CA1112774A - Method for removing ammonia from wastewater - Google Patents

Abstract

ABSTRACT OF THE INVENTION

A method for removing dissolved ammonia from waste-water by using an insoluble polymeric polyamine:metal complex to bind the ammonia thereby removing it from the wastewater.
The complex can then be regenerated and used again.

Description

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I METHOD FOR REMOVING A~ONIA FROM WASTEWATER
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j BACKGROUND OF THE INVENTION
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1. Field of the Invention j This invention relates to was-tewater treatment, and more ¦'particularly, to a method for r~emovin~ ammonia from wastewater.
¦i2. Description of the Prior Art ! The presence of ammonia in surface and groundwater sup-plies has many adverse efects. A~monia has a toxic efect on fish and aquatic life, stimulates excessive algal growth, consumes oxygen from water it is discharged into, and may be oxidized to nitrates causing a health hazard. Ammonia t~pically enters the ¦!water supply as the result of commercial and household wastewater ¦!discharges. Thus, if feasible means were available for remov1ng ¦lammonia, the method could be employed in commercial and municipal -- lwater treatment plants.
:, ', Processes for controlling ammonia levels are divided into two broad categories: biological and physical-chemical. Pre-~sently, the most widely used nitrogen removal process is biologi--cal nitrification-denitrification. In this process, microorgan- ~' isms convert ammonia to nitrate after which other or~anisms con-ive~i the nitrate to nitrogen gas.
` Three basio physical-chemical processes are available for removal of ammonia. These processes include ammonia sSripping, breakpoint chlorination, and ion exchange. Ammonia stripping in-volves raising the pH of the wastewater to about 11, forming water droplets in a stripping tower, and then providing air-water contact by circulating large quantities of air through the tower~
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;Breakpoin~ chlo,rination invsilves adding chlorine or hypo,hlorite to ammonia-containing water to form ch:Loramines. As more chlorine !
is added, a "breakpoint" is reached where the ch.loramines are con-vexted to nitrogen gas. Ion exchange trea~ment involves the use if cation exchange resins to remove ammonia, the resin being re-~lyenerated by ~he use of a lime slurry containing sodium chloride.
- ¦¦ Another physical-cheniical process of the prior art in-¦lvolv~s "ligand exchange", described by F. Helfferich in two sep-!arate articles: "Ligand Exchange: A Novel Separation Technique"y !Nature, 139, 1001 (1961), and "Ligand Exchange, I. Equilibria", J. Am.Chem.Soc., 84, 3237 (1962). The present invention employs ,;
,a similar process a In ligand exchange, a suitable ion exchanger ilcontaining a complexing metal ion (e.g., Cu ~, Ni , etc.) as the !,counterion/ is used as a highly selective sorbent for molecules ,ox anions that can act as ligands. Among the ~arious possible li- ¦
gands is ammonia. The complex between the metal ion and the li-~and is formed in the exchanger when ligands in the external sol-'ution replace water molecules in the solvation shell o the metal ,ion. The ligand exchange reaction for ammonia using an exchang~r in the cupric form can be written as follows:
~R-)2tCu~H20)4+ J ~ 4NH3 ~ (R )2[Cu(N 3)4 2 where R- is the fixed ionic group o~ the exchanger, and brackets refer to the exchanger phase. It is- important to note that the ammonia complex results from reaction of undissociated ammonia and ~5 ,not the ammonium ion. In the ligand exchange reaction, no ion exchange takes place. The exchanger merely acts as a 5olid car-rier for the complexing metal ion.
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i, To apply -the ligand exchange process to the treatment of wastewater, three requirements must be met. 1) Displacement o the complexing metal ion from the exchanyer must be avoided~ Loss of metal ions from the exchanger results in a loss of liyand ex-S ;~change capacity, and the displaced metal ions in the external sol~
llution counteract ligand sorption by forming complexes iD solution.
- ¦,In addition, loss of metal ions results in contamination of the ¦¦treated wastewater. In generaL, protection against bleed can be ¦¦obtained by using an exchanger that is highly selective for the ¦Icomplexing metal ion. 2) Competing ligands w~ch form strony ,~complexes with the metal ion of the exchanger, must be absent or present only in relatively low concentrations. 33 Finally, a suitable process must be available or regeneration of the ex~
,hausted exchanger. In the prior art, regeneration is achieved by acid or base, or by displacement with another ligand that has a greater affinity for the complexing metal ion.
~, U.S. Patents 3,382,034 and 3,522,187 describe the use of hydrous oxides as cation exchangers. The '187 patent describes the use of hydrous zirconium oxide to adsorb a copper ammonium com-~0 , plex~ which i~ then e~uted with a lM ammonium chloride solution.
Paper ~o.72D entitled l'Ammonia Removal from Wastewater by Li~and Exchange", presented at the 67th Annual Meeting, AIChE, Washington ~- ' DC, on December 1-5, 1974, describes the commercial use of such a hydrous zirconium oxide system. Copper is loaded onto the hydrous zirconium oxide, aftex which the complex is used to remove ammonia from ~:astewater whose pH has been increased ~o around 11. Regen-eration of the column (i.e., desorption of the ammonia) is accom-plished by the use of steam. While the process is efective in ~4~ _ .
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removing ammonia from wastewater, only 0.59 millimoles of copper can be loaded onto a gram o~ the hydrous zirconiwn oxide. In addition, the amount of ammonia xemoved by the complex is only about 0.1 millimole per millimole of copper.
Thus, while it appears that ligand exchange has been suggested for use in ammonia removal, a need exists for more efficient materials to which copper or other metals can be attached.

SUMMARY OF THE INVENTION
According to the present invention there is provided a method for removing ammonia from aqueous solutions thereof, the method comprising the steps of: a) contacting an aqueous solution containing dissolved ammonia with an insoluble polymeric polyamine: metal complex, the metal being selected from the class consisting of metal ions (1) having a yalence of +2, +3, and +4, (2) forming at least one complex with ammonia having a Kn value between ~: :
about 0.75 and about 9.0, and (3) complexing more strongly with the polymeric polyamine than with the ammonia, and the polymeric polyamine being selected from the class consisting of polymeric polyamines 1) having at least one primary or secondary amino group per monomer unit, of which at least 60% are free and available for binding the metal and 2) having an average molecular weight of from about 500 to about I06; and b) desorbing the ammonia from the complex.
DETAILED DESCRIPTION OF THE INVENTION
In its broadest form, the present invention comprises a method for removing ammonia from wastewater by employing a polymeric. polyamine which is either water insoluble in its natural state or which has been previously water insolubilized. The polymeric polyamine is complexed with a metal, and then used to bind dissolved ammonia thereby A - 5 _ sb/ ~
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removing it from wastewaterAfter ~he complex has bound the maximum amount of al~monia, it can be regenerated and reused.
The polymeric polyamines used in the present invention can be divided broadly into two classes: those which are naturally water i.nsolub:Le and those which must be insolubilized before sb/ ~

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use in the present invention. An example of the first type of ~polymeric polyamine is chitosan. Chitosan is formed b~ t~e re-laction of chitin with concentrated alkali~ Chitin is a hiyh ¦molecular weight linear polymer of anhydro-~-acetyl-D-glucosamine.
5 l~he use of chitin and chitosan for bindiny metal ions is well Iknown in the prior art. ~or instance, U.S. Patent 3,635,818, ¦describes the use of the amine groups on chitin and chitosan ¦for the reversible collection of ~etal ions from organic and ¦aqueous solutions, and sea water.
¦ The second type of polymeric polyamines are those ¦which require insolubilization before their use in the presen-t linvention. These polymeric polyamines are prepared by poly-¦merizing various nitrogen containing compounds. These polymeric Ipolyamine~ have at least one primary or secondary amino group ,per monomer unit of which at lea~t 60~ are free and avail~ble ~or binding. The average molecular weight of pol~meric poly-amines so produced is from about 500 to about 10 , One such pOlyamiIle i6 polyethylenimine.
~- In order to employ normally water soluble polymeric ,polyamines in commercial water treatment systems, they must 'be insolubilized. One means of insolubilization is to crosslink ; Ithe polymeric polyamine by use of a crosslinking ayent (e.g.
1,5-dibromopentane). Another means of preparing polymeric Ipolyamines for use in the present invention is by graftin~ to ~an insoluble pol~meric backbone. The reaction of a polyvinylw benz~1 chloride backbone with an amine is described in Volume 21 i ~
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of the Journa~l of App e Poly~er Science, on pp. 2481-2488 (1977). While an aromatic pendant group is shown in that example, the pendant ~roup of the monomer could also be aliphatic.

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The next step in preparing the ligand exchange complex is to bind a metal ion to the insoluble polymeric polyamine. Me-tal ions useful in the present invention may be chosen based on the l'stability constant", in an aqueous solution, of the complex l,formed by reaction of the metal ion with ammonia.
I The term ~Istability constant",as used conventionally and !l as used herein, reEers to the e~uilibrium reaction oE a metal llcation and a ligand to ~orm a chelating mononuclear complex. The ¦¦stability constant (K) is defined as the product of the concen-o ! tration of the reaction products divided by the product of the ! concentrations of the reactants. For instance, when ammonia is ~added ~o a water solution of a copper (II) salt, there is a rapid reaction in which the four water molecules coordinated with the ~mstal ion are repla~ed by ammonia molecules. Although the product ~of this reaction is normally represented as [Cu~NH3) 4] , in fact a variety of products results, the relative amount of eaoh species depending upon the concentration of cupric ion and ammonia. The 'various ions produced have one or more of the w~ter molecules re-~ plaGed by ammonia rather than complete substitution. This rç-~placement occurs on a stepwise basis, one ammonia molecule at a time. For each ~step, a "stepwise stability constant" (Kl, ~2~
...Kn) can b~ expressed which describes the stability of the com-;,plex produced by bonding an additional ammonia molecule. Thus, !
a Xl value expresses the stability of the metal ion ~ith one ammonia molecule, K2 with two ammonia molecules, etc. The larger the K value :Eor a particular complex, the greater its stability.
For convenience, stability constants are expressed herein as the logarithm to base 10. K values referred to herein are Eor com-plexes at 30~C.

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Depending upon the metal employed, a single metal ion may bind up to six ammonia molecules. However, to be useEul in the practice of the present invention, the stepwise stability con-'stant for at least one of the complexes formed must be in the ,range from about 0.75 to about 9.0, preferably from about 2.0 to jabout 6.0, and more pre~erably from about 2.5 to about 5Ø For lexample, even though all six possible complexes (i.e., the metal ¦Iwith one, two, three, four, five, or six ammonia molecules~ might Ilbe formed in a solution, it is possible that only one or two of ¦~the complexes would have stepwise stability constants in the above ¦jrange. If Kn is too low, either no complex is formed or the com-plex formed is unstable, prematurely releasing its bound ammonia.
On the other hand, a complex having a ~n value higher than t~e ~above xange will bind the ammonia so strongly that regeneration ,will be difficult. Ob~iously, the larger the number o complexes !.
a metal forms with ammonia that have stepwise stability constants within the above range, the more desirable that metal is for use in the present invention~ Preferably, the metal chosen should form at least four complexes with ammonia which have stepwise stability constants within the above range. ~
~y~ical metal ions use~ul in the practice of the present ~ invention include Hg , Co , Cd , Ni , Zn , Cr , Pd , Cu , ; 1~h3~, and Pt ~ The preferred metal ion is Cu . Each of these imetal ions,~when complexed with a suitable pol~msric polyamine, will bind one or more ammonia molecules, thus removing them from aqueous solution~ The number of ammonia molecules bound by each metal ion wl:Ll be determined by the stability constant for the `reaction of that metal with ammonia. While the above list is rep-resentative of metal ions use~ul in the present invention, any , .

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metal ion which binds ammonia in aqueous solution with K values ~within the above described range can be employed.
The final re~uirement for a suitable metal ion is that llit bind more strongly to the polymeric polyamine ligand than to ',ammonia~ Otherwise, regeneration would be impossible due to leaching of the~metal. The greater the difference in value be-tween the s~ability constan~ of the metal with the polymeric poly-amine ligand and ~he s~ability constant of the same metal with ammonia,and the lower the metal-ammonia stability constant, the more easily regeneration is performed. The suitability of a par-ticular metal with a particular polymeric polyamine can be detex-¦mined by monitoring the treated water during regeneration. An lexample of such a monitoring system when Cu2+ is the metal ion, ¦would involve the addition of oxalic acid bis-(cyclohexylidene-l~hydra2ide) to a sample of the treated water. That compound ~om-~ llplexes with Cu2 to give a visible blue color down to 0.025 ppm.
¦l In practicing the inventio~, the metal ion is loaded onto the polymeric polyamine as an aqueous solution. Where cop~
,'per is the aesired ion ~or example, an aqueous solution o~ cupric j chloride or cupric sulfate could be used.
jl The procedure used to load the metal ion wili vary with i; .
the type of apparatus usea. If a ligand exchange column is to be used, the metal ion solution is pumped through the column several ; l¦times. Loading can also be accomplished ~y stirring the exchanger 25 1l with an aqueous solution of the metal ion i~ a batch method is '~chosen.
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~5 ~L2~774 The first step in using the polymeric polyamine:m2~al complex is to adjust the pH of the solution to be treated with an alkali ~e.g., sodium hydroxide) to about pH 7.5 to 11.5, prefer- I
ably 10.5 to 11.5, to convert NH4-~ to NH3 which can function as a ¦
~,ligand. Where the ammonia-containing water is concentratea enough the pH will not re~uire adjustment, since the solution will al-llready be ~asic enough. The a~ueous solution is fed through a ,¦column having a monitox at its exit end to determine the amoun~ o~
¦lammonia passing through the column without being complexed by the o !l ligand exchanger. When the concentration of unbound ammonia reaches a level which indicates saturation of the complex, the flow of ammonia-con-taining water is stopped and regeneration is ! performed.
Il Regeneration of the complex is accomplished by stopping .j .
!Ithe flow of ammonia-containing water, followed by flushing the A , ,. ' ~' column with dilute acid, preferably a mineral acid, (e.g. 0.02M
hydrochloric acid). Bound NR3 is thereby converted to NH4~ and replaced by water molecules. Care must be exercised in this pro cess to avoid leaching the metal ion from the polymeric polyamine ~0 ` at the same time. By careful ad,iustment of the pH, it is possible to remove the majority of the ammonia without signiicantly affectl ing the complex. While the above discussion has described the use¦
of the complex in a chromatographic column, the present invention may also be u~ed in a fluidized bed, or as a batch method~
The followin~ examples are given by way of illustration only and are not to be considered as limiting ~he scope o the invention.
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77~ 1 1, ES~AMPLE
IIA. Pre~ar~tion of Crosslinked Poly_thxlenimine I ....
! To prepare a water insoluble polymeric pol~amine, 51~72g of a 1 33% aqueous solution of polyethylenimine (molecular weight il 100,000) was mixed with 34.5g dibromopentane and the mixture ¦j heated at 70-75 for five hours. The mixture gels within one ¦¦ hour. Water and unreacted dibromopentane were removed by ! washing the amker elastomer in acetone. -! B. Complexin~ of Crosslinked Polyethylenimine with Cu :
ll 5.19g of crosslinked polyethylenimine ~rom step A above, was ¦ dispersed in 1~0ml distilled water using a blender. As 0.54g CuSO4 was added to the pale amber mixture, the mixture turned I deep blue. After allowing the mixture to stand, i~ became i apparent due to the intensity of the blue color in the ~! supernatant, that some polyethylenimine had solubilized.
The solids were separated and allowed to air dry, and were then water-washed to remove solubilized polyethylenimine, i and ~iltered~ ~ -,'C. Complexin~ of ~H~ by Polyethylenimine:Cu Complex - 20 ' One gram of water-washed polyethylenimine:Cu complex fxom step B was placed in 20ml distilled water followed by the addition of 25ml 0.066 N NH OH. Titration of the resul~ing ¦ co~plex with 0.1 N ~Cl released the bound ammonia and demon-¦' strated that one gram of polyethy1enimine~Cu complex ¦, removes 0.06 meq. or 1.02 mg. of NH3.
EX2~IPLE II
,A. Comp1exing of Chitosan with Cu ~
i 1.6g of CUSO4 and Sg of a chitosan having 85~ free amino and ' 15% acetylamino groups ~2.0 mmoles of Cu per gram of chito-san) were added to 160ml of water. The dispersion was stirred i . ~--.
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for about 0.5 hour, washed with l.5 liters of distilled water, and then vacuum oven dried.
iB. Ammonia Uptake b~ Chitosan:Cu Complex !~ One ~ram of the complex from A was dispersed in lOOml oE
ll distilled water. O.l N N~I40H was added dropwise to the i stirred solution while the NH uptake was followed by means of pH measurement. The NH40H addition rate was adjusted ts ! maintain a pH range of 8.9-9.0 (this pH range corresponds to ~i 5xlO 4 meq. of excess NH3). The one gram o~ complex, whioh ¦ gradually became deeper blue, took up 20ml of O.l N NH40H, or ¦¦ 2 meq~ of N~3, equivalen-t to an ammonia uptake o l meq. NH3/
¦~ meq. Cu~O
¦,EXAMPLE III
i'~. Complexiny of Chitosan with Cr , .
i 15 -- i l.25g of Cr2(50 ) 6H20 and 5g of a chitosan having 85% free amino and 15% acetylamino groups tl.O mmoles of Cr3+ per gram of chitosan) is added to lOOml of water. The dispersion ' is stirred for about 0.5 hour9 washed with l.O liters o i distilled water, and then vacuum ~ven dried.

B. Ammonia Uptake by Chitosan:Cr3 ¦comple~
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i One gram of the complex from A is dispersed in lOOml o distilled water. O.l N NH~OH is added dropwise to the stirred ¦
I' solution while the NH3 uptake is followed by means o~ pH ~

1~ measurement. The NH40H addition rate is adjusted to maintain ! a pH ~ange of 8.9-~.0 (this pH xange corresponds to 5xlO
l~ meq. o~ excess NH3). The one gram of complex, which graduall~

becomes blue-green, takes up 10ml ~f O.l N NH~OH, or l me~.

of NH3, equivalent to an ammonia uptake of l meq. NH /meq~
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EXAMPLE IV
¦A. Preparation of 4-~inylbenzyl Chloride Polymer Into a 500ml round bottom flask itted wi.th a magnetic stirrer i l. and condenser was charged 15.25g of~4-vinylb~nzyl chloride, 150ml toluene, and 0.15g azobisisobutyronitrile. The flask was immersed in an oil bath heated to loo-llo& . After the reaction was allowed to proceed with stirring for five hours, .
~¦ the flask was cooled to room temperature. 10g of 5.25%/wt.
~¦ NaOCl solution was added and the contents of the flask stirred 10 ~¦ vigorously for 0.5 hours at ambient temperature. The solu-¦ tion was water-washed three times with 100ml of distilled water and then dried over Na2SO~.
~ nsolubilizing Polyethylenimine by Grafting to a Polymex ¦~ To a flask containing the total product from Step A was Ijl added 6g of polyethylenimine ~molecular weight 1800). ~he i` flask was immersed in an oil bath heated to 60C while the .' contents were stirred vigorously for five hours af~er which i', the heating and stirxing were discontinued and the contents ¦,. of the flask allowed to cool. The li~uid from the ~lask was 1 2~ !. then decanted, leaving a solid which was mascerated in dis-j, tilled water, filtered, mascerated again in absolute ethanol, ' filtered, and air dried.
. Complexing ~ith Cu2 -~ne gram of the dry, solid product of Section B was pulverized ¦ and dispersed in 100 ml of distilled water~ Four grams o~ a solution prepared by disso~ving 1~6g anhydrous CuSO~ in 27,2g distilled water was added to the dispersion of insolubilized polymeric polyamine.

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The resulting mixture was stirred at room temperature for one I hour, after which it was filtered, water-washed, and redis-i persed in 100 ~ distilled watQr. 5j~
¦;D. Use of the Polyamine-Cu Com lex to Bind Ammonia ,, _ . P ,,, __ . ___ '1 One ml of 15 N NH40H was diluted with distilled water to 250 j ml to yield a 0.06N ~H40H solution. ~en ml of the 0.06N
I NH40~I solution were added to the polymeric polyamine:CuZ
¦I complex from Step C, raising the pH to 8.2. At that pH, .
j the complex was able to bind 0.6 meq. of ammonia per gram 1 of complex.
E. Regeneration of the Complex To desorb the complexed ammonia and thereby reqenerate the i complex, the complex is filtered, and then washed with three Il lOml ali~uots of 0.02M hydrochloric acid. The acid wash is 5 ¦' followed by flushing with distilled water to remove any re-!' sidual acid. Once the bound ammonia is removed by the above ii procedure, the complex is ready to be used a~ain.
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Claims (5)

1. A method for removing ammonia from aqueous solutions thereof, said method comprising the steps of:
a) contacting an aqueous solution containing dissolved ammonia with an insoluble polymeric polyamine:metal complex, said metal being selected from the class consisting of metal ions (1) having a valence of +2, +3, and +4, (2) forming at least one complex with ammonia having a Kn value between about 0.75 and about 9.0, and (3) complexing more strongly with said polymeric polyamine than with said ammonia, and said polymeric polyamine being selected from the class consisting of polymeric polyamines 1) having at least one primary or secondary amino group per monomer unit, of which at least 60% are free and available for binding said metal and 2) having an average molecular weight of from about 500 to about 106; and b) desorbing said ammonia from said complex.

2. A method as claimed in Claim 1 in which said metal is selected from the class consisting of Hg2+, Cd2+, Ni2+, Zn2+, Pd2+, Cu2+, Co3+, Cr3+, Rh3+, and Pt4+.

3. A method as claimed in Claim 1 in which said metal is Cu2+.

4. A method as claimed in Claim 1 in which said poly-meric polyamine is insolubilized polyethylenimine.

5. A method as claimed in Claim 1 in which said poly-meric polyamine is a chitosan having at least 60% of its amino groups free and available for binding said metal.