.3 Spectral output for UV lamps .............................................................. 24
Figure 4.4 Experimental setup.............................................................................. 24
Figure 4.5 Temporal absorption spectral pattern of MB under UV radiation only . 25
Figure 4.6 Temporal absorption of methylene blue degradation in the with catalyst
loading under UV irradiation................................................................................. 26
Figure 4.7 %Absorption of methylene blue at maximum absorption wave length 27
Figure 4.8 Methylene blue concentration over 60 minutes of photocatalysis ....... 27
Figure 5.1 final design concept............................................................................. 32
Figure 5.2 methyl orange degradation by P25 (purple), silica beads, and %doped
glass tubes (blue & green) (M. Adams, et al., 2012) ............................................ 33
Figure 0.1 Lower lid Drawing................................................................................ 40
Figure 0.2 Top Lid 1 Drawing .............................................................................. 41
Figure 0.3 Top lid 2 Drawing ................................................................................ 42
9. ix
Figure 0.4 Glass tube drawing.............................................................................. 43
Figure 8.5 Pump data sheet ................................................................................. 44
10. x
Nomenclature
TiO2 – Titanium Dioxide
e- – Electron
h+ – Proton
Eev – Excitation energy
ΔEgap/Eg – Band Gap Energy
ZnO – Zinc Oxide
Zn(OH)2 – Zinc Hydroxide
hv – UV irradiation
e-
ch – Conductance band electron
h+
vb – Valent band hole
OH- – Hydroxyl ions
OH• – Hydroxyl Radical
O2 – Oxygen
O2
•- – Super Oxide
HO2
• – Hydroperoxyl Radical
H2O2 – Hydrogen peroxide
Re – Reynolds Number
Q – Volumetric Flow rate
A – Cross sectional Area
V – Flow velocity
D – Diameter
ρ – Density
η – Kinematic Viscosity
11. xi
Abbreviations
UV – Ultraviolet
PMMA – Polymethylmethacrylate
PTFE – Polytetrafluoroethylene
RTV – Room temperature Vulcanization
PVC – Polyvinyl Chloride
UVLCR – Ultraviolet Light Containment Reactor
MB – Methylene Blue
MO – Methylene Orange
12. 1
1 Introduction
With the growing population of the world, the supply of clean water diminishes which
is cause for environmental concern. With the diminishing supply of clean water
wastewater remediation methods are now at a premium and although current
conventional methods for wastewater treatment are capable of meeting current
water standards in most cases, improvements on current processes are necessary.
Photocatalysis shows great potential for improving upon current tertiary cleaning
methods due to its versatility, ease of deployment and suitability for various
pollutants. One of the main concerns with wastewater is that industrial wastewater
can contain a variety of pollutants harmful to the environment, pesticides, heavy
metals or organic compounds which cannot be sufficiently treated by conventional
means most particularly in developing regions where even conventional facilities are
lacking. For both problems photocatalysis is ideally suited as it poses the ability to
completely destroy organic pollutants and toxins as well as bacteria and other
microorganisms within a water stream, and when operated using sunlight it is
suitable for developing regions by requiring less energy in order function. Many pilot
studies have been undertaken in the wastewater treatment field, Adams et al.,
(2013) developed a drum reactor for the remediation of wastewater containing
hydrocarbons, and Chong et al. developed nanofiber catalysts in order to solve
catalyst filtration problems in slurry reactors. Further improvements in this field will
result in better access to clean water which will improve sanitation, hygiene etc.
which would consequently result in healthier populations and environments.
Photocatalysis is the acceleration of a chemical reaction in the presence of a
photocatalyst.
Photocatalysis is beginning to gain traction in industry as it’s applicable for a wide
variety of fields and its various potential environmental applications one of which
includes the treatment of industrial wastewater. Traditional wastewater treatment
methods often employ the use of potentially hazardous materials or pollutants which
poses a problem for the environment, Photocatalysis solves this problem as it
employs the use of non-toxic semiconductor photocatalysts. A Semiconductor
13. 2
photocatalyst when illuminated at appropriate wavelengths will produce very
powerful oxidants which decompose organic materials into carbon dioxide and water
thereby facilitating the photocatalytic reaction.
The industrial applications of Photocatalysis are ever increasing as research into
photocatalysis develops new methods improved catalyst configuration etc.
photocatalysis will begin to gain traction as it has been proven to be a low cost and
sustainable technology for the treatment of various pollutants in air and water
including organics and heavy metals (Ibhadon and Fitzpatrick 2013). Photocatalysis
can be performed under sunlight or UV radiation, making it extremely cost effective,
environmentally friendly and as such can be applied worldwide. Considering that
photocatalysis can be performed using very basic equipment it is also very suitable
for developing regions. Unfortunately the limitations of this technology for industrial
deployment are still relatively unsolved as very few pilot studies show feasible
results in terms of industrial scale processes as industrial waste output rates and
volumes are still far too great for the capacity of current photoreactor concepts as
there are many variables to be considered when scaling up pilot designs.
One of the major issues being that to tackle industrial waste volumes large area will
be needed in order to construct reactors capable of tackling that load which will incur
high costs which will not justify the redundancy of current means in favour of
photocatalysis.
1.1 Project Aim
To design a lab scale Recirculating Photocatalytic Reactor for the treatment of
wastewater which can later be scaled up for industrial use.
1.2 Objectives
1. To carry out literature review.
2. To develop continuous flow recirculation.
3. To investigate means of effective mixing.
4. To build and test reactor.
5. Evaluate results and determine large scale feasibility.
6. Investigate possible further developments or improvements where required.
14. 3
2 Literature Review
2.1 Introduction
Semiconductor Photocatalysis over the last few decades has started to gain a lot of
industrial attention as its various applications become even more apparent and as
a result of this interest, a lot of work is being put into determining its validity for
industrial scale uses.
In the 1970s, Fujishima and Honda had discovered the photocatalytic splitting of
water on the surface of Titanium dioxide (TiO2) electrodes. This discovery had now
set the pace for the current research being carried out on Photocatalysis and its
various potential uses, resulting from this more effort was now being put into
researching the fundamentals processes and investigating the efficiency of the TiO2
Semiconductor catalyst, studies in this field had started to advance into energy
storage and renewal and more recently into environmental applications due to the
potential of TiO2 based Photocatalysis for the total destruction of organic pollutants
in wastewater and air. Research in this field now focuses primarily on ways in which
the catalytic reactions can be enhanced and used efficiently in industry. Some of the
most important aspects of these enhancements being reactor configurations and
developments in how the catalyst are deployed.
2.2 Semiconductor Photocatalysis Fundamentals
Photocatalysis is a compound word composed of two parts namely photo and
catalysis. Photo meaning light and catalysis being the term used to describe the
process in which a reaction is accelerated using a substance known as a catalyst.
This Catalyst remains unchanged in the reaction and is not used up after the
reaction takes place. Catalysts use in Photocatalysis are known as photocatalysts.
Semiconductors are beneficial for photocatalysis due to a combination of factors like
their electronic structures, light absorption properties, charge transport
characteristics and life times of the excited state (Kumar P.P., 2005). The Main
contributing factor to their suitability for use as a catalyst however is the electronic
structure comprised of the conductance and valence bands. The Valence band is
comprised of completely occupied orbitals at low energy while the conductance
15. 4
band is at high energy, enough to allow free movement of electrons between atoms
under the influence of external applied energy and is generally empty (Kumar P.P.,
2005). Between the conductance and valence band of the semiconductor is a space
devoid of charge known as the band gap it is generally small and in order for an
electron to move from the valence band to the conductance band it must be excited
by energy equal to or more than the energy required by the band gap (or band gap
energy). Just as there are different semiconductor materials band gap energy differs
as well. When sufficient photon energy is absorbed by the semiconductor and
electron from the valence band is excited and will jump from the low energy valence
band to the high energy conductance band. This electron is now free to move around
the semiconductor lattice. Although the electron has now left the full valence band
only partially filled leaving behind an electron hole, which is also free to move. This
excitation could cause the electron being promoted to the conductance band to
recombine with vacant holes in the valence band to create heat (undesired effect),
or cause the hoes and electrons to migrate to the surface of the semiconductor to
initiate redox and oxidation reactions with oxidants and reductants absorbed at the
catalyst surface. Which will ultimately result in the complete destruction of organic
compounds with absorbed species in the semiconductor material.
Figure 2.1 Generation of electron hole pairs
Vacuum Label
Valence Band
h+
Egap
EeV
Conduction Band
e-
16. 5
2.2.1 Semi-Conductor Photocatalyst
As described previously a catalyst is a substance used in order to accelerate or
instigate a chemical reaction which is not used up and remains unchanged at the
end of the chemical reaction (Jim Clark, 2002), therefore a photocatalyst can be
defined as a substance which upon exposure to light will work as a catalyst to alter
the rate of reactions.
There are various semiconductor photocatalyst that have been reported and tested
in literature, Examples are TiO2 which is generally the preferred catalyst at lab scale
experiments, like with the thin filmed multi tubular reactor developed by Adams M.
et al (Adams M., 2013), or ZnO (ZincOxide) investigated by Roselin et al., (2002)
for degradation of reactive red (RR 22). TiO2 and ZnO are the most widely
researched photocatalyst as of present day but TiO2 is more widely accepted
because although ZnO is tried and proven as an effective catalyst it remains
unstable as it yields Zn(OH)2 on the ZnO particle surface leading to the development
of inactive sites and loss of catalyst efficiency.
TiO2 is more often the catalyst of choice because it has many advantages which
justify its position over other available catalysts as TiO2 is inexpensive, insoluble in
most conditions and chemically stable with respect to Photo corrosion (Kumar P.P.,
2005), it is also a non-reactive substance and can be activated by low energy near
UV light.
TiO2 Photocatalyst comes in many different commercially available samples which
all favour the powder suspension configuration examples are Degussa P-25,
Millennium PC500, and DuPont R-900 etc. Different Samples of TiO2 will show
different photocatalytic activity when placed under identical conditions, this can be
attributed to differences in morphology, crystalline phase, specific surface areas,
doping, presence of impurities etc. TiO2 samples generally exist in two crystalline
configurations, anatase and rutile although still possible they are not commonly
available in brookite form. Anatase has been shown to possess more photoactivity
in comparison to rutile due to its lower band gap energy (3.0eV) in comparison to
rutile (3.2eV) stemming from the small difference in conduction band energies
(Kumar P.P., 2005). This means there will be a higher chance for recombination of
holes and electron in the rutile structure.
17. 6
Degussa P-25 is fast becoming the industry standard for photocatalysts mainly due
to its high photocatalytic activity which make it a more superior catalyst. The activity
of various TiO2 samples was tested by Sivakumar and Shanthi, (2001) for the
decolourization of reactive textile dyes under illumination by sunlight and both
concluded that Degussa P-25 Produced superior results to other samples tested
(CDH and CERAC).
2.3 Mechanism of TiO2 Photocatalysis.
TiO2 functions as a photocatalyst due to its Semi Conductor nature characterized
by its electron filled valence band and conductance band which is filled with holes
separated by a band gap. When energy equal to or greater than the band gap
energy Eg, is absorbed by TiO2, an electron will move from the valence band to the
conductance band, generating a reducing electron in the conductance band and an
oxidising hole in the valence band. This allows the holes and electron to get trapped
in surface states, and will undergo reactions with electron donating or accepting
species which have been absorbed at the TiO2 surface. This results in highly
charged electrons and holes which will then facilitate redox reactions, which will
result in the mineralisation of aqueous pollutants (Adams M. et al, 2013). Hydroxyl
radicals are generated on the surface of TiO2 through reactions of valence band
holes with absorbed water, hydroxide or surface titanol groups. Conductance band
electrons will react with electron acceptors such as oxygen in order to produce
superoxide (O2
-). Redox potential of TiO2 electron/hole pair allows for the production
of hydrogen peroxide, primarily via reduction of absorbed oxygen (eq1-7)
(McCullagh C. et al, 2011)
TiO2 + h TiO2(e-
cb + h+
vb) (1)
h+
vb + OH-
,ads OH
,ads (2)
OH
,ads + Reactant Oxidized Products (3)
e-
tr + O2,ads O2
- (4)
O2
- + H+ HO2
(5)
HO2
+ HO2
H2O2 + O2 (6)
H2O2 + e-
cb OH + OH- (7)
18. 7
Figure 2.2 Photo excitation of Titanium Dioxide
2.4 Photoreactors and Types of Configurations
In order to demonstrate viability of semiconductor photocatalysis for industrial use,
Reactor deign is extremely important. Reactor Design research and development
aims to scale up laboratory scale projects into industrially feasible applications,
however this is a complex process as a lot of contributing factors are to be
considered in order to develop an acceptable efficient process. Factors which affect
the reactor design include distribution of pollutant and photocatalyst, pollutant mass
transfer, reaction kinetics and irradiation characteristics (McCullagh C. et al, 2011).
The most important consideration for a photoreactor design however is effective
photocatalyst illumination as it essentially determines the amount of water that may
be treated per effective unit area of deployed catalyst. Central to scaling up of
photoreactor is the problem of providing uniform distribution of illumination across
the sufficiently high specific area of photocatalyst required at larger scale.
Examples of reactor configurations are considered below
OH
O2
O2
-
OH-
Bandgap
3.2eV
e-
h+
Conduction Band
Valence Band
UV light
19. 8
2.4.1 Multi Tubular reactors
TiO2 catalyst has been tested using multi tubular Photoreactors in order to lessen
the demand for excessively large surface area of reactors which could have big
implications for the consideration of reactors for industrial use as one of the biggest
issues surrounding Photoreactors is the need for large reactors due to the
requirement for large surface area for the catalyst. This type of system is
investigated by Adams Morgan et al. Using a lanthide doped Titania catalyst in order
to overcome the TiO2 catalysts restriction to UV wavelengths. The catalyst is used
as a coat for thin glass tubes that serve as the method of catalyst deployment. The
reactor is tested comparing results with similar reactors using alternate methods of
deployment (silica beads and Degussa P25). All reactors are tested under same
conditions, under UV radiation and then visible light. The results show similar
degradation of the methyl orange dye in the coated tube reactor to the use of
powdered catalyst under UV radiation and 70% degradation under visible light. The
use of the multi tubular reactor addresses issues encountered when using powdered
catalyst by eliminating the need for a filtering system as well as the use of excess
power required to run suspended powder reactors, which raises environmental
issues. The report further concludes that the multi tubular reactor can be seen to be
the more industrial friendly option as despite its significant reduction in surface area
degradation displays very comparable results.
Figure 2.3 Thin filmed multi tubular photoreactor and illumination box (M. Adams, et al. 2012)
20. 9
2.4.2 Suspended Liquid Reactors
TiO2 catalyst are often used in slurry/suspended reactors due to the large surface
area available to facilitate a reaction. Although this is seen as an advantage, the
need for filtration systems to filter out the fine powdered catalyst in order to separate
it from the effluent is an expensive feature and is a very large setback for industrial
consideration. Nan Chong et al. investigate the use of H-titanate nanofibers in an
annular slurry reactor for the degradation of Congo red. The aim was to develop a
potential solution for the catalyst separation problems experienced by conventional
slurry reactor systems. The H-titanate fibres possessed a high settling velocity (8.38
x 10-4 ms-1) as such could be easily separated from the effluent through
sedimentation. This provided a more cost effective approach to catalyst separation.
Although the benefits of this investigation are clear it is stated that irradiation of the
catalyst was difficult due to shielding of the light source by nanofiber particles closer
to the reactor walls therefore light penetration was limited.
Figure 2.4 Drum reactor finished model and schematic (C. McCullagh, et al., 2011)
Alternative to this method it is possible to attach the catalyst to a transparent
support. This method does provide adequate illumination of the catalyst but the
drawback being that it relies heavily on the mass transport of the pollutant to the
catalyst, which could be affected by any number of things within the reactor like the
causing slower rates of degradation.
In order to increase the degradation rate in slurry reactors an effective way of mixing
is required. M Adams et al. (2013), developed a novel drum reactor for photo
catalytic water treatment with the aims of finding an effective way for catalyst
21. 10
treatment that could be used at industrial scale. The drum reactor concept proposed
a drum which would serve as the reactor which would be continuously rotated in
order to provide an adequate method of mixing the catalyst-effluent slurry. Three
reactor designs were proposed and developed for batch and then continuous-flow
systems. The first of the three reactors consisted of a drum fitted with agitation
baffles to allow for high level of wastewater-catalyst interaction during rotation. The
second iteration of the reactor was designed based of the first with the aim of
increasing the agitation between the wastewater and catalyst suspension. A series
of paddles are incorporated into the inside of the drum so upon rotation agitation
would occur by the movement of the paddles within the drum resulting in turbulent
flow. The third iteration of the reactor taking inspiration from the first 2 included
paddles on the inside of the reactor constructed along the longitudinal length of the
drum in a V arrangement in order to counteract a corkscrew effect due to rotation
that would cause the catalyst to gather at one end of the vessel. The third design
further developed into a modular system of reactors capable of industrial use. The
third reactor is further investigated and it is found that the addition of the internal
paddles greatly increases mass transport and also the rate of pollutant degradation
showing an 85% reduction in organic content.
Mass transport with respect to slurry reactors has been largely ignored as an
impediment to the use of slurry reactors as the effects are not regarded as
consequential to degradation rates. The effects of photocatalyst irradiation, loading,
flow rates, total suspension volume, and changes in illumination length of the reactor
are investigated by Ballari et al. it is found that the limitations of mass transport can
result from non-uniformity of the irradiation surface. It is further stated that said
limitations are difficult to avoid but can be removed with fully turbulent flow within
the reactor. In Conclusion it is stated that can be overcome using 1g L-1 catalyst
loadings, 1 x 10-7 Einstein’s cm-1 s-1
accompanied by effective mixing.
2.4.3 Flat Plate Reactors.
Flat plate reactors are reactors consisting of a rectangular sheet on which the
catalyst of choice is adhered to. The sheet is positioned at an incline allowing for
laminar flow of the wastewater down the sheet which is irradiated by a light source
usually UV radiation. Flat plate Photoreactors are still very much developmental but
the use of this type of reactor possesses a relatively large catalyst surface area
22. 11
which means there is more space for the photocatalytic reactions to take place. Also
the flat plate reactors benefit from a uniform light distribution over the catalyst
surface which ensures uniform rate of degradation across the plate. Bearing the
obvious advantages in mind it is also important to note that the flat plate reactors
suffer from being mass transfer limited, and the fact that only a thin layer of
wastewater can be treated at a time massive areas will be needed for industrial
scale up.
Figure 2.5 Fixed bed Reactor schematic (Nogueira and Jardim, 1994)
Nogueira and Jardim developed and immobilised catalyst reactor for water
decontamination using solar light by adhering a TiO2 aqueous suspension to a flat
glass plate in order to produce a thin film of photocatalyst along a the flat plate which
would serve as the reaction site. The immobilised catalyst support (glass pate) is
faced towards the equator at a 22° incline. The reactor would have wastewater
delivered to it by a pump at the top at a pre-determined flowrate and allowed to flow
down by gravity while irradiated by sunlight to be collected and the base. The test
was carried out using single pass and then recirculating configurations. Using
methylene blue as a model substance, the reactor is observed to show 95.8%
degradation at a 22° slope and 89% degradation at a 25° slope.
23. 12
Figure 2.6 Flat plate reactor prototype (M. Adams, et al., 2008)
Adams et al, developed a flat plate reactor for removal of hydrocarbons from water
subsequently developing a multi-layer lab unit intended as a concept for a scaled
up design. The multi-layer flat plate reactor was developed based on an initial
prototype which was a conventional setup similar to development undertaken by
Nogueira and Jardim. Two Tests were carried out using a TiO2 catalyst testing two
different substrates (plates) one made of polymethylmethacrylate (PMMA) and
titanium metal. Both plates possess their own benefits as PMMA is known to be
transparent to UV light and that titanium produces titanium dioxide (TiO2) upon
oxidation which is also the catalyst of choice also it is thought that the adhesion
between the catalyst and titanium plate will be very good. The catalyst Plates are
prepared by coating the plates in an evenly distributed TiO2 and methanol
suspension and then allowed to dry. The plates are then mounted on to a support
at an angle to allow for effluent mass transport through gravity the support
incorporates a UV lamp help right above the plate. The Prototype setup as seen in
Fig 6. Shows all parameters described above. The Multi-layer system incorporates
the same design with multiple plates beneath each other with effluents moving from
one plate to the next creating a “concertina” multi plate reactor model. The results
from the experiments undertaken show a clear dominance of the PMMA plates to
the titanium plates as can be seen in the graph below (Fig 2.7). The graph also
shows that with a reduction in angle of the plate destructive efficiency increases due
to lower angles providing longer contact times between the catalyst and effluent.
The image below displays the multi-layer concept design developed by Adams et
al., (2008) for industrial scale up.
24. 13
Figure 2.7 Comparison of substrate with angle at optimum TiO2 loading (M. Adams, et al., 2008)
Figure 2.8 Multiple thin film plate reactor stack, Lab unit (left) concept design (right) (M. Adams, et al., 2008)
Although above a few reactors are considered there are still many reactor types that
have been developed and recorded in recent literature. In a review of photocatalytic
reactors McCullagh et al. produce a list of some reactors recorded in literature over
30 years predating the publication of the journal (2011). Below is a list of other
reactor types in previous literature (McCullagh et al., 2011).
Annular photoreactor
Packed bed photoreactor
Photocatalytic Taylor vortex reactor
Fluidised bed reactor
Coated fibre optic cable reactor
Falling film reactor
Thin film fixed bed sloping plate reactor
Swirl flow reactor etc.
25. 14
3 Design Development
3.1.1 Design Criteria
Based on research carried out on current technologies and recent developments
Key parameters for reactor design are identified to be an effective means of catalyst
deployment to allow for suitable interaction between catalyst and wastewater,
effective method of mixing in order to eliminate mass transport dependencies,
optimizing design for effective irradiation, method of on line catalyst separation to
eliminate need for additional separation processes.
3.1.2 Recirculation Mechanism
The recirculation mechanism was developed as a simple set of pipe one leading
from the stock solution to the pump and then from the pump to the reactor flow will
continue out the reactor and back into the stock solution.
3.1.3 Design Development
Based on all the parameters listed above a number of design ideas were considered
for development, taking cues from other successful reactors the design ideas are all
evaluated for suitability. Different Reactor configurations are considered for
development but due to time constraints and available resources some design are
cut from the evaluation process as the timescale for production will impede progress
of research. As a result the reactor configuration considered is a slurry/batch type
reactor as they are simple designs and have been extensively research for water
remediation which provides respectable expectations for the final design. Batch
reactors suffer from mass transport limitations and effective catalyst deployments
and as such considered design varied by mixing methods and catalyst deployments.
Design sketches for considered design can be found in the appendix.
26. 15
Design 1
Figure 3.1 Paddle concept design
The first proposed design featured a paddle mixer deployed on the inside of the
reactor to be powered by a motor. This mixer is to be made of glass as to allow for
light propagation through it in order to allow effective photocatalysis. The mixer
effects agitation allowing for even spread of the photocatalyst within the reactor
vessel.
Disadvantages that this design present are that a design such as this scaled up
would involve development of expensive components for example the glass mixer
would be a relatively costly component to develop. Powering the glass mixer at
industrial scale will also incur more cost as the motor required to power the mixer
would consume energy which will also have to be factored into cost.
Catalyst configuration options for this design would be limited to powder or pelletized
catalyst which present filtration problems as catalyst effluent separation
mechanisms would have to be included.
27. 16
Design 2
Figure 3.2 Glass Bead concept design
This design features photocatalyst coated glass beads within the reactor. The glass
beads are to remain within the reactor chamber in place with the effluent as to void
the need for mixing as the glass beads provide even distribution of the catalyst
around the reactor. Filtration also becomes unnecessary as the large beads will be
incapable of passing through pipes. This method of catalyst deployment provides a
high surface area for irradiation although less than a powder configuration but
greater than alternative immobilized catalyst configurations.
Drawback for this design are the possibility of a glass bead blocking outflow of
wastewater causing pressurisation of the reactor and then eventual failure of the
reactor. Also despite the availability of good reaction surface area, the glass beads
reduce available volume for the wastewater to occupy the reactor which reduces
reaction sped.
28. 17
Design 3
Figure 3.3 Internal drum concept design
The third reactor design involved the insertion of a smaller glass cylinder coated
with a catalyst deployed inside of the reactor chamber this smaller glass cylinder
was to feature small paddles along the inner diameter in order to agitate the
wastewater as well as a powdered catalyst which would also be loaded into the
reactor. The benefits of this model were that it the mixer instead of serving no
function other than agitation would also serve as added catalyst surface area to that
of the powdered catalyst within.
The drawback of this design similar to the first, it would involve the use of a motor
for power which would increase energy costs at larger scale as well as the difficulty
in manufacturing the internal cylinder at a larger scale will incur additional cost
making this an expensive system to manufacture. Also filtration methods will need
to be considered for the powdered catalyst.
29. 18
3.2 Developed Design
In order to develop a suitable system a prototype model was designed for testing.
This model features a simple design with a glass tube and plastics caps on both
ends fitted with ports to accommodate pipe fittings.
Figure 3.4 Reactor Model
The prototype was designed with the aim of testing a variety of catalyst loading and
as such easy access to the reactor chamber is included through the splitting of the
upper end cap into two sections. The upper end are held together with using screws
and bolts while a seal is created using silicone grease at the interface of the two
parts. The outer end caps are fitted with 2 holes each to accommodate pipe push
fittings which would be connected to ball vales to control flow. In operation the
wastewater would be pumped through the top of the reactor and flow out of the
reactor through the bottom back into the stock solution to be recirculated back into
the reactor. Both holes at the base will be kept open to allow flow In order to increase
flow rate out of the reactor to prevent filling the reactor as the filters placed in each
fitting will impede causing the reactor to fill up faster than it can be drained, which
would lead to leaks as the silicon grease seal would not hold up under pressure.
The interfaces between the caps and glass were joined using a silicon sealant in
30. 19
order to prevent leaks and four tie rods running through all caps secured using nuts
hold the entire reactor together.
In order to eliminate mass flow rate dependencies, the recirculating nature of the
system was considered acceptable agitation as through recirculation all of the
wastewater would pass over the catalyst within the reactor. In order to prevent the
catalyst settling at the base of the reactor, it was assumed that partially filling the
reactor to allow the inflow of water to create a plunge which would move the catalyst
around within the reactor.
3.2.1 Build Procedure
Reactor vessel end caps are made of Polytetrafluoroethylene (PTFE) more
commonly known as Teflon due to its good resistance to UV radiation. Caps are
Machined from Bar according to drawings contained in the appendix. The RS
components bought glass tube is then capped at both ends and bonded to Teflon
caps using a RTV silicone sealant. Tie rods are incorporated at 4 point on both caps
to maintain the integrity of the seal as Teflon is renowned for its not stick properties
and as such the silicon seal will only serve to prevent leaks. Silicone seal is deemed
fit for purpose due to the low pressure the reactor will be operating at. Another four
bolts are used to secure the end caps on the top of the reactor and silicone grease
is applied at the interface in order to prevent leaks from this section. Each port is
connected to a pipe push fitting and then subsequently connected to ball valves
which lead to two tanks on either end of the reactor one for wastewater and one for
effluent. The effluent will then be recirculated into the wastewater tank and then
back into the reactor.
Model technical drawings are as seen in (appendix A)
31. 20
Figure 3.5 Reactor parts and assembled prototype
3.2.2 Design Calculations
The Design for the prototype was highly reliant on the incoming turbulent flow to
produce sufficient agitation. In order to determine the flow regime of the incoming
solution, Reynolds number of the flow coming into the reactor from the pipes had to
be calculated.
The pipes used in the prototype design were smooth transparent flexible PVC pipes
with dimensions as follows:
Outer diameter: 7.35mm
Inner Diameter: 6.35mm
Flow is classed as turbulent when Reynold’s Number (Re) is greater than 4000
(Re>4000)
𝑅 𝑒 =
𝜌𝐷𝑉
𝜂
(1)
Where: ρ = density
D = diameter
V = velocity
η = dynamic viscosity
32. 21
Density of water is taken as 1000kg/m3 while dynamic viscosity is taken to be 1 ×
10−3
𝑘𝑔/𝑚𝑠
Pump volumetric flow rates: 9 x 10-6m3/s - 25.7 x 10-6m3/s
In order to calculate required flow rate for turbulent flow, Re was required to be 4100 in
order to avoid possibility of transition flow (Re 1000 – 4000).
Through volumetric flow rate, flow velocity can be calculated using the following equation.
𝑄 = 𝐴𝑉 (2)
Where: Q = Volumetric flow rate
A = Pipe Cross sectional area
V = Flow velocity
𝑖𝑓 𝑅 𝑒 = 4100
𝑉 =
𝑅 𝑒 𝜂
𝜌𝐷
=
4100 × 1 × 10−3
1000 × 0.00635
= 0.6457𝑚/𝑠
𝑄 = 𝐴𝑉 =
𝜋 × 0.006352
4
× 0.6457 = 20.45 × 10−6
𝑚3
/𝑠
Therefore in order to implement turbulent flow, incoming flow rate will have to be
set at 20.45 x 10-6m3/s.
Pump specifications located in Appendix B
Pump specs are in imperial values unit conversion calculations are located in
Appendix C.
33. 22
4 Testing
4.1 Experimental setup
In order to determine the suitability of developed ideas, the reactor was put through
a photocatalysis tests using methylene blue as a model compound for degradation
which would give indications off how this design would fair in larger scale.
4.1.1 Methylene blue
Two Methylene blue stock solutions were prepared at 100𝜇𝑀/𝑙 concentration. The
solutions were prepared by adding 0.03739 grams of methylene blue dye (Fisher
Brand) in 100ml of water. Two sets of solution both 600ml, were then produced at
10𝜇𝑀/𝑙 through further dilutions of the stock solutions. Calibration curve for
methylene blue solution displayed below in (Fig 4.1).
Figure 4.1 Methylene blue Calibration curve
The graph in Fig 4.1 was developed by diluting the methylene blue stock solution at
10μM/L by decrements of 2 in order to develop a linear relationship for methylene
blue concentration and UV absorbance which can be used to asses absorbance of
the solution during test phases to obtain methylene blue concentrations through the
use of the line equation.
4.1.2 Catalyst loading
Pelletized TiO2 was used as the photocatalyst for the reaction for ease of catalyst
and effluent separation. Catalyst loading was set to 30g/l. For the reactor volume of
y = 0.0917x - 0.0151
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12
Absorbance
Concentration (μM/L)
Calibration Curve
34. 23
249ml the catalyst loading was calculated to be 7.47g. Catalyst and solution were
allowed to sit in dark prior to testing to reach dark absorption equilibrium.
4.1.3 Pump
For the recirculation mechanism a verderflex EV1500 peristaltic pump was used
with flow rates ranging from 3.17ml/s - 42.83ml/s. The pump also provided a means
of agitation for the reactor so as to circumvent mass transport limitations of the
reactor. Reactor was filled to about 80% capacity to create a plunge within the
reactor chamber which also allowed for better mixing. The pump is run at the mean
flow rate between max and min flows approximately 22.9985 x 10-6m3/s which is
sufficient enough to effect turbulent flow.
4.1.4 UV Light Containment Reactor (illumination source)
The UV Light containment reactor (Fig 3.1) obtained from prior experiments run
within the CRE-E lab consisted of 4 UV lamps, one on each wall of the box. The box
was fitted with ports which accommodated fans to keep the system temperature at
safe levels. The UV lamps used in the UVLCR are commercially available low power
36W compact non-integrated fluorescent lamps the box was constructed using
Perspex which is mirrored on the interior. Spectral output of UV lamps within the
UVLCR are shown in Fig 3.2 below.
Figure 4.2 Ultraviolet Light Containment Reactor (UVLCR)
35. 24
Figure 4.3 Spectral output for UV lamps
4.2 Experimental Procedure
The photoreactor vessel was placed into the UV light containment reactor (UVLCR)
and two tests were ran.
Figure 4.4 Experimental setup
The first test was a control test with the photoreactor and methylene blue solution
inside the UV light containment reactor without any catalyst. The experiment was
ran for a period of 60 mins with a 1ml sample collected every 10mins using a pipette.
The second experiment was carried out using the photocatalyst and methylene blue
within the photoreactor and then placing it into the UVLCR. The process was
allowed an equilibrium time of 30 mins in the dark (with UVLCR turned off). In order
36. 25
for the dark absorbance to be determined 1ml sample was taken before and after
equilibrium period. After equilibrium period the UVLCR was turned on and then the
process was allowed to run continuously for 60mins with 1ml samples taken every
10mins. The samples were analyzed using UV-vis spectrometry and the absorbance
recorded. The experiment was run with agitation produced by incoming flow o the
reactor. Catalyst and solution separation was carried out within the reactor by mesh
filters placed inside of each outlet fitting.
4.3 Results
The first experiment carried out on the MB solution irradiated in UV light without any
photocatalyst loading, in order to determine MB degradation under UV light without
the photocatalyst to induce a reaction. The following absorption spectral pattern was
produced as a result.
Figure 4.5 Temporal absorption spectral pattern of MB under UV radiation only
Fi 4.5 above shows the Degradation of the methylene blue solution over 60 minutes
of irradiation by UV light alone. The graph shows a relatively insignificant drop in
absorbance of the methylene blue solution which indicates little or no degradation
can occur without the presence of the photocatalyst.
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
390 440 490 540 590 640 690 740 790
Absorbance
Wavelength, nm
MB absorbance pectral pattern over 60 miuntes
60
37. 26
The 2nd experiment ran to show methylene blue degradation under UV irradiation
with a photocatalyst loading. The following absorption spectral pattern was
observed.
Figure 4.6 Temporal absorption of methylene blue degradation in the with catalyst loading under UV irradiation
Fig 4.6 shows the degradation of methylene blue over a 60 minute UV irradiation
period in the presence of a TiO2 photocatalyst.as seen over the 60 minute period,
significant drops in the absorbance of the methylene blue solution can be observed
which gives indication of the performance of the reactor.
Following collection of both results Fig 3.7 below is developed through calculating
percentage absorption.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
390 440 490 540 590 640 690 740 790
Absorbance
Wavelength, nm
MB Absorbance spectral pattern over 60 minutes
38. 27
Figure 4.7 %Absorption of methylene blue at maximum absorption wave length
Fig 4.7 shows a comparison of the percentage drop in absorbance of MB solution
over the 60 mins comparing how much of an effect the photocatalyst has on the
reaction further highlighting the importance of catalyst loadings
Using the equation of the line governing the methylene blue calibration curve, the
following graph showing the drop in methylene blue concentration in both tests.
Figure 4.8 Methylene blue concentration over 60 minutes of photocatalysis
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50 60
%Absorption
Time (min)
Methylene blue %absorbance at 667nm
UV + Cat
UV
0
2
4
6
8
10
12
0 10 20 30 40 50 60
Methyleneblueconcentration(μM/l)
Time (minutes)
Methylene Blue degredation over 60 mins
UV only
UV+CAT
39. 28
Figure 4.8 shows a comparison of MB concentration drop as time elapses. With a
near constant degradation in the presence of catalyst and then relatively no
degradation in the UV control test.
40. 29
5 Discussion
5.1 General Overview
For the design of the reactor various parameters were put into consideration.
Factors like catalyst loadings, effective mixing amongst others play a huge part in
how effective a reactor design will be in the long run. For the final design chosen,
the major challenges involved were finding suitable methods to effect photocatalyst
and wastewater separation within the pump. Although it would have been beneficial
to have incorporated more advanced catalyst loading design like coated silica beads
or the multi tubular design developed by Adams Morgan, time constraints would
prove an obstacle to such endeavors. Regardless however the availability of
pelletized TiO2 proved the ideal solution. Although proven that Degussa P25 powder
would produce more efficient and quicker degradation of methylene blue, it was
ultimately dismissed as an option due to the difficulty that separation of this powder
would create for the reactor. The initial final design which featured just end caps and
glass tube joined by a silicon sealant proved ineffective as the Teflon material used
for the end caps is a non-stick compound and without the use of a primer bonding
of the Teflon to the glass could not be achieved which lead to leaks and caps falling
off in the original design. The revised design which incorporated tie rods served to
better hold the reactor together while silicon grease and a sealant kept fluid from
leaking out of the reactor and proved a better all-round design and held together for
the duration of the experiment.
Under experimental conditions, the implementation of turbulent inflow although
successful coupled with the plunge created by the partially filled reactor, upon
observation was not a successful enough approach as the photocatalyst was drawn
to the bottom of the reactor by the outflowing liquid which could lead to reduced
degradation rates. Regardless of this fact, it can also be said that through
recirculation mass transport is negated as the photocatalyst will make contact with
all the MB solution present as it is passed out of the reactor and back in.
Bearing in mind all fall backs of the final design, improvements can be made in order
to better performance of the reactor. Firstly retention times within the reactor are
relatively a lot lower than you would have in a non-continuous flow system which
leads to less time for photocatalyst and solution to react causing less degradation
41. 30
rates. This problem can be easily combated by including multiple passes in the
reactor system. This sort of design will also be better suited for handling larger
volumes of wastewater although incurring more cost. Efficient mixing of the catalyst
and MB solution was not achievable using methods discussed in the original design
and as such simplified mixing methods i.e. the use of paddles or rotation of the
reactor are viable options for improvements on the photocatalyst interaction with the
available solution. Improvements upon this area should ensure a more even spread
of photocatalyst around the reactor.
5.2 Test Results
Adsorption of organic pollutants is an important indicator for determining the
degradation rates of photocatalytic oxidation. Methylene Blue (MB) adsorption on
the surface of the TiO2 greatly affects the degradation process as it is theorized that
oxidation of organic compounds occurs following adsorption of the organic
compounds on the photocatalyst surface.
The control experiment which was carried out using the methylene blue within the
reactor irradiated within the UVLCR. Using ultraviolet visible spectral analysis, to
monitor the MB absorbance the absorption spectral pattern in Fig 4.5 was produced
in order to show how much degradation the UV light alone was responsible for this
would demonstrate how much degradation of the MB solution is truly photocatalyst
reliant. As seen in the Fig 4.5, the drop in absorbance over the 60 minute irradiation
period was quite minimal. Over the first 30 mins it can be seen that the UV does
degrade the methylene blue to some extent before the absorbance eventually
stagnates. Fig 4.6 which represents the photoreactor experiment carried out with
the photocatalyst loading of a concentration of about 30g/l of pelletized TiO2. This
graph shows that over the 60 minutes about 47% of the MB has been degraded
within the solution. This in stark contrast to the experiment carried out with UV alone
and shows just how much the effect of the photocatalyst has upon the entire
process. The methylene blue solution shows peak absorbance at around 667nm
wavelength. At that peak the drop in methylene blue absorbance is clearly
pronounced when photocatalyst absorbs UV radiation work to initiate the
photocatalytic reaction. Although, it is important to note that in prior experiments of
this type most notably the drum reactor developed by Adams et al., (2013), 90%
degradation over a 60 minute period was reported for continuous flow using 36W
42. 31
UV lamps deployed through the drum reactor. Failure of the reactor designed in this
report to reach benchmarks of similar systems reported in literature can be attributed
to the lack of multiple passes, insufficient agitation for the mixing of the catalyst, or
distance from illumination source.
Assessing results at peak absorbance (667nm wavelength), a comparison of the UV
and UV + Catalyst tests can be developed Fig 4.7 depicts the percentage drop in
absorbance of the methylene blue over the 60 minute irradiation time. For the UV
only test it shows the absorbance reaches an equilibrium at the 30 minute mark
where after that point degradation ceases to take place Whereas the UV +
photocatalyst test shows a relatively constant degradation in MB. This comparison
serves to further highlight the importance of the photocatalyst loading within the
photoreactor. Fig 4.8 the drop in methylene blue concentration as calculated using
the calibration curve using absorbance at the same wavelength as the calibration
curve. Although the concentration of methylene blue in the experiments was higher
or lower in the UV and UV+CAT experiments due to difficulties in precisely weighing
out the exact amount of methylene blue required, the rate of degradation is the
relevant parameter. This just reiterates the findings of Fig 4.7 but better depicts the
near constant degradation of methylene blue in the UV and photocatalyst test.
The testing phase for the photoreactor was carried out to achieve only the most
essential results to prove functionality of the proposed design. The tests carried out
do provide sufficient information which allows for assessments of how a similar
design at larger scale would fare.
43. 32
5.3 Improved Design
Figure 5.1 final design concept
For the improved design taking information from results derived from the prototype,
this final concept design was created. The tested photoreactor’s performance gives
indication of how a singular pass system would perform and through analysis of
results covered in the sections ahead, a multiple pass system was developed
incorporating the same accommodation for versatility in catalyst loadings. The
concept system would include a 3 pass system designed on the premise of the
prototype with the wastewater flowing through 3 reactor vessel sections before
finally flowing into the stock solution for recirculation. The addition of the 3 phase
system would allow for larger volumes of waste water to be treated within a given
time and also faster degradation rates as the photocatalyst surface area would triple
as well as contact time for the wastewater. Improvements on catalyst loading would
also be necessary and tighter seas effected by O-rings and sealants would allow for
higher pressure flow than the prototype. Suggested catalyst loading would be
coated Multi tubular set up similar to those developed by M. Adams, et al (2012) as
they would void the need for mixing of the catalyst and wastewater which is
beneficial for the recirculation as mixing would interfere with flow. The coated tubes
system have also been shown to produce highly efficient degradation in comparison
to what is reported as the most efficient catalyst choice (Degussa P25 powder). Fig
5.2 shows the relation developed by M. Adams, in the investigation carried out on
Multi-tubular and silica bead systems under UV irradiation clearly displaying the
multi tubular system at different doping percentages( green and blue) showing
44. 33
equally as high efficiencies as the powder catalyst (purple). Using coated tube
although reducing available volume within the reactor will allow for quicker reaction
times due to increase in surface area.
Figure 5.2 methyl orange degradation by P25 (purple), silica beads, and %doped glass tubes (blue & green)
(M. Adams, et al., 2012)
45. 34
6 Conclusion
All things considered, the prototype design achieved the intended primary result
which was to effect degradation of methylene blue through photocatalysis. The
primary aim was to design a labs-scale recirculating photocatalytic reactor for
wastewater remediation. Although the first iteration did fail to hold together, the
addition of tie rods served to solve the problem. The photoreactor successfully
degraded approximately 4 of the MB within a stock solution of about twice its volume
over a 60 minute time period. Given that other batch processes run with similar
reactor set ups show about 90% degradation at the reactors capacity without
recirculation, the prototype can be deemed a success.
Assessing the suitability of a lab scale reactor for larger scale development is a
difficult process as many factors come into play. As at larger scale effective
irradiation might prove problematic as well as ability to handle the massive volumes
of wastewater at an industrial level as well as the pumping power that would be
required for a photoreactor at that size. Adding all those factors the cost of such
operations begin to grow. The lab scale reactor designed in this project although
effecting successful degradation, was very reliant on pumping power for the
effective mixing which at larger scale will drive up cost. Also development of UVLCR
at larger scale might prove difficult as energy consumption will rise and the heat
produced by the UVLCR would have to be managed in for safety reasons.
Design stage problems like sealant failure could have been avoided through better
material selection or further research on the Teflon material used in order to have
implemented the use of a primer. Discrepancies in the testing phase like the
difference in base absorbance of the methylene blue solution arose from slight
differences in the concentrations of the two prepared solutions. This could have
been avoided through preparation of one larger stock solution which could then be
divided for testing. Regardless of errors present, the design can be concluded as a
success as the results provide an adequate benchmark for the development of the
improved concept design.
46. 35
7 Further Development
For further development on the photoreactor tested in this report, the suggested
improved design would be an ideal start as that design shows greater potential for
industrial scale use due to use of multiple phases. Further work will also benefit from
more extensive testing on developed reactor such as implementing various catalyst
loadings, or methods of catalyst deployment. Other improvements to consider are
development of integrated UV illumination into the design so as to reduce the
reliance on an external UVLCR system as used in the experiments detailed in this
report. Also recommended is developing the improved design into a modular system
which would allow for the addition of various phases which will increase the available
volume for reaction and as such fair better in industrial processes and also possess
a sort of versatility to be able to handle different volume requirements. Further
testing should include the development of multiple reactor sizes to discern a certain
linearity of degradation if any so as to accurately determine what a much larger scale
design would require for successful operation. Investigation into developing
catalysts for use in the visible light spectrum should also be considered as this is
seen as an ideal way to drive down cost as it would allow the photocatalysis process
ease of deployment in rural areas without easy access to electricity implement
sunlight for efficient irradiation.
47. 36
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