GAS RECOVERY FROM WASTEWATER

Abstract

The present invention is in the field of a system for gas recovery from wastewater, a method for treating wastewater, and a method wherein ammonia and carbon dioxide are recovered. Typically a wastewater stream is fed into the system, treated and stripped from ammonia and carbon dioxide, and a cleaner stream is released.

Claims

1. Wastewater gas recovery system (100) for recovering NH.sub.3 and CO.sub.2 comprising at least one ion exchange unit (30), each exchange unit comprising at least three ion exchange compartments (31, 32, 33), each ion exchange compartment being in contact over a membrane with at least one adjacent compartment, a first alkaline ion exchange compartment (31) being in fluidic contact with a positive side of first bipolar membrane (11a) and with a cation exchange membrane (12) and comprising aqueous NH.sub.3.sup.+ and OH.sup.−, a second ion exchange compartment (32) being in fluidic contact with an anion exchange membrane (13) and with a cation exchange membrane (12) and comprising water, NH.sub.4.sup.+, and HCO.sub.3.sup.−, and a third acidic ion exchange compartment (33) being in fluidic contact with a negative side of a bipolar membrane (11b) and with an anion exchange membrane (13) and comprising aqueous H.sup.+ and HCO.sub.3.sup.−, a wastewater input (70) for providing wastewater to the second compartment, a treated water output (71) adapted to receive output from the second compartment, a cathode (42) and an anode (41) for providing a voltage, at least two electrode rinse compartments (21, 22) being in electrical contact with the cathode (42) or with the anode (41) and with a membrane (11a,b, 12, 13), and comprising salt, at least three recirculation units (51, 52, 74a,b), a first alkaline recirculation unit (51) adapted to receive input from the first compartment (31), comprising a pump (81), an gaseous ammonia stripper (61), and for providing stripped output to the first compartment, a second acidic recirculation unit (52) adapted to receive input from the third compartment (33), comprising a pump (82), an gaseous CO.sub.2 stripper (62), and for providing stripped output to the third compartment, and a third recirculation unit (74a,b) adapted to receive input from a first electrode rinse compartment (21, 22), and for providing output to at least one of, wherein at least one recirculation unit (51, 52) comprises a hydrophobic membrane (61a, 62a), a molecular sieve for ammonia or for CO.sub.2, respectively, a pervaporation membrane, or a combination thereof, wherein the third recirculation unit (74a,b) is adapted to receive input from the first electrode rinse compartment (21), and for providing to the second electrode rinse compartment (22), and vice versa, and at least one of a tube (72) for removing gaseous ammonia, and a tube (73) for removing gaseous CO.sub.2.

2. System according to any of claim 1, wherein the first electrode rinse compartment (21) comprises NH.sub.4.sup.+ or H.sup.+, or wherein the second electrode rinse compartment (22) comprises OH.sup.− or HCO.sub.3.sup.−, or wherein the first electrode rinse compartment (21) comprises NH.sub.4.sup.+ or H.sup.+ and wherein the second electrode rinse compartment (22) comprises OH.sup.− or HCO.sub.3.sup.−.

3. System according to any of claims 1-2, wherein at least one recirculation unit comprises a pump (82).

4. System according to any of claims 1-3, wherein at least one membrane (61a, 62a) in the stripper is impermeable to liquids, and permeable to gases.

5. System according to any of claims 1-4, wherein the hydrophobic membrane (61a, 62a) is macroporous, with an average pore size of 50-500 nm, or microporous, with an average pore size of 0.4-10 nm (as determined by electron microscopy).

6. System according to any of claims 1-5, wherein the membrane (61a, 62a) is selected from polymeric material, inorganic material, and combinations thereof.

7. System according to any of claims 1-6, wherein the exchange unit (30) comprises a stack of a cation exchange membrane (12), an alkaline ion exchange compartment (31), a bipolar membrane (11a), an acidic ion exchange compartment (33), an anion exchange membrane (13), and a wastewater ion exchange compartment (32), and wherein the second electrode rinse compartment (22) is in fluidic contact with a further cation exchange membrane (12), and wherein the third recirculation unit (74a,b) is adapted to receive input from a first electrode rinse compartment(21), and adapted to provide output to electrode rinse compartment (22), or wherein the exchange unit (30) comprises a stack of an anion exchange membrane (13), an acidic ion exchange compartment (33), a bipolar membrane (11a), an alkaline ion exchange compartment (31), a cation exchange membrane (12), and a wastewater ion exchange compartment (32), and wherein the second electrode rinse compartment (22) is in fluidic contact with a further anion exchange membrane (13), and wherein the third recirculation unit (74a,b) is adapted to receive input from a first electrode rinse compartment (22), and adapted to provide d output to electrode rinse compartment (21), or wherein the exchange unit (30) comprises a stack of an bipolar membrane (11a), an alkaline ion exchange compartment (31), a cation exchange membrane (12), a wastewater ion exchange compartment (32), an anion exchange membrane (13), and an acidic ion exchange compartment (33), and wherein the second electrode rinse compartment (22) is in fluidic contact with a further bipolar membrane (11b), and wherein the third recirculation unit (74a,b) is adapted to receive input from a first electrode rinse compartment (21), and adapted to provide output to electrode rinse compartment (21), and vice versa to electrode rinse compartment (22).

8. System according to any of claims 1-7, comprising 2-2.sup.10 ion exchange units (30) in parallel.

9. System according to any of claims 1-8, wherein membranes (11a,b, 12 and 13) are separated by spacers (2) and the membranes 11a,b, 12 and electrodes are separated by spacers (2).

10. System according to any of claims 1-9, wherein in operation at least one of a voltage of 0.1-5 V per ion exchange unit (30) is applied, a pH in the first alkaline ion exchange compartment (31) is from 7-14, a pH in the third acidic ion exchange compartment (33) is from 1-7, a current density is from 5-500 A/m.sup.2, a flow parallel to a membrane is each individually from 0.01-0.20 m/s, a NH.sub.4.sup.+ flux over a membrane is each individually 0.2-20 mole/m.sup.2/h, a HCO.sub.3.sup.− flux over a membrane is each individually 0.2-20 mole/m.sup.2/h, an operating temperature is from 10-80° C., the [NH.sub.4.sup.+] and [HCO.sub.3.sup.−] in the second ion exchange compartment (32) is each individually 10.sup.−3-2 mole/1, a vacuum of 0.1-90 kPa is each individually applied over membranes (61, 62), a flux of wastewater and recirculation is each individually 0.01-10 kg/m.sup.2/h, and an NH.sub.3 flux and a CO.sub.2 flux in recirculation units (51, 52) is each individually 50-5000 g/m.sup.2/h.

11. Method for treating wastewater comprising providing a system (100) according to any of claims 1-10, applying an electrical potential difference over the anode (41)/cathode (42), providing wastewater in second ion exchange compartment (32) comprising NH.sub.4.sup.+, and HCO.sub.3.sup.−, transferring NH.sub.4.sup.+ from the wastewater (70) to an alkaline recirculation solution (51), simultaneously, transferring HCO.sub.3.sup.− from the wastewater to an acidic recirculation solution (52), depleting NH.sub.4HCO.sub.3 in the wastewater, and splitting water over bipolar membranes (11a, 11b) thereby providing H.sup.+ to the third ion exchange compartment (33) and thereby providing OH.sup.− to the first ion exchange compartment (31), wherein transferring NH.sub.4.sup.+ from the wastewater (70) to an alkaline recirculation solution (51) is through a first ion exchange compartment (31), wherein transferring HCO.sub.3.sup.− from the wastewater to an acidic recirculation solution (52) is through a third ion exchange compartment (33), wherein NH.sub.4 is converted into NH.sub.3 in the presence of OH.sup.− in the first compartment (31), and wherein HCO.sub.3.sup.− is converted into CO.sub.2 in the presence of H.sup.+ in the third ion exchange compartment (33), wherein NH.sub.3 is stripped in ammonia stripper (61), and wherein CO.sub.2 is stripped in CO.sub.2 stripper (62).

12. Method according to any of claims 11, wherein at a gaseous side of stripper (61, 62) an under pressure is applied.

13. Method according to any of claims 11-12, further comprising forming NH.sub.4HCO.sub.3.

14. Method according to any of claims 11-13, wherein wastewater is provided by at least one of a domestic sewage treatment plant, a manure treatment facility, a fertilizer production plant, food and beverage industry, and an industry producing nitrogen loaded wastewater.

Description

FIGURES

[0062] The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying figures.

[0063] FIG. 1-5 show schematics of the present system.

DETAILED DESCRIPTION OF THE FIGURES

[0064] In the figures: [0065] 100 present system [0066] 2 spacer [0067] 11 bipolar membrane [0068] 11a first bipolar membrane [0069] 11b second bipolar membrane [0070] 12 cation exchange membrane [0071] 13 anion exchange membrane [0072] 21 electrode rinse compartment (anodic) [0073] 22 electrode rinse compartment (cathodic) [0074] 30 ion exchange unit [0075] 31 first alkaline compartment [0076] 32 second salt compartment [0077] 33 third acidic compartment [0078] 41 anode [0079] 42 cathode [0080] 51 alkaline recirculation unit [0081] 52 acidic recirculation unit [0082] 61 ammonia stripper [0083] 61a (hydrophobic) membrane [0084] 61b strip chamber [0085] 62 gaseous CO.sub.2 stripper [0086] 62a (hydrophobic) membrane [0087] 62b strip chamber [0088] 70 wastewater input [0089] 71 treated water output [0090] 72 tube for removing gaseous ammonia [0091] 73 tube for removing gaseous CO.sub.2 [0092] 74a electrode rinse recirculation unit [0093] 74b electrode rinse recirculation unit [0094] 81 liquid pump [0095] 82 vacuum pump

[0096] FIG. 1-3 show an exemplary set-ups of the present system.

[0097] FIG. 4 shows a stacked variant of the present system.

[0098] FIG. 5 shows optional spacers.

[0099] The figures have been detailed throughout the description.

[0100] FIG. 1 shows a cell triplet provided with cation exchange membranes at the electrodes.

[0101] FIG. 2 shows a cell triplet provided with anion exchange membranes at the electrodes.

[0102] FIG. 3 shows a cell triplet provided with bipolar membranes at the electrodes.

[0103] FIG. 4 represents a plural version of FIG. 1.

[0104] FIG. 5 shows that all membranes (11, 12 and 13) are separated by spacers 2. The spacers are made of polyethylene/silicone material and woven into a mesh. The liquids flow through the void fraction of the spacers, forming the salt, acid and alkaline chambers. The spacers are sealed on the top and bottom, making sure that the liquids are not leaking out of the membrane stack. The electrodes (anode and cathode) and the membranes next to the electrodes are also separated by spacers, forming the electrode rinse chambers.