WO1990015025A1

WO1990015025A1 - Electrolytic water purification

Info

Publication number: WO1990015025A1
Application number: PCT/US1990/003161
Authority: WO
Inventors: Leland G. Cole
Original assignee: Virontec, Inc.
Priority date: 1989-06-05
Filing date: 1990-06-05
Publication date: 1990-12-13
Also published as: AU5929490A

Abstract

Disclosed is a method for purifying contaminated water containing heavy metal impurities, comprising the steps of directing a flow of the contaminated water through a first electrolytic oxidation chamber (26), comprising a plurality of electrodes arranged parallel with the direction of the flow, wherein the electrodes include at least one cathode, at least one sacrificial iron anode, and at least one sacrificial magnesium anode, and wherein the water passes over and around the electrodes, applying a voltage to the electrodes to electrolytically generate oxidized iron and magnesium irons from the anodes, and to oxidize the heavy metal impurities in the water, rendering the impurities insoluble, wherein the magnesium irons constitute flocculating moieties, permitting a floc to form in water exiting the chamber (100), separating the floc from the water to generate purified water and sludge (110), and directing the sludge into a rotary vacuum filter (118) to generate a sludge cake. The method may also comprise the step of combining the sludge cake with a cementaceous material (120) to form a nonleachable solid. A corresponding apparatus is also disclosed.

Description

ELECTROLYTIC WATER PURIFICATION Background of the Invention The present invention relates to an electrolytic process for removing heavy metals and other impurities from waste water.

Waste water treatment is an area of ever-increasing importance as waterways and ground water become polluted by industrial processes. In the United States, water purity regulations are set at the Federal, State, and local levels.

These regulations typically specify acceptable levels for a wide range of contaminants in water discharged into public sewer systems, into waterways, or discharged in other manners. These regulations are becoming increasingly restrictive. Therefore, water purification measures that have been utilized in the past often are not suitable for meeting the more stringent water purity standards that presently exist or that are likely to be imposed in the future.

Many industrial processes produce water contaminated with hydrocarbons, such as oil and grease residues, suspended solids of a wide variety of origins, and toxic metals, such as cadmium, lead, mercury, arsenic, and the like.

Industrial laundries are one such source of contaminated water. Other industrial operations that create contaminated water include steel processing operations, mining, power stations, chemical factories, electroplating and metal finishing and refinishing operations, manufacturing process, and the like. Industrial laundries and many other polluting facilities are typically located in or near metropolitan areas, and often discharge the waste water into municipal sewer systems or may re-circulate and use the purified water.

It is important that the water so discharged meet the applicable standards of purity. For example, some municipalities reguire that the total oil and grease content of water discharged into municipal sewers be no greater than 100 parts per million (pp ) , and some standards are as low as 20 ppm. Moreover, typical maximum levels for total suspended solids (tss) are 250 ppm, and acceptable levels for heavy metals are often measured in parts per billion (ppb) . One municipality sets the maximum acceptable level of cadmium at 100 ppb, and the maximum acceptable level for lead at 500 ppb. In addition, many industrial processes are heavy users of municipal water. Much of this water is for rinsing operations, where relatively clean water is necessary, but where water need not meet culinary standards. In such operations, it would be advantageous to provide a means for re-using water in order to lower total water costs and conserve water resources.

Some experimental work has been done over the years on electrolytic precipitation of impurities from waste water. Typical of the prior art in this area is U.S. Patent No. 3,933,606 to Harms. This patent discloses a device having perforated plate-shaped anodes and cathodes through which waste water flows. The anodes are made of iron and are sacrificial. The electrolytic reaction generates oxidized iron compounds, which form hydrated hydroxides, which lead to formation of a floe. This floe facilitates the precipitation of impurities in the water. The process also oxidizes metallic impurities in the waste water, forming insoluble hydroxides which are precipitated with the iron floe material. While such processes of the prior art are successful in removing a certain level of impurities, many difficulties remain with such prior art process. First, such iron-anode electrolytic processes reguire large amounts of electricity to form an acceptable level of floe. This, in turn, leads to high electrical costs, and frequent down-time for replacement of the sacrificial anodes. Second, the floe that is formed is fine and is extremely difficult to remove from the waste water. Third, perforated electrodes of the type used by Harms tend to plug up when threads, strings, fibers, and other large particulate are present in the water being treated. Fourth, even when one is successful in separating the flocculated solids from the waste water, those solids themselves present disposal problems. Most landfills will not accept waste that includes leachable heavy metals. Fifth, prior art processes have not reduced waste materials to the levels required under today's more stringent regulations, and have not been effective in removing oil and grease to acceptable levels.

Accordingly, it is an object of the present invention to provide a process and apparatus for purifying waste water that addresses and solves many of the problems of prior art processes and apparatuses.

Summary of the Invention The process• of the present invention can remove all types of suspended matter, including soil, colloidal particles, bacteria, and the like, as well as lead, tin, nickel, cobalt, cadmium, chromium, zinc, mercury, silver, platinum, antimony salts, cyanide complexes, and the like.

Thus, in accordance with one aspect of the present invention, there is provided a method for purifying contaminated water containing heavy metal impurities, comprising the steps of directing a flow of the contaminated water through a first electrolytic oxidation chamber, comprising a plurality of electrodes arranged parallel with the direction of the flow, wherein the electrodes include at least one cathode, and at least one sacrificial floe-forming anode, and wherein the water passes over and around the electrodes, applying a voltage to the electrodes to electrolytically generate oxidized metal ions from the anodes, and to oxidize the heavy metal impurities in the water, rendering the impurities insoluble, wherein the oxidized ions constitute flocculating moieties, permitting a floe to form in water exiting the chamber, separating the floe from the water to generate purified water and sludge, and directing the sludge into a rotary vacuum filter to generate a sludge cake. The preferred sacrificial anodes materials are iron and magnesium, and a combination of the two types of anodes is particularly advantageous. The method may also comprise the step of combining the sludge cake with a cementaceous material to form a nonleachable solid. In one permutation of the method, the contaminated water further contains hydrocarbon materials, and wherein formation of the floe removes the hydrocarbon materials from the water. In another permutation, the voltage is a square wave. In one preferred embodiment, the method further comprises simultaneously directing a portion of the contaminated water into a second electrolytic oxidation chamber, wherein the square wave is created from a steady d.c. voltage by alternately directing the voltage to electrodes in the first and second chambers respectively. The method may further include the step of adding a chemical flocculating agent to the water after the electrolytic oxidation but before formation of the sludge. Additional purification can occur by directing the purified water through a rotary vacuum filter. The method also optionally includes the step of facilitating the formation of the floe by providing ferrous sulfate, calcium hydroxide, and/or by adding a polymeric flocculant to the water.

In another embodiment of the invention, the contaminated water further contains cyanide compounds, and the method oxidizes the cyanide compounds and removes the cyanide compounds in the sludge. Often, the contaminated water contains at least 10 ppm lead and the water from which the sludge has been removed contains no more than 500 ppb lead. Similarly, the contaminated water often contains at least 1 ppm cadmium and the treated water contains no more than 100 ppb cadmium. Further, the contaminated water often contains at least 1500 ppm oil and grease, and often up to 0.5 percent oil and grease and the purified water contains no more than 100 ppm oil and grease. Substantial reductions in total suspended solids are also achieved. Some use of reclaimed water is also contemplated. Thus, where the contaminated water was generated in an industrial process, the method may further comprise the step of directing the purified water back into the industrial process. One such industrial process is a commercial laundry operation where the reclaimed water can be used for wash water make-up.

In addition to the purification method, the present invention also includes a purification apparatus. Thus, it includes an apparatus for purifying water containing heavy metals, comprising a first electrolytic oxidation chamber adapted to accommodate flow of water therethrough and comprising a plurality of elongated electrodes arranged inside the first chamber parallel to the direction of water flow through the first chamber, so that water can flow over and around the electrodes, wherein the electrodes include at least one cathode, and at least one sacrificial anode, wherein the anodes are adapted to generate oxidized species (preferably iron and/or magnesium moieties) in the water when a voltage is applied to the electrodes, to oxidize and flocculate impurities in the water, means for directing contaminated water through the first chamber, means for applying a voltage to the electrodes, means for receiving water from the first chamber and permitting a floe to form, a clarifier for receiving the water containing the floe and separating the floe from the water to form a sludge and purified water, and a rotary vacuum filter for removing water from the sludge and forming a sludge cake.

The apparatus may further include means for combining cementaceous material with the sludge cake to form a nonleachable solid. Also contemplated are means for adding one or more chemical flocculating agents to the water after it leaves the chamber but before formation of the sludge. In one preferred embodiment, the means for applying a voltage to the electrodes is a square wave generator. The apparatus may further comprise a second electrolytic oxidation chamber adapted to function in parallel with the first chamber, wherein the square wave generator generates two square waves of opposite phase from a single d.c. power supply and is adapted to deliver the two square waves, respectively, to the electrodes in the first and second chambers. The apparatus may additionally comprise means for receiving contaminated water from an industrial process, and means for directing the purified water back into the industrial process.

In order to reduce levels of contaminants even further, the apparatus can also include means for directing purified water from the clarifier through the rotary vacuum filter.

Also included within the scope of the present invention is an electrolytic flocculating reactor for treating waste water having entrained solids. This reactor has an elongated chamber containing a plurality of elongated electrodes arranged in parallel. The electrodes include at least one cathode, and at least two anodes, one of which may be iron and the other of which may be magnesium.

Brief Description of the Drawings Figure 1 is a flow diagram schematically setting forth the process and apparatus of the present invention. Figure 2 is an exploded perspective view of the electrolytic reactor of the present invention.

Figure 3 is a schematic diagram of the power supply for the electrolytic reactor.

Figure 4 is a graph of the dual output of the power supply of Figure 3. Detailed Description of the Invention

With reference to Figure 1, the purification apparatus

10 is connected to a waste water reservoir 12 or other source of waste water. The apparatus 10 may optionally include a sand or particulate separator 14 of conventional design for removing larger particulate from the waste water prior to treatment of the waste water. The sand separator removes much of the sand, lint, threads, plant material, and other macroscopic particulate materials, and directs the water into an optional equalization tank 16, where the water is collected prior to being fed into the remainder of the apparatus 10.

It is preferred that the equalization tank 16 be of sufficient volume that process water may be collected in the tank for a period of time even when the purification apparatus 10 is not in operation.

In the purification process per se, waste water is moved out of the equalization tank 16 at a predetermined rate by means of a first pump 20. To the extent necessary, the pH is adjusted by adding either an acid or base into the water leaving the equalization tank 16. In one embodiment of the invention, an acid tank 22 is provided for providing an acid such as εulfuric acid (H2SO4) into the water leaving the equalization tank to maintain the pH of that water within a predetermined range. It is preferred, for example, that the pH of the water entering the process from the equalization tank 16 be between about 7 and 9.5, preferably between about 8 and 9.

While the embodiment of the invention illustrated in Figure 1 is particularly adapted for use in combination with the effluent from an industrial laundry, which has a high pH, it should be understood that a similar apparatus can be used for treatment of waste water having a low pH or a widely varying pH. Where water having a low pH is introduced into the process, the acid tank 22 may be replaced by a base tank (not shown) . Alternatively, both an acid tank and a base tank may be provided. A first valve or metering pump 24 may advantageously be provided to introduce the proper amount of acid (or other pH adjusting material) from the acid tank 22 into the water leaving the equalization tank 16. The first valve 24 is preferably under feedback control to maintain the water entering or leaving the first pump 20 within a predetermined pH range. Thus, the first valve 24 may be a metering valve or a valve in combination with a metering pump.

In an alternative embodiment, the pH adjusting acid or other material may be introduced into the process downstream of the first pump 20, and may be mixed with the ' water entering the process by means of a conventional mixer (not shown) .

The pH-adjusted water leaving the first pump 20 enters one or more electrolytic reactors 26. One preferred embodiment of the electrolytic reactor 26 is illustrated in more detail in Figure 2. In this exploded view, the reactor 26 is illustrated as having an elongated reactor body 30. This reactor body 30 is preferably of cylindrical design, although rectangular and other configurations are also contemplated. Although the reactor body 30 is foreshortened in Figure 2, it will be understood that the length of the reactor body 30 (taken along the axis line 32) is substantially greater than the width or diameter of the reactor body 30 (taken in a direction orthogonal to the axis line 32) . Indeed, the length of the reactor body 30 is preferably at least two times the width, preferably at least three times the width, and more preferably at least four times the width of the reactor body 30. In one particularly preferred embodiment, the length of the reactor body 30 is approximately six times the width thereof. Thus, the reactor body 30 may have a width of about 10 inches and a length of about 60 inches. Of course, the exact dimensions may be varied depending upon the installation, on the amount of water to be treated, and on the number of reactors in use in the process. The reactor 26 may advantageously be provided with an inlet 34, preferably located near the top 36 of the reactor 26, and advantageously located in the reactor body 30 itself. The process water preferably flows downward through the reactor body 30 and out of the outlet 40, which is preferably located in the vicinity of the bottom 42 of the reactor 26. In one preferred embodiment, the bottom 42 of the reactor 26 tapers down to the diameter of the outlet 42. At the top 36 thereof, the reactor 26 is provided with an insulating electrode plate 44 which closes the top of the reactor body 30. The electrode plate 44 supports a plurality of electrodes, which comprise at least one cathode 46 and at least two anodes 50. The cathode 46 and the anodes 50 extend downwardly from the electrode plate 44 into the interior of the reactor body 30. These electrodes are aligned with the axis line 32 of the reactor 26, and are spaced apart from each other.

In one particularly preferred embodiment, there is one cathode 46, preferably located in the center of the reactor body 30 along the axis line 32. This cathode 46 is surrounded by a plurality of anodes 50, which extend downwardly through the . reactor body 30 parallel to the cathode 46. At least some of the anodes 50 are made out of iron, and it is preferred that one or more of the anodes 50 are made of magnesium. In one particular embodiment of the invention, a central cathode 46 is surrounded by at least 4 anodes, preferably at least 6 anodes and more preferably at least 8 anodes, all radially spaced from the cathode 46 and circumferentially spaced from the other anodes 50.

The parallel electrode design of the present invention provides significant advantages in flow through of waste water containing macroscopic materials, such as lint, threads, plant material, and the like. We have found that this design not only provides excellent results from the standpoint of water purification, but also is highly resistant to plugging. The electrode plate 44 includes means for mounting the electrodes. In the illustrated embodiment, an annular anode bus plate 52 is provided on the electrode plate 44, radially spaced from the axis line 32 of the reactor 26. The anode bus plate 52 is in electrical contact with the anodes 50, which are preferably threaded into the anode bus plate 52 or otherwise removably connected thereto. A first connector 54 is provided on the anode bus plate 52 for. allowing connection of the anode bus plate 52 to a source of electricity. The provision of removable anodes 50 facilitates maintenance of the reactor 26 for the inevitable replacement of the sacrificial anodes 50.

In a similar manner, a means is provided for connecting the cathode 46 to a source of electricity. This may advantageously be a second electrical connector 56 on the top of the electrode plate 44 to which a source of electrical current can be connected. In the illustrated embodiment, the first and second electrical connectors 54, 56 may advantageously be adapted for connection to first and second wires 60, 62, respectively. These wires 60, 62 carry power to the electrodes.

In the embodiment where a single central cathode 46 is surrounded by a plurality of anodes 50, in a reactor body 30 having a diameter of about 10 inches, one preferred design has a cathode of approximately 2 inches in diameter, surrounded by about 9 anodes, each having a diameter of about one half inch and spaced radially outward from the axis line 32 of the reactor 26 about 4 inches.

The electrode plate 44 fits down over the top of the reactor body 30 in a water tight manner. The seal between the electrode plate 44 and the reactor body 30 may be facilitated by any appropriate means, such as by an ^■lO" ring 64. Moreover, in order to facilitate lifting of the relatively heavy electrode plate 44 off of the reactor body 30, a lifting bracket 66 may be provided on top of the electrode plate 44 in solid connection therewith. A cover cap 70 may be provided on top of the electrode plate 44 in order to protect the anode bus plate 52, the electrical connectors 54, 56, and the uninsulated ends of the wires 60, 62. The cover cap 70, in one embodiment, is made from PVC material, as is the reactor body 30. The cathode 46 may be made of any relatively non-reactive electrically conductive material, such as stainless steel tubing, nickel plated material, or other suitable material compatible with the process water. In use, contaminated water is introduced into the inlet 34 of the reactor 26, and flows through the reactor 26 and out of the outlet 40. At the same time, a voltage is applied between the electrodes 46, 50 in the reactor 26. While a wide range of voltages may be used, the voltage is preferably in the range of from about 8 volts to about 40 volts, and more preferably from between about 10 volts and about 20 volts. The power supply preferably is capable of providing at least 10 amps, more preferably 15 amps or more to the electrodes. We have used a power supply capable of delivering 50 amps, with good results.

In one preferred embodiment of the invention, the apparatus 10 includes a plurality of reactors 26 arranged in parallel. In this embodiment, a single power supply may be used to power two separate reactors. One suitable power supply configuration is illustrated in Figure 3. In that figure, a current limited, adjustable voltage DC power supply 72 provides a constant output, which is directed to a switch 74 of any suitable design. The switch 74 alternately directs the output from the DC power supply 72 to load 1, indicated by the reference number 26A, or load 2, indicated by the reference number 26B in Figure 3. The switch 74 may be a mechanical switch; however, a solid state switch such as a MOS or CMOS switch is preferred. The switch 74 may be controlled by a signal source 82, which can be a source of alternating current. In one preferred embodiment, the signal source 82 is simply the 50 or 60 hertz line voltage from the electrical utility. Alternatively, conventional timers or triggers may be used as a signal source 82 to control the switch 74.

The outputs of the switch 74 into load 1 and load 2 are graphically represented in the two graphs of Figure 4, in which O± is the output to load 1 and O2 the output to load 2 as a function of time. As can be seen, each output 0*L and O2 receives a square wave output having a 50% duty cycle. Of course, load 1 is one reactor 26 and load 2 is another reactor 26. This power supply configuration permits use of a single power supply 72 to drive two reactors 26 while maintaining a substantially constant load on the power supply 72, conserving power.

The switching frequency of switch 74 is preferably between 1 hertz and 600 hertz, more preferably between about 10 hertz and about 120 hertz. The use of a square wave output of this type is believed to increase the electrolytic efficiency of the reactor 26 and avoid the build up of charge in the vicinity of the electrodes 46, 50. If desired, a means for providing a constant current output to the electrodes 46, 50 may be provided to compensate for varying conductivity of the water being treated. Suitable constant-current power supplies are known in the art and are discussed e.g., in U.S. Patent No. 3,993,606.

It is desireable that the electrical field in the vicinity of the electrodes be on the order of magnitude of at least about 10⁵-10⁶ volts/cm.

With reference again to Figure 1, the contaminated water from the first pump 20 enters one or more reactors 26. In these reactors 26, electrolytic reactions occur that facilitate the removal of a multitude of impurities from the water. A large number of metals are converted to insoluble hydroxide forms. A hydrated ferrous hydroxide or ferric hydroxide is created from the sacrificial iron anodes, forming a floe. At the same time, a very effective floe is formed electrolytically from the magnesium anodes. The use of such magnesium anodes for formation of a floe substantially improves the performance of the electrolytic reactor and facilitates much more complete removal of a wide range of impurities from the waste water. Waste water leaving the reactors 26 may optionally proceed into a high speed mixer 83, where it is intimately combined with additional materials that facilitate floe formation. These materials may include ferrous sulfate, a supplemental floe forming material that is useful for heavy metals and organics, and particularly useful for oil and grease flocculation, as well as a combination of calcium chloride and sodium hydroxide, which together form calcium hydroxide, another effective floe former. The ferrous sulfate may be provided from a ferrous sulfate reservoir 84, the calcium may be provided from a calcium chloride reservoir 86, and the sodium hydroxide may be provided from a sodium hydroxide 90. These reservoirs 84, 86, 90, are provided, respectively, with second, third, and forth metering pumps, 92, 94, 96, respectively. These metering pumps, 92, 94, 96 meter their respective reagents into the mixer 83 at a predetermined rate. For example, we have found that ferrous sulfate, as FeS04'7H20 dissolved in water, may advantageously be provided at the rate of about 500-2000 mg/liter (of the hydrate) , and calcium chloride and sodium hydroxide may advantageously be provided at the rate of 200-500 mg/liter in treating waste water from an industrial laundry. Of course, waste water from other sources may require different levels of these reagents. Appropriate levels for these reagents may readily be determined by empirical measures.

The output of the mixer 83 is directed into a floe tank 100. The floe tank 100 is slowly stirred while the floe particles are permitted to grow. Typically, the residence time of the waste water in the floe tank 100 should be from about 2 to about 20 minutes.

In one preferred embodiment, formation of the floe is further facilitated by the addition of a chemical flocculant of known type from a flocculant reservoir 102 through a fifth metering pump 104 and into the water that has left the reactor 26, preferably into the floe tank 100. Any of a number of conventional flocculating agents may be use, including polymeric flocculant materials. These flocculating materials may be anionic, cationic, or non- ionic, and can be selected based on the particular impurities being removed from the waste water. We have used a nonionic polymeric flocculating agent sold under the trademark PERCOL by Allied Colloids, Suffolk, Virginia with good results at the rate of about 2-10 mg/liter in treating the effluent of an industrial laundry.

After a predetermined residence time, sufficient to permit adequate formation of the floe, the floc-containing waste water is directed into a clarifier 110 to separate the solids from the liquid. The clarifier 110 can be of any conventional design, such as an inclined plate clarifier, an inverted "v" element clarifier, or a conventional clarifier of other design. Suitable inverted "v" clarifiers are manufactured by Eimco Corporation, Salt Lake City, Utah under the trademark DELTA-STAK. Suitable inclined plate clarifiers are manufactured by Great Lakes Environmental Inc., Addison, Illinois, and include model designation IPC- 4-880. The clarifier 110 will typically remove from 90 to 96% of the water from the solids. As solids build up in the clarifier, they are removed by a sixth pump 112 and directed to a sludge tank 114. Periodically, the sludge in the sludge tank 114 is pumped by means by a seventh pump 116 into a rotary vacuum filter 118 of conventional design. We have found that due to the nature of sludge formed by the process of the present invention, the combination of a rotary vacuum filter 118 with the remainder of the purification apparatus 10 provides vastly superior results. The rotary vacuum filter 118 is very resistant to plugging, and rapidly removes water from the sludge to provide a relatively dry filter cake. A typical rotary vacuum filter 118 according to the present invention has a cylindrical drum (which can be made of perforated steel covered with a polypropylene fabric) partially submerged in a filter submergence tank. The drum is coated with a filter aid, which may be diatomaceous earth or other suitable material, such as the filter aids sold under the trademarks HARBORLITE by Harborlite Corp., Escondido, California, and CELITE by Mannsville Sales Corp., Lompoc, California. The filter aid is typically coated onto the drum to a predetermined thickness, such as three inches. The drum rotates slowly through the submergence tank, as a vacuum is applied to the interior of the drum, drawing liquid into the drum and depositing solids on top of the filter aid. The solids that collect on the filter aid are then shaved off of the drum by a doctor blade, which slowly advances toward the drum (e.g., at a rate of about 0.004 to 0.040 inches/minute).

The filter cake removed from the drum of the rotary vacuum filter 118 contains approximately 50% moisture. This filter cake is directed into a blender 120 (such as a plow blender) , where it is combined with a solidifying agent from a hopper 122. The solidifying agent is a cementacious material that solidifies the filter cake.

Suitable cementacious solidifying agents are commercially available. One suitable cementacious material is an organophilic silicate cement available commercially from Silicate Technology Corporation, Scottsdale, Arizona, under the trademarks SOILSORB HM and SOILSORB HC. SOILSORB HM is preferred, but good results are also obtained with SOILSORB HC. These organophilic cements are particularly advantageous when substantial quantities of organic material are present in the filter cake, and they provide a nonleachable solid that can readily be disposed of in landfills. In an alternative embodiment of the present invention, the filter cake may be solidified by combining it with other cementaceous materials, such as Portland cement, or plastic cement. When the cementaceous material is not lipophilic, organic materials are preferably removed from the filter cake by roasting (e.g., heating to a temperature of 500^βF to 900*F) in a suitable incinerator, such as a rotary kiln, prior to the solidifying process.

The water leaving the clarifier 110 and the rotary vacuum filter 118 contains very low levels of metals, oil, grease, and total suspended solids. This purified water can either be directed to a municipal sewer, or in accordance with one aspect of the invention, it can be recycled to the process in which the water is generated. Thus, in a commercial laundry operation, the recycled water can be used, e.g., as makeup water for washing steps.

To the extent necessary, the pH of the purified water can be adjusted by sulfuric acid or other pH adjusting material directed through the first valve 24 into the purified water.

In still another embodiment of the present invention, the water leaving the clarifier 110 is directed through a second valve 124 and into the rotary vacuum filter 118 for further purification. By means of this additional step, we have been able to lower the levels of oil and grease (determined by infrared spectroscopy) from approximately 250 ppm down to <20ppm, total suspended solids have been lowered from 200 ppm down to <20 ppm, cadmium from about 70 ppb down to about 4 ppb, and lead from about 400 ppb down to about 2 ppb.

As can readily be seen, reduction of impurities by an additional order of magnitude is accomplished by this step of routing the clarifier effluent water through the rotary vacuum filter when the rotary vacuum filter is not being used to process sludge. The clarifier effluent can be purified in this manner while the purification apparatus 10 is on line, and the sludge tank 114 can be emptied while the purification apparatus 10 is off line by running the sludge through the rotary vacuum filter 118 during that time. Alternatively, the apparatus 10 can be provided with two rotary vacuum filters, one for clarifier effluent water, and the other for sludge. This would provide continuous on-line operation of the purification apparatus 10. Solids removed by the sand separator 14 can be combined with solidifying agent in the blender 120 for landfill disposal.

The operation of the apparatus 10 of the present invention can be further understood by reference to the following example.

EXAMPLE 1 A waste water purification apparatus 10 was provided having a design capacity of 62.5 gallons per minute and operated at 50 gallons per minute. The pump 20 directed waste water from an industrial laundry at pH 10.5-12.5, adjusted to pH 8-9, through 6 reactors 26, each having a reactor body 30 formed of 10 inch diameter PVC and having a volume of approximately 15.5 gallons each. The residence time of the water in each reactor operating at design capacity is 1.5 minutes, but in this example the residence time in each reactor was approximately 1.9 minutes. Each reactor had one central cathode and nine anodes, five of which were iron and four of which magnesium, arranged radially around the central cathode in a circle of 4 inch radius. The anodes, which were alternately arranged around the cathode, were approximately 1/2 inch in diameter and 48 inches long. The cathode was approximately 2 inches in diameter, was formed of No. 360 stainless steel tube and was approximately 48 inches long. Square wave power was delivered to the reactors at 60 hertz and 15 volts from a 50 amp power supply. The current supplied to each reactor 26 was adjusted to approximately 20 amps.

The electrolytically treated water leaving the 6 reactors 26 entered the mixer 83, where it was combined with FeSO₄-7H20 (1000 mg/liter), calcium chloride (about 300 mg/liter) and sodium hydroxide (about 300 mg/liter) . The mixer 83 had a working capacity of about 26 gallons, and the residence time of the water in the mixer 83 was about 1/2 minute. The mixer 83 was connected to the floe tank 100, which has a volume of approximately 426 gallons. The residence time of the liquid in the floe tank was about 8.5 minutes.

Water leaving the floe tank 100 was directed into an EIMCO/DELTA-STACK clarifier which had a retention time of about 30 minutes. Both the sludge and the effluent water from the clarifier were directed through a rotary vacuum filter. The values of several contaminants in the water entering the process were compared with the values of the water leaving the rotary vacuum filter, with the following results: CONTAMINANT BEFORE AFTER

Oil and Grease 2750 ppm 18 ppm

Suspended Solids 3100 ppm 23 ppm

Cadmium 2000 ppb 4 ppb Lead 11000 ppb 2 ppb

The levels all of these contaminants in the purified water are well below typical Federal, State, and local water purity standards.

Although the present invention has been described in the context of the certain preferred embodiments, it should be recognized that the invention has broad applicability. Accordingly, it is not intended that the scope of the inventions be limited to the particularly disclosed embodiments. Rather, the scope of the invention should be determined by reference to the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method for purifying contaminated water containing heavy metal impurities, comprising the steps of: directing a flow of said contaminated water through a first electrolytic oxidation chamber, comprising a plurality of electrodes arranged parallel with the direction of said flow, wherein said electrodes include at least one cathode, and at least one sacrificial magnesium anode, and wherein said water passes over and around said electrodes; applying a voltage to said electrodes to electrolytically generate oxidized magnesium ions from said anodes, and to oxidize said heavy metal impurities in said water, rendering said impurities insoluble, wherein said magnesium ions constitute flocculating moieties; permitting a floe to form in water exiting said chamber; separating said floe from said water to generate purified water and sludge; and directing said sludge into a rotary vacuum filter to generate a sludge cake.

2. The method of Claim 1, further comprising the step of combining said sludge cake with a cementaeeous material to form a nonleachable solid.

3. The method of Claim 1, wherein said contaminated water further contains hydrocarbon materials, and wherein formation of said floe removes said hydrocarbon materials from said water.

4. The method of Claim 1, wherein said voltage is a square wave.

5. The method of Claim 4, wherein said method further comprises simultaneously directing a portion of said contaminated water into a second electrolytic oxidation chamber, wherein said square wave is created from a steady d.c. voltage by alternately directing said voltage to electrodes in said first and second chambers respectively.

6. The method of Claim 1, further including the step of adding a chemical flocculating agent to said water after said electrolytic oxidation.

7. The method of Claim 1, further comprising the step of directing said purified vater through a rotary vacuum filter.

8. The method of Claim 1, further comprising the step of facilitating the formation of said floe by adding to said water ferrous sulfate.

9. The method of Claim 1 or 8, further comprising the step of facilitating the formation of said floe by providing calcium hydroxide in said water.

10. The method of Claim 1 or 8, further comprising the step of facilitating the formation of said floe by adding a polymeric flocculent to said water.

11. The method of Claim 1, wherein said electrolytic oxidation chamber further comprises at least one sacrificial iron anode, which generates flocculating moieties by electrolytic oxidation of said iron anode.

12. The method of Claim 1, wherein said contaminated water contains at least 10 ppm lead and wherein the water from which said sludge has been removed contains no more than 500 ppb lead.

13. The method of Claim 1, wherein said contaminated water contains at least 1 ppm cadmium and wherein the water from which said sludge has been removed contains no more than 100 ppb cadmium.

14. The method of Claim 1, wherein said contaminated water contains at least 1000 ppm percent oil and grease and wherein the water from which said sludge has been removed contains no more than 100 ppm oil and grease.

15. The method of Claim 1 or 7, wherein said contaminated water was generated in an industrial process, further comprising the step of directing said purified water into said industrial process.

16. An apparatus for purifying water containing heavy metals, comprising: a first electrolytic oxidation chamber adapted to accommodate flow of water therethrough and comprising a plurality of elongated electrodes arranged inside said first chamber parallel to the direction of water flow through said first chamber, so that water can flow over and around said electrodes, wherein said electrodes include at least one cathode, at least one sacrificial floc-generating anode, wherein said anodes are adapted to generate oxidized flocculating moieties in said water when a voltage is applied to said electrodes, to oxidize and flocculate impurities in said water; and means for applying a voltage to said electrodes.

17. The apparatus of Claim 16, further comprising: means for directing contaminated water through said first chamber; means for receiving water from said first chamber and permitting a floe to form; a clarifier for receiving said water containing said floe and separating said floe from said water to form a sludge and purified water; and a rotary vacuum filter for removing water from said sludge and forming a sludge cake.

18. The apparatus of Claim 17, further comprising means for combining cementaeeous material with said sludge cake to form a nonleachable solid.

19. The apparatus of Claim 17, further comprising a means for adding a chemical flocculating agent to said water after it leaves said chamber but before formation of said sludge.

20. The apparatus of Claim 16, wherein said means for applying a voltage to said electrodes is a square wave generator.

21. The apparatus of Claim 20, further comprising a εecond electrolytic oxidation chamber adapted to function in parallel with said first chamber, wherein said square wave generator generates two square waves of opposite phase from a single d.c. power supply and is adapted to deliver said two square waves, respectively, to said electrodes in said first and second chambers.

22. The apparatus of Claim 20, further comprising means for receiving contaminated water from an industrial process, and means for directing said purified water into said industrial process.

23. The apparatus of Claim 20, further comprising means for directing said purified water through said rotary vacuum filter.

24. The apparatus of Claim 16, wherein at least one of said anodes is iron.

25. The apparatus of Claim 16 or 24, wherein at least one of said anodes is magnesium.