GB2367072A

GB2367072A - Mineraliser reaction cell for purifying liquids

Info

Publication number: GB2367072A
Application number: GB0007013A
Authority: GB
Inventors: Robert John Spencer; Abdul Jabban Chaudhary; Susan Mary Grimes; John Dallas Donaldson
Original assignee: FLUID DYNAMICS INTERNAT Ltd; Brunel University
Current assignee: FLUID DYNAMICS INTERNAT Ltd; Brunel University
Priority date: 2000-03-22
Filing date: 2000-03-22
Publication date: 2002-03-27
Also published as: GB0007013D0

Abstract

A system for the continuous destruction of organic matter and dyes that uses adsorptive surfaces (12) to trap organic particles and matter and then uses the electricity delivered to electrodes (20, 22) to produce oxygen that then oxidises the trapped organic species thus freeing up sites on the adsorptive surfaces for further organic adsorption and subsequent destruction. In this way a fluid which is preferably aqueous is purified by the removal of the organic matter and dyes. In a modification each electrode can act as the material trapping organic particles.

Description

METHOD AND APPARATUS FOR THE DESTRUCTION OF DYES AND OTHER ORGANIC MOLECULES This invention relates to a method and apparatus for the treatment of fluids, to destroy colour and other organic molecules as well as bacteria.

With ever-increasing controls and limits on the amounts of colour and other organic materials that may be discharged to the environment there is a need for an efficient method for the destruction of colour and organic materials as well as for bacterial destruction. This need applies to final end-of-pipe effluent and to in-situ treatment of process streams and waters.

Historically methods such as oxidation, photochemical oxidation, electrochemical oxidation, chemical treatment, precipitation, ultrafiltration, flocculation followed by filtration, and chemical adjustment have been used for colour removal and the mineralisation of organic compounds.

The known methods require substantial investment in capital equipment. Drawbacks arising in treating the production of dilute solutions of organic materials include the development of large amounts of sludge that has to be transported to landfill or otherwise disposed of. For bacteria, the consumption of gas, ozone, silver ions and other chemicals of a potentially harmful nature is required.

The present invention seeks to provide an improved method and apparatus for the in-situ treatment of fluids. The embodiments disclosed are particularly well suited to application in the destruction of dyes and other organic materials.

According to an aspect of the present invention there is provided a method for the destruction of colour by the breaking up of the organic molecules that cause colour and the destruction of other organics by oxidation.

In a further aspect of the present invention, there is provided a method of oxidising a compound (such as an organic molecule) comprising adsorbing the compound on an adsorption medium

(such as an absorption surface), and oxidising the adsorbed compound, wherein the oxidising of the compound frees the adsorption site for further absorption.

Preferably, the method includes the step of generating an oxidising agent by passing an electric current through a suitable electrolyte. The electrolyte is preferably the fluid to be treated, which is preferably aqueous. The electric current may be generated by immersing a cathode and anode, preferably two anodes with a cathode there between, into the electrolyte.

The advantage of the latter arrangement is that both sides of the cathode are exposed to the anodes and the whole cathode surface is therefore utilised.

In a preferred embodiment of the equipment for the destruction of dye molecules and other organic materials, means for adsorbing organic molecules are combined with electrodes in an arrangement referred to hereinafter as a mineralisation. The adsorption medium can be selected from layers of activated carbon, ion exchange resins, activated carbon cloth, activated carbon, specific metal ion-complexing agents, any other adsorption (concentrating) medium or a combination thereof. Preferably, the adsorption medium operates to store the species to be destroyed within the expected transport layer of the destination electrode. The mineralisator can be provided in the form of concentric cylindrical electrodes or circular flat disc electrodes or plate electrodes or rod electrodes all of which are immersed in the adsorption medium.

It is preferred to employ an electrically conductive, fluid (though not necessarily liquid) adsorption medium such as activated carbon granules, and to employ an arrangement in which the electrodes are in electrical contact with the adsorption medium, since this results in the adsorption medium's surrounding and contacting each electrode to become in effect an extension of the electrode itself, i. e. to become either anodic or cathodic as the case may be. This increases the effectiveness of each electrode by increasing its surface area. The use of a"bed"of activated carbon also slows down the flow of electrolyte through the system, making adsorption more likely.

If the adsorption medium is not electrically conductive itself, then it is preferred that the system includes an electronically conductive spacer between the electrodes (though this should not create a continuous electrical link between the electrodes, or it will create an electrical"short").

Although the preferred oxidising agent is oxygen gas or free radicals generated by electrolysis, suitable oxidising agents include ozone, chlorine dioxide, hydrogen peroxide, or any known suitable oxidising agent. In an alternative embodiment, ozone, hydrogen peroxide or gas (which may be heated) may be bubbled through the liquid to be treated and the adsorption medium (e. g. carbon granules), in which case electrodes are not needed.

By immersing cathodes and anodes in the electrolyte and passing a current through them, free oxygen, peroxide or ozone is developed which oxidizes the colours that are trapped on the activated carbon. By oxidizing the colours they are totally destroyed and revert back to carbon dioxide and water. Their destruction also means that fresh sites for adsorption of the colours or other organic species are always being created and as such the activated carbon/catalytic bed can never become saturated and need replenishing or replacement.

In certain cases the anode may be coated in special material such as boron-doped diamond that causes the production of free radicals. These free radicals are highly efficient in organic destruction and are continuously generated by the electrolytic process.

The dye destructor is preferably housed in a watertight receptacle.

A cathode and two anodes are then put in the receptacle. The distance between them is not important but there must be a distance. There can be more than three electrodes but there are preferably always more anodes than cathodes and the cathodes should be sandwiched between the anodes. An increase in the electrodes will increase the rate of destruction.

The electrodes can be any shape but are preferably circular cylinders, flat plates or flat discs and more preferably are of mesh configuration.

The tank is then filled completely with the adsorption medium and the electrodes are embedded therein.

A potential difference is applied across the electrodes and the material to be treated is pumped through the system.

Preferred cells achieve the destruction of colour and organic matter by oxidation with no chemical addition. However, other methods for destroying organic contaminants for example the addition of hydrogen peroxide may be used in combination with the preferred apparatus for fluid treatment.

Embodiments of the invention will now be described below, by way of example only, with reference to the accompanying drawings, in which: Fig 1 is a schematic illustration of a reactor with circular electrodes; Fig. 2 is a schematic illustration of the operation of a concentrator cell in with concentric electrodes; Fig. 3 is a schematic illustration of a concentrator cell with plate electrode system which can be incorporated into a combined clean-up and recycling system.

With reference generally to Figs. 1-3, preferred features of an apparatus particularly well suited for use in the destruction of organics and colour from process streams and dilute effluent streams, include an arrangement of complementary electrodes 10 having a concentrator medium 12 disposed therebetween. The electrodes 10 and concentrating medium 12 are contained substantially within a fluid-tight receptacle, in this example, an electrolysis chamber 14 made of high density polypropylene or other suitable material.

Referring specifically to Fig. 1, a first configuration includes conductive anode 20 and cathode 22 plates. The cathode 22 is provided integrally with the receptacle 14. The concentrator medium

12, in this example, granular activated carbon fills the entire void of the vessel. Anode 20 and cathode 22 plates are in contact with the medium to form a reaction cell 36. The concentrator medium 12 shown is activated carbon but could be any concentrator medium. The various configurations are represented schematically below each diagram. A current is applied to the cathodes and anodes 20 and 22.

In use, receptacle 14, holds the solution to be treated (electrolyte) up to a level sufficient to immerse the electrodes 20,22 and the concentrator medium 12. Under the driving force of an electrical current, oxygen and free radicals are produced at the anode 20.

The preferred approach enables oxygen and free radicals to be generated continuously. A particularly advantageous feature of reaction cell 36 is that the adjustment of electrolyte pH is not required. Preferred apparatus configurations are versatile, for example, in that they permit a combination with equipment for other purposes, such as the further photocatalytic or photolytic destruction of organic contaminants or simultaneous or subsequent removal of metal impurities.

The overall size and other geometric aspects of the apparatus will be a matter of design choice and depend on the application including treatment rates and volumes. Optimisation may be in terms of, for example, the efficiency of colour destruction, or volume throughput/processing time.

The choice of material for the receptacle 14 ultimately depends upon the nature of the electrolyte fluid and the conditions required for electrolysis. The choice of materials for the concentrator media 12 and electrodes 20,22 will be apparent to a skilled person and depend, among other things, on the electrolyte, the metal impurity content, the conditions of electrolysis, and the selectivity required.

Typical choices for the electrode materials include, for example, platinum, stainless steel, titanium, activated carbon, graphite and other appropriately conducting materials. The anode 20 and cathode 22 materials of any apparatus may, if desired, be selected from different materials.

The electrodes may take any number or shape including, for example, plates, rods, tubes or cylinders.

Typical choices of material for the concentrator media include ion exchange materials, activated carbon cloth, or any other material with adsorption, selectivity and/or concentrating properties.

In this regard, combinations of materials are often desirable. The concentrator media may be any desired shape and any number may be provided.

A number of modifications will be immediately apparent to one skilled in the art. The anode 20 may comprise one or more separate electrode elements, it may be a continuous cylindrical element or a plurality of such elements. The same applies to the cathode 22.

In another modified version, each electrode can act as a concentrator means in itself. For example, the relevant electrode can be provided in a material which itself behaves as a concentrator medium. Any material with appropriate conductivity for the electrode function and the ability to releasably store the species to be destroyed can be used; certain suitable materials correspond to those suggested elsewhere in this description for the concentrator medium itself.

Claims

CLAIMS 1. A mineraliser reaction cell composed of a container filled with adsorptive material filling the void of the container through which fluid can flow and on which organic matter present in the fluid will deposit and in which are placed throughout the material at various intervals electrodes connected to a power supply and whereby the passage of an electric current through the electrodes causes the destruction of organic species that are trapped on the surface of the adsorptive material
2. A reaction cell that can be any shape and contain any number of electrodes some of which my generate their own free radicals
3. A cell wherein the electrodes may be composed of various materials such as stainless steel, carbon, mixed metal oxides or any other conductive material
4. A cell as described in claim 1 containing for the destruction of organic species containing adsorptive medium and electrodes where flow may be from any direction
5. A cell as described in claim 1 where the power applied may be by means of direct current either from a transformer or battery or any other source
6. A cell as described in claim 1 wherein any number of electrodes may be placed in a concentrator medium
7. A cell as described in claim 1 containing anodes and cathodes in concentric, sheet or disc form immersed in a concentrator medium.
8. A cell as described in claim I except that the electrodes are surrounded by the adsorptive media but in the rest of the vessel there is a void filled by the liquid to be treated
9. A mineralisator cell for the destruction of organic and other chemical species substantially as herein described and illustrated in the accompanying drawings

8. A cell as described in claim 1 except that the electrodes are surrounded by the adsorptive media but in the rest of the vessel there is a void filled by the liquid to be treated 9. A mineralisator cell for the destruction of organic and other chemical species substantially as herein described and illustrated in the accompanying drawings Amendments to the claims have been filed as follows CLAIMS 1. A mineraliser reaction cell composed of a container filled with a conductive adsorptive material filling the void of the container through which fluid can flow and on which organic matter present in the fluid will deposit and in which are placed throughout the material at various intervals electrodes that are at all times in contact with the material constantly connected to a power supply and whereby the passage of an electric current through the electrodes causes the destruction of organic species that are trapped on the surface of the adsorptive material 2. A reaction cell containing adsorbtive material containing electrodes constantly connected to a power supply constantly in contact with that material that can be any shape and contain any number of electrodes some of which my generate their own free radicals 3. A cell wherein the electrodes connected to a constant power supply may be composed of various materials such as stainless steel, carbon, mixed metal oxides or any other conductive material where the electrodes are constantly in contact with a bed of adsorptive conducting material 4. A cell as described in claim 1 containing for the destruction of organic species containing adsorptive medium and electrodes where flow may be from any direction 5. A cell as described in claim 1 where the power applied may be by means of direct current either from a transformer or battery or any other source 6. A cell as described in claim 1 wherein any number of electrodes may be placed in a concentrator medium 7. A cell as described in claim I containing anodes and cathodes in concentric, sheet or disc form immersed in a concentrator medium connected to a constant power supply.