The normal composition of the efluent samples at Abbott Laboratories is within the maximum tolerated impurity levels as listed in the Illlnois State Standards (1968). These tolerances are partially summarized in Table I and do not interfere in the assay. Wiersma (1970) employed 2,3-diaminonaphthalene as a fluorometric reagent for nitrite ion and in addition performed
Table I. Illinois Effluent Standards Constituenta Standard Ammonia nitrogen Arsenic BOD
Chromium (VI) Chromium (111) Cyanide Mercury Nitrate PH Phenol Selenium Total suspended solids Total dissolved solids
2 . 5 ppm 1 . 0 ppm 40 mg/l. 0.05 ppm 1 . 0 ppm 0.025 ppm 0 . 5 ppb 45 PPm 6-1 0 0 . 2 ppm 10 PPb 45 mg/l. 750 mg/l.
Illinois Sanitary Water Board.
a
0
z
z
Acknowledgment
Table 11. Effect of Foreign Ions on the Fluorometric Determination of Selenite Ion added” bg Selenite found* None Nitrite Al(II1) Ca(I1) Cd(I1) Cr(II1) Cu(I1) Fe(II1) Ni(I1) Pb(I1) Sn(I1) Zn(I1)
a detailed study into the effects of foreign ion interferences. He reported that Se(IV), Cu(II), Al(III), Bi(TII), Ni(II), Cr(111) and Sn(I1) at the 0.05mM level induced errors of greater than 25 a t the 0.5 pg level of nitrite ion. The effect of foreign ions, in particular, nitrite, on the selenium assay was found to be negligible. Table I1 indicates only aluminum(II1) with an error of 15 was greater than the relative standard deviation. The addition of the bromine-bromide oxidation step oxidizes selenium metal to selenious acid. The maximum level of conversion from selenium metal to selenious acid has been established at 25 pg (2500 ppb). The buffer does not interfere in the fluorescent assay as the fluorescent excitation and emission curves for equal amounts of the piazselenol of sodium selenite determined both with and without the addition of the redox buffer in the initial reaction step are quantitatively identical. The redox buffer does not further oxidize the selenious acid to selenic acid nor does it reduce selenates to selenites. An equivalent of 10 ppb selenate was processed according to the procedure without any resultant fluorescent maximum at 522 nm. The procedure is sensitive to selenium(0) and selenium(1V). If it is desirable to determine all forms of selenium, the digestion method of Watkinson (1966) for the determination of selenium in biological fluids should be applied to the effluent samples.
0.048 0.051 0.055 0.048 0.048 0.048 0.051 0.052 0.052 0.053 0.049 0.046
0.05mM foreign ion added to each sample.
* Theoretical 0.048 pg selenite.
The author is indebted to L. T. Sennello, H. Stelmach, and D. C. Wimer of Abbott Laboratories for their consultation on the development of this technique. Literature Cited Atomic Absorption Newsletter, 7 , 5 (1968). Cheng, K. L., Anal. Chem., 28,1738 (1956). Illinois Sanitary Water Board, Illinois Department of Public Health, Sewage and Industrial Waste Treatment, Requirements and Effluent Criteria, Technical Release T R 20-22, 2nd ed. (revised April 1,1968). Kovar, Lawrence E., Gulf General Atomic, San Diego, Calif., personal communication, 1970. Luke, C. L., Anal, Chim. Acta., 41,237 (1968). Marcie, F. J., ENVIRON. SCI.TECHNOL., 1,164 (1967). Parker, C. A,, Harvey, L. G., Analyst, 87,558 (1962). Shimoishi, Y . ,TGei, K., Talanta, 17,165 (1970). Watkinson, J. H., Anal. Chem.,38,92 (1966). Wiersma, J. H., Anal. Lett., 3,123 (1970). Received for review November 16, 1970. Accepted February 7, 1972.
Ammonia-Nitrogen Removal by Breakpoint Chlorination Thomas A. Pressley,’ Dolloff F. Bishop, and Stephanie G . Roan US. Department of the Interior, Federal Water Quality Administration, Advanced Waste Treatment Research Laboratory, Robert A. Taft Water Research Center, Cincinnati, OH 45268
T
he chief nitrogenous pollutants in municipal waste waters have been categorized (Sawyer and McCarty, 1967; “Standard Methods for the Examination of Water and Wastewater,” 1965) into three main groups: ammonia nitrogen, organic nitrogen, and nitrite and nitrate nitrogen.
1
To whom correspondence should be addressed.
622 Environmental Science & Technology
Ammonia nitrogen in waste water is formed by the enzymatic breakdown of urea, proteins, and other nitrogen-containing materials. Most of the organic nitrogen in waste waters is in the form of amino acids, polypeptides, and proteins. Little nitrite and nitrate nitrogen is present in waste waters unless biological oxidation of ammonia to nitrite or nitrate occurs or unless the nitrite and nitrate nitrogen is introduced in industrial or agricultural discharges.
rn Sodium hypochlorite was used to oxidize the ammonia in buffered distilled water systems and in raw, secondary, and lime-clarified municipal waste waters. In systems with only ammonia as the chlorine demand, the breakpoint exhibited a minimum chlorine dose at approximately an 8 : 1 wt ratio of C1:NH3-N in the pH range of &7. End products at the breakpoint were N2, NC13, and NO3-. Qualitatively, the formation of the N2 was completed in less than 1 min. At the breakpoint in buffered distilled water with 20 mg/l. of NH3-N, the formation of N03--N decreased from about 2.0 mg/l. at
pH 8.0 to 0.3 mg/l. at pH 5-6. NC13-N formation in the same system at the breakpoint decreased from approximately 0.3 mg/l. at pH 5.0 to 0.05 mg/l. at pH 8.0. In the pH range of 5-8, less than 0.3 mg/l. of NCl,-N formed before the breakpoint. In waste water, the breakpoint required a minimum chlorine dose of approximately an 8: 1 wt ratio of C1:NHa-N in lime-clarified secondary effluent. The chlorine dosage to achieve the breakpoint increased as the degree of waste water treatment decreased. The organic nitrogen in the waste water was not removed within the 2-hr reaction period.
The various waste water treatment processes-Le., conventional activated sludge, lime clarification and filtration, carbon adsorption-designed for the removal of phosphorus, particulate matter. and dissolved organics are also successful in removing much of the organic nitrogen from waste waters; however, these processes do not significantly remove the dissolved ammonia nitrogen. Several processes have been employed for the removal of ammonia nitrogen from waste waters including selective ion exchange, air stripping, and biological nitrification-denitrification. Ammonia removal by ion exchange employs naturally occurring zeolite exchangers in columns (Mercer et al., 1970). The ammonia is removed from the zeolites by elution with alkaline brine solutions. The process is costly and requires further disposal of the ammonia in the regenerant brine solution. Ammonia removal by air stripping (OFarrell et al., 1970) requires pH elevation to convert the to ammonia. The process requires large stripping towers which are subject to C a C 0 3 scaling and also to tower freezing in the winter. In addition, the volatility of ammonia and thus the stripping efficiency decreases sharply with temperature. Ammonia removal by biological nitrification and denitrification processes (Barth et al., 1968) involves the biological oxidation of ammonia to nitrate followed by the reduction to nitrogen gas with methanol and bacteria. The process requires extensive tankage and is subject to biological upsets. Breakpoint chlorination, as practiced for many years in the water treatment industry, provides an additional physicalchemical means for removing ammonia from waste waters. Detailed studies of the effect which chlorination exerts on bound nitrogen (Taras, 1953; Faust and Hunter, 1967) reports the total nitrogen oxidized during chlorination follows a well-defined general pattern. Ammonia is oxidized within the first minute. The simple and unsubstituted amino nitrogen of many common amino acids is oxidized more slowly over an extended period of time. Protein nitrogen shows negligible loss of nitrogen even after prolonged chlorination periods. Since organic nitrogen removal can be accomplished by other processes, chlorine oxidation provides a selective means for ammonia removal. In water, at NH3-N concentrations usually below 1 mg/l., chlorine reacts with the ammonia to form various chloramines :
Chlorine is added to process waters until a point is reached where the total dissolved residual chlorine has reached a minimum (the breakpoint) and the NH3-N has disappeared. In water at NH3-N concentrations of less than 1 mg/l., and before the breakpoint, the type of chloramine formed depends on the pH. Spectrophotometric analyses (Chapin, 1931 ; Corbett et al., 1953; Czech et al., 1961 ; Moore, 1951 ; Palin, 1952) indicate that the chief constituent is monochloramine in the pH range of 7-8.5. As the pH decreases below 7, increasing amounts of dichloramine appear. In the pH range of 4.5-5.0, dichloramine is the chief product; below pH 4, nitrogen trichloride is the chief product. Breakpoint chlorination studies (Yutaka, 1967) on buffered synthetic ammonia samples at pH 7.0 reveal that monochloramine concentration reaches a maximum at the 5 :1 wt ratio of C1:NH3-N. As the wt ratio of C1:NH3-N exceeds 5 :1, the monochloramine breaks down (Faust and Hunter, 1967) to form dichloramine and ammonia (Equation 5).
Clz
+ H20
+ HOCl NH2C1 + HOCl NHCl2 + HOCl NHIS
+ HC1 NH7C1 + H20 + H' NHC1, + H20 NC13 + H?O
+ HOCl
(1)
+
(2)
+
+
(3)
(4)
2NHsCl
+
NHClr
+ NH3
(5)
The dichloramine reaches a maximum concentration at the C1:NH3-Nwtratioofabout7.5:l. The literature (Griffin and Baker, 1941) indicates that in water with less than 1 mg/l. of NH3-N, the reaction proceeds in competition with monochloramine formation (Equation 2 ) until the chlorine dosage reaches the breakpoint at approximately a 1O:l wt ratio of C1:NH3-N. Other studies (Cole and Taylor, 1956; Griffin and Chamberlain, 1956; Palin, 1952), however, indicate that monochloramine is oxidized by excess chlorine under slightly alkaline conditions to nitrogen gas (Equation 6). 2NH2C1
+ HOCl
+
NL
+ 3HC1 + H20
(6)
Stoichiometrically, the ammonia oxidation through monochloramine to N2 corresponds to a 7.6:l wt ratio of C1:NH3-N. The literature (Chapin, 1931; Corbett et al., 1953; Griffin and Baker, 1941; Palin, 1952) also suggest the occurrence of other end products, including nitrate and nitrogen trichloride. In fact, the nitrogen trichloride produced (Equation 4) in water treatment plants (Kirk and Othmer, 1964) during breakpoint chlorination has been a serious problem. Previous studies (Faust and Hunter, 1967; Moore, 1951; Taras, 1953) of the kinetics of the reaction of chlorine with ammonia have produced reaction orders and rate constants for the formation of mono- and dichloramine. The rate constants indicate the formation of monochloramine and dichloramine to be complete well within 1 min. Kinetic data concerning the oxidation of monochloramine to nitrogen is unavailable. In waste waters, the NH3-N concentration may be more Volume 6, Number 7, July 1972 623
than an order of magnitude higher than those normally encountered in natural waters. For use of breakpoint chlorination for nitrogen removal at the NH3-N concentrations encountered in waste waters, the end products of the reaction need to be known. This study identified the major products of the breakpoint reaction in synthetic buffered solutions and in waste waters and determines the formation and behavior of the nuisance residuals of NcI3 and NO,- as a function of pH, chlorine dosage, and temperature. Experimental
The chlorination studies were performed in synthetic standard phosphate-buffered systems with initial “3-N concentrations of 20 mg/l., to eliminate effects from other substances reacting with chlorine. Studies were also performed in raw, secondary, and lime-clarified municipal waste waters with “3-N concentrations ranging from 8-15 mg/l. In end product identification studies on buffered synthetic aqueous systems, the gaseous products were qualitatively analyzed for NP,0 2 , and N 2 0 .The procedure involved purging the aqueous sample containing 20 mg/l. NH3-N and buffered at pH 7.5 with helium to remove atmospheric nitrogen in a closed system attached to a gas chromatograph. The sample was then treated with nitrogen-free standard sodium hypochlorite at a dosage equal to a 1O:l wt ratio of C1:NH3-N. The gaseous products of the reaction were then flushed through the gas chromatograph with helium. A test was also performed to identify the presence of any nitric oxide (NO) or nitrogen dioxide (NOn). An enclosed breakpoint chlorinated sample was purged with air into a cold solution of 0.02N HzS04to remove any NO or NO2 formed during the chlorination. In the procedure (Nebergall and Schmidt, 1957), the NO was oxidized to NOz by the oxygen in the air and absorbed in the 0.02N H2S04as nitrous and nitric acids. The 0.02N HzSO4 solution was then analyzed for (NO3- NOz-)-N. Spectrophotometric scanning of both chlorinated aqueous samples and their CCl, extracts was also performed to determine other end products. The samples, after 2 hr of contact with the chlorine, were placed in a recording spectrophotometer and scanned over the spectral range of 200-500 mp. In the quantitative studies, aqueous ammonia or waste water samples were manually mixed in separatory funnels with increasing dosages of standard sodium hypochlorite over the pH range of 5-8. A 2-hr contact time (Yutaka, 1967) was provided for all systems. The samples, after chlorination, J O - ) - N , NC13-N, NH3-N, were analyzed for (NO3NHzCl and NHC12-N, TK-N; total residual chlorine, free available chlorine, and pH. Quantitative temperature studies were also conducted at 5 O , 15O, 25O, and 4OoC on aqueous ammonia samples containing 20 mg/l. NH3-N and buffered at pH 6.0 to determine temperature effects on the end products. Multiple samples in separatory funnels were cooled to the designated temperature in a constant temperature bath and treated with increasing dosages of precooled sodium hypochlorite. The samples were then manually mixed and allowed to stand at the selected temperature for 2 hr before analysis. A modified automated hydrazine reduction method (Kamphake et al., 1967) with an alkaline digestion to eliminate chloramine interferences was developed for the (NO3N02-)-N analysis. In this procedure, the sample was made alkaline with NaOH, digested to dryness, redissolved and neutralized with HCl, and diluted to volume for analysis. This modified procedure was reliable to 10.05 mg/l. N03--N.
+
+
+
624 Environmental Science & Technology
Nitrogen trichloride was analyzed according to the spectrophotometric procedure of Czech (1961) in the synthetic ammonia samples and in waste water samples by both the spectrophotometric procedure of Czech and the Modified Palin Method [Water (Chlorine Residuals No. 1) Study #35, 19691. The results of spectrophotometric analysis of NC1, on waste water samples were reproducible to 1 0 . 0 5 mg/l. NC13-N. While analyses from the Palin Method were similar to those from the spectrophotometric procedure, they were poorly reproducible ; therefore, the analyses from the spectrophotometric procedure were employed in the evaluation of the breakpoint studies on waste waters. The spectrophotometric procedure for the analysis of NC13, however, represented all compounds extracted from the waste water that absorb at 265 and 345 mp in CC1,. Free available chlorine, mono- and dichloroamine were analyzed according to the Modified Palin Method with N,N-diethyl-p-phenylenediamineoxalate as the indicator, and by amperometric titration. All other analyses employed the procedures of “Standard Methods for the Examination of Water and Wastewaters” (1965). A Varian Aerograph Gas Chromatograph (Model 1532-2B) equipped with an ionization detector (with a tritium source) and a Molecular Sieve-type column, designed to detect Nz, 0 2 , and N 2 0 , was used to qualitatively analyze the gaseous product. A Forma (Model 2095) circulating-constant temperature bath was used to control the temperature of the studies to =kO.l”C.Uv absorbancies were determined on a Beckman DU spectrophotometer or on a Beckman DBG recording spectrophotometer, both with 10-mm quartz cells. The NCl, standard was prepared by the method of Noyes (Booth, 1939) and assayed. Aliquots of the stock were diluted in carbon tetrachloride to make standard solutions ranging from 0-100 mg/l. NC13. The NC13 standards scanned in the spectrophotometer produced peaks only at 265 and 345 mp with linear absorbancies for increasing NC13 concentrations. The molar absorptivities calculated from the standards were 228 for the peak at 345 mp and 445 for the peak at 265 mp. The molar absorptivities reported by Czech et al. (1961) were 232 for the peak at 345 mp and 450 for the peak a t 265 mp. Spectrograde CC14 was used throughout the study for extraction and dilution of standard and unknown samples. All other reagents used in the study were of reagent quality. End Products
In buffered solutions at pH 7.5 with 20 mg/l. NH3-N, gas chromatographic analysis for NP, 02,and N 2 0 at the breakpoint detected only Nn. Since 0 2 was not detected, the formation of NzO with subsequent decomposition to N2 and Ondid not occur. The tests for nitric oxide (NO) and nitrogen dioxide (NOn)revealed that neither of these compounds were present. Attempts to determine reaction rate in the laboratory revealed the disappearance of combined chlorine residuals, and the appearance of nitrogen gas to be complete within 1 min at the breakpoint with ammonia-nitrogen for concentrations of 20 mg/l. in the pH range of 6-8. Detailed kinetic studies were not performed in this work because for reactor design the reaction may be considered essentially instantaneous. Spectrophotometric scans (200-500 mp) of the buffered solution treated with increasing dosages of chlorine up to C1:NH3-N wt ratio of 7.5:1 revealed adsorption peaks at 243 mp for monochloramine (Kleinberg et al., 1954) and at 205 mp for nitrate; (“Standard Methods for the Examination
I20
-
,110
2 100 E
W
$ 5 I LJ -I
90 80 70 60
2
50
E
40
n W
-1
2 0 +
30
20
IO 0
CLcNH3-N
CL:NH;N
WT. R A T I O
W % RATIO
Figure 1. Chlorination and p H
Figure 2. Breakpoint chlorination and pH
Buffered distilled water; NHa-N = 20 mgll.; temp = 25°C
Buffered distilled water; NHa-N = 20 mg/l.: temp = 25°C
of Water and Wastewater," 1965) above the 7 . 5 : l ratio the peak at 243 mp disappeared and a peak at 287 mp appeared and increased with increasing chlorine doses. The control sample containing only the buffered solution with free chlorine and without NH3-N, produced a peak only at 287 mp. Thus, the peak at 287 mp above the 7.5 : 1 ratio of Cl:NH3-N was produced by free aqueous chlorine. The absorbance produced by monochloramine at 243 mp increased linearly with increasing chlorine dosages to a maximum at the 5 : l wt ratio of C1:NH3-N and then decreased to near zero at approximatelythe 7.6 :1 ratio. The strong peak produced by NO3- at 205 mp increased with increasing chlorine dosage through the 12:l wt ratio of C1:NH3-N and confirmed the formation of NO3- during chlorination. In summary, spectral scanning of the aqueous solutions indicated only the formation and decomposition of monochloramine, the gradual formation of NO3--N and the presence of free available chlorine after the breakpoint. The CC1, extracts, scanned in the spectrophotometer in the range of 200-500 mp against a reference control blank, produced strong NC13 peaks (Czech et al., 1961) at 265 and 345 mp only after the chlorine dosage exceeded the 7.5:l wt ratio of C1:NH3-N. p H and Temperature The addition of chlorine to buffered aqueous samples containing 20 mg/l. "3-N at pH 7.0 produced a typical breakpoint curve with the complete removal of the ammonia and a minimum total residual chlorine concentration of about 0.6 mg/l. at approximately 8 : l wt ratio of C1:NH3-N (Figures 1 and 2). The chlorination studies of buffered solutions at pH 7.0 containing 1 mg/l. NH3-N also reached the breakpoint at approximately an 8 :1 wt ratio of C1 :NH3-N. In all tests on buffered aqueous systems in the pH range of 6-7, the breakpoint occurred at chlorine doses approximately equal to an 8 :1 (stoichiometric ratio 7.6 :1 , Equations 2 and 6) wt ratio of Cl:NH3-N. Outside of the 6-7 pH range, the chlorine dose required for the breakpoint increased (Figure 1). In pH studies on synthetic samples containing 20 mg/l. "3-N, the formation of NO3--N at the breakpoint (Figure 3) increased with increasing pH from about 0.3 mg/l. (1.5% of the NH3-N) at pH 5.0 to about 2.0 mg/l. (10% of the "3-N) at pH 8.0. With increasing chlorine dosages above the breakpoint, the N03--N formation increased sharply at pH 6.0 and above, but increased only slightly in the pH
\ CI .
E
?
I N
z +
1"
z 0
CL:NHa-N WT RATIO
Figure 3. Nitrate and nitrite formation and pH Buffered distilled water; "3-N = 20 mg/l.; temp = 25°C pH 8.0: breakpoint between the 8 : l and 9 : l wt ratio of C1:NHa-N pH 7.0: breakpoint at approximately 8:l wt ratio of C1:NHa-N pH 6.0: breakpoint at approximately 8:l wt ratio of C1:NHI-N pH 5.0: breakpoint between the 9 : l and 1O:l wt ratio of C1:NHa-N
z '10
-1 U
z
CL:NH.-N
W% R A T I O
Figure 4. Nitrogen trichloride formation and pH Buffered distilled water; NHa-N = 20 mg/l. ;temp = 25 "C pH 8.0: breakpoint between the 8:l and 9 : l wt ratio of C1:NHa-N pH 7.0: breakpoint at approximately 8:l wt ratio of C1:NHa-N pH 6.0: breakpoint at approximately 8 : l wt ratio of C1:NHa-N pH 5.0: breakpoint between the 9 : l and 1O:l wt ratio of C1:NHa-N Volume 6, Number 7, July 1972 625
3 NOitNOi- N NCL3-N
Table I. Breakpoint Chlorination Temperature Studies Contact time = 2 hr., pH 6.0 Temp, 'C
+ nitrite
22 NHa-N
0 00 0.10 0.18 0.27 0.43 0.50 0.60 0.70
0.00 0.00 0.00 0.00 1.10 1.89 3.91 5.67
15
0 5:l 6:l 7:l 8:l 9:l 1O:l 11:l
20.0 9.69 6.00 1.22 0.00 0.00 0.00 0.00
0.00 0.05 0.05 0.16 0.30 0.43 0.52 0.60
0.00 0.00 0.00 0.00 1.10 1.90 3.90 5.67
0
20.0 9.20 6.70 3.90 0.00 0 00 0 00 0.00
0.00 0.00 0.10 0.15 0.42 0.47 0.55 0.66
0.00 0.00 0.00 0.00 1.10 1.92 4.00 5.70
5:l 6:l 7:l 8:l 9:l 1O:l 11.1
W
z
E
s
0
CL NH3-N W T RATIO
Figure 6. Chlorination of raw waste water Temp = 23'C; "3-N = 15.0 mg 1.; suspended solids = 234 mg 1.; total alkalinit? = 120 mg 1. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 9 : l and 1O:l wt ratio of C1:NHa-N
range of 5-6. Thus, low pH (5-6) produced minimum amounts (0.3 mg,'l.)of N03--N. In contrast, the amount of NC13-N formed at the breakpoint decreased from approximately 0.3 mg,'l. (1.5z)at pH 5.0 t o 0.05 mg'l. (0.25 %) at pH 7 (Figure 4). In the pH range of 7-8, a NC13-N concentration of less than 0.1 mg/l. occurred at the breakpoint. As chlorine dosages exceeded the breakpoint, the formation of NC1, increased sharply at and below pH 7.0. At pH 8.0, however, the NCI, concentration increased but never exceeded approximately 0.3 m g l . for chlorine dosages LIPto a 12:l wt ratio of C1:NH3-N. Thus, chlorination at the 9 : l wt ratio of C1:NH3-N (slightly above the breakpoint) minimized NCl3 residuals at pH 8 but maximized nitrate formation (Figure 5). The 0.05 m g l of NC13 at the breakpoint (produced by the oxidation of dichloramine) (Faust and Hunter, 1967) also indicated only small amounts of dichloramine formed above pH 7. The modified Palin Analysis for dichloramine revealed less than 0.1 mg '1. NHCh-N above pH 7 after 2 hr of contact time for all chlorine dosages. Breakpoint chlorination studies on buffered aqueous systems a t pH 6.0 were conducted in the temperature range of 626 Environmental Science & Technolog?
NC13-N mg/l.
20.0 9.20 6.10 1.19 0.00 0.00 0.00 0.00
40
50
N o s - -b NO~C-N, mg/l.
0 5:l 6:l 7:l 8:l 9:l 1O:l 11:l
Formation vs. pH: 9 : l wt ratio of CI:NHa-N (above breakpoint) Buffered distilled water; KHI-N = 20 mg,l.; temp = 25°C
20
NHrN, mg/l.
5
PH
Figure 5. Nitrogen trichloride and nitrate
C1:N wt ratio
5540°C. These tests did not reveal significant changes in the reaction products after the 2-hr contact time. Complete removal of the NH3-N was achieved at all temperatures (Table 1).
Chlorination of Waste Waters
I n breakpointing of unclarified and lime-clarified raw and secondary waste waters (NH3-N concentrations of 8-1 5 mg/l.) with sodium hypochlorite, the C a C 0 3 alkalinities of 80-120 mg 1. in the water maintained the pH of all the samples between 6.5 and 7.5. The chlorine demand required for the breakpoint decreased and approached the stoichiometric amount (Equations 2 and 6) for oxidation of NH3 to N 2 as the degree of waste water pretreatment increased. As a n example, a chlorine dosage equivalent to a 1O:l wt ratio of C1:NH3-N was required to breakpoint raw waste water (Figure 6), while a 9 : 1 wt ratio was required in the secondary effluent (Figure 7), and less than an 8 : 1 wt ratio of C1 :NH3N for lime-clarified and filtered secondary effluent (Figure 9). Thus the highly pretreated waste water exhibited breakpoint performances similar to the synthetic buffered system. If chlorine is employed rather than sodium hypochlorite, the breakpoint chlorination of ammonia concentrations normally encountered in waste waters may produce more acid than can be neutralized by the buffer capacity of the waste water. Stoichiometrically (Equations 1 and 6) 14.28 mg'l. of bicarbonate and phosphate alkalinity (expressed as equivalent CaC03) are required to neutralize the acid produced by the oxidation of 1 mg'l. NH3-N to N2. Therefore, a waste water containing 20 mg'l. NH3-N requires an alkalinity of about 286 mg/l. Since the amount of NC13 formed
16
I
80
~
~
14
A
r
T. Res. CI.
15
m T o t a l Residual Chlorine
TK- N
i 0
E
z m W
/
0
a
/.
YY
/. '*x
t z 4
1
CL:NH,-N
CL:NH3-N WT. R A T I O
Figure 7. Chlorination of lime-clarified and filtered raw waste water Temp = 23°C; NHI-N = 11.2 mg/l.; suspended solids = 4 mg/l.; total alkalinity = 84 mg/l. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 8:l and 9:l wt ratio of C1:NHa-N
12
m T o t a l Residual Chlorine
-
NH3- N
I I -
10
-30
ATK-N
-
5 E W
WT. R A T I O
Figure 9. Breakpoint chlorination of lime-clarified and filtered secondary effluent Temp = 23°C; "3-N = 9.2 mg/l.; suspended solids = 4 mg/l.; total alkalinity = 84 mg/l. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 7:l and 8:l wt ratio of C1:NHa-N
1
,
0.61
0.5
E
,
,
I
NO;+NOi-N A NCL3- N
0
6 5 -
*\
q/,
,
0
I
2
, 3
4
,
,
5
6
..
, 7
\
, 8
9
L .-.-.0 1 0 1 1 1 2
CL: N H3-N WT R A T 1 0 CL:NHa-N
Figure 8. Chlorination of secondary effluent Temp = 22°C; NHI-N = 8.1 mg/l.; suspended solids = 40 mgll.; total alkalinity = 90 mg/l. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 8:l and 9 : l wt ratio ofCI:NH3-N
before the breakpoint increases with decreasing pH, any excess acid produced must be neutralized with proper mixing to avoid both excess local chlorine concentrations and low pH. Thus if a lime-clarified secondary waste water contained 20 mg/l. NHs-N, approximately 160 mg/l. of chlorine would be required for breakpoint Chlorination. At chlorine costs of $0.04/lb, the chlorine cost would be $0.05/1000 gal. of treated water. The variable cost of neutralizing excess acid in a specific waste water and other handling costs must be added to the chlorine cost. Total Kjeldahl nitrogen analyses revealed near complete removal of the NH3-N, but only a slight reduction of the organic nitrogen within the 2-hr contact time (Figures 6-9). The nuisance residuals of nitrate and nitrogen trichloridenitrogen at the breakpoint were always less than 1 rng/l. (Figures 10-13). The formation of NCll decreased with decreasing waste water pretreatment, and did not occur in the raw waste water.
WT RATIO
Figure 10.Nitrogen trichloride and nitrate formation during chlorination of raw waste water Temp = 23°C; "3-N = 15.0 mg/l.; suspended solids = 234 mg/l.; total alkalinity = 120 mg/l. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 9:l and 1 O : l wt ratio of C1:NHa-N
1.4,
I
,
,
,
,
I
,
,
I
,
,
I
NCLs-N
0.6 0.4 0.3
0.2
0.I
O0
1
2
3
4
5
CL:NH3-N WT. R A T I O
Conclusions
Figure 11. Nitrogen trichloride and nitrate formation during the chlorination of lime-clarified and filtered raw waste water
Breakpoint chlorination in buffered aqueous solutions of 20 mg/l. of NHI-N in the pH range of 5.0-8.0 oxidized the
Temp = 23°C; "I-N = 11.2 mg/l.; suspended solids = 4 mg/l.; total alkalinity = 84 mg/l. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 8:l and 9:l wt ratio of CI:NHI-N Volume 6, Number 7, July 1972 627
NO?+NO;-N
5
0.5
-
0.4
-
A
NCL3-N
E
E
0.3
-
0.2
-
(3
a
&
CL:NH3- N WT. R A T I O
Figure 12. Nitrogen trichloride and nitrate formation during chlorination of secondary effluent Temp = 22°C; “3-N = 8.1 mgjl.; suspended solids = 40 rngjl.; total alkalinity = 90 rngjl. CaC03; pH range during chlorination = 6.5-7.5; breakpoint between the 8:1 and 9:1 wt ratio of C1:NHa-N
0.8
-
2
0.7
-
0.6
-
NOS+NO;-N
A NCL3-N
,I
2W 0.40 E 0.3 z 0.2 0.I 0.5
at the breakpoint decreased from approximately 1.5 of the NH3-N at pH 5 to 0.25% at pH 8.0. In the 2-hr contact time of the study, breakpointing at temperatures of 5-40°C did not chang: the amounts of the products or the required chlorine dose. In the pH range of 6.5-7.5, breakpoint chlorination of ammonia in waste waters oxidized 95-99z of the ammonia to nitrogen gas. When chlorine demands other than ammonia were minimized by pretreatment (lime-clarified secondary effluent), the chlorine dosages (8:l wt ratio of C1:NHI-N) required for the breakpoint approached the stoichiometric (7.6:l wt ratio) dosage to oxidize ammonia to Nz. Residuals of NO3- and NCl3 were also formed in the waste waters but with initial NH3-N concentrations of 8-15 mg/l., the N03--N residual never exceeded 0.5 mg/l. at the breakpoint; and the NCls-N residual never exceeded 0.5 mg/l. Literature Cited Barth, E. F., Brenner, R. C., and Lewis, R. F., J . Water Pollut. Contr. Fpd,, 42, R 95 (1968). Booth, H. S., Ed., “Inorganic Syntheses,” McGraw-Hill, New York, N.Y., Vol. 1, p 65, 1939. Chapin, R. M., J . Amer. Chem. Soc., 53, 912 (1931). Cole, S. A., Taylor, W. C., Tappi, 39, 62A (1956). Corbett, R. E., Metcalf, W. S., Soper, F. G., J. Chem. SOC. (London), 1927 (1953). Czech, F. W., Fuchs, R. J., Antczak, H. F., Anal. Chem., 33, 705 (1961). Faust, S. D., Hunter, J. D., “Principles and Applications of Water Chemistry,” Wiley, New York, N.Y., p 23, 1967. Griffin. A. E.. Baker. R. J.. J . New Enaland Water Works Ass.. 55, 1941. ’ Griffin, A. E., Chamberlain, N. S., ibid., No. 3. Kamuhake. L. J.. Hannah. S. A,. Cohen. J. M.. Water Res.., 1., 205 (1967). ’ Kirk, R. E., Othmer, D. F., “Encyclopedka of Chemical Technology,” Wiley, New York, N.Y., 2nd rev. ed., Vol. 4, p 916 (1964). Kleinberg, J., Tecotzky, M., Audrieth, L. E., Anal. Chem., 26, 1388 (1954). Mercer, B. W., Ames, L. L., Touhill, C. J., VanSlyke, W. J., Dean, R. B., J . Water Pollut. Contr. Fed., 42, R 95 (1970). Moore, E. M., Water Sewage Works, 98 (3), 1951. Nerbergall and Schmidt, “College Chemistry,” Heath, Boston, Mass., p 361 (1957). O’Farrell, 1.P., Frauson, F. P., Cassel, A. F., and Bishop, D. F., “Nitrogen Removal by Ammonia Stripping,” EPA Office of Research and Monitoring, Advanced Waste Treatment Research Laboratory, Robert A. Taft Water Research Center, Cincinnati, Ohio, presented at the 160th National Meeting, ACS, Chicago, Ill., September 1970. Palin, A. T., J . Amer. Water Works Ass., 44, 48 (1952). Sawyer, C. N., McCarthy, P. L., “Chemistry for Sanitary Engineers,” 2nd ed., McGraw-Hill, New York, N.Y., p 425 (1957). “Standard Methods for the Examination of Water and Wastewater,” 12th ed., American Public Health Assoc., New York, N.Y., 1965. Taras, M. J . , J . Ainer. Water Works Ass., 45, 47 (1953). Water (Chlorine Residuals No. 1) Study No. 35, Analytical Reference Service, Dept. of Health, Education and Welfare, Public Health Service, 1969. Yutaka, I., Bull. Chem. SOC.Jap., 40, 835 (1967).
-
I
2
3
4
5
CL:NH,-N
7
6
WT
8
9
1011
12
RATIO
Figure 13. Nitrogen trichloride and nitrate formation during chlorination of lime-clarified and filtered secondary effluent Temp = 23°C; ”3-N = 9.2 mg/l.; suspended solids = 4 mg/l.; total alkalinity = 84 mg/l. CaCOa; pH range during chlorination = 6.5-7.5; breakpoint between the 7 : l and 8 : l wt ratio of C1:NHa-N
ammonia chiefly to Nz with only small amounts of NO3and NCI3 also formed. During chlorination, monochloramine concentrations increased with chlorine dose through about a 5 : l wt ratio of C1:NH3-N and then decreased to zero at the breakpoint. Only traces of NHCl2 occurred in the 5-8.0 pH range with less than 0.1 mg/l. above pH 7. Potential products of NzO, On(from the decomposition of NzO), NO, and NOn did not occur. The minimum chlorine dosage for the breakpoint of less than 8 : l wt ratio of C1:NH3-N occurred in the range of pH 6-7. The amount of NO,- produced at the breakpoint increased from about 1.5% of the NH3-N at pH 5 to about 10% at pH 8.0 in the aqueous systems. In contrast, the NCI, production
628 Environmental Science & Technology
Receiced for reciew March 19, 1971. Accepted January 4, 1972. Presented at the Dicision of Water, Air, and Waste Chemistry: 160th Meeting, A C S , Chicago, I[[., September 1970.
