REMOVAL OF PHOSPHORUS FROM SEWAGE BY ELECTRODE METAL ADDITION

Abstract

In an apparatus for treating wastewater, e.g sewage water, the water passes through a standard treatment process stream to promote production of dissolved reactive phosphate ions (PO4). Iron (or aluminum) ions are generated by electrochemical means and added to the process stream at one or more locations to produce metal-P coagulant solids removed in part by pump-out, with the substantial remaining P removed by mineralization and filtration in a biological filter such as a sand filter or leach field. In another apparatus, the water passes through a standard aerobic treatment process stream to promote production of dissolved reactive phosphate ions. Iron (or aluminum) ions are generated by electrochemical means and added to the process stream at one or more locations to produce a flocculant of Fe—P minerals that are separated out by sedimentation, physical filtration or magnetic means.

Claims

1. A process for removing phosphorus from sewage waste water in a waste water treatment system comprising: (a) flowing sewage waste water to be treated through an anaerobic station from an anaerobic station inlet to an anaerobic station treated water outlet, the anaerobic station comprising a volume which, in use, has a clear zone through which the sewage waste water flows to the anaerobic station treated water outlet, the waste water comprising phosphate ions; (b) conducting electrolysis in the waste water in the clear zone to provide metal ions to the waste water whereby the metal ions and the phosphate ions present in the waste water combine to form a metal-phosphate mineral; and, (c) passing the sewage waste water through a biological filtration station positioned downstream of the anaerobic station and removing metal-phosphate compounds from the sewage waste water.

2. The process of claim 1, further comprising selecting the metal ions from at least one of aluminum ions and iron ions.

3. The process of claim 1, wherein the biological filtration station is comprised of peat, soil leach field, textile, filter sand, pea-gravel or plastic foam media.

4. The process of claim 1, further comprising selecting iron ions as the metal ions.

5. The process of claim 1, further comprising selecting ferrous iron ions as the metal ions.

6. The process of claim 1, further comprising filtering the waste water downstream of the anaerobic station.

7. The process of claim 1, further comprising conducting the electrolysis proximate the anaerobic station treated water outlet.

8. The process of claim 1, further comprising conducting the electrolysis towards a downstream end of the anaerobic station.

9. The process of claim 1, wherein the metal-phosphate mineral comprises non-flocculent microscopic mineral particles.

10. The process of claim 9, wherein the non-flocculent microscopic mineral particles form solid phosphate minerals and the process further comprises forming more than half of the solid phosphate minerals downstream of the anaerobic station.

11. The process of claim 1, wherein metal which produces the metal ions in the clear zone is introduced separately from the waste water into the anaerobic station.

12. The process of claim 10, wherein metal which produces the metal ions in the clear zone is introduced upstream of an electrolysis zone in which electrolysis occurs.

13. The process of claim 10, wherein the metal ions are periodically introduced into the anaerobic station.

14. The process of claim 1, wherein the anaerobic station comprises a septic tank and the process further comprises conducting the electrolysis in the waste water in the septic tank and removing waste water containing metal ions and/or metal-phosphate mineral from the septic tank.

15. The process of claim 1 wherein the anaerobic station comprises a septic tank and the process further comprises passing the sewage waste water a single time through the septic tank.

16. A process for retrofitting a septic tank comprising installing an electrolysis cell in a septic tank and towards a downstream end of the septic tank.

17. The process of claim 16, wherein the septic tank comprises a volume which, in use, has a clear zone through which sewage waste water flows to a septic tank treated water outlet, and wherein the process further comprises installing the electrolysis cell such that water in the clear zone flows between electrodes of the electrolysis cell.

18. The process of claim 16, further comprising connecting the septic tank to a source of metal that under electrolysis produces metal ions.

19. The process of claim 18, further comprising providing a connection for the source of metal is separate from a waste water septic tank inlet.

20. The process of claim 19, further comprising providing the connection for the source of metal upstream of an electrolysis zone in which electrolysis occurs.

21. The process of claim 16 wherein the process further comprises retrofitting a single pass septic tank.

Description

LIST OF DRAWINGS

[0065] FIG. 1 shows a simple small wastewater-treatment-station, in which the wastewater passes through a septic-tank and then into a combined aerobic leach-field and infiltration soakaway. The electrolysis-facility is placed outside the wastewater-treatment-station.

[0066] FIG. 1A is the same view as FIG. 1, but shows the components of the wastewater-treatment-station without the electrolysis-facility.

[0067] FIG. 1B is the same view as FIG. 1, but shows the components of the electrolysis-facility without the wastewater-treatment-station.

[0068] FIG. 2 shows the electrolysis-facility located in the septic-tank.

[0069] FIG. 3 shows the electrolysis-facility located in a pump tank (recirculation tank), downstream of the septic-tank.

[0070] Where access to an existing treatment system is difficult or when contact with potable water only is preferred, the electrodes can be placed above grade or inside an adjacent building in a flooded pipe or tank. The generated iron or aluminum ions are flushed periodically into the treatment unit inlet area using a timed valve release or other suitable means that will preferably direct flow past the electrodes and be energetic enough to remove solids from the electrode chamber. This scenario is depicted in FIG. 1.

[0071] Iron-based electrodes are immersed in water or wastewater and connected to a DC current power supply and a controller. There is generally no requirement for pumping or piping when the electrodes are immersed in the wastewater. When immersed in a container of water outside of the treatment system, a mechanism such as a timed valve flushes the contents into a sewer or to the treatment system.

[0072] The power supply can be a commercially available unit, a series of batteries, an AC-DC converter, or solar panels that provide DC current in the required voltage for the electrode size and dissolution requirements.

[0073] The power through the electrodes is controlled so that the electrode material is consumed evenly for longevity and so that mineral scale build-up precipitated from the water is minimized. The controller may be designed to shut off power to the electrodes when no sewage flow is detected for a period of 3-4 days or more, and then turn on when flow resumes, similar to a demand-controlled water softener appliance. Otherwise, the system can be designed to operate on a dedicated basis like a timed-operation water softener.

[0074] The electrode size and configuration is designed according to the volume of wastewater to treat and the concentration of TP expected in the wastewater. With a control mechanism, they are sized to last a year or more at residential sites without replacement, and 3-6 months or more at larger facilities where maintenance visits can be more frequent.

[0075] Ferrous ions enter the water or wastewater directly and are oxidized to the ferric state by bubbling air diffusers (active submerged aeration). Depending on the treatment system design, the iron can be added at various points, but typically only one point is necessary for phosphorus removal, provided it allows thorough intermingling of iron and phosphate ions. Treatment scenarios suitable for smaller flows are described below, but the invention is not restricted to these described configurations, nor is it restricted to small flows.

[0076] In FIG. 1, wastewater from a house 20 passes through a wastewater-treatment-station. A sewer 21 conveys the water to an in-ground septic-tank 23. Here, heavy solids in the sewage settle on the floor of the tank, and light solids form a scum on the surface. From the septic tank 23, the water is pumped into a biofilter 25, where the water is aerated by trickling down through the biofilter medium, which removes or lowers BOD, and nitrification occurs. The biofilter may be constructed from a variety of materials, including soil, sand, pea gravel, open-cell foam, peat, textiles, or the like. From the biofilter, the water passes to an infiltration-station 27, which includes a soakaway of sand or gravel, to take kinetic energy out of the discharged water, thereby enabling the treated water to enter the ground distributed evenly over the ground.

[0077] To this existing conventional wastewater-treatment-station is added a phosphorus removal facility. An electrolysis-facility is arranged to drive iron into solution in the wastewater. The electrolysis-facility includes an electrolytic-cell 29, comprising a pair of electrodes 30 (or, usually, more than one pair), and a source of DC electricity which in this case is a solar panel 32. A controller 34 feeds the electricity into the anode 30A and cathode 30C, and is set to automatically maintain constant current-density in the current-surfaces of the electrodes 30 and to handle the once-a-day reversals of voltage and current.

[0078] The controller 34 also controls an (optional) powered pump for moving the cell-water through the cell 29. The generated iron ions are flushed periodically into the water-distributor using a timed valve release, by natural gravity flow of the sewage through the wastewater-treatment-station, or by other suitable means that will preferably direct flow past the electrodes energetically enough to help remove, solids from the electrodes and from the container.

[0079] The electrodes 30 are of hot-rolled mild-steel. From the current-surfaces of the electrodes, all oxide and other coatings have been removed by grinding or other methods.

[0080] The cell includes a container 36, having an inlet 38 and an outlet 39 for conveying water through the cell. The electrodes are supported on a frame inside the container 36, the frame being arranged to hold the electrodes 30 in the desired spaced-apart relationship.

[0081] Cell-water is supplied to the inlet 38, in this case, from a rain-barrel 43. The outlet conveys the iron-laden cell-water to a cell-water-distributor 45, which feeds cell-water to selected locations in the wastewater-treatment-station. As shown, the iron-laden cell-water is fed through pipes to the sewer 22, to the septic tank 23, to the biofilter 25, and to the conduit through which water is conveyed to the infiltration station 27. In fact, it would be usual to send the cell-water to just one location of the wastewater-treatment-station, but the cell-water can easily be sent to the multiple locations if desired. The pipework to move the cell-water is very simple.

[0082] The cell-water mixes with the wastewater at the various mixing-points (or single mixing-point). As a result, the iron-ions and the phosphate-ions are brought together, and the transformation to the solid mineral can now start to take place. Once the waters have been mixed, of course they remain mixed for the remainder of the journey through the wastewater-treatment-station, enabling continuing on-going transformations.

[0083] As will be understood, the electrolysis-facility is inexpensive and can be sold as a factory-manufactured product, which can be added or incorporated into the existing wastewater-treatment-station very simply. Coupling up the electrical conductors and the water conduits is also very simple. No excavation is necessary, for installation, and very little physical access to the components and treatment stations of the wastewater-treatment-station is required.

[0084] In FIG. 2, the cell 50 is not housed in its own container, but rather the cell is placed within the wastewater-treatment-station itself, in this case in the septic tank 23.

[0085] The septic-tank can be an advantageous place to locate the electrodes. It is often very convenient and simple to provide a cell-unit that can be physically lowered into and placed inside the septic-tank.

[0086] Thus placed, the iron ions start to combine with the phosphate ions actually in the septic-tank. The solid iron-phosphate minerals come out of solution in the septic tank, and a portion of the minerals accumulates in the scum and sludge in the septic tank. The minerals are removed when the septic tank is cleaned out, during regular servicing.

[0087] Accumulating the solid minerals in the septic tank may be compared with what happens in known electro-coagulation and electro-flocculation processes—in which the phosphate is removed from solution, and is placed in the septic-tank.

[0088] In the known electro-coagulation and flocculation processes, which use strong electric fields and electrically-induced oxidation and reduction reactions, the phosphorus is removed from the wastewater by flocculation and agglomeration of suspended solids to make a sludge, and then by physical separation of this sludge. The phosphorus still remains as a pollutant in the sludge. In the known processes, the sludge must be removed periodically and the phosphorus therein still remains to be treated, again, at another treatment facility.

[0089] In the present technology, the low energy input (just enough to dissolve the iron at an adequate rate) means that the phosphorus collected as sludge in the septic tank solids is minimized, and also the coagulation and agglomeration of solids is minimized. Thus, most of the sewage phosphorus is mineralized, not in the septic tank, but in the treatment stations of the wastewater-treatment-station downstream of the septic tank, e.g in the biofilter. The iron-phosphate minerals precipitate as a fine coating on e.g the biofilter medium material. The phosphorus is thereby permanently and safely removed from the wastewater. The present technology departs from the known practices of flocculating the metal and phosphorus as sludge, of separating, storing, collecting, managing, the sludge, and having to incur the additional cost of treatment at the sludge management facility.

[0090] In the present technology also, when the electrodes are placed in the septic-tank, the water leaving the septic-tank contains the reacted iron-phosphate molecules predominantly as non-flocculent microscopic mineral particles. A portion of the untreated iron-ions and phosphate-ions will be present, and as that mixed-iron-phosphorus-water passes out of the septic tank, and passes downstream through the subsequent stations of the wastewater-treatment-station, the ions have ample opportunity to continue to combine, and to precipitate out as e.g stable mineral coatings on available surfaces. The ions also can continue to combine as the water passes through the infiltration station, and into the ground.

[0091] Typically, in the present technology, in FIG. 2, more than half of the overall transformation of the dissolved or microscopic particulate phosphate into solid phosphate mineralization takes place after the water leaves the septic-tank. Thus, in FIG. 2, where the electrodes are placed in the septic tank, the amount of phosphorus that accumulates in the septic-tank is much smaller than the amount of phosphorus that accumulates in the septic-tank in the known electro-coagulation and electro-flocculation systems.

[0092] When the cell-unit 50 is located in the septic tank, it can be placed towards the downstream end of the tank, just before the water leaves the tank, or (as shown) towards the entry end. Using the present technology, a proportion of the phosphorus will be mineralized actually within the septic-tank and will settle into the sludge on the floor of the septic-tank. The rest of the phosphorus will be present (with the dissolved iron) in the water flowing out of the septic-tank, and through the subsequent treatment stations, and out, through the discharge-station, into the ground, or into a stream, etc.

[0093] The mineralization of the phosphorus continues as the water makes its way along its flow-path through the wastewater-treatment station. By placing the cell-unit 50 at the entry end of the septic tank, the systems designers can maximize the percentage of phosphorus that remains (in solid mineral form) in the septic-tank; by placing the cell-unit at the downstream end, the proportion of the phosphorus that precipitates in the downstream treatment stations can be maximized.

[0094] In FIG. 2, the cell-unit 50 includes an insulative frame for supporting the electrodes, now in the form of a support-cage. The support-cage 52 mounts the electrodes 30A,30C in a parallel spaced-apart relationship, and electrically insulated from each other. The support-cage 52 is of open construction, to allow water to pass over and between the electrodes.

[0095] The cell-unit 50 includes electrical connections, by which the electrodes can be connected to the electrical control panel 34 of the electrolysis-facility, and thereby to the electrical source.

[0096] As a coordinated whole structure, the cell-unit 50 has the capability to be picked up and handled as a unit, to be inserted into the wastewater-treatment-station at a point along the flow-path, to be connected electrically to the controller, and to be mounted in and left in the wastewater-treatment-station for an operational period of at least several months.

[0097] In the inlet area of a septic-tank, 50% to 80% of the total phosphorus can be in the form of soluble phosphate ions available for reaction with iron ions. At the downstream effluent end, the proportion can rise to 70% to 80%. After aerobic filtration treatment, this ratio can be expected to rise to 90% or more. Transformations to both ferrous and ferric iron-phosphate minerals can take place, and both minerals are stable and safe.

[0098] The electrodes should be submerged in the middle “clear” zone of the septic-tank, to avoid sludge and scum, and along the flow-path of the sewage to disperse the iron and promote reaction between iron and phosphate ions. The strength of the electromagnetic field set up around the electrodes is insignificant so that corrosion of concrete or reinforcing steel in a tank is not a concern.

[0099] The septic tank inlet area provides the benefit of longer residence time and potentially more retention of Fe—P mineral suspended solids in scum or sludge, but care must be taken to keep e.g., toilet paper from accumulating on the electrodes in the inlet area. 50% to 60% of total-phosphorus may be retained in the septic tank by coagulation, flocculation, and solids separation, lowering the P-loading on subsequent treatment components such as biological filters or leach fields, or where allowed lowering the P-loading to surface water bodies. The P is retained as low-solubility minerals in the solids, as in Fe.sub.3(PO.sub.4).sub.2, and removed from the site when the septic tank has its regular pump-out maintenance. The electrodes are preferably placed where water flows past them, e.g under the influent pipe.

[0100] Placing the electrodes in the outlet location lowers the residence time for reactions to take place, and will have less TP retained in the tank. However, it has the advantage of the electrodes being in clearer water with fewer potential operational problems. The septic tank must be periodically pumped out to remove its proportion of the entrained P-rich coagulant solids, but the frequency of pump-outs will not be increased with the very low volume of sludge created by the addition of iron ions to the system.

[0101] The following reports an actual test. A standard single-pass sand filter, constructed of 100% C-33 type medium grained sand, but with no easy-dissolve electrode, removed only 20-25% of the TP from the sewage after septic tank and after e.g a metre of filtration.

[0102] In a second test, a soil filtration system constructed of 60% C-33 sand and 40% silt loam might be expected to remove TP to a level of about 0.2-0.5 mg/L within 15-30 cm depth, by itself, at least for an unknown period of time. Adding an easy-dissolve iron electrode system to the inlet end of the septic tank enabled 15 cm of the 60-40 mix to lower TP to a level of 0.2 mg/L within 60 days of operation, steadily increasing the removal rate to 0.05 mg/L TP within 8-9 months.

[0103] In this second test, the septic tank effluent removed about 30% TP in the first five months, then about zero percent in the second five months. The initial good removal in the septic tank, during start-up of the electrode system, was followed by a fall-off, likely due in part to the lack of scum in the tank during the later period. This minimal removal in the septic tank (with effluent median values of total phosphorus of 6.0. mg/liter and total iron of 8.2. mg/L) suggests that phosphorus does not necessarily have to concentrate in the septic tank to undesirable levels (in contrast to what happens in the known electro-coagulation technologies, using the septic tank to store the phosphorus-rich sludge). Almost all of the phosphorus was removed in the soil filter as insoluble mineral coatings, with no need for further treatment or disposal.

[0104] Over the on-going 10-month study, median TP values of the 12″, 24″ and 36″ pan lysimeter effluents were 0.09, 0.04, and 0.02 mg/L, removal rates of 99% or more. Total iron values in the soil effluents were 0.4-0.8 mg/L similar to the 0.9 mg/L median value of the raw sewage, and down from the 8.2 mg/L in the septic tank effluent following the easy-dissolve iron electrodes.

[0105] These studies indicate that dissolution of iron into septic tank effluent or into partially treated effluent increases the removal rate of phosphorus substantially over standard sand and soil filtration systems. The process is precipitation of iron-phosphorus mineral coatings on the sand or soil filtration medium, removing it from the water permanently. Sludge production and sludge management to concentrate and relocate the phosphorus is not required. Nor is re-treatment.

[0106] Studies using synthetic plastic foam medium in the biofilter section show a similar removal rate of phosphorus. In a third test, on a retrofitted school sewage system, the median value of the treated effluent was 0.4 mg/L TP, down from 7.1 mg/L in the raw sewage for a 94% removal rate. The final effluent contained 0.4 mg/L Fe, same as the 0.4.mg/L in the influent sewage, and down from 8.8 mg/L in the septic tank effluent following the easy-dissolve iron electrodes. Reddish coloration in the foam biofilter, without sludge accumulation, indicates iron-phosphate mineral precipitation process is active. The pH of the treated effluent was 7.2, similar to the raw sewage value of 7.3. The septic tank removed about 55% TP consistently over the first 7-8 months, presumably as sludge. The remainder of the phosphorus was removed in the foam biofilter as a reddish coating.

[0107] Alternatively, the electrodes can be placed at some other location of the wastewater-treatment-station. But generally the other containers/conduits/tanks/stations of the wastewater-treatment-station are not so accommodating of the cell-unit as the septic-tank. On the other hand, the electrodes being located downstream of the septic-tank, of course none of the solid phosphate mineral collects in the septic-tank.

[0108] In FIG. 3, the effluent from the septic-tank 23 passes into a pump tank 61 that doses the disposal leach field or a biological filter plus a smaller leach field. A pump 63 doses water from the pump tank into a recirculating sand filter 65, with a large component of filter-treated effluent returning back to the pump tank 61, typically to dilute strong sewage or to remove nitrate by denitrification. A benefit of putting the cell-unit 67 in the pump/recirculation tank 61 is that the tank typically has adequate space for the unit and contains cleaner wastewater with no appreciable sludge, scum or raw sewage to interfere with the electrodes.

[0109] The cell-unit 67 can be placed in the pump tank 61 if the tank is large enough, and the unit should be located deep enough that the water level drop during pumping does not excessively expose the electrodes on a regular basis. The electrodes should be away from metal components and physically constrained to prevent contact and short-circuiting.

[0110] A benefit of the pump tank location is that a small side-flow of water from the pump 63 can be directed at the electrodes during pumping to help dispersal and mixing of the iron ions to react with the phosphate ions, and thereby minimize solids accumulating on the electrodes.

[0111] It should be noted that the “mixing” of the ions generally need not be assisted by a mechanical mixing device. The mixing can take place by diffusion, by mildly turbulent flow, by turbulence near a pump, by gravity-flow from or into a pipe, etc.

[0112] A substantial voltage increase indicates the end of electrode service life or unusual scale build-up on the electrode surface. In this case, the electrode needs to be cleaned or replaced.

[0113] The electrodes are preferably placed where water flows past them, i.e under the pipe for re-circulated filtered water.

[0114] The following reports a fourth actual test. Testing was carried out over several years on a recirculating sand filter, with coarse pea gravel as a filter medium, showed that little to no phosphorus attenuation had occurred. Treated effluent contained 5-6 mg/L TP, down only from 6-7 mg/L TP in the raw sewage, most likely contained in the septic tank sludge. Adding an easy-dissolve iron electrode system to the recirculation tank, which received about 80% treated effluent and about 20% septic tank effluent, removed phosphorus to a level of 0.4-0.5 mg/L TP in the effluent, or 90-95% removal. Red coloration of the pea gravel indicates that ferric phosphate minerals coated the pea gravel, thereby removing TP by mineralization, and without the need of sludge production to remove the phosphorus. When the electrode was disconnected, residual iron on the filter medium removed additional phosphorus from the water, over a period of two months, as the concentration climbed from 0.5 mg/L to 6.0 mg/L, where it remained. This testing shows that placing the electrodes after the septic tank can remove almost all the phosphorus permanently as mineral coating precipitates in the biofilter station, where the phosphorus does not have to be managed or treated again.

[0115] In the technology described herein, the major function of the electrolysis is to cause metal to dissolve into the wastewater. It is not an intended function of this electrolysis to energize treatment reactions; in fact it is intended to avoid energizing reactions upstream of the biofilter station. Nor is it intended to dissociate the water into hydrogen and oxygen for treatment purposes. Insofar as those things happen (i.e cannot be avoided) in the present system, the energy thus consumed can be regarded as an inefficiency.

PRIOR ART

[0116] Electrolysis has been featured in previous systems for attenuating phosphorus from wastewater. In US-2012/0,138,482 (Premier Tech/Fanfan, 7 Jun. 2012), electrolysis is employed to aid electro-coagulation and electro-flocculation of metal-phosphate, in which the phosphorus is taken out of the water by producing a sludge. The sludge is separated out by laminar plates and fed back into the septic tank, where the phosphorus remains, ready to be pumped out with the sewage sludge, e.g every one to five years. This is unlike the present system in that, in '482, the phosphate has not actually been removed from the water by mineralization, but has been concentrated and moved as a sludge from one vessel to another upstream. In '482, the accumulation of phosphorus in the sludge can be very high, e.g in the thousands of mg/L overall. Even a large municipal water treatment plant has difficulty dealing with such phosphorus concentration, and will likely impose surcharges, or even refuse to take the sludge.

[0117] Again, in the present technology, the aim is to use electrolysis predominantly to cause metal to enter into solution, whereby the metal ions can mix with the phosphorus ions, and form stable solid metal phosphate minerals. The aim is to do so without the need for electro-coagulation and sludge management. Such a build-up of total phosphorus (TP) in the septic tank could very well increase the concentration of TP leaving the septic tank from normal 6-10 mg/L values to perhaps 5-10 times that, confounding the phosphorus removal technology, and concentrating TP in the septic tank contents to e.g 100-1000 times that. In '482, there is no disclosure of the metal being an easy-dissolve metal, as described herein. There is no disclosure in '482 of minimizing sludge formation or of encouraging metal-phosphorus mineral coatings.

[0118] In U.S. Pat. No. 6,645,366 (Iseki, 2003), a catalyst is associated with the electrodes. Again, there is no disclosure of the metal being an easy-dissolve metal, as described herein. There is no disclosure of moving mixed-iron-phosphate-water through the treatment station to a ground infiltration station. There is no disclosure of minimizing sludge formation or of encouraging metal-phosphorus mineral coatings.

[0119] In U.S. Pat. No. 6,719,893 (Sakakibara, 2004), the treatment involves electrolyzing the water, rather than causing a metal electrode to dissolve into the wastewater. Again, there is no disclosure of the metal being an easy-dissolve metal, as described herein. There is no disclosure of minimizing sludge formation or of encouraging metal-phosphorus mineral coatings.

[0120] The list of reference numerals used in this specification is: [0121] 20 house (FIG. 1A, FIG. 1) [0122] 21 sewer [0123] 23 septic tank [0124] 25 biofilter [0125] 27 infiltration station [0126] 29 electrolysis cell (FIG. 1B, FIG. 1) [0127] 30A anode [0128] 30C cathode [0129] 32 solar panel [0130] 34 electrical control panel [0131] 36 container for cell [0132] 38 container inlet [0133] 40 container outlet [0134] 43 rain-barrel [0135] 45 cell-water-distributor [0136] 50 electrolysis-cell unit (FIG. 2) [0137] 52 support cage for supporting electrodes in cell [0138] 61 recirculation tank (pump tank) (FIG. 3) [0139] 63 pump [0140] 65 recirculating sand filter [0141] 67 electrolysis-cell unit