WO2005033016A1

WO2005033016A1 - Apparatus and method for treating fluid by means of a treatment container

Info

Publication number: WO2005033016A1
Application number: PCT/GB2004/004139
Authority: WO
Inventors: Peter Robertson; Ian Campbell; Donnacher Russell
Original assignee: The Robert Gordon University
Priority date: 2003-09-30
Filing date: 2004-09-29
Publication date: 2005-04-14
Also published as: EP1673309A1

Abstract

An apparatus for treating a fluid, typically degrading pollutants is disclosed. In a preferred embodiment of the invention, the apparatus comprises a transparent container (12) which is rotated proximate to a uv-light source (14). Inside the container a plurality of paddles are provided which turbulate a mixture of the fluid and pelletised TiO2 catalyst.

Description

APPARATUS AND METHOD FOR TREATING FLUID BY MEANS OF A TREATMENT CONTAINER

This invention relates to an apparatus and method fo r treating a fluid, and more particularly but not exclusively, relates to degrading pollutants in ef fluent .

Ef luent can be generated domestically and by a number of industries , including pharmaceutical , textile, oil and gas , agricultural , food and chemical sectors . The effluent produced by these industries contains organic compounds that are harmful to the environment and must be treated to remove or break down these compounds .

There are many types of water that need to be de contaminated, and these consist of drinking water, industrial waste , produced water (oil and gas ) and pharmaceutical waste streams/by-products .

Current techniques for the treatment of waste ef fluents include coagulation, chlorination, ozonation, Ultraviolet (UV) disinfection and adsorption methods.

However, these techniques often produce unsatisfactory results. For example, chlorination can produce chlorinated organic compounds which are mutagenic, hydrogen peroxide treatment is expensive and adsorption methods using granular activated carbon produce large volumes of hazardous waste which must be disposed of in the proper manner.

The use of photocatalysis in an advanced oxidation process is thought to be a more efficient way of treating effluent. Known apparatus to treat effluent in this way include tubular flow reactors, batch reactors and flat plate reactors.

A tubular flow reactor comprises a UV lamp enclosed within a tube and a catalyst film adhered to the inside of the tube. Effluent is pumped into one end of the tube and released from the other. Although generally satisfactory, this reactor has a limited number of interactions between the pollutant molecule and the catalyst surface; that is, it is mass transport controlled.

Mass transport can be improved somewhat by using batch reactors which operate simply by adding catalyst into effluent and irradiating them with light. However, the light distribution is poor and the catalyst has to be separated from the effluent after use which leads to further costs. A. flat plate reactor comprises an angled plate with a thin film of catalyst on its surface and a light source provided above the plate. The effluent flows over the plate and is degraded as it passes over the catalyst surface. Mass transport is also a limiting factor in such a reactor. Also, the limited surface area limits the amount of water which can be treated.

According to a first aspect of the present invention, there is provided an apparatus for treating a fluid, the apparatus comprising a container, and a means to move the container.

Preferably, the apparatus is exposed to a light source in use. More preferably, the apparatus comprises a light source and the container is adapted to move with respect to the light source. Alternatively the apparatus may be exposed to sunlight or another light source such as an artificial visible light source.

Preferably, the light source is a UV light source. Preferably, the container is adapted to allow the passage of light therethrough. Preferably therefore, the container is transparent.

Preferably, the container is adapted to receive the fluid within a void thereof. Preferably, the container comprises agitation means so that, in use, the fluid is agitated, preferably in a turbulent manner.

Preferably, the agitation means comprise at least one blade provided on the container. The agitation means may be helically shaped.

The agitation means may include curved portions or slots .

Even more preferably, the agitation means comprise a plurality of paddles. Preferably, the paddles are spaced apart from each other in, or on, the container.

Preferably, the container is substantially cylindrical. Where the agitation means are provided in a helical shape, a first end of the agitation means is preferably offset by its second opposite end by around 90°. Preferably, the paddles are arranged in a helical pattern on the container.

Alternatively, the paddles may be arranged in a V- shaped formation.

Preferably, the light source comprises a plurality of light generation means which are preferably equi— spaced around the outer circumference of the cylindrical container. Typically, the light generation means comprise UV tubes arranged with their longitudinal axis parallel to the longitudinal axis of the cylindrical container.

Preferably, the container is adapted to rotate relative to the light source, and preferably it is the container that rotates and the light source is stationary.

A catalyst may be provided by any suitable means, for example, on walls of the container or added to the container.

Preferably the catalyst comprises Ti0₂. More preferably the Ti0₂ is in the form of pellets. Even more preferably the Ti0₂ pellets are prepared by the process described in US 6,660,243, the disclosure of which is incorporated herein in its entirety by reference. Alternatively the catalyst may be a semi-conductor photo-catalyst such as tungsten oxide, barium titanate, zinc sulphide or tin oxide. Powder or pellets may be used

Preferably, the apparatus is adapted to degrade a portion of any pollutants in the fluid.

Preferably, the container is rotated by a motor means. Preferably, a drive shaft of the motor means is connected directly to the container. Alternatively the container may be belt driven or geared. Optionally a plurality of containers may be provided. The containers may be connected together by any suitable means, such as fluid transfer plates, which allow fluid to flow between a first container and a second container.

According to a second aspect of the invention there is provided a method for treating a fluid, the method comprising inserting a fluid into a container, exposing the container to a light source and moving the container relative to a light source. Preferably, the container is moved, more preferably rotated, and the light source is stationary.

Preferably, the method according to the second aspect of the invention is performed using the apparatus according to the first aspect of the invention.

Preferably, the fluid is placed within a void of the container.

Preferably, the light is shined through the container onto a portion of the fluid.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: - Fig. 1 is a perspective view of an apparatus for treating a fluid in accordance with the present invention; Fig- 2 is an end view of the apparatus of Fig. 1; Fig. 3 is a diagrammatic front view of a second embodiment of an apparatus for treating a fluid in accordance with the present invention; Fig. 4a is a side sectional view of a drum comprising straight blades which can form part of the apparatus of Fig. 1 and Fig. 3; Fig. 4b is a partially cut-away perspective view of the drum of Fig. 4a; Fig. 5 is a portion of a curved blade for use with the apparatus of Fig. 1 or Fig. 3 instead of the straight blades of Fig. 4a; Fig. 6 is a partially cut-away perspective view of a second drum comprising spiral blade (s) which can form part of the apparatus of Fig. 1 or Fig. 3; Fig. 7 is a side view of a third drum comprising longitudinally and rotationally spaced apart blade portions which can form part of the apparatus of Fig. 1 or Fig. 3; Fig. 8 is a perspective view of a further development of the drum of Fig. 7 which can form part of the apparatus of Fig. 1 or Fig. 3; Fig. 9 is a graph showing the absorbance of light at 664nm by methylene blue against time for a variety of different speeds of a first drum; Fig. 10 is a graph showing the natural log of (Absorbance by methylene blue/Absorbance at T=0) against time for the variety of different speeds of the first drum; Fig. 11 is a graph showing the absorbance of light at 664nm by methylene blue against time for a variety of different distances between a light source and the said first drum; Fig. 12 is a graph showing the absorbance of light at 664nm by methylene blue against time for a variety of different H₂0₂ concentrations for the said first drum; Fig. 13 is a graph showing the natural log of (Absorbance by methylene blue/Absorbance at T=0) against time for the variety of different H₂0₂ concentrations for the said first drum; Fig. 14 is a graph showing the absorbance of light at 664nm by methylene blue against time for a variety of different speeds of a second drum; Fig. 15 is a graph showing the natural log of (Absorbance by methylene blue/Absorbance at T=0) against time for the variety of different speeds of the second drum; Fig. 16 is a graph showing the absorbance of light at 664nm by methylene blue against time for a variety of different distances between a light source and the said second drum; Fig. 17 is a graph showing the absorbance of light at 664nm by methylene blue against time for a variety of different H₂0₂ concentrations for the said second drum; Fig. 18 is a perspective view a yet further drum which can form part of the apparatus of Fig. 1 or Fig. 3; Fig. 19 is a side view of the Fig. 18 drum; Fig. 20 is second embodiment of the invention comprising a plurality of drums; Fig. 21 is a third embodiment of the invention comprising two drums; Fig. 22 is a fluid transfer plate which forms part of the Fig. 21 embodiment; Fig. 23 is a perspective view of a fourth embodiment of the invention comprising three reactor drums; Fig. 24 is a top view of the Fig. 23 embodiment; and, Fig. 25 is a side view of the Fig. 23 embodiment.

A first embodiment of an apparatus 10 for treating a fluid in accordance with the present invention is shown in Figs. 1-2 and comprises a cylindrical drum or container 12, a series of circumferentially equi- spaced ultraviolet (UV) lamps 14, support wheels 16, a drive shaft 18 and a drive band 20.

The drive shaft 18 is connected to a motor 19 which rotates the shaft 18 and the drive band 20 and in turn causes the drum 12 to rotate on the support wheels 16.

Removable end caps (not shown) are preferably provided for the ends 34, 36 of the drum 12 in order to seal fluid therein. The end caps are round pieces of Perspex stuck to the drum 12 and have a shoulder (not shown) adapted to sit firmly within the end of the drum 12 to prevent leaks therefrom. A hole (not shown) is provided within the end caps to allow fluids to be added and removed from the drum 12. The hole can be plugged during use. Alternatively an input hole may be provided in the centre of the end cap for the end 34 and an output hole provided in the end 36 in an off-centre position. For such embodiments the fluids are allowed to come up to but not rise above the central input hole in the end 34 in use and can drain out of the off-centre output hole of the end 36 once they have been treated.

The drum 12 is formed from a transparent material such as Perspex™ and so permits the passage of light from the UV lamps 14 into the drum 12. In the experiments described below, the Perspex chosen was common PMMA although better quality Perspex is preferred to allow more UV light to reach a catalyst (not shown) present in the drum 12. An ultraviolet spectrum was obtained on a sample of the Perspex using a Perkin-Elmer Lambda Series/PECSS Spectrometer to determine the wavelength at which Perspex will not allow the absorbance of light. This was found to be under 190nm. The UV lamps 14 used in the experiments described below operate between 360 and 490nm and so the use of this Perspex did. not distort the experimental results.

A preferred embodiment of an apparatus 100 is shown in Fig. 3. The apparatus 100 comprises a number of like parts with the apparatus 10 and such like parts will not be described further. A significant di ference is that a motor 122 is connected directly to a drive shaft 118 rather than via a drive band. This allows the drum 112 to rotate freely on support wheels (not shown in Fig. 3) without drag from the elasticity of a drive band. Preferably, frictionless drive shaft support bearings 124 are provided to reduce the friction generated. The provision of a direct drive shaft 118 in this way and frictionless bearings reduce the friction and thus reduce the torque required from the motor 122. A similar arrangement of UV lamps to the UV lamps 14 of Fig. 1 and Fig. 2 is also used in the apparatus 100 but is not shown in Fig. 3.

The rate at which any apparatus or reactor for treating a fluid operates to break down pollutants is preferably as high as possible. A variety of parameters affect the rate of a given reaction and in this case these include the speed at which the drum 12 rotates, the distance between the lights 14 and the catalyst, the concentration of hydrogen peroxide added to the fluid and the frequency of collisions between the pollutant molecules and the catalyst - known as the "mass transfer". Each of these parameters were investigated to determine the optinum level.

A solution of methylene blue was prepared for all the experiments to simulate pollutants in water and was poured into a void 26 of the drum 12 via the hole in the end cap using an appropriate measuring container (not shown) . Ti0₂ pellets described in more detail below, (or alternatively P25 Degussa) , were chosen as the catalyst for all the experiments and was weighed and then emptied into the drum 12. The solution and catalyst were sealed into the drum 12 by means of a plastic bung (not shown) plugging the hole in the end cap. The drum 12 was then agitated manually and attached to the drive shaft 18. The drum 12 was rotated for 10 seconds to ensure effective, equal distribution of the catalyst in the solution and then stopped and the first sample taken. The UV lamps were then activated and the light travelled through the Perspex drum 12 into its void 26 and degraded the methylene blue in the presence of the catalyst. Further samples were then taken at ten-minute increments up to the 1-hour running time for each experiment. For experiments 1- 3, the samples could be taken without having to stop the drum, however, for experiments 4-6 it was necessary to stop the rotation of the drum 12 to extract the samples.

The Ti0₂ pellets are prepared by the process described in US 6,660,243 and EP 1 175 259 the disclosures of which are incorporated herein by reference. The pellets have a mean grain size dso of 0.1 to 50mm, and are in each case composed of primary crystallites of titanium dioxide in the anatase modification. Their primary crystallite size, in accordance with the Scherrer equation, is up to 40nm and have a specific surface area determined according to the BET method of from 20 to 150m²/g. Their pore volume is between 0.1 and 0.45cm³/g and their pore diameter of 100 to 30θA. The Ti0₂ is formed into pellets with the addition of water, the pellets are annealed at temperatures of 300 to 500°C, and are then impregnated in vacuo with titanium dioxide sol or 1 to 20% concentration nitric acid. Then they are dried and annealed at a temperature of 400 to 1000°C for 3 hours, preferably 1.5 to 2.5 hours.

After each experiment the drum 12 was drained and washed out using distilled water. All the samples were labelled and stored away. After the samples were taken, it could be seen that the solution had a ^λmilky' consistency to it. This is due to the presence of the catalyst and in order for the samples to be analysed, the catalyst had to be separated from the solution. To achieve this the catalyst was allowed to settle to the bottom of the sample jar naturally over a period of 1 week.

The concentration of the methylene blue remaining following the experiments was determined by measuring absorbance at 664nm using an absorbance spectrometer. A high absorbance is indicative of a high level of methylene blue and thus low destruction efficacy of the reactor whereas a low absorbance is indicative of a low level of methylene blue and thus a high destruction efficacy of the reactor.

The experimental specifications are as follows : Methylene Blue - 250ml @ 5 x 10^~5 mols\l Catalyst, Ti0₂ 0.25 grams (0.1% weight/volume) Running Time 1 Hour Sample Time 10 min increments (starting at 0 mins)

For experiments 1-3 the apparatus used was that shown in Fig. 3, there being no agitation means, such as blades or paddles, present. UV lamps (not shown) are provided around the drum 112. Experiment 1

The first experiment carried out involved an investigation on the variation in methylene blue destruction rate due to the variation in rotational speed of the reactor. For this experiment, the distance between the UV lamps and the drum 112 was 4cm.

The four speeds chosen were 15, 30, 45 and 60 rpm. When the catalyst had settled, the samples were analysed. The results are shown in Table 1.

Table 1. Results of Absorbance at 664nm for Speed Variation

These results are plotted on a graph, Fig. 9, and from there it is observed that the optimum performance of the reactor occurs when the speed is 60 rpm.

Taking the results from the optimum speed and plotting them as In (Absorbance/Absorbance at T = 0) against time, Fig. 10, it is observed that the degradation is a pseudo first order reaction and is linear.

From here it can be defined that the rate constant (k) for the Ti0₂ photocatalysis of methylene blue at 60 rpm is equal to the gradient of the plot which is -0.0757 min^-1. A complete list of the rate constants found for the speed variations is given in Table 2.

Table 2 Results rate constant (k) for Speed Variation

With visual observation of the experiment in progress, it could be seen that at 60 rpm, the methylene blue solution tended to deploy itself more consistently around the drum walls. This is due to the friction caused between the solution and the drum wall and is also due to small amounts of centrifugal forces. In turn this helps promote a larger surface area of solution/catalyst to the distribution of light. It also increases the turbulence within the solution thus increasing the mass transport, which is a key factor. These results indicate that mass transport is the rate determining step of this type of reactor design.

Experiment 2

Light distance can affect the performance of the apparatus due to the light dependence of the photocatalytic process which occurs when the methylene blue or pollutant molecules degrade. In the second experiment the destruction rate of methylene blue was investigated with the UV lamps at various distances from the drum 12 viz . 4cm, 8cm, 16cm and 32cm. Doubling the distance between the UV lamps and the drum 12 causes a four-fold reduction in the light intensity reaching the catalyst, i.e. it is a square root relationship.

The obj ective of investigating the effect of light intensity was to determine if the reactor was purely mass transport controlled or if other factors influence the rate of pollutant destruction. The specifications are identical to that of the first experiment and the speed used was the optimum speed. Table 3 shows the results obtained.

Table 3. Results of Light Distance Variation

These results are plotted on a graph, Fig. 11, and from there it can be noted that the light distance that gives the lowest destruction time is 4 cm. As the optimum light distance is 4 cm, the results are the same as that of the optimum speed because the speed variation experiments were conducted with a light at a distance of 4cm. Thus the plot of In (Absorbance/Absorbance at T = 0) against time will apply to both and is shown in Fig. 10. A complete list of the rate constants is given in Table 4.

Table 4. Results of rate constants for Light Distance Variation.

Thus the distance between the UV lamps and the reactor 112 does affect the rate of the reaction.

Experiment 3

Here, hydrogen peroxide was added to the solution to promote the generation of hydroxyl radicals (OH) . For this experiment the distance from the UV lamps to the drum 112 was 4cm. The hydroxyl radicals help with the degradation of the contaminant species thus increasing the destruction rate since the concentration of the oxidising species is higher. Four different percentages of H₂0₂ were used - 0.05%, 0.1%, 0.5% and 1%. With the addition of H₂0₂ the solution starts degrading as soon as the catalyst is inserted into the drum 12. This can be observed form the results in Table 5.

Table 5. Results of Absorbance at 664nm for H₂0₂ Percentages

These results are plotted on a graph, Fig. 12, from which it can be seen that the greater concentrations of H₂0₂, i.e. 0.5% and 1%, initially degrade the methylene blue more than the lower concentrations of H₂0₂, i.e. 0.1%, 0.05%. This is because the greater concentration of H₂0₂ is generating a greater number of OH radicals in the reactor which enhances the methylene blue destruction.

From Fig. 12 it can be observed that the majority of the methylene blue was degraded in the first ten minutes of the experiment. Even though the greater two percentages of H₂0₂ initially cause more degradation than the other two percentages, the four variation values come close to each other after 10 mins and more so at 15 mins. With this in mind, it was concluded that the lowest percentage of H₂0₂ be chosen as the optimum result. The data from 0.05% H₂0₂ experiment is plotted on Fig. 13. Here this graph represents a plot of In (Absorbance/Absorbance at T = 0) against time.

It can be noted from the graph that the resulting plot does not represent a linear function. In order to obtain linear values and thus obtain a value for the rate constant k, the plot would need to be converted into a second order system. In this case the methylene blue destruction rate is dependent on both methylene blue and peroxide concentrations.

The concentration of H₂0₂ varies for different pollutants and it has previously been reported that higher peroxide concentrations can lower the destruction rate by competing for sites on the photocatalysis with the pollutant. Also with the addition of H₂0₂, it was noted that the catalyst settled to the bottom of the solution far more rapidly than in the absence of H₂0₂. It is thought that the peroxide is influencing the surface charge on the catalyst and reducing its tendency to suspend.

After the analysis of the results, is was observed that the overall optimum performance of the drum 112 was when it was operated at 60 rpm, with the UV lamps at a distance of 4 cm and the addition of 0.05% H₂0₂.

From the analysis of the results from the drum 12, increase speed was found to increase mass transport. However, with speed increase, there is also an increase in the power required to operate the reactor thus making the process less cost effective. In order to bring the power requirements down, a method in which mass transport could be increased was required.

With all the results and analysis from experiments 1-3 taken into consideration, it was decided that the most suitable parameter in which to optimise in the design of a new reactor was that of the mass transport.

Where the rate determining step in any reaction depends on the mass transport, new, more efficient, catalysts that are developed will provide no rate enhancement. Thus it is highly desirable to develop reactors so that mass transport control is not the rate determining step.

The drum 212 shown in Fig. 4a and 4b includes an agitation means in the form of four blades 230 provided equi-spaced on the inner face of the drum 212. The blades 230 extend parallel to the main longitudinal axis of the drum 212 from a first end 234 to a second end 236. The blades 230 increase the agitation of fluid within the drum 212 is when it is rotated since they act as baffles against which the flow of fluid contacts and must circumvent thus increasing the mass transport. Slots 232 may be provided to allow some fluid to pass through the slots or between the blades 230 and an inner face of the drum 212.

Fig. 5 shows a modified blade 330 which is curved at its end 348 which further increases the agitation of fluid in the drum 212 in use.

Fig. 6 shows a further drum 412 comprising agitation means in the form of a spiral blade 430. The blade 430 extends from a first end 434 to the second end 436 of the drum 412 in a spiral or helical fashion. In such an embodiment the blade preferably turns around 90° or 180° as it extends from the first 34 to the second 36 end. Although not shown in Fig. 6, it is preferred to have a number of equi-spaced blades 430 extending in a spiral fashion within the drum 412.

In a more preferred embodiment, a plurality of smaller paddles or blade portions 540 are provided within the inner face of a drum 512. The paddles 540 are spaced apart along the longitudinal axis and are also spaced apart in a helical fashion around the longitudinal axis from a first end 534 to a second end 536 of the drum 512, as shown in Figs. 7 & 8. The paddles 540 also create a baffle for the fluid flow within the rotating drum 512, although they are spaced apart from each other and allow fluid to flow unhindered between them. The first paddle 544 at the first end 534 is offset from the last paddle 546 at the second end 536 by 90° as shown in Fig. 8 or 180° as shown in Fig. 7. In the embodiments shown there are seven paddles 40 extending between each end 534, 536 of the drum 12. As shown in Fig. 8, each paddle is spaced apart from an adjacent paddle 40 by 15° on each side and there are 4 sets of seven paddles, each set extending from the first end 534 to the second end 536 of the drum 512.

The spacing of the paddles 540 posed a problem in terms of placing the paddle sections at the correct increments and spacing. This was overcome by producing a template from tracing paper of the exact area of the inside of the drum 512. The positions in which the sections had to be placed were drawn onto the template. The template was then inserted into the drum 512 and fixed in place. Since the drum 512 was made from transparent Perspex, the lines of where the sections were to be place were visible from the outside and the outside of the drum 512 was then marked with non-permanent marker. The template was then removed and the sections were glued in place using Loctite (RTM) superglue. The sections were then given the appropriate time to dry and then they were individually checked, to ensure each individual section had adhered properly etc. End caps were then glued in place and left to dry. The assembled drum 512 is shown in Figure 8.

In use, the effluent water is inserted into the drum 212, 412, 512 by any suitable means and a catalyst (not shown) is added to the water. A suitable catalyst is the Ti0₂ pellets although others may be used. The drum 212, 412, 512 is sealed by the use of end plates (not shown) and the drum is rotated at a suitable speed within the circumferential arrangement of ultraviolet lamps 14.

On rotation of the drum 212, 412, 512 agitation of the fluid is caused by the movement of the agitation means, for example paddles 540, through the effluent water thereby creating turbulent flow and increasing the mass transport.

Experiments 4-6 were performed using the drum 512 with the paddles 540 to compare the results against the drum 112 without the paddles or agitation means. The only difference between experiments 4-6 and 1-3 is that the drum 512 with paddles 540 was stopped in order to remove the samples. This was achieved in ten seconds and as it is relatively short time period, it is assumed to have negligible effect on the performance of the process. Experiment 4

The experiment specifications for experiment 4 (speed) were as follows: Methylene Blue - 250ml @ 5 x 10^"5 mols\l Catalyst, Ti0₂ - 0.25 grams (0.1% weight/volume) Running Time - 1 Hour Sample Time - 10 min increments (starting at 0 mins) Light Distance - Positioned at 4 cm from Drum Experiment 1 found that the speed of the reactor had a significant effect on the performance of the process by increasing the mass transport. In order for a significant improvement to be made to the performance of the reactor in terms initially of the power requirements, it is preferable for the destruction rate obtained from the original drum at 60 rpm, be obtained at a reduced speed.

The results obtained from the experiments of speed variation for drum 512 are shown in Table 6.

Table 6 Results of Absorbance at 664nm for Speed Variation of drum 512

These values are plotted on a graph of absorbance against time, Fig. 14, from where it can be observed that there is no significant variation between the plotted lines for each speed. This indicates that the influence of mass transport on pollutant destruction has been significantly reduced. Observing; Fig. 14 more closely, it can be identified that at 30 minutes into the experiment, the methylene blue concentration obtained for 15 rpm is lower than the other speeds. At 40mins the methylene blue concentrations for each speed falls on almost the same point. These results indicate that the reactor performance has little variation between the speeds thus enabling the lowest speed to be taken as the optimum result. In turn this will reduce the power requirements.

A plot of In (absorbance/absorbance at T = 0) against time is shown in Fig. 15 to determine the rate constant k. The rate constant k for the Ti0₂ photocatalysis of methylene blue at 15 rpm in the drum 512 is equal to the gradient of the plot which is -0.0839 min^"1. Table 7 shows all the values for the rate constant k obtained from the interpolation of the results.

Table 7 Result of rate constants for Speed Variations Experiment 5

The degradation or photocatalytic process depends considerably on the distribution of light to a large surface area of the catalyst . On inspection of operation of the drum 512, the agitation phenomenon of the paddles 540 was such that as well as enhancing the mass transport properties, it tends to carry the solution around the drum by means of transport due to a ^λscoop' action of the paddles 540 as well as friction between the fluid and the drum. This in turn causes an increase in the light distribution to the catalyst surface. The recorded results for destruction of pollutant as influenced by the light distance variations are given in Table 8. Other than the variation in distance between the UV lamps and the reactor 512, the same parameters were used as detailed for experiment 4.

Table 8. Results of Absorbance at 664nm for Light Distance Variations. These values are plotted on a graph, Fig. 16, from where it was found that at the light distance of 4 cm the process was at its optimum performance. When compared to the results obtained from the light distance experiments on the drum 112, the results for the new reactor tended to be similar in their form and performance between each variation. The drum 512 however, has an overall better performance in destruction time.

The optimum light distance for this set of experiments was found to be 4 cm, which is the same distance as that used to find the optimum speed variation. The rate constant (k) for the optimum light distance will then be the same value as that obtained from the plot of In (Absorbance/Absorbance at T=0) against time for speed variation, i.e. -0.0839 min^"1. Table 9 lists the rate constants for all variations of light distance.

Table 9. Results of rate constants for Light Variations Experiment 6

The addition of H₂0₂ into the drum 512 also proved to enhance the photocatalytic process. The degradation of the methylene blue started as soon as the catalyst was introduced into the solution within the drum. The parameters used for this experiment are the same as those detailed for experiment 4. The results from this set of experiments are given in Table 10.

Table 10. Results of Absorbance at 664nm for H₂0₂ Percentages

Plotting these values on Figure 17, it can clearly be observed that the addition of H₂0₂ in the experiments on the new reactor increases the rate of destruction significantly. All percentages of H₂0₂ have degraded the contaminant species by the 10- minute interval. The lowest percentage of H₂0₂ can therefore be selected as the optimum result. It may also be interpreted from the graph that the percentages of H₂0₂ added to the solution are too severe because they all degrade the methylene blue within 10 minutes. To get a true optimum for the addition of H₂0₂, the percentage range would require to be smaller and the samples taken over a shorter period.

With analysis carried out on all the results, it is determined that the drum 512 with the paddles 540 was highly successful and thus preferred embodiments of the invention include agitation means, such as paddles 540. The mass transport was increased and in doing so, this enabled the speed to be lowered. This in turn reduces the power requirements of the reactor and by achieving this, it reduces the costs associated with the process. In addition the mass transport control of the process was also significantly reduced, increasing the degree of kinetic control.

The drum 112 without the agitation means was found to have its optimum destruction rate at 60 rpm. By measuring the voltage and current required to rotate the drum at this speed, the power and torque required from the motor can be determined.

The increase in performance of the drum 512 with paddles 540 over the drum 112 without paddles can be determined by interpreting the power requirements established from calculations. At 60 rpm the motor required 2.025 watts to drive the drum. At 15 rpm the motor required 0.52 watts to drive it. This is a reduction in the power required of a ratio of 3.89 : 1, or 256.7%.

In an even more preferred embodiment, a drum 612 (shown in Figs. 18 & 19) also comprises a plurality of paddles or blade portions 640 spaced apart along the longitudinal axis of the drum 612 from a first end 634 to a second end 636 thereof but arranged in a V-shaped formation. The paddles 640 function in a similar manner to the paddles 540 of the drum 512 in that they provide a baffle for the fluid flow within the drum 612 although they allow some fluid to flow between them unhindered. Preferably, there are four sets of nine paddles 640, each set provided in such a V-shaped formation. A benefit of such an arrangement is that the catalyst is more evenly distributed within the drum 612 which maintains the catalyst under maximum illumination from the ultra- violet lights 14, compared with, for example, the drum 512 -where the catalyst tended to migrate towards one end of the drum 512 in use.

A further embodiment of an apparatus 700 is shown in Fig. 20. The apparatus 700 comprises a plurality of drums 712 which may include the internal configuration of any of the drums 212, 412, 512, 612 or the blades 330. The apparatus 700 comprises uv lights (not shown) , drum support rails (not shown) , drum support plates 762 which support the drums 712 at either end, and backing plates 764 for the drum support plates 762. The drum support plates 762 include locating holes 766 for the drum support rails which extend between the drum support plates 762 and provide further support to the each drum 712. Liquid transfer cavities are provided in the drum support plates 762 to transfer fluid from one drum 712 to another. Typically the uppermost drums 712a, 712d, 712g are adapted to receive fluids in an aperture (not shown) in its end which is concentric with the rotational axis thereof, and release fluid from a further aperture (not shown) in its opposite end which is not concentric with the rotational axis of the respective drum 712a, 712d, 712g. A liquid transfer cavity connects said further aperture to a central aperture (not shown) in a lower drum 712b. The lower drum 712b also has a non-concentric aperture at its opposite end which is in fluid communication with a concentric aperture in a lower drum 712c via a further liquid transfer cavity and so on.

The drum support plates 764 comprise mountings for the drum motors (not shown in Fig. 20) and drum support rail bearing races (not shown) .

To operate the apparatus 700, fluid is injected into the central aperture in the end of the uppermost drums 712a, 712d & 712g. The uv lights are activated and the drums 712 are rotated as described for earlier embodiments. The fluid slowly proceeds through the drums and out of the non-concentric apertures in their opposite end, through fluid transfer cavities and into lower drums and so on. In an alternative embodiment apparatus 800 shown in Fig. 21 comprises drums 812 which may include the internal configuration of any of the drums 212, 412, 512, 612 or the blades 330. The apparatus 800 comprises uv lights (not shown) , drum support rails (not shown) and fluid transfer plates 864. Further fluid transfer plates 864 may be provided for onward connection to further drums. The fluid transfer plates 864 comprise a channel (not shown) which allows fluid to flow from the outlet of a first drum 812a to the inlet of a second drum 812b.

Experiment 7

A further embodiment 900 is shown in Figs. 23-25 where there are three drums 912 surrounded by 8 uv lights 914. A fluid transfer plate 964 transfers the fluids through each of the drums 912.

A further series of experiments were performed to determine the functional operation of the reactor 900 for removal of hydrocarbons in waste water. In these experiments, a sample of wastewater effluent containing a mixture of hydrocarbon compounds was examined. The effluent used was taken from petrol station forecourt interceptors, which contain primarily drain water, oil, silt and sand.

The reactor 900 has an internal configuration of the reactor 512, that is comprising paddles (not shown in Figs. 23-25) spaced apart in a helical formation. The overall breakdown of the hydrocarbons was monitored at first by measuring the Chemical Oxygen Demand (COD) . The COD is commonly used as a standard measurement for chemical pollutants in natural and waste waters, particularly prior to effluent discharge. Waste effluents contain both organic and inorganic compounds which directly and indirectly consume the available oxygen in its surrounding ecosystem. COD is defined as the amount of specified oxidant that reacts with a sample under controlled conditions. The quantity of oxygen consumed is expressed in terms of its oxygen equivalent: mg/L of 0₂.

One maximum discharge concentration set by Scottish Water for certain types effluent analysed here is 2000 mg/L of 0₂.

Table 11 shows the values of COD measured from a raw sample of effluent, a sample after one run through the reactor with photocatalysis and two runs through the reactor with photocatalysis. From the results it is clear that a significant drop in COD was achieved bringing the effluent to a level where discharge would be permissible in the UK.

Table 11 COD of Effluent, before and after treatment in the photocatalytic reactor.

A ter completion of the COD experiment examination of the effect on fluorescence was examined. This was performed as COD is may not be completely effective in measuring aromatic hydrocarbons, but these are readily detectable using fluorescence spectroscopy. The change in fluorescence intensity of the effluent following a single pass through the reactor sample is displayed in table 12. From these results it is clear that the concentration of fluorescent hydrocarbons in the effluent sample were also significantly reduced following treatment in the reactor.

Table 12 Effluent fluorescence before and after treatment through reactor.

Further analysis of the effluent samples were also performed using Gas Chromatography/Mass Spectroscopy (GC/MS) . This instrument provides both qualitative and quantitative analysis of hydrocarbons in effluent samples . The results of the analysis are detailed in table 13. The effluent sample was found to contain a mixture of aliphatic hydrocarbons as shown in table 13. Following treatment of varying levels of catalyst it is clear that a significant drop in the concentration of each of these hydrocarbons is achieved.

Table 13 The reduction in volatile organic hydrocarbons of three effluent samples following treatment in the photocatalytic reactor with varying loadings of Ti0₂ catalyst .

The results of experiment 7 demonstrate the effectiveness of the reactor for removal of hydrocarbons from aqueous effluents, reducing the level to concentration where discharge would be permissible in the UK.

Certain embodiments of the invention reduce the costs of degrading pollutants compared to other methods of treatment and may also be less harmful to the environment compared with known techniques.

It was observed that conventional tubular flow and flat plate reactors were dependent on flow and hence mass transport properties within the solution, whereas certain embodiments of the present invention are dependent on kinetic control. The development of the drum 512 has proved also to increase the kinetic control properties associated with the process. This means enhanced photocatalysis may be emphasised by using a drum 512 enabling a significant improvement in the overall viability of the process.

In experiments 1-3, the results showed that the process was dependent on the rotational speed of the drum to produce movement within the fluid and in doing so, improving the mass transport properties.

The addition of the paddles 540 within the drum 512 was found to be an efficient method of achieving the required agitation. From the analysis of the experiments carried out on the drum 512, it was determined the rate of destruction of the pollutant was increased and at a lower rotational speed. This also led to a decrease in power required to drive the reactor making it more efficient to use. Thus, preferred embodiments of the invention have an agitation means, such as the paddles 540.

Improvements and modifications may be made without departing from the scope of the invention. For example, the catalyst may be provided as a thin film on the inside of the drum 512. Moreover the apparatus can be adapted to be a continuous operation by continually pumping in effluent water into one end of the drum and draining out the relatively clean water at another end of the drum.

Claims

1. An apparatus for treating a fluid, the apparatus comprising a container, and a means to move the container.

2. Apparatus as claimed in claim 1, wherein the container is adapted to allow the passage of light therethroug .

3. Apparatus as claimed in claim 1 or claim 2, further comprising a light source, preferably a UV light source.

4. Apparatus as claimed in claim 3, wherein the container is adapted to move with respect to the light source.

5. Apparatus as claimed in claim 3 or claim 4, wherein the light source comprises at least one tube arranged with its longitudinal axis parallel to the main longitudinal axis of the container.

6. Apparatus as claimed in any preceding claim, wherein the container is shaped to receive the fluid within a void thereof.

7. Apparatus as claimed in any preceding claim, wherein the container comprises agitation means so that, in use, the fluid is agitated.

8. Apparatus as claimed in claim 7 , wherein the agitation means comprises at least one blade.

9. Apparatus as claimed in claim 7 of claim 8, wherein the agitation means includes slots.

10. Apparatus as claimed in any one of claims 7 to 9, wherein the container is substantially cylindrical and the agitation means are a helically shaped or provided in a helical formation.

11. Apparatus as claimed in any one of claims 7 to 10, wherein the agitation means comprise a plurality of paddles.

12. Apparatus as claimed in claim 11, wherein the paddles are spaced apart from each other in, or on, the container.

13. Apparatus as claimed in claim 11 or claim 12, wherein the paddles are arranged in a V-shaped formation.

14. Apparatus as claimed in any preceding claim, wherein the container is rotated by a motor and the rotational axis of the container and the rotational axis of the main drive shaft of the motor, are co- linear.

15. Apparatus as claimed in any preceding claim, wherein a plurality of containers are provided, said containers being in fluid communication with each other.

16. A method for treating a fluid, the method comprising inserting a fluid into a container, exposing the container to a light source and moving the container relative to the light source.

17. A method as claimed in claim 16, wherein the fluid is placed within a void of the container.

18. A method as claimed in claim 16 or 17, wherein the light is shined through the container onto a portion of the fluid.

19. A method as claimed in any one of claims 16 to 18, wherein a catalyst is added to the container.

20. A method as claimed in claim 19, wherein the catalyst comprises Ti0₂ pellets.

21. A method as claimed in any one of claims 16 to 20, wherein a portion of any pollutants in the fluid are degraded.