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Removal of organics in water using hydrogen peroxide in presence of ultraviolet light
Water Research Vol. 14, pp. 1131 to 1135 O Pergamon Pros Ltd 1980. Printed in Great Britain
0043-1354/80/0801-1131102.00/0
REMOVAL OF ORGANICS IN WATER USING HYDROGEN PEROXIDE IN PRESENCE OF ULTRAVIOLET LIGHT MURUOAN MAt~Y~DI, M. HUSAINSADAR,PAULINELr~ and RON O'G|o, DV Monitoring and Criteria Division, Bureau of Chemical Hazards, Health and Welfare Canada, Ottawa, Ontario, Canada K1A 0L2 (Received January 1980)
Ab~mct--The optimum conditions for the removal of dissolved organic impurities from water using hydrogen peroxide (.50%) followed by ultraviolet irradiation were investigated. The photochemically initiated hydroxyl radical (.OH) oxidation reduced the total organic carbon (TOC) content of distilled water samples by about 88~ and of tap water by 98%. Extraction with hexane of equal volumes of water samples before and after H,O2/u.v. treatment followed by gas chromatographic analysis of the concentrated extracts indicated that about 12% of the electron-capturing, residual organics remained after this treatment. These results support the conclusion drawn from total organic carbon analYSis that this simple method yields water nearly free of organic impurities.
INTRODUCTION
The presence of numerous, potentially-harmful, organic contaminants in surface and underground waters has been established (Shackelford & Keith, 1976). Since the need for producing "organic-free" water has become extremely important, especially in the industrialized nations, continuous efforts are being made to develop methods of purifying water either by removing these impurities or by converting them into harmless products. Although a number of physical and chemical techniques for water purification are available, the oxidation of trace organic impurities in water is an attractive method because of its low cost high efficiency and simplicity. Moreover, the intermediate oxidation products so formed are usually easilydegraded, low molecular weight oxygenated compounds. The reaction generally gives highly desirable end products such as carbon dioxide and water. Direct reaction of most organic compounds with oxygen at ambient temperatures is, in most cases, impractically slow. Some source of free radicals or singlet oxygen is, therefore, generally sought to initiate the oxidation which, through a series of radical chain reactions, completes the degradation of organic materials in a very short time. Several recent reports have described the use of molecular oxygen in conjunction with hydrogen peroxide-metal ion catalytic systems to degrade organic contaminants in water (Walling, 1975; Bishop et al., 1968). These systems preferentially hydroxylate many organic molecules. In several instances, however, the decomposition of the oxidant itself predominates over the oxidation of the organic species and results in excessive loss of the oxidant.
The main objective of this study was to find a simple and practical method for the removal of dissolved organic impurities present in drinking water and also to obtain high purity water for research purposes. It is known that hydrogen peroxide or ozone when used in water under u.v. light is partimflarly well-suited for the break-down of organic molecules as the cleavage of the O - - O bond gives OH radicals or oxygen atoms (sehumb et al., 1955). The OH radical is known to be extremely reactive with most organic molecules with H-atom donor properties (Walling, 1975; Anbar & Neta, 1967), and promptly attacks such species to produce new types of radicals which may subsequently initiate several radical chain reactions. Also, OH radicals are more effective than .OR and .OOR (Hendry et al., 1974) (R --alkyl or aryl group) in producing carbon radicals from organics and hence the use of H , O , as the source of free radicals is very attractive. Further, autoxidation involving hydroxyl and/or peroxy radicals seems to be most effective within the pH range of 6-8. Outside this pH range, a source other than hydrogen peroxide is needed to produce hydroxyl radicals (Uri, 1961; Koubek, 1975). In the present work, hydrogen peroxide (~ 1.0%) and u.v. light of wavelength above the 200 nm system has been used to generate the reactive OH radicals. The choice of water samples was confined to the tap water and the distilled water available in our laboratory. Since the nature and the amount of organic impurities present in these samples could vary from day to day, it was deemed essential to cheek the effectiveness of the purification process by comparing the dissolved organic contents of every sample before and after the H,O2/u.v. treatment. The two techniques employed for this comparison were analysis of TOC
1131
1132
\,It Rt GAS NIALAI'~ANDI ~'r ~al
content of water samples per se and gas chromatographic analysis of the concentrated hexane extracts of the water samples. The development of reliable instrumental technique has made it very easy to determine the T O C content of potable a n d waste waters (Kehoe, 1977). This analytical technique for the T O C measurement using the peroxydisulfate/u.v, system has been shown to convert organic carbon almost quantitatively to carbon dioxide (Takahashi, 1976; Goulden & Anthony, 1978). Therefore T O C values are a good measure of trace levels of organic impurities in water provided that the instrument is calibrated properly and the measurements taken carefully (Reijnders, 1977). Further, since the method described in this c o m m u n i c a t i o n for the removal of organics in water is similar to the T O C analytical method (Takahashi, 1976), the values of total organic c a r b o n reported here, are only relative to the values obtained for the standard, potassium biphthalate, using the peroxydisulfate,,u.v, oxidation system. MATERIALS AND M E T H O D S
Reagent grade, stabilized hydrogen peroxide (50o/,3* was stored at -20°C. The concentration of hydrogen peroxide in each container was determined at room temperature by the potassium permanganate titration method (Vogel, 1955). Appropriate volumes of hydrogen peroxide reagent were added to water samples so that they contained 0 1-2.0°o of the 50°,/0 HzO 2 as the oxidant. Distilled water samples were obtained from Coming AG-II automatic distillation-collection system provided with disposable 3508-ORC "Organic free" and 3508-B high capacity demineralizer cartridges. Drinking water samples were taken from a laboratory tap that was run for l min before sample collection. All water samples were collected in duplicate. Glass-distilled hexane~" was further purified using the method of Malaiyandi and Benoit (In preparation). Irradiation was carried out in a custom-made 5-1. vessel (Fig. 1) or in a 1-1. vessel (net capacity ca. 600 ml when the quartz immersion well was in place). The contents of the 5-1. reactor were thoroughly mixed by a stirrer-impeller attached to an Eastern Mixer, Model 5:1:. The photolysis vessels were equipped with water-cooled quartz immersion wells to house the u.v. lamp (not shown in the Figure). A 450 W medium-pressure u.v. lamp (No. 679-036)~ was used as the source of radiation. The flow of cooling water through the quartz jacket-was adjusted to maintain the temperature at 40-45"C during irradiation. Water samples were treated with ca. 50°{, HaO 2 reagent to give a maximum concentration of 0.55{, HaOa by weight in the total volume of the sample. After vigorous stirring for 30 rain at ambient temperature, the samples were irradiated with u.v. light. A few minutes after the onset of irradiation, profuse evolution of a gas was observed and after about 3.5 h, it subsided. At the end of a 4 h period the treated water was sampled in duplicate in rinsed 250 ml
* Fisher Scientific Co., Chemical Manufacturing Division, Fairlawn, N J, U.S.A. -I-British Drug House Ltd, Toronto, Ontario, Canada. ++Eastern Industries Division, Hamden, CT. U,S.A. § Canrad-Hanovia Co., Newark, N J, U.S.A. ¶ Technical Marketing Associates, Mississauga, Ontario. Canada.
pyrex bottles which were previously washed w~,h chromic acid, thoroughly rinsed with distilled water, heated at 540:C overnight in a muffle furnace and cooled. The TOC analysis was carried out on a single day after collecting sixteen samples. Before sampling, each tot of the irradiated water was tested with acidified iodide-starch solution for any residual hydrogen peroxide. Gas chromatographic analyses were carried out using a Hewlett-Packard GC, Model 5710. fitted with a ~'3Ni electron-capture detector and a I mV Honeywell recorder, Model Electronic 196, under the following conditions: Coiled glass column (180 × 0,4cm i,d.) packed with chro-mosorb W(HP)coated with 2°o OV-17 and t~.50o OV-225: injection port temperature, 200:C: column temperature, I80"C: detector temperature. 300 C: carrier gas. argon methane mixture (95:5t with a flow rate of 33.3 ml mm ~ . attenuation, i x 4: and chart speed I" 5 rain The total organic carbon (TOC) contents oI water samples were determined with a Dohrmann Ultra Low Level TOC Analyser, Model DC-54¶. This instrument was calibrated using a standard solution containing 2000 #g lpotassium hydrogen phthalate in deionized, distilled water which had been exposed to u.v. irradiation for at least 4 h. The distilled water, which was used for preparing the phthalate standard, was found, after calibration of the instrument, to contain TOC values in the range of S0-100 #g 1-L The other optimum operating conditions of the TOC analyser were as follows: carrier gas, zero grade nitrogen at 90 ml rain-~; Purgeable organic carbon, measured for 2.36min; transfer time = exposure time to u.v. irradiation, 2.40 ~--0.05 rain; system b l a n k - t h e u.v.irradiated, acidified water containing peroxydisulphate was
~ 34z4 5
g, 7~/6c
i
HiP !llhl 3cm
[I
[
ii
li
j
'
fl
~, 4
x
r
fMRELLER STIRRER
STOPCOCK
Fig. l. The 5-1. reactor for holding water samples during u.v. irradiation.
Removal of organics in water using hydrogen peroxide recycled within the system until a constant TOC value was obtained. This value, after calibrating the instrument, was found to be 40 + 2 #g 1-1. The effect of hydrogen peroxide concentration on the reduction of dissolved organic carbon was followed by the TOC analysis of duplicate water samples (from the same source) with 0.1, 0.5, 1.0 and 2% (v/v) of 50% H202. At 2 . 0 % H 2 0 2 ( v / v ) concentration, traces of H202 persisted for hearly 9 h without any improvement in the reduction of organic carbon. Similarly, the optimum time required for obtaining maximum decrease in organic carbon content was evaluated by irradiating the water samples (in duplicate) containing 1% H=O2 (v/v) and following the reduction in TOC levels after 2, 4, 6, 8, 10 and 12 h of treatment. The determination of non-polar organic contents of both distilled and tap water samples before and after H2Oa/u.v. treatment was carried out to evaluate the effects of this treatment on the non-polar organics. Five liter water samples containing 1% H202 (v/v) were irradiated for a 4 h period as described earlier. Aliquots (200ml) of water sample~(in duplicate) we're extracted with three 50 ml portions of purified hexane. The combined extract was concentrated to a 10ml volume according to the method of Malaiyandi (1978) and 1 #1 of this concentrate was gas chromatographically analysed.
RESULTS AND DISCUSSION
In order to produce water of very low TOC content within a 4 h period, a minimum amount of hydrogen peroxide is necessary to hasten the oxidation of the dissolved organic carbon to carbon dioxide. This amount was determined by varying the hydrogen peroxide concentration from 0.5 to 2.0% (v/v) in 5.0 liter distilled water and irradiating it at 42 + I°C and measuring its TOC value, Table 1 shows that, in two separate runs, a 98-100% reduction of the dissolved organic carbon was observed at the 0.5% H202 level. However, in all later experiments, 1% hydrogen peroxide was used to make sure an excess of reagent was present. It is noteworthy that, in the large scale run with distilled water, a reduction of 28% in TOC values was observed with u.v. irradiation in the absence of H:O2. At the end of the irradiation period, all the water samples gave a negative test for H 2 0 v It is also apparent that H202 concentrations in excess of l ~ (v/v) do not appreciably increase the effectiveness of the oxidation process as shown by the reduction in TOC levels. Since the distilled water sample containTable 1. Effect of hydrogen peroxide concentration on %TOC reduction in distilled water* under u.v. irradiation % H:O2 Concentration (v/v)
0.1 0.5 1.0
2.0
To Reduction in TOC÷ Run No. 1 84 98 100 104
Run No. 2 72 100 95 --
* u.v. Irradiation time 4 h. f Calculation is made after subtracting the system blank 39 #g 1- ~ from initial and final TOC values.
1133
too !
z O
80
60 ¢..) O
o~
* I
0--0
RUN
n--..~
RUN ~ 2
40 o
20 _t
I
4
I
i ....
6 8 TIME (hr)
I
I0
I
12
Fig. 2. Rate of reduction of TOC during H2Oa/u.v. treatment with 50% H202 at 1% (v/v) level.
ing 2.0% H202 required 9 h to give a negative test for H202 and no further decrease in TOC values was observed, this expeTiment was not repeated. Typically, the reduction of TOC values, as a function of irradiation time, increases, passes through a maximum, and then slightly decreases as shown in Fig. 2. Four minutes after start of photolysis the gases formed in the reactor streamed through the side arm and were expelled through the annuLar space between the impeller rod and the bushing. This evolution of gas kept the system under positive pressure, thus preventing any atmospheric impurities from entering the system. It should be noted that the evolution of gases ceased after 3.5 h, and the TOC values increased slightly after 4 h. This slight increase in TOC values may be due to the atmospheric contaminants entering the system after the positive pressure in the reactor has ceased. Since the lowest TOC values were observed at the end of the 4 h period, Later irradiation experiments were carried out only for 4 h to ensure maximum treatment efficiency. Table 2 shows the comparative % reduction in total organic carbon content of small and large size samples of water before and after H202/u.v. treatment. Before treatment, an aliquot of the 500ml "organic-free" deionized, distilled water samples obtained on three different days showed TOC levels ranging from 55 to 135 #g l - i with an average value of 83/~g l-] and with a standard deviation (SD) of + 2 9 # g l - t . Addition of 1% (v/v) of H 2 0 2 (50%) to the same samples followed by u.v. irradiation brought about a 70% reduction in TOC levels with a standard deviation of +11%. However, when 5-1. distilled water samples with TOC values in the range of 24--70 #g1-1 and with an average value of 4 6 + 13#g1-1 were subjected to H202/u,v. treatment, an 88 +_ 14% reduction in TOC levels was observed. This is probably due to efficient stirring employed in the irradiation of these large scale Samples.
1134
ML'RLGAN MALAIkANDIet
ui.
Table 2. TOC values I,ug 1- t), of water samples before and after H,O2/u.v. treatment in small and bulk quantities Sampling day
BT+ Lugl -~ )
Small scale (500 mll ATt o Reduction {./~g1- ~J in TOC
Sampling day
BT+ (,ugl- 1i
Large scale (5000 ml) AT + o, Reduction (#gt -~) in TOC
Distilled water 1 2
3 Ave. ± SD
55 86 135 89 69 66 83 29
18 10 39 23 23 31 24 10
67 88 69 74 67 53 70 I1
70 45 43 54 24 43 40 45 46 13
5 6 2 10 11 z 0 i 5 4
~ ~7 95 81 54 91 l(~) 98 88 i4
3398 3602 3419 3289 3585 3765 3719 3606
55 57 41 46 38 63 58 66 53 10
98 98 99 98 99 98 98 98 98 ~
4 5 6 7 Ave. ± SD Tap water
1
3193
127
96
2
3152
69
98
3
3117
25
99
74 51
98 1
Ave.
±SD
4 5 6 7 Ave. ±SD
* All TOC values shown above were obtained after deducting the exact system blank (range 38-42 #g I- i). t BT--Before treatment; AT--after treatment. The T O C values of the distilled water obtained on the 4th, 5th, 6th, and 7th days are definitely lower than the values obtained for the first three days since the C o m i n g cartridge 3508-ORC for organic removal was changed before sampling. Since the T O C values of large water samples before treatment were not very high compared to the system blank (40 + 2 / a g l - t ) , the average percent reduction of TO(7 values appears to be lower than the value obtained for tap water after treatment. In the case of tap water, the total organic carbon contents in both small and bulk samples before treat-
ment ranged between 3117 and 3765/~g 1- t for all the seven days of s~apling. From Table 2, it can be seen that there is a marked and consistent reduction (98%) in T O C levels after photolysis of the H20~-treated tap water. This decrease is in good agreement with the 97% reduction reported by Koubek (1975) for the removal of acetic acid from water using a similar approach. Considering T O C values as a reliable indicator of organic content in water, and comparing columns (6) under "Distilled water" and (7) under 'q'apwater" in Table 2, it would appear that the HzO2/u.v. treatment of tap water is as effective as the
'°°1 W
o ~"
50
oo
0
0
i
I
l0
i
i
20
t
t
30
t
RETENTION
4JO
I
510
I
t
c~0
/ /
t
t
90
,
TiME (MIN)
Fig. 3. Gas chromatogram of hexane extract of glass distilled water; ( H2Oz/u.v. treatment.
) before and ( - - - ) after
Removal of organics in water using hydrogen peroxide
1135
I00-
o n50-
o
RETENTION TIME (MIN)
Fig 4. Gas chromatogram of hexane extract of Ottawa tap water; ( H2Oz/u.v. treatment.
Coming distillation system for the removal of organics, although the organic compounds in these waters may not be identical. Most polar organics are very susceptible to hydroxyl radical attack and undergo oxidative degradation especially in the presence of u.v. light (Walling 1975; Koubek, 1975). An attempt was made to determine the fate of electron-capturing, non-polar organics. Gas chromatograms of the hexane extractives from distilled water before and after H202/u.v. treatmeet (Fig. 3) shows the comparative peak heights of the four major peaks with retention times 12.2, 14.3 (identified as di-n-butyl phthalate), 20.5 and 23.3 win. It was observed that 88% reduction of the electroncapturing, less polar organic compounds having the above-mentioned retention times has been achieved. Moreover, in the case of tap water (Fig. 4) a reduction of 96-97% was noted for the above mentioned peaks. Under the conditions used, the gas chromatographic analysis can detect the presence of electronattracting non-polar compounds only, and the above comparisons are meaningful simply in terms of relative purity of water before and after HzO2/u.v. treatment. No attempt was made to identify individual peaks as both the nature and the extent of contamination could vary from day to day, especially in the tap water. Our preliminary experiments have shown that ozone treatment (2.0 mg 1-1 of air) up to 8 h without u.v. light is much less effective than H202/u.v. treatment for removal of non-polar organics in water. In conclusion, the addition of small amounts of H,O2 to water in presence of u.v. light is a very simple, and efficient way to obtain highly purified water.
) before and ( - - - ) after
Acknowledgements--The authors wish to thank Rein Otson for advice on the use of the TOC analyser and Martha Bowran for technical assistance. One of us, MHS, thanks the National Research Council of Canada for a Visiting Fellowship for the year August 1977-July 1978.
REFERENCES
Anbar M. & Neta P. (1967) Int. J. appl. Radiat. Isotopes lg, 493.
Bishop D. F., Stern G., Fleishmann M. & Marshall L. S. (1968) Ind. Enono Chem. Process Res. Develop. 1, 110. Goulden P. D. & Anthony D. H. J. (1978) Analyt. Chem. 50, 953-958. Hendry D. G., Mill T., Piszkiewicz L., Howard J. A. & Eigenmann H. K. (1974) J. phys. Chem. 3, 937. Kehoe T. J. (1977) Environ. ScL Technol. 11, 137. Koubek E. (1975) Ind. Engng Chem., Process Res. Develop. 14, 348. Malaiyandi M. (1978) J. Ass. off. Anal. Chem. 61, 1459--64. Malaiyandi M. & Benoit F. In preparation. Reijnders H. F. R., Romer F. G. & Griepink B. (1977) Z. Analyt. Chem. 285, 21. Schumb W. C., Satterlield C. N. & Wentworth R. L. (1955) Hydrogen Peroxide, ACS Monograph No. 128, Chapter 8. Reinhold Publishing Co., New York. Shackelford W. M. & Keith L. H. (1976) United States EPA Report, EPA-600/4-74-062. Takahashi Y. (1976) Presentation No. 2A at the Water Quality Technology Conferenc,~, AWWA, held at San Diego, CA, U.S.A. Vogel A. I. (1955) A Text-Book of Quantitative Inorganic Analysis 2nd edition, pp. 283-84. Longman, Green & Co., New York. Walling C. (1975) Acct. Chem. Res. 8, 125. Uri N. (1961) Autoxidation and Antioxidants (Edited by Lundberg W. V.), Vol. 1, Chapter 2. Interscience, New York.
0043-1354/80/0801-1131102.00/0
REMOVAL OF ORGANICS IN WATER USING HYDROGEN PEROXIDE IN PRESENCE OF ULTRAVIOLET LIGHT MURUOAN MAt~Y~DI, M. HUSAINSADAR,PAULINELr~ and RON O'G|o, DV Monitoring and Criteria Division, Bureau of Chemical Hazards, Health and Welfare Canada, Ottawa, Ontario, Canada K1A 0L2 (Received January 1980)
Ab~mct--The optimum conditions for the removal of dissolved organic impurities from water using hydrogen peroxide (.50%) followed by ultraviolet irradiation were investigated. The photochemically initiated hydroxyl radical (.OH) oxidation reduced the total organic carbon (TOC) content of distilled water samples by about 88~ and of tap water by 98%. Extraction with hexane of equal volumes of water samples before and after H,O2/u.v. treatment followed by gas chromatographic analysis of the concentrated extracts indicated that about 12% of the electron-capturing, residual organics remained after this treatment. These results support the conclusion drawn from total organic carbon analYSis that this simple method yields water nearly free of organic impurities.
INTRODUCTION
The presence of numerous, potentially-harmful, organic contaminants in surface and underground waters has been established (Shackelford & Keith, 1976). Since the need for producing "organic-free" water has become extremely important, especially in the industrialized nations, continuous efforts are being made to develop methods of purifying water either by removing these impurities or by converting them into harmless products. Although a number of physical and chemical techniques for water purification are available, the oxidation of trace organic impurities in water is an attractive method because of its low cost high efficiency and simplicity. Moreover, the intermediate oxidation products so formed are usually easilydegraded, low molecular weight oxygenated compounds. The reaction generally gives highly desirable end products such as carbon dioxide and water. Direct reaction of most organic compounds with oxygen at ambient temperatures is, in most cases, impractically slow. Some source of free radicals or singlet oxygen is, therefore, generally sought to initiate the oxidation which, through a series of radical chain reactions, completes the degradation of organic materials in a very short time. Several recent reports have described the use of molecular oxygen in conjunction with hydrogen peroxide-metal ion catalytic systems to degrade organic contaminants in water (Walling, 1975; Bishop et al., 1968). These systems preferentially hydroxylate many organic molecules. In several instances, however, the decomposition of the oxidant itself predominates over the oxidation of the organic species and results in excessive loss of the oxidant.
The main objective of this study was to find a simple and practical method for the removal of dissolved organic impurities present in drinking water and also to obtain high purity water for research purposes. It is known that hydrogen peroxide or ozone when used in water under u.v. light is partimflarly well-suited for the break-down of organic molecules as the cleavage of the O - - O bond gives OH radicals or oxygen atoms (sehumb et al., 1955). The OH radical is known to be extremely reactive with most organic molecules with H-atom donor properties (Walling, 1975; Anbar & Neta, 1967), and promptly attacks such species to produce new types of radicals which may subsequently initiate several radical chain reactions. Also, OH radicals are more effective than .OR and .OOR (Hendry et al., 1974) (R --alkyl or aryl group) in producing carbon radicals from organics and hence the use of H , O , as the source of free radicals is very attractive. Further, autoxidation involving hydroxyl and/or peroxy radicals seems to be most effective within the pH range of 6-8. Outside this pH range, a source other than hydrogen peroxide is needed to produce hydroxyl radicals (Uri, 1961; Koubek, 1975). In the present work, hydrogen peroxide (~ 1.0%) and u.v. light of wavelength above the 200 nm system has been used to generate the reactive OH radicals. The choice of water samples was confined to the tap water and the distilled water available in our laboratory. Since the nature and the amount of organic impurities present in these samples could vary from day to day, it was deemed essential to cheek the effectiveness of the purification process by comparing the dissolved organic contents of every sample before and after the H,O2/u.v. treatment. The two techniques employed for this comparison were analysis of TOC
1131
1132
\,It Rt GAS NIALAI'~ANDI ~'r ~al
content of water samples per se and gas chromatographic analysis of the concentrated hexane extracts of the water samples. The development of reliable instrumental technique has made it very easy to determine the T O C content of potable a n d waste waters (Kehoe, 1977). This analytical technique for the T O C measurement using the peroxydisulfate/u.v, system has been shown to convert organic carbon almost quantitatively to carbon dioxide (Takahashi, 1976; Goulden & Anthony, 1978). Therefore T O C values are a good measure of trace levels of organic impurities in water provided that the instrument is calibrated properly and the measurements taken carefully (Reijnders, 1977). Further, since the method described in this c o m m u n i c a t i o n for the removal of organics in water is similar to the T O C analytical method (Takahashi, 1976), the values of total organic c a r b o n reported here, are only relative to the values obtained for the standard, potassium biphthalate, using the peroxydisulfate,,u.v, oxidation system. MATERIALS AND M E T H O D S
Reagent grade, stabilized hydrogen peroxide (50o/,3* was stored at -20°C. The concentration of hydrogen peroxide in each container was determined at room temperature by the potassium permanganate titration method (Vogel, 1955). Appropriate volumes of hydrogen peroxide reagent were added to water samples so that they contained 0 1-2.0°o of the 50°,/0 HzO 2 as the oxidant. Distilled water samples were obtained from Coming AG-II automatic distillation-collection system provided with disposable 3508-ORC "Organic free" and 3508-B high capacity demineralizer cartridges. Drinking water samples were taken from a laboratory tap that was run for l min before sample collection. All water samples were collected in duplicate. Glass-distilled hexane~" was further purified using the method of Malaiyandi and Benoit (In preparation). Irradiation was carried out in a custom-made 5-1. vessel (Fig. 1) or in a 1-1. vessel (net capacity ca. 600 ml when the quartz immersion well was in place). The contents of the 5-1. reactor were thoroughly mixed by a stirrer-impeller attached to an Eastern Mixer, Model 5:1:. The photolysis vessels were equipped with water-cooled quartz immersion wells to house the u.v. lamp (not shown in the Figure). A 450 W medium-pressure u.v. lamp (No. 679-036)~ was used as the source of radiation. The flow of cooling water through the quartz jacket-was adjusted to maintain the temperature at 40-45"C during irradiation. Water samples were treated with ca. 50°{, HaO 2 reagent to give a maximum concentration of 0.55{, HaOa by weight in the total volume of the sample. After vigorous stirring for 30 rain at ambient temperature, the samples were irradiated with u.v. light. A few minutes after the onset of irradiation, profuse evolution of a gas was observed and after about 3.5 h, it subsided. At the end of a 4 h period the treated water was sampled in duplicate in rinsed 250 ml
* Fisher Scientific Co., Chemical Manufacturing Division, Fairlawn, N J, U.S.A. -I-British Drug House Ltd, Toronto, Ontario, Canada. ++Eastern Industries Division, Hamden, CT. U,S.A. § Canrad-Hanovia Co., Newark, N J, U.S.A. ¶ Technical Marketing Associates, Mississauga, Ontario. Canada.
pyrex bottles which were previously washed w~,h chromic acid, thoroughly rinsed with distilled water, heated at 540:C overnight in a muffle furnace and cooled. The TOC analysis was carried out on a single day after collecting sixteen samples. Before sampling, each tot of the irradiated water was tested with acidified iodide-starch solution for any residual hydrogen peroxide. Gas chromatographic analyses were carried out using a Hewlett-Packard GC, Model 5710. fitted with a ~'3Ni electron-capture detector and a I mV Honeywell recorder, Model Electronic 196, under the following conditions: Coiled glass column (180 × 0,4cm i,d.) packed with chro-mosorb W(HP)coated with 2°o OV-17 and t~.50o OV-225: injection port temperature, 200:C: column temperature, I80"C: detector temperature. 300 C: carrier gas. argon methane mixture (95:5t with a flow rate of 33.3 ml mm ~ . attenuation, i x 4: and chart speed I" 5 rain The total organic carbon (TOC) contents oI water samples were determined with a Dohrmann Ultra Low Level TOC Analyser, Model DC-54¶. This instrument was calibrated using a standard solution containing 2000 #g lpotassium hydrogen phthalate in deionized, distilled water which had been exposed to u.v. irradiation for at least 4 h. The distilled water, which was used for preparing the phthalate standard, was found, after calibration of the instrument, to contain TOC values in the range of S0-100 #g 1-L The other optimum operating conditions of the TOC analyser were as follows: carrier gas, zero grade nitrogen at 90 ml rain-~; Purgeable organic carbon, measured for 2.36min; transfer time = exposure time to u.v. irradiation, 2.40 ~--0.05 rain; system b l a n k - t h e u.v.irradiated, acidified water containing peroxydisulphate was
~ 34z4 5
g, 7~/6c
i
HiP !llhl 3cm
[I
[
ii
li
j
'
fl
~, 4
x
r
fMRELLER STIRRER
STOPCOCK
Fig. l. The 5-1. reactor for holding water samples during u.v. irradiation.
Removal of organics in water using hydrogen peroxide recycled within the system until a constant TOC value was obtained. This value, after calibrating the instrument, was found to be 40 + 2 #g 1-1. The effect of hydrogen peroxide concentration on the reduction of dissolved organic carbon was followed by the TOC analysis of duplicate water samples (from the same source) with 0.1, 0.5, 1.0 and 2% (v/v) of 50% H202. At 2 . 0 % H 2 0 2 ( v / v ) concentration, traces of H202 persisted for hearly 9 h without any improvement in the reduction of organic carbon. Similarly, the optimum time required for obtaining maximum decrease in organic carbon content was evaluated by irradiating the water samples (in duplicate) containing 1% H=O2 (v/v) and following the reduction in TOC levels after 2, 4, 6, 8, 10 and 12 h of treatment. The determination of non-polar organic contents of both distilled and tap water samples before and after H2Oa/u.v. treatment was carried out to evaluate the effects of this treatment on the non-polar organics. Five liter water samples containing 1% H202 (v/v) were irradiated for a 4 h period as described earlier. Aliquots (200ml) of water sample~(in duplicate) we're extracted with three 50 ml portions of purified hexane. The combined extract was concentrated to a 10ml volume according to the method of Malaiyandi (1978) and 1 #1 of this concentrate was gas chromatographically analysed.
RESULTS AND DISCUSSION
In order to produce water of very low TOC content within a 4 h period, a minimum amount of hydrogen peroxide is necessary to hasten the oxidation of the dissolved organic carbon to carbon dioxide. This amount was determined by varying the hydrogen peroxide concentration from 0.5 to 2.0% (v/v) in 5.0 liter distilled water and irradiating it at 42 + I°C and measuring its TOC value, Table 1 shows that, in two separate runs, a 98-100% reduction of the dissolved organic carbon was observed at the 0.5% H202 level. However, in all later experiments, 1% hydrogen peroxide was used to make sure an excess of reagent was present. It is noteworthy that, in the large scale run with distilled water, a reduction of 28% in TOC values was observed with u.v. irradiation in the absence of H:O2. At the end of the irradiation period, all the water samples gave a negative test for H 2 0 v It is also apparent that H202 concentrations in excess of l ~ (v/v) do not appreciably increase the effectiveness of the oxidation process as shown by the reduction in TOC levels. Since the distilled water sample containTable 1. Effect of hydrogen peroxide concentration on %TOC reduction in distilled water* under u.v. irradiation % H:O2 Concentration (v/v)
0.1 0.5 1.0
2.0
To Reduction in TOC÷ Run No. 1 84 98 100 104
Run No. 2 72 100 95 --
* u.v. Irradiation time 4 h. f Calculation is made after subtracting the system blank 39 #g 1- ~ from initial and final TOC values.
1133
too !
z O
80
60 ¢..) O
o~
* I
0--0
RUN
n--..~
RUN ~ 2
40 o
20 _t
I
4
I
i ....
6 8 TIME (hr)
I
I0
I
12
Fig. 2. Rate of reduction of TOC during H2Oa/u.v. treatment with 50% H202 at 1% (v/v) level.
ing 2.0% H202 required 9 h to give a negative test for H202 and no further decrease in TOC values was observed, this expeTiment was not repeated. Typically, the reduction of TOC values, as a function of irradiation time, increases, passes through a maximum, and then slightly decreases as shown in Fig. 2. Four minutes after start of photolysis the gases formed in the reactor streamed through the side arm and were expelled through the annuLar space between the impeller rod and the bushing. This evolution of gas kept the system under positive pressure, thus preventing any atmospheric impurities from entering the system. It should be noted that the evolution of gases ceased after 3.5 h, and the TOC values increased slightly after 4 h. This slight increase in TOC values may be due to the atmospheric contaminants entering the system after the positive pressure in the reactor has ceased. Since the lowest TOC values were observed at the end of the 4 h period, Later irradiation experiments were carried out only for 4 h to ensure maximum treatment efficiency. Table 2 shows the comparative % reduction in total organic carbon content of small and large size samples of water before and after H202/u.v. treatment. Before treatment, an aliquot of the 500ml "organic-free" deionized, distilled water samples obtained on three different days showed TOC levels ranging from 55 to 135 #g l - i with an average value of 83/~g l-] and with a standard deviation (SD) of + 2 9 # g l - t . Addition of 1% (v/v) of H 2 0 2 (50%) to the same samples followed by u.v. irradiation brought about a 70% reduction in TOC levels with a standard deviation of +11%. However, when 5-1. distilled water samples with TOC values in the range of 24--70 #g1-1 and with an average value of 4 6 + 13#g1-1 were subjected to H202/u,v. treatment, an 88 +_ 14% reduction in TOC levels was observed. This is probably due to efficient stirring employed in the irradiation of these large scale Samples.
1134
ML'RLGAN MALAIkANDIet
ui.
Table 2. TOC values I,ug 1- t), of water samples before and after H,O2/u.v. treatment in small and bulk quantities Sampling day
BT+ Lugl -~ )
Small scale (500 mll ATt o Reduction {./~g1- ~J in TOC
Sampling day
BT+ (,ugl- 1i
Large scale (5000 ml) AT + o, Reduction (#gt -~) in TOC
Distilled water 1 2
3 Ave. ± SD
55 86 135 89 69 66 83 29
18 10 39 23 23 31 24 10
67 88 69 74 67 53 70 I1
70 45 43 54 24 43 40 45 46 13
5 6 2 10 11 z 0 i 5 4
~ ~7 95 81 54 91 l(~) 98 88 i4
3398 3602 3419 3289 3585 3765 3719 3606
55 57 41 46 38 63 58 66 53 10
98 98 99 98 99 98 98 98 98 ~
4 5 6 7 Ave. ± SD Tap water
1
3193
127
96
2
3152
69
98
3
3117
25
99
74 51
98 1
Ave.
±SD
4 5 6 7 Ave. ±SD
* All TOC values shown above were obtained after deducting the exact system blank (range 38-42 #g I- i). t BT--Before treatment; AT--after treatment. The T O C values of the distilled water obtained on the 4th, 5th, 6th, and 7th days are definitely lower than the values obtained for the first three days since the C o m i n g cartridge 3508-ORC for organic removal was changed before sampling. Since the T O C values of large water samples before treatment were not very high compared to the system blank (40 + 2 / a g l - t ) , the average percent reduction of TO(7 values appears to be lower than the value obtained for tap water after treatment. In the case of tap water, the total organic carbon contents in both small and bulk samples before treat-
ment ranged between 3117 and 3765/~g 1- t for all the seven days of s~apling. From Table 2, it can be seen that there is a marked and consistent reduction (98%) in T O C levels after photolysis of the H20~-treated tap water. This decrease is in good agreement with the 97% reduction reported by Koubek (1975) for the removal of acetic acid from water using a similar approach. Considering T O C values as a reliable indicator of organic content in water, and comparing columns (6) under "Distilled water" and (7) under 'q'apwater" in Table 2, it would appear that the HzO2/u.v. treatment of tap water is as effective as the
'°°1 W
o ~"
50
oo
0
0
i
I
l0
i
i
20
t
t
30
t
RETENTION
4JO
I
510
I
t
c~0
/ /
t
t
90
,
TiME (MIN)
Fig. 3. Gas chromatogram of hexane extract of glass distilled water; ( H2Oz/u.v. treatment.
) before and ( - - - ) after
Removal of organics in water using hydrogen peroxide
1135
I00-
o n50-
o
RETENTION TIME (MIN)
Fig 4. Gas chromatogram of hexane extract of Ottawa tap water; ( H2Oz/u.v. treatment.
Coming distillation system for the removal of organics, although the organic compounds in these waters may not be identical. Most polar organics are very susceptible to hydroxyl radical attack and undergo oxidative degradation especially in the presence of u.v. light (Walling 1975; Koubek, 1975). An attempt was made to determine the fate of electron-capturing, non-polar organics. Gas chromatograms of the hexane extractives from distilled water before and after H202/u.v. treatmeet (Fig. 3) shows the comparative peak heights of the four major peaks with retention times 12.2, 14.3 (identified as di-n-butyl phthalate), 20.5 and 23.3 win. It was observed that 88% reduction of the electroncapturing, less polar organic compounds having the above-mentioned retention times has been achieved. Moreover, in the case of tap water (Fig. 4) a reduction of 96-97% was noted for the above mentioned peaks. Under the conditions used, the gas chromatographic analysis can detect the presence of electronattracting non-polar compounds only, and the above comparisons are meaningful simply in terms of relative purity of water before and after HzO2/u.v. treatment. No attempt was made to identify individual peaks as both the nature and the extent of contamination could vary from day to day, especially in the tap water. Our preliminary experiments have shown that ozone treatment (2.0 mg 1-1 of air) up to 8 h without u.v. light is much less effective than H202/u.v. treatment for removal of non-polar organics in water. In conclusion, the addition of small amounts of H,O2 to water in presence of u.v. light is a very simple, and efficient way to obtain highly purified water.
) before and ( - - - ) after
Acknowledgements--The authors wish to thank Rein Otson for advice on the use of the TOC analyser and Martha Bowran for technical assistance. One of us, MHS, thanks the National Research Council of Canada for a Visiting Fellowship for the year August 1977-July 1978.
REFERENCES
Anbar M. & Neta P. (1967) Int. J. appl. Radiat. Isotopes lg, 493.
Bishop D. F., Stern G., Fleishmann M. & Marshall L. S. (1968) Ind. Enono Chem. Process Res. Develop. 1, 110. Goulden P. D. & Anthony D. H. J. (1978) Analyt. Chem. 50, 953-958. Hendry D. G., Mill T., Piszkiewicz L., Howard J. A. & Eigenmann H. K. (1974) J. phys. Chem. 3, 937. Kehoe T. J. (1977) Environ. ScL Technol. 11, 137. Koubek E. (1975) Ind. Engng Chem., Process Res. Develop. 14, 348. Malaiyandi M. (1978) J. Ass. off. Anal. Chem. 61, 1459--64. Malaiyandi M. & Benoit F. In preparation. Reijnders H. F. R., Romer F. G. & Griepink B. (1977) Z. Analyt. Chem. 285, 21. Schumb W. C., Satterlield C. N. & Wentworth R. L. (1955) Hydrogen Peroxide, ACS Monograph No. 128, Chapter 8. Reinhold Publishing Co., New York. Shackelford W. M. & Keith L. H. (1976) United States EPA Report, EPA-600/4-74-062. Takahashi Y. (1976) Presentation No. 2A at the Water Quality Technology Conferenc,~, AWWA, held at San Diego, CA, U.S.A. Vogel A. I. (1955) A Text-Book of Quantitative Inorganic Analysis 2nd edition, pp. 283-84. Longman, Green & Co., New York. Walling C. (1975) Acct. Chem. Res. 8, 125. Uri N. (1961) Autoxidation and Antioxidants (Edited by Lundberg W. V.), Vol. 1, Chapter 2. Interscience, New York.