WO2008149114A1

WO2008149114A1 - Effluent treatment process

Info

Publication number: WO2008149114A1
Application number: PCT/GB2008/001960
Authority: WO
Inventors: Andy Dargue; Philip Grainger
Original assignee: INTEGRATED EFFLUENT SOLUTIONS Ltd
Current assignee: INTEGRATED EFFLUENT SOLUTIONS Ltd
Priority date: 2007-06-08
Filing date: 2008-06-06
Publication date: 2008-12-11
Anticipated expiration: 2009-12-08
Also published as: GB0711055D0; GB0810364D0; GB2449996A; GB2449996B

Abstract

The present invention relates to a method for the removal of contaminants from effluent and in particular, to ah improved method for the removal of anions, for example sulphates, from trade effluents. In particular, there is provided an effluent treatment method comprising the steps: adjusting the pH of the effluent; adding a source of aluminium; adjusting the pH of the effluent to a second pH value and adding a source of calcium ions to the effluent and in the preferred embodiment accelerating means providing oscillatory pressure speed up the rate of reaction.

Description

Effluent Treatment Process

The present invention relates to a method for the removal of contaminants from effluent and in particular, to an improved method for the removal of anions, for example sulphates, from trade effluents.

According to the UK Environment Agency, trade effluent is any effluent (liquid waste) that is discharged from any premises being used to carry on trade or industry. Any liquid with or without suspended particles, which is wholly or partially produced in the course of any trade or industrial activity, carried out at trading premises will be classed as trade effluent. Examples of trade effluent include waste chemicals, liquid processing wastes, detergents, biodegradable liquids, wash water and contaminated mine or quarry water.

The discharge of trade effluents into sewers is regulated, and consent is required from the Statutory- Sewage Undertaker before a commercial concern can discharge effluents into public sewers. Contaminants in trade effluents can have deleterious effects on the sewerage systems, which include damage to the sewers themselves, health hazards and inhibition of the microorganisms which carry out sewage treatment processes. For example highly acidic solutions can result in damage to the sewerage system leading to deterioration of the pipe work and fittings, while dissolved metals such as tin, mercury and cadmium are all highly toxic in relatively small concentrations. Therefore, the costs associated with discharging effluent into public sewei s are based not only upon the volume of effluent discharged but also on the concentration of contaminants present therein.

Sulphates are of particular concern as contaminants in effluents because they can cause erosion of concrete, thus damaging the insides of sewers and pipework. At present, any company that has sulphate in their effluent must reduce the concentration prior to discharge to meet the limits imposed by the local water authority or the environment regulator (depending on where they are discharging) .

The standard method of removing sulphates from effluent comprises the addition of lime to the effluent to form calcium sulphate (gypsum) .as per the reaction:

Ca²⁺ + 20H^" + 2H⁺ + SO₄ ^{2" ~}Z_ CaSO₄ . 2H₂O

The levels to which sulphate concentrations are reduced using this method are controlled by the solubility of the gypsum. Gypsum has a theoretical solubility of l,500mg/l. However, in practice the solubility is found to be as high 2, 000-3, OOOmg/1 due to interferences, for example the presence of species such as sodium or potassium in the effluent. Thus this solubility figure is up to 3 times the limit imposed by the regulatory authorities. This often necessitates dilution of the effluent which is beneficial neither environmentally nor financially. Considering the relatively high sulphate levels remaining in the treated effluent after the reaction with lime, this method is increasingly considered to be more suitable as a pre-treatment step for effluents with high dissolved sulphate concentrations. Furthermore, the gypsum obtained during this treatment method is produced as a sludge by-product which must be removed and discarded as solid wa^te. There are also problems associated with the use of lime powders, which bring about significant operational difficulties, for example, lime powder is highly corrosive, necessitating the use of large moisture-free storage facilities.

Due to the obvious disadvantages associated with the abovementioned lime treatment method, it has become more common to precipitate sulphates in the form of hydrated calcium trisulphqaluminate (ettringite) , a

Ϊ crystalline compound which! has a lower solubility than gypsum. The formation of 'the ettringite crystals takes place by the addition of calcium aluminate to the effluent according to the reaction:

3CaO - Al₂O₃ + 3CaSO₄ + 26H₂O \ ^ 3CaO . Al₂O₃. 3CaSO₄ . 32H₂O ^j

However, the ettringite method also has various associated disadvantages. ! Firstly, the technique is costly to perform, as it requires the use of significant volumes of expensive reagents. Furthermore, this method often requires an intermediary settlement step to remove calcium sulphate before the addition of calcium aluminate to avoid excessive consumption of reagents. Therefore, this reaction is often performed in conjunction with a pre-treatment step, such as the abovementioned lime treatment method, i.e. lime is added to produce gypsum, which is then removed prior to the addition of the calcium aluminate. The kinetics of the ettringite reaction are also an issue, as the ettringite formation requires 3-5 hours to take place in an industrial application. If the lime addition pre-treatment step is incorporated this increases the overall treatment time yet further by an additional 45-60 minutes. ' A further disadvantage is that both the powdered calcium aluminate and powdered lime typically employed for this method are difficult to handle and dose.

Other treatment techniques which have been applied to effluent treatment for the removal of anions include evaporation or membrane filtration. However, in each case the techniques produce a secondary waste product that requires further treatment before it can be ultimately disposed of.

The present invention identifies certain drawbacks of conventional effluent treatment methods and proposes an improved method which obviates or mitigates one or more of the limitations of the conventional methods and generally provides a method of treatment of trade effluents resulting in low levels of the anions of interest and which is simple and cost effective to perform. Further advantages of the invention will become apparent from reading the following description.

According to a first aspect of the present invention there is provided an effluent treatment method comprising the steps:

Initially adjusting the pH of the effluent to a first pH value of ≤ 2;

After adjusting the pH to a first pH value of ≤ 2, adding a source of aluminium;

^fter adding a source of aluminium to the effluent:

Adjusting the pH of the effluent to a second pH value of >10; and

Adding a source of calcium ions to the effluent.

The pH may be adjusted to the second pH value of ≥IO by the addition of the source of calcium ions to the effluent, or the pH may be adjusted independently. When the pH is adjusted by an independent step, this may be performed either before or after the addition of the source of calcium ions.

Preferably, the pH is adjusted to the first pH value by the addition of an acid tc the effluent. Preferably, the acid is an inorganic acid.

Preferably, the acid is hydrochloric acid.

Choosing a suitable acid will depend on any additional species present in the acid as it is obviously important to avoid introducing any additional problematic species into tihe effluent.

Alternatively, the inorganic acid can be any suitable inorganic acid including, for example sulphuric acid, nitric acid or phosphoric acid.

Optionally, the acid is an organic acid.

The organic acid can be any suitable organic acid including, for example, carboxylic acid, sulfonic acid, ethanoic acid, benzoic acid, formic acid, or acetic acid.

Preferably the source of aluminium is a liquid.

Throughout the specification, the term "liquid" is i intended to broadly encompass suspensions and mixtures of insoluble substances which will flow or can be pumped as liquids such as cements and slurries.

Preferably the source of aluminium is aluminium hydroxide chloride (Pluspac 1000™) . Optionally, the source of aluminium is selected from the group consisting of: sodium aluminate, aluminium chlorohydrate, poly aluminium chloride or chargepac 121™, aluminium sulphate, polyaluminium silicate sulphate (PASS™) .

Preferably, the source of calcium ions is a liquid.

Preferably, the source of calcium ions is kalic™ [Kalic, or milk of lime is generally accepted to be a suspension of approximately 18% Calcium Hydroxide

(Ca(OH)₂ in water with small quantities of calcium carbonate, magnesia and trace elements. CAS No. 1305-

62-0] .

Alternatively the source of calcium ions is lime slurry.

Optionally, the source of calcium ions can be any suitable source including,' for example calcium carbonate or calcium chloride. The source of calcium may be added to the effluent along with a base such as sodium hydroxide or sodium carbonate to raise the pH of the effluent.

Preferably, the effluent is raw effluent.

The term "raw effluent" means that the effluent has not been subjected to any pre-treatment steps prior to the effluent treatment process of the invention. Preferably the first pH value is ≤ 1.3

Preferably the second pH value is ≥ 11.5.

Preferably, the method further comprises the step: Applying accelerating means to speed up the rate of reaction.

Preferably, the accelerating means is the provision of oscillatory pressure to the reaction.

The provision of oscillatory pressure to the reaction causes acoustic cavitation within the reaction mixture. The phenomenon of acoustic cavitation is for example described in the publication by T. G. Leighton, "The acoustic bubble", Academic Press, London, 1994, on pages 531-551. It is assumed that in the phenomenon of acoustic cavitation, acoustic waves break the cohesion of a liquid medium and create microcavities . Then, from an initial size smaller than one micrometer, gas bubbles trapped in the liquid medium grow to a few tens of micrometer and become unstable. These bubbles then start to implode or collapse, and the conditions within these bubbles can be dramatic, with temperatures of 5000 K and pressures of up to 2000 atmospheres, which in turn produces very high shear energy waves and microstreaming (high velocity liquid flows in the cavitation zone) .

Preferably, the oscillatory pressure is generated by ultrasonic energy. Optionally, the oscillatory pressure can be provided by any suitable means.

It can for example be envisaged that acoustic cavitation can be generated by pumps suitable to transmit oscillatory pressure into the reaction mixture .

Advantageously, the application of sonochemistry to the reaction speeds up the reaction and allows the solids formed in the reaction to be precipitated out more quickly.

Optionally, the accelerating means is ultraviolet radiation or microwave technology.

Preferably, the method further comprises the step: Adding a metal precipitant to the effluent.

Advantageously, adding a metal precipitant to the effluent precipitates any heavy metals present in the effluent. This is particularly important as the reaction is taking place at a high pH (i.e. ≥ pHIO) and most heavy metals will be in solution at this pH.

Preferably, the metal precipitant is Epofloc Ll-R™.

Optionally, the metal precipitant is selected from the group consisting of: TMT™, Metalsorb™, Metalsorb FZ™, Metalsorb HCO™, Scavenger F55™ and Epofloc 1™. Preferably, the method further comprises the step: Adding a flocculant to the effluent.

Advantageously, flocculation allows any remaining soluble contaminants present in the effluent to aggregate and thus come oiit of solution in the form of floe or "flakes". The flakes can then be easily separated from the liquid ^'effluent , for example by gravitational settling.

Preferably, the flocculant is a modified polyacrylamide .

Alternatively, the flocculant can be any suitable flocculant, for example alum, aluminium chlorohydrate, aluminium sulphate, calcium oxide, iron (III) chloride, iron (II) sulphate, sodium aluminate or sodium silicate .

Preferably, the method further comprises the step: Separating the solids from the liquid.

After flocculation, the aggregated solids and the metal precipitant-bound solids are removed from the effluent.

Conveniently, for example/ this can be performed by i passing the effluent through a clarifier wherein the solids are removed by gravitational separation, or by other suitable methods such as filtration.

Optionally, the method further comprises the step: After treatment of the effluent according to the previous steps, adjusting the pH of the effluent.

As the pH of the effluent :±s quite high during the ettringite formation, i.e.¹ ≥ 10 and preferably in the range 11.5-11.8, the pH of the effluent may be adjusted before it is released.

Preferably, the pH is adjusted by the addition of an acid.

As before, any suitable inorganic or organic acid may be employed to adjust the pH of the effluent.

The present invention provides an efficient and cost- effective method of treating effluent to remove or reduce contaminants. Whilst reference is made to the reduction of sulphates in effluent to remove or reduce contaminants. The preferred embodiment includes using ultrasound energy/cavitation for increasing the efficiency of chemical reactions. In the preferred practice of the invention, the efficiency of chemical reactions can be significantly increased as compared to conventionally carried out chemical reactions and can be used to enhance the removal of unwanted components in the effluent water compared to existing technology.

The term "ultrasonic probe", as used herein, means any sort of system or apparatus suitable for delivering ultrasonic energy into a reaction mixture. The term "ultrasound emitting surface area" means any surface area where ultrasonic energy is emitted into the reaction mixture, i.e. the sonotrode surface in Figure 3 or the flow cell tube surface in Figure 4 and 5.

The term "amplitude" mean? the magnitude of the maximum disturbance in the medium during one wave cycle of an ultrasound wave.

The term "specific energy" refers to the energy consumed by the ultrasonic system.

' Average specific energy" in this context means the total specific energy applied to the reaction mixture divided by the total volume of the reaction mixture (in litres) .

The "ultrasonic energy density per volume reaction mixture" is calculated as an average value over the total reaction mixture volume (in cm³) .

/-. preferred embodiment of the invention will now be described with reference to the accompany drawing in which:

Figure 1 illustrates a flow chart of the effluent treatment method;

Figure 2 is a schematic illustration of a typical ultrasound system wherein the sonotrode' s (214) ultrasound emitting surface is in direct contact with the reaction mixture. The reaction mixture passes through A into a flow cell (215) and leaves the flow cell through B. A generator (211) is connected to a transducer (212) which is 'further connected via booster horn (213) to the sonotrode (214);

Figure 3 is a schematic illustration of an ultrasound system wherein one or more transducer/booster (322/323/324) are welded to the outside of a flow cell tube (325) . This makes the flow cell tube (325) ultrasonically active and transfers ultrasound energy into the reaction mixture. This is therefore a system where the ultrasound energy is transmitted indirectly into the reaction mixture.' A generator is connected to the transducer (321) as in Figure 2;

Figure 4 schematically illustrates an ultrasound system wherein the ultrasound energy is indirectly transferred into the reaction mixture* from the sonotrode (434) via a suitable medium (435) (water, oil, organic fluid) to the flow tube (436); and

Appendix 1 comprises details of an analysis of the solids obtained as precipitate via the method of the invention for the removal Df sulphates from trade effluent .

Turning to Figure 1, step ,1 involves the addition of hydrochloric acid to the effluent to reduce the pH to a value equal to or less thεϊn 2. The acid ionises the calcium and the sulphate present in the effluent, so that they can react with the aluminium in the next i step. Step 2 involves the movement of the effluent into an agitated tank, at ^;which point aluminium hydroxide chloride is added to the effluent. The aluminium hydroxide chloride is added in liquid form, which is convenient for handling and dosage. The aluminium ions present in Jthis compound react with the

_* sulphate ions present in solution, yielding aluminium sulphate. In step 3, lime milk (kalic) is added in excess to the reaction. The lime milk has a dual purpose and provides both 'calcium ions for the reaction while at the same time increasing the pH to within the range of approximately 11 J 5 - 11.8 at which the solid will- precipitate out of solution. The calcium ions present in the lime milk react with the aluminium sulphate to form a calcium aluminium sulphate oxide. The solids have been identified as a form of zeolite, and an analysis of the solids can be seen in Appendix 1. The precipitation of the solid starts from the addition of the lime milk to the effluent and is optimised when the effluent reaches the correct pH band. An advantage of the effluent treatment technique is the use of the source qf calcium ions in excess, for example the lime milk. Previous techniques have required the use of an excess of the aluminium compound. As aluminium is far more costly than calcium, it is obviously cost effective to use the latter in excess. In this case, the calcium ions in the lime milk are reacting with the aluminium sulphate to form the solid precipitate, in contrast with previous methods in which the aluminium ions reacted with calcium sulphate. In addition, as calcium aluminate binds preferably with the bound sulphate (i.e. in calcium sulphate) rather than with the free sulphate ions, previous techniques often necessitated a separate step in which the calcium sulphate was removed from the effluent in order to avoid excessive consumption of the expensive calcium aluminate reagent.

In alternative embodiments a source of calcium ions can be provided separately to the means for increasing the pH to the preferred range.

Although the above method alone is a significant improvement, further step∑: can be incorporated for maximum benefit. In the inventors preferred embodiment, the reaction is then accelerated in step 4, which involves the application of sonochemistry to the reaction. The application of sonochemistry to the reaction allows the solid to be precipitated out in a matter of minutes, in comparison with previous reaction times of typically 3-5 hours for ettringite formation. Results using the treatment method of the invention have resulted in sulphate levels of 60 parts per million (ppm) for raw effluents, which have initial

(i.e. before treatment) concentrations of 4000-7000ppm. Recent experimental result s obtained by the inventors have shown sulphate reduction of up to 98%, from levels of 7910mg/L down to 100mg/L. These extremely low levels are well below current environmental limits (typically 800 - lOOOppm) and surpass results of previous techniques. The .inventors surmise that formation of microbubbles (cavities) in the liquid reaction medium via the action of ultrasound waves may also allow more sites for -'binding, thus contributing to the high levels of binding and low residual sulphate levels in the effluent.

In step 5, a metal precipitant is added to the effluent solution. The metal precipitant binds with any heavy metals present in the effluent, which will predominantly be in solution at the high working pH range. The metal precipitant will also bind with any remaining calcium and aluroinium ions, leaving very low residual levels remaining in the effluent. Recent experimental results obtained by the inventors have shown heavy metals reduced by 99.7%, from a starting amount of 16.7βppm down to 0.05ppm. Furthermore, the metal precipitant aids the subsequent flocculation step.

After the metal precipitation step, step 6 involves the addition of a flocculant to the effluent solution. The flocculant causes any remaining soluble contaminants to aggregate and precipitate lout of solution as flakes. In step 7, the effluent is moved to a settling chamber where the solids are separated out of the effluent by settling (i.e. gravity).

In the final step of the treatment method, step 8, the pH of the effluent is corrected, if required. This typically involves the addition of an acid to the effluent to neutralise the high pH of the effluent before the effluent is released, for example into a sewer. Again, the acid will be chosen to minimise the addition of deleterious species into the effluent. Solids are also dewatered.

The above description has '^"been written in the context of the removal of sulphates. However, the method can also be applied to suitable anions such as chlorides and phosphates, with optimisation of the chemicals used. For example the hydrochloric acid can be replaced with sulphuric acid and the Pluspac 1000™ with aluminium sulphate for the removal of chlorides. Recent experimental results obtained by the inventors have shown phosphate reduction of up to 99.9%, from levels of 1859mg/L down to 1.3mg/L

As well as providing a generally improved method, the inventors of the present; invention have surprisingly found that by subjecting the reaction mixture to acoustic cavitation, an increase of the efficiency of the reaction is obtained'. Such an increase of the reaction efficiency can save starting materials and reaction time, and can therefore lead to substantial cost savings in the waste jeffluent treatment.

Acoustic Cavitation

Systems for generating ul.trasonic energy are available from commercial source.s, e.g., Hielscher GmbH, Stuttgart, Germany. Such- systems generally comprise a transducer which is the source of the vibrational energy. A transducer within this meaning transforms electrical energy into- vibrational (oscillatory) energy. Transducers are; available in discrete power units, e.g. 1 kW, 2 kW, 4,kW, 8 kW, 16 kW, which can be used as a single unit, or as a combination of units. It is possible to use a; whole series of transducers within one ultrasonic system, each of them providing ultrasonic energy at its specific power. There are two main types of transducers in the field of ultrasonic energy, i.e. piezoelectric and magnetostrictive . In a preferred embodiment of the current invention, at least one transducer has a power in the range between 0.01 and 40 kW and more preferably in the range between 8 and 16 kW.

In a preferred embodiment of the method of the current invention, the ultrasonic energy emitted per cm² from at least one of the ultrasound emitting surface areas is in the range from 0.001 W/ cm² to 1000 W/ cm², preferably from 1 to 500 W/ cm², more preferably from 1 to 200 W/ cm².

In another embodiment of the method of the current invention, the ultrasonic energy has a wave with an amplitude in the range of 0.1 micrometer to 1000 micrometer, preferably 0.1 to 500 micrometer, more preferably 0.1 to 50 micrometer.

Furthermore, the ultrasonic energy is preferably applied to the reaction mixture at an average specific energy between IxIO^"5 kWh and IxIO^"1 kWh ultrasonic energy per litre reaction mixture, more preferably between IxIO^"4 kWh and IxICT² kWh ultrasonic energy per litre reaction mixture.

In a further embodiment of the current invention, the emitted ultrasonic energy has a frequency of more than 15 kHz, preferably from 15 to 500 kHz, more preferably from 16 to 60 kHz. Most preferably, the emitted ultrasonic energy has a frequency from 16 to 22 kHz.

In a further embodiment of the invention, the ultrasonic energy density per volume reaction mixture is in the range from 0.001 W/cm³ to 1000 W/cm³, more preferably in the range fcom 1 W/cm³ to 500 W/cm³, even more preferably in the rarge from 1 W/cm³ to 200 W/cm³.

Turning now to the remaining Figures, Figures 2-4 show various feasible ways in which an ultrasonic system suitable for the purpose of this invention can be setup.

Ultrasonic systems generally utilize a probe, a so- called sonotrode, for transmitting ultrasonic energy into the reaction mixture.. These include for example, axial probes and radial probes, each of which is suitable for the method described herein. However, generally, there are three main ways to transmit ultrasonic energy into a reaction mixture: (1) A sonotrode can be .directly in touch with the reaction mixture and _^transfer ultrasonic energy directly into the reaction mixture via the sonotrode' s surface which is in direct contact with the medium being processed (Figure 2), or

(2) Ultrasonic energy can be transmitted indirectly via one or more transducers attached to the outside of a flow cell or tube (made of steel or other metal) making the tube ultrasonically active (Figure 3) . The transducers can be welded_s to the tube, or screwed onto the tube via a thread connection, or there could be a strap around the tube attaching the transducer to the tube, or '

(3) Ultrasonic energy can be transmitted by the transfer of ultrasonic energy waves indirectly via a suitable medium (water, oil, organic fluid) through the walls of the flow cell/tube and into the medium being processed (Figure 4).

The three basic setups are illustrated in Figures 2 to 4. The typical ultrasound system comprises a generator, a transducer, a booster, and a sonotrode as illustrated in Figure 2. Figure 2 represents a flow cell wherein a sonotrode is placed. The reaction mixture passes the sonotrode and absorbs ultrasonic energy. Additionally, an <anti-vibrational flange is often used to stop vibrations going into the surrounding equipment, i.e. in Figure 2 the flow cell, and makes sure that all or most of the energy goes into the reaction mixture. A booster is provided to reduce or amplify the ultrasonic energy as needed. It is obvious to a person skilled in the art that the design of the flow cell has therefore an impact on the reaction itself. Appendix 1 details the results of chemical analyses on the resultant precipitate ■, from the reaction according to the invention, for the removal of sulphate.

De-tails of samples

Five filter cake samples: sample 1 to be analysed by X- Ray Diffraction (XRD) , samples 2 to 5 to be analysed by Energy Dispersive X-Ray Fluorescence (EDXRF) .

Details of analysis

The samples still retained a substantial water content and it was necessary to dry them at 40⁰C for 48 hours.

Once dried, the samples destined for EDXRF analysis were powdered and pelletised after addition -of a wax binder. Sample 1, for XRD, was analysed as received.

Results :

The results of the EDXRF analysis are given in Appendix 1, Part 1 and are all broadly similar, with substantial amounts of calcium, sulphur, aluminium and silicon. The total elemental composition, even with the addition of oxygens as part of the isulphate and silicate falls well below 100%, and it is likely that there may still be significant amounts of ;water, as water of hydration, and also possibly other compounds that will not show up with EDXRF analysis, for example carbonates.

The XRD analysis results are shown in Appendix 1, Part 2. There are strong peaks present that are largely accounted for by the presence of a type of zeolite (predominant) , calcium aluminium sulphate, iron and calcium carbonate.

It has to be understood that according to the current invention, chemical reactions, which are carried out on a commercial scale according to established processes, can be made more efficient and lead to substantial chemical waste reductions and therefore cost reductions. The current invention therefore provides a significant progress in the field of effluent treatment

An advantage of the technique is that the method demonstrates the same processing capability and superior treatment results as those achieved using powder reagents, but without the disadvantages associated with using such powders. Furthermore, the method does not require a separate pre-treatment step which is advantageous as it reduces the overall time of the reaction and provides a quicker and more convenient means to remove sulphates from trade effluents. The acceleration of the method by the application of an accelerating means such as sonochemistry, dramatically decreases the reaction time, from hours down to minutes .

It has to be understood that according to the current invention, chemical reactions, which are carried out on a commercial scale according to established processes, can be made more efficient and lead to substantial chemical waste reductions and therefore cost reductions. The current invention therefore provides a significant progress in the field of commercial waste effluent treatment using a combination of chemicals and ultrasound.

It will be evident that various modifications and improvements could be made to the above-described method within the scope of the invention. For example, the above description is written in the context of a method for the removal of sulphates from effluent. However, the method can also be applied to the removal of other suitable anions from effluents.

Further modifications may be made without departing from the scope of the invention herein intended.

Claims

1. An effluent treatment method comprising the steps:

5 adjusting the pH of the effluent to a first pH value of ≤ 2;

after adjusting the pH to a first pH value of ≤ 2, adding a source of aluminium; 10 after adding a source of aluminium to the effluent :

adjusting the pH of the effluent to a second pH ^"15 value of ≥IO; and

adding a source of calcium ions to the effluent.

20 2. A method as in Claim 1 wherein the pH is adjusted to the second pH value of ≥IO by the addition of the source of calcium ions to the effluent.

3. A method as in Claim 1 wherein the pH may be

25 adjusted independently from the addition of the source of calcium ions to the effluent.

4. A method as in Claim 3 wherein the pH is adjusted before the addition of the source of calcium ions

30

5. A method as in Claim 3 wherein the pH is adjusted after the addition of the source of calcium ions

6. A method as in any of the previous Claims wherein the pH is adjusted to the first pH value of ≤ 2 by the addition of an acid to the effluent.

7. A method as in Claim 6 wherein the acid is an inorganic acid.

8. A method as in Claims 3 or 4 wherein the acid is hydrochloric acid.

9. A method as in Claims 3 or 4 wherein the acid is sulphuric acid, nitric acid or phosphoric acid.

10. A method as in Claim 6 wherein the acid is an organic acid.

11. A method as in Claim 6 wherein the organic acid is carboxylic acid, sulfonic acid, ethanoic acid, benzoic acid, formic acid, or acetic acid.

12. A method as in any of the previous Claims wherein the source of aluminium is a liguid.

13. A method as in any of the previous Claims wherein the source of aluminium is aluminium hydroxide chloride

14. A method as in any of Claims 1 to 12 wherein the source of aluminium is selected from the group consisting of: sodium aluminate, aluminium chlorohydrate, poly aluminium chloride or chargepac 121™, aluminium sulphate, polyaluminium silicate sulphate.

15. A method as in any of the previous Claims wherein the source of calcium ions is a liquid.

16. A method as in any of the previous Claims wherein the source of calcium ions is kalic™

17. A method as in any of Claims 1 to 15 wherein the source of calcium ions is lime slurry.

18. A method as in any of Claims 1 to 15 wherein the source of calcium ions is calcium carbonate or calcium chloride.

19. A method as in any of the previous Claims wherein the source of calcium is added to the effluent along with a base.

20. A method as in any of the previous Claims wherein the first pH value is ≤ 1.3

21. A method as in any of the previous Claims wherein the second pH value is ≥ 11.5.

22. A method as in any of the previous Claims further comprising the step: applying accelerating means to speed up the rate of reaction.

23. A method as in Claim 22 wherein the accelerating means is the provision of oscillatory pressure to the reaction.

24. A method as in Claim 23 wherein the oscillatory pressure is generated by ultrasonic energy.

25. A method as in Claim 22 wherein the accelerating means is ultraviolet radiation or microwave technology.

26. A method as in any of the previous Claims further comprising the step: adding a metal precipitant to the effluent.

27. A method as in Claim 26 wherein the metal precipitant is Epofloc Ll-R™.

28. A method as in Claim 26 wherein the metal precipitant is selected from the group consisting of: TMT™, Metalsorb™, Metalsorb FZ™, Metalsorb HCO™, Scavenger F55™ and Epofloc 1™.

29. A method as in any of the previous Claims further comprising the step: adding a flocculant to the effluent.

30. A method as in Claim 29 wherein the flocculant is a modified polyacrylamide.

31. A method as in Claim 29 wherein the flocculant is alum, aluminium chlorohydrate, aluminium sulphate, calcium oxide, iron (III) chloride, iron (II) sulphate, sodium aluminate or sodium silicate.

32. A method as in any of the previous Claims further comprising the step: separating the solids from the liquid.

33. A method as in any of the previous Claims further comprising the step: after treatment of the effluent according to the previous steps-, adjusting the pH of the effluent.

34. A method as in Claim 33 wherein the pH is adjusted by the addition of an acid.