GB2424875A

GB2424875A - Electrode assembly and method for treating and separating contaminants from fluids

Info

Publication number: GB2424875A
Application number: GB0506764A
Authority: GB
Inventors: Philip Graeme Morgan
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-04
Filing date: 2005-04-04
Publication date: 2006-10-11
Also published as: GB0506764D0

Abstract

An electrode assembly and method for treating and separating contaminants from fluids comprising a multiplicity of inclined plate electrodes 1 and an external voltage controller 11 that provides an asymmetric pulsed voltage. In operation the electrode assembly is submerged into channel, tank or container such that the electrode plates are tangential to the flow of the fluid. Electrochemical reactions occur on lower and upper electrode surfaces of the electrodes which create a treatment zone 10. The lower electrode promotes the build-up of suspended matter and the upper electrode promotes the production of electrically charged micro-bubbles which trap contaminants and remove them to the top of the electrode assembly. The external voltage controller may be only attached to the first and last electrodes in the assembly, the inner electrodes becoming charged by induction alone. The assembly may be capable of coagulation, oxidation and disinfection treatments. Multiple electrode assemblies may be combined together horizontally or vertically to form either a 'deck' layer for treating larger flows or a deep bed treatment process respectively. The assemblies may be combined both horizontally and vertically.

Description

1 2424875 Electrode assembly and method for treating and separating

contaminants from fluids The present invention relates to an electrode assembly for treating and separating contaminants from fluids. The invention is particularly suitable for use in the decontamination of fluids and purification of fluids.

Decontamination of fluids is frequently required to destroy, disinfect or remove impurities.

The fluid to be decontaminated may especially be contaminated water, for example, wastewater sewage, industrial effluents, process waters, ground waters, leachates, rivers, streams, recreational waters, lakes, marine or coastal waters, sewage, storm water overflows or other products such as oil coolants, foods and beverages, paints of which water is the main constituent. The fluids may contain one or more contaminants, for example, heavy metals, inorganic and organic material, soaps and detergents, suspended and dissolved colloidal material, organo-metalloid compounds and other inorganic-heavy metal-organic complexes, man made chemicals such as endocrine disrupting chemicals and their derivatives, herbicides, pesticides and radioactive derivatives.

Contaminants may also be of biological origin such as viruses, bacteria, algae, fungi and moulds as well as protozoans and other such aquatic animals.

To date, decontamination has been widely achieved essentially by physical, chemical and biological treatment methods either as a single stage process or as a combination of processes.

Physical treatment generally relates to the entrainment or capture of suspended material and biological organisms by filtration, sedimentation or flotation (Dissolved Air Flotation) but is inadequate to remove dissolved materials such as organics and soluble forms of heavy metals.

Biological treatment requires careful growth and culture of biological organisms to feed on the contaminants in order to decontaminate the sample. Biological systems are limited to applications where the contaminants are of a bio-degradable nature and require large areas of space / land for construction. Chemical treatment requires the addition of liquid chemicals such as coagulants which increase the amount of sludge produced as a result of charge neutralisation and adsorption.

This leads to increased sludge disposal. Furthermore, chemical treatment requires secure storage for the chemicals, which may be toxic or hazardous and require stringent control on dosing, handling, transport to minimise their environmental impact on the environment.

The term "decontamination" as used herein includes processes in which the concentration of one or more undesirable substances in a treatment fluid are reduced or eliminated and is not intended to be limited in meaning to the complete removal of the undesired substance and/or of any harmless or less harmful derivative(s).

The use of electrochemistry for the treatment of liquids, for example, in the treatment, disinfection and conditioning of water, wastewater, industrial effluents and other liquid streams is well-known. Such techniques were first employed by early civilisations over 2000 years BC, who used silver storage containers and sunlight to purify and disinfect water for drinking. More recently (1888), London County Council applied electrolysis on sewage. Untreated sewage blended with salt water and treated with iron electrodes was used to treat sewage for subsequent removal of suspended solids and reduce organic load by downstream processes prior to discharge into the River Thames. Electrolysis has subsequently been applied to heavy metal removal, suspended solids removal (electro-coagulation), and in the reduction of organic and chemical pollution and for removing dissolved and soluble forms of organics (Fenton chemistry) and disinfection (electro- poration). Such reactions are accompanied by oxidation, reduction, charge neutralisation, pH change and capacitance, which all aid the decontamination process.

The known processes for decontamination of liquids that make use of electrolysis have to date been carried out in tanks or elongate, tubular devices in which electrodes are fixed or suspended into the liquid medium or enclosed between non-conducting surfaces through which water is passed and which turbulence promoters are included. Examples in include Patent US 5,314,589; Japan publication number 560000288; US 2,887,444 which in addition has defined inlets and outlets through slots in the electrodes; US Patent 5,314,589, German Patent DE 44 43 297 Cl and DE 44 14 264 Al describe apparatus in which a number of electrodes are held in a device such that the flow of fluid is parallel the axis of the electrodes.

In all these cases, the flow of water is parallel to the axis of the electrodes either in the horizontal or vertical plane. In addition a feature of all these systems is the inclusion of turbulence promoters or stirrers to mix the fluid to prevent settlement of suspended material and to aid mass transfer between the contaminants and the electrode surface. Such systems may be operated in batch, continuous, semi-continuous or recirculation operation and may have liquid chemical coagulants and or salt' (sodium or potassium chloride) added to increase the conductivity of the fluid medium to aid electrolysis; Other designs include 3- dimensional systems whereby mass transfer is enhanced by using horizontally stacked metallic gauzes or carbon weave or granules to give a high surface area to volume ratio through which water is passed. These latter designs would be used predominantly for electro-deposition whereby it is advantageous to have a high surface area to collect the deposited contaminants. The supplementary use of chemical coagulants and salt solutions to improve conductivity and electrolytic performance is a disadvantage because it negates the advantages of electrolysis as an environmentally clean' technology having reduced environmental impact and reduced health and safety risks usually associate with chemical handling.

In addition, recent research has indicated that chlorination of organics, by adding salt, can produce carcinogenic type compounds in the liquid medium of drinking waters. The addition of a salt solution as described in many of the above patents would now be detrimental to decontamination of fluids especially in the drinking water and municipal sewage sector of the industry.

A further aspect of these processes, with exception of German Patent DE 44 43 297 Cl is that electrolysis requires further downstream processing for separating the contaminants from the fluids. Typicalty, the previously known electrolytic treatment processes have employed an AC or a pulsed DC or continuous DC current or DC switching arrangements for symmetric polarity reversal between each of the positive and negative electrodes to aid cleaning of the electrode surface.

One known aspect of physical treatment for separating contaminants from fluids after chemical or biological treatment is a single stage combined flocculation and clarification process.

Advantageously, it has been demonstrated that by maintaining high concentration of suspended matter that the flocculation process is improved resulting in clarified water of good and constant quality. By including inclined plates into the sludge contact clarifier it has been further demonstrated that both water quality and sludge settlement are both improved. As mentioned above, electrochemical treatment systems have to date employed turbulence promoters, mixers to avoid such high concentrations of suspended matter especially along electrode surfaces to minimise electrode surface fouling. The applicant's GB2342658A patent describes a flat plate electrode arrangement containing filaments to promote turbulence and GB0416050.3 patent application describes impeller electrodes to promote mixing to minimise surface fouling (high concentration of suspended matter) on the surface face of the electrode.

The applicant now provides a third invention for an electrode arrangement which contrary to existing prior art for electrolytic treatment, actively promotes high concentrations of suspended matter along the surface of electrodes by omitting turbulence promoters and mixers to aid electrolytic treatment of fluids and also provides a means of separating contaminants from fluids by electrolysis. This invention uses electrically charged inclined electrode plates submerged in the fluid to promote build up of suspended matter (sludge contact clarification) on the lower inclined electrode plate and production of electrically charged micro-bubbles on the corresponding upper inclined electrode plate, such a treatment system offering the benefits of chemical free electrolysis with advantages of simultaneously separating the contaminants from the fluid by flotation to produce consistent and good water quality and highly de- watered sludge.

In accordance with a first aspect of the present invention there is provided an electrode assembly for treating and separating contaminants from fluids comprising of a multiplicity of parallel electrode plates submerged in the fluid, spaced from one another and defining between them treatment zones, wherein the electrode plates are arranged and spaced accordingly and transverse across the direction of flow at an inclined angle to the horizontal such that contaminated fluid may enter the treatment zones evenly and treated fluid exit from below and have electrical connections to an external voltage controller source capable of generating asymmetric pulsed voltages across any of the electrodes contained therein to bring about electrolysis such that the lower electrode promotes the build up of suspended matter and the upper electrode promotes the production of electrically charged micro-bubbles which trap contaminants in the treatment zone which are subsequently removed from above.

The term multiplicity of electrodes' as used herein is intended to means at least two, preferably 4, 6 or 8 electrodes and preferably less than 50 per electrical power source. The term inclined angle to the horizontal' as used herein is intended to mean an angle of between 30 to 800 but preferably at an angle of 60 and or 45 . The term asymmetric pulsed voltages' refers to a voltage that can operate at one fixed voltage for one period of time and a second fixed voltage for a second period of time independent of the first. The selection of voltages and operating times may be determined from external signals or from internal operating settings.

This electrode arrangement combines the benefits of physical treatment with environmental benefits of electro-chemical treatment to offer a single stage process for both treating contaminants and for separating contaminants within the same apparatus. It provides good performance, whilst being simple to manufacture and for placement / replacement and maintenance of electrodes. It also allows for a standard design to be used for a variety of fluids of differing influent quality, negates the need for re-circulation pump, turbulence promoters, mixers as in the case with flow-through reactors and separate agitators and mixers in the case of tank systems to create turbulence, mass transfer and to maintain suspended material in suspension to prevent solids settlement and electrode fouling. Advantageously the assembly can be used as a stand- alone process by submerging into a channel or tank, retro-futted to existing tanks or supplied as an engineered tank solution. Various hydraulic flows can be catered for by increasing or decreasing the number of electrode plates and electrode assemblies.

The electrode assembly described is the preferred construction and consists preferably of 6 inclined plate electrodes preferably of rectangular shape but not excluding other shapes or numbers of electrode plates. Preferably each electrode plate is mounted onto an insulated panel frame which secures the electrode plate between two the retaining side panels of the electrode assembly. Preferably the fixing of the panel frame to the slide panel of the electrode assembly is by guide sleeves such that the frame panel and electrode plates can easily be placed or removed from the assembly by fixings or handle cut-out in the frame panel by manual or mechanical means.

Preferably, the guide sleeves are mounted preferably at 60 , but not less than 30 or greater than 800 angle to the horizontal and transverse across the direction of flow across the two insulated side panels which define the sides of the assembly. The guide sleeves are mounted evenly at a spacing of preferably of 80mm but not less than 2mm or greater than 200mm from one another. Preferably, electrical connections to the external voltage controller are made to the front electrode plate and to the rear electrode plate only. The inner electrode plates being charged by inductance from the front and rear plates (referred to as multi-polar by those in the art of electro- chemical reactor design). Advantageously this arrangement reduces operating currents and leads to more energy efficient operation. The electrodes provide both a treatment means for treating the fluid and a sensing means for the voltage controller to measure the electric current across the electrode assembly. An algorithm contained in the voltage controller continually calculates the voltage required to maintain a set electric current or voltage across the electrode assembly.

Advantageously, such a control system provides continues feed-back and adaptive control to changing influent quality of the influent feed. Preferably the electrode plates for the assembly are constructed of similar metals such as aluminium or iron, However it is advantageous sometimes to use a mix of metals in some applications on difficult fluids or the use of oxygen over potential electrodes or specially coated electrodes for oxidation and or disinfection. As different metals have different electro-chemical equivalents, the rate at which different metal ions are sacrificed from various mixed metallic electrode surfaces change. Accordingly for such combinations, asymmetric voltages and treatment times are required to ensure that the correct concentration of ions are released from the respective electrode materials. Advantageously such asymmetric pulsing provides better electrode cleaning, anti-fouling properties than prolonged symmetrical electrode polarity reversal when used on coated electrode materials which can result in sloughing off of the coated material. Preferably the electrode plates are flat sheet however plates could also be grooved, serrated or corrugated to further enhance the surface area of the electrode surface.

"Electrode assembly" as used herein is intended to define the fluid treatment apparatus and includes the panel frame, side panels and guide sleeves, electrodes, voltage controller, treatment zones, inlets and discharge outlets. "Contaminant" as used herein is intended to have its broadest meaning i.e. the chemical make-up of the fluid including chemical, physico-chemical, inorganic, organic and microbial biomass and other substances, impurities and contaminants in the fluid which affect its treatment.

The invention will now be described by way of example only with reference to the following figures of which: Fig. 1 is a schematic view of the electrode assembly and process Fig. 2 is a detailed view of the electrode and panel frame.

Fig. 3 is a detailed view of the electrode, panel frame and side panels Referring to Fig. 1, each electrode plate 1, inclined at a 600 angle to the horizontal and equally spaced apart at 80mm intervals so that between 6 electrode plates are mounted in one electrode assembly. Electrical connector 9 secure the first electrode plate and last electrode plate to an external voltage controller 11. In operation the electrode assembly is submerged into a channel, tank or container (not shown) such that the electrode plates are tangential to the flow of direction of the fluid. Cocurrent and counter current flows between the bottom and top electrode plates surfaces create a treatment zone 10 comprising of coagulation, oxidation, reduction, disinfection, charge neutralisatjon processes and production of electrically charged micro-bubbles which results in treated fluid exiting the electrode assembly 12 from below and contaminants from above.

Referring to Fig. 2, the electrode assembly consists of an electrode plate 1 and a panel frame 2. The electrode plate is secured to the panel frame by means of electrode-panel fasteners 3 around the perimeter of the electrode plate and panel plate. The electrode-panel fasteners 3 also allow external power cables to be connected using suitable electrical connectors 9 to the electrode plate(s) from an external voltage controller. A handle cut out 4 in the top of the panel frame aids manual placement / replacement, maintenance and changing of electrode plates in electrode assembly.

Referring to Fig. 3 shows a detailed side view and front view of the electrode assembly 12 the guide sleeves 7 which are inclined at 60 angle to the horizontal and extends for the whole length of the panel frame 2 to give strength and rigidity to the assembly. The side panels 6 are secured by six side panel fasteners 8 to give rigidity to the assembly. In addition the side panel fasteners may be used to secure the side panels and electrode assembly to one another (for scale-up) or to other fixing points suitable for installation, application and operation.

In the embodiment described above the composition of the electrode plates 1 is aluminium however depending upon the purpose of application other materials such as iron, oxygen over- potential electrodes such as platinum, diamond, coated materials and other carbon and metallic materials and mixtures or combinations may be used. In the embodiment each electrode plate 1 has a length of 760mm, a width of 450mm and thickness of 10mm, depending upon the flow volumes to be treated and sample complexity different sized electrodes could be employed such as varying from 100mm to 10000mm length or width or from 1mm to 500mm thickness. In the embodiment the treatment zone 10 is 80mm wide; for different application and properties of fluids inter-electrode gaps of 2mm to 500mm may be employed. The embodiment includes six inclined plate electrodes 1 inclined at 60 to the horizontal; for some application the angle of inclination may be from 30 to 80 to the horizontal. In the embodiment shown the number of electrode plates 1 within the electrode assembly is six. The actual number of electrode plates 1 may vary from at least two to preferably less than one hundred. In the embodiment shown electrical connections are only made to the first electrode plate and the last electrode plate so that the inner plates receive an electncal charge by inductance also known as multi-polar arrangement; Depending upon the nature of the fluid to be treated i.e. its electrical conductivity it may be advantageous connect more electrode plates to create multiples of bi-polar and mono-polar arrangements. In the embodiment the electrode plates 1 are rectangular flat sheet plate, other shaped electrodes, or contoured surfaces or corrugated surfaces could be employed. In use, the above apparatus provides a method of treating and separating fluid as described: The electrode assembly is immersed in the fluid to be treated such as a tank or channel.

Electrolytic treatment is effective by maintaining a fixed current density across the electrode assembly 12 of about 120 Am2. This can however vary for different fluid compositions for example current densities of 20 Am2 to 10,000 Am2 may be required to treat some contaminants, flow regimes or applications etc. The voltage to achieve this current across the electrode assembly 12 is maintained by the external voltage controller 11 via electrical connector 9 attached across the first and last electrode plates 1 of the electrode assembly 12. In operation electrode plates 1 also provide a means for the voltage controller to detect the electrical current across the electrode assembly. The power required to maintain a fixed current across the electrode assembly is determined in part by the electrical conductivity of the fluid contained between the plates. To maintain a set treatment threshold current the voltage controller 11 has a microprocessor and algorithm which continually monitors and controls the outgoing voltages to maintain the desired treatment in addition periodic cleaning cycles of asymmetric polarity reversal are introduced to maintain the electrode surface free of fouling. Fastenings in the above embodiment are fasteners.

Welded seams or similar fabrications could also be used appropriate for the application. Guide sleeves 7 have been used to secure the electrode plates 1 to the electrode assemblyl2 in this embodiment, however the electrode plates could be mounted direct to the assembly or other structures or framework as necessitated by the application.

The following Example illustrates the invention:

EXAMPLE

Trial 1 A biologically treated municipal waste effluent taken before secondary clarification was treated (1000 litres) with an apparatus similar to that Fig. 1. The apparatus was fitted with 6 electrode plates (760mm x 450mm x 10mm); immersed to a depth of 200mm in the waste effluent was treated at 15A at 350V for 6 minutes (equivalent to flow of 10m3/hr): Parameter Untreated Sample Treated Sample % Removal Discharge __________________ ________________ _______________ consent BOD 5ATU mg/I 34 2 94 30 Suspended solids mg/I 124 9 93 20 Phosphate mg/I 2.7 0.7 75 2 L!1monia mg/I 3.5 1.6 54 5 The results demonstrate the effectiveness of the electrode assembly as a secondary clarification process for municipal sewage treatment and that the treated parameters are below the required Discharge consent criteria for satisfactory discharge to water course.

Trial 2 The apparatus in Trial 1 was compared to a parallel plate electrode whereby the electrodes were not inclined at a 60 angle to the horizontal. The electrode area and inter-electrode gap distances, reaction times and operating voltages and amperages were the same for each apparatus.

Performance was compared by measuring sludge production i.e. the time required to achieve flotation immediately after treatment: Parallel Plate vertical Inclined plate % Improvement ___________________ electrode electrodes ___________________ Time (minutes) for 6 minutes 2.5 minutes 58 sludge blanket formation _____________________ The results indicate that the inclined electrode plate apparatus was more effective than the equivalent vertical plate arrangement for contaminant removal.

Claims

1. An assembly for treating and separating contaminants from fluids comprising of a multiplicity of parallel electrode plates submerged in the fluid, spaced from one another and defining between them treatment zones, wherein the electrode plates are arranged and spaced accordingly and transverse across the direction of flow at an inclined angle to the horizontal such that contaminated fluid may enter the treatment zones evenly and treated fluid exit from below, the electrode plates have electrical connections to an external voltage controller capable of generating asymmetric pulsed voltages across any of the electrodes contained therein to bring about electrolysis such that the lower electrode promotes the build up of suspended matter and the upper electrode promotes the production of electrically charged micro-bubbles to remove which trap contaminants to the top of the electrode assembly for removal.

2. A unit according to claim 1, in which the electrode plates are mounted at an inclined angle of between 300 to 80 to the horizontal.

3. A unit according to claim 1, in which the electrode plates are mounted onto panel frames which locate in guide sleeves of the side panels of the electrode assembly to provide easy manual or mechanical replacement of the electrode plates from the electrode assembly.

4. A unit according to claim 1, in which only the first and last electrode plates are attached to an external voltage controller and the inner electrode plates become charged by induction alone.

5. A unit according to claim 4, in which inner electrode plates have internal connections to create multiple bi-polar electrode plates.

6. A unit according to claim 4, in which the electrode plates have multiple connections to an external voltage control to form multiple monopolar electrode plates.

7. A unit according to claim 1, in which external voltage controller generates an asymmetric pulsed voltages across any of the electrodes plates across the assembly.

8. A unit according to claim 1, in which the electrode materials for the electrode plate may have a mixture of coagulating, inert or oxygen overpotential properties capable of coagulation, oxidation and disinfection treatments.

9. A unit according to claim 1, in which electrode assembly form a sensing and control circuit to monitor the electrical current flowing through the fluid and across the across electrode plates.

10. A unit according to claim 9, in which the information about the current status across the electrode assembly is relayed to the voltage controller.

11. A unit according to claim 10, in which the voltage controller further comprises of a control means to alter the applied voltage across the electrode assembly in accordance with predetermined values or algorithms supplied to the control means.

12. A unit according to claim 11 in which the voltage controller further comprises a control means to provide asymmetric voltage (independently vary the applied voltage and reaction times) to the electrode assembly to compensate for different electrode materials having different electrochemical equivalent properties.

13. A unit according to claim 10, in which the voltage controller further comprises a control means to provide asymmetric voltage to the electrode assembly to aid electrode surface cleaning and minimise fouling.

14. A unit according to claim 11 in which the current across the electrode assembly is not less than 20 Am2 and not greater than 10,000 Am2.

15. A unit according to claim 1 in which the distance between the electrode plates is not less than 10mm and not greater than 200mm from one another.

16. A unit according to claim 1 in which the size of the electrode plates is not greater than 10,000mm length or width or not greater than 500mm thickness.

17. A unit according to claim 1 in which multiple electrode assemblies can be combined together horizontally at the front, back and sides to form a substantive deck' layer for treating larger flows.

18. A unit according to claim 1 in which multiple electrode assemblies can be combined together vertically to form a deep bed treatment process.

19. A unit according to claim 17 and 18 whereby electrode assemblies can be combined together horizontally and vertically.

20. A unit substantially as described herein with reference to and as illustrated by any of Figs. 1-3.

21. A method of simultaneously treating and separating contaminants from fluid, the method comprising of contaminated fluid entering tangentially into a treatment zone defined by the space between two or more inclined parallel electrode plate surfaces of the electrode assembly, the electrode plates have electrical connections to an external voltage controller capable of generating asymmetric pulsed voltages across any of the electrodes, such that the lower electrode plate brings about coagulation, oxidation, disinfection, charge neutralisation and the upper plate produces electrically charge micro-bubbles and contaminated fluid passing through the treatment zones is decontaminated allowing treated fluid to exit from below and contaminants to be removed from above.

22. A method according to claim 21 in which treatment effectiveness is improved by asymmetric polarity reversal when dissimilar electrode materials are used and whose electro-chemical equivalents are different.

23. A method according to claim 21 in which treatment effectiveness is improved by asymmetric polarity reversal to remove debris and fouling of the electrode surfaces and to aid electrode cleaning.

24. A method according to claim 21 in which flexibility for treating increasing flow can be achieved by mounting multiple electrode assemblies together at the front, back and sides on the horizontal plane.

25. A method according to claim 21 in which flexibility for treating increasing flows can be achieved by mounting multiple electrode assemblies together vertically.

26. A method of treating a fluid substantially as described herein.