WO2017158348A1

WO2017158348A1 - Treatment of fluids

Info

Publication number: WO2017158348A1
Application number: PCT/GB2017/050699
Authority: WO
Inventors: Philip Morgan
Original assignee: Kp2M Limited
Priority date: 2016-03-15
Filing date: 2017-03-15
Publication date: 2017-09-21
Also published as: GB201604397D0; GB2548491B; GB2548491A; EP3429966A1; GB201704081D0

Abstract

A method of treating fluid and a fluid treatment system (100), the system (100) comprises a fluid treatment zone (101) defined a pair of electrodes (5, 7), a ballast addition means (BA), a mixing means (121) and ultrasound generators (12) to sonicate fluid within the fluid treatment zone (101), wherein said ballast addition means (BA) is arranged to add ballast to the treatment zone (101) and/or downstream of the fluid treatment zone (101).

Description

Treatment of Fluids

The invention relates to the treatment of fiuids. More particularly, the invention relates to the treatment or decontamination of fluids using electrochemistry.

Treatment or decontamination of fluids is frequently required to remove entrained matter (e.g. suspended or dissolved matter) and/or to disinfect impurities. The fluid to be treated or decontaminated may especially be contaminated water, for example, drinking water, waste water, industrial effluents, shipboard waters, process waters, ground run -off waters or leachate water. The fluids may contain one or more contaminants, for example, inorganics, organics, suspended material, colloidal matter, metals, organo-metalloids, radionuclides, herbicides, pesticides and bacteria, viruses and other microorganisms.

To date, decontamination has been widely achieved by physical and/or chemical means. For example, utilising, oxidation and reduction, using filters, settlers, chemicals and biological processes. As contaminants in fluids have become more complex over the last century due to increasing industrialization, the use of conventional treatment methods has become less effective. At the same time, the increase in the stringency of the requirements as to the purity of waste streams, in particular, effluent streams, has increased the areas of industrial operation for which decontamination of waste or other fluid streams is needed or required.

The use of electrolysis for the treatment of liquids is well documented. Similarly the use of sonochemistry for treating liquids, as well as a means for changing the chemical properties of fluids, has been proposed. Typically, in electrolysis, a DC or AC current applied across the anode and cathode electrodes immersed in the fluid (electrolyte) results in dissolution of the anode to produce reactive reagents (e.g. aluminium ions, ferrous and ferric ions) whilst at the cathode electrode water hydrolyses to produce hydrogen ions and hydroxyl ions. The net result of these reactions is the production of, for example, aluminium hydroxide, ferric hydroxide or ferrous hydroxide which acts as a coagulant and adsorbs contaminants from the fluid. These reactions are typically referred to as electro-coagulation and electro- flocculation. Sonochemistry (ultrasound) has been long established for cleaning and for mixing, and to accelerate chemical processes. Ultrasonication (typically 15 - 200 kHz or 20 to 200 kHz frequency) generates alternating low pressure and high pressure waves in fluids. leading to the formation and violent collapse of small vacuum bubbles. This phenomenon is termed cavitation and causes high speed impinging liquid jets and strong hydrodynamic shear-forces. These effects together with the applied energy input and material transfer through the boundary layers of the fluid are used for de-agglomeration of contaminants, disintegration of cells, mixing of reactants, production of free radicals (e.g. hydroxyl radical). Such sonochemical effect leads to a substantial reduction in reaction time and cleaning effect of objects immersed in an ultrasonic device and in some cases may lead to the increased density of agglomerated material.

The combination of sonochemistry with electrolysis offer the advantage of increased rates of chemical reaction, negate electrode fouling by destroying the Helmoltz-Stem boundary layers on the anode electrode surfaces and passivation when electrically excited, increase oxidative reactions through the production of hydroxyl radicals and increase mixing effects within the reactor device. The present state of the art publications describe such devices as consisting of a metallic ultrasonic horn (also known as acoustic horn, sonotrode, acoustic waveguide, ultrasonic probe) immersed in an electrolytic reactor containing contaminated fluids and immersed anode and cathode attached to an electrical power supply.

There is a need to increase the rate of flocculation and/or agglomeration or particles which are removed from a fluid process stream and this invention is related to that aim.

Accordingly, a first aspect of the invention provides a method of treating fluid, the method comprising the steps of:

a) passing a fluid to be treated into a fluid treatment zone defined between electrodes and electrolysing the fluid within the treatment zone to form an electrolysed fluid,

b) adding a ballast to the fluid and/or to the electrolysed fluid within the fluid treatment zone and/or downstream of the fluid treatment zone,

c) sonicating fluid within the fluid treatment zone, and

d) mixing the electrolysed fluid to cause flocculation.

Sonication may be achieved by one or more ultrasound generators

It may be beneficial to add at least some of the ballast to the fluid to be treated and before it enters the treatment zone because the ballast may provide a scouring effect on the electrodes, thereby helping to break up and/or remove deposits and/or to interfere with any boundary layer that is present. In any case it is beneficial to add the ballast before or when the fluid is exposed to ultrasound energy because cavitation may occur on the surfaces of the ballast. Preferably a flocculating agent may be added before, during or after mixing the electrolysed fluid. We prefer to add the flocculating agent after commencement of the mixing of the electrolysed material. We prefer mixing the flocculating agent to the fluid after the ballast material, and preferably after the ballast material has been added and subsequent to commencement of mixing. The flocculating agent may be a polymer, preferably a high molecular weight polymer and/or an anionic polymer.

A further aspect of the invention provides a fluid treatment system, the system comprising an electrolysing means or electrolyser, a ballast addition means or ballast adding or dosing device and a mixing means or mixer in accordance with Claim 6.

The system may form a component of a unit. The ballast addition means may be arranged to add ballast as a fluidic dispersion, for example a nozzle or pipe comprising ballast provided (e.g. dispersed or suspended) in a gas or liquid, preferably a liquid. Additionally or alternatively, ballast may be added as a solid and introduced directly to the treatment zone (or downstream thereof). The ballast may comprise one or more of an inorganic particle, for example silica or carbon, or a polymeric particle. We prefer particles with an average diameter in the range of from 20 to 300 μιτι, say in the range of 40 to 250 μιη. In some embodiments the ballast will have a specific gravity of greater than 2, and in some embodiments greater than 2.6, for example about 2 6 to 2.7.

Ballast may be added in the range of, say, 1 to 50 g/l (measured as mass of ballast to volume of fluid to be treated), for example 2 to 20 g/l and in some embodiments 5 to 20 g/l, for example 10g/l.

There may be further provided flocculating agent addition means or flocculating agent adding or dosing device, preferably arranged to add flocculating agent before, within or after the mixing means.

There may be further provided plural ultrasound generators.

Mixing may be completed by a high shear mixer, commonly termed a flash mixer and/or by a paddle stirrer. In a preferred embodiment mixing takes place in plural stages. In a first stage a relatively more rigorous mixing, for example a relatively fast mixing speed is employed and in a subsequent stage a relatively less rigorous mixing, for example a relatively lower mixing speed, is employed.

In one embodiment there is provided a mixing zone or unit with a first mixing stage fluidly connected to and upstream of a subsequent mixing stage, the first mixing stage comprises a mixer, for example a flash mixer, capable of stirring a propeller or impeller at, say 100-300 rpm, say for 2 to 15 minutes, and the subsequent mixing stage may comprise one or more mixers, for example a paddle stirrer, capable of mixing at say 30 to 160 rpm. In an embodiment there may be two subsequent mixing stages provided with means to effect successively less rigorous mixing.

There may be provided clarifying means to clear the mixed fluid from agglomerated and/or flocculated particles. Such clarifying means may comprise a lamella clarifier at a surface loading / application rate of 10 - 140 m³hr¹m ², preferably 30 - 100 m³hr¹m ² preferably 40 - 80 m³hr¹nr². This is advantageous because it potentially enhances the clarification process and settlement rate. Alternatively, other forms of clarifying means may be deployed such as a centrifuge, decanter, disc separator, hydro cyclones and the like. It has been surprisingly found that it is possible to use a centrifuge, decanter or disc separator, cyclone and the like in this invention without destroying agglomerate/flocculated particles.

The fluid treatment system of the invention enables decontamination of fluids, especially of contaminated water and waste streams to be carried out in a simple, efficient, effective and rapid manner. In particular, because the decontamination can rely, at least in part, on electrolysis and, in some embodiments, on sonication, together with the ballast addition, flocculation and rapid clarification, decontamination can be rapid. Moreover, sonication can negate electrode fouling and build-up of passivation layers along the electrode surfaces in the treatment zone. It is believed that the unit of the invention enables electrolysis (and where present sonication) to be applied satisfactorily to both a continuous decontamination procedure and/or batch process because the arrangement is such that the liquid stream is caused to flow along the surfaces of the electrodes at which electrolysis (and where present sonication) reactions can occur and when in batch mode (and where present) the sonication process prevents any electrode fouling from passivation such as build-up of gas bubbles or 'floe' material which can reduce the amperage and increase the voltage power across the electrodes. In the system of the invention, however, such reaction products are prevented from occurring in the reactor which may process flow rates of up to 10 MLD (million litres per day) or up to or over 100 MLD or up to or over 200 MLD or up to or over 500MLD. A further aspect of the invention provides a fluid treatment unit comprising first anode electrode, a second grounded electrode and externally mounted ultrasonic probe mounted to the grounded electrode, defining between the first anode and second grounded electrode a treatment zone having inlet means for introduction of fluid in the said treatment zone and outlet for exit of fluid from the said treatment zone, the treatment zone providing a flow path along which fluid entering through the inlet means can flow towards the outlet, the flow path extending substantially along the surface of each of the electrodes, a ballast introduction means for adding ballast to the fluid within or downstream of the treatment zone and a mixing zone downstream of the treatment zone.

The ultrasonic generators or probe may comprise a single piezoelectric element or a plurality of piezoelectric elements arranged in an array on the second grounded electrode. The first anode electrode may comprise a plate electrode with a pair of matching major surfaces and/or the grounded electrode may define a tank or container. Preferably, the first anode electrode is located within the tank or container, such that fluid flowing from the inlet to the outlet flows over and/or across both major surfaces of the anode electrode. The system may comprise an inlet. The inlet may comprise a channel that extends across the treatment zone in a direction transverse to the principal direction of flow within the treatment zone. The purpose of such a construction is to enable fluid to be introduced into the treatment zone in a relatively even laminar flow. The outlet may comprise a channel that extends across the treatment zone in a direction transverse to the principal direction of flow within the treatment zone.

The ultrasonic generators may comprise a single piezoelectric element or a plurality of piezoelectric elements arranged in an array on the second grounded electrode. Said ultrasonic generator means or ultrasonic generators may be operable or may operate at an operating frequency of 15 - 200 kHz or 20 - 200 kHz.

Preferably the system comprises a grounded electrode and an anode electrode. The grounded electrode may define a tank or container. The first anode electrode may comprise a plate electrode with a pair of matching major surfaces. The first anode electrode may be located within the tank or container, such that fluid flowing from the inlet to the outlet may flow over and/or across a, the, one or both major surfaces of the anode electrode. The anode electrode is electrically insulated from the grounded electrode. The ultrasound generators may be mounted on or to the grounded electrode.

The system or unit may include a power source for applying electrical current to the electrolysis means. For example the power source may provide a positive voltage to the first electrode and a ground (earth) to the second grounded electrode. The arrangement may be such that an AC voltage and or DC voltage of varying frequencies and waveform may be applied to the first electrode to provide an operating amperage of 1 - 100,000 amps or 1 - 10,000 amps. The system may include a power source for applying a voltage to the ultrasonic generator means or ultrasonic generator.

The system or unit advantageously comprises means for monitoring (e.g. a monitor) one or more electrical characteristics between the first and second electrodes in the treatment zone such that the voltage between the first and second electrodes can automatically vary to achieve a set current amperage across the first and second electrodes, and a monitoring means for monitoring one or more chemical parameters of the fluid either upstream and or downstream of the treatment zone and automatically set the operating amperage for the treatment zone defined by the first and second electrode. Advantageously, the system comprises a control means or controller. The control means is preferably arranged to control one or more of the applied current for electrolysis, dosage rate of the bailast, the applied frequency and/or power to the ultrasonic generator means and array of piezoelectric elements and/or rate and amount of addition of the flocculating agent, in dependence on one or more characteristics monitored by the monitoring means,

The method of the invention treatment may comprise causing fluid to flow along a surface of each of first anode electrode and second opposed grounded electrode and simultaneously applying a voltage across said first and second electrodes in order to generate an electrolytic current through the flowing liquid and, if present, energising an ultrasonic generator means mounted to the second electrode and to generate an ultrasonic sound wave through the flowing liquid. Advantageously, the liquid is caused to flow along a flow path that is bounded on opposing sides by the opposed electrodes. Preferably, in transverse section relative to the direction of flow, the flow path is of elongate rectangular configuration. Advantageously, however, the area of cross section of the flow path is substantially uniform along the direction of flow of the fluid. The separation between the first anode electrode and facing second grounded electrode may be 100mm or less. Advantageously, the separation between the first anode electrode and second electrodes is 80mm or less. Advantageously, the separation between first and second electrodes is 5mm or greater.

The length of the flow path may be 100mm or more and advantageously, 500mm or more. Advantageously, the length of the flow path is 20,0000mm or less or 10,000mm or less.

Oxidants and oxidizing or hydroxyl radicals may be generated in the fluid by the ultrasonic probe and/or electrode as the fluid passes through the treatment zone. Hydrogen peroxide may be generated as a result of the sonoelectrochemistry as the fluid passes through the treatment zone. Hydrogen peroxide in the presence of ferrous ion or ferric salts (which can be generated when iron electrodes are used), can further generate hydroxyl radicals via Fenton chemistry for organic mineralization. Further, chloride ions when reacted with oxygen over-potential electrodes can generate powerful oxidants and radicals for the destruction of organic and nitrogenous contaminants. Further when combined with a UV light source a photo-Fenton reaction can be initiated for the destruction of organic contaminants. Such reactions generating hydroxyl radicals are commonly referred to as advanced oxidation processes (AOP).

The present invention may provide a fluid treatment unit compnsing first anode electrode, a second grounded electrode and externally mounted ultrasonic probe mounted to the grounded electrode, defining between the first anode and second grounded electrode a treatment zone having inlet means for introduction of fluid in the said treatment zone and outlet for exit of fluid from the said treatment zone, the treatment zone providing a flow path along which fluid entering through the inlet means can flow towards the outlet, the flow path extending substantially along the surface of each of the electrodes, a ballast introduction means for adding ballast to the fluid within or downstream of the treatment zone and a mixing zone downstream of the treatment zone,

The system or unit may further comprise a source of UV light, which is arranged to irradiate fluid that passes through the unit. The UV source may be arranged to irradiate fluid that is downstream of the treatment zone. The UV source may be at or in the vicinity of the outlet means. The treatment method of the invention may be used for the treatment of any fluid, especially contaminated liquid streams such as contaminated water streams selected from wastewater, industrial effluents, process waters, ground water, rivers and leachates. The method may be used, with appropriate selection of conditions in the treatment zone, to decontaminate fluids containing inorganics, organics, suspended and colloidal material, metals, organo-metalloids, radionuclides, bacteria, viruses and other microorganisms.

Where UV irradiation is included, the treatment method is especially effective in the removal or metals and oxidative destruction of organic contaminants such as PCBs or breakdown of surfactants, pesticides and herbicides or long chained organics into short chain residues.

A further aspect of the invention provides a method of cleaning a sludge received from a clarifier, which sludge comprises ballast and agglomerated or flocculated contaminant having been generated subsequent to electrolytic treatment of a waste water, the method comprising exposing said sludge to ultrasonic energy to thereby separate the ballast and contaminant.

The invention will now be described by way of example only and with reference to the accompanying drawings, in which. -

Figurel is a schematic representation of a system of the invention

Figure 2 is a longitudinal cutaway section of a treatment unit according to the invention;

Figure 3 is a transverse cutaway section through the treatment unit of Figure 1 ; and Figure 4 shows a graph of comparative data showing the effectiveness of the invention.

Referring first to Figure 1 , there is shown a schematic representation of a fluid treatment system 100 for treating fluid F, for example wastewater, non-potable water, industrial effluent, water from a sewerage plant, run-off water and so on.

The fluid treatment system 100 comprises an electrochemical treatment system 101 , a mixing zone or unit 102 and a clarifying zone or unit 103. There is further provided ballast addition means BA for adding ballast B to the fluid into or downstream of the electrochemical treatment system 101. Some ballast B (preferably a minor proportion of that to be added) may be added upstream of the electrochemical treatment system 101 but this is not essential.

The electrochemical treatment system 101 is provided with ultrasound generators and other water treatment devices, as will be explained below.

The mixing zone or unit 102, may comprise a tank 120 in which is provided one or more mixers 121. The tank 120 may be divided into two or more fluidly-coupled compartments (two shown 120a and 120b). If the tank 120 is divided into two or more compartments different mixing regimes may be deployed in each compartment. Preferably, fluid in the upstream compartment 120a will experience relatively more rigorous mixing whereas fluid in the downstream compartment 120B will experience relatively less rigorous mixing. A relatively more rigorous mixer is a flash mixer, a relatively less rigorous mixer is a paddle stirrer.

The tank 120 may be simply divided by one or more baffles (indicated by the dotted line) or by another physical separation barrier for example a mesh, a tube or other conduit. Indeed, the tank 120 may comprise plural tanks fluidly coupled to one another. In a preferred embodiment the mixing zone or unit 102 comprises an intermediate mixing zone, downstream of the upstream compartment 120a and upstream of the downstream compartment 120b. The fluid will be able to experience an intermediate level of mixing in that zone. Shown downstream of the mixing zone or unit 102 is flocculant addition means FA. However, the flocculant addition means can add flocculant to the fluid within the mixing zone or unit 102, and preferably does. Indeed, where there is an upstream zone 20a in which the fluid will experience, or is able to experience, relatively more rigorous mixing the flocculant agent addition by the flocculant addition means FA may be introduced to that zone 120a. Additionally or alternatively, flocculant agent addition may occur in the downstream zone 120b in which the fluid experiences, or is able to experience, relatively less rigorous mixing.

Downstream of the mixing zone or unit 102 is the clarifying zone or unit 103. Within the clarifying zone or unit 103 there may be provided clarifying means to cause particles within the entrained fluid to settle, or otherwise be removed from the fluid, thereby to ensure that fluid exiting the clarifying zone or unit 103 has a reduced particle burden (for example, as measured in grams of particles per cubic centimetre [g/cc] or numbers of particles per cubic centimetre [N/cc] as compared to that entering the clarifying zone or unit 103). Examples of such clarifying means 131 include filters, lamella settlers, centrifuges, decanters, disc filters, hydro-cyclones and the like. We prefer the use of lamella clarifiers although other clarifying means may be used alternatively or additionally.

Referring now to Figures 1 and 2, an electrochemical treatment system 101 for use in the system of the invention comprises a treatment unit TU, the treatment unit TU comprises an electrochemical cell provided with ultrasound generators to form a sonoelectrochemical cell 1 , in this embodiment a pair of parallel sonoelectrochemical cells 1 a, 1 b, and an inlet conduit 2 and an outlet conduit 3. The system TS further comprises an electrolysis power supply 4, an electrode 5 for each cell 1 a, 1 b connected to the electrolysis power supply 4 by a busbar 6. The grounded electrode 7 provides a reactor housing or tank T fluidly connected to the inlet conduit 2 and outlet conduit 3. The inlet conduit is provided or formed with a perforated channel 8 to provide even laminar flow into the treatment zone 9 for the cell 1 (in this embodiment for each cell 1 a, 1 b). The treatment zone 9 is defined as the space between electrode 5, ground electrode 7 (which provides the housing or tank T) and extending to the transverse outlet weir 10 The electrodes 5 extend into the treatment zone 9 of each cell 1 a, 1 b and are secured to the ground electrode 7 by means of insulated sheathed fixings 1 1 (x3 shown). The ultrasound probe consists of an array of piezoelectric transducers 12 (xS shown and four for each cell 1 a, 1 b) connected to the ultrasonic power supply 13. An optional UV lamp 14 may be secured downstream of the treatment zone 9 after the transverse outlet weir 10 and preferably receives power from UV power supply 16. In addition or instead of the UV lamp 14, a water quality monitoring device 17 may be included along with its water quality probe 18.

An electrical monitoring instrument 19 may be included in the electrolysis power supply 4. The electrical monitoring instrument 19, water quality monitoring device 17, UV lamp power supply 16, ultrasonic power supply 13 feed-back to a master controller 20. An overflow outlet 15 is provided in the sonoelectrochemical cell 1. It will be appreciated that, if desired, the positions of the inlet conduit 2 and outlet conduit 3 may be interchanged (or the direction of flow may be reversed) or the positions of the inlet conduit 2 and outlet conduit 3 may be altered, provided that the liquid passes across the electrodes 5 for treatment. It may be advantageous under some circumstances to use the overflow outlet 15 as a return outlet to return partially treated liquid for recycling through the sonoelectrochemical cell 1. Such a recycle facility allows poorly conducting liquids, difficult 'hard' liquids, or liquids with high pollution loading to receive multiple passes to achieve the appropriate level of required treatment. Whilst the ground electrode 7 is preferably constructed of stainless steel or similar material, the electrode 5 (anode) may be constructed of various conducting materials. Selection of appropriate materials may be based on waste stream characteristics and treatment requirements. For example iron is especially advantageous for oil removal because it provides effective destabilization for oil removal, aluminium is effective for phosphate, suspended solids and metal removal and oxygen over-potential materials as a mixed metal oxides of platinum are effective for oxidation.

With reference to Figure 3, the ground electrode 7 integrates the inlet conduit 2 and outlet conduit 3 and provides the reaction tank T. The electrode 5 is fixed centrally by the insulated sheathed fixings 11 such that the ground electrode 7 wraps around the outside opposing surfaces of the electrode 5. The piezoelectric transducers 11 are mounted externally on the ground electrode so that there are two opposing treatment zones 9 defined between ground electrode 7, electrode 5 and ground electrode 7. Such an electrode design is mono-polar and has the advantage of simple design, doubles the flow and treatment capabilities and has increased electrical capacitance over bi-polar electrode arrangements resulting in lower voltage requirements of the treatment unit TU. The perforated channel 8 along the bottom edge of the ground electrode 7 provides laminar flow past each of the outer surfaces of electrode 5. In the embodiment shown the thickness of the electrode 5 is advantageously within the range of 3 to 25mm or 3 to 50mm or 3 to 100mm and shows two electrodes each of approximately 1200mm x 800mm. Advantageously having the facility to house multiple electrodes 5 also allows various electrode materials to be used simultaneously within the treatment zone 9 such as aluminium, iron, magnesium, oxygen over potential metals, carbon based materials, impregnated carbon and graphite and other conducting and semiconducting materials. In such a reaction cell typical volumes of flow may be 20,000 liters an hour. The treatment unit TU may be varied in size to cater for appropriate volumes of liquid to be treated by adding or subtracting the first anode electrode and the size of the second grounded electrode casing. Referring to Figure2, in the embodiment eight piezoelectric transducers are show on each side of the ground electrode 7, extending across the treatment zone 9. It will be appreciated that a plurality of piezoelectric transducers may be required depending upon the size of the treatment unit, application, contaminant level and desired treatment outcome. In the drawing, the sonoelectrochemical cell has been drawn as rectangular but may be square, cylindrical or any other shape, provided that the electrode and ground electrode are spaced from one another and liquid can enter and leave the treatment zone.

In use, liquid is pumped by an external pump (pump not shown) at a controlled rate, such that any ballast added prior to the sonoelectrochemical cell is maintained in suspension in the downstream treatment zone, through the inlet conduit 2 of the sonoelectrochemical cell 1 and passes up through the perforated channel 8 into the treatment zone 9 flowing between the outer ground electrode 7 and inner electrode 5 which are themselves acting as probes to monitor the electrical characteristics of the fluid-electrode medium by the electrical monitor 19. The fluid then weirs over the transverse outlet weir 10 into the chamber containing the UV lamp 14 and/or water quality probe 18 of the water quality monitoring device 17 before exiting the sonoelectrochemical cell 1 via the outlet conduit 3. It will be appreciated the water quality probe 18 could also be situated in the treatment zone 9, upstream of the sonoelectrochemical cell 1 or downstream of the sonoelectrochemical cell 1 together with multiple combinations of devices to monitor a range of water quality characteristics. In full automation the liquid characteristic are determined by the electrical monitor 9 and water quality monitoring device 17 along with external data such as flow rate and communicated to the master controller 20. The information is used by the master controller 20 to determine the appropriate settings of voltage and electrical current for the electrolysis power supply 4, and ultrasound frequency and power for the ultrasonic power supply 13. The correct treatment regime may, for example, be determined by reference to stored mathematical- chemical models, daily flow rate and contaminant loading profiles, algorithms and may involve the use of fuzzy logic control, neural networks and predictive computational software. In manual or semi-automatic mode, the voltage, current, ultrasound frequency and power may be manually selected by switches, HMI or similar on the master controller 20. Information relayed back to the master controller 20 may be stored on an internal data card, displayed on HMI screen or similar or relayed to a remote location by data transfer. Remote control of the sonoelectrochemical cell 1 may also be controlled by use of web-enabled software or similar data transfer networks.

During operation the pumped flow rate, volume of ballast, flocculating agent dose rate, voltage and/or amperage and ultrasound frequency and power are selected to give the optimum degree of treatment and efficiency. This may be done manually or automatically as described above. Dunng normal operation it is preferred to continually pump liquid through the sonoelectrochemical cell 1 and to continually apply a voltage, current, ultrasound frequency and power to the electrode 5. Whilst the sonoelectrochemical cell 1 is suitable for use in the treatment of a continuous flow of liquid, it will be appreciated that the unit could also be used in batch mode in which a predetermined volume of liquid is pumped into the treatment zone 9, a voltage, current, ultrasound frequency and power is applied across the treatment zone to treat the liquid for a pre-determined time after which the electrolysis and sonication systems are switched off and the pump started to flush the treated liquid from the treatment unit and to introduce the next aliquot of liquid for treatment

In the embodiment described above, the UV treatment process is integral with the electrolysis and sonochemistry. For high solids loading it may be desirable to increase effectiveness of the treatment process, for the material to be removed prior to the UV treatment as the UV process relies on light penetration through clear liquids. That may be achieved by solid-liquid separation or fractionation prior to the UV treatment. Thus, it may be preferred for the UV source to be provided downstream of the sonoelectrochemical cell 1. In the embodiment described above and shown in the drawings, only one sonoelectrochemical cell (with parallel cell units 1a, 1 b) has been described which has a monopolar electrode configuration. It may be advantageous, for large volume waste streams, to include a number of electrodes and size of sonoelectrochemical cell and also to increase the number of sonoelectrochemical cells into a treatment process. In that case a number of cells could be configured so that the electrodes for each cell may be configured as bipolar or multipolar. The treatment cells could also be configured as simplex (single units), duplex (duty, standby and duty and assist) or multi-stage. In these cases the individual treatment units could consist of units mounted onto support frames with common inlet and outlet manifolds. Such a system could consist of cells in series or parallel arrangement, depending upon waste stream characteristics and degree of treatment required. For mixed waste streams it may also be advantageous to include treatment units having different electrode materials and combinations. For high solids throughput it may also be advantageous to carry out pre-treatment before the liquid is introduced into the unit. Also, although the embodiment shows parallel cells 1 a, 1 b, it would also be possible to use the cells 1a, 1 b in series with different anodes 5.

The following non-limiting example illustrates the invention: Example

A liquid waste stream F consisting of water contaminated mains water was pumped through a treatment system 100 according to Figure 1 , equipped with a sonoelectrochemical cell as shown in Figures 2 and 3 as a treatment unit TU. The fluid F was pumped at a flow rate 5 of 11 liters/second. A current of 1 amp was a maintained between an aluminium anode and stainless steel ground electrode.

Micro sized silica sand was added to the fluid stream downstream of the treatment unit TU as a ballast. The sand comprised microspheres or micro-particles with a mean diameter of 150pm. About 10g/litre of fluid was added.

The ballast-infused water was then mixed with a flash mixer for 4 minutes at 200 rpm

Flocculating agent was added to the water as it exited the flash mixer and upon entering an intermediate mixing zone, in which the mixer operated at a mixing speed of 140 rpm for 5 minutes.

Downstream of the intermediate mixing zone the fluid entered the downstream mixing zone whereupon it was arranged to experience mixing at about 60 rpm. The intermediate and downstream mixing zones were compartments of equal size.

The fluid showed clear evidence of agglomeration or flocculation of particles. The resultant fluid was passed to a lamella clarifier at a surface loading of 58 m³hr¹m ². The agglomerated particles rapidly settled as a result of adding ballast material (1 Ogl ¹) and the concomitant increase in density.

It was possible to recycle the solid to form at least a portion of the ballast. In some embodiments this was achieved using a hydro-cyclone. However, we have found that this can lead to wear in the vessel and associate pipework, due to the abrasive action of the ballast

We have surprisingly found that sand can be separated from the agglomerated or flocculated contaminant by passing the sludge received from the clarifier (for example from the lamella clarifier) - which includes both contaminant and ballast, through an ultrasonic field. The ultrasonic filed causes the two components to settle with respect to one another enabling the ballast portion to be re-used as part of the ballast introduction and a more concentrated contaminant portion to be passed to a settling tank.

The combination of ballast flocculation with electrolysis (and optional sonochemistry) offers advantages over conventional water and wastewater treatment, industrial effluent processing, and ballast settling or electrolysis when used on their own for the decontamination of fluids A drawback with existing processes is that, when combining the electrolysis and sonochemistry systems, electrical interference occurs between the electrodes of the electrolytic unit and the transducers of the sonication unit. The present invention overcomes this electrical interference by placing the piezoelectric (ultrasonic) transducers on to the outside surface of a grounded electrode (cathode). The anode electrode is placed on the opposing side of the grounded electrode and defines a treatment zone through which liquid can be passed and simultaneously be treated by electrolysis and sonication. Trials using the present invention demonstrated improved treatment effectiveness, efficiency and fast rate of settlement thereby reducing treatment process time, plant footprint and associated capital and operating costs. Moreover, addition of ballast upstream of the electrolysis unit can improve operation of both the electrolysis system and the optional ultrasound generators. To demonstrate the effectiveness of the invention we conducted a comparative test. The results are shown in Figure 4.

Comparative Example 1

An aliquot of water to be treated was left in a 1 litre jar to determine if any solid separated therefrom. The results are shown as line CE1.

A sample of water to be treated was exposed to a sonoelectrochemicai treatment and mixing (but without any ballast addition) and an aliquot was left in a 1 litre jar to determine if any solid separated therefrom. The results are shown as line CE2. Example 1 A sample of water to be treated was exposed to an identical sonoelectrochemicai treatment as the sample of Comparative Example 2 with subsequent ballast addition and mixing and an aliquot was left in a 1 litre jar to determine if any solid separated therefrom. The results are shown as line E1.

The results clearly show that downstream ballast addition had a marked effect on the rate at which solid separated and the amount of solid which separated from the aliquot, clearly demonstrating the efficacy of the method.

Claims

1. A method of treating fluid, the method comprising the steps of:

c) sonicating fluid within the fluid treatment zone, and

d) mixing the electrolysed fluid to cause flocculation.

2. A method according to Claim 1 , comprising adding at least some ballast to the fluid to be treated.

3. A method according to Claim 2, comprising adding said at least some ballast to the fluid before the fluid enters the fluid treatment zone.

4. A method according to any preceding Claim, comprising adding a flocculating agent before, during or after mixing the electrolysed fluid.

5. A method according to any preceding Claim, comprising settling the fluid after step d.

6. A fluid treatment system, the system comprising a fluid treatment zone defined a pair of electrodes, a ballast addition means, a mixing means and ultrasound generators to sonicate fluid within the fluid treatment zone, wherein said ballast addition means is arranged to add ballast to the treatment zone and/or downstream of the fluid treatment zone.

7. A fluid treatment system of Claim 6, wherein said pair of electrodes comprises a grounded electrode and an anode, the grounded electrode providing a housing to define the fluid treatment zone and in which the anode is located, and said ballast addition means, are arranged to add ballast to fluid within the housing and/or downstream of the housing.

8. A fluid treatment system according to Claim 7, wherein the ultrasound generators are mounted on or to the grounded electrode.

9. A fluid treatment system according to Claim 6, 7 or 8, wherein the ballast comprises one or more of an inorganic particle, for example silica or carbon, or a polymeric particle.

10. A fluid treatment system according to any one of Claims 6 to 9, wherein the ballast comprises particles with an average diameter in the range of from 20 to 300 μιτι, say in the range of 40 to 250 pm and/or the ballast has a specific gravity of greater than 2, and in some embodiments greater than 2.6, for example about 2.6 to 2 7.

11. A fluid treatment system according to any of Claims 6 to 10, wherein said ballast addition means is arranged to add ballast in the range of 1 to 50 g/l (measured as mass of ballast to volume of fluid to be treated), for example 2 to 20 g/l and in some embodiments 5 to 20 g/l, for example 10g/l.

12. A fluid treatment system according to any of Claims 6 to 11 , further comprising flocculating agent addition means, preferably arranged to add flocculating agent before, within or after the mixing means.

13. A fluid treatment system according to any of Claims 6 to 12, wherein said mixing means comprises a high shear mixer.

14. A fluid treatment system according to any of Claims 6 to 13, wherein said mixing means comprises plural stages.

15. A fluid treatment system according to Claim 14, wherein said plural stages comprises a first stage in which a relatively more rigorous mixing, for example a relatively fast mixing speed, is employed and a subsequent stage in which a relatively less rigorous mixing, for example a relatively lower mixing speed, is employed.

16. A fluid treatment system according to any of Claims 6 to 15, comprising a mixing zone or unit with a first mixing stage fluidly connected to and upstream of a subsequent mixing stage, the first mixing stage comprises a mixer, for example a flash mixer, capable of stirring a propeller or impeller at, say 100-300 rpm, say for 2 to 15 minutes, and the subsequent mixing stage comprises one or more mixers, for example a paddle stirrer, capable of mixing at say 30 to 160 rpm.

17. A fluid treatment system according to Claim 15 or 16, comprising two subsequent mixing stages provided with means to effect successively less rigorous mixing.

18. A fluid treatment system according to any of Claims 6 to 17, comprising clarifying means to clear the mixed fluid from agglomerated and/or flocculated particles

19. A fluid treatment system according to Claim 18, wherein said clarifying means comprises a lamella clarifier, preferably having a surface loading / application rate of 10 - 140 m³hr¹nr², preferably 30 - 100 m³hr¹nr² preferably 40 - 80 m³hr¹nr².

20. A fluid treatment system according to Claim 18 or 19, comprising ultrasonic generators to expose material settled in said clarifying means to ultrasonic energy and thence to circulate reclaimed ballast to said ballast addition means.

21. A fluid treatment system according to Claim 19, wherein said clarifying means may comprise a centrifuge, decanter, disc separator, hydro cyclones and the like.

22. A fluid treatment system according to any of Claims 6 to 20, further comprising a power source for applying electrical current to the electrolysing means.

23. A fluid treatment system according to any of Claims 6 to 21 , comprising means for monitoring one or more electrical characteristics between the electrodes of said electrode pair in the treatment zone such that the voltage between the electrodes of the electrode pair is automatically variable to achieve a set current amperage across the electrodes electrodes of the electrode pair, and a monitoring means for monitoring one or more chemical parameters of the fluid either upstream and or downstream of the treatment zone and automatically set the operating amperage for the treatment zone defined by the pair of electrodes.

24. A fluid treatment system according to any of Claims 6 to 22, further comprising a control means arranged to control one or more of the applied current for electrolysis, dosage rate of the ballast, the applied frequency and/or power to the or a ultrasonic generator means and/or rate and amount of addition of the or a flocculating agent, in dependence on one or more characteristics monitored by the or a monitoring means.

25. A fluid treatment system, the system comprising an electrolysing means, a ballast addition means, and a mixing means, comprising means for monitoring one or more electrical characteristics between first and second electrodes of said electrolysing means in the treatment zone such that the voltage between the first and second electrodes is automatically variable to achieve a set current amperage across the first and second electrodes, and a monitoring means for monitoring one or more chemical parameters of the fluid either upstream and or downstream of the treatment zone and automatically set the operating amperage for the treatment zone defined by the first and second electrode.

26. A fluid treatment system according to any one of Claims 6 to 24, further comprising a source of UV light, which is arranged to irradiate fluid that passes through the unit, preferably the UV source is arranged to irradiate fluid that is downstream of the treatment zone.

27. A fluid treatment system or unit according to Claim 25, wherein the UV source is located at or in the vicinity of the outlet.