Abstract:
A method and apparatus for treating radioactive waste water containing contaminating ions, colloids and suspended solids having like (usually negative) charges preventing their precipitation. An electric current is passed through the waste water in an EC assembly to cause electro-coagulation of the contaminants and anodes of this assembly are made of a metal that dissolves to provide cations for neutralizing the negative charges and forming precipitates containing neutralized contaminants. Precipitates are then separated from waste water by an electro-magnetic or other filtering unit. The water pH and conductivity may be adjusted before the EC assembly and additives may be introduced into its effluent for enlargement of precipitate particles, improvement of filtration, improvement of dewaterability, and/or enhancement of magnetism.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 11/303,065, entitled “Method and System for Treating Radioactive Waste Water,” filed on 14 Dec. 2005, and published as U.S. Patent Application Publication No. 2007/0131621, which is incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The method and apparatus of the invention relate to processing waste water from nuclear power reactors and other sources of water contaminated with radionuclides. In particular, the present method and apparatus are related to processing waste waters contaminated with colloidal, suspended and dissolved radionuclides. 
     BACKGROUND 
     In the commercial nuclear power industry, there are primarily two types of reactor systems, namely boiling water reactors (BWR) and pressurized water reactors (PWRs). Both use water to moderate the speed of neutrons released by the fissioning of fissionable nuclei, and to carry away heat generated by the fissioning process. Water flows through the reactor core, is recycled, and inevitably becomes contaminated with iron, Fe-55, colloidal and soluble cobalt, Co-58, and Co-60, and other radionuclides. The water further becomes contaminated with organics (e.g., oils and greases), biologicals and non-radioactive colloids (e.g., iron rust). 
     In a boiling water reactor (BWR), the water passing through the core will be used directly as steam in driving turbine-generators for the production of electricity. In a pressurized water reactor (PWR), the primary water that flows through the reactor is isolated from the secondary water that flows through the turbine generators by steam generators . In both cases, while the chemical constituents of the waste water will be different, these reactor systems will produce colloidal, suspended and dissolved solids that must be removed before the waste water may be reused or released to the environment. 
     The presence of iron (as iron oxide from carbon steel piping) in Boiling Water Reactor (BWR) circuits and waste waters is a decades old problem. The presence and buildup of this iron in condensate phase separators (CPS) further confounds the problem when the CPS tank is decanted back to the plant. Iron carryover here is unavoidable without further treatment steps. The form of iron in these tanks, which partially settles and may be pumped to a de-waterable high integrity container (HIC), is particularly difficult and time consuming to dewater. The addition of chemicals upstream from the CPS, such as flocculation polymers, to precipitate out the iron only produces an iron form even more difficult to filter and dewater. Such chemically pretreated material contains both sub-micron particles and floc particles of sizes up to 100 microns. It is believed that the sub-micron particles penetrate into filter media, thus plugging the pores and preventing successful filtration of the larger micron particles. 
     Like BWR iron waste waters, fuel pools, or basins, (especially during the decontamination phase) often contain colloids which make clarity and good visibility nearly impossible. Likewise, miscellaneous, often high conductivity, waste steams at various plants contain such colloids as iron, salts (sometimes via seawater intrusion), dirt/clay, surfactants, waxes, chelants, biologicals, oils and the like. Such waste streams are not ideally suited for standard dead-end cartridge filtration or cross-flow filtration via ultrafiltration media (UF) and/or reverse osmosis (RO), even if followed by demineralizers. Filter and bed plugging are almost assured. 
     There are a number of prior art techniques used for removal of colloidal, suspended and dissolved solids, and the requirement to remove such materials from waste waters is not unique to nuclear reactors. However, the nature of nuclear reactors raises special concerns about the use of additives for chemical treatments because of the desire to avoid making radioactive wastes also chemical wastes. 
     There are other concerns as well. The processed waste water must be quite free of radioactive contaminants if it is to be released to the environment. The radioactive material extracted from the waste water during processing must be stable or in a form that can be stabilized for disposal in a way that meets disposal site requirements, particularly with respect to preventing the leaching out of radioactive contaminates by liquid water. Finally, the volume of the waste must be minimized because of both the limited space available for disposal of radioactive waste and the high cost of its disposal. 
     Accordingly there is a need for better ways of processing radioactive waste water containing suspended solids and dissolved ions from nuclear power reactors and other sources. 
     SUMMARY 
     The key to solving the above dilemmas is 1) to break the colloid by neutralizing the outer radius repulsive charges of similar charged colloidal particles, and 2) to cause these neutralized particles to flocculate and form a type of flocculent (floc) that is more readily filterable, and thus de-waterable. In the present invention, these tasks are carried out with the innovative application of an electro-coagulation (EC) unit to electrolytically seed the waste feed stream with a metal of choice, and without prior addition of chemicals common to ferri-floccing or flocculation/coagulation polymer addition. Once the colloid has been broken and floccing has begun, removal of the resultant floc can be carried out by standard backwashable filters, cross-flow filters (e.g., UF), or, in simple cases, dead-end filters. Such applications include low level radioactive waste (LLW) from both PWRs and BWRs, fuel pools, storage basins, salt water collection tanks and the like. 
     For the removal of magnetic materials, such as some BWR suspended irons (e.g., boiler condensates and magnetite and hemagnetite), an electromagnetic filter (EMF) unit may be coupled with the EC unit. For the removal of non-magnetic materials, the EC treatment may be followed by treatment with a flocculating chemical, such as a flocculating polymer like Betz-1138 which is a polyacrylamide copolymer available from the Betz Corporation. For a waste stream containing magnetic materials and one or more non-magnetic species, e.g., cesium (Cs), a magnetic seeding step for coupling the non-magnetic species to a magnetic moiety, e.g., CHFC (Cobalt hexaferricyanate), to form a magnetic chemical complex may be followed by the EMF for the effective removal of this complex. 
     Thus, the invention provides a method, apparatus and system for removing contaminants from radioactive waste waters by using electro-coagulation in combination preferably with magnetic filtration and/or treatment with a flocculation agent. The electro-coagulation may also be used to enhance the subsequent removal of contaminants by dead end filtration, high gradient magnetic filtration (HGMF), ultra-filtration (UF), back flushable filters (BFF), and high integrity containers (HICs) that are dewaterable with sheet filters. The electro-coagulation takes place after adjustments of the pH and the conductivity of the waste water, if needed. Sacrificial metal electrodes, which may be iron but preferably are aluminum, are used in batch or continuous electrolytic processing of the waste water to seed it with positively charged metal ions that neutralize and agglomerate negatively charged ions, suspended particles and colloidal particles. 
     The electro-coagulation (EC) process of the invention works on an electricity-based technology that passes an electric current through radioactive waste waters. Thus, electro-coagulation utilizes electrical direct current (DC) to provide cations from the sacrificial metal electrode ions (e.g., Fe or Al) that agglomerate and thereby precipitate out undesirable contaminates, including dissolved metals and non-metals, e.g., antimony (Sb). The electrical DC current is preferably introduced into the aqueous feed stream via parallel plates constructed of the sacrificial metal of choice. This process avoids the use of undesirable chemical additions (e.g., ferric chloride). 
     Moreover, the anode and cathode will hydrolyze water molecules, liberating oxygen and hydrogen, respectively, as tiny bubbles, the latter combining with many of the dissolved ions in the water to form insoluble oxides. The oxygen and hydrogen also will cause small, light particles to float and flocculate (e.g., oils and greases) so that they can also be skimmed off or filtered out. Some of these lighter particles are biological particles such as bacteria that have been destroyed by electro-osmotic shock. 
     The use of electro-coagulation with radionuclides has several specific advantages in addition to the fact that it will cause the precipitation or flotation of radionuclide species in the waste water. One of these is the oxidation of some species to render them stable in water. The oxidized species are then not toxic hazards and are not likely to be leached into the ground water if buried. They will generally pass the EPA TCLP test, which will result in significant cost savings in disposal. The production of oxygen through hydrolysis also acts as a bactericide and fungicide to further remove wastes other than purely radioactive wastes. 
     In addition to radionuclides, the waste waters may be contaminated by one or more of heavy metals, colloids, clay, dirt, surfactants, cleaners, oils, greases, biologicals, and the like. As these contaminated waste waters are passed through one or more EC cells, the following four treatment reactions occur:
         1. Coagulation—Ions, colloids and suspended solids will remain suspended indefinitely in solution due to their like charges, which are usually negative. Thus, they repel each other and do not allow coagulation or floccing. As contaminated water passes through the cell assembly, DC power is applied continuously, or is pulsed, to the cell electrodes. Metallic ions from the positive cell electrodes (anodes) slough off and provide bridging seeds to the suspended solids and other contaminates present. Only as much electrode seed material is supplied as there are dissolved, colloidal and/or suspended solids present, thus controlling the solids addition. The metallic seed ions cause the charge of suspended or dissolved solids, colloids, oils and greases, and the like, to be neutralized. This charge neutralization causes the contaminants to coagulate, or floc, so that they become large enough to settle or float or be filtered by standard filtration media, ultra-filtration (UF), or reverse osmosis (RO), or, if magnetic, by electro-magnetic filtration (EMF) or High Gradient Magnetic Separation (HGMS) filtration. This coagulation process does not require the addition of chemicals with the exception of those for adjusting the pH or conductivity, if required.   2. Oxidation—As waste water contaminated by heavy and/or radioactive metals is passed through the EC cell(s), the metals are reduced to an oxide. The metal ions are thereby changed from a dissolved state to a suspended state and then are precipitated from the water. Heavy metals that are thus oxidized by passing through the electric current will generally pass a TCLP test, which provides significant savings in the cost of sludge disposal.   3. Aeration—A natural byproduct of this EC process is aeration. No air or any other gases need to be injected into the process, as the dissociation products of water form tiny bubbles giving the coagulated contaminants buoyancy. Thus, after treatment of the waste water, oils and greases therein can either be skimmed off, or re-mixed and settled or filtered with the rest of the coagulated sludge.   4. Biologicals—A further advantage of this EC Process is that it is a natural biocidal process because it ruptures microorganisms and the like by electro-osmotic shock.       

     The magnetic filter may comprise a ferromagnetic filtering medium that is temporarily magnetized when an electro-magnetic field is passed through it via a surrounding coiled electrical conductor. The medium (or media) may comprise steel sheets, screens, beads or balls, the latter being preferred. Upon de-energizing the electro-magnetic field, this filtering medium, which is preferably made of soft magnetic material (e.g. 430 stainless steel), is no longer magnetized to allow the filter to be back-flushed for removal of the coagulated contaminates by flushing them off the filtering media. Thus, the core of the magnetic filter preferably is not made of a permanently magnetizable material but of a soft magnetic material that is electro-magnetizable and then can be demagnetized by simply removing the magnetizing electrical current from the surrounding coil so that the filtering media, preferably 400 series (e.g. 430 S.S.) stainless steel balls, can be backflushed for reuse. The agglomerated particles from the EC unit can also be removed from the waster water by conventional filtration techniques. Furthermore, many of the agglomerated particles may quickly settle out and these may be removed by simply decanting the clarified water. However, the use of an EMF for removal of radioactive precipitates is particularly advantageous because once removed, these waste solids may be easily backflushed to and handled by conventional radioactive waste (radwaste) disposal systems, thereby avoiding the radioactive filter waste generated by mechanical filtering equipment. As used in this specification and the appended claims, the term electromagnetic filtration (EMF) includes high gradient magnetic filtration and other magnetic filtration techniques that magnetically remove ferromagnetic particles or precipitates and that permit the filtered out material to be backflushed to a radwaste system. 
     Another particular feature of the present invention is that radionuclides which are not ferromagnetic, such as cesium-137, can be removed by the addition of a magnetic complexing agent, such as cobalt hexaferricyanate, which forms a magnetic complex with the radionuclides that can be removed by a magnetic filter. 
     Some of the advantages of the invention over conventional processes for chemical coagulation and mechanical filtration include the following:
         (1) Less Waste Volume is created because there is no need for post ion exchange coupled with UF or the like.   (2) Provides consistent introduction of the seeding agent and only as needed, such as Fe or Al, at high throughputs.   (3) Provides improved water quality for those radioisotopes that cannot be taken out by UF or standard filtration.   (4) Provides operational advantages because there is no chemical introduction, no chloride introduction, and no significant pH swings.   (5) Less waste volume is created as compared to using chemical coagulants such as alum or lime, and to using flocculation polymers alone.   (6) The coagulant is significantly easier to dewater than chemical and purely polymer sludges because the electrocoagulated floe tends to contain less bound water, is more shear resistant, and is thus more readily filterable.   (7) The EC process is capable of acting as a biocide for the destruction of biological organisms because electron flooding of the waste water eliminates the polar effect of water complexes allowing colloidal materials to precipitate, and the increase of electrons creates an osmotic pressure that ruptures bacteria, cysts, and viruses.   (8) Metal oxides are formed that will pass TCLP disposal requirements.   (9) The EC process is not adversely effected by oils and greases and these contaminates are removed so that the output may be sent to deadend filtration, BFF, EMF, UF or RO.   (10) The EC process may be utilized without the introduction of chemicals, including polymers.   (11) The process equipment has an extremely small foot print.   (12) EC requires simple equipment and is easy to operate with sufficient operational latitude to handle most problems encountered on running.   (13) Wastewater treated by EC gives clear, colorless and odorless water.   (14) Sludge formed by EC tends to be readily settable and easy to de-water, because it is composed of mainly metallic oxides/hydroxides. Above all, it is a low sludge producing technique.   (15) Flocs formed by EC are similar to chemical floc, except that EC floc tends to be much larger, contains less bound water, is acid-resistant and more stable, and therefore, can be separated faster by filtration.   (16) EC produces effluent with less total dissolved solids (TDS) content as compared with chemical treatments. If this water is reused, the low TDS level contributes to a lower water recovery cost.   (17) The EC process has the advantage of removing the smallest colloidal particles, because the applied electric field readily neutralizes them, thereby facilitating the coagulation.   (18) The EC process avoids uses of chemicals and so there is no problem of neutralizing excess chemicals and no possibility of secondary pollution caused by chemical substances added at high concentration as when chemical coagulation of wastewater is used   (19) The gas bubbles produced during electrolysis can carry certain pollutants to the top of the solution where it can be more easily concentrated, collected and removed (e.g., by skimming).   (20) The electrolytic processes in the EC cell are controlled electrically and with no moving parts, thus requiring less maintenance.   (21) The EC technique can be conveniently used in rural areas where electricity is not available since a solar paned attached to the unit may be sufficient to carry out the process.       

     The sacrificial electrodes are expended by being dissolved into the wastewater stream and eventually need to be replaced. The regularity here depends on the wastewater composition and the volume treated. For nuclear applications, replaceable canisters containing the electrodes would be used. An impermeable oxide film may be formed on the cathode leading to loss of efficiency of the EC unit. However, this does not occur if the unit for the process water is forced into turbulence and this oxide is never allowed to form. Self cleaning by periodic current application, controlled by the computer, will also prevent scaling. 
     Reasonable levels of conductivity of the wastewater suspension is required. This can be compensated for in low conductivity applications by increasing the electrode area, increasing the residence time (e.g., recycle or additional cells in series), increasing the amperage (e.g., jumpering electrodes to place them in parallel), and/or adding innocuous chemicals to increase conductivity and/or pH (e.g., sodium sulfate or sodium bicarbonate or baking soda). 
    
    
     
       DRAWINGS 
       The invention, including its operational steps and the components and systems for carrying out those steps, may be further understood by reference to the detailed description below taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagrammatic illustration of the system of the invention for carrying out its processing of radioactive waster water; 
         FIG. 2  illustrates the electro-coagulation unit of the invention; 
         FIG. 3  illustrates the electromagnetic filtering unit of the invention; 
         FIG. 4  is an exploded view illustrating details of a modified housing and filtering media for the electromagnetic filtering unit of  FIG. 3 ; 
         FIG. 5  is an enlarged view of a portion of the ferro-magnetic filtering media identified by the circle  5  in  FIG. 4 ; 
         FIG. 6  is an exploded view similar to  FIG. 4  showing an alternative embodiment of the ferro-magnetic filtering media; 
         FIG. 7  is an exploded view similar to  FIG. 4  showing a farther alternative embodiment of the ferro-magnetic filtering media; and, 
         FIG. 8  is an exploded view similar to  FIG. 4  showing another alternative embodiment of the ferro-magnetic filtering media. 
     
    
    
     DETAILED DESCRIPTION 
     In the electrocoagalation (EC) unit of the invention, a direct current is applied to a cathode-anode system in order to destabilize any dissolved ionic or electrostatically suspended contaminants. During this electrolytic process, cationic species from the metal of sacrificial anodes dissolve into the water. These positively charged cations neutralize and thereby destabilize negatively charged contaminants and also create metal oxides and hydroxides which precipitate and bring down the neutralized contaminants as part of the precipitate. If aluminum anodes are used, aluminum oxides and hydroxides are formed. If iron anodes are used, iron oxides and hydroxides form. Aluminum anodes are preferred for the present invention because iron anodes become readily coated with iron oxide, which interferes with the electrolytic process. 
     The formation of the metal oxides and hydroxides, and their subsequent precipitation, are similar to the processes which occur during coagulation or flocculation using alum or other chemical coagulants. The difference is that in electrocoagulation, the cations are produced by electrolytic dissolution of the anode metal instead of by adding a chemical coagulant. In addition, the activation energy provided by the application of an electrical current will promote the formation of oxides, instead of hydroxides which may be in a slimy form that may clog filters, if the electrical energy supplied by the unit exceeds the activation energy for formation of the metal oxide. The metal oxides are more stable than the hydroxides and therefore more resistant to breakdown by acids. The dissolved contaminants are incorporated into the molecular structure of these acid resistant precipitates by ion bridging and/or adsorption. Also, the weak intermolecular force known as van der Waalls&#39; force causes these molecules to be attracted to one another and thereby coagulated into a floe. The precipitated floe is often capable of passing the requirements of the TCLP (the EPA&#39;s Toxicity Characteristic Leaking Procedure), which will significantly reduce solid waste disposal costs. 
     In addition, during the electrolytic process, oxygen gas is produced at the anode by the electrolysis of the water molecules. Simultaneous reactions take place at the cathode producing hydrogen gas from the water molecules. These gases can cause the coagulated floe molecules to float, and can also cause flotation and coagulation of oils, greases, and biological materials, such as the residue produced by the rupturing of bacteria and other microorganisms by electro-osmotic shock. The floating floe can be skimmed off for disposal, or it may be subjected to shaking or other turbulence to degas the floc and cause it to settle with the metal precipitates. The coagulation process preferably increases the size of submicron particles to particles as large as 100 microns, preferably to an average size of at least 20 microns so that the precipitate particles are easily removable by a standard 20 or 25 micron filter. 
     Another important cathodic reaction involves the reduction of dissolved metal cations to the elemental state so that they plate out as a metal coating on the cathodes. Since at least some of these metals will be radioactive, the cathodes of the invention must be regenerated in place by reversing their polarity so that the process anodes become regenerating cathodes and the process cathodes become regenerating anodes to thereby unplate the metal coating from the process cathodes, and by providing a fluid flow past the regenerating anodes (i.e., the process cathodes) to carry off the unplated metal cations to a conventional radioactive waste disposal system. 
     Referring now to  FIG. 1 , there is shown a radioactive water treatment system, generally designated  10 , wherein the pH and the conductivity of an influent waste water stream  12  may be adjusted, if needed, in a tank  14 . High pH may be adjusted downward by the introduction of an acid solution (such as sulfuric) from a tank  16 , or low pH may be adjusted upward by the introduction of a base solution (such as sodium hydroxide or sodium bicarbonate) from a tank  18 . To raise the waste water conductivity, an electrolytic solution (such as sodium sulfate or sodium bicarbonate) may be introduced into tank  14  from a tank  20 . The conductivity also may be raised by introducing an iron component, such as magnetite into the adjusting tank  14 , especially where the precipitates in the effluent water from the EC unit  26  are to be subsequently removed by the EMF unit. Some of the isotopes of concern in the waste water to be treated are transition metal activation products, such as Mn-54, Fe-55, Fe-59, Co-58, Co-60 and Zn-65, and their relatively short-lived decay progeny. 
     The acid solution may be transferred to the adjusting tank  14  by a metering pump  17 , the base solution by a metering pump  19 , and the electrolytic solution by a metering pump  21 . When the influent waste water is within the desired pH range from 6 to 8, preferably from 6.5 to 7.5, more preferably about 7.0, and the conductivity is in the range of 2 to 1000 μmhos, preferably at least 5.0 μmhos, more preferably at least 20 μmhos, most preferably in the range of 200 to 800 μmhos (tap water being about 200 μmhos), the adjusted waste water is transferred by a pump  24  to an electro-coagulation (EC) unit  26  having a plurality of sacrificial metal anodes  28  connected in parallel to the positive terminal of a power source  30 , and a plurality of cathodes  29  connected in parallel to the negative terminal of the power source  30 . 
     The waste water fed to the EC unit  26  functions as an electrolyte  34  for carrying a current between the anodes  28  and the cathodes  29 , the amount of this current depending on the conductivity of the waste water and the voltage across the terminals of the power source, which is regulated by a control panel  32 . The amount of current is preferably at least 3 amps, more preferably in the range of 4 to 6 amps. As explained elsewhere, electrolytic reactions and dissolution of the metal of the sacrificial anodes  28  cause coagulation of the dissolved, colloidal and suspended contaminants in the waste water to produce precipitates in the form of floc or sediment. From the EC unit  26 , the thus treated waste water flows to a floc and sediment tank  36 , in which a portion of the precipitants may float as a floe F and a portion of the precipitants may settle out as a sediment S, an intermediate volume between the two being a clarified body of water C. 
     At this point, the floating flow F may be skimmed off, the clarified water C decanted from the sediment S and sent on for further processing if needed, and the sediment S may be transferred to a dewatering container such as a high integrity container (HIC) with sheet filters and thereafter disposed of in conventional fashion. However, in many cases, further processing of the contents of tank  36  may be preferable to provide an effluent water containing even less contaminants that are present in the clarified water C. For further processing, either or both the sediment S and the floe F may be remixed with the clarified water C and the mixture transferred by a pump  38  to a conventional separation device for separating the precipitates from the waste water, such as a high gradient magnetic filtration unit, an ultrafiltration unit, a microfiltration unit, a dewaterable HIC with sheet filters, or preferably a backflushable filter (BFF), all as represented by the box  40  designated as a conventional filter in  FIG. 1 . The filtered precipitates separated from the waste water by conventional filter  40  are then transferred to a conventional radwaste system  42  for disposal. To further enlarge the size of the floc and sediment precipitates and any still suspended precipitates in tank  36 , a flocculation polymer, such as BETZ-1138, may be added to the contents of tank  36  from a supply tank  35  via a metering pump  37 . 
     Preferably the mixture from tank  36  is transferred by pump  38  to an electromagnetic filter (EMF) unit  44  made and operated in accordance with the invention as described below. When the magnetic field of the EMF is activated by applying to its electrical coils  46  a direct current from a power source  48 , the portion of a ferro-magnetic filtering media bed  50  surrounded by the coil  46  is magnetized and thereby rendered capable of magnetically removing from the wastewater any electro-coagulated precipitates containing a ferro-magnetic component, such as iron containing precipitates where the waste water influent  12  comes from a boiling water reactor (BWR). The ferro-magnetic filtering media bed  50  is made up of a plurality of small ferro-magnetic pieces, preferably small stainless steel balls of a soft, or temporary, magnetic material (e.g. 430 S.S.) that may have a smooth or multi-faceted surface (the former being preferred). The balls are stacked in a tubular housing  52  that is made of a non-magnetizable material and passes through the center of electrical coil  46 . The precipitate containing waste water preferably passes downward through the housing  52 , the media bed  50  and the coil  46 . The effluent from the EMF unit  44  may thereafter be sent to a recovered water tank  54  for discharge or recycle. 
     While electric current from the power source  48  is passing through coil  46 , the filtering media bed  50  is magnetized and therefore attracts and accumulates the ferro-magnetic precipitates in the waste water influent from floc tank  36 . When the filtering efficiency of the EMF unit deteriorates to an unacceptable level, electrical current to coil  46  is turned off and the filtering media  50  is backflushed with a flow of uncontaminated water from a pump  56  to remove the now demagnetized precipitates from the filtering media bed  50  and carry them into a dewatering component  58 , which is preferably a HIC with sheet filters or a BFF, but also may be another type of conventional filter. The clarified water recovered from dewatering container  58  may then be sent to the recovered water tank  54  for discharge or recycle. 
     If the effluent from the EC unit as collected in tank  36  contains non-ferro-magnetic species such as cesium (Cs), this species may also be removed by the EMF unit by first adding to the contents of tank  36  a magnetic complexing agent from a magnetic seeding tank  60  via a metering pump  57 . The complexing agent has a ferro-magnetic component. The complexing agent therefore forms a magnetic complex with the non-ferromagnetic species so that the EMF unit may be used for separating the resulting ferro-magnetic complex from the waste water. Where the non-ferromagnetic species is Cs, a preferred complexing agent is as cobalt hexaferricyanate. 
     As previously indicated, the cathodic reaction involves the reduction of dissolved metal cations to the elemental state so that they plate out as a metal coating on the cathodes  29 . Since at least some of these metals will be radioactive, the cathodes  29  must be periodically regenerated in place by reversing their polarity so that the process anodes  28  become regenerating cathodes and the process cathodes  29  become regenerating anodes to reverse the direction of the current flow and thereby unplate the metal coating from the process cathodes. Pump  24  may be used to provide a fluid flow past the regenerating anodes (i.e., the process cathodes) that serves as a regenerating flush  55  to carry off the unplated metal cations to a conventional radioactive waste disposal system, such as radwaste system  42 . 
     The details of a preferred embodiment of the EC unit is shown in  FIG. 2 , wherein the sacrificial anodes  28  are connected in parallel to the positive terminal of the power source  30  via a positive terminal  62  and a connecting wire  63 . The cathodes  29 , which alternate with the sacrificial anodes, are connected in parallel to the negative terminal of the power source  30  via a negative terminal  65  and a connecting wire  66 . The anodes  28  and the cathodes  29  are mounted on a header or cap  69  so as to be suspended within an electrolyte chamber  68  of a housing  70 , which has fluid inlet  71  and a fluid outlet  72 . The fluid flow through the electrolyte chamber  68  is preferably upward in the direction of arrow  73 , and the flow rate may be in the range of 1 liter per minute (lpm) to 200 gallons per minute (gpm), preferably at least 5 gpm per cell. The housing for a typical cell would be about four to six inches in diameter and about three to four feet long, and would contain about three to four anodes and about three to four cathodes. A typical production unit would comprise about 6 to 12 cells in parallel so that the overall flowrate would be preferably about 30 to 60 gpm for a PWR, BWR, fuel pool, or storage basin. Although an upflow in the direction of the arrow  73  is preferred, the waste water being treated may flow through the housing chamber  68  in either direction. Upflow through the EC unit  26  is preferred both for treatment of the waste water and for cleaning in place the electrodes  28  and  29  because the electrodes are preferably mounted and suspended down from the cap  69  such that there is less interference to fluid flow if that flow enters between the plates at their distal ends. 
     The EC unit  26  alone will bring down as a precipitate at least 99 percent of the metal contaminants (whether present as ions, colloids and suspended particles) in the waste water influent stream of 12, so that subsequent filtration, preferably by an EMF unit of the type described, will remove from the radioactive waste water substantially all of the contaminants. Testing of an EC unit similar to that shown in  FIG. 2 , where measurements were made of the metals content of the influent and of the clarified water (supernate) in a settling container receiving the EC unit effluent, has demonstrated the following removal efficiencies: 99.0% to 99.9% for copper, 99.8% for iron, 99.5% for nickel, and 98.7% to 99.9% for zinc. The demonstrated removal efficiency for total suspended solids was 97.9%. 
     A preferred embodiment of the EMF unit is shown in  FIG. 3 , which shows more clearly than  FIG. 1  that the filtering media bed  50  comprises a plurality of small pieces, preferably stainless steel ball bearings  74 , and that the longitudinal centerline of the media housing  52  is preferably aligned with the central axis of the electrical coil  46  surrounding the housing  52 . Ball bearings with smooth round surfaces are preferable for use in the packed bed  50  because such a packed bed has a large void volume, which allows a high loading of ferro-magnetic precipitates. The coil  52  is made up of a continuous electrical conductor  76  that is coiled around a spool  77 . The respective ends of the conductor  76  are connected to the direct current power source  48  via electrical connectors  78  and  79  and their corresponding connector wires. The EMF unit includes a support screen  80  of a mesh size large enough to provide free liquid flow but small enough to prevent passage of the filter media balls  74 . Thus, screen  80  supports the filter media above the outlet  82  of the housing  52 . The unit  44  is connected to the outlet of pump  38  by a conduit  84  and to the recovered water tank  54  by a conduit  87 , which may also include a valve  86  for controlling the rate of fluid flow through the filtering media  50 . The direction of fluid flow through the filtering media bed  50  is preferably downward as illustrated by the arrows  83  and  85  so as to facilitate a subsequent upward backwashing flow that is more effective than a downward flow for removing accumulated precipitates because the heavier crud accumulates at and near where flow enters the bed, and support screen  80  would interfere with using a downward flow to dislodge this crud. However, the EMF unit is also effective for the removal of ferro-magnetic precipitates irrespective of the direction of flow of the waste water being treated or of the backflush water. The rate of fluid flow through the EMF housing  52  may be in the range of 1 lpm to 200 gpm, depending on the overall flow rate through the production EC unit, such that the production EMF unit flow would preferably also be in the range of 30 to 60 gpm. 
     In  FIG. 4 , there is shown a modified EMF housing  52 ′ having an end cap  90  at each end for retaining the filtering media within the housing and for connecting the housing to the influent and effluent conduits. Each housing end cap contains a wall  91  for supporting the filtering media and through which passes a flow tube  92  containing a screening member  93  for preventing passage of the individual pieces of the filtering media. Also shown is a modified filtering media comprised of multifaceted 430 stainless steel balls  74 ′, the facets of which are shown more clearly in  FIG. 5 . 
     In  FIG. 6 , there is shown an alternative modification of the EMF unit wherein the filtering media is a 430 stainless steel screen  94  with a 10 micron mesh size, the punched out or woven screen apertures  95  of which are shown more clearly in  FIG. 7 . In  FIG. 8 , there is shown a further alternative embodiment of the EMF unit wherein the filtering media comprises one or more tubular sheets  97  of 430 stainless steel. 
     The preferred parameters for electrolytic coagulation of ions and colloids and other solids suspended in radioactive waste water are: adjust waste water pH into range of 5.5 to 8.0, preferably 7.0-8.0, by adding if needed sodium hydroxide or bicarbonate of soda, adjust resistivity to 5 μmhos per centimeter or greater, preferably 20 to 30 μmhos per centimeter (micro-siemens per centimeter, i.e., μmhos are the reciprocal of μohms and may also be referred to as micro-siemens) by adding if need sodium sulfate or sodium bicarbonate, and then apply 4 to 6, preferably 5, amps of direct current (DC) at 23-24 volts. The coagulated floc produced by these parameters can be removed by a 20 to 25 micron filter. Waste water with resistivity of less than 5 μmhos may be adjusted into the desired range by the addition of sodium sulfate or bicarbonate of soda. 
     The effectiveness of electro-coagulation (EC) may be increased by providing greater electrode contact time by lowering the flow rate or recycling the flow, by increasing the electrode area immersed in the electrolyte, by increasing the current density between the anodes and cathodes, such as by jumpering electrodes of the same type where they are connected in series between the positive and negative terminals (thereby connecting them in parallel), and by raising the conductivity by adding sodium sulfate or bicarbonate of soda. 
     Because radioactive metals will plate out on the cathode of the electro-coagulation apparatus, it is preferable that these electrodes be cleaned of the deposited metals while remaining in place, instead of being removed for cleaning in a decontamination facility. Such cleaning in place is preferably accomplished by a temporary current reversal during which the EC anode becomes a cathode and the EC cathode becomes an anode to accomplish electro-cleaning. This current reversal causes the plated metals to be redissolved into a waste liquor which is then back flushed to a conventional radioactive disposal system. 
     The preferred parameters for the magnetic filter is to apply 10 amps of direct current at 36 volts to the conductor coils surrounding the core of stainless steel ball bearings  74 , each preferably having a diameter of about 0.2-0.5 centimeters (cm), more preferably 7/32 inch diameter balls. The stainless steel balls used should serve as a soft magnetic core that does not stay magnetized in the absence of direct current through the surrounding coils. If a hard magnetic core is used, an alternating current must subsequently be applied to the coil to “demagnetize” the hard metal core that would otherwise retain its magnetism. 
     Since the floc in BWR waster water contains iron, it is magnetic and can be separated from the waste water by the electromagnetic filter. If the amount of ferromagnetic material in the waste water is low, the effectiveness of electromagnetic filtering (EMF) may be enhanced by the addition of magnetite as a seeding agent to the wastewater before it is subjected to electro-coagulation. If the clarified water leaving the combined EC-EMF system has a conductivity that is too high for disposal, reuse or recycle, the conductivity may be lowered by passing the clarified water through an ion exchange system. 
     The following is an example of the operation of the system of  FIG. 1  for the treatment of radioactive waste water containing contaminants in the form of a solution or slurry comprising ions, colloidal particles and suspended solids. The slurry is fed to the adjusting tank  14 , wherein its pH is adjusted from 5.5 to 7 by the addition of sodium hydroxide (or sodium bicarbonate, which adjusts both pH and conductivity) and its conductivity is adjusted from about 2 μmhos to about 100 μmhos by the addition of a saturated sodium sulfate solution or a sodium bicarbonate solution. The lower conductivity would have resulted in negligible current flow between the EC electrodes, whereas the higher conductivity will provide a current of about 4-5 amps. The adjusted influent from the adjusting tank  14  is fed to the EC unit  26  at a flow rate, and the power supply  30  is operated at a voltage, sufficient to apply a current of 1-amp-minute through the waste water as it flows through the EC unit on its way to the floc tank  36 . In the floe tank  36 , sufficient Betz-1138 could be added to provide about 4-10 parts per million (ppm) of this flocculation polymer, which serves to make the sediment S and the floe F in tank  36  significantly larger. However, the EC unit alone is more readily dewaterable due to having less bound water, higher sheer strength, etc. 
     The thus treated waste water is then conveyed by pump  38  through the EMF unit  44  where this waste water passes through a packed bed of ball bearings made of 430 stainless steel and having smooth surfaces (as most preferred). A current of 7.5 amps is applied to the coils during passage of the waste water through the electromagnetic field generated thereby. The flow rate of this water through the housing  52 , and the axial length of the coil  46 , are such that the residence time of the waste water within the magnetic field is about 2.5 seconds. The effectiveness of this treatment is evident by the visual clarity (clear and colorless) of the EMF effluent delivered to the recovered water tank  54 , as compared with the densely clouded (opaque) suspension of red/brown precipitates of the stirred contents of floe tank  36  as it is fed to the pump  38 . This treated water also has no detectable non-volatile radioactivity (there could still be some volatile tritium gas). 
     Thereafter, the EMF unit is cleaned by turning off the current and providing a liquid flow reversal through the packed ball core by activating pump  56  to flush away the accumulated floc and convey this floc to a dewatering container  58 , such as a high integrity container (HIC), or some other conventional disposal system for handling radioactive sludges. The deposited settlement from this cleaning liquid will usually meet the EPA&#39;s TCLP requirements for disposal, and therefore may usually be sealed in the HIC and shipped to a low level waste site for disposal. 
     It will be apparent to one of ordinary skill in the art of waste treatment that many other modifications and substitutions may be made to the preferred embodiments described above without departing from the spirit and scope of the present invention as defined by the claims set forth below.