System for simultaneous elimination of orthophosphate and ammonium using electrolytic process

Abstract

An electrolytic system for treating wastewater by electrocoagulation, electroflotation or a combination of both is disclosed. The electrolytic system comprises a first electrolytic reactor adapted for receiving the wastewater to be treated, the first electrolytic reactor comprising at least one cathode and at least one anode to perform a first electrolytic treatment for eliminating organic matter and calcium present in the wastewater that impact on nucleation of struvite; and a second electrolytic reactor downwardly connected to the first electrolytic reactor, the second electrolytic reactor comprising at least one cathode and at least one magnesium anode to perform a second electrolytic treatment for producing Mg.sup.2+ ions which react with NH.sub.4.sup.+ and orthophosphates from said wastewater to form a struvite precipitate. The electrolytic system allows eliminating simultaneously orthophosphate and ammonium from the wastewater while enabling the production of struvite.

Claims

1. An electrolytic system for treating wastewater by electrocoagulation, electroflotation or a combination of both, the electrolytic system comprising: a first electrolytic reactor adapted for receiving the wastewater to be treated, the first electrolytic reactor comprising at least one cathode and at least one anode to perform a first electrolytic treatment for eliminating organic matter and calcium present in the wastewater that impact on nucleation of struvite; and a second electrolytic reactor downwardly connected to the first electrolytic reactor, the second electrolytic reactor comprising at least one cathode and at least one magnesium anode to perform a second electrolytic treatment for producing Mg.sup.2+ ions which react with NH.sub.4.sup.+ and orthophosphates from said wastewater to form a struvite precipitate, whereby, in use, the electrolytic system allows eliminating simultaneously orthophosphate and ammonium from the wastewater while enabling the production of struvite.

2. The electrocoagulation system of claim 1, further comprising a first decanter downwardly connected to the first electrolytic reactor for separating solid/liquid fractions.

3. The electrolytic system of claim 1, further comprising a second decanter downwardly connected to the second electrolytic reactor for isolating the struvite precipitate from the wastewater.

4. The electrolytic system of claim 2, further comprising a second decanter downwardly connected to the second electrolytic reactor for isolating the struvite precipitate from the wastewater.

5. The electrolytic system of claim 1, wherein the first electrolytic reactor is made of an inert material.

6. The electrolytic system of claim 5, wherein the inert material comprises magnesium, aluminum, or iron.

7. The electrolytic system of claim 1, wherein at least one anode of the first and second electrolytic reactor is tubular.

8. The electrolytic system of claim 1, wherein at least one of the first and second electrolytic reactors comprises nine tubular anodes disposed circularly and parallel to a central axis of the reactor.

9. The electrolytic system of claim 1, wherein at least one of the first and second electrolytic reactors comprises one cylindrical anode disposed along a central axis of the reactor.

10. The electrolytic system of claim 1, wherein the at least one cathode of the first and second electrolytic reactors consists in a central cathode or a peripheral cathode.

11. The electrolytic system of claim 1, wherein at least one of the first and second electrolytic reactors comprise both a central and a peripheral cathode.

12. The electrolytic system of claim 1, wherein the cathodes are made of stainless or galvanized steel.

13. The electrolytic system of claim 1, wherein the cathodes are made of a material having a potential close to a potential of the material of anodes.

14. The electrolytic system of claim 1, wherein the cathodes are made of the same material as the anodes provided that in the second electrolytic reactor, the cathodes and anodes are made of magnesium.

15. The electrolytic system of claim 1, further comprising a conditioning tank upwardly connected to the first reactor for receiving wastewater to be treated, the conditioning tank comprising a level captor for measuring and controlling a level of fluid in the tank.

16. The electrolytic system of claim 15, wherein the conditioning tank further comprises sensors for measuring wastewater's conductivity, pH, initial concentrations in NH.sub.4.sup.+, calcium and orthophosphates as well as initial organic content.

17. The electrolytic system of claim 15, further comprising a prefilter upwardly connected to the conditioning tank for retaining particles and allowing colloidal fractions to access the conditioning tank.

18. An electrolytic system for treating wastewater by electrocoagulation, electroflotation or a combination of both, the electrolytic system comprising: a first electrolytic reactor adapted for receiving the wastewater to be treated, the first electrolytic reactor comprising at least one cathode and at least one anode to perform a first electrolytic treatment for eliminating organic matter and calcium present in the wastewater that impact on nucleation of struvite; a first decanter downwardly connected to the first electrolytic reactor for separating solid/liquid fractions; a second electrolytic reactor downwardly connected to the first electrolytic reactor, the second electrolytic reactor comprising at least one cathode and at least one magnesium anode to perform a second electrolytic treatment for producing Mg.sup.2+ ions which react with NH.sub.4.sup.+ and orthophosphates from said wastewater to form a struvite precipitate; and a second decanter downwardly connected to the second electrolytic reactor for isolating the struvite precipitate from the wastewater; whereby, in use, the electrolytic system allows eliminating simultaneously orthophosphate and ammonium from the wastewater while enabling the production of struvite.

19. The electrolytic system of claim 18, further comprising a conditioning tank upwardly connected to the first reactor for receiving wastewater to be treated, the conditioning tank comprising: a level captor for measuring and controlling a level of fluid in the tank; and sensors for measuring wastewater's conductivity, pH, initial concentrations in NH.sub.4.sup.+, calcium and/or orthophosphates as well as initial organic content.

20. The electrolytic system of claim 19, further comprising a prefilter upwardly connected to the conditioning tank for retaining particles and allowing colloidal fractions to access the conditioning tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Referring now to the drawings which form a part of this original disclosure:

(2) FIG. 1 is a schematic illustration of the electrolytic system with at least one embodiment of the invention; and

(3) FIG. 2 is a schematic illustration of a modular electrolytic apparatus in accordance with at least one embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) A preferred embodiment of the present invention is described bellow with reference to the drawings.

(5) The electrolytic system 10, as illustrated in FIG. 1, comprises a prefilter 12 that retains particles and allows the colloidal fraction to access a conditioning tank 14. In the conditioning tank 14, there is a level captor 16 measuring and controlling the level of fluid in the tanks. Also, they are sensors (not shown in FIG. 1) that allow for the measurement of conductivity, pH, initial concentrations in NH.sub.4.sup.+, calcium and orthophosphates as well as initial organic content. Those measured values allow the continuous evaluation of the conductivity of the affluent, its pH and allows the adjustment of the quantity of orthophosphate in solution with respect to the NH.sub.4.sup.+ concentration in order to respect the stoechiometry of the reaction desired. Conductivity and pH probes are well known in the art and are easily available. The measure of NH.sub.4.sup.+ can be made, for example, with an ISE WTW probe coupled with a VARION PLUS 7001Q sensor. Phosphate analysis can be made using colorimetric devices such as PHOS200 and TOPHO. The organic charge can be evaluated using a CSS70 sensor. Also, UV sensors allow for the measurement of absorbance at 254 nm, which can be easily correlated with the chemical demand in oxygen.

(6) The measurement of the NH.sub.4.sup.+ concentration in solution also allows for the determination of the Mg concentration needed to precipitate the struvite. The second law of Faraday is used to convert the Mg concentration into current intensity and treatment time in order to maximize the production of struvite.

(7) Once conditioned, the effluent is pumped in a first electrolytic reactor 18 comprising a fixed electrocoagulation module 20. For the purpose of the present invention, the electrocoagulation could be interchanged with an electrofloatation module. The first electrolytic treatment reduces of about 85% the organic charge of the effluent and the treated effluent is brought in a first decanter 22 to separate the solid-liquid fractions. An automatic dosing device (not shown in FIG. 1) is placed between the exit of the first decanter 22 and the entry of a second electrolytic reactor 26. This automatic dosing device allows the adjustment of the quantity of orthophosphate in the effluent needed to react with all the NH.sub.4.sup.+ in solution. After this second conditioning step, the effluent is introduced in a second electrolytic reactor 26, which also comprises a fixed electrocoagulation module 20. The second electrolytic reactor 26 comprises in its fixed electrocoagulation module 20 at least one soluble anode made of magnesium. The ions Mg.sup.2+ generated while applying the electrical current react with the NH.sub.4.sup.+ and orthophosphate in solution and therefore produce a struvite precipitate. Both first and second electrolytic reactors 18 and 26 optionally comprise a motor 70 allowing the rotation of the electrocoagulation module 20, providing for an additional agitation of the fluid in the reactors 18 and 26.

(8) After this second electrolytic treatment, the effluent is brought in a second decanter 28 for isolating the struvite precipitate.

(9) An exemplary electrocoagulation module 20 is illustrated in FIG. 2 with a section view allowing a better view of its construction. The electrocoagulation module 20 comprises an anode module 30 and a cathode module 32 adapted to interact in an electrolytic process producing electrocoagulation. The electrocoagulation module 20 of the present embodiment includes an inlet 34 and an outlet 36 configured to respectively receive and extract the fluid to and from the electrocoagulation module 20. The fluid, once introduced in the electrocoagulation module 20, follows a path or a fluidic circuit configured to put the fluid in communication with the electrolytic process that is produced in the electrocoagulation module 20. In the present example, the fluid follows a path identified by a series of arrows 38 defined by internal walls 40. A pump, which is not illustrated in FIG. 1, pushes the fluid through the electrocoagulation module 20. An opening 42 disposed on a bottom portion 44 of the electrocoagulation module 20 is normally closed with a plug (not illustrated) to prevent the fluid to exit the electrocoagulation module 20. The opening 42 can be opened to remove the fluid from the electrocoagulation module 20 to purge the electrocoagulation module 20 for maintenance purposes, for instance. The electrocoagulation module 20 can also be purged to remove particles and debris. A larger closure member 46 is used to close the bottom portion of the electrocoagulation module 20 lower body 48. The closure member 46 can be optionally removed to provide a larger access in the electrocoagulation module 20. The lower body 48 can threadedly engage the upper body 56 and be removed from the upper body 56, if desirable.

(10) Still referring to FIG. 2, the closure member 46 is located at the lower portion of the electrocoagulation module 20 to receive particles therein. The cathode module 32 is bottomless and allows the particles to drop in the closure member 46 acting as a particles-receiving member 46. The removable particles-receiving member 46 is preferably disposed in the center of the cathode module 32 as illustrated in the present embodiment and is used for removing decanted particles from the cathode module 32. The opening 42 in the closure member 46 can alternatively be used to inject gas, like air, or liquids for further conditioning the liquid in the electrocoagulation module 20 and/or influence the electrocoagulation process inside the cathode module 32.

(11) The electrocoagulation module 20 further includes body portions 48, 56 that can optionally include insulating material to prevent heat transfer with the environment. Conversely, the electrocoagulation module 20 might be equipped with heating/cooling elements 58 to keep the electrocoagulation apparatus 20 at a predetermined operating temperature. The upper body 56 of an embodiment can be made of an insulating material preventing heat transfer between the inside of the electrocoagulation module 20 and the outside of the electrocoagulation module 20. The lower body 48 of the embodiment illustrated in FIG. 2 is made of a material that is less insulating the electrocoagulation module 20. Heating or cooling elements 58 are disposed, for example, in a spiral around the lower body 48 to either heat or cool the lower body 48. The heating or cooling elements 58 can use a fluid circulating in a tubular system or electric elements in contact with, or nearby, the lower body 48. Another embodiment is using the upper body 56 to transfer heat to/from the electrocoagulation module 20 in cooperation or not with the lower body 48.

(12) Still referring to the embodiment of FIG. 2, the anode module 30 is secured to the upper body 56 and extends above the upper body 56 to allow electrical connection 62 thereto. The cathode module 32 of the present embodiment is also secured to the upper body 56 and extends therefrom 60 to allow electrical connection thereto. A power supply (not illustrated) is connected to the cathode module 32 to provide negative power thereof. Electrical polarity reversal is provided when desired to avoid passivation of the anode module 30 and the anodes 68 secured thereon. Insulators may be placed between two adjacent electrodes to prevent short circuits thereof. The cathode 32 and the anodes 68 are subjected to DC current. One skilled in the art can also appreciate that the upper body 56 is made of an insulating material to prevent establishing an electrical connection between the cathode 32 and the anode module 30.

(13) The anode module 30 can be made of soluble or inert materials. The cathode module 32 can be made of steel, aluminum, stainless steel, galvanized steel, brass or other materials that can be of the same nature as the anode module 30 material or having an electrolytic potential close to the electrolytic potential of the anode 68. The cathode module 32 of the present embodiment has a hollowed cylindrical shape, fabricated of sheet material, and can be equipped with an optional lower frustoconical portion (not illustrated in FIG. 2). The inter electrode distance of an embodiment of the invention is about between 8-25 mm and preferably 10 mm for electro floatation and 20 mm for electrocoagulation. The interior of the cathode module 32 electrically interacts with the outside of the anode module 30. The electrocoagulation module 20 internal wall includes non-conductive material, like polymer, in an embodiment of the invention. The cathode module 32 could alternatively serve as a reservoir, or reactor, at the same time thus holding the liquid to treat therein in other embodiments. The cathode module 32 can be made of a material different from the anode material 30 or can alternatively be made of the same material, like, for instance, magnesium.

(14) The size and the available active surface area of the cathode module 32 can be adapted to various conditions without departing from the scope of the present invention. The surface ration of the cathode/anode can be identical or vary to about 1.5. The cathode module 32 of other embodiments can alternatively be oval or conical; its diameter expending upward or downward. The electrocoagulation module 20 can include therein an optional fluid agitator module 64 adapted to apply kinetic energy to the fluid contained in the electrocoagulation module 20 by moving or vibrating the fluid in the electrocoagulation module 20 as it is illustrated in the embodiment depicted in FIG. 2.

(15) As mentioned above, the movement of the fluid increases the kinetic energy contained therein to destabilize the colloidal solution. This can be achieved by turbulently injecting the fluid in the electrolytic module (the speed and tangential injection of the fluid are possible ways to create turbulences in the fluid). The fluid agitator module 64 in this embodiment is a spiral shaped protrusion member 64 that is secured to the anode module 30. The movement of the fluid between the anode module 30 and the cathode module 32 is intensified by the protrusion member 64, which influences the electrolytic process. The anode module 30 of an alternate embodiment that is not illustrated in FIG. 2 could be rotatably secured to the upper body 56 of the electrocoagulation module 20 and be rotated by an external motor to rotate the anode and the protrusion members secured thereon to apply additional kinetic energy to the fluid as it will be discussed below. As it is illustrated in FIG. 2, the anode module 30 is preferably centered inside the electrocoagulation module 20 and preferably located at equal distance from the cathode module 32.

(16) The electrocoagulation module 20 of FIG. 2 further comprises a pair of electrocoagulation module connectors 66 adapted to operatively install the electrocoagulation module 20 in a larger fluid treatment process if desired. The electrocoagulation module 20 can removably be mounted in series, or in parallel, in the fluid treatment process. This way, the electrocoagulation module 20 can easily be added, maintained, replaced and/or removed from the fluid treatment process.

EXAMPLE 1

(17) An effluent from the agri-food industry has been treated using the method and process of the present invention. This effluent was providing from a pork transformation plant and was charged in urine, feces and blood with a pH of 6.8. The effluent has been treated with the process of the present invention using a 2 reactor and decanter process, with a variable tension generator (0-30V) offering current between 1 and 120 A. The anodes of the reactors were in magnesium and the measures of the chemical oxygen demand, orthophosphate concentration, NH.sub.4.sup.+ concentration, calcium concentration and magnesium concentration made using HACH chemicals.

(18) TABLE-US-00001 TABLE 1 Analysis Brut Conditioned Treated Treated Sample effluent effluent sample sample Time 10:00 am 11:00 am 1:30 pm 2:30 pm Temperature (C.) 28 28 43 43 pH 7.02 1.02 9.03 8.85 M.E.S (mg/l) 1700 1900 0 8.85 Turbidity (NTU) 817 1100 2 9 PO.sub.4.sup.3 (mg/l) 43 135 0.4 0.4 NH.sub.4.sup.+ (mg/l) 55 55 26 13

(19) It is shown in Table 1 that the brut effluent has an initial concentration of orthophosphate of 43 ppm and ammonium concentration of 55 ppm. To eliminate these two elements, the stoechiometric ratio has to be respected. An initial concentration in orthophosphates of 555=275 ppm should have been needed according to the initial data. However, the effluent has been conditioned to have an orthophosphate concentration of 135 ppm, which allowed a reduction in NH.sub.4.sup.+ of 135:5=27 ppm corresponding to the results obtained (26 ppm). This example shows the importance of respecting the stoechiometric ratio to allow an optimal reduction of NH.sub.4.sup.+ as well as maintaining a pH of about 9.2.

(20) TABLE-US-00002 TABLE 2 NH.sub.4.sup.+ PO.sub.4.sup.3 PO.sub.4.sup.3 PO.sub.4.sup.3 PO.sub.4.sup.3 NH.sub.4.sup.+ (mg/l) (mg/l) (mg/l) (mg/l) (mg/l) NH.sub.4.sup.+ Elimination Initial 1 initial 2 Theory 3 added 4 final 5 Final 6 (%) 9:00 am 68 57 340 0 0 55 19 12:30 pm 70 73 350 174 0 28 60 1:30 pm 55 43 275 152 0.4 26 52 2:30 pm 55 43 275 230 0.4 13 77 3:00 pm 50 51 250 235 0 7 86

(21) Table 2 illustrates that the ions ortho phosphate are needed to eliminate NH4+ and that the closer the ratio orthophosphate/NH.sub.4.sup.+ is closer to 5:1, the better is the NH.sub.4.sup.+ elimination.

EXAMPLE 2

(22) A lixiviat has been treated using the method and process of the present invention. The effluent has been treated with the process of the present invention using a 2 reactor and decanter process, with a variable tension generator (0-30V) offering current between 1 and 120 A. The anodes of the reactors were in magnesium and the measures of the chemical oxygen demand, orthophosphate concentration, NH.sub.4.sup.+ concentration, calcium concentration and magnesium concentration made using HACH chemicals.

(23) The effluent was treated with a tension of 27.3V and a current of 100 A.

(24) TABLE-US-00003 TABLE 3 Analysis Sample Brut lixiviat Conditioned lixiviat Treated lixiviat Temperature 0 0 27 pH 7.19 3.75 9.09 M.E.S (mg/l) 234 352 27 Turbidity (NTU) 276 390 45 PO.sub.4.sup.3 (mg/l) 29 225 0.5 NH.sub.4.sup.+ (mg/l) 190 190 140

(25) In this example, it is demonstrated again that the reduction of the NH4+ is in accordance with the stoechiometric ratio. To eliminate the residual NH4+, an total amount of 950 ppm of orthophosphate should have been in the conditioned lixiviat.

EXAMPLE 3

(26) A combined effluent from landfill sites has been treated using the method and process of the present invention. The effluent has been treated with the process of the present invention using a 2 reactor and decanter process, with a variable tension generator (0-30V) offering current between 1 and 120 A. The anodes of the reactors were in magnesium and the measures of the chemical oxygen demand, orthophosphate concentration, NH.sub.4.sup.+ concentration, calcium concentration and magnesium concentration made using HACH chemicals. Several batches (A-H) of the initial effluent have been treated and the results are shown in Table 4.

(27) TABLE-US-00004 TABLE 4 Sam- Conductivity M.E.S PO.sub.4.sup.3 NH.sub.4.sup.+ ple Time T ( C.) pH (mS/cm) (mg/l) (mg/l) (mg/l) initial 0 min 22 7.84 5.94 1140 90 310 A 5 min 42 8.82 3.90 24 6.2 220 B 4 min 42 8.77 3.98 39 7.4 280 C 5 min 43 8.66 3.74 21 4.3 120 D 4 min 42 8.77 3.98 29 6.2 280 E 5 min 43 8.63 3.75 20 5.4 270 F 4 min 42 8.62 3.95 22 4.8 290 G 5 min 43 8.56 3.60 18 8.6 290 H 4 min 41 8.51 3.72 25 10.6 150

(28) The results shown in Table 4 demonstrate that both the stoechiometric ratio and the time of treatment need to be sufficient for allowing a satisfactory elimination of NH.sub.4.sup.+. If the stoechiometric ratio is not respected, the complete, or at least satisfactory, elimination of NH.sub.4.sup.+ is impossible. Also, the treatment needs to be performed for a time sufficient to allow the production of a minimal quantity of Mg.sup.2+ ions; otherwise the reaction cannot be optimal.

(29) While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments and elements, but, to the contrary, is intended to cover various modifications, combinations of features, equivalent arrangements, and equivalent elements included within the spirit and scope of the appended claims. Furthermore, the dimensions of features of various components that may appear on the drawings are not meant to be limiting, and the size of the components therein can vary from the size that may be portrayed in the figures herein. Thus, it is intended that the present invention covers the modifications and variations of the invention, provided they come within the scope of the appended claims and their equivalents.