Abstract:
A method for separating contaminants from a aqueous source containing contaminants. In one embodiment, the method involves the use of a high powdered oxidant dissolved within the aqueous system. The gas is dissolved within a reservoir in the aqueous solution and the pressure within the reservoir is controllable. This allows maximum contact of the oxidizing dissolved gas with the contaminant material. Once oxidized, the outlet of the reservoir is adapted to permit hydraulic cavitation. The net effect of the cavitation is to induce a foam formation which foam transports a floc into a separate phase from the aqueous solution. In this manner, the process is effectively a dissolved oxidizing gas mass transfer process. In another embodiment, the process may be augmented by electrocoagulation. This involves the use of an electric cell which is disposed within the reservoir containing the oxidant material. By providing electrodes and exposing the electrodes to a source of current, the contaminants within the aqueous solution are either oxidized or otherwise degraded and this complements the oxidation by the dissolved gaseous oxidant. An apparatus is also disclosed to effect the methods set forth above.

Description:
FIELD OF THE INVENTION 
     The present invention relates to waste water treatment method and apparatus and more particularly, the present invention relates to separating contaminants from an aqueous solution using mass transfer techniques and electrocoagulation. 
     BACKGROUND OF THE INVENTION 
     The problem of separating or removing contaminants from aqueous systems has been a complication that the art has lamented over for many decades. To this end, the art developed along with further industrial processes as water contamination grew commensurately with industrial progress. Initially, water treatment was simply a matter of adding materials suitable for inducing precipitation of certain materials, filtration, ion exchange and other processes. With the continual increase in strict requirements for clean water, electro chemistry was brought into favor. Broadly, the use of electrodes disposed within a cell and subjected to electric current was found to be useful for treating solutions containing contaminants. In some instances, other unit operations were combined with this treatment process in order to render inert compounds. 
     One of the references that was selected for review is U.S. Pat. No. 1,095,893, issued to Landreth, May 5, 1914. This patent relates to electrochemical treatment and in this patent, the patentee has identified that such cells are useful for the treatment of water. As stated in the disclosure electrodes of copper, aluminum, brass or other alloys are useful as cell plate material. In addition, the disclosure discusses the fact that settling tanks may be useful to assist in material settling (floccing). Column 2 of the disclosure indicates that the series of electrodes are arranged so that the water passes up through the apparatus and is forced to “ . . . to take a circuitous course whereby any material added to it or found in it may be thoroughly mixed and all particles of the liquid be brought into contact with the electrodes . . . ”. It is also as stated in the text at column 2, that the electrodes are in the form of horizontally disposed plates and that the plates may be provided with apertures which may be centrally arranged with the plates of alternating series of other plates have recesses at their ends. Column 3 of the disclosure states: 
     “To provide for the proper passage or circulation of the liquid between plates  14  and its movement throughout the apparatus, alternate plates are provided with apertures indicated at  14 A, while the intermediate plates have their cut-away corners notched or recessed as at  14 B as clearly illustrated in FIGS. 8 and 9. By this means, the liquid under treatment is diverted in its flow and caused to contact with the entire surface of the respective plates, insuring the desired electrical treatment.” 
     Although this disclosure is useful for instructing the procedure for electrochemical treatment of water, there is no indication of the addition of an oxidant material such as ozone. Further, the teachings of this patent are limited to electrochemistry; the disclosure fails to set forth any details with respect to dissolved air flotation, fluid hydrodynamics, cavitation, flocculation or any other fluid dynamic principles that would augment the utility of the electrochemical cell taught in this patent. 
     In U.S. Pat. No. 1,146,942, issued to Landreth, Jul. 20, 1915, a variation on what has been discussed in the previous patent is set forth. In this reference, there is a clear indication that the electrodes are of a different polarity and that a suitable pole changing switch, an example is given as number  26  in the drawings, could be used to switch the current in order that one set of plates act as cathodes for a certain length of time while another set of plates act as anodes during this period of time. This reference advanced the art by providing a reverse polarity arrangement for changing the polarity of the individual cells within the unit. The reference, similar to its companion, is deficient on appreciation of countercurrent oxidation with a dissolved gas. Further, it is believed that this apparatus would not be particularly well suited to handling a wide variety of contaminant types (organic, inorganic, combinations thereof, etc.) 
     In a further reference issued to Landreth, namely U.S. Pat. No. 1,131,067, issued Mar. 9, 1915, there is a discussion of reintroducing treated liquid for further treatment by the apparatus as well as a discussion concerning oxidizing treatment or a treatment for the production of flocculent formed either from the metal electrodes or from simple chemical reaction or the latter stimulated by electric current; or any other treatment. At column 2, beginning at line 25 et seq., discusses recirculation of the material for further treatment in the apparatus. 
     Preis et al., in U.S. Pat. No. 3,728,245, issued Apr. 17, 1973, teach an apparatus for treating sewage incorporating a series of electrolytic plates for the purpose of electrocoagulation. The patentees discuss a need for maintaining pressure in the circuit so that chlorine and ozone are maintained in solution in order to enhance bactericidal action. This reference advanced the art developed by Landreth et al., by employing an oxidant to enhance the electrocoagulation. The reference, although providing further instruction in this art, is deficient any discussion cavitation or floc generation by pressure discontinuities in an outlet stream of treated aqueous material. 
     Other generally relevant references include U.S. Pat. No. 913,827, issued to Korten, Mar. 2, 1909, U.S. Pat. No. 3,523,891, issued to Mehl, Aug. 11, 1970, U.S. Pat. Nos. 5,928,493; 5,705,050; 5,746,904 and 5,549,812, 3,846,300, 5,587,057 and 5,611,907. 
     The electrolytic processes were found to be generally useful, however, the cellular design was such that the electrodes often would accrue debris and, therefore, would change the requirements of the current of the cell. In addition, many of the plates in the existing arrangements were fairly large and did not provide any improvement to enhance the surface area to therefore increase the number of reactions with the contaminants to be treated in the water. This, of course, leads to lower degree of interactions and a higher cost of running the cell in terms of the current requirements due to debris buildup. 
     It has also been proposed to employ dissolved air flotation systems. One such arrangement is made by the Precision Environmental Systems Company. This company manufactures devices which are useful for flocculation and coagulation within the same unit. This unit is quite useful for the purpose for which it was designed, however, the arrangement has an extremely large footprint and does not provide for different chemical processes to occur within the same unit. 
     Of the more desirable arrangements that have evolved in this art for water treatment are perhaps the use of dissolved gases for the purpose of oxidation has been moderately successful. In the art that is currently known, typically oxidation cells are open to atmospheric pressure where a gas dissolved in solution is allowed to evolve out of the solution. The arrangement in the art provide a tortuous path or other applied force in order to keep the bubbles in solution as long as possible. This has the advantage of providing a reaction site (the surface of the bubble) of the oxidant material so that the contaminant can be oxidized. Once the gaseous material then evolves to the surface, the contaminant is flocculated and the materials then separated. This is broadly known as aeration and various devices have been proposed in this art in order to maintain the bubbles in solution and thus enhancing the degree of interaction of the bubble surface with the material to be oxidized or otherwise decontaminated. 
     It would be desirable if there were a process whereby a gaseous oxidant could be introduced into a reservoir or other chamber or confined area under sufficient pressure to maintain the gas in solution. This affords the opportunity for the smallest possible bubbles in solution to oxidize contaminants present in the solution. It would be particularly desirable if there were a system available where the dissolved oxidant gas could be maintained in solution in order to provide the smallest possible bubbles and therefore the greatest possible degree of surface area for reaction with the contaminants to be separated and further, affording control of the bubble size. 
     The present invention is directed to providing a mass transfer mechanism and advanced oxidation technologies for the separation of contaminants from an aqueous solution where the oxidant is maintained in solution until such time as it is desirable to allow the pressure to be reduced and the oxidant to come out of solution. 
     SUMMARY OF THE INVENTION 
     One object of one embodiment of the present invention is to provide an improved method of separating contaminants from aqueous solution. A countercurrent mass transfer mechanism is employed. 
     A further object of one embodiment of the present invention is to provide a continuous method of separating contaminants from an aqueous solution comprising the steps of: 
     providing an aqueous solution containing contaminants; 
     providing a closed reservoir having an inlet and an outlet, the inlet at a higher elevation than the outlet; 
     introducing the aqueous solution into the reservoir; 
     entraining an oxidant into the aqueous solution; 
     maintaining super atmospheric pressure in the reservoir to minimize bubble size of the oxidant to thereby maximize available surface area of bubbles of oxidant with the contaminants in the aqueous solution; 
     oxidizing the contaminants; and 
     selectively inducing a pressure discontinuity extraneous of the reservoir to flocculate oxidized contaminants into a separate phase from the aqueous solution. 
     With respect to the oxidant, ozone is one of the preferred oxidants for use in the present invention, however, it will be readily appreciated that any other suitable oxidant could be used such as chlorine, bromine, hydrogen peroxide, suitable nitro compounds, inter alia. 
     It has been found that by effectively providing an inverted or reversed aeration system that effective oxidation of the contaminant can be achieved. The reservoir may be an isolated chamber, tube with closed ends or, alternatively, may comprise an earth formation for subterranean treatment of contaminants in an aqueous solution. In the instant methodology, the inlet is disposed at a higher elevation than the outlet. In this manner, the incoming entrained gaseous oxidant is forced downwardly through the solution and, therefore, will act in a countercurrent manner with the aqueous solution to be treated. By maintaining a super atmospheric pressure in the chamber reservoir container, etc., the gaseous oxidant is maintained in solution and in very fine bubbles. This has produced marked results, since the smaller bubbles provide a significantly improved surface area for contact with the contaminants to oxidize the latter. This is achieved by control of the pressure into the reservoir and the pressure at the outlet thereof. In this manner, the pressure is effectively adjustable and can be customized by the user. This is in marked contrast to the prior art which effectively provide open vessels and, therefore, allowed the pressure to equalize at atmospheric pressure and simply provided convoluted or otherwise tortuous paths through which a gas was forced. The concept in the prior art was to provide the tortuous path in order to try and keep the bubbles in solution and, therefore, at least partially in contact with the material to be treated. The technique of the prior art is effectively an aeration technique where a gas is forced through a solution for oxidation purposes. 
     The difference in the instant application is quite pronounced and results in a significant advance in this art. It has been found that by maintaining the pressure within a confined chamber, the gaseous oxidant can be maintained in solution for a user selected duration; this is in contrast to what the prior art proposes. The instant case permits control of the bubble size of the oxidant within the chamber and facilitates countercurrent contact with the oxidant bubbles and aqueous solution and further allows for user selected pressure discontinuity in the form of, for example, hydraulic cavitation, to induce floc formation. Control on this level has not been previously proposed in the prior art whatsoever; the prior art effectively used a “hit and miss” process of aeration as opposed to a controlled process, which also results in the formation of a rich floc and clean aqueous solution. 
     As a generic overview of the present invention, the same unifies a series of technologies including dissolved air flotation, hydraulic cavitation, fluid dynamics, mass transfer and electrocoagulation. These concepts are linked together to provide an effective contaminant separation process, which is indiscriminatory as to the contaminant. This is a feature that was not possible in the prior art; the existing art, in most cases, proposes methods which are sensitive to the materials present in the system to be treated. Conveniently, by providing pressure control to the material inlet of the reservoir relative to the outlet, the maximum amount of gaseous oxidant can be retained in solution, thereby providing the smallest possible bubbles in the highest possible density with the greatest possible duration in solution. These features together with the principles of electrocoagulation contribute to the success of the protocol set forth herein. 
     In order to augment the mass transfer process set forth hereinabove, it has been found that the combination of that technology together with electrocoagulation produces super results and significantly reduces the limitations and problems associated with the art. In effect, as a further object of one embodiment of the present invention, the control provided with the gaseous oxidant system could be unified with the benefits of electrocoagulation. Accordingly, as a further object of one embodiment of the present invention, there is provided a continuous method of separating contaminants from an aqueous solution comprising the steps of: 
     providing an aqueous solution containing contaminants; 
     providing a closed reservoir having an inlet and an outlet, the inlet at a higher elevation than the outlet; 
     positioning an electrocell with the reservoir for applying an electric field to the aqueous solution; 
     introducing the aqueous solution into the reservoir; 
     entraining an oxidant into the aqueous solution; 
     maintaining super atmospheric pressure in the reservoir to minimize bubble size of the oxidant to thereby maximize available surface area of bubbles of oxidant with the contaminants in the aqueous solution; 
     oxidizing the contaminants and the oxidant and flocculating the contaminants by exposure to the electric field; and 
     selectively inducing a pressure discontinuity extraneous of the reservoir to flocculate any remaining oxidized contaminants into a separate phase from the aqueous solution. 
     A further object of one embodiment is to provide a method of separating contaminants from an aqueous solution, comprising the steps of: 
     a. providing an aqueous solution containing contaminants; 
     b. oxidizing the aqueous solution with an oxidant under adjustable super atmospheric pressure to maintain the oxidant in solution; 
     c. exposing the aqueous solution to an electrocell for electrocoagulating contaminants; and 
     d. selectively inducing a pressure discontinuity to flocculate coagulated and oxidized contaminants into a separate phase from the aqueous solution. 
     Of particular value is the fact that the aqueous solution may contain both organic, inorganic waste material or a combination of both. 
     A still further object of the present invention is to provide an apparatus for separating contaminants from an aqueous solution, comprising: 
     an aqueous source containing contaminants; 
     a closed pressurizable reservoir having an inlet and an outlet, the inlet being disposed at a higher elevation than the outlet, the inlet in communication with the aqueous source; 
     means for introducing an oxidant under pressure into the reservoir; 
     an electrocell disposed within the reservoir for electrocoagulating material in the aqueous source; 
     means for supplying current to the electrocell; and 
     means for selectively inducing hydrodynamic cavitation in treated aqueous solution to flocculate oxidized contaminants into a separate phase from the aqueous solution. 
     Having thus described the invention, reference will now be made to the accompanying drawings illustrating preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of one embodiment of the present invention; 
     FIG. 2 is a schematic illustration of a second embodiment of the present invention; 
     FIG. 3 is a schematic illustration of a third embodiment of the present invention; 
     FIG. 4 is a schematic illustration of a fourth embodiment of the present invention; 
     FIG. 5 is a schematic illustration of a fifth embodiment of the present invention; 
     FIGS. 6A and 6B are schematic illustrations of a back flushing circuit for use in the present invention; 
     FIGS. 7A and 7B are schematic illustrations of an alternate of FIGS. 6A and 6B; 
     FIGS. 8A and 8B are schematic illustrations of alternatives to FIGS. 6A and 6B and FIGS. 7A and 7B; 
     FIG. 9 is a longitudinal cross-section of one embodiment of a cell in accordance with the present invention; 
     FIG. 10 is a partially cut away view of an alternate of FIG. 9; 
     FIG. 11 is a top plan view of a plate for use in the present invention; 
     FIG. 12 is a sectional view along line  12 — 12  of FIG. 11; 
     FIG. 13 is a schematic illustration of the circuit for use in the present invention; 
     FIG. 14 is a schematic illustration of a switching circuit for use in the present invention; 
     FIG. 15 is a schematic illustration of a microprocessor circuit for use in the present invention; 
     FIG. 16 is a further schematic illustration of the switching circuit for use in the present invention; 
     FIG. 17 is a schematic illustration of a further embodiment of the present invention; 
     FIG. 18 is a cross-sectional view of FIG. 17; 
     FIG. 19 is a schematic illustration of plasma cell for use in the present invention; 
     FIG. 20 is a schematic illustration of a further embodiment of the present invention; 
     FIG. 21 is a schematic illustration of a still further embodiment of the present invention; and 
     FIG. 22 is a schematic illustration of a still further embodiment of the present invention. 
    
    
     Similar numerals in the figures denote similar elements. 
     PREFACE 
     BOD when used herein refers to biological oxygen demand; COD when used herein refers to chemical oxygen demand; and, TOD when used herein refers to total oxygen demand. Quantities when indicated by percentage (%) will be understood to reference percentage (%) by weight unless otherwise indicated. The symbol w/v will mean weight in volume. The symbol O 3  will mean ozone gas. All other chemical symbols referenced herein will have there usual meaning. TSS when used herein refers to total suspended solids. TDS when used herein refers to total dissolved solids. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIG. 1 illustrates an overall schematic representation of the apparatus for use in practicing the methodology. In the example, a source of water contaminated with organic contaminants, inorganic contaminants or a combination thereof, is represented by numeral  10 . A pump  12  may be provided to pump the fluid from the source  10  thereof into a reservoir  14 . Intermediate the source  10  and reservoir  14  is disposed a venturi  16 , which venturi  16  is in fluid communication with a source of an oxidizing agent, the source being denoted by numeral  18 . The oxidizing agent, when in the state of a gas, may comprise ozone, bromine, chlorine, nitro compounds. If the oxidizing agent is selected to be a liquid, hydrogen peroxide and other related oxidants will be useful. In the instance where the oxidant selected is not in a gaseous state, this oxidant can be converted from, for example, a liquid state to a gaseous state by any suitable means known to those skilled in the art. Oxidant from source  18  is introduced into reservoir  14  by making use of the venturi  16 . 
     Reservoir  14 , in the example shown, comprises a pressurizable container, constructed of material capable of withstanding at least several atmospheres of pressure. The reservoir  14  includes an inlet  20  in fluid communication with venturi  16  and an outlet  22 . Inlet  20  is positioned at a higher elevation than outlet  22 . The venturi  16  introduces the oxidant into the aqueous source by entrainment. When the entrained oxidant and aqueous solution enter reservoir  14 , the contents are pressurized. 
     It is important with the technology set forth herein that the pressure is maintained within reservoir  14 . This facilitates the dissolution of ozone gas into the solution and promotes the formation of minute bubbles (not shown). The flow is downward from the inlet  20  to the outlet  22 . In this manner, the oxidant bubbles rise countercurrent to the aqueous solution. This flow pattern is very effective when the solution is dense with small bubbles. The small bubbles, as will be appreciated by those skilled, provide an enormous amount of surface area relative to larger bubbles. In addition, if the pressure is maintained, the smaller bubbles have a longer life span in solution and thus provide the maximum amount of oxidizing power. The countercurrent flow mechanism is indicated broadly by arrows  24  and  26  within reservoir  14 . 
     After a sufficient residence time in reservoir  14 , oxidized material exiting at outlet  22  is then subjected to a pressure discontinuity in order to induce hydrodynamic cavitation. By this mechanism, if the pressure is released, the gaseous oxidant evolves out of solution and the flocculated material is effectively floated so that the flocculated phase is distinct from the aqueous phase. The pressure discontinuity may be effected by a flow constrictor, variable orifice plate or other pressure relief mechanism, broadly denoted by numeral  28 . Once distinct phases have been created and thus the contaminants separated from the aqueous solution, the individual phases may be subjected to further unit operations. In the case of the aqueous phase, the water may undergo additional purification by way of specialized distillation techniques, ion exchange, inter alia. With respect to the floc, this may be processed by specific techniques to recover any values that may be matrixed within the floc. The subsequent unit operations referenced above are not shown in the drawings. 
     Turning to FIG. 2, shown is a variation of the apparatus in FIG.  1 . In this embodiment, a sensor apparatus, broadly denoted by numeral  30 , is provided to ensure supersaturation of aqueous solution prior to exiting outlet  22  and control the quantity of oxidant induced by venturi  16 . This is achieved by providing a float valve  32 , which floats at the level of the liquid within reservoir  14  and is in electrical communication with a sensor  34 . Sensor  34  is, in turn, in electrical or mechanical communication with a valve  36 . Valve  36  is directly linked to the supply of oxidant  18  and, therefore, when the liquid level in reservoir  14  is detected by float  32  to be substantially decreasing, sensor  34  signals valve  36  to suspend introduction of oxidant into the system and particularly into inlet  20  via through venturi  16 . This arrangement could alternatively be replaced with a simple vent tube (not shown). 
     Referring now to FIG. 3, shown is an alternate embodiment of that which has been discussed in FIGS. 1 and 2. In this embodiment, the reservoir  14  is represented as a subterranean formation within which is disposed a source of contamination and an aqueous phase  10 . This embodiment establishes the fact that this technology can be immediately applied to field applications. This would be of use where a deposit of hydrocarbons, or other petroleum/organic compounds were present in an earth formation. In the instance where the earth formation is composed of a material insufficient to sustain periods of superatmospheric pressure, the formation could be pre-treated with a material to render impermeable the internal surface, harden the surface, or otherwise prepare the same for sustained pressure treatment. Suitable techniques, compounds or other treatments will be appreciated by those skilled in the art. 
     In this process, oxidant could be introduced in much the same way as that which has been discussed. The oxidant would be introduced into the formation  14  through an inlet  20  in the formation. As established above, the formation  14  contains an aqueous mixture of organics, inorganics, etc., and therefore, pressurized introduction of the oxidant into the formation would result in the oxidation of the contaminants in the same mechanism (countercurrent) as discussed regarding FIGS. 1 and 2. The oxidized material could be transported from an outlet  22  in formation  14  via pump  38  to flow constrictor  28  for pressure discontinuity and thus floccing of the oxidized compounds. Once flocced, the contaminants are effectively separated from the aqueous phase and may undergo subsequent unit operations as mentioned herein previously. 
     In order to augment the effectiveness of the system discussed in FIGS. 1 through 3, the aqueous solution may be subjected to an electrocoagulation unit operation. Various embodiments will now be specified. 
     Referring to FIG. 4, shown is a further variation of the apparatus. In this embodiment, waste water from a tank  40  is pumped by a pump  12  through a venturi device  16  downstream of the pump  12 . Ozone produced by an ozone source  18  is entrained in the waste water via venturi  16 . The waste water then passes through an electro-flocculation cell  42 , disposed in reservoir  14 . The reservoir  14  and cell  42  will collectively be referred to as the cell  42  hereinafter. The waste water is forced to pass in a turbulent manner through an intense electric field produced by cell excitation electronic circuitry  44 . The waste water then passes from the reservoir  14  through a flow constrictor, an example of which is an orifice plate  28  and thence back into the tank  40 . 
     In the waste water flow line between the pump  12  and the venturi  16  there is provided a cell shut-off valve  46 . Between the pump  12  and the cell shut-off valve  46 , there is connected a tank discharge line  48  having a discharge shut-off valve  50 . The cell shut-off valve  46  is open during the treatment of the waste water and closed when the operator wishes to discharge the waste water from tank  40  following treatment. Conversely, the discharge shut-off valve  50  may be closed during treatment of waste water and open for discharge of the treated waste water. 
     A gas valve  52  is provided to regulate the flow of ozone into the waste water. The gas valve  52  may optionally be electrically controlled in some embodiments of the inventive apparatus as described in more detail below. 
     The orifice plate  28  may comprise a disk of stainless steel or other material resistant to dissolution by the waste water interposed in the piping connecting the cell  42  and the tank  40  and having at least one sharp-edged opening (not shown). In the exemplary apparatus described in detail below, a single opening in the orifice plate  28  is used that is approximately 10% larger than the passage through the venturi  16  so that during operation of the apparatus, the pressure of the waste water in the cell  42  is acceptably lower than the pump outlet pressure, so as to ensure proper operation of the venturi  16 , within the designed operational parameters of the latter. 
     It will be appreciated that higher pressures in the cell  42  may be advantageous for some waste water compositions, but if a higher pressure is indicated, then a pump  12  will have to be selected to provide a higher pressure to the venturi  16  in order to provide a pressure drop across venturi  16  to entrain the amount of ozone in the waste water that is desirable for the particular composition of the waste water being treated. Simply reducing the area of the opening or openings in the orifice plate  28  to increase the pressure in cell  42  is not desirable as then not enough ozone will be entrained in the flow through the venturi  16  as the pressure drop across the venturi will be reduced. It is also not desirable for the area of the opening or openings in the orifice plate  28  to be too large, even if the desired pressure in the cell  42  is maintained, as that would result in too large a pressure drop across the venturi  16  and the entraining of too much ozone in the waste water, leading to a build up of gas in the cell  42  and a waste of ozone as well as less effective operation of the cell  42 . 
     Referring now to FIG. 5, shown is a further variation of the apparatus. In this embodiment, a group of cells  42 ,  42 ′ and  42 ″ are shown having different arrangements of electrodes. The electrodes within the cell  42  are represented by numeral  54  and are connected to rods  56  and  58 , which rods  56  and  58  are, in turn, connected to a constant current supply  60  including control circuiting therein. Greater detail with respect to the cell  42  specifics will be discussed hereinafter. In this configuration, the outlet  22  of cell  42  becomes the inlet  20  of cell  42 ′ and so on with respect to cell  42 ″. Oxidant  18  may be added as necessary and further, a liquid/solid separation device  61 may easily be incorporated in the circuit to isolate floc and aqueous phases before passage into a subsequent cell. 
     Regarding the differing electrode geometry, cell  42  provides a parallel plate system arranged coaxially in spaced apart vertical relation. Cell  42 ′ provides an elongate electrode arrangement while cell  42 ″ includes a plurality of loose beads. 
     Although FIG. 5 illustrates three differing electrode geometries, this is only exemplary. The cells  42  may all include the same electrode geometry or any other combination and quantity. 
     FIGS. 6A and 6B illustrate an arrangement for back flushing cells while online. In FIG. 6A, cell  42  is in use with entrained oxidant and aqueous solution entering at inlet  20  with a flow direction denoted by arrow  62  and exiting at outlet  22  to enter a back flush cell  43  at an inlet  20  thereof. A suitable valve  64  is disposed between outlet  22  and inlet  20 . The direction of flow in cell  43  is indicated by arrow  66 . The material in cell  43  is transported to outlet  22 and eventually to flow constrictor  28 . A suitable valve is positioned between outlet  22  and constrictor  28 . 
     FIG. 6B illustrates the inverse of FIG. 6A, where cell  42  functions as the back flush cell and cell  43  as the service cell. The flow in the cells is also reversed as indicated. In operation, treated material from cell  43  is transported into the inlet  20  of cell  42 . Valve  64  can be used to restrict or eliminate flow. Treated material exits outlet  22  and constrictor  28 . A valve  70  is provided between constrictor  28  and outlet  22 . 
     The cells  42  and  43  can be alternatively operated to facilitate back flushing and thus alternate between the flow of FIGS. 6A and 6B. As such, reference to outlets and inlets of the cells have to be interchanged in the description; this is not due to a structural difference, but rather an operational difference. 
     Cycling between FIGS. 6A and 6B will vary in time depending upon requirements; a short cycle, may be from 30 seconds to approximately 10 minutes, a larger cycle may be from one hour to eight or more hours. Any number of cells may be in a service mode or a back flushing mode at any time. 
     Referring now to FIGS. 7A and 7B, a similar arrangement to that shown in FIGS. 6A and 6B is shown with provisions for capturing debris in the aqueous solution. As illustrated, debris traps, referenced by numeral  72 , are provided generally adjacent each inlet and outlet of a respective cell. The traps may comprise any suitable material which is capable of capturing and retaining debris such as fine mesh filters, pads, ceramic balls or other porous media., but will allow passage of fluid. This feature has the benefit of maintaining cleanliness in each cell and, therefore, optimum performance. 
     FIGS. 8A and 8B illustrate an embodiment where the back flushing circuit can be used to fluidize the loose beads, referenced by numeral  72 . The beads  72  are composed of an electroconductive material (discussed in further detail hereinafter) and are partially consumed in the cell  42 / 43 . Concomitant with mass reduction is stratification; the reverse flow cycling inherent in the arrangement illustrated refluidizes the strata and further provides the benefit of self-cleaning of the beads. 
     FIGS. 9 and 10 illustrate two alternative internal configurations of the cell  42 . FIG. 9 illustrates one embodiment in which the electronic circuitry  74  (not shown in FIG. 9 configuration) for exciting the cell  42  is not enclosed within the cell  42 ; FIG. 10 shows the bottom portion of a configuration of the cell  42  in which a lower cavity  76  is provided in which the electronic cell-excitation circuitry  74  is encapsulated inside a treat sink  76  The embodiments shown in FIGS. 9 and 10 include a gas vent tube  30 ′ for venting excess gas to regulate the waste water level inside the cell  42 . Optionally, the waste water level inside the cell  42  may be regulated by a float valve sensor system  30 , shown in FIG.  2 . 
     As illustrated in FIG. 9, the electro-flocculation cell  42  is comprises a generally cylindrical elongated multi-part casing  80  of generally circular radial cross-section, which may be composed of suitable non-conductive material such as PVC pipe or plastics extrusion material or fibre glass. 
     The casing  80  has a cavity  82  in which is mounted a set of spaced parallel plates  84 , sixteen such plates  84  being illustrated by way of example. The cavity  82  is sealed except for an inlet  20  into which the waste water from the venturi  16  flows, an outlet  22  out of which waste water flows to the orifice plate  28 , and the gas vent tube  30  previously mentioned. 
     The plates  84  may be made of suitable metal, such as aluminum. A representative one of the plates  84  is illustrated in FIGS. 11 and 12. Plate  84  has three off-centre flow openings  86 , each of whose centres are located on a discrete one of three equal angularly spaced radial lines  88 ,  90 ,  92 . The flow openings  86  have sharp edges  94 . Plate  84  also has a central opening  96  and three rod openings  98  each centred on a discrete radial line bisecting the radial lines  88 ,  90 ,  92 , preferably so that the centres of the rod openings  98  are spaced from the centre of plate  84  by about the same radial distance as the centres of the flow openings  86 . The plate 84 has circular symmetry; the rod openings  98  alternate in a circumferential sense with the flow openings  86 . 
     As illustrated in FIG. 9, the plates  84  are mounted upon a rod  100  of chemically inert and strong material such as nylon is threaded at each end to receive mating nuts  102 . A set of  15  identical annular spacers  104  mounted alternately with the plates  84  about rod  100  maintain a suitable spacing between successive plates  84 . The assemblage of plates  84 , spacers  104 , and rod  100  is held together by tightening the nuts  102  against the outermost of the plates  84 . As mentioned earlier, it is desirable that the waste water take a tortuous path through the cell  42  to improve flocculation. It is also desirable to create a strong electric field in the vicinity of the openings  86  and  98  through which the waste water is forced to pass. To create a tortuous path for the waste water flow, the plates  84  alternate in phase relationship along the rod  100  so that the centres of the flow openings  86  of any selected plate  84  are aligned with the centres of the rod openings  98  of adjacent plates  84  on either side (in a longitudinal sense) of the selected plate  84  in the assembly, thereby forcing the bulk of the waste water flow-to generally follow a tortuous path in order to pass through the larger flow openings  86 . Further, the sharp edges  94  of the openings  86  facilitate turbulence in the waste water flow and locally concentrate the electric field. 
     To connect the plates  84  to the cell excitation circuitry  74  and to hold the plates  84  in the desired alignment described above, two metal rods  106 ,  108  are inserted through radially opposed rod and flow openings  86 ,  98  in each plate  84  and welded to the edges of the rod openings  98  at weld locations  110 . The rods  106 ,  108  therefore run parallel to the rod  100  in a plane passing through the centres of the plates  84 . Each rod  106 ,  108  alternately passes freely through the centre of a flow opening  86  in one plate  84  and passes through and is welded to rod opening  98  in the next plate  84 . The resulting structure divides the plates alternately into two sets, each set welded to and therefore electrically connected to a discrete one of the rods  106 ,  108 . The rods  106 ,  108  are in turn connected to the cell excitation circuitry  74  by leads  1   10 ,  112  and are provided with electric current in the manner described below. 
     Electric current is distributed to the plates  84  by the two rods  106 ,  108 . The plates  84  of the may be made from aluminum plate, but may also be manufactured from iron and other materials that will permit metallic dissolution into a solution. It is advantageous for some waste water compositions to use two or more cells  42  in series, each cell  42  having a different plate material so as to generate different electrochemical effects. The plate materials are best chosen empirically to suit the target pollutant. For example, copper, carbon, or titanium may be useful for some pollutants. 
     It has been found that a configuration of the plates  84  in which waste water is forced collide turbulently with the plates  84  (which constitute partial obstructions to flow) together with the controllable dissolved oxidant concept discussed with respect to FIGS. 1 through 3 results in an enhancement of the electro-coagulation effect as compared to the simple previously proposed rectangular plates immersed in a flow chamber or concentric pipes arranged in a flow through cell configuration design in both of which previous designs the waste water flows parallel to the plates. 
     Generally, the cell excitation electronic circuitry  74  rectifies and controls line current received from an external source (not shown) that is pulse width modulated and applied via leads  110 ,  112  to the plates  84  thereby to periodically energize the plates  84  such that alternate plates differ in potential by a voltage sufficient to establish a relatively strong electric field in the vicinity of the plates  84 . By varying the pulse width of the current pulses applied to the plates  84 , the integrated current (and therefore the power consumed by the cell  42 ) can be regulated. A pulse frequency in the range from about 1 Hz to about 1000 Hz and an integrated current density in the range from about 0.1 Ain −2  to 10 Ain −2  is generally adequate for most conditions. As the current flow depends upon the conductivity of the waste water and the conductivity can vary during operation of the apparatus, the cell excitation electronic circuitry  74  uses measurements of the conductivity between the plates  84  taken between the pulses to determine the optimum pulse width for the next pulse. The cell excitation circuitry  74  also reverses the polarity of the pulses periodically to prevent build-up of agglomerates on the plates. 
     The cell excitation electronic circuitry  74  may be expected to include a cell excitation signal generator, power switching devices, analogue-to-digital converter, timer, signal multiplexer, and other circuit elements to optimize the cell operation. Such electronics may be implemented in discrete devices such as diodes and transistors, but are preferably digital logic devices capable of manipulating the electronic equivalent of mathematical expressions, as illustrated in FIGS. 13 and 14. The cell excitation circuitry  74  may instead make use of a microprocessor  114  so as to be programmable with external computing devices such as lap-top computers or other serial data transfer systems as illustrated generally in FIGS. 15 and 16. 
     FIGS. 13,  15 ,  16  and  14  provide detailed schematic circuit diagrams (in the case of FIGS. 13 and 14) or functional block diagrams (in the case of FIGS. 15 and 16) of suitable embodiments of the cell excitation circuitry  74 . 
     The preferred embodiment of the circuitry  74  includes a single-polarity power supply comprising a bridge rectifier (not shown) that provides a rectified DC output to the cell  42 . A polarity reversing circuit is provided for periodically reversing the polarity of the current flowing through the cell  42 . Polarity reversal may be accomplished by locating the cell  42  within the “H” pattern of current switching devices shown in FIG. 14 (indicated generally in FIG. 13 by reference numeral  116 ) or as shown in FIG. 16 when a microprocessor based control system such as that shown in FIG. 15 is used. Such devices can be semiconductor switching components such as silicon controlled rectifiers, insulated gate bi-polar transistors or other devices capable of switching large currents, an example of which would be over a wide range of frequencies. The frequency of polarity reversal is best determined empirically and will be expected to depend upon the nature and quantity of the pollutants to be removed from the waste water. 
     In addition to being periodically reversed in polarity, the current supplied to the cell  42  is pulse-width modulated by that portion of the electronic circuitry  74  shown in FIG. 13 or  15 . The pulse width is determined from the conductivity of the waste water and selection of pulse width in turn determines the time-averaged current flow through the cell  42 . The pulse width may range from a few nanoseconds to several seconds, permitting treatment of waste water having a wide range of conductivity to be treated by a single cell configuration and fixed power supply. In an exemplary embodiment to be described below, the range of treatable waste water is from near fresh water conductivity of 50 micro-mhos typical of lake drinking water to concentrated seawater having a conductivity in excess of 100 mmhos. Since the circuitry  74  continuously measures conductivity, the apparatus can treat waste water than varies rapidly in conductivity, e.g., fish processing plant waste water flow which alternates in conductivity from fresh water to salt water conductivity. The circuitry  74  measures in situ the real time conductivity of the waste water flowing through the cell. Such measurement is used to limit the current-supplied to the cell to that level sufficient for the electro-coagulation phenomena to be maximized. Such conductivity-data can be obtained by an external conductivity sensor (not shown) interfaced to the electronic circuitry  74 , or using time division multiplexing the internal electrodes (rods  106 ,  108 ) of the cell  42  can be time-shared for conductivity measurements with the excitation current to provide similar data. Cell current is measured by a current transformer current measuring device, indicated by reference numeral  118  in FIG. 15, to generate an input to the microprocessor  114  so as to regulate the energy consumption of the cell; this same current value data can also be used to calculate the conductivity of the waste water. 
     FIGS. 15 and 16 illustrate generally the use of a microprocessor  114  to implement PWM control. Reference numerals  120 ,  122 ,  124  in FIG. 15 respectively indicate data lines from temperature, conductivity, and turbidity sensors to the microprocessor  114 . FIG. 16 shows a discrete component embodiment of the portion of FIG. 15 outlined in dashed lines, Block  126  in FIG. 15 indicates a function that is carried out by four discrete devices  128 , 130 , 132 ,  134  shown in FIG.  16 . Similarly, the data flow indicated by reference numeral  136  in FIG. 15 represents four signal lines  138 ,  140 ,  142 ,  144  as shown in FIG.  16 . Reference numeral  146  indicates a data line providing current flow data to the microprocessor  114  from the current transformer current measuring device  118  via the operational amplifier  146 . Reference numeral  148  indicates a communication data flow from an external computing device such as lap-top computers or other serial data transfer systems for programming the microprocessor  114 . 
     As discussed previously, the venturi  16  and the orifice plate  28  are selected so that the cell  42  is operated under pressure to provide dissolution of gases within the cell  42 . Gases generated in the cell  42  by electrolysis during the electro-coagulation process will remain in solution until a pressure discontinuity occurs in the form of pressure reduction. Ozone entrained in the waste water via the venturi  16  will be dissolved within the waste water within the cell  42  as long as that waste water is maintained at higher than atmospheric pressure. Ozone is recognized as a strong oxidant and as a coagulant (alternatively hydrogen peroxide, chlorine, bromine, nitro-compounds or other suitable oxidants may be used). 
     The mechanical configuration of the cell  42 , which embodies the preferred characteristics of providing a concentrated electric field through which the waste water is forced under pressure in a turbulent manner, can be replaced by other configurations. As indicated, for example, in the spiral configuration  150  of FIG. 17, the waste water is subjected to centrifugal acceleration that creates a separation of solids as the fluid is acted upon by concentrated electric fields applied between upper plate  152  and lower plate  154  (FIG. 18) that confine the water flowing between the vertical walls  156  of the spiral configuration. Two separate effluent flows are created as the water flows to the centre of the spiral configuration  150  from inlet  158  at its outer extremity; one effluent flow for solids slurry, and the other one for treated liquid. The two effluent flows are separated after they reach the centre by baffle  160  so as to separate the flow of treated water from the flow of treated water to the outlet  162  and solids slurry to outlet  164 . 
     Optionally, an additional contribution to the overall electrochemical reaction within the cell  42  can be provided by a high voltage pulse plasma discharge between the plates  84  that is applied to the cell  42  by the circuit shown outlined in dashed lines in FIG.  19 . Pulsed power discharge into water or water-solid slurries is an electro-hydraulic phenomenon characterized by a periodic rapid release of accumulated electrical energy across a submerged electrode gap. The plates  84  of the cell  42  are time shared under the control of the cell excitation circuitry  74 . In this manner, normal excitation of the plates  84  stops for a short predetermined interval during which a plasma discharge is triggered between the plates  84 . After the plasma discharge is complete, normal excitation resumes. The resulting highly ionized and pressurized plasma transfers energy to the waste water flow via dissociation, excitation, and ionization. The plasma discharge produces high pressure shock waves (&gt;14,000 ATM). Intense cavitation occurs with the associated chemical changes and, further, to separate suspended and dissolved solids from water. The plasma discharge also imparts a cleansing action to the plates and helps to maintain a free electron surface. 
     FIG. 19 illustrates how a plasma discharge has been successfully produced in a test cell  166  having one pair of plates  168  during a short interruption in the normal excitation of the plates  168 . The plasma discharge is produced by a large capacitor bank  170  charged from a suitable power supply input  172  coupled through an inductor  174  to the cell  166 . The voltage across the capacitor bank  170  is not sufficient to cause a plasma discharge between the plates  168  of the cell  166 . The discharge is initiated by a tickler comprising a pulse generator  176  and step-up transformer  178 . The pulse generator  176  is controlled by a signal line  180  under the control of the cell excitation circuitry  74 . The pulse generator  176  applies a trigger pulse to the step-up transformer  178  inducing a high voltage pulse which is applied across the plates  168  to produces a spark across the plates  168 . The spark creates an ionized path through the cell  166 . Once the path is made, the charge stored in the capacitor bank  170  is able to flow along the ionized path. The inductor  174  prevents the spark current from passing through the capacitor bank  170  to ground. 
     In a typical production cell  42  with multiple plates  84 , it is expected that a spark between any adjacent pair of the plates  84  will create a plasma discharge sufficient to cleanse all of the plates  84 , and that therefore it will suffice to apply high voltage pulses to all of the pairs of plates  84  through time-sharing of the same connecting lines  110 , 112  used to supply normal excitation to the plates  84 , despite the likelihood that the spark will jump between only one adjacent pair of plates  84  in any particular discharge. Hence the circuit shown outlined in dashed lines in FIG. 19 may be used with a cell  42  having a multiplicity of plates  84 . However, time-sharing circuitry (not illustrated) is needed to isolate the shock effect of the spark discharge from the excitation voltage. 
     Alternatively, a separate spark gap (not shown) in the vicinity of the plates  84  could also be used. Preferably the separate spark gap should be located near the inlet  20 , where there tends to be some gas (mostly ozone) that facilitates the formation of the spark. 
     Optionally, an additional contribution to the overall electrochemical reaction within the cell  42  can be provided by a magnetic field coil  182  wound about the cell  42  as shown in FIG.  20 . The field coil  182  is repetitively pulsed to create a magnetic field. In the exemplary apparatus of the sort discussed below in the Example, a magnetic field strength in excess of in excess of 10,000 Gauss was obtained using 180 volt pulses. An decrease in the time or number of passes through the cell required to remove impurities from waste water of up to 20% has been observed as a result of this modification. 
     Prior to providing examples of the effectiveness of the arrangements of the invention, reference will be made to FIGS. 21 and 22 illustrating two further alternatives for the cell  42 . 
     In FIG. 21, parts have been removed for clarity and rod  100  (refer to FIG. 9 for background) is rotatably mounted within cell  42  and is rotatable by motor  182 . Motor  182  may be activated by circuitry  74  or otherwise a suitable power source (not shown). The individual plates  84  are mounted on rod  100  and may by rotated in-situ within casing  80 . The rotation of plates  84  assists in maintaining the cleanliness thereof and thus maintains performance of the overall cell. For further enhancement of the oxidation/floccing process, rod  100  may have an auger profile  184  to transport fluid within the cell  42 , and assist in the counter current interaction of dissolved gas and aqueous solution. These concepts have been discussed with respect to FIGS. 1 through 3. 
     FIG. 22 illustrates a similar view of cell  42 , but with the use of beads  72  in place of plates  84 . The beads  72 , will comprise a material similar to those set forth for plates  84 . The beads  72  may range in size from 50 mesh to 1.5″ and this will, of course, depend on the specific requirements of the cell  42 . Current supplied from supply  60  (not shown) is connected to rods  56  and  58  and which interact with electroconductive beads  72 . The provision of the auger rod  184  serves to circulate or refluidize the beads  72  within the cell and as a benefit, the beads are effectively cleansed of debris in the process, thus presenting a fresh reaction surface for the process regularly. This fluidization also promotes a more uniform mass loss of the beads rather than having sections of beads having disproportionate mass relative,to other beads. As an accompanying benefit, this promotes process control. 
     It has been found with the bead or granule version of the apparatus, that the beads provide a high surface area relative to interspatial aqueous volume resulting in equivalent treatment for low feed quantity conductivities. In essence, a significantly lower amperage is required to operate the cell when the beads are used to achieve the same effect provided with large plate type electrodes. 
     Having thus described the invention, reference will now be made to the examples. 
     EXAMPLES 
     An exemplary tested apparatus constructed in accordance with the invention as described above had the following characteristics. 
     For use with the exemplary cell  42  illustrated in FIGS. 9 through 12, the pump  12  was chosen to be capable of pumping gray water or polluted effluent at a rate of 6 gallons per minute at a nominal pressure of 60 psi gauge, the venturi  16  was a model 684 Mazzie Injector, the gas valve  52  was a needle valve, and the ozone source  18  was chosen to provide approximately 4 grams of ozone per hour. The pressure of the waste water in the cell  42  was chosen to be approximately half the pump pressure, in this case 30 psi gauge for a pump outlet pressure of 60 psi gauge. Generally, in designing such cells  18 , a pressure drop across the venturi  16  of about half the pump pressure is satisfactory. A higher pressure in cell can be used to improve the efficiency of the process, but at a higher cost for a larger pump and power to run the pump. 
     In the following description, exact dimensions are provided for the particular cell  42  for which test results are provided below, but it should be understood that the cell  42  may be scaled to any size that the designer deems appropriate. 
     The diameter of the casing  80  is not critical. A 3-inch inside diameter was employed for illustrative purposes in the following discussion. 
     Plates  84  were composed of 0.125″ thick type 6061-T6 aluminum, 2.990″ in diameter. Openings  86  were 1.000″ in diameter, and the centres located at a distance of 0.875″ from the centre of the plate on a discrete one of radial lines  88 ,  90 ,  92 . Opening  96  had a 0.380″ diameter and three 0.265″ diameter rod openings  98  each centred at a distance of 0.875″ from the centre of the plate, the discrete radial line bisecting the radial lines  88 ,  90 ,  92 . 
     The plates  84  were mounted upon a ⅜″ diameter 6.500″ nylon rod  100  threaded at each end for nylon nuts  102 . The plates  84  were equidistantly longitudinally spaced from one another by a set of fifteen 0.500″ diameter Teflon” spacers  104  each having a central opening of 0.375″ and a thickness of 0.250″. 
     The metal rods  106 ,  108  were chosen to be ¼″ in diameter and 14.250″ in length were spaced 1.750″ from one another. 
     The cell excitation circuitry  50  drew power from a three-phase 220 VAC 60 Hz line. The potential between successive plates  84  was chosen relative to the conductivity of the waste water. For high-conductivity waste water, voltages as low as about 30 volts in a cell passing 20 amperes of current would be typical for, say, fish processing plant waste water. This reflects a power dissipation in the cell of about 600 watts, which tends to be a suitable dissipation value for lower conductivity water in 3-inch diameter cells of the size and configuration described above. The plates were energized at a pulse frequency of 600 Hz by pulses of widths varying from 6.5 microseconds to 2 seconds, so as to produce a time-averaged current of 20 to 25 amperes. Larger currents would be possible and desirable (although at higher operating cost) in larger cells, but the current must be limited to prevent overheating in small cells. Polarity reversal of the applied pulses at intervals ranging between 30 seconds and 2 minutes was found to be suitable for the pollutants sought to be removed in the tests. 
     If plasma discharge is used, for average salt water sewage, a discharge voltage of about 4000 V was found to be satisfactory, discharged at 5-second intervals. 
     Test results for use of the exemplary waste water treatment apparatus described above are set out below. “BOD” means BOD over a five day period. 
     Example 1 
     A spot sample of effluent was taken from a large fish processing plant in Killybegs, Ireland. The plant was processing horse mackerel and herring at the time of sampling. The sample was taken after screening and before discharge to the Council sewerage system. 
     Approximately 6 litres of effluent sample was treated using the test unit. The raw and treated effluents were sampled and analyzed. The analytical results are outlined in Table 1. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Treatment Trial on Fish Processing Waste 
               
             
          
           
               
                   
                 Raw Effluent After 
                   
               
               
                   
                 Screening 
                 Treated Effluent 
               
               
                   
                 (Sample 1) 
                 (Sample 2) 
               
               
                   
                   
               
             
          
           
               
                 pH 
                 6.7 
                  7.3 
               
               
                 BOD 5  mg/l 
                 1160 
                 50* 
               
               
                 BOD mg/l 
                 2080 
                 70 
               
               
                 Suspended Solids mg/l 
                 580 
                 23 
               
               
                   
               
               
                 *Calculated from the BOD, COD ratio or Treated Sample 4.  
               
             
          
         
       
     
     The effluent flocculated well during the treatment process, most of the flocculated material coming to the top of the liquid. The BOD of the effluent was reduced by approximately 95% (a significant reduction) with similar reductions in COD and Suspended Solids levels. The pH of the sample rose slightly to 7.3 but this is of no consequence to the discharge. There were three passes through the cell  42  in this test. 
     Example 2 
     A sample of effluent was taken after screening from a second fish processing plant in Killybegs, Ireland. The results of the treatment test are given in Table 2. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Treatment Trial of Fish Processing Waste 
               
             
          
           
               
                   
                 Raw Effluent After 
                 Treated 
               
               
                   
                 Screening 
                 Effluent 
               
               
                   
                 (Sample 3) 
                 (Sample 4) 
               
               
                   
                   
               
             
          
           
               
                   
                 pH 
                 6.6 
                 7.7 
               
               
                   
                 BOD 5  mg/l 
                 2580 
                 104 
               
               
                   
                 BOD mg/l 
                 6400 
                 152 
               
               
                   
                 Suspended Solids mg/l 
                 1560 
                 30 
               
               
                   
                   
               
             
          
         
       
     
     The BOD, COD, and Suspended Solids reductions were all in excess of 95%. The pH of the sample rose to 7.7 after treatment. There were three passes through the cell  42  in this test. 
     Example 3 
     A sample was taken from a third fish processing plant in Killybegs, Ireland after screening. The plant was processing mackerel and a large oil input to the effluent could be expected (up to 20%). Plant management said that in their opinion this activity represented one of the worst possible conditions for effluent strength. The results of the sample are given in Table 3. 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Sample of Mackerel Processing Waste 
               
             
          
           
               
                   
                 Raw Effluent After 
                 Treated 
               
               
                   
                 Screening 
                 Effluent 
               
               
                   
                 (Sample 3) 
                 (Sample 4) 
               
               
                   
                   
               
             
          
           
               
                   
                 pH 
                 6.4 
                 6.85 
               
               
                   
                 BOD 5  mg/l 
                 7400 
                 24 
               
               
                   
                 BOD mg/l 
                 28800 
                 320 
               
               
                   
                 Suspended Solids mg/l 
                 5460 
                 78 
               
               
                   
                   
               
             
          
         
       
     
     The results indicate a BOD, COD and suspended Solids reduction of greater than 95%. There were six passes through the cell  18  in this test. 
     The plates  84  in the apparatus according to the invention have been found to erode very slowly relative to the plates in previously disclosed electro-flocculation cells known in the art. It is believed this is due to a combination of countercurrent dissolved gas and the reduced surface area of the plates  84  as relative to prior plates and the sharp edges of the openings  86 ,  98  in the plates  84  and the sharp edges of the opening in the orifice plate  28 . Such sharp edges localizing electric fields and the optional use of plasma discharge are thought to result in cavitation. Cavitation causes solids to break up, but once broken up the resulting fragments appear to recombine and result in clearer water than before the cavitation. However, cavitation by either the sharp edges of the openings  86 ,  98  in the plates  84  and the opening in the orifice plate  28  or by the optional use of plasma discharge is not essential to the operation of the cell  42 . Back pressure on the cell  42  is essential, so the orifice plate  28  may be replaced by any appropriately sized constriction. 
     In summary, the use of the oxidant in a closed cell or reservoir with the back pressure enhances the availability of small bubbles of oxidant for reaction in the system. This protocol, standing alone, is extremely effective for contaminant separation in an aqueous system. When this protocol is augmented with the electrochemical embodiments discussed, a synergy results providing a highly powerful separation system which has the appeal of being incorporated into further processes as a unit operation. 
     Although embodiments of the invention have been described above, it is not limited thereto and it will be apparent to those skilled in the art that numerous modifications form part of the present invention insofar as they do not depart from the spirit, nature and scope of the claimed and described invention.