GB2444114A - An electrolytic process for the treatment of effluent - Google Patents

Abstract

The invention relates to an electrolytic process for the treatment of effluent. The process involves having a first cell having an aluminium electrode structure, and a second cell having an electrode structure comprising a core composed of an electrically conductive electrochemically stable material, such as titanium, and, as a cladding on the core, a composition of mixed metal oxides. The effluent is contacted directly with aluminium ions (Al<3+>), generated from an aluminium anode to produce insoluble aluminium fluoride. Aluminium ions (Al<3+>) are oxidised to aluminium dioxide (Al2O3) and hydroxide (Al(OH)3) by the oxidation power of free radicals and the oxidants produced from mixed oxides coated titanium anodes. Fluoride ions absorbed on the aluminium hydroxide matrix, free radicals and oxidants eradicating bacteria. Free radicals and oxidants along with aluminium hydroxide reduce COD and BOD substantially, eliminating obnoxious odour, creating electro-coagulation and electro-flocculation, this in turn clearing turbidity and settling down suspended solids. Hard scale formation is inhibited very effectively on the walls of the pipes and tanks due to the electromagnetic field created by mixed oxides coated titanium cell and the formation of soft scale that will not adhere to the walls of the pipes and tanks resulting in the reduction of scale forming ions in the aqueous media.

Description

RIDDING WATER OF CONTAMINANTS

FIELD OF THE INVENTION

This invention relates to a method of ridding water of fluorides and other contaminants and to apparatus for use in performing the method.

BRIEF DESCRIPTION OF PRIOR ART

Fluoride is an acute toxin with a rating slightly higher than that of lcad.

Other contaminants, that cause high biological oxygen demand (BOD) and chemical oxygen demand (COD), organic. non-organic, suspended solids, bacteria (including legionella), are very damaging to marine life and environment also causing obnoxious odour.

Hardness in processing water is problematic issue for many industrial processes using natural water supplies. In Britain alone the formation of scale in industrial process plant where water is heated or used as a coolant is estimated to cost over 1 billion per year. Such costs can be attributed to cleaning (i.e. dc-scaling) or poor thermal conductivity of scaled surfaces.

For many years now, a battle has been going on over the use of fluoride. As early as 1961, fluoride was exposed as a lethal poison In the early part of this century fluoride was recognized as a dominant industrial pollutant. It is emitted from iron and steel manufacturing operations, from aluminium, copper. lead, and zinc manufacturing operations, and is a by-product of certain fertilizers. About 30% of industrial waste from semiconductor plants is fluorine-containing waste.

The Lreaunent of water containing Fluorides has traditionally been realized using Lime in alkaline pH range as shown in the following equation: Ca(OH)2 +2 HF * CaF2 + 2H20 The fundamental problem that exists using this technique, arises from the low solubility of the Calcium Hydroxide (around 0,07%). a solubilitv that therefore calls for an excess of rcagent in an effort to achieve complete precipitation. However. the soluhility of the Calcium Fluoride (Ksp = 4*10 exp.1 I) precludes the possibility of complete removal of Fluoride, as required by limits set on the discharge of fluorides into the aqueous environment.

Calcium hydroxide, frequently sold as slaked lime, is relatively inexpensive, but its solubility being low the proportion of calcium hydroxide that dissolves in water as calcium ions is very small. In consequence, large quantities of treatment agent must be added to deal with the concentration of a treatment target for fluorine. Excess calcium hydroxide added in the wastewater is recovered with calcium fluoride, in great quantity, as waste sludge.

Because of its low solubility, calcium hydroxide is unable to produce a decrease in concentration of fluorine in treated water below I 5mg/litre. To achieve a concentration of 8mg/litre or less, as is required, a secondary treatment (second reaction tank -second coagulating sedimentation tank) using an aluminum treatment agcnt is generally employed. When this is insufficient for the fluorine treatment, a new aluminum treatment agent is added. By pH control, fluorine contained in waste-water is deposited as aluminum fluoride. A calcium treatment agent is added to the recovered sludge. By pH control, the aluminum of aluminum fluoride is substituted with calcium and is deposited as calcium fluoride.

US Patent No. 3926753 dated l6 December 1975 discloses and claims an electro-chemical process employing an electrode structure of aluminium in the removal from an aqueous solution of fluoride. The process disclosed in the abovcmentioned US Patent has the great disadvantage, however, of consuming large amounts of aluminium in the removal of the fluoride. Taking in consideration that aluminium is a not inexpensive metal, and that after treatment an environmentally unacceptable amount of aluminium ions (Al3') remains in the effluent treated. The sludge generated as a result of the treatment has a poor dehydrating capability. For these reasons, the process disclosed in US Patent No. 3926753 is unsatisfactory and has not found acceptance in the art. Even for low concentration fluorine wastewater treatment is not favoured, the level of aluminum ions left in the effluent after the treatment being environmentally unacceptable.

Focusing on the high fluorine removal capability of aluminum, and the good dehydrating capability and low cost of calcium. we examined a treatment method that decreases waste sludge, this involving the use of Iron salts (II) (Sulfate) to produce (FeF6)3. This approach proved to be unsatisfactory.

Wastewaters containing fluoride are generally treated with lime or calcium salt supplemented with aluminium salts. Wastewaters generated from different industries do not, as a result of the presence of interfering contaminants, behave uniformly. A number of techniques have been developed and studied for the removal of excessive fluoride. Most of these are based on use of aluminium salt, in alum coagulation the sorption properties of product of hydrolysis of aluminium salts and capacity of fluoride for complex formation play an important role.

The methods available for treating effluent with high BOD and COD, bacteria and obnoxious odour from the effluent depend mainly on aeration, biomass degradation, RO or the use of such chemicals as chlorine, chlorine dioxide, hydrogen peroxide etc. All these methods may be shown not to be 100% effective and entail high cost.

Similarly, for Total Suspended Solids (TSS) the use of flocculants arid coagulants is also expensive.

Hardness is a major problem for industry. Scale formation arises as a result of precipitation of sparingly soluble salts, most commonly calcium and magnesium carbonate, these forming an incrustation on susceptible surfaces.

Traditional chemical methods of scale control or water using a softening resin involve either the pre-precipitation of the scale formation with lime or soda ash. The additidn of scale inhibiting reagents or the replacement of the scale formation with soluble ions by ion exchange, usually sodium ions, as a substitute for calcium and magnesium ions undesirable and can be used only on small scale, though effective in scale control substantially changes the solution chemistry and is very costly and impractical for industrial high volume of processing water. As for magnetic water treatment this is yet to be proved scientifically and conclusively in a peer reviewcd journal. In fact, such laboratory and field studies have, in general. reported mixed results as to the overall usefulness of this technology.

Anti-scale magnetic treatment and other physical methods of scale suppression remain controversial. The effect of hardness on aquatic life is a function of the cations responsible for the hardness. Calcium carbonate deposited as a coating on the inside of water holding tanks and pipes walls leads to diminished how and even complete clogging. Extreme hardness may interfere with chemical process.

SUMIVIARY OF THE INVENTION

The method and apparatus for use in the performance of the method, all in accordance with the invention, share characteristic features as set forth in the claims schedule hereof and, accordingly, wording corresponding to that contained in said claims and the inter-dependencies there between, are deemed to be here set forth, mutatis mutandis, also.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. I is schematic diagram of a monopolar aluminium cell; Fig. 2 is a schematic diagram of a monopolar titanium cell: Fig. 3 is schematic diagram of FRI polypropylene box unit: Fig.4 is a schematic diagram for Fluoride and contamination treatment plant; Fig 5 is a schematic diagram for water hardness treatment plant A: Fig.6 is a schematic diagram for a cylindrical Titanium cell; Fig.7 is the schematic diagram of the cylindrical hardness treatment unit; Fig.8 is a schematic diagram for hardness treatment plant B: Figs.9a to 9f are graphs showing, respectively, rates of elimination of various contaminants present in water during trials using the process and apparatus hereinafter described and claimed.

A DESCRIPTION OF CHARACTERISTIC FEATURES OF A PREFERRED

EMBODIMENT OF THE INVENTION

The present process of removing fluorides from an aqueous solution involves the generation of free aluminium ions in the effluent to be treated from aluminium cell, at the same time to oxidize these aluminium ions to Al203 which undergo further oxidation to Al(OH)3 by the action of free radicals. i.e. oxygen, hydroxyl and perhydroxyl radicals, from the effluent to be treated and oxidants generated by the action of mixed oxides coated anodes.

A useful electrolytic cell for practising such method comprises a plurality of parallel plate electrodes between which effluent to be treated flows, the electrode structure helping to maintain the insoluble compounds product in suspension until it is removed from the effluent by extraction or filtration.

In practising the invention regardless of the nature of the contaminant being treated, two types of electrolytic cell are employed, one, to produce aluminium ions (hereinafter referred as to the Al-cell), the other, (hereinafter referred to as the Ti-cell), to create the above mentioned free radicals, that is to say oxygen, hydroxyl and perhydroxyl radicals, these, in turn, serving in the generation of derivative oxidants, ozone, hydrogen peroxide, oxygen molecules and hydroxyl ions, in the effluent under treatment.

An Al-cell cell employed in a trial of the invention is depicted in Fig. 1. The cell comprises an electrode structure composed of plate-form elements of substantially pure aluminium (99.5%). Polypropylene spacers provide an 8mm gap between the anodes, and the cathodes, of the electrode structure of the cell. The gaps between the anodes and cathodes may be varied depending upon the application. Thc dimensions chosen for both the anodes and the cathodes was 250mm by 250mm by 5mm. These dimensions and the number of electrodes employed is chosen according to the flow rate and volume of the effluent and the nature of the contaminant to be treated.

The Ti-cell (Fig.2) employed in association with the Al-cell of Fig. I has a plate-form electrode structure comprising a core of an electrically conductive electrochemically stable material, advantageously titanium, with a cladding of precious metals oxides thereon, the oxide coating being applied by any suitable means and method, painting, pyrolysis or annealing coating techniques. In the course of electrolysis, free radicals, oxygen, hydroxyl and perhydroxyl radicals are created.

these triggering a chain reaction generating, ozone, hydrogen peroxide. hydroxyl ions and oxygen molecules. The mixed oxides coating material is chosen not to exceed the hydrogen and oxygen over-voltage to reduce hydrogen and oxygen evolution to a minimum during electrolysis. Instead hydrogen peroxide and ozone are produced during electrolysis.

The aluminium cell (AL-cell) and the titanium cell (Ti-cell) are installed in a box-shaped vessel, suitably of polypropylene, with the plate electrodes of the cells in line with the flow of effluent. as shown in Fig. 3. The polypropylene vessel contain FRT unit is to be immersed at a suitable position in the effluent tank. Oii one side the polypropylene vessel is connected, by way of a conduit, to a pump serving to circulate the effluent through the two cells. The opposite side of the vessel has an effluent outlet. The top of the polypropylene vessel has apertures through which gases formed during electrolysis are discharged.

The cells are connected to independent power supplies adapted to develop different voltages and currents. For the treatment of some effluents, however, the power supply for the Al-cell may, comprise a photovoltaic cell: or the aluminium cell may dcpending on the nature of the contaminant effluent, the pH and the conductivity.

The cells shown arc monopolar though bipolar arrangements could be employed.

For the monopolar configuration the current will be high and the voltage low, whereas ibr bipolar cells the reverse will usually be true.

Several experiments have been performed on diftrent effluents common in the pharmaceutical industry for fluoride removal, at paper mills for treatment of odOurs, COD, BOD, ferrous and manganous ions, turbidity and suspended solid in effluent, eradication of bacteria including Legionella and treating hard scale deposition on pipes and tanks walls in processing water. Line precipitation removes fluorides down to between 0.00 to 10.00 mgfl. The same result can be achieved with bacterial disinfections, COD & BOD being reduced to a prescribed environmentally safe level.

suspended solid reduced substantially to zero, turbidity cleared, obnoxious odour eliminated and scale formation substantially inhibited.

Automatic reversible polarity of current applied through the cells prevents deposition of insulative insoluble reaction products on the electrodes, deposition that would reduce the current flowing through the cell. Such current reduction would call for an increase in voltage this, in turn, leading to a greater power consumption and shorter Ti-cell life.

The treatment power can be controlled according to the type and level treatment required. based on the fact that the current efficiency is a function of the current applied and is the proportion of the current supplied to the electrochemical ccli whether Al-cell or Ti-cell that goes towards the desired production of the oxidants and aluminium ions. Consistent efficiency has been obtained using a current ranging between 1-30 amps for the Al-cell and 50 amps and 1000 amps for Ti-cell and voltages of between 0.5-4.00 volts for Al-cell and 2.00 and 8.00 volts for Ti-cell.

The current density applied it depends on the nature and contamination of the effluent. For the aluminium cell range between l0-200amps per square metre, and lbr the titanium coated cell ranges between 100-600 amps per square metre.

In the course of treatment, the effluent experiences two circulations. one through the FRI polypropylene vessel, the other through an extraction/filtration system in which the effluent is filtered, passing through a ceramic cylindrical type filter having a porosity of from 5 to 10 microns, waste sludge accumulating on the outer surfitce of the filter forming cake waste sludge eventually to fail away to deposition at the bottom of the filter housing for subsequent discharge from the filter housing. The treated effluent can be disposed of or re-circulated back to a settling tank for further treatment, if required.

The process does not call for pH adjustment or the addition of any chemical. The reaction starts when the power supply of one or each cell is switched on. By applying the appropriate voltage, the current generated starts the electrolysis process at both the Al-cell and the Ti-cell. The Al-cell commences to produce aluminium ions by means of the sacrificial aluminium anodes, and hydroxyl ions as well as hydrogen at the cathode, in accordance with the following reactions, that is to say: Anode reaction: Al -) Al +3c Cathode reaction: 2H20 + 2e -) 20W + H2 Fluoride removal When the effluents pass through the cells via the polypropylene vessel, fluoride ions combine with aluminium ions to form insoluble aluminium tn-fluoride (AIF1), then separated from the effluent as insoluble salt which is carried by the cfflucnt to the separation system where it is separated from the effluent. The effluent may be circulated back to the polypropylene vessel for further treatment by the electrolytic cells or it may be disposcd of to a sewer. The separated sludge containing AIF3 and other contaminants is disposed of in a collection skip iii accordance with environmental regulations. Alternatively where the sludge with fluorides does IiOL contains high contamination of other material, it may bc a commodity capable of being sold for appropriate industrial use in. for examples, the aluminium industry or in the electronic industry for use in the production of microchips. especially where the sludge contains cryolite (3NaF X AIF3,/ NaAlF6), separated from effluent containing the fluoride as sodium fluoride, cryolite being a relatively rare mineral essential in the aluminium industries; it has theoretical fluoride content of [5459/kgj.

As the aluminium ion is trivalent ion and the fluoride ion is univalent, each Aluminium ion will combine with three Fluoride ions as it is shown in the Ibllowing equation: Al3+3F -+ AIF Alum inium fluoride (AIF3) a compound which is less toxic than free fluoride ions and which is insoluble and easily removed.

At the same time the titanium cell produces the oxygen, hydroxyl and perhydroxyl radicals, this triggering a chain reaction to produce the derivative products. ozone.

hydrogen peroxides and oxygen, as well as hydroxyl ion 0H. These species will act to oxidize any free aluminium ions ( Al) lefl in the effluent after removal of most or all the fluoride in the effluent. More specifically, Al ions passing through the Ti-cell are oxidized to aluminium oxide A1203 which then undergoes further oxidation to form, in situ, the gelatinous substance, aluminium hydroxide Al(OH)3 3+.

In this application there will be no any environmentally undesirable tree Al in the effluent because all the extra free aluminium ions will have been oxidiscd to aluminium oxide itself undergoing further oxidation to form gelatinous aluminium hydroxide that can be coagulated with other contamination, insoluble salt and suspended solids to settle out of the effluent.

At the same time fluoride ions have the tendency to be absorbed on the aluminium hydroxide, this will enhance and secure complete removal ol' fluoride ions in the effluent.

Experimental trials confirmed the ability of absorption of Fluoride ions on the aluminium Hydroxide matrix due to the dimension of the fluoride ion ( F) that is similar to the hydroxyl ion (01-F). This process in association with the formation of insoluble aluminium fluoride will remove the fluoride very efficiently and rapidly clear fluoride from the effluent.

Treatment of other contaminants: The free radicals and their products, the oxidants, will, at the same time. oxidise any bivalent metals available in the effluent medium. Ferrous iron is oxidised to ferric oxides then hydrolysed to ferric hydroxide and precipitated from the water. Similarly, manganous ions are oxidised to manganic, fbrming manganese dioxide precipitated.

as with ferric hydroxide from the water. Some organic compounds arc oxidised to carbon dioxide and water and other organic material is partially oxidised by the free radicals and their derivative products, the oxidants, are quite polar and will combine with polyvalent metal cations in the water; in the presence of the gelatinous aluminium hydroxide this will cause coagulation and flocculation, at the same time enhancing the ferric hydroxide, manganese dioxide and other contamination to settle out of the effluent.

The double actions of the clectro-coagulation or electro-precipitation and electro-flocculation initiated by the two cells the Al-cell and Ti-cell acting together constitutes an clcctrochemical technique with many advantages in that a variety of unwanted dissolved particles and suspended matter can be removed from the effluent by electrolysis. At the same time the coagulation or co-precipitation in the effluent by the adsorption power of the gelatinous aluminium hydroxides Al (011)3 and oxidation power-of free radicals and the oxidants produced by the Ti-cell can effectively eliminate any unwanted particles, some chemicals or harmful organic material.

As a result of the above mentioned factors food sources lbr the living micro-organisms are almost destroyed, reducing substantially Biological Oxygen Demand (130D) and Chemical Oxygen Demand (COD). eliminating suspended solids and clearing turbidity.

Scale Inhibition: The technology involved is very effective to inhibit the formation of scale, and even of benefit in descaling existing scaling in the system by reducing the f concentration of the scale forming ions in the effluent or any aqueous media especially aro,.md the walls of the pipes and tanks, the process leading to the formation of soft scale not adherent to the walls of the pipes and ranks. Such scale as may form on the cathodes of the cells will be deposited as insoluble calcium carbonate or magnesium carbonate, will descale out of the walls of the cathodes upon polarity reversal. By the action of the gelatinous aluminium hydroxide, they will coagulate and agglomerate to settle out of the effluent causing no harm, It can be separated completely from the system by the extraction process.

The unit cmploycd in the inhibition of scale formation and the removal of scale comprises a tirst electrolytic cell formed of a multiplicity of coaxial alternating anodes and cathodes, each such electrode having a core of titanium and a relatively thin cladding of mixed oxides and a second cell comprising as earlier described a multiplicity of plate-form alternating aluminium anodes and cathodes. The two cells together create an electromagnetic field within the bulk aqueous media flow, whether in the pipes or in the Lank. This initiates nucleation of scale minerals in bulk aqueous media leading to the precipitation as soft scale of calcium and iiagnesiurn carbonate in the bulk aqueous media or in aqueous media flow in the pipes. At the same time scale formed on the surfaces of the cathodes will fall from the cathodes upon polarity reversal as calcium and magnesium carbonate to settle out very effectively with the gelatinous aluminium hydroxide of the aqueous media used for industrial processing.

Scale forming ions combine with the partially oxidized organic material that.

polarised by the action of the electrolytic cells employed, combine with the calcium (Ca25 and magnesium(Mg 2$-) ions to flocculate and coagulate with the gelatinous aluminium hydroxide to settling down for easy filtration or other methods of extraction.

Through the electrolysis process hydroxyl ions are produced in the aqueous media these combining with the calcium ions to form sparingly soluble calcium hydroxide ( Ca(OH) ) which will coagulate with the gelatinous aluminium hydroxide to settle down and separate from the aqueous media.

The electrolytic cells act effectively to reduce the concentration of scale forming ions i.e calcium (Ca2+) and magnesium ions (Mg 2+) the aqueous media and around the walls of the pipes and the tanks for the reasons mentioned above i.e. soft scale arid f calcium hydroxide formation. This will prevent the super saturation of the scale Ibrming ions at the walls of the pipes and tank that in turn will prevent the nucleation of the scale minerals on the susceptible areas e.g. walls of the pipes and tanks.

As a result of some of the organic material oxidation in the aqueous media, carbon dioxide is produced. Raising the concentration of carbon dioxide in the aqueous media will increase the solubility of the calcium carbonate due to the formation of carbonate ions from the dissolved carbon dioxide. This will result in disturbing the equilibrium of the scale already deposited on the pipes and tanks and the calcium carbonate in the aqueous media leading to gradual dissolving of the existing scale deposits.

Independent control of the voltages and currents applied to the electrode pairs of the two cells and the choice of the dimensions and the numbers of electrode pairs employed in the cells may be calculated to produce the optimum selective removal of fluorides and other contaminants and the inhibiting hard scale on the pipes and tank's walls, such adjustments will depend on the nature of the effluent, contaminants and hardness.

The technology can operate at room temperature up to 80 Celsius and atmospheric pressure.

The two types of cell arc used simultaneously have synergistic action/effect on the fluoride removal and other contamination treatment from the effluent.

Electro-coagulation, electro-flocculation, and agglomeration cause suspended Linwanted solid dissolved matcrials, and several heavy metal ions in the effluent to be efficiently removed from the industrial wastewater. these being speedily and effectively deposited from the water.

The oxidation, electro-coagulation, electro-flocculat ion, and agglomeration actions of both cells can also be used to decolourise dye-containing effluent, by cleaving carbon=carbon double bond which disturbs the conjugation causing the colour to disappear.

The action of the gelatinous aluminium hydroxide and the oxidants fimied by Al-cell and the Ti-cell will cause the agglomeration of the suspended solid to settle to the bottom of the tank.

Whereas treatment of waste water for the removal of fluoride, and other contaminants as aforementioned, by the addition of chemicals, such, for examples. as salts of aluminium and iron, flocculants, coagulants, chlorination. ozonization, R.O, or mechanical treatments such as aeration or biomass treatment, the process of the present invention and the electrolytic cells employed in the performance of the process arc simple and predictable in their performance. The method results in a shortened reactive retention period, an amount of precipitate or sludge which is small by comparison with the conventional prior art methods previously alluded to and, in consequence, readily disposed of. The salt content of the waste water does not suffer an increase as is the case with conventional chemical treatments, and, a most important factor arising from the employment of the method and apparatus of the invention, is that the waste water does not become enriched with anions, on the contrary tests show that the anions and cations show a reduction in concentration.

Fig. 1 is schematic diagram of monopolar aluminium ccli (Al-cell). The electrodes are made of aluminium of 99.5% purity of 250 X 250 X 5mm, the anodes being separated from the cathodes by 8mm polypropylene spacers supported by polypropylene rods of 3mm dia., passing through [thej holes in the electrodes where the spacers are fixed. The rods and the spacers are arranged as cross-bracings adapted to prevent racking between the electrodes of the electrode structure. The connection between the cathodes is by titanium rods of 5mm diameter passing centrally through 10mm holes in the anodes this to avoid contact with the anodes. So too with the anodes. Two cables are connected to the cell, one to the anode No. I by means of' a titanium rod on the left hand side and the other to cathode No.6 by means of titanium rod on. the right hand side. Both cables are connected to a power supply or to a photovoltaic cell.

Fig. 2 is a schematic diagram of a monopolar titanium cell (Ti-cell). The electrodes are made of titanium plate coated with precious metal mixed oxides. The arrangement of the anodes and the cathodes as the same like Fig. I. The spacing of the electrodes is, however, 3mm.

However, for both cells, Al-cell and Ti-cell, different nunibers of anode-cathode combinations may be employed, both greater and less, and if desired..

Fig. 3 is schematic diagram of polypropylene box No. I containing the Al-cell which is connected to power supply, photovoltaic cell or to nothing, and the Ti-cell which is connected to power supply. The box has an opening near the Al-cell, of 100.00mm diameter connectcd to poLypropylene pipe 150mm long can be easily joined to pipe number 16 (circulation pipe Fig 4). The opposite side has opening near the Ti-cell side of 125mm diameter for the effluent outlet from the p.p box No.1.

P.p.box is positioned on a p.p.base No.20 so that Box No. I can easily joined to the circulation pipe No.16.

Fig.4 is a schematic diagram for Fluoride and contamination treatment plant.

Effluent containing fluoride and for other contamination passing through valve Nol I and pipe 3 to the settling tank No.2.The effluent is circulated by pump No.5 through pipe No.16 flowing through p.p.box I which contain the Al-cell and Ti-cell. Al-cell is connected to a power supply, photovoltaic cell or without any connection, depending on the nature of the contamination and pH of the effluent. Ti-cell is connected to separatepower supply.The p.p vessel No.i is connected to stainless steel or plastic cord run to winch No.17 for loading down and lifting up the p.p essel No I for services, maintenance or replacing any of the cells. After certain period of time sample should be taken for analysis to measure the fluoride and/or any other contamination i.e. COD, DOD, S.S., Turbidity, bugs and bacteria, heavy metals, TDS.

according to the treatment required. Upon analysis test, if the contaminant level reached the required environmental standard, then valve No. 7 opened so that the effluent and the sludge will pumped out of tank No.2 via pipe No. (4 to the extractor tank so insoluble contaminant salt or complex is removed from the effluent to separate the sludge from the effluent. Another analysis test can be applied by on line test instrument to ensure that the effluent's contaminants is acceptable to the environmental agency, then the effluent will be dispose via pipe No. 13. alternatively the effluent will be circulated back via pipe 15 to the settling tank No.2 for further treatment, in some cases, a disposal line connecting to a sewer, recycle line or other line.

Fig. 5 is schematic diagram for water hardness treatment plant A. The processing water flowing to tank 2 via valve 11 and pipe line 3. The processing water is circulating via pump 8, valve 12, and pipe line 4 through the hardness treatment unit I f which consist of cylindrical Ti-cell(a) and Al-cell (b) placed in polypropylene box Unit I is connected to a winch by means of stainless steel or plasitic cord. l3oth cells connected to separate power supplies. The treated water will [low through pipe line 5 by pump 9 to the industrial process.

Fig.6 is schematic diagram for the cylindrical Ti-cell of the hardness treatment unit I of Fig. 5,and Fig7 Fig.7 is the schematic diagram of the cylindrical hardness treatment unit. It consists of polypropylene pipe with two connecting tianges I and 2 on both ends of the pipe.

The unit contains Al-cell (b) made of I X anode and I X cathode near flange I and cylindrical Ti-cell (a) made of 2 x cylindrical anodes (1+3) and 2 x cylindrical cathodes (3+4) near flange 2. The number of' the electrodes for both cells can be varied according to the treatment required. The unit is connected to inlet pipe 9 and valve 8 to pour cleaning solution inside the unit, and outlet pipelO and valve 7 to discharge the cleaning solution. Both inlet and outlet located near Ilange 2.

Fig.8 is a schematic diagram for hardness treatment plant B. The cylindrical hardness treatment uniti is connected as shown in Fig.8 to tank No.2. Processing water circulating through pipe 7 and pump 13 passing through hardness treatment unit I back to tank 2 via valve 12 and line 4. Al-cell (A) and cylindrical Ti-cell (B) are connected to different power supplies to feed them with different voltages. Both cells undergo electrolysis to generate aluminium ions (Alp), by Al-cell (A) and free radicals and oxidants by Ti-cell (B). The water is passing through unit I through Al-cell (A) carrying with it Al3 which will be oxidised to aluminium oxides and undergo further oxidation to aluminium hydroxide by the action of the free radicals and the oxidants generated by the electrolysis of Ti-cell (B). The water carrying aluminium hydroide and oxidants is circulated through valve 12 and pipe line 4 back to tank No.2.

Claims (6)

1. An electrolytic process for the treatment of effluent, being a process lbr bringing any of a range of contaminant components as may be present in the effluent to accepted environmental standards or better, the process comprising: causing first and second independently controllable electrical currents, being currents the magnitudes of which lie within ranges respectively determined by the contaminant component chosen, for the time being, for treatment under the process, to flow in tirsi and second electrolytic cells, respectively, said first cell having an aluminium electrode structure such as, with the passage of electric Current therethrough, to produce. in the effluent.

aluminium ions, and said second cell having an electrode structure comprising a core composed of an electrically conductive electrochemically stable material and, as a cladding on said core. a composition of mixed oxides, said oxide composition being such as, with the passage of current as aforesaid through said core, to create, in the effluent, in the presence of said aluminium ions. free oxygen. perhvdroxyl. and hydroxyl radicals, and their derivative oxidants.

2. A process as claimed in claim I in which said core is of Titanium.

3. A process as claimed in claim I or 2 in which said first and second electric currents are derived from first and second power supplies, respectively.

4. A process as claimed in claim 3 in which said first power supply comprises a photo-voltaic cell.

5. A process as claimed in any preceding claim in which said first current is developed by said first cell by chemical reaction of said first cell with said effluent.

6. Apparatuses for use in performing the process as claimed in any of claims I to 5, in the ridding water of contaminants as hereinbefore referred to. being apparatus substantially as hereinbefore described with reference to Figs. I to S or any of them, as appropriate.