SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS

Abstract

Sanitary landfill leachate treatment by oxyammonolysis comprises three steps: 1.sup.st physical-chemical step with withdrawal of inert solid class II-B, 2.sup.nd step of filtration and 3.sup.rd step of catalytic oxidation and ammonolysis by cathodic reduction, obtaining treated effluents that complies with environmental legislation in terms of disposal or re-use of water.

Claims

1. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS comprising the following consecutive steps: (i) physico-chemical treatment of a slurry, such slurry is inserted into a stirred reactor until 60% of its volume is filled and mixed with ferric chloride from 0.35% to 0.70% by volume of the reactor, said mixture is shaken at 40 rpm for five minutes to coagulate; to the resulting coagulated mixture is added an anionic flocculating polymer, the stirring being maintained at 20 rpm for three minutes, when a cationic flocculating polymer is added and the stirring is maintained at 20 rpm for another three minutes; the resulting mixture rests for forty minutes and is then transferred to a flotation tank by dissolved air; (ii) filtration of a liquid fraction from the flotation tank in a sand filter, followed by a microfiltration and a nanofiltration resulting in a nanofiltration permeate and a retentate of the nanofiltration; the sanitary landfill leachate treatment process by oxyammonolysis is characterized by the fact that it further comprises the step of: (iii) oxyammonolysis wherein the nanofiltration permeate is transferred to an aeration tank and ozone is injected to such tank resulting in an oxidized effluent which is transferred to an ammonolysis conduit where it is subjected to the electric potential difference until reaches the concentration of 3 mg/L of ammonium nitrogen obtaining an effluent, said effluent is then pumped to a press filter for retention of ionic residues, iron and nitrogen.

2. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that in the flocculation step of the physico-chemical step is added between 600 ppm and 800 ppm of flocculant anionic polymer.

3. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that in the flocculation step of the physico-chemical step is added between 600 ppm and 1000 ppm of polyacrylamide cationic flocculant polymer.

4. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that in the microfiltration step particles greater than 1 micrometer are retained.

5. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that the retentate from nanofiltration returns to the retainate tank.

6. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that the final concentrate of the nanofiltration is raw material for soil conditioners or NPK fertilizer.

7. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that the aeration tank receives from 10 g to 20 g of ozone (O.sub.3) per cubic meter (m.sup.3) of effluent to be oxidized.

8. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that the passage conduit comprises electrodes having graphite cathode and stainless steel anode is mounted inside the conduit and the continuous current source maintains the electric potential difference between 4 volts and 6 volts in the electrodes.

9. SANITARY LANDFILL LEACHATE TREATMENT PROCESS BY OXYAMMONOLYSIS, according to claim 1, characterized in that the effluent of the press filter returns to the ammonolysis conduit.

Description

[0010] The drawings illustrate the equipment involved in the steps of the landfill leachate treatment process, the object of the present patent. The drawings are illustrations that contribute to an improved understanding of the present specification, wherein:

[0011] FIG. 1 shows the equipment involved in the 1.sup.st physical-chemical step;

[0012] FIG. 2 shows the equipment involved in the 2.sup.nd filtration step;

[0013] FIG. 3 shows the equipment involved in the 3.sup.rd step of catalytic oxidation and ammonolysis by cathodic reduction.

[0014] The 1.sup.st step is physical-chemical and takes place in a physical-chemical reactor (1), endowed with stirrer (2) and uses a property from the humins present in the slurry, originating from the degradation of the lignin present in the waste; the slurry is pumped from the slurry pond to the physical-chemical reactor until it occupies 60% of the volume thereof, adding 0.35% to 0.70%, in volume of such reactor, of ferric chloride (FeCl.sub.3), to be defined by jar-test; Fe chelates the humins forming organo-metals which by allosteric effect causes the chelation of other metals present in the slurry and co-adsorption to amine groups forming the clot; FeCl.sub.3 acidifies the mediums which decomposes the carbonates (CO.sub.3.sup.2?) present, with a large release of carbon gas (CO.sub.2), which causes the formation of a foam that occupies from 20% to 30% of the volume of the physical-chemical reactor; the clot reaction takes place with fast stirring in the medium, 40 rpm on the shaft of the stirrer; after five (5) minutes the flocculation reaction begins by adding 600 ppm to 800 ppm of flocculant anionic polymer, with slow stirring, 20 rpm on the shaft of the stirrer, to prevent rupture of the flakes formed, for three (3) minutes; the flocculant anionic polymer promotes the aggregation of the clots and uptake of oils and grease, suspended solids, etc.; the final size of the flake and the final encapsulation of the contaminant is obtained by adding 600 ppm to 1000 ppm of polyacrylamide cationic flocculant polymer, with slow stirring, 20 rpm on the shaft of the stirrer, for three (3) minutes; the stirrer is switched off and the system rests for forty (40) minutes; due to the formation of carbon gas, the flakes formed float promoting the separation of the medium into two phases, supernatant solids and a gold-yellow colored liquid smelling of ammonium, mainly composed of humates and fulvates having different molecular weights, of ammonium, sodium, iron and chlorides; the physical-chemical reactor is unloaded onto a solid separation ramp, with a grid measuring 0.5 mm, a liquid phase containing the solids under 0.5 mm that falls into the flotation tank by dissolved air (3); the centrifugal pump (4) withdraws the liquid phase from the floater; a scraper withdraws the floated solids, the solid phase of the physical-chemical reactor forms a solid substrate which is taken to a dumpster for final disposal in the landfill itself; the dry solid is class II-B and not leachate.

[0015] The 2.sup.nd step is that of filtration which involves a quartz sand filter (5) for retaining coarse solids, a microfiltration (8) with polypropylene cartridges and retaining particles greater than 1 micrometer, for protecting the nanofiltration membrane (9); the post-physical-chemical (liquid phase) effluent is withdrawn from the floater by the pump (4) passing through the sand filter (5) and up to the retainate tank (6) of the nanofiltration; a multiple-stage pump (7), having pressure of 1470000 Pa, pumps the effluent to pass through the microfiltration (8) and the nanofiltration membrane (9); the nanoretained matter returns to the retainate tank (6) and the permeate follows on to the effluent treatment step; when the temperature of the permeate at the nanofiltration outlet reaches 40? C., the pressures being maintained, the nanofiltration process will be concluded.

[0016] The concentrate from the nanofiltration is rich in humic substances which are solid conditioners for agriculture, humates and ammonium fulvate; the humic and fulvic acids belong to humins and are organic nitrogen compounds having excellent absorption by plants because they originate from the biological degradation of the organic vegetable matter present in the waste deposited in the landfill; by ionic exchange resins the traces of chloride and sodium are withdrawn from the concentrate, which is ready to be used as raw material for producing NPK fertilizer, with the addition of phosphorus (P) and potassium (K) to obtain fertilizer to recover the soils of farmable land.

[0017] The 3.sup.rd treatment step, in which the effluent permeated in the nanofiltration undergoes catalytic oxidation of the organic matter having lower molecular weight in the aeration tank (13); an ozone generator (11) injects ozone via the venturi circulation pump (12), at the bottom of the tank there are air diffusers and a radial compressor blows the air towards the diffusers; the oxidation consists of the in situ production of oxygen-reactive species (ERO) such as superoxide anion radical (O.sub.2..sup.?), hydrogen peroxide (H.sub.2O.sub.2), singlet dioxygen (O.sub.2), hydroxyl radical (HO.), and the effluent receives from 10 g to 20 g of O.sub.3 (ozone) per m.sup.3 (cubic meter) of effluent to be oxidized, via venture pump (11), furnished by the ozone generator (10); the oxidized effluent presenting a concentration of Cl.sup.? between 1000 mg/l and 2000 mg/l, of Fe.sup.3+ between 500 mg/l and 1500 mg/l, of Nh.sub.4.sup.+ between 250 mg/l and 350 mg/l passes through the ammonolysis conduit by cationic reduction.

[0018] Ammonolysis by cathodic reduction involves a passage conduit (14), circulation pump (14), press filter (15); a set of electrodes, with graphite cathode and stainless steel anode is mounted inside the conduit and the continuous current source maintains the electric potential difference between 4 volts and 6 volts in the electrodes; ammonolysis is a technique that consists of breaking the nitrogen-hydrogen bonds in the azo groups to increase the valence state of the nitrogen atom up to the formation of molecular nitrogen (N.sub.2), with release of H.sup.+, acidifying the medium; Fe.sup.2+ present in the medium acts to inhibit the reaction of nucleophilic addition of chloride in organic compounds; pursuant to the kinetic principles below:

(anode) Cl.sup.?+H.sub.2O.fwdarw.ClO.sup.?+2H.sup.++2e.sup.?;Kinetic 1:

(cathode) Fe.sup.2++2e.sup.?.fwdarw.Fe.sup.0;Kinetic 2:

(decomposition of the ammonium): 3Cl.sup.?+2NH.sub.4.sup.+.fwdarw.3Cl.sup.?+N.sub.2+3H.sub.2O+2H.sup.+;Kinetic 3:

the electrodes have a power difference of 4 v in continuous current; the cathodic ammonolysis reaction will be interrupted when the concentration of ammonium nitrogen reaches 3 mg/l; during ammonolysis the effluent is pumped to pass through a press filter, in which Fe.sup.0 hydrate is retained and recovered as ferric chloride by the addition of hydrochloric acid and to be re-used in the 1.sup.st physical-chemical step; the effluent of the press filter returns to the ammonolysis conduit.

[0019] FIG. 1 illustrates the equipment involved in the 1.sup.st physical-chemical step; physical-chemical reactor (1), stirrer (2), flotation tank by dissolved air (3) and pump (4).

[0020] FIG. 2 illustrates the equipment involved in the 2.sup.nd step of the treatment process, the filtration step; centrifugal pump (4); sand filter (5); retainate tank (6); high pressure centrifugal pump (7); micro filtration (8); nanofiltration (9).

[0021] FIG. 3 illustrates the equipment involved in the 3.sup.rd catalytic oxidation step and ammonolysis by cathodic reduction; aeration tank (12), ozone generator (10), venture pump (11), ammonolysis conduit (14), circulation pump (15) and press filter (16).