CA2783519C

CA2783519C - Method for simultaneous elimination of orthophosphate and ammonium using electrolytic process

Info

Publication number: CA2783519C
Application number: CA2783519A
Authority: CA
Inventors: Abderrazak Berrak
Original assignee: E2metrix Inc
Current assignee: E2metrix Inc
Priority date: 2012-07-23
Filing date: 2012-07-23
Publication date: 2018-06-19
Anticipated expiration: 2032-07-23
Also published as: CA2783519A1

Abstract

The present invention provides a method for the treatment of nitrogen-rich effluent and production of struvite comprising introducing the effluent in an electrolytic system and performing a first electrolytic treatment to the effluent in a first electrolytic reactor in order to organic matter that impact on nucleation of struvite, followed by a second electrolytic treatment in a second electrolytic reactor, thereby injecting Mg ions which react with NH4+ and orthophosphates from the effluent to form a struvite precipitate.

Description

2 METHOD FOR SIMULTANEOUS ELIMINATION OF ORTHOPHOSPHATE AND

3 AMMONIUM USING ELECTROLYTIC PROCESS

4 FIELD OF THE INVENTION
6 This invention relates to a method for the simultaneous elimination of orthophospate 7 and ammonium (NH4) from a nitrogen-rich effluent using an electrolytic process and 8 thereby electro-synthesis of struvite.

BACKGROUND OF THE INVENTION
11 Electrocoagulation was already proposed in the late 19th and early 20th century. The 12 use of electrocoagulation with aluminum and iron was patented in 1909 in the United 13 States (Robinson, Australian Water & Wastewater Association, Joint NSW
and 14 Victoria State Conference in Wodonga, 22-24 November 1999 (www.electropure.com.au/paper.htm); Vik etal. WaterResearch, volume 18, Issue 1, 16 1984, pages 1355-1360).
17 Coagulation is essentially to neutralize, or reduce, the electric charge of colloids and 18 hence promote the aggregation of colloidal particles. To destabilize a suspension it is 19 necessary that the attractive forces between particles are greater than the repulsive forces thereof. Attractive forces are mainly van der Weals forces, which act at a short 21 distance thereof. In general, the total energy that controls the stability of the energy 22 dispersion comprises attractive van der Weals energy of repulsion at short distance, 23 the electrostatic energy and energy due to the steric effect of molecules solvent.
24 Coagulation can be done by chemical or electrical means. Alun, lime and/or polymers have been used as chemical coagulants. Chemical coagulation is becoming less MTC-070-013-CAI =
1 popular today because of high costs associated with the chemical treatments of a 2 significant volume of sludge and hazardous heavy metals such as metal hydroxides 3 generated thereof in addition to the cost of chemical products needed for coagulation 4 itself. Chemical coagulation has been used for decades.
Although the electrocoagulation mechanism resembles chemical coagulation, 6 although, some differences benefit electrocoagulation. Indeed, electrocoagulated 7 flocs differ from those generated by chemical coagulation. Flocs created with the 8 electrocoagulation process tend to contain less bound water, are more resistant to 9 shearing and are more easily filterable.
Flocs are created during the electrocoagulation water treatment with oxydo-reduction 11 reactions. Currents of ions and charged particles, created by the electric field, 12 increase the probability of collisions between ions and particles of opposite signs that 13 migrate in opposite directions. This phenomenon allows the aggregation of 14 suspended solids to form flocs.
The electrolytic reactions that take place at the electrodes are accompanied by 16 production of micro bubbles of hydrogen (at the cathode) and oxygen (at the anode).
17 These micro bubbles heading up will result in an upward movement of the flocs 18 formed thereof that are recovered at the surface (this mechanism is named flotation).
19 The complexity of the mechanisms involved in the process of electrocoagulation in the treatment of water is not well scientifically elucidated (Yousuf et aL, Journal of 21 Hazardous Material B84, 2001). There are various features of the mechanism of the 22 process and the geometry, or design, of the reactor in the literature.
The different 23 physico-chemical treatment, the shape of the reactor and the shape and size of 24 electrodes affect the performance of the treatment. The wide variety of processing . parameters reported in the literature and the lack of scientific data for efficient model 26 processing and optimal processing conditions translate into a lack of development in 27 this field. At this time, electrocoagulation is still problematic and therefore not popular 1 (Holt et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 211(2002); Holt et 2 al., Chemosphere 59(2005) 355-367).
3 The existence of an electric current in a body of water implicitly requires Faraday 4 reactions surrounding the electrodes. The formation of chemical gradients depends on the electrolytic magnitude. The consequences of chemical reactions become more 6 pronounced and significant in the prolonged application of electrokinetic. The effects 7 include electrolytic of water with the simultaneous development of pH
gradients and 8 the transfer of electrolytic dissolution of the anode producing metal ions (Fe3+, Al3+, 9 Mg, etc..) or cations of the electrolyte from the anode to the cathode.
Chemical reactions can, in ion exchange or precipitation, form new mineral phases for cleaning 11 water for instance.
12 At the cathode, the main reaction is:
13 4H20 + 4e" 2H2 + 40H" (Equation 1) 14 The increase in hydroxyl ions can increase the precipitation of metal hydroxide. The pH of the cathode's region is basic. The following equations describe the chemical 16 reactions at the anode:
17 2H20 -- 02 + 4H+ + 4e- (Equation 2) 18 If the anode is made of magnesium:
19 Mg Mg2+ + 2e" (Equation 3) It is noted that twice as many water molecules are electrolysed at the cathode 21 compared to the anode for the same quantity of electricity.
22 The struvite is a compound with a little solubility and used as a fertilizer in agricultural 23 fields. This compound is of the formula NH4MgPO4, 6H20 and comprised P043" and 24 NH4+ ions, both essential to plants growth. Struvite is known as a fertilizer and have been proved potent in soils having a pH between 5.5 and 6.5.

1 Precipitation of struvite in a wasted water allows the elimination of the ortho-2 phosphate, NH4+ and magnesium present in the wasted water. Currently, processes 3 for precipitating struvite use fluidized beds, or contained tanks reactors. In Japan, the 4 precipitation of struvite has been tested in a sludge treatment reactor.
To obtain a good performance, it is essential to optimized both nucleation and precipitation by 6 optimizing the treatment time in the reactor and the nature of the support particules 7 for the precipitation.
8 Precipation of struvite is controlled by the pH, the supersaturation, the temperature 9 and the presence of impurities such as calcium and can occur when the concentration in magnesium, ammonium and phosphore ions exceed the solubility 11 product of the complex as per the following expression:
12 Ksp = [ Mg2+ ][NH41[P043] pKs = 13.26 13 The presence of organic matter impact on the nucleation and growth of struvite 14 crystals and reduce the precipitation rate. In a wasted water to be treated, NH4 + and P043" are among the components to be eliminated. While adding Mg2+ in the solution 16 with a basic pH, the precipitate is formed. Several conditions are required for the 17 reaction to occur:
18 a phosphorous concentration higher than 5Oppm 19 a pH value between 7 and 11, preferably between 8 and 9.2 a molar ratio Mg/P of 0,9 to 1,5 21 a strong agitation 22 a simultaneous increase in pH and temperature to reduce time of precipitation 23 Mg2+ + NH4 + + P043" + 6 H20 MgNH4PO4.6H20 24 Many patent applications have been filed for the synthesis of the struvite. WO
01/19735 discloses a process for the treatment of manure. WO 95/05347 discloses 1 an electrolytic system using a series of electrodes. WO 2007/009749 17 by addressing one or more of the existing needs in the art.
18 Accordingly, the present invention provides for a method for the treatment of nitrogen-19 rich effluent and production of struvite comprising the steps of introducing the effluent 20 in an electrolytic system comprising a first electrolytic reactor having at least one 21 cathode and at least one anode adapted to perform electrolytic treatment of the 22 effluent in the first electrolytic reactor; and a second electrolytic reactor comprising at 23 least one cathode and at least one magnesium anode adapted to perform electrolytic 24 of the effluent in the second electrolytic reactor; performing a first electrolytic 25 treatment to the effluent in the first electrolytic reactor, thereby eliminating organic 26 matter that impact on nucleation of struvite; and performing a second electrolytic 27 treatment to the effluent in the second electrolytic reactor, thereby injecting Mg ions 1 which react with ammonium and orthophosphates from the effluent to form a struvite 2 precipitate.
3 In one embodiment of the present invention, the method further comprises a 4 conditioning step prior to the first electrolytic treatment, the conditioning step comprising adjusting the stoechiometric ratio of orthophosphate in the effluent and 6 determining, based on initial concentration of NH4, orthophosphate and calcium 7 comprised in the effluent, the current intensity and treatment time needed to be 8 applied.
9 In one embodiment of the present invention, the method further comprises a conditioning step prior to the second electrolytic treatment, the conditioning step 11 comprising adjusting stoechiometric ratio of orthophosphate in the effluent and 12 determining, based on initial concentration of NH4, orthophosphate and calcium 13 comprised in the effluent, the current intensity and treatment time needed to be 14 applied.
The present invention provides for a method wherein at least one anode of the first 16 electrolytic reactor is made of a material selected from the group consisting of 17 magnesium, aluminium, iron and an other inert material.
18 In one embodiment of the present invention, at least one anode of at least one of the 19 first and second electrolytic reactor is tubular. Preferably, at least one of the first and second electrolytic reactors comprise 9 tubular anodes disposed circularly and 21 parallel to the central axis of the reactor.
22 In an alternative embodiment of the present invention, at least one of said first and 23 second electrolytic reactors comprises one cylindrical anode disposed along the 24 central axis of the reactor.
The present invention provides for a method wherein the at least one cathode of the 26 first and second electrolytic reactors consists in a central cathode or a peripheral 27 cathode. In one embodiment of the present invention, at least one of the first and 1 second electrolytic reactors comprise both a central and a peripheral cathode. It is 2 provided that the cathodes used in the present invention are made of a material 3 selected from the group consisting of stainless, galvanized steel and a material 4 having a potential close to the one of the material of anodes. It is also provided that the cathode can be of the same material as the anode provided that in the second 6 electrolytic reactor the cathode and anode are made of magnesium.
7 The present invention provides for a method wherein the effluent is treated at a pH
8 between 7.0 and 9.5, preferably between 8.0 and 9.5 and most preferably at a pH of 9 9.2.
In a preferred embodiment of the present invention, the amount of orthophosphate in 11 the effluent is adjusted to be about five time the amount of NH4.
12 In a preferred embodiment of the present invention, the concentration of 13 orthophosphate in the effluent is adjusted to be between 50 and 300 ppm.
14 In a preferred embodiment of the present invention, the effluent is agitated while being treated in the electrolytic reactors.
16 In a preferred embodiment of the present invention, the second electrolytic treatment 17 generates Mg2+ ions in a quantity such to obtain a molar ratio Mg/P
between 0.9 and 18 1.5.
19 In a preferred embodiment of the present invention, the electrical current intensity used in the electrolytic treatments is between 1 and 120 A.
21 The present invention is suitable for any nitrogen-rich effluent, but most particularly 22 for wasted water from industrial source, wasted water from agricultural source and 23 manure.
24 In the present invention, the electrolytic treatment used can be electrocoagulation, electrofloatation or a combination of both.

1 Other objects and further scope of applicability of the present invention will become 2 apparent from the detailed description given hereinafter. However, it should be 3 understood that the detailed description and specific examples, while indicating 4 preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will 6 become apparent to those skilled in the art from this detailed description.
7 Additional and/or alternative advantages and salient features of the invention will 8 become apparent from the following detailed description, which, taken in conjunction 9 with the annexed drawings, disclose preferred embodiments of the invention 12 Referring now to the drawings which form a part of this original disclosure:
13 Figure 1 is a schematic illustration of the electrolytic system with at least one 14 embodiment of the invention; and Figure 2 is a schematic illustration of a modular electrolytic apparatus in accordance 16 with at least one embodiment of the invention.

19 A preferred embodiment of the present invention is described bellow with reference to the drawings.
21 The electrolytic system 10, as illustrated in Figure 1, comprises a prefilter 12 that 22 retains particules and allows the colloidal fraction to access a conditioning tank 14. In 23 the conditioning tank 14, there is a level captor 16 measuring and controlling the level 24 of fluid in the tanks. Also, they are sensors (not shown in Figure 1) that allow for the measurement of conductivity, pH, initial concentrations in NH4, calcium and 1 orthophosphates as well as initial organic content. Those measured values allow the 2 continuous evaluation of the conductivity of the affluent, its pH and allows the 3 adjustment of the quantity of orthophosphate in solution with respect to the NH4 4 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 6 measure of NH4 + can be made, for example, with a ISE WTW probe coupled with a 7 VARION PLUS 700IQ sensor. Phosphate analysis can be made using colorimetric 8 devices such as PHOS200 and TOPHO. The organic charge can be evaluated using 9 a CSS70 sensor. Also, UV sensors allow for the measurement of absorbance at 254nm, which can be easily correlated with the chemical demand in oxygen.
11 The measurement of the NH4 + concentration in solution also allows for the 12 determination of the Mg concentration needed to precipitate the struvite. The second 13 law of Faraday is used to convert the Mg concentration into current intensity and 14 treatment time in order to maximized the production of struvite.
Once conditioned, the effluent is pumped in a first electrolytic reactor 18 comprising a 16 fixed electrocoagulation module 20. For the purpose of the present invention, the 17 electrocoagulation could be interchanged with an electrofloatation module. The first 18 electrolytic treatment reduce of about 85% the organic charge of the effluent and the 19 treated effluent is brought in a first decantor 22 to separate the solid-liquid fractions.
An automatic dosing device (not shown in Figure 1) is placed between the exit of the 21 first decantor 22 and the entry of a second electrolytic reactor 26.
This automatic 22 dosing device allows the adjustment of the quantity of orthophosphate in the effluent 23 needed to react with all the NH4 + in solution. After this second conditioning step, the 24 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 26 fixed electrocoagulation module 20 at least one soluble anode made of magnesium.
27 The ions Mg2+ generated while applying the electrical current react with the NH4 + and 28 orthophosphate in solution and therefore produce a struvite precipitate.
Both first and 29 second electrolytic reactors 18 and 26 optionally comprises a motor 70 allowing the 1 rotation of the electrocoagulation module 20, providing for an additional agitation of 2 the fluid in the reactors 18 and 26.
3 After this second electrolytic treatment, the effluent is brought in a second decantor 4 28 for isolating the struvite precipitate.
An exemplary electrocoagulation module 20 is illustrated in Figure 2 with a section 6 view allowing a better view of its construction. The electrocoagulation module 20 7 comprises an anode module 30 and a cathode module 32 adapted to interact in an 8 electrolytic process producing electrocoagulation. The electrocoagulation module 20 9 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 11 20. The fluid, once introduced in the electrocoagulation module 20, follows a path or a 12 fluidic circuit configured to put the fluid in communication with the electrolytic process 13 that is produced in the electrocoagulation module 20. In the present example, the fluid 14 follows a path identified by a series of arrows 38 defined by internal walls 40. A pump, which is not illustrated in Figure 1, pushes the fluid through the electrocoagulation 16 module 20. An opening 42 disposed on a bottom portion 44 of the electrocoagulation 17 module 20 is normally closed with a plug (not illustrated) to prevent the fluid to exit the 18 electrocoagulation module 20. The opening 42 can be opened to remove the fluid 19 from the electrocoagulation module 20 to purge the electrocoagulation module 20 for maintenance purposes, for instance. The electrocoagulation module 20 can also be 21 purged to remove particles and debris. A larger closure member 46 is used to close 22 the bottom portion of the electrocoagulation module 20 lower body 48.
The closure 23 member 46 can be optionally removed to provide a larger access in the 24 electrocoagulation module 20. The lower body 48 can threadedly engage the upper body 56 and be removed from the upper body 56, if desirable.
26 Still referring to Figure 2, the closure member 46 is located at the lower portion of the 27 electrocoagulation module 20 to receive particles therein. The cathode module 32 is 28 bottomless and allows the particles to drop in the closure member 46 acting as a 29 particles-receiving member 46. The removable particles-receiving member 46 is 1 preferably disposed in the center of the cathode module 32 as illustrated in the 2 present embodiment and is used for removing decanted particles from the cathode 3 module 32. The opening 42 in the closure member 46 can alternatively be used to 4 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 6 32.
7 The electrocoagulation module 20 further includes body portions 48, 56 that can 8 optionally include insulating material to prevent heat transfer with the environment.
9 Conversely, the electrocoagulation module 20 might be equipped with heating/cooling elements 58 to keep the electrocoagulation apparatus 20 at a predetermined 11 operating temperature. The upper body 56 of an embodiment can be made of an 12 insulating material preventing heat transfer between the inside of the 13 electrocoagulation module 20 and the outside of the electrocoagulation module 20.
14 The lower body 48 of the embodiment illustrated in Figure 2 is made of a material that is less insulating the electrocoagulation module 20. Heating or cooling elements 58 16 are disposed, for example, in a spiral around the lower body 48 to either heat or cool 17 the lower body 48. The heating or cooling elements 58 can use a fluid circulating in a 18 tubular system or electric elements in contact with, or nearby, the lower body 48.
19 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.
21 Still referring to the embodiment of Figure 2, the anode module 30 is secured to the 22 upper body 56 and extends above the upper body 56 to allow electrical connection 62 23 thereto. The cathode module 32 of the present embodiment is also secured to the 24 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 26 negative power thereof. Electrical polarity reversal is provided when desired to avoid 27 passivation of the anode module 30 and the anodes 68 secured thereon.
Insulators 28 may be placed between two adjacent electrodes to prevent short circuits thereof. The 29 cathode 32 and the anodes 68 are subjected to DC current. One skilled in the art can 1 also appreciate that the upper body 56 is made of an insulating material to prevent 2 establishing an electrical connection between the cathode 32 and the anode module 3 30.
4 The anode module 30 can be made of soluble or inert materials. The cathode module 32 can be made of steel, aluminium, stainless steel, galvanized steel, brass or other 6 materials that can be of the same nature as the anode module 30 material or having 7 an electrolytic potential close to the electrolytic potential of the anode 68. The cathode 8 module 32 of the present embodiment has a hollowed cylindrical shape, fabricated of 9 sheet material, and can be equipped with an optional lower frustoconical portion (not illustrated in Figure 2). The inter electrode distance of an embodiment of the invention 11 is about between 8-25 mm and preferably 10 mm for electro floatation and 20 mm for 12 electrocoagulation. The interior of the cathode module 32 electrically interacts with 13 the outside of the anode module 30. The electrocoagulation module 20 internal wall 14 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 16 same time thus holding the liquid to treat therein in other embodiments.
The cathode 17 module 32 can be made of a material different from the anode material 30 or can 18 alternatively be made of the same material, like, for instance, magnesium.
19 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 21 invention. The surface ration of the cathode/anode can be identical or vary to about 22 1.5. The cathode module 32 of other embodiments can alternatively be oval or 23 conical; its diameter expending upward or downward. The electrocoagulation module 24 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 26 vibrating the fluid in the electrocoagulation module 20 as it is illustrated in the 27 embodiment depicted in Figure 2.
28 As mentioned above, the movement of the fluid increases the kinetic energy 29 contained therein to destabilize the colloidal solution. This can be achieved by 1 turbulently injecting the fluid in the electrolytic module (the speed and tangential 2 injection of the fluid are possible ways to create turbulences in the fluid). The fluid 3 agitator module 64 in this embodiment is a spiral shaped protrusion member 64 that 4 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, 6 which influences the electrolytic process. The anode module 30 of an alternate 7 embodiment that is not illustrated in Figure 2 could be rotatably secured to the upper 8 body 56 of the electrocoagulation module 20 and be rotated by an external motor to 9 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 Figure 2, 11 the anode module 30 is preferably centred inside the electrocoagulation module 20 12 and preferably located at equal distance from the cathode module 32.
13 The electrocoagulation module 20 of Figure 2 further comprises a pair of 14 electrocoagulation module connectors 66 adapted to operatively install the electrocoagulation module 20 in a larger fluid treatment process if desired.
The 16 electrocoagulation module 20 can removably be mounted in series, or in parallel, in 17 the fluid treatment process. This way, the electrocoagulation module 20 can easily be 18 added, maintained, replaced and/or removed from the fluid treatment process.
19 Example 1 An effluent from the agri-food industry has been treated using the method and 21 process of the present invention. This effluent was providing from a pork 22 transformation plant and was charged in urine, feces and blood with a pH
of 6.8. The 23 effluent has been treated with the process of the present invention using a 2 reactors 24 and decantors process, with a variable tension generator (0-30V) offering current between 1 and 120A. The anodes of the reactors were in magnesium and the 26 measures of the chemical oxygen demand, orthophosphate concentration, 27 concentration, calcium concentration and magnesium concentration made using 28 HACH chemicals.

1 Table 1 Analysis Sample Brut effluent Conditioned Treated sample Treated sample effluent 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/I) 1700 1900 0 8.85 Turbidity (NTU) 817 1100 2 9 P043" (mg/I) 43 135 0.4 0.4 NH4+ (mg/I) 55 55 26 13 It is shown in Table 1 that the brut effluent has an initial concentration of 6 orthophosphate of 43 ppm and ammonium concentration of 55 ppm. To eliminate 7 these two elements, the stoechiometric ratio has to be respected. An initial 8 concentration in orthophosphates of 55 x5 = 275 ppm should have been needed 9 according to the initial data. However, the effluent has been conditioned to have an orthophosphate concentration of 135 ppm, which allowed a reduction in NH4 + of 135:5 11 = 27 ppm corresponding to the results obtained (26 ppm). This example shows the 12 importance of respecting the stoechiometric ratio to allow an optimal reduction of 13 NH4 + as well as maintaining a pH of about 9.2.

1 Table 2 NH4 + P043" P043" P043" P043" NH 4+
NH4+
(mg/I) (mg/I) (mg/I) (mg/I) (mg/I) final eliminati initial initial theory added final on (%) 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 4 Table 2 illustrates that the ions ortho phosphate are needed to eliminate NH4 + and that the closer the ratio orthophosphate/NH4 + is closer to 5:1, the better is the NH4+
6 elimination.
7 Example 2 8 A lixiviat has been treated using the method and process of the present invention.
9 The effluent has been treated with the process of the present invention using a 2 reactors and decantors process, with a variable tension generator (0-30V) offering 11 current between 1 and 120A. The anodes of the reactors were in magnesium and the 12 measures of the chemical oxygen demand, orthophosphate concentration, NH4+
13 concentration, calcium concentration and magnesium concentration made using 14 HACH chemicals.
The effluent was treated with a tension of 27.3V and a current of 100A.

1 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/I) 234 352 27 Turbidity (NTU) 276 390 45 P043" (mg/I) 29 225 0.5 NH4+ (mg/I) 190 190 140 4 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 6 amount of 950ppm of orthophosphate should have been in the conditioned lixiviat.
7 Example 3 8 An combined effluent from landfill sites has been treated using the method and 9 process of the present invention. The effluent has been treated with the process of the present invention using a 2 reactors and decantors process, with a variable 11 tension generator (0-30V) offering current between 1 and 120A. The anodes of the 12 reactors were in magnesium and the measures of the chemical oxygen demand, 13 orthophosphate concentration, NH4 + concentration, calcium concentration and 14 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.

1 Table 4 Sample Time T(C) pH Conductivity MES (mg/I) P043" NH4+
(mS/cm) (mg/I) (m9/1) initial 0 min 22 7.84 5.94 1140 90 310 A 5 min 42 8.82 3.90 24 6.2 B 4 min 42 8.77 3.98 39 7.4 C 5 min 43 8.66 3.74 21 4.3 D 4 min 42 8.58 3.84 29 6.2 E 5 min 43 8.63 3.75 20 5.4 F 4 min 42 8.62 3.95 22 4.8 G 5 min 43 8.56 3.60 18 8.6 H 4 min 41 8.51 3.72 25 10.6 The results shown in Table 4 demonstrate that both the stoechiometric ratio and the 6 time of treatment need to be sufficient for allowing a satisfactory elimination of NH4.
7 If the stoechiometric ratio is not respected, the complete, or at least satisfactory 8 elimination of NH4 + is impossible. Also, the treatment needs to be performed for a 9 time sufficient to allow the production of a minimal quantity of Mg2+
ions, otherwise the reaction cannot be optimal.
11 While the invention has been described in connection with what is presently 12 considered to be the most practical and preferred embodiments, it is to be understood 13 that the invention is not to be limited to the disclosed embodiments and elements, but, 14 to the contrary, is intended to cover various modifications, combinations of features, equivalent arrangements, and equivalent elements included within the spirit and 16 scope of the appended claims. Furthermore, the dimensions of features of various 17 components that may appear on the drawings are not meant to be limiting, and the 18 size of the components therein can vary from the size that may be portrayed in the 1 figures herein. Thus, it is intended that the present invention covers the modifications 2 and variations of the invention, provided they come within the scope of the appended 3 claims and their equivalents.

Claims

What is claimed is:

1. A method for the treatment of nitrogen-rich effluent and production of struvite comprising the steps of:
- introducing said effluent in an electrolytic system comprising - a first electrolytic reactor comprising at least one cathode and at least one anode adapted to perform electrolytic of said effluent in said first electrolytic reactor; and - a second electrolytic reactor comprising at least one cathode and at least one magnesium anode adapted to perform electrolytic of said effluent in said second electrolytic reactor;
- performing a first electrolytic treatment to said effluent in said first electrolytic reactor, thereby eliminating organic matter that impact on nucleation of struvite; and - performing a second electrolytic treatment to said effluent in said second electrolytic reactor, thereby injecting Mg ions which react with NH4+ and orthophosphates from said effluent to form a struvite precipitate.

2. The method of claim 1, further comprising a conditioning step prior to performing said first electrolytic treatment, said conditioning step comprising adjusting stoechiometric ratio of orthophosphate in said effluent and determining, based on initial concentration of NH4+, orthophosphate and calcium comprised in said effluent, current intensity and treatment time needed to be applied.

3. The method of claim 1 or claim 2, further comprising a conditioning step prior to performing said second electrolytic treatment, said conditioning step comprising adjusting stoechiometric ratio of orthophosphate in said effluent and determining, based on initial concentration of NH4+, orthophosphate and calcium comprised in said effluent, current intensity and treatment time needed to be applied.

4. The method of any one of claims 1 to 3, wherein said at least one anode of said first electrolytic reactor is made of a material selected from the group consisting of magnesium, aluminium, iron and an other inert material.

5. The method of any one of claims 1 to 4, wherein said at least one anode of at least one of said first and second electrolytic reactor is tubular.

6. The method of any one of claims 1 to 5, wherein at least one of said first and second electrolytic reactors comprise 9 tubular anodes disposed circularly and parallel to the central axis of said reactor.

7. The method of any one of claims 1 to 4, wherein at least one of said first and second electrolytic reactors comprises one cylindrical anode disposed along the central axis of said reactor.

8. The method of any one of claims 1 to 7, wherein said at least one cathode of said first and second electrolytic reactors consists in a central cathode, a peripheral cathode or a combination of both.

9. The method of any one of claims 1 to 8, wherein said at least one cathode of said first and second electrolytic reactors is made of a material selected from the group consisting of stainless, galvanized steel and a material having a potential close to the one of the material of said at least one anode.

10. The method of any one of claims 1 to 9, wherein said effluent is treated at a pH
between 7.0 and 9.5.

11. The method of any one of claims 1 to 10, wherein said effluent is treated at a pH
between 8.0 and 9.5.

12. The method of any one of claims 1 to 11, wherein said effluent is treated at a pH
of 9.2.

13. The method of any one of claims 1 to 12, wherein the amount of orthophosphate in said effluent is adjusted to be about five time the amount of NH4+.

14. The method of any one of claims 1 to 12, wherein the concentration of orthophosphate in said effluent is adjusted to be between 50 and 300 ppm.

15. The method of any one of claims 1 to 14, wherein the effluent is agitated while being treated in said first and second electrolytic reactors.

16. The method of any one of claims 1 to 15, wherein said first and second electrolytic treatments are selected from the group consisting of electrocoagulation, electrofloatation and a combination thereof.

17. The method of any one of claims 1 to 16, wherein said effluent to be treated is selected from the group consisting of a wasted water from industrial source, a wasted water from agricultural source and manure.

18. The method of any one of claims 1 to 17, wherein said second electrolytic treatment generates Mg2+ ions in a quantity such to obtain a molar ratio Mg/P
between 0.9 and 1.5.

19. The method of any one of claims 1 to 8, wherein said first and second electrolytic treatment are performed using an electrical current intensity between 1 and 120 A.