Envlron. Scl. Technol. 1903, 17, 738-742
Transfer of Active Chlorine from Chloramine to Nitrogenous Organic Compounds. 1. Kinetics Russell A. Isaac"?and J. Carrel1 Morris
Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02 138 Rate constants for the transfer of active chlorine (denoted C1+) from NH2Cl to four amino acids, two glycine derivatives, three amines, and an amide were determined at 25 "C. The reactions were determined to be second order-first order in each reactant. Observed second-order rate constants for the amino/amine reactions with NH2Cl ranged from 0.140 (dimethylamine,pH 8) to 13.8 (mol/L)-l s-l (morpholine, pH 7). Introduction Chlorine is used extensively for water and wastewater disinfection. A major gap in knowledge of the fate of aqueous chlorine in natural systems is a lack of information about the rates and mechanisms of transfer of active chlorine (denoted Cl+) from NH2C1to nitrogenous organic compounds. Numerous qualitative statements in the literature have indicated that transfer does occur and that it may have important consequences for the ultimate environmental impact of discharged available chlorine. Accordingly, a series of investigations were undertaken to assess rate constants at 25 "C for the transfer of C1+ from NH2Clto a number of types of environmentally important nitrogenous organic compounds: (1) amines (methylamine, dimethylamine, and morpholine), (2) amino acids (glycine, serine, alanine, tryptophan, and sarcosine), (3) glycine derivatives (glycylglycineand glycine ethyl ester), and (4) amides (N-acetylglycine). Occurrence of Nitrogenous Compounds in Water Investigations of the reactions between aqueous chlorine and nitrogenous compounds in water date from at least 1909 (1). However, knowledge of the nitrogenous organic compounds present in natural waters and wastewaters is sketchy, so that the significance of many of these reactions in practical chlorination is still unclear. Hutchinson (2) reported average free amino, peptide, and non-amino N concentrations of 0.076,0.172, and 0.194 mg/L, respectively, in 15 U.S.lakes. Vallentyne (3), in a review of aqueous organic materials, states that a-amino N has been found to comprise as much as 60% of the total organic N in fresh waters. He notes that some amino acids have been detected also in sewage and activated sludge. Gmdner and Lee (4) identified several amino acids in water from Lake Mendota. Concentrations of individual amino acids were approximately 0.2 pmol/L (-0.2 mg/L). Ram (5, 6) was able to identify several heterocyclic nitrogen compounds including uracil and adenine in natural waters at concentrations up to 860 pg/L. The heterocyclic compounds represented 0.2-18.8% of the total organic nitrogen, which varied from 0.34 to 21.7 mg/L as N. In addition, he identified similar compounds in filtered water from laboratory-grown blue-green algal cultures. Recent data (7)reveal median values €or the ratio of org-N/TKN in secondary effluents and nitrified effluents +Towhom correspondence should be addressed at the Massachusetts Division of Water Pollution Control, Lyman School, Westborough, MA 01581.
738 Environ. Sci. Technol., Vol. 17, No. 12, 1983
Table I. Ratio of Organic Nitrogen/Kjeldahl Nitrogen in Secondary and Nitrified Municipal Wastewater Treatment Facility Effluents ( 7 ) effluent secondary nitrifiedb a
samplesu plants 29 21
24-h composites.
20
9
median value
0.59 0.92
range 0.00-0.91
0.45-1.00
Defined as (NO,--N) > (NH,-N).
to be 0.59 and 0.92, respectively (Table I). Ram (5),in his summary of the occurrence of nitrogenous compounds, lists several amino acids excreted by humans. By use of these limited data, calculated concentrations of amine nitrogen associated with only amino acids in a domestic wastewater are estimated to be between 0.3 and 1mg/L. The average ammonia concentration in the nonnitrified secondary effluents reported on in Table I was 11.6 mg of N/L. Thus, while the concentration of organic nitrogen can be a relatively large fraction of the reduced nitrogen in an effluent, the amine N may be up to 10% or greater of the ammonia N concentration in a nonnitrified secondary effluent. Experimental Procedures Materials. In all cases, reagent grade chemicals were used without further purification. Solutions were made with chlorine-demand-free water produced from glassdistilled water which was chlorinated to effect a residual concentration of approximately 10 mg/L, allowed to stand for at least 24 h, and then dechlorinated by UV radiation. Stock chlorine solutions were prepared by sparging high purity chlorine gas from a lecture bottle into chlorinedemand-free water to a concentration of approximately 5 X 10" mol/L. The solutions were adjusted to pH 3-4 with NaOH. Storage was in a low actinic glass vessel at 5 "C. New solutions were made up regularly (1-2 weeks). Chloramine (NHzC1) was prepared from solutions of ammonium chloride (approximately 3.7 X mol/L) and stock aqueous chlorine, both of which had been adjusted to pH 10 with NaOH prior to mixing. Approximately 10% excess of ammonia was employed. The aqueous chlorine was added to the ammonium chloride solution while the latter was being mixed rapidly with a magnetic stirrer. The solution (approximately 1 x mol/L) was stored in an actinic glass vessel at 5 OC. New solutions were made up on a regular basis (1week to 10 days if not used entirely before that time). Solutions retained 90-95% of their active chlorine during these periods. The buffers for the solutions of N organic compounds were mixtures of either KH2P04-NaOH or KHZPO4NaZB4O7.10H20 to obtain pH values in the ranges 6.0-7.0 and 8-9, respectively. Mixtures of Na2B407.10Hz0-NaOH were employed to obtain pH values between 9 and 11. Methods. Transfer of unipositive chlorine from NH&l to each nitrogenous compound was investigated by mixing a solution of chloramine with one containing the nitrogenous compound and then manually monitoring the ultraviolet transmission of the solution at two significant, selected wavelengths.
0013-936X/83/0917-0738$01.50/0
@ 1983 American Chemical Society
Table 11. Extinction Coefficients Employed for N-Chloro Compounds at 25 "C
chloramine ammonia glycine serine alanine sarcosine glycylglycine methylamine dimethy lamine morpholine glycine ethyl ester a
extinction coefficients, (M cm)-', at wavelength of 244nm 280nm 455 470a 316 324a 318 348 182 314 325 208 231 311
62 73a 183 196a 176 156 27 7 148 135 223 220 139
-2, I
-11 0
ItC(l"0t
Figure 1. Glycine plus NH,CI, run G47. Variatlon of percent transmission at 280 and 244 nm wlth time. Vertical lines used to estimate simultaneous values of transmission so that the concentration of both N-chloro compounds could be calculated: [NH,CI], = 0.488 X M. T = 25 OC; pH = 8.68. M; [Gly], = 13.35 X
At 46 "C.
Chloramine (NH2C1)and organic chloramines both absorb UV radiation. Therefore, the absorbance of UV radiation at any moment is dependent on the concentration of both chlorinated species. Since the absorption characteristics of NH2Cl and the organic chloramines are generally different, the changes in absorbance reflect changes in the concentrations of the two chlorinated species. If one determines the absorbance of UV radiation at two wavelengths, at the same time, the concentration of each of the two chloramines can then be calculated. Because UV transmission could be monitored at only one wavelength at a time, alternate measurements were made at the two selected wavelengths as rapidly as possible and the results interpolated to provide estimates of the transmission values at the two wavelengths at the same time. Thus the absorbance at the two wavelengths at a given time can be used to calculate the concentration of the two N-chloro compounds through the two simultaneous equations: A244 = C1E1244L C2E244L
+ A280= C1E1280L + C2E280L
where A244 and Azso are absorbance at 244 and 280 nm, respectively, C1and C2 are the molar concentrations of the two N-chloro compounds, El and E2 are molar absorptivities of N-chloro compounds 1 and 2, respectively, a t the indicated wavelengths, and L is the cell length (cm). The molar absorptivities of the N-chloro compounds are presented in Table 11. Measurements were made with a Beckman DB spectrophotometer with a temperature-controlled cell compartment connected to an external water bath. The transmission values were converted to absorbances which were then used to calculate the concentrations of NH2Cl and N-chloro organic compound as a function of time. Most of the reactions were conducted under pseudofirst-order conditions with an excess of the organic nitrogenous compound, usually 10-20 times the concentration of the NH2C1,which was generally 5 X lo4 mol/L after mixing. Ten milliliters of NH2Cl solution was added to 10 mL of buffered solution of the nitrogenous organic compound. The reaction solution was mixed rapidly by a magnetic stirrer during the addition of the NH2C1. Prior to mixing, each of the solutions was kept in the water bath used for temperature control (25 "C) of the spectrophotometer. The mixed solution was then placed in the spectrophotometric cells (4-cm path length) and monitored alternately a t 280 and 244 nm, since all of the N-chloro compounds absorb UV radiation at these wavelengths.
I, I
2'0
:I
8'0
1'1
!dl
110
,io
,io
, 110
tlii
)IO
I4 0 7 0
lirllol
Figure 2. Alanlne plus NH,CI, run All. Variation of percent transmission at 280 and 244 nm with time. Vertical lines used to estimate simultaneous values of transmission so that the concentration of both N-chloro compounds could be calculated: [NH,CI], = 0.472 X M. T = 25 OC; pH = 6.15. M; [Ala], = 11.25 X
The transmission values were plotted with time, and simultaneous readings were interpolated from the plots. Typical results are presented in Figures 1 and 2 in which the vertically drawn lines represent the simultaneous transmission values. For instance, in Figure 1,the transmission value at 280 nm and 35 s represents an actual measurement and while the simultaneous transmission value at 244 nm is determined by interpolating between the readings at 25 and 40 s. The vertical line connects these two points, which were used to calculate the concentration of NH2Cl and N chloroglycine at this time. The change in the concentration of NH2Cl with time is plotted in Figure 3 for this run.
Results Preliminary analysis of the data indicated that the transfer of C1' from NH2CI to other nitrogenous compounds is a second-order process, first-order in each reactant according to the rate expression -
d[NH,Cl] = k(obsd)[NH2C1][org-N] dt
where d[NH,Cl]/dt is the rate of change in concentration of monochloramine, k(obsd) is the observed rate constant with units of (mol/L)-l time-l, [NH2C1]is the molar concentration of NH2C1, and [org-N] is the molar concentration of the nitrogenous substrate being chlorinated by the monochloramine. Plots of data, therefore, were based on this determination. Data from experiments in which the nitrogenous receptors were 23-30 times the molar concentrations of Environ. Scl. Technol., Vol. 17, No. 12, 1983 739
Table 111. NH,CI plus N Organic Compounds Mean Observed Reaction Rate Constants [h(obsd)] at 25 'Ca nitrogenous compound
6.0-6.5
6.5-7.0
glycine
1.54
1.85
serine
2.62
alanine glycylglycine
0.811 6.21
1.19 7.76
methylamine dimethy lamine sarcosine glycine ethyl ester morpholine
0.194 0.143 0.440 6.05 8.12
0.483
7.0-7.5 1.05 2.40b 2.55 2.67b 0.846 4.77 5.3gb 0.189
k(obsd), (mol/L)-' s-I, at pH 7.5-8.0 8.0-8.5 8.5-9.0 9.44 1.49
1.30
1.30
2.53 0.960 4.08
1.20
9.62
9.73
10.71
0.985
0.816
0.129
1.82 0.880 3.06
0.806 2.19
0.140 0.473 2.64 13.8
0.556 5.08
a Based on pseudo-first-order conditions: N compound in excess. centrations.
Based on second-order conditions: equimolar con-
lo-?# B
--I -B -5 --
4
--
3
--
. 4
i2--
I ] E 10
80
IO
120
150
110
SECOlDS
Flgure 3. Glyclne plus "$3, run G47, at T = 25 OC and pH 8.68. Variation of [NH,CI] with time: [NH,CI], = 0.488 X M; [Gly], = 13.35 X M.
NH2Cl were plotted and analyzed by techniques appropriate to pseudo-first-order reactions as exemplified by Figures 3 and 4. Data from experiments which employed approximately equal molar concentrations were analyzed by techniques appropriate to second-order reactions (Figure 5). The concentrations of the N-chloro compounds were calculated from UV spectrophotometry as described previously. Amino Acids, Amines, and Glycine Derivatives. Reactions between glycine and NH&l were studied over the widest range of conditions. Experiments extended from pH 6.08 to pH 10.72. All but three runs (one set of conditions done in triplicate) were conducted at approximately 25 "C; the remaining three were conducted at approximately 46 OC. In addition to experiments with glycine in molar excess of NH2Cl (Le., pseudo-first-order conditions), several experiments consisted of nearly equal molar concentrations of the reactants. 740
Environ. Sci. Technol., Vol. 17, No. 12, 1983
20
I
I
I
00
io
00
I
100
120
I
140
SECONDS
Flgure 4. Alanlne plus "&I, run All, at T = 25 OC and pH 6.15. Variation of [NH,CI] with time: [NH,CI], = 1.91 X M; [Gly], = 1.91 X M.
Figures 3 and 4 illustrate the results from plotting log [NH,Cl] with time when pseudo-first-order conditions prevailed (runs G47 and AL1). Figure 5 is based on data from a reaction involving equimolar concentrations of glycine and NHzCl (run G22). The plot is based on second-order reaction techniques in which [NHzC1]-l is plotted with time. The slope of the line is the estimate for the observed second-order reaction rate coefficient. The results from reactions of NH2Cl with amines and amino acids, including the glycine derivatives, indicate nearly pH-independent observed second-order rate constants over varying intervals in the neutral pH range but considerable decrease beyond that when experiments were conducted at higher pH values as shown in Table 111, as well as in Figures 6-8 for glycine, serine, and glycine ethyl ester, respectively. There are several plausible mechanisms which would account for the pattern of the results. However, kinetic data do not aid in differentiating among these mechanisms.
Table IV. Half-Times for Equimolar Mixtures of NH,C1 and Nitrogenous Organic Compounds at pH 7 and T = 25 "C
t , , , , days, at
t,,,, h, at
C, =
a
compound
h( obsd), (mol/L)-' s-l
direct transfer
alanine glycine serine glycylglycine sarcosine methylamine dimethy lamine morpholine glycine ethyl ester
0.8 1.0 2.0 5.1 0.48 0.19 0.14 14.0 4.2
3.5 2.8 1.4 0.5 5.8 14.6 19.8 0.2
0.7 s-'.
Hydrolysis rate constant of NH,Cl= 2.1 X 40
C, =
mol/L hydrolysis"
direct transfer
9.2 9.2 9.2 9.2 9.2 9.2 9.2 9.2 9.2
1.4 1.2 0.6 0.2 2.4 6.1 8.3 0.1 0.3
mol/L hydrolysisa 0.4 0.4 0.4 0.4 0.4 0.4
0.4 0.4 0.4
Assumes no reformation of "$1.
i
*/
T=ZCC I
1
I 40
30
20
MINUTES
Fiaure 5. Glycine ~ l u NH,CI. s run 022. at T = 25 OC and DH 7.16. Variation of [NH2CI]-' withiime: [NH2Cl], = 1.91 X loT3M;'[Gly], = 1.91 x 10-3 M. T-25.C
r
T
I
lo',
4 4
3
TT
5
6
i
8
9
10
11
1'2
PH
Figure 6. Glyclne plus NH,CI. Variation of k(obsd) with pH, at T = 25 OC. Solid line is k(obsd) calculated from estimate of fundamental rate constant (8).
All of the plausible mechanisms will result in identical calculated values for the observed rate constants. This
theoretical, calculated value for the observed rate constant in each set of experiments is represented by each of the solid lines in Figures 6-8. This topic is discussed further in a paper now in preparation (8). The half-reaction times (tl12) for equimolar concentrations of chloramine and the individual nitrogenous compounds vary from several hours at lo-* mol/L to several days at lod mol/L (Table IV). The former concentrations are representative of wastewater systems, while the latter serve as a model for clean water systems. At the lower concentrations, transfer of C1+ by NH2C1hydrolysis can be comparable to that by direct interaction of NH2Cl and the nitrogenous substrate as indicated in Table IV. Note that the HOC1 produced by hydrolysis of NH2Cl also may react with any chlorine demand that remains or with already formed N-chlorinated species, or with remaining/ reappearing NH, and remaining organic N. The less stable N-chloro organic compounds are likely to decompose inEnviron. Scl. Technol., Vol. 17, No. 12, 1983 741
drolysis and direct interaction will be important in the transfer of C1+ to nitrogenous organic compounds. Thus, the initial kinetically determined distribution of C1’ will progress toward a greater proportion of organic N-chloro compounds through (a) hydrolysis of NH2Cl to form HOC1 which will react with remaining unchlorinated nitrogenous organic compounds (or any chlorine demand as well) and (b) direct transfer of C1+ from NH2Cl to organic nitrogen. The modification of the distribution of C1+ is important because other studies have found the organic N-chloro compounds to be weaker disinfectants than NH2Cl (9,10) and many, though not all, to be less toxic to fish (11). Registry No. “&I, 10599-90-3;methylamine, 74-89-5; dimethylamine, 124-40-3; morpholine, 110-91-8; glycine, 56-40-6; serine, 56-45-1;alanine, 56-41-7; sarcosine, 107-97-1;glycylglycine, 556-50-3; glycine ethyl ester, 459-73-4;N-acetylglycine, 543-24-8.
Literature Cited
‘ r - 1 6
7
8
I
PH
Flgure 8. Glycine ethyl ester plus NH,CI. Variation of k(obsd) with pH, at T = 25 O C . Solid line 1s k(obsd) calculated from estimate of fundamental rate constant (8).
stead of maintaining the hydrolysis equilibrium. Amides. Solutions of NH2Cl (1.0 X mol/L) and N-acetylglycine (1.71 x mol/L) were mixed, and the UV spectrum of the mixture (pH 6.25, T = 25 “C) was monitored. Transfer of C1+ to the amide bond was not readily demonstrable under these conditions. Conclusions
It has been demonstrated that NH2Clcan react directly with nitrogenous organic compounds to form N-chlorinated species. At chloramine and organic nitrogen concentrations mol/L, formation of N-chlorinated compounds of will proceed primarily by direct reaction between NH2Cl and the N substrate. At reactant concentrations representative of fresh water (mol/L), both NH2C1 hyN
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Environ. Sci. Technol., Vol. 17, No. 12, 1983
Langheld, K. Chem. Ber. 1909, 2360-2375. Hutchinson, G. E. “A Treatise on Limnology”; New York, 1957; Vol. 1, p 1015. Vallentyne, J. J. Fish. Res. Board Can. 1957, 14, 33-57. Gardner, W. S.; Lee, G. F. Environ. Sei. Technol. 1973, 7, 719-724. Ram,N. M.; Morris, J. C. Environ. Sci. Technol. 1982,16, 170-174. Ram, N. Ph.D. Thesis, Harvard University, Cambridge, MA, 1979. Massachusetts Division of Water Pollution Control, unpublished data, 1979. Isaac, R. A.; Morris, J. C., unpublished results, 1983. Feng, T. J. Water Pollut. Control Fed. 1966,38,614-628. Stringer, R. W.; Cramer; Kruse, C. In “Disinfection: Water and Wastewater”; Johnson, J. D., Ed.; Ann Arbor Science Publishers, Inc.: Ann Arbor, MI, 1975; pp 193-209. Tsai, S. C.; Mattice, J. S.; Packard, K. B., presented at the 111th Annual Meeting of the American Fisheries Society, Albuquerque, NM, 1981. Received for review March 8,1983. Accepted June 27,1983. This work was supported in part by U S . Army Medical Research and Development Command Contract DAMD 17- 77-C- 7051, with David Rosenblatt as project manager. R. A. Isaac was on educational leave from the Massachusetts Division of Water Pollution Control with a U.S. Environmental Protection Agency Fellowship. A preliminary version of this paper was presented a t the Third Conference on Water Chlorination: Environmental Impact and Health Effects, Colorado Springs, CO, 1979, and appears in the proceedings.
