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Title:
ELECTROLYTIC APPARATUS AND METHOD FOR TREATING WATER TO REMOVE AMMONIUM AND PHOSPHATE IONS
Document Type and Number:
WIPO Patent Application WO/2013/009671
Kind Code:
A2
Abstract:
An apparatus for treating contaminated water includes an electrolytic cell, first connecting plumbing, and an air-stripping apparatus. The electrolytic cell includes an anode chamber, a cathode chamber, an anode, a cathode, and a membrane. The anode is in the anode chamber and the cathode is in the cathode chamber. The membrane is positioned between the anode chamber and the cathode chamber. The cathode chamber has a cathode chamber inlet and a cathode chamber outlet. The anode chamber has an anode chamber inlet and an anode chamber outlet. The water for treatment is provided to the cathode chamber inlet. The connecting plumbing connects the cathode chamber outlet with the anode chamber inlet. The air-stripping apparatus is positioned in the connecting plumbing first connecting the cathode chamber outlet and the anode chamber inlet.

Inventors:
GREENBERG BERNARD (US)
Application Number:
PCT/US2012/045899
Publication Date:
January 17, 2013
Filing Date:
July 09, 2012
Export Citation:
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Assignee:
AQUA VECTORS INC (US)
GREENBERG BERNARD (US)
International Classes:
B01D61/42; C02F1/461; C02F1/469; C25B9/19; C02F101/16
Foreign References:
US5470669A1995-11-28
KR19980042172A
US6471873B12002-10-29
US4765873A1988-08-23
US7018543B22006-03-28
Attorney, Agent or Firm:
LEAS, James, Marc (37 Butler DriveSouth Burlington, VT, US)
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Claims:
What is claimed is:

Claims

1. An apparatus for treating contaminated water, comprising an electrolytic cell, first connecting plumbing, and an air-stripping apparatus, wherein said electrolytic cell includes an anode chamber, a cathode chamber, an anode, a cathode, and a membrane, wherein said anode is in said anode chamber and said cathode is in said cathode chamber, wherein said membrane is positioned between said anode chamber and said cathode chamber, wherein said cathode chamber has a cathode chamber inlet and a cathode chamber outlet, wherein said anode chamber has an anode chamber inlet and an anode chamber outlet, wherein the water for treatment is provided to said cathode chamber inlet, wherein said first connecting plumbing connects said cathode chamber outlet with said anode chamber inlet, wherein said air-stripping apparatus is positioned in said first connecting plumbing connecting said cathode chamber outlet and said anode chamber inlet.

2. An apparatus as recited in claim 1, wherein said membrane is positioned in said

electrolytic cell to maintain a pH difference between said anode chamber and said cathode chamber when a voltage is applied between said anode and said cathode.

3. An apparatus as recited in claim 2, wherein the contaminated water for treatment

includes ammonium ions, wherein the contaminated water for treatment is provided with hydroxyl ions at said cathode and hydrogen ions at said anode when a sufficient voltage is applied, wherein when a sufficient voltage is applied said ammonium ions react with said hydroxyl ions in said cathode chamber to form ammonia gas, wherein said air-stripping apparatus is positioned for removing dissolved ammonia gas from said contaminated water.

4. A apparatus as recited in claim 3, wherein said water for treatment also includes

dissolved matter, further comprising providing a filter in said first connecting plumbing for filtering out materials that precipitate in presence of said hydroxyl ions.

5. A apparatus as recited in claim 4, wherein said dissolved matter include ions of at least one from the group consisting of calcium, phosphorus, fluorine, and iron.

6. A apparatus as recited in claim 3, wherein said air-stripping apparatus includes a first nozzle and a fan, wherein said first nozzle is positioned for providing said contaminated water as droplets in said first connecting plumbing and wherein said fan is positioned in said first connecting plumbing for providing a flow of air through said droplets for removing said ammonia gas from said water and providing said ammonia gas in said flow of air.

7. An apparatus as recited in claim 6, further comprising second connecting plumbing, wherein said ammonia laden air flows in said second connecting plumbing, wherein said second connecting plumbing further includes a device positioned for spraying droplets of sulfuric acid through said ammonia laden air to produce liquid ammonium sulfate and air with most ammonia gas removed.

8. A apparatus as recited in claim 7, further comprising a reservoir, wherein said device for spraying droplets of sulfuric acid includes a second nozzle, wherein said second connecting plumbing is connected to direct said liquid ammonium sulfate for collection in said reservoir.

9. An apparatus as recited in claim 7, wherein said system further includes a third

connecting plumbing for directing said air with most ammonia removed for reuse in stripping ammonia from additional contaminated water droplets.

10. An apparatus as recited in claim 3, wherein said first connecting plumbing includes a portion for collecting said water droplets with ammonia gas removed and directing said water with ammonia gas removed to said anode chamber, wherein said anode provides hydrogen ions for reducing pH of said water with ammonia gas removed before discharge through said anode chamber outlet.

11. An apparatus as recited in claim 10, wherein water discharged through said anode chamber outlet has substantially a neutral pH.

12. An apparatus as recited in claim 10, further comprising equipment for aluminum

processing, fourth connecting plumbing, and fifth connecting plumbing, wherein said fourth connecting plumbing connects said equipment for aluminum processing to said cathode chamber inlet, and wherein said fifth connecting plumbing connects said anode chamber outlet to said equipment for aluminum processing, wherein contaminated water containing ammonium ions is provided from said equipment for aluminum processing to said cathode chamber inlet through said fourth connecting plumbing, and wherein cleaned water from said anode chamber outlet that is substantially free of said ammonium ions is returned for reuse in said aluminum processing equipment through said fifth connecting plumbing.

13. An apparatus as recited in claim 1, wherein said membrane includes a porous material, wherein said membrane has a pore size sufficiently large to allow electrically driven ion transfer, wherein said membrane has a pore size sufficiently small to maintain a pH difference between said anode chamber and said cathode chamber.

14. An apparatus as recited in claim 13, wherein said electrolytic cell with said membrane provides greater than or equal to pH 12 at said cathode when a voltage is applied to said anode and said cathode.

15. An apparatus as recited in claim 13, wherein said porous material has multiple pores, wherein said porous material has an average pore size, wherein said average pore size is from 0.5 to 10 micrometers.

16. An apparatus as recited in claim 13, wherein said porous material has multiple pores, wherein said porous material has an average pore size, wherein said pores vary from said average pore size within a range, wherein said range is +/- 5% of said average pore size. An apparatus as recited in claim 13, wherein said membrane is made of PTFE.

An apparatus as recited in claim 1 , wherein said first connecting plumbing includes at least one flow directing device for directing flow of water from said cathode chamber to said anode chamber.

An apparatus as recited in claim 1 , wherein said anode has an anode surface, wherein said anode surface contains iridium oxide.

An apparatus as recited in claim 19, wherein said anode contains titanium coated with said iridium oxide.

21. A method of treating water, comprising: a. providing water for treatment, wherein said water contains a contaminant

material including ammonium ions; b. providing an electrode having a negative voltage to react with the water for treatment to provide hydroxyl ions in the water for treatment, wherein a portion of said hydroxyl ions react with said ammonium ions to form ammonia gas dissolved in said water; c. air-stripping said ammonia gas from said water to provide water substantially free of ammonia gas; and d. providing an electrode having a positive voltage to substantially neutralize said water that is substantially free of said ammonium ions.

22. A method as recited in claim 21, wherein said water for treatment also includes

dissolved ions, further comprising reacting said dissolved metal ions with said hydroxyl ions and filtering out materials that precipitate.

23. A method as recited in claim 22, wherein said dissolved ions include ions of at least one from the group consisting of calcium, phosphorus, fluorine, and iron.

24. A method as recited in claim 21, wherein said air-stripping involves providing said water as droplets and providing a flow of air through said droplets.

25. A method as recited in claim 21, further comprising removing said ammonia gas from air used in said air-stripping.

26. A method as recited in claim 25, wherein said removing said ammonia gas from said air used in said air-stripping involves passing said ammonia containing air through a mist of sulfuric acid to form ammonium sulfate and cleaned air, and collecting said ammonium sulfate.

27. A method as recited in claim 26, further comprising reusing said cleaned air to remove additional ammonia gas from said water.

28. A method as recited in claim 27, further comprising providing said water for treatment from an aluminum processing and providing said water that is substantially free of said ammonium ions for reuse.

29. A method of removing a contaminant from water, comprising: a. providing an electrolytic cell that includes an anode chamber, a cathode

chamber, and a membrane there between, wherein said anode chamber includes an anode and wherein said cathode chamber includes a cathode; b. directing the water containing said contaminant into said cathode chamber; c. directing the water from said cathode chamber to said anode chamber; d. providing a voltage between said anode and said cathode sufficient to

electrically generate hydrogen ions in the water at said anode and hydroxyl ions in the water at said cathode, wherein said membrane maintains a pH difference between said anode chamber and said cathode chamber and wherein the water directed from said cathode chamber includes said electrically generated hydroxyl ions providing an alkaline pH; e. providing a reaction with said hydroxyl ions for rendering said contaminant removable from said water; and f. providing a reaction with said hydrogen ions before said water leaves said anode chamber wherein said water exiting said anode chamber has an exiting pH, wherein said exiting pH is about equal to a neutral pH.

30. A method as recited in claim 29, further comprising removing said reaction product of said contaminant and said hydroxyl ions from said water.

31. A method as recited in claim 30, wherein said contaminant includes ammonium ions.

32. A method as recited in claim 31 , wherein said reaction product includes ammonia gas dissolved in said water. A method as recited in claim 32, further comprising stripping said ammonia gas from said water to provide water substantially free of said ammonium ions.

Description:
Electrolytic Apparatus and Method for Treating Water to Remove Ammonium and

Phosphate Ions

Related Applications

This application is related to US Provisional Patent Application 61/507,102 filed July 12, 2011, incorporated herein by reference.

This application is also related to US Provisional Patent Applications 61/371,926 filed August 8, 2010 and 61,430,264 ("the '264 application") filed January 6, 2011, both of which are incorporated herein by reference.

This application is also related to PCT/US 11/46978 filed on August 8, 2011 , incorporated herein by reference.

This application is also related to US Patent 6,471,873, incorporated herein by reference.

Field

This patent application generally relates to techniques for treating and purifying contaminated water. More particularly, this patent application is related to electrolytic techniques for removing ions including ammonium, phosphate, chloride, calcium and fluoride ions from water.

Background

Various chemical and electrochemical methods have been used, with varying deg success, for treating industrial waste streams containing ammonia gas/ammonium ions, phosphate, chloride, calcium and fluoride. Chemical treatment has included addition of coagulants, flocculants, adsorbents, filter aids and oxidants. Secondary processes are generally required to remove the by-products of reactions stimulated by these added chemicals and agents. These by-products are often toxic and voluminous, and their removal and destruction or neutralization is expensive and time consuming, so in general they have not enjoyed

wide-spread adoption.

More recently electrolytic treatment of contaminated water has been proposed by Greenburg, et al. in U.S. patent 6,471,873 ("the '873 patent"), incorporated herein by reference. The '873 patent describes an electrolytic cell having an anode chamber and cathode chamber separated by a membrane of submicron porosity. An electric current is applied through the cell. Contaminated water is fed into the cathode chamber, then into a holding tank, and then into the anode chamber. At the cathode electrically driven reactions occur to bring about the

agglomeration of colloidal particles which can then be filtered out. At the anode, high current densities facilitate the oxidation of ammonia to nitrogen gas and produce chloric acid to oxidize any residual soluble organic material and act germicidally. While the electrolytic treatment can be carried out on a smaller foot print, produce fewer odors, consume less energy, and greatly reduce sludge byproduct, further improvement is needed to reduce the amount of electricity used, extend the life of the electrodes, eliminate the production of chlorine gas, and reduce costs, and these improvements are provided by the present patent application.

Summary

One aspect of the present patent application is an apparatus for treating contaminated water that includes an electrolytic cell, first connecting plumbing, and an air-stripping apparatus. The electrolytic cell includes an anode chamber, a cathode chamber, an anode, a cathode, and a membrane. The anode is in the anode chamber and the cathode is in the cathode chamber. The membrane is positioned between the anode chamber and the cathode chamber. The cathode chamber has a cathode chamber inlet and a cathode chamber outlet. The anode chamber has an anode chamber inlet and an anode chamber outlet. The water for treatment is provided to the cathode chamber inlet. The connecting plumbing connects the cathode chamber outlet with the anode chamber inlet. The air-stripping apparatus is positioned in the first connecting plumbing connecting the cathode chamber outlet and the anode chamber inlet.

Another aspect of the present patent application is a method of treating water, comprising providing water for treatment in which the water contains a contaminant material including ammonium ions. The method also includes providing an electrode having a negative voltage to react with the water for treatment to provide hydroxyl ions in the water for treatment in which a portion of the hydroxyl ions react with the ammonium ions to form ammonia gas dissolved in the water. The method also includes air-stripping the ammonia gas from the water to provide water substantially free of ammonia gas. The method also includes providing an electrode having a positive voltage to substantially neutralize the water that is substantially free of the ammonium ions.

Brief Description of Drawings

The foregoing and other aspects and advantages of the invention will be apparent from the following detailed description as illustrated in the accompanying drawings, in which:

FIG. 1 is a schematic diagram of one embodiment of an electrolytic cell connected with an air-stripping system and an air cleaning system for first converting ammonium ions in contaminated water into ammonia gas, much of which remains dissolved in the water, then using the air-stripping system to remove the dissolved ammonia gas from the water and provide the ammonia gas mixed in with the air, and then reacting the ammonia gas to remove the ammonia gas from the air and provide an ammonia compound that has commercial value while providing water cleaned of the ammonium ions and with neutral pH as the water exits the electrolytic cell and while providing air cleaned of ammonia gas for reuse in the air stripping system; Detailed Description

In one embodiment, the present patent application provides for removal of unwanted ammonium ions from waste water and provision of a commercially valuable ammonia containing compound as a side benefit. In the process a highly elevated pH is provided in the stream of waste water containing the ammonium ions in the cathode chamber of an electrolytic cell. In the presence of a highly elevated pH the ammonium ions are converted to ammonia gas. After a step to remove dissolved ammonia gas from the contaminated water the pH of the water is adjusted in the anode chamber of the electrolytic cell to provide a neutral pH prior to discharge. The electrolytic cell and the process for using the electrolytic cell to provide large changes in pH is similar to that described in the copending 61/371,926 and 61,430,264 provisional patent applications, in the PCT/US11/46978 application, and in the '873 patent.

The dissolved ammonia gas is removed from the water with a closed loop air-stripping apparatus. The air-stripping removes the ammonia gas from the water and provides it mixed in with the air. Next, the ammonia laden air resulting from the air-stripping is cleansed of the ammonia gas in a sulfuric acid mist to produce concentrated liquid ammonium sulfate which is collected for sale. The now cleaned air is circulated back for reuse in air-stripping ammonia gas from a subsequent portion of the incoming stream of waste water.

As part of the smelting process, aluminum at a temperature in the range of about 950 to 980 C is cast into a solid state and when it cools to a temperature in the range of about 600 to 640 C is quenched to quickly cool the solid cast aluminum with a stream of quenching water. Both the molten aluminum and the very hot solid aluminum combine readily with nitrogen in the air to form aluminum nitride:

2A1 + N2(g) = 2A1N

When the hot aluminum with its aluminum nitride coating is exposed to the quenching water, hydrogen from the water and nitrogen from the aluminum nitride combine to form relatively high concentrations of ammonium ions and ammonia gas dissolved in the quenching water waste stream.

2A1N + 6H 2 0 = 2NH 3 + 2 Al(OH) 3 (s)

2NH 3 + H 2 0 = NH 4 OH + NH 3 (g)

The water contains both ammonia gas dissolved in the water and ammonium ions. Keeping the aluminum away from air has been tried, but it is too expensive and technically very challenging, so it is not done except in unusual processes. The fluorides, phosphates and calcium come from two places: tramp materials in the bauxite ore and the liquid medium in the electrolytic bath where the ore is smelted (the liquid medium contains fluoride in particular). The waste stream is slightly alkaline (pH 10) and highly conductive due to its dissolved aluminum metal and other dissolved ionic materials (not just because of ionic materials).

In one embodiment, the electrolytic cell of the present patent application was used for removing an equilibrium mixture of ammonia gas and ammonium ions and other unwanted materials from the waste stream resulting from the quenching process used in aluminum smelting. Applicant found that the waste stream from this quenching process included ammonium ions with a concentration in the range of 180 ppm. A variety of fluorides, including hexa-fluoro-iron (III) FeF 6 3" , phosphates, including CaHP0 4 , and calcium ions were also found in the water discharged from this quenching process.

The waste stream of cooling water is also slightly alkaline and highly conductive due to its dissolved aluminum metal and other dissolved ionic material. Further processing of the waste stream is needed to remove the ammonia and ionic material before the water can be discharged to the environment.

Chemicals, such as lime, have been used to raise the pH of ammonia containing waste streams. However, lime has limited utility for multiple reasons. First, alkalinity must reach levels of pH 12 or higher to be effective in converting ammonium ions to ammonia gas, and additions of lime can stimulate pH levels of 12.6 in laboratory conditions but generally do not even reach pH 12 in real world applications. Second, in addition to capturing the ammonium ions, lime also captures toxic materials that may have been in the raw waste, such as hexa-fluoro-iron (III) (tramp iron will form this extremely stable species in the presence of the fluoride ion). Thus, a great mass of toxic calcium-containing sludge would be produced, and disposal of this toxic mass is expensive and cumbersome. Furthermore, there is additional cost in further treating the resulting treated waste water to bring the pH back down to safe discharge limits.

Applicant found that he could adjust the pH of the cooling water waste stream from aluminum smelting with the electrolytic cell of the present application and avoid all of these disadvantages, substantially lowering the cost, avoiding the creation of a large volume of toxic sludge, and capturing toxic materials in a small volume. With the electrolytic cell no chemical is added to raise the pH to remove the ammonium ion. No sludge is created, toxic or otherwise. And no additional chemical is added to bring the pH back down after the ammonium ion has been removed.

The membrane of the electrolytic cell is fabricated of a stable porous material, such as PTFE. The porous material has a pore size sufficiently large to allow electrically driven ion transfer and a pore size sufficiently small to maintain a pH difference between the anode chamber and the cathode chamber. In one embodiment the membrane provides greater than or equal to pH 12 at the cathode when a sufficient voltage is applied between the anode and the cathode. In one embodiment the porous material has multiple pores and an average pore size in the range from 0.5 to 10 micrometers. In one embodiment the average pore size is less than 1.0 micrometers. In one embodiment, the pores vary from the average pore size within a range, wherein the range is +/- 5% of the average pore size.

Applicant found that at the elevated pH produced by the electrolytic cell of the present patent application fluorides, including calcium fluoride, which is a toxic ionic material, reacts and precipitates into a small mass residue that is immediately filtered out. The small mass of this precipitate allows for it to be handled and disposed of at very low cost. Further, the present applicant found that electrolytic cell allows for heating the quench water to facilitate the desired reactions if the incoming temperature of the waste stream is particularly low. Water temperature is raised merely by raising the voltage applied across the cell. For example, applicants found that most of the power goes into I 2 R heating when the voltage across the cell is above 20 V DC, and this affords a simple, low cost way to keep operating temperatures sufficiently high, such as above 30 C, for reacting ammonium ions in the water, for air stripping the water, and for removing ammonia gas from the air. A control system for maintaining the desired temperature that includes a temperature sensor and a control unit that regulates the voltage applied to the electrodes can be used.

At the normal pH of the quench water, which is about pH 10 constituent calcium phosphate is largely present as CaHP0 4 . The calcium phosphate comes from the mineral electrolyte - bauxite ore which is not highly purified prior to smelting and contains many tramp materials normal to the earth's surface. This salt has a solubility of 200 ppm, well above the level at which phosphate discharge is permissible. By elevating the pH to the pH 13 level conversion of CaHP0 4 to Ca 3 (P0 4 )2 is effected.

Ca 2+ + 2CaHP0 4 + 20H " = Ca 3 (P0 4 ) 2 + 2H 2 O

The solubility of Ca 3 (P0 4 ) 2 is far below that of its precursor, the mono-calcium phosphate CaHP04. Solubility is 200 ppm for CaHP04, unreported but far lower for

Ca 3 (P0 4 ) 2 . The precipitation of the Ca 3 (P0 4 ) 2 sufficiently reduces the concentration of phosphate in the water to avoid environmental limits on phosphate discharge.

The quench water contaminated water from the aluminum smelting is also laden with fluoride-containing species of some complexity, for example the complex ion FeF 6 3" . The elevation of the pH acts against the presence of these complex ions, using the abundance of quench water calcium ions.

3Ca +2 + FeF 6 3" + 60H " = 2Fe(OH) 3(s) + 3CaF 2(s) While the pH of a saturated calcium hydroxide is 12.4, this level is not easily achieved by addition of chemicals under other than laboratory conditions, there being major handling problems with the gross amounts of lime required. With the electrolytic method of treating wastewater of this ionic content, pH values of 13 are quite ordinarily achieved— the higher the pH, the better for the chemistry. Certainly, the main equilibrium, that of the formation of dissolved ammonia from ammonium ion, is driven in the desired direction by the higher elevation of pH.

Given that the chemical equation

NH 4 OH + OH " = NH 3 + H 2 0 sets up the equilibrium equation

[NH 3 ]

K eq. =

[NH 4 OH] [Off]

Some of the NH3 gas does escape and some remains dissolved, but the escaping gas does not drive the reaction. In this scheme the reaction is taking place in an enclosed system and the ammonia may volatalize but cannot escape to the atmosphere.

Thus, to maintain the equilibrium constant (K eq ), the higher the concentration of OH-, the higher the concentration of NH 3 . Thus, providing a highly basic condition drives down the ammonium ion concentration and drives up the ammonia gas concentration.

Electrolytic Cell Methodology

The present patent application uses the same electrolytic cell design described in the nitrate removal process of the 61/371,926 and 61,430,264 applications and in PCT/US11/46978. Electrolytic cell 20 includes cathode chamber 22, anode chamber 24, and membrane 26 separating the two chambers. Cathode chamber 22 contains stainless steel cathode 28. Other materials can be used for cathode 28. In an embodiment of this patent application process water 30A is a waste stream that includes a high concentration of ammonia and ammonium ions and metallic and other ionic substances, either in suspension or in solution, making the water highly conductive. Metallic substances include calcium, iron, sodium, and others normally found in the earth's surface.

Process water 30A flows into cathode chamber 22 through cathode chamber inlet 32. Cathode 28, when energized, hydrolizes process water 30A, releasing large volumes of hydroxyl ions and elevating the alkalinity of this process water 30A to pH 12 or higher. The high pH causes a number of reactions, including making the soluble ammonium ions in solution significantly more volatile and converting them to dissolved ammonia gas much of which remains dissolved in the water. The solubility of ammonia gas in water is 470g/liter at 0 degrees C, 310 g/liter at 25 degrees C, which are high values in comparison to other compounds. In addition, a number of other dissolved salts are converted to solids, including the calcium, phosphate, and fluoride containing salts. The high-pH process water 30B containing dissolved ammonia gas and that may contain such solids then exits cathode chamber 22 through cathode chamber outlet 38 and passes through filter column 40 and filter 42 where the solids are removed in discharge stream outlet 43.

For process efficiency purposes, a back-pulse filter is used, such as a back-pulse filter available from Pall Corporation, Port Washington, NY, permitting filter stripping of solids 43 without significant disruption of process flow. From there, the filtered, high pH process water with dissolved ammonia gas and with solids removed 30C flows to an ammonia stripping process 44 where the ammonia gas is removed and then converted to a concentrated ammonium sulfate, a saleable product, and ammonia-free and solid-free process water 30D is directed back to anode chamber inlet 46 of anode chamber 24 of electrolytic cell 20 by pump

47 or other flow directing device, such as a gravity feed. Anode chamber 24 contains an anode

48 made of titanium with an iridium oxide coating. Applicants found that the iridium oxide coating avoids the production of chlorine, as described in the '264 application, but other materials can also be used.

When energized, anode 48 produces a large volume of hydrogen ions in ammonia- free and solid- free process water 30D. The alkalinity of the waste stream—that was elevated to about pH 10 before entering cathode chamber inlet 32 because of the presence of the ammonia in process water 30A~is now completely neutralized by the removal of the ammonia and by the reaction of the hydrogen ions in anode chamber 24 with remaining hydroxyl ions in ammonia- free and solid-free process water 30D so that ammonia- free discharge water 30E from anode chamber outlet 50 of electrolytic cell 20 is in the neighborhood of pH 7.

Air-stripping Methodology

In a waste stream, ammonium ions exist in equilibrium with ammonia. Below pH 7, virtually all the ammonia will be soluble ammonium ions. o Above pH 12, virtually all the ammonia will be present as a dissolved gas. o The range between 7 and 12, both ammonium ions and dissolved gas exist together. o Percentage of dissolved gas increases with temperature and pH, so higher

temperature and higher pH favors removal of ammonium ions from solution.

Air-Stripper Design

As alkaline process water with its dissolved ammonia gas 30C enters air-stripping column 56, pump 58A or another flow directing device, impels alkaline process water 30C through fine nozzles 60, to create a fine mist, as shown in FIG. 1, or distributes it over internal packing media (not shown), where it is broken up into small droplets 30C, either of which methods creates a tremendous amount of surface area for the process water 30C as process water 30C moves down air-stripping column 56 by gravity. Air 62 A enters at bottom 64 of ammonia stripper column 56, impelled by fan 66. Air 62A travels upward through the spray of small droplets 30C'or through the packing material. The ammonia that is present as a dissolved gas in small droplets of process water 30C transfers from droplets 30C to air 62 A to form ammonia gas laden air 62B. The major factors favoring high efficiency in this process are (a) high pH, (b) high temperature, (c) high air flow, and (d) increased exposure to surface area of water droplets 30C as described in the Encyclopedia of Chemical Technology by Kirk-Other, and in US patent 6,866,779, both of which are incorporated herein by reference, While a range of operating conditions is possible, the most common designs call for pH 11 (or higher) with room temperature water or pH as low as 9.5 with water heated to 120 degrees (F). The discharge air stream with ammonia gas 62B has its ammonia gas removed in a separate step, as described below.

Ammonia Gas Removal from Air

The three most common methods for removing ammonia gas from air are release to the atmosphere, ammonia absorption, and thermal destruction. In situations where release to the atmosphere is not an acceptable alternative, the choice between absorption and thermal destruction is driven by the following considerations:

Disadvantages • Initial cost of installation • Higher installation cost

• Must dispose of ammonium sulfate • Higher operating costs

• Thermal/energy losses

For absorption, air laden with ammonia gas 62B is impelled by fan 68 upward and out of air-stripping column 56 and into the ammonia recovery column 76 by another fan 78 or other flow directing device. Inside ammonia recovery column 76, dilute sulfuric acid solution (H 2 S0 4 ) 80 is sprayed through a set of fine nozzles 82 by pump 84, to create fine mist 86 flowing counter to the flow of ammonia- laden air 62B. The ammonia in ammonia laden air 62B reacts with fine mist 86 of sulfuric acid to form ammonium sulfate ( H 4 ) 2 S0 4 liquid 87 that drains by gravity through ammonia recovery column 76 to reservoir 88. The ammonia having been recovered from ammonia laden air stream 62B, air 62A, cleaned of ammonia, now flows through cleaned air connector plumbing 90 back into air-stripper column 56, forming a closed loop.

While the disclosed methods and systems have been shown and described in connection with illustrated embodiments, various changes may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.