AN IMPROVED DEWATERING METHOD AND APPARATUS

Abstract

The present invention provides a method and an apparatus for treating sewage sludge, the method comprising applying a plurality of ultrafine bubbles to a sludge to form an at least partially aerated sludge, applying acoustic energy to the aerated sludge to agitate at least a portion of the ultrafine bubbles and applying an electric field to the aerated sludge to impart an electrophoretic mobility to the ultrafine bubbles to thereby facilitate separation and transport of water molecules from solid matter within the sludge.

Claims

1. A dewatering method for treating sewage sludge, the method comprising: applying a plurality of ultrafine bubbles to a sludge to form an at least partially aerated sludge; applying acoustic energy to the aerated sludge to agitate at least a portion of the ultrafine bubbles; and applying an electric field to the aerated sludge to impart an electrophoretic mobility to the ultrafine bubbles to thereby facilitate separation and transport of water molecules from solid matter within the sludge.

2. The method of claim 1, wherein agitating the ultrafine bubbles produces a cavitation effect on the bubbles.

3. The method of claim 2, wherein the cavitation effect creates micro-convection to further facilitate the separation and transport of the water molecules from the solid matter within the sludge.

4. The method of claim 1, wherein the acoustic energy is applied in the form of ultrasound.

5. The method of claim 4, wherein the frequency of the ultrasound is varied during treatment.

6. The method of claim 4, further comprising generating ultrasound standing waves within the aerated sludge.

7. The method of claim 1, further comprising repeating the step of applying ultrafine bubbles to the sludge to increase the concentration of bubbles.

8. The method of claim 1, wherein the ultrafine bubbles have an average diameter of less than 50 microns or less than 10 nanometres.

9. (canceled)

10. The method of claim 1, further comprising applying a vacuum to the sludge.

11. The method of claim 1, further comprising the step of collecting effluent water in a retaining tank.

12. The method of claim 1, further comprising the initial step of passing the sludge through a macerator to break up at least a portion of a solid matter in the sludge.

13. A dewatering apparatus for treating sewage sludge, comprising: means for generating and injecting a plurality of ultrafine bubbles into a sludge; means for applying acoustic energy to the aerated sludge to agitate at least a portion of the ultrafine bubbles; and means for applying an electric field to the aerated sludge to impart an electrophoretic mobility to the ultrafine bubbles to thereby facilitate separation and transport of water molecules from solid matter within the sludge.

14. The dewatering apparatus of claim 13, wherein the means for generating and injecting the ultrafine bubbles comprises a bubble generator.

15. The dewatering apparatus of claim 13, wherein the means for applying acoustic energy comprises an ultrasound generator.

16. The dewatering apparatus of claim 15, wherein the ultrasound generator is operable to vary the frequency of the ultrasound during treatment.

17. The dewatering apparatus of claim 15, wherein the ultrasound generator is operable to generate standing waves within the aerated sludge.

18. The dewatering apparatus of claim 13, wherein the means for applying an electric field comprises an electrokinetic reactor.

19. The dewatering apparatus of claim 18, wherein the electrokinetic reactor comprises at least one porous electrode for attracting water molecules, or wherein the electrokinetic reactor comprises at least one surface including zeolite, a carbonaceous material and a resin.

20. (canceled)

21. The dewatering apparatus of claim 18, wherein the electrokinetic reactor comprises at least one jet injector to promote sludge mobility.

22. The dewatering apparatus of claim 13, wherein the apparatus comprises an array of electrokinetic reactors.

Description

[0089] Embodiments of the present invention will now be described in detail by way of example and with reference to the accompanying drawings in which:

[0090] FIG. 1shows a schematic of a dewatering method according to an exemplary embodiment of the present invention;

[0091] FIGS. 2a & 2bshows graphical representations of CST (Capillary Suction Time) profiles in accordance with the application of UFB and US at 16 kHz and 20 kHz, respectively;

[0092] FIG. 3shows a schematic of an example EKR reactor according to a preferred embodiment of the present invention;

[0093] FIG. 4shows a plan view of example anode configurations for use with the EKR reactor of the present invention;

[0094] FIGS. 5a-5cshow respective example transducer plate geometries for use within an EKR reactor according to the present invention;

[0095] FIG. 6shows a graphical representation of the relationship between EKR applied voltage and the percentage of the total solids at 105 C. (% TS).

[0096] Referring to FIG. 1, there is a shown an exemplary embodiment of a dewatering method 100 for treating sewage sludge according to the present invention.

[0097] As an initial pre-treatment step, the sewage sludge 102, in this case a primary sludge, is passed through a maceration unit 104 to ensure that all relatively large extraneous materials or solids are broken up or crushed via comminution to a size at least <12 mm, and ideally <2 mm. The maceration unit 104 comprises a pre-treatment tank 104a and a maceration pump 104b.

[0098] The sludge is then subjected to the application of ultrafine bubbles (UFB), which are injected into the sludge via an ultrafine bubble generator 106. By ultrafine bubbles or UFB, we mean any bubbles that have a bubble diameter generally in the range of <10-50 microns. The step of applying UFB to the sludge can be repeated as many times as required, so that any degree of concentration of UFB can be built up in the sludge, depending on the particular treatment and processing requirements.

[0099] After dosing the sludge with UFB, the aerated sludge is pumped into an ultrasound flow reactor 108, whereupon the sludge is subjected to the application of ultrasound waves. The ultrasound waves are applied with frequencies in the range of about 10 kHz to about 50 MHz.

[0100] As shown in FIG. 1, the ultrasound flow reactor 108 may be integrated into a single unit 110 together with the ultrafine bubble generator 106. However, in other arrangements, the ultrasound flow reactor may be separate to the ultrafine bubble generator depending on the particular installation and treatment conditions.

[0101] The function of the ultrasound is to agitate at least a portion of the UFB in the sludge to thereby produce cavitation and other secondary effects. In the process of cavitation, the UFB grow, expand and undergo radial motion as acoustic energy propagates through the sludge. The resulting bubbles range in size from microns down to 4-300 nm in diameter, and are found to be generally stable. During stable cavitation, the radii of the UFB undergo radial oscillation by periodically expanding and shrinking within several acoustic cycles. However, when the bubbles reach their resonant size, at least some will undergo transient cavitation and others will break apart gently, whereby the resulting fragments will start a new cycle of stable cavitation. The collapse of the bubbles produces physical and/or chemical effects. These effects can enhance thermochemical/biochemical reactions etc. according to one or more of the following mechanisms:

[0102] Cavitating bubbles are sufficient to cause rupture of the OH bond itself. This is because the collapse of the cavitation bubbles is also near adiabatic and generates temperatures of thousands of degrees within the bubbles for a short period of time. Under these temperature conditions, highly reactive radicals are generated. In water, H and OH radicals are generated by the homolysis of water. This results in the formation of radical species and the production of oxygen gas and hydrogen peroxide

H.sub.2O.fwdarw.H.sup.++OH.sup.

OH.sup.+OH.sup..fwdarw.H.sub.2O.sub.2

OH.sup.+OH.sup..fwdarw.H.sub.2O+O

OH.sup.+OH.sup..fwdarw.H.sub.2+O.sub.2

H.sup.++O.sub.2.fwdarw.HO.sub.2.sup.

HO.sub.2.sup.+H.sup.+.fwdarw.H.sub.2O.sub.2

HO.sub.2.sup.+HO.sub.2.sup..fwdarw.H.sub.2O.sub.2+O.sub.2

OH.sup.+H.sub.2O.fwdarw.H.sub.2O.sub.2+H.sup.+

H.sup.++H.sup.+.fwdarw.H.sub.2

H.sup.++OH.sup..fwdarw.H.sub.2O

[0103] In the presence of a metal ion present, an alternative mechanism may be

M.sup.2++H.sup.+.fwdarw.M.sup.++H.sup.+

H.sup.++O.sub.2.fwdarw.HO.sub.2.sup.

M.sup.2++HO.sub.2.sup..fwdarw.M.sup.++H.sup.++O.sub.2

OH.sup.+H.sub.2O.sub.2.fwdarw.HO.sub.2.sup.+H.sub.2O

OH.sup.+OH.sup..fwdarw.H.sub.2O.sub.2

HO.sub.2.sup.+HO.sub.2.sup..fwdarw.H.sub.2O.sub.2+O.sub.2

[0104] These resulting free radicals may then participate in chemical reactions within the sludge. The formation of hydroxyl radicals during sonification, enhances the negative electrophoretic movement of the UFB towards the cathode.

[0105] It is found in the present invention, that an unsymmetrical collapse of bubbles typically produces micro-jets at high speed, which propagate toward the walls of the ultrasound flow reactor 108. The collapse of the bubbles also produces relatively strong shockwaves within the sludge, while the resulting impulsive movement of liquid toward or away from the collapsing bubbles leads to micro-convection. This micro-convention enhances the transport of liquid and solid particles within the sludge, which may also lead to forces that can cause emulsification or dispersion depending on the particular conditions within the ultrasound flow reactor.

[0106] The strong shockwaves and micro-jets generate significant shear forces that are able to scatter liquid within the sludge into tiny droplets and/or crush solid particles into finer material, such as powder (which remains in solution).

[0107] It is found that the degree of cell disruption/damage of the solid matter in the sludge is proportional to the number of bubble collapses with sufficient energy to overcome the minimum (activation energy) required for cell damage, and is related to collision frequency, number of bubbles and cell concentration per unit volume of sludge.

[0108] The addition of UFB to the sludge prior to the ultrasonication greatly enhances the above effects. The solid matter is composed of dissolved organic solids, insoluble solids and biomass cell matter. Removing free water is relatively easy, but energy use and complexity increase when removing interstitial, colloidal and intercellular water. Therefore, the combined application of UFB dosing and ultrasound to the sludge breaks through the cell structure and enables the water bound up in the cells to be recovered as free water, without significantly increasing the energy input to the system.

[0109] Referring now to FIGS. 2a & 2b, there are shown graphical representations of CST (Capillary Suction Time) profiles in accordance with the application of UFB and ultrasound at the respective frequencies of 16 kHz and 20 kHz. The graphs clearly show the effect of the ultrasound on the sludge at 16 kHz (with and without UFB dosing) and 20 kHz (with and without UFB dosing) respectively, using the CST as a direct measure of the dewaterability of the sludge, while also being a measure of the specific resistance to filtration (SRF) of wastewater sludges and of sludges in general. CST is a standard technique in the industry and is used by wastewater operators to assess dewatering efficiency. The time measured by a CST apparatus is dependant on viscosity, temperature, sludge particle size, floc size, percentage of total solids (% TS) and particle bound water content.

[0110] The cavitation effect on the UFB via the application of ultrasound leads to a reduction in sludge particle size, together with a breakup of flocculated particles and a reduction in floc and particle fractal dimension. Due to the resulting rupturing of the particle, bound up water is released into the sludge medium. This effect leads to a reduction in sludge viscosity, which thereby reduces the measured CST. The impact of increasing the dosage of UFB within the sludge media causes an increase in global cavitation activity, which in turn promotes greater sludge disintegration. As a result, the measured CST is further reduced and consequently the CST value provides a direct indictor of the effectiveness of the dewaterability of the sludge.

[0111] As shown in FIG. 2a, the combined effect of the ultrasound and the UFB dosing leads to lower CST values as compared to the ultrasound alone (i.e. in the absence of any UFB). Therefore, it is clear that the combined effect produces a higher dewatering efficiency than conventional ultrasound alone. Likewise, in FIG. 2b, the same effect is evident, but at a higher ultrasound frequency of 20 kHz, which when compared to FIG. 2a indicates that for this particular test sludge and apparatus, is slightly less efficient than the combined effect at 16 kHz. The reason for this difference is that when the UFB collapse, as a result of transient cavitation, this creates high pressures and temperatures exceeding 5000K. These conditions produce a shock wave, or a high-speed jet, capable of destroying cellular structure (cell lysis), which thereby releases cell water. By contrast, stable cavitation produces large cyclic pulsations at resonance that can cause large shear forces in the region around the bubble, leading to cell disruption or dislodgement of the cell within the floc to release interstitial water. For a set wave amplitude and energy input, the power density will be lower at 16 kHz than at 20 kHz, and therefore it is found that a lower power density promotes conditions more suited for stable cavitation as opposed to transient cavitation, although both processes will operate together. However, in any particular setup, the best mode of operation will be to favour stable cavitation, while not excluding transient cavitation.

[0112] Moreover, an additional advantage of the present method is that it also enhances the destruction, or otherwise weakens, the cell walls of any pathogens in the sludgeresulting in the waste solid and released effluent water being virtually pathogen free.

[0113] The frequency of the ultrasound applied to the sludge is varied during the treatment in the ultrasound flow reactor 108. The varying of the frequency is found to maximise the impact of the sonification and further enhance the cavitation effect on the UFB, since it causes the bubbles to undergo enhanced agitation leading to a greater number of bubble collapses per unit volume of sludge.

[0114] Although not shown in FIG. 1, the ultrasound flow reactor 108 may include an ultrasound generator that comprises at least two transducers, each generating an acoustic wave of the same frequency but propagating in opposing directions. As a result, an ultrasound standing wave may be created in the sludge, which is found to yet further enhance the cavitation and secondary effects on the UFB.

[0115] Alternatively, the ultrasound flow reactor 108 may include an ultrasound generator that comprises at least two transducers, each generating an acoustic wave of a different frequency.

[0116] As an example, there is shown in each of FIGS. 5a-5c, a specific geometry of transducer plates for use with the present invention. In FIG. 5a, there are four plates arranged in a square (or cube in 3-dimensions), with opposing pairs being driven at respective ultrasound frequencies of 16 kHz and 18 kHz. In FIG. 5b, there is shown a modified form of the cube arrangement, in which two cubic geometries of plates are stacked, with the top plates being driven at ultrasound frequency of 16 kHz and the bottom plates at 18 kHz. While in FIG. 5c, an octagonal arrangement of plates is adopted, with respective opposing pairs being driven at frequencies of 16 kHz, 18 kHz, 19 kHz and 20 kHz.

[0117] The sludge is then transferred to another unit 112 comprising an electrokinetic reactor (EKR) 114, which enables an electric field to be applied to the sludge. As shown in FIG. 3, an example EKR 114 is constructed as individual plates or panels (e.g. forming the walls) that are assembled into the specific EKR geometry for that particular application. The EKR 114 can adopt the form of a long rectangular tank, with an angled bottom face (at inclination angle i), as shown in FIG. 3. The anode 114.sub.1 is located generally towards the centre of the tank, while the cathode/filter media 114.sub.2 forms the outer walls of the tank. A voltage is applied between the anode 114.sub.1 and the cathode 114.sub.2 (as shown in FIG. 3). UFB are injected into the tank through conduit 114.sub.3 from the bubble generator 106 into a mixing means 114.sub.4. Of course, any suitable shape may be used in conjunction with the present invention.

[0118] The EKR 114 is constructed from inert and/or electrically conductive materials, such as sand, zeolite or other semi-conductive materials, while the walls of the EKR act as a porous cathode electrode.

[0119] The walls of the EKR 114 are cast and moulded into a required form using a particulate media of a zeolite/carbonaceous mixture and a composition epoxy, or other non-corrosive resin/binder that will not dissolve or corrode in use. The resin binder composition may range between about 10-50% by weight of the overall zeolite/carbonaceous mixture. The properties of this resin binder can be further enhanced by the addition of carbon based powders and/or particulates, such as graphite particles, expanded graphite, carbon black, carbon nanoplatelets and graphene etc.

[0120] The conductivity of the EKR walls can be further enhanced by the application of an additional fine layer of a mixture of a carbonaceous powder and zeolite or zeolite powder alone or by the addition of a carbonaceous material such as graphite particles, expanded graphite, carbon black, carbon nanoplatelets and graphene etc. The carbonaceous material may comprise between about 1%-60% of the composition of the walls.

[0121] The anode may be fabricated from the same material as the cathode or may be made from carbon, (sacrificial) metal or a metal composite. The anode can have any suitable shape or configuration depending on the geometry of the EKR etc. As shown in FIG. 4, the anode 114.sub.1 may be generally rectangular in form with a central longitudinal aperture 122 running the length of the anode, or may comprise separate rectangular 124 or circular 126 spaced apertures along its length instead.

[0122] Examples of possible compositions for the material of the EKR 114 are presented in Table 1 below. This list is intended to be illustrative and not exhaustive. The type of zeolite used in the present apparatus is a Clinoptilolite. However, it is to be understood that other types of materials may alternatively be used.

[0123] For ease of reference, the following acronyms are used in Table 1:

[0124] d.sub.pavgAverage particle diameter

[0125] N/ANot applicable

[0126] NCPNanocarbon platelets

[0127] NG-92Nuclear graphite (ultrapure flake graphite)

[0128] EFGExpanded flake graphite

[0129] ACBActivated carbon Black

[0130] FG-92Flake graphite

[0131] UP-FGUltrapure flake graphite

[0132] CNTCarbon nanotube

[0133] To fabricate the EKR cathode and anode, the constituent particulates are mixed with 10-15% of an adhesive binder and left to set for a period of time that can range from a minimum of 3-25 minutes. The mixed material is cast in a mould and allowed to set. This technique allows for any shape or geometry of EKR 114 to be created. If the cathode and/or the anode are cast as individual walls/plates, then the EKR 114 can be assembled by binding the edges of the walls using a conductive adhesive or the resin binder. The conductivity of the EKR walls may be further enhanced by the application of an additional fine layer of a mixture of a carbonaceous powder and zeolite or zeolite powder alone.

TABLE-US-00001 TABLE 1 Material Carbon Resin Sand (d.sub.pavg 180 m) N/A Araldite Zeolite (d.sub.pavg 100 m) N/A Araldite Zeolite (d.sub.pavg 980 m/ N/A Araldite d.sub.pavg 100 m) Zeolite (d.sub.pavg 980 m) N/A Araldite Zeolite (d.sub.pavg 980 m) 1% NCP Araldite Zeolite (d.sub.pavg 980 m) 3% NCP Araldite Zeolite (d.sub.pavg 980 m) 5% NCP Araldite Zeolite (d.sub.pavg 980 m) 3% NG-92 Araldite Zeolite (d.sub.pavg 980 m) 5% NG-92 Araldite Zeolite (d.sub.pavg 980 m) 9% NG-92 Araldite Zeolite (d.sub.pavg 980 m) 14% NG-92 Araldite Zeolite (d.sub.pavg 980 m) 9% NG-92/3% NCP Araldite Zeolite (d.sub.pavg 980 m) 9% NG-92/5% NCP Araldite Zeolite (d.sub.pavg 980 m) 9% NG-92/3% EFG Araldite Zeolite (d.sub.pavg 980 m) 9% NG-92/5% EFG Araldite Zeolite (d.sub.pavg 980 m) 5% ACB Araldite Zeolite (d.sub.pavg 980 m) 9% FG-92/5% ACB Araldite Zeolite (d.sub.pavg 980 m) 14% UP-FG Araldite Zeolite (d.sub.pavg 980 m) 9% UP-FG/5% EFG Araldite Zeolite (d.sub.pavg 980 m) 9% UP-FG/5% NCP Araldite Zeolite (d.sub.pavg 980 m) 14% UP-FG/3% NCP/5% EFG Araldite Zeolite (d.sub.pavg 980 m) 14% UP-FG CNT/Epoxy Zeolite (d.sub.pavg 980 m) 14% FG-92 CNT/Epoxy Zeolite (d.sub.pavg 980 m) 11.5% FG-92/2.5% EFG CNT/Epoxy Zeolite (d.sub.pavg 980 m) 14% FG-92/3% EFG Araldite Zeolite (d.sub.pavg 980 m) 14% FG-92/5% EFG Araldite

[0134] The anode of the EKR 114 is located towards the centre of the reactor to ensure a symmetrical electric field within the EKR. However, alternative and/or additional anodes can be located at other specific locations within the EKR to create any desired electric field topography depending on the particular EKR geometry and/or the treatment conditions to be adopted for the sludge.

[0135] Hence, it is to be appreciated that the geometry of the EKR and/or the number of anodes used (including their relative positions within the EKR) are not intended to be limiting. An example of a suitable geometry of the EKR is shown in FIG. 3. With this geometry, an electric field topology is created within the EKR that promotes or otherwise gives rise to electro-osmosis and electrophoresis effects on the sludge being treated.

[0136] The electrical supply to the EKR 114 can be AC or DC, and can be continuous or pulsed at set intervals. Preferably the electrical supply to the EKR is DC. The electrical supply to the EKR walls is generally connected to respective sides of the EKR 114. However, in other arrangements this can be replaced with a single cathode/anode electrical connection. The applied voltage is in the range of between 5V-100V AC/DC, and typically between 30V-70V. Of course, it is to be appreciated that the particular voltage range will depend on factors such as the EKR geometry and/or the sludge to be treated.

[0137] When an electric voltage is applied to the EKR 114, the aerated sludge is then subjected to an electric field. The action of the electric field on the UFB causes a negative electrophoretic mobility due a preferential adsorption of hydroxyl (OH.sup.) ions, arising from the orientation of the water dipoles near the interphase with their positive poles directed towards the liquid in the sludge. This effect causes the water molecules in the sludge to effectively stick to the UFB, which essentially act as transport carriers (i.e. transport medium) for the water as they migrate towards the cathode of the EKR 114. In this way, water molecules are then dragged along with the bubbles towards the porous cathode, whereupon they are then absorbed by the cathode.

[0138] In addition, the UFB may also act as carriers for other particles (e.g. charged particles and dipole molecules etc.) and enable those particles to migrate through the sludge under the effect of the electric field. Moreover, the presence of the UFB also advantageously reduces the effective viscosity of the sludge by providing porosity, there enhancing the transport of water molecules through the EKR 114 to the cathode.

[0139] Any solid matter or solid particulates in the sludge are transported to the anode or anodes under a corresponding electrophoretic mobility. Therefore, applying an electric field to the aerated sludge facilitates separation and transport of water molecules from solid matter within the sludge.

[0140] Referring now to FIG. 6, it is shown that the percentage total solids at 105 C. (% TS) is found to be positively related to the EKR applied voltage. Therefore, it is evident that the efficiency of the dewatering process increases as the electrophoretic effect becomes stronger in the sludge, such that more water is transported and recovered from the sludge (and hence a greater percentage total solids remain) as the voltage increases.

[0141] It is found that there is a limit to enhancing the electrophoretic effect with increasing voltage due, for example, to steric effects and changes to the zeta potential (arising from the pH gradient within the EKR). In an example setup, the optimum dewatering voltage was found to be around 50V DC. However, the range of effective voltages that could be applied was between 15V and 80V, but could be between 10V and 100V, depending on the particular sludge/wastewater being treated.

[0142] The effect of the combined UFB and ultrasonication of the sludge according to the present invention can be seen in Table 2 below for two test ultrasound frequencies of 16 kHz and 20 kHz.

TABLE-US-00002 TABLE 2 16 kHz 16 kHz + UFB 20 kHz 20 kHz + UFB % TS 23.5 34.8 22.7 32.0 Power (kWh/m3) 23.0 17.8 29.3 22.8

[0143] Hence, it is clear that the application of the UFB to the sludge not only increases the percentage total solids remaining, and thus recovered water, but it also leads to significantly lower energy input (i.e. power consumption) as compared to the absence of UFB in the sludge. Therefore, the combination of UFB and ultrasonication according to the present invention provides a method and apparatus, which gives increased dewatering rates and lower power requirements than conventional dewatering systems.

[0144] The mobility of the UFB under the action of the electric field is found to be further increased by subjecting the EKR 114 to a vacuum of about 300 Pa-5 kPa, and typically about 500 Pa-1.5 KPa.

[0145] Although not shown in FIG. 1, the EKR 114 comprises at least one jet injector to promote sludge mobility. Therefore, one or more jets or jet injectors can be provided in the base of the EKR 114, to allow a jet of air or additional UFB to be injected into the sludge to promote improved mobility. The jets prevent the occurrence of any initial sludge compaction or build up of a static layer of solid matter in the sludge, thereby assisting with sludge mobility and rapid dewatering rates.

[0146] The recovered effluent water 118 from the cathode may be collected in a retaining tank or other suitable vessel (not shown). The solid waste 120 may be mechanically removed from the EKR 114 after treatment and both the effluent water 118 and solid waste 120 can be used for agricultural, livestock or similar purposes due to being virtually or completely pathogen free. Indeed, the dewatered sludge can be used as a valuable fertiliser or as a feedstock to a combustion system. The dewatered sludge is virtually or completely pathogen free, while the claimed invention may also be applied to sanitation purposes. The effluent water may be processed to drinking water standards.

[0147] Of course, it is to be understood that the method and apparatus of the present invention are inherently scalable, and therefore the apparatus, and in turn, the electrokinetic reactor, can be sized to treat a sludge or slurry according to any particular requirement depending on the desired use and/or implementation. Hence, none of the embodiments or examples disclosed herein are to be taken to be limiting on the size of the apparatus.

[0148] Indeed, a typical laboratory EKR as used herein can be scaled up to a full-scale plant reactor by utilising the ratio of the internal laboratory EKR volume to the full scale EKR dewatering unit. In one example, the ratio of this scale-up can be 244 (i.e. numerical multiplying factor), but in other arrangements can range between 30 and 300. The scale up between laboratory EKR and full-scale plant reactor may also be based on surface area ratio between the laboratory EKR and full-scale reactor. In one example, the ratio of this scale-up is 39.06, but in other arrangements can range between 10 and 50.

[0149] Thus, the above embodiments are described by way of example only. Many variations are possible without departing from the invention.