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.

1 . Procedure for removing phosphorus from sewage wastewater, including:
 passing the wastewater along a flowpath through an overall wastewater-treatment-station that includes at least one treatment-station, being a station in which the physical or chemical constituents of the wastewater undergo substantive change;   the wastewater having passed along the flow-path through the wastewater-treatment-station, passing the now-treated water into a discharge-station;   providing an electrolysis-facility, and passing water therethrough, termed cell-water;   where the electrolysis-facility includes an anode and cathode, and a source of electrical energy;   where the anode is of, or includes, a metal having the following properties:   (i) the metal of the anode is capable of dissolving into the cell-water electrolyte passing through the electrolysis-facility;   (ii) the cell-water and the wastewater having been mixed, the metal ions in the cell-water are capable of combining with the phosphate ions in the wastewater to form a metal phosphate;   (iii) the metal phosphate is substantially insoluble, and forms a solid mineral;   passing current through the electrodes, such that metal from the anode passes into solution in the cell-water at a substantial rate;   mixing the wastewater and the cell-water together at a mixing-point;   where the mixing-point is a point along the flow-path of the wastewater-treatment-station, upstream of the discharge-station;   at, and downstream of, the mixing-point, the now-dissolved metal-ions in the cell-water mix with the phosphate-ions present in the wastewater;   the wastewater at, and downstream of, the mixing-point is now also termed mixed-metal-phosphate-water;   so configuring the wastewater-treatment-station that metal-ions and phosphate-ions in the mixed-metal-phosphate-water combine to form a metal-phosphate mineral;   passing the mixed-metal-phosphate-water downstream of the mixing-point, along the flow-path of the wastewater-treatment-station, towards, and into, the discharge-station.   
     
     
         2 . As in  claim 1 , wherein the metal of the anode is in easy-dissolve form. 
     
     
         3 . As in  claim 2 , including:
 where the electrodes have respective current-surfaces, being the surface of the electrode that faces the corresponding current-surface on an adjacent electrode;   where the metal is in an easy-dissolve form in that the metal is mild steel and at least the current-surface is substantially bare metal;   ensuring that the current-surface is free of oxide or other coating that could substantially inhibit the rate at which the anode iron can enter solution in the cell-water.   
     
     
         4 . As in  claim 3 , including:
 the metal being hot-rolled mild-steel;   grinding or otherwise working at least the current-surface of the electrodes, to the extent that substantially all mill-scale and other oxides have been removed from the current-surfaces, leaving the current-surface bare metal.   
     
     
         5 . As in  claim 3 , wherein the metal is cold-rolled mild-steel. 
     
     
         6 . As in  claim 4 , including:
 passing current between the electrodes, at a voltage that is:   (a) high enough that the metal of the anode passes into solution at a substantial rate; and   (b) low enough that oxygen gas is released at the anode at no more than an insignificant rate;   
     
     
         7 . As in  claim 4 , including:
 passing current through the electrodes at a voltage that maintains a current-density in the electrodes of between 0.4 and 3.0 milliamps/sq.cm of the current-surface of the electrode; and   so forming the electrodes that that current-density can be achieved at an applied potential difference of fifteen volts or less.   
     
     
         8 . As in  claim 4 , including structuring the electrodes to be capable of releasing iron into the cell-water at a rate of fifteen or more grams of iron per day, at a current-density of 3.0 mA/sq.cm or less. 
     
     
         9 . As in  claim 1 , including:
 locating the electrolysis-facility outside the wastewater-treatment-station;   whereby the cell-water is separate from the wastewater; and   whereby the mixed-metal-phosphate-water is the water downstream of the mixing-point.   
     
     
         10 . As in  claim 1 , including:
 locating the electrolysis-facility in the wastewater-treatment-station;   whereby the cell-water and the wastewater are one and the same; and   whereby the mixed metal-phosphate water is the water downstream of the electrolysis-facility.   
     
     
         11 . As in  claim 10 , including:
 where the wastewater-treatment-station includes a septic-tank;   locating the electrodes within the septic tank, whereby the mixing-point is in the septic-tank; or   locating the electrodes within a conduit or tank of the wastewater-treatment-station other than the septic-tank, whereby the mixing-point is in the conduit or tank; or   locating the electrodes in the sewer through which wastewater is conveyed into the inlet of the septic-tank, whereby the mixing-point is in the sewer.   
     
     
         12 . As in  claim 2 , wherein:
 the electrolysis-facility includes a cell, comprising:   at least one pair of the metal electrodes;   a support-cage for mounting and maintaining the electrodes in a parallel spaced-apart relationship, and electrically insulated from each other;   the support-cage is of such open construction as to allow water to pass over and between the electrodes;   the cell includes electrical connections, by which the electrodes can be connected to an electrical controller of the electrolysis-facility, and thereby to the electrical source;   the cell is structured to be capable:   (a) of being picked up and handled, as a unitary whole;   (b) of being inserted into the wastewater-treatment-station at a point along the flow-path;   (c) of being connected electrically to the controller;   (d) of being mounted in and left in the wastewater-treatment-station for an operational period of at least several months.   
     
     
         13 . As in  claim 12 , including:
 opening the septic-tank;   mounting the cell in the septic-tank;   so positioning the cell that the electrodes lie clear below the level at which light solid materials accumulate on the surface of the wastewater, and lie clear above the level at which heavy solid materials settle on the floor of the septic tank;   making the electrical connections;   closing the septic-tank;   operating the electrolysis-facility such as to drive iron to dissolve in the water of the septic-tank.   
     
     
         14 . As in  claim 1 , including:
 passing the wastewater through a septic-tank and leach-field wastewater-treatment-station;   so locating the cell in the wastewater-treatment-station that the iron ions and the phosphate ions can combine, and the metal-phosphate mineral can form, prior to the water being discharged from the wastewater-treatment-station.   
     
     
         15 . As in  claim 1 , including:
 where the wastewater-treatment-station includes a biofilter-station, in which the wastewater is treated by being aerated;   where the biofilter-station lies downstream of the mixing-point, whereby the mixed-iron-phosphate-water passes through the biofilter-station;   where the biofilter-station includes a body of biofilter medium material;   where the biofilter medium material is:   (a) exposed to air; and   (b) wetted by the mixed-iron-phosphorus-water passing through the station; and   the procedure includes so arranging the wastewater-treatment-station that the metal-phosphate mineral that forms in the mixed-metal-phosphate-water precipitates in or on the biofilter medium material.   
     
     
         16 . As in  claim 1 , including removing the metal-phosphate mineral from the wastewater by passing the mixed-metal-phosphate-water through a physical filter, which is located downstream of the mixing-point and upstream of the discharge-station. 
     
     
         17 . Procedure for removing dissolved phosphate from wastewater, including:
 passing the wastewater through a wastewater-treatment-station;   providing an electrolysis-facility, and passing water therethrough;   where the electrolysis-facility includes: an anode and cathode immersed in water, and a source of electrical energy;   where the anode includes a metal that has the following properties:   (i) the metal of the anode is in easy-dissolve form, and dissolves in the cell-water passing through the cell;   (ii) the resulting metal ions in the wastewater combine with the phosphate ions in the cell-water, to form a metal phosphate;   (iii) the metal phosphate is substantially insoluble in the wastewater;   passing current between the electrodes, at a voltage that is:   (a) high enough that the metal of the anode passes into solution at a substantial rate; and   (b) low enough that oxygen gas is released at the anode at no more than an insignificant rate;   so arranging the wastewater-treatment-station and the electrolysis-facility that the now-dissolved metal-ions mix with the phosphate-ions present in the wastewater.