ELECTROFLOCCULATION

Field of the Invention

The present invention relates to an electroflocculation apparatus. The present invention also relates to waste-water treatment systems which include an electroflocculation stage.

Background of the Invention

This International patent application claims priority to Australian provisional patent application 2006906307, the specification of which is herein incorporated by reference.

Waste-water presents a significant disposal problem in domestic, industrial and agricultural settings. Much of the water considered to be waste-water contains less than 0.1 % of pollutant. As such, substantial quantities of water are often wasted in order to dispose of relatively small amounts of a given pollutant. Having said that, in the case of some pollutants, even low concentrations present in water make the water unsuitable for release into the environment or unsuitable for re-use.

Water wastage is significantly reduced when techniques are employed that concentrate or remove the small amount of pollutant and leave the majority of the water in a condition suitable for re-use or release into the environment (eg. oceans, lakes, rivers etc.). Many different technologies have been developed for this purpose including a variety of filters, chemical dosing, and reverse osmosis. However, these technologies tend to be pollutant specific or more expensive than simply dumping or storing polluted water.

One of the more common methods of treating polluted water has been to dose it with chemical coagulating agents, such as aluminium sulphate and ferric chloride. The metal ions coagulate pollutants, causing them to either sediment out or become sufficiently large that they can be filtered out, or floated out using dissolved air flotation. One of the difficulties associated with this process is that the ionic content of the water is increased by the addition of these salts. Thus although the metal ions are removed during the process, the salt content of the water is greatly increased, often preventing the ability of the water to be re-used or released into the environment.

Electroflocculation provides an alternative technique for the removal of these pollutants from waste-water. In electroflocculation, metal ions (which act as a coagulating or flocculating agent) are released into solution from an anode by the action of a current. In this manner, the same effect is achieved as would be done using chemical coagulating agents, but without the addition of any anions, thus leaving the residual salinity of the water substantially unaltered.

Electroflocculation also leads to the generation of hydrogen gas at the cathode as a result of the chemical reduction of water molecules. With this in mind, the coagulating agent (metal ions) combines with the pollutants and the coagulated pollutants may then be captured by the rising gas bubbles, resulting in most of the pollutant floating to the surface. Additionally, pollutant which does not rise to the surface with the gas bubbles often sediments out, thus facilitating its removal.

Electroflocculation has also been shown to remove many common waste-water impurities including for example large dissolved molecules, bacteria, algae and other materials. As specific examples, electroflocculation has been shown to be effective for the removal of the following from waste-water: textile and printing dyes, humus; dissolved heavy metal cations; emulsified fats, oils and greases; and phosphates.

In electroflocculation systems, it is eventually necessary to separate the treated water from the floe generated during the process. In existing electroflocculation processes, separation of the floe from the treated water is typically achieved by sedimentation or filtration. However, sedimentation systems are generally amenable only to situations where the treated liquid can be left to settle with little or no disturbance. Furthermore, filtration-based systems generally require a further system to prevent blockage of the filter by the floe, which (in addition to the extra filters themselves) add to the complexity, cost and size of the apparatus.

As such, a need exists for an electroflocculation system with a relatively simple means to separate floe generated during electroflocculation from the treated liquid. Furthermore, this need is particularly applicable to mobile electroflocculation systems (including systems for use in vehicles such as buses or boats) which are both subject to movement and disturbance and generally must be relatively small.

Before turning to a summary of the invention, it must be appreciated that the above description of the prior art has been provided merely as background to explain the context of the invention. Accordingly, reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art is known or forms part of the common general knowledge in any country.

Summary of the Invention

The present invention is predicated, in part, on the recognition that a perforated cathode may be used as a sieve to separate floe generated during electroflocculation from an electrolyte in an electroflocculation apparatus. In some embodiments, the present invention also recognizes that rising bubbles of gas produced at the cathode during electroflocculation serve to lift off, or otherwise dislodge, sieved floe from the cathode and/or prevent the buildup of

- A -

floc on the perforated cathode. In this way, blockage of the perforated cathode by the buildup of floe is reduced or eliminated.

Accordingly, the present invention provides an electroflocculation apparatus including: a reaction chamber having an inlet for introducing an electrolyte to the reaction chamber and an outlet for removing the electrolyte from the reaction chamber; an anode located within the reaction chamber; and a perforated cathode located within the reaction chamber, the cathode being located such that an electrolyte passing through the reaction chamber from the inlet to the outlet passes through the perforated cathode; wherein, in use, the perforated cathode sieves at least a portion of floe generated during electroflocculation from the electrolyte as the electrolyte flows from the inlet to the outlet; and wherein the cathode is arranged in a substantially upright orientation in the reaction chamber.

Before turning to a general description of the apparatus of the invention, it must be appreciated that while various terms used throughout this specification have meanings that will be will understood by a skilled addressee, for ease of reference, some of those terms will now be clearly defined.

The "electrolyte" used in accordance with the present invention may be any liquid which produces a gas at a cathode under reductive conditions. In one embodiment the electrolyte is an aqueous liquid, and in this embodiment, the gas evolved at the cathode generally includes hydrogen. In further embodiments, the electrolyte is waste-water. Various types of "waste-water" would be evident to a skilled addressee, and may include, for example: grey- water (ie. waste-water generated from laundries, kitchens or showers and which does not include sewage), black water (ie. waste-water which does contain sewage) or water including one or more impurities such as chemicals, dyes,

heavy metals or the like. In one specific embodiment, the apparatus of the present invention is preferably used to treat grey-water.

In further embodiments, the electrolyte may also include other liquids which would produce a gas at a cathode under reductive conditions, such as alcohols

(alkanols). For example, in the case of an alcohol, the gas produced at the cathode would include an alkane gas of a corresponding carbon chain length to the alcohol (for example the use of methanol as an electrolyte would lead to the production of methane at the cathode; ethanol would lead to the production of ethane and so forth).

The term "floe" should be understood to include any coagulated material produced as a result of an electroflocculation process. The floe may either be less dense than the electrolyte and float on the surface or may be denser than the electrolyte and form a sediment.

The term "sieve", as used with reference to the perforated cathode, should be understood to include the cathode reducing or eliminating the egress of floe from the inlet side of the perforated cathode to the outlet side of the perforated cathode, thus reducing the amount of floe in the electrolyte as it passes through the perforated cathode.

Also, throughout this specification, spatial terms such as "upright", "horizontal", "vertical" and the like will be used. It should be appreciated that these terms are used for ease of reference and relate to the apparatus of the present invention in its normal, in use, orientation.

Turning now to a general description of the apparatus of the invention, and as mentioned above, the present invention is predicated, in part, on an electroflocculation apparatus including a perforated cathode located within the reaction chamber such that an electrolyte passing through the reaction chamber from the inlet to the outlet passes through the perforated cathode. In one embodiment the perforated cathode is located such that it divides the reaction

chamber into an inlet-containing region and an outlet-containing region. Also, in some preferred embodiments of the present invention, gas evolved at the perforated cathode during electroflocculation serves to reduce or eliminate a build-up of the floe on the perforated cathode.

The perforated cathode is generally arranged in a substantially upright orientation in the reaction chamber. As referred to herein, the term "upright" should be understood to refer a non-horizontal orientation when the device is in its normal, in use, orientation. However, it should be understood that the term "upright" is not limited to a vertical or substantially vertical orientation and should be understood to include, for example, the cathode being canted up to about 45 ^Q off vertical. In one embodiment, for example, the cathode is canted about 10 ^Q off vertical.

In further embodiments, the cathode is ideally canted such that the upper edge of the cathode is canted back toward the outlet of the reaction chamber. Canting of the cathode in this way causes the gas produced at the cathode to generate a bubble curtain in the reaction chamber on the inlet side of the cathode which further serves to reduce or prevent floe from reaching the perforated cathode and building up thereon. Furthermore, the depth of the bubble curtain produced by the cathode may be altered by altering the angle that the cathode is canted back, with the depth of the bubble curtain increasing with the increasing angle (off vertical) of the cathode.

The cathode of the apparatus of the present invention includes one or more perforations to allow the electrolyte to pass through the cathode while sieving at least some of the floe (generated during electroflocculation) from the electrolyte as it passes through the perforated cathode. As such, the perforated cathode may include perforations of any suitable size to sieve out floe of a desired size. However, in specific embodiments, the perforated cathode includes one or more perforations, each having an area of about less than 5 mm ² , less than 2 mm ² , less than 1 mm ² , or about 0.8 mm ² .

In constructing the apparatus of the present invention, the materials used in the fabrication of electrodes of the electroflocculation apparatus may be any suitable material. Examples include corrosion resistant, conductive materials, metals and alloys. In addition, the electrodes should also be as resistant to chemical reaction with the electrolyte as is possible. Typical anode materials include: metals which release trivalent anions that act as coagulating agents when a voltage is applied to the anode, such as iron or aluminium; antimony- lead; platinum; conductive oxide coatings on tantalum or titanium; and the like.

Cathode materials may include, for example, cathodic metals such as stainless steel and aluminum. In one embodiment, however, the perforated cathode includes a perforated stainless steel sheet. In another embodiment, the cathode includes a stainless steel mesh.

The anode of the electroflocculation apparatus may be located anywhere in the reaction chamber. However, in one embodiment, the anode is located in the reaction chamber between the inlet and the cathode (with reference to the flow path of the electrolyte). In this embodiment, the flocculating agent (eg. metal cations) generated at the anode is primarily produced in the inlet containing portion of the reaction chamber. In this way, floe is generally produced on the inlet side of the cathode in the reaction chamber, and at least a portion of the floe is sieved out of the electrolyte as it travels through the perforated cathode from the inlet to the outlet.

The present invention also contemplates the use of a secondary anode to increase the production of gas at the cathode. The secondary anode, if present, is preferably placed proximal to the cathode such that the current running through the cathode is increased. The secondary anode is generally made of a less reactive metal, or other material, than the main anode used in the apparatus. For example if the anode is aluminium, the secondary anode may be made of, for example, carbon (eg. graphite), zinc, iron, tin, lead, copper, silver, gold or platinum. In this way, corrosion and degradation of the secondary anode

is reduced or eliminated while the main anode is present. In one specific embodiment, the secondary anode includes graphite.

The present invention also provides a waste-water treatment system including an electroflocculation apparatus of the present invention. In this respect, a waste-water treatment system according to the present invention includes one or more of the electroflocculation apparatus described herein, and may optionally include one or more additional treatment stages, such as one or more filtration stages, chlorinating stages, ozonating stages, sedimentation stages, carbon filtration stages and the like. A wide range of additional water purification stages or apparatus that may be incorporated into the waste-water treatment system of the present invention would be readily ascertained by one of skill in the art, and the present invention should not be considered limited to the additional purification means mentioned above.

The size, capacity and configuration of the waste-water treatment system may be altered to suit the nature (eg. volume and pollutant level) of the waste-water to be treated and to suit the location and conditions under which the system will operate.

For example, in one embodiment, the waste-water treatment system is adapted for use on a boat. In another embodiment, the present invention contemplates a grey-water treatment system for a boat. For example, the electroflocculation apparatus of the present invention may be incorporated into a waste-water treatment system for a boat as described in Australian innovation patent 2006100035.

The electroflocculation apparatus of the present invention may also be incorporated into land-based waste-water treatment systems, such as waste- water treatment systems in industrial, mining, agricultural or domestic use. Also, the waste-water treatment systems of the present invention may also be installed and used in other vehicles such as cars, buses, trucks, trains and the like.

The present invention also provides a method for removing one or more impurities from an electrolyte, the method including treating the electrolyte with the electroflocculation apparatus of the present invention.

In one specific embodiment of the third form of the invention, the electrolyte contemplated is waste-water and, thus, in one embodiment, the present invention provides a method for removing one or more impurities from wastewater.

Brief Description of the Figures

Having briefly described the general concepts involved with the present invention, exemplary embodiments of the present invention will now be described with reference to the following figures:

Figure 1 shows a perspective view of an electroflocculation apparatus according to one embodiment of the present invention; and

Figure 2 shows an example of a grey-water treatment system for a boat, which incorporates an electroflocculation apparatus of the present invention.

Description of Exemplary Embodiments

It is to be understood that the following description is for the purpose of describing particular embodiments only, and is not intended to be limiting with respect to the above description.

The electroflocculation apparatus 100 shown in figure 1 includes a reaction chamber 1 10 having an inlet 1 12 and an outlet 1 14. An electrolyte, such as waste-water, may be introduced into the reaction chamber 1 10 via inlet 1 12 and

released via outlet 114. In this embodiment, the inlet 1 12 is located in the upper region of the reaction chamber 1 10 such that the electrolyte is introduced into the upper region of the reaction chamber 1 10. In this way, introduced electrolyte must flow through any floe present in the reaction chamber 1 10 (from a prior or current electroflocculation reaction) and the existing floe (if present) may capture at least a portion of any solids suspended in the electrolyte.

Aluminium blocks 1 16 are attached to a reactor plate 1 18. The reactor plate 1 18 is secured to the reaction chamber 1 10 by screws 1 19, but is electrically insulated from the reaction chamber 1 10 by insulators 120.

A stainless steel sheet 122 including a plurality of holes 124 formed therein is located in the reaction chamber 1 10 and spans an internal cross section thereof. The sheet 122 is canted back 10° from vertical with the top of the sheet 122 canted back toward the outlet 1 14. The stainless steel sheet 122 is also electrically insulated from the reaction chamber 1 10, for example by insulating strips at the contact points between the sheet 122 and the reaction chamber 1 10.

In use, a voltage is applied between the reactor plate 1 18 (including aluminium blocks 1 16) and the stainless steel sheet 122 by a direct current (DC) power source (not shown). In this way, when an electrolyte (not shown) fills the reaction chamber 1 10 and the voltage is applied across the reactor plate 1 18 and sheet 122, the aluminium blocks 1 16 function as anodes and the stainless steel sheet 122 functions as a cathode in an electroflocculation reaction.

During electroflocculation, trivalent aluminium ions are released from the aluminium blocks (anodes) 1 16. These trivalent aluminium ions coagulate impurities present in the electrolyte (waste-water) to form floe in the electrolyte. At the same time, water molecules in the electrolyte are chemically reduced at the cathode (stainless steel sheet 122) to produce bubbles of hydrogen gas. Bubbles of gas may be incorporated into some of the floe produced in the reaction chamber and cause the floe to float to the surface of the electrolyte,

while other floe may settle to the bottom of the reaction chamber 1 10 as sediment.

In use, the anodes 1 16 are consumed and may require periodic replacement. This may involve replacement of the anodes 1 16 per se or replacement of the reactor plate 118 and anodes 1 16.

During electroflocculation, as the electrolyte flows from the inlet 1 12 to the outlet 1 14, the holes 124 (not shown to scale) in the stainless steel sheet 122 allow the passage of the electrolyte, but block the passage of at least a portion of the generated floe in the electrolyte. In this embodiment, the cathode is a 5mm thick stainless steel sheet (316 or 304 grade) having holes of 0.8 mm ² formed therein. The holes in the sheet are spaced at a pitch of 1.5 mm such that the sheet has an open area of 25%.

The buildup of floe on the sheet 122 is reduced or eliminated by the production of hydrogen gas at the sheet 122 during electroflocculation. Specifically, as bubbles of gas rise from the sheet 122 through the electrolyte they lift off floe built up on the sheet 122. In addition, the bubbles of gas being produced at the sheet 122 and rising through the electrolyte produce a curtain of rising gas bubbles which reduce or prevent floe from reaching the sheet 122 and building up thereon. The canting of the sheet 122 off the vertical axis, as described above, increases the width of the bubble curtain relative to the width of the curtain if the sheet 122 was vertical. Accordingly, the width of the bubble curtain may be adjusted by changing the angle of the sheet 122.

The size, capacity and configuration of the electroflocculation apparatus may be altered to suit the nature (eg. volume and pollutant level) of the electrolyte to be treated and to suit the location and conditions under which the system will operate.

For example, the electroflocculation apparatus may have a reaction chamber capacity in the order of tens of litres for small mobile applications such as

mobile water treatment systems in cars, trucks, small buses or small boats. Larger examples of the electroflocculation apparatus of the present invention (for example having reaction chamber volumes in the hundreds of litres) may be used in larger buses, boats, trains and the like. Finally, even larger examples of the electroflocculation apparatus of the present invention (for example having reaction chamber volumes in the thousands of litres) may be used in large treatment systems such as stationary water treatment systems for use in industrial, mining, agricultural or domestic use.

As set out above, the electroflocculation apparatus of the present invention may be incorporated into a waste-water treatment system. An exemplary system which is adapted for the treatment of grey-water produced on a boat is shown in Figure 2.

The waste-water treatment system 200 shown in Figure 2 is designed to float when connected to a boat. Details of floating water treatment systems of this type are set out in Australian innovation patent 2006100035. The waste-water treatment system floats in the water such that the external water level is at level 205.

The grey-water treatment system includes an electroflocculation apparatus 100 as described above. Waste-water is introduced into the treatment system via the inlet 1 12 of the electroflocculation apparatus 100. Electroflocculation of introduced waste-water occurs in the electroflocculation apparatus 100 as described above. In use, electroflocculated waste-water flows out of the electroflocculation apparatus 100 through outlet 1 14 and builds up against weir 220. Once the level of waste-water in the electroflocculation apparatus 100 and behind weir 220, reaches the level 210, the treated water flows over weir 220.

At the top of weir 220 is a tray 230 into which a water treatment chemical, such as chlorine may be placed. In this way, waste-water flowing over weir 220 also flows across tray 230, thus further treating the waste-water by chlorination. Other chlorination or sterilisation means may also be incorporated into tray 230,

or the upper region of weir 220, such as electrolytic chlorination or ozonation devices.

After flowing over weir 220 and tray 230, the waste-water flows through a coarse filter unit including a filter membrane 260 wrapped around a series of bollards 250. This forms a lamellate structure which causes the waste-water to pass through several separated layers of filter membrane as it progresses through the coarse filter. The filter membrane 260 used in the filter may be any filter membrane having a suitable pore size to capture particulate matter down to a desired size threshold. For example, the filter membrane may be a fabric such as nylon, polyester or cotton. In one embodiment, the filter membrane 260 is made from shade-cloth fabric.

After coarse filtration, the waste-water flows though aperture 262 and builds up against weir 264. Once the water level reaches level 272, the waste-water flows over weir 264 into the fine filter matrix 266. The fine filter matrix 266 is adapted to remove small particles (eg. in the micron range) and/or dissolved chemicals from the waste-water. As such, the fine filter matrix 266 may be any suitable material for this purpose including, for example, one or more of: activated carbon, zeolite, activated alumina, anthracite, brim, calcite, magnesium oxide (corosex), garnet, zinc/copper granules (KDF55/KDF85), manganese greensand, manganese dioxide, sand and ceramic filter matrices. In the embodiment shown in Figure 2, the filter matrix includes activated carbon and zeolite.

After flowing through the fine filter matrix 266, waste-water flows into detention tank 268. A pump 270 is present in detention tank 268 and when (or before) the water level in detention tank 268 reaches level 272, the pump 270 pumps treated water from detention tank 268 out into the environment, which may be a waterway (such as an ocean, lake or river) or may be onto land.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically

described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps or features referred to, or indicated in this specification, individually or collectively, and any and all combinations of any two or more of the steps or features.