Frontiers in Environmental Engineering (FIEE) Volume 5, 2016 doi: 10.14355/fiee.2016.05.005
www.seipub.org/fiee
Research on Rapid Determination of Total Chlorine and Chlorine Dioxide by DPD Method in Drinking Water Nan Nan Lua, Wu Chang Songb, Rui Bao Jiac*, Shao Hua Sund, Fu Min Chue, Yan Xuf Shandong province city water supply and drainage water quality monitoring center, Jinan, 250021, China nanwang316@163.com, bsongwuchang@ 163.com, cjiaruibao68@126.com, djnsunshaohua@163.com,
a e
chufumin3908@163.com; fxu_yan_0318@163.com
Abstract Chlorine and chlorine dioxide are widely used for water disinfection nowadays. To establish standard technical process for total chlorine and chlorine dioxide determination, the factors affected total chlorine and chlorine dioxide determination by DPA method were researched in this paper. Temperature should be balanced at 20℃ in determination and pH value should be controlled between 5 and 9. The reaction time should be controlled within 5 minutes for the best results. The interference of metal ions can be eliminated by adding glycine or potassium iodide solution in determination of chlorine dioxide. The results using this method showed no significant difference with using the method GB/T 5749-2006. The research provides support on establishing the standard technical process for rapid determination of total chlorine and chlorine dioxide in drinking water. Keywords Total Chlorine; Chlorine Dioxide; Portable Colorimeter; Temperature; pH; Reaction Time; Influencing Factor
Introduction Chlorine and chlorine dioxide (ClO2) are common disinfectants used for water disinfection, which are not stable in water. National Health and Family Planning Commission of the People’s Republic of China has established a minimum residual disinfectant level of 0.3 mg L−1 for chlorine and 0.1 mg L−1 for ClO2 in finished water. In order to obtain accurate results, determination of chlorine and chlorine dioxide should be completed on site. Many equipment manufacturers have developed portable instruments for instant site measurement. They are widely used in environmental monitoring, drinking water and hospital sewage treatment and other fields [1-4]. Detection range of portable instrument is below 0.1 mg L−1and it can be used in drinking water [5-7]. However, the use of portable instruments was mostly based on the manufacturer's instructions at present and part of the detection process had no detailed provisions. Also because of complex environmental condition in field monitoring, the effect of various water quality conditions and so on, it is difficult to guarantee the accuracy of the test results. The factors affected total chlorine and chlorine dioxide determination by portable colorimeter with DPA method were researched in this paper, in order to establish standard technical process for rapid determination with total chlorine and chlorine dioxide in drinking water. Materials and Methods Main instruments and reagents. All chemicals for experiments were of analytical grade without reagent wrap. Determination of chlorine and chlorine dioxide was completed by pocket colorimeter (Hach, USA) and reagent wraps (Hach, USA). Pure water was obtained from a water purifier (Millipore, USA). Experimental Methods 1) Water Sample Collection Finished water (effluent of clean water tank in water plant) and distribution water (pure water that chlorine dioxide or chlorine was added into it in laboratory) were researched in the paper. Finished water samples were collected by glass containers and sent to laboratory as soon as possible.
29
www.seipub.org/fiee
Frontiers in Environmental Engineering (FIEE) Volume 5, 2016
2) Laboratory Test Method Total chlorine and chlorine dioxide determination in laboratory was carried out according to standard examination methods for drinking water (GB/T 5749-2006) [8]. 3) Test Method for Effect of Temperature Four different temperatures were selected to study the effect on the result. Four colorimetric tubes were added 100 mL same finished water samples (after chlorine or ClO2 disinfection) or distribution water. Then the four tubes were sealed and bathed into water with different temperatures (4℃, 10℃, 20℃ and 30℃) until the temperature was balanced. At last 10mL water was taken out from each tube into sample cell and added reagent wrap. The result was read out in one minute. Results were decided by the average of three repeated test. 4) Test Method for Effect of pH Five different pH values were selected to study the effect on the result. Five colorimetric tubes were added 100 mL same finished water samples (after chlorine or ClO2 disinfection) or distribution water. Then water samples were adjusted pH to different values (5, 6, 7, 8 and 9) with sulfuric acid or sodium hydroxide solution. At last 10mL water sample was taken out from each tube into sample cell and added chlorine reagent wrap. The result was read out in one minute. Results were decided by the average of three repeated test. 5) Test Method for Interference Cancellation Same water samples (finished water or distribution water) were added into several colorimetric tubes. Then different metal ions with the concentration of five time’s standard limit value were added into each tube. Pure water of same volume was added into the control tube. Concentration of total chlorine or ClO2 in each tube was tested before and after adding glycine or potassium iodide. Results were decided by the average of three repeated test. Data Analysis The results were compared by nonparametric tests. Average value of concentration data was used in this study. Statistical significance was accepted at p<0.05. Results and Discussion Effect of Temperature 2 1.8 Concentration (mg/L)
1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 A
B C 4℃（Rapid determination） 10℃（Rapid determination） 20℃（Rapid determination） 30℃（Rapid determination） national standard method (GB/T 5749-2006)
D
FIG.1 DETECTION RESULT OF CHLORINE DIOXIDE IN DIFFERENT TEMPERATURE FINISHED WATER SAMPLE (A) AND DISTRIBUTION WATER SAMPLE (B, C, D)
30
Frontiers in Environmental Engineering (FIEE) Volume 5, 2016
www.seipub.org/fiee
Water temperatures are different in distinct regions and seasons, which may influence the result. Four different Temperatures were selected to study the effect on the result. Result showed that chromogenic reaction speed was lower at low temperature in determination. Measured value at high temperature (30℃) was lower than the value at 20℃, so water temperature should be balanced at 20℃ in field determination for accurate result. Lin found that results are affected by temperature and temperature should be stabilized at about 20℃ in free residual chlorine determination with DPD method [9]. The conclusion is consistent with the result in this paper. Effect of pH Value Different water pH values may affect the determination result. Five different pH values were selected to study the effect on the result in this paper. Result showed that measured values in five pH value had no significant difference (p>0.05) either in total chlorine or chlorine dioxide test. Similar conclusion was found that appropriate pH value was 5 to 8 in free residual chlorine determination with DPD method [10]. TABLE 1 THE DETECTION RESULT OF TOTAL CHLORINE AND CHLORINE DIOXIDE WITH DIFFERENT PH VALUE
Total chlorine (mg/L)
Chlorine dioxide (mg/L)
pH
A
B
C
D
E
F
G
H
5
0.58
1.13
0.94
0.52
0.42
0.94
1.35
0.21
6
0.58
1.02
0.91
0.56
0.38
0.89
1.32
0.18
7
0.59
1.04
0.93
0.54
0.39
0.90
1.34
0.19
8
0.59
1.10
0.97
0.60
0.40
0.89
1.33
0.20
9
0.60
1.15
0.98
0.61
0.40
0.81
1.28
0.20
GB/T5749-2006
0.58
1.08
0.95
0.58
0.39
0.88
1.30
0.20
Note: A, D, E, H Finished water sample B, C, F, G distribution water sample.
Effect of Reaction Time Seven time points (30s、1min、2min、5min、10min、20min、30min) were selected to study the effect on the result. Result showed that test value reached the maximum in 5 minutes in total chlorine determination and kept stable within 30 minutes. Test value reached the maximum in 2 minutes in chlorine dioxide determination and kept stable within 20 minutes while the concentration was less than or equal to 2mg/L. If concentration exceeded 2 mg/L, test value reached the maximum in 2 minutes and kept stable within 2 minutes. TABLE 2 DETECTION RESULT OF TOTAL CHLORINE AND CHLORINE DIOXIDE WITH DIFFERENT REACTION TIME
Total chlorine (mg/L)
Chlorine dioxide(mg/L)
Reactio n time
A
B
C
D
E
F
G
H
30s
0.43
0.62
1.19
2.9
0.97
1.30
2.84
0.19
1min
0.44
0.63
1.19
2.9
0.97
1.30
2.83
0.18
2min
0.45
0.63
1.20
3.0
0.95
1.30
2.82
0.19
5min
0.46
0.64
1.22
3.0
0.96
1.31
2.75
0.20
10min
0.46
0.64
1.22
3.0
0.96
1.32
2.70
0.19
20min
0.46
0.64
1.22
3.0
0.96
1.31
2.65
0.20
30min
0.44
0.61
1.20
2.9
0.92
1.27
2.56
0.17
Note: A, H Finished water sample. B, C, D, E, F, G distribution water sample.
Interference Cancellation Metal ions in water may affect the result in total chlorine and ClO2 determination, such as Mg2+, Ca2+, Mn2+, Cr6+ and Fe3+. Metal concentrations of five time’s national standard limit were studied. All results showed in table 4 were measured by rapid determination. Result showed that metal ions studied in the paper have little effect on the test
31
www.seipub.org/fiee
Frontiers in Environmental Engineering (FIEE) Volume 5, 2016
value in total chlorine determination. In ClO2 determination interferents can be categorized into two groups. In the first group, interference can be eliminated by adding glycine, such as Mg2+, Ca2+. Glycine should be added into the water sample before reagent wrap was added in rapid determination, and so Mg2+, Ca2+ had actually no effect on the result. In the second group, interference can be avoided by the addition of potassium iodide, such as Mn2+, Cr6+ and Fe3+. Similar phenomena were observed in previous research that manganese, chromium had no effect on the result by adding potassium iodide into water. In contrast to our work, iron had little effect on chlorine dioxide determination [7]. TABLE 3 ELIMINATION OF DISRUPTORS IN CHLORINE DIOXIDE DETECTION
Disruptors
Mg2+
Ca2+
Mn2+
Cr6+
Fe3+
Disruptor concentration(mg/L)
5.0
5.0
0.5
0.25
1.5
0.61
0.61
0.61
0.61
0.61
0.71
0.73
0.73
0.69
0.56
Elimination method
Glycine
Glycine
Potassium iodide
Potassium iodide
Potassium iodide
Concentration after anti-interference(mg/L)
0.62
0.62
0.63
0.64
0.60
Chlorine dioxide concentration (mg/L) Concentration after interference (mg/L)
Difference Analysis The results by using this method showed no significant difference with the method by using GB/T 5749-2006 (p>0.05). The conclusion is identical with previous research [11]. Rapid determination technology of total chlorine and chlorine dioxide is accurate and reliable, so it can be used for field monitoring. TABLE 4 COMPARISON BETWEEN PORTABLE RESIDUAL CHLORINE COLORIMETER AND NATIONAL STANDARD METHOD
Total chlorine (mg/L)
Chlorine dioxide (mg/L)
Water sample
Rapid determination
GB/T 5749-2006
Water sample
Rapid determination
GB/T 5749-2006
A
1.22
1.27
E
0.45
0.49
B
0.60
0.56
F
1.19
1.33
C
0.45
0.48
G
1.33
1.36
D
0.15
0.20
H
0.22
0.19
Note: C, H Finished water sample A, B, D, E, F, G distribution water sample.
Conclusions In this study, the factors affected total chlorine and chlorine dioxide determination were researched in order to establish the standard technical process of rapid determination. The conclusions showed that temperature should be balanced at 20â&#x201E;&#x192; in determination and pH value should be controlled between 5 and 9. The reaction time should be controlled within five minutes for the best results. The interference of metal ions can be eliminated by adding glycine or potassium iodide solution in determination of chlorine dioxide. The results using this method showed no significant difference with using the method GB/T 5749-2006. ACKNOWLEDGEMENTS
This work was financially supported by China water pollution control and treatment national science and technology major project (Grant No. 2012ZX07404-003), China science and technology program for public wellbeing (Grant No. 2013GS370202), project of mount Taishan scholar of Shandong province for drinking water safety ensuring technology (Grant No. ts200640025).
32
Frontiers in Environmental Engineering (FIEE) Volume 5, 2016
www.seipub.org/fiee
REFERENCES
[1] J. Ivars, R. Howard, Water and Wastewater International; Vol. 20 (2005), pp. 37-40. [2] L. Moberg, B. Karlberg, Analytica Chimica Acta. Vol.407 (2000), pp. 127-133 [3] Z. M. Li, S. Chen, X. Z. Zhao, China Water & Wastewater. Vol. 26 (2010), pp. 132-34. (In Chinese) [4] Y. F. Fu, J. H. Deng, W. Chen, Modern Instruments & Medical Treatment, Vol. 5 (2010), pp. 80-82. (In Chinese) [5] S. Z. Cai, J. H Deng, Q. P Wu, et al. Modern Instruments & Medical Treatment, Vol. 6(2008), pp. 52-54. (In Chinese) [6] Z. Y Chen, Y. F Fu, J. H. Deng, et al. Modern Instruments & Medical Treatment, Vol. 4(2011), pp. 87-89. (In Chinese) [7] J. H. Zhang: Sci-Tech Information Development & Economy. Vol. 21(2011), pp. 172-74. (In Chinese) [8] Drinking water standard testing method (GB5749-2006). (In Chinese) [9] Q. H Lin: Journal of Taiyuan Urban Vocational College. Vol. 2(2005), pp. 173-74. (In Chinese) [10] S. B. Wang, L. Liu, P. S. Yuan: The Administration and Technique of Environmental Monitoring.Vol. 20 (2008), pp. 62-64. (In Chinese) [11] M. J. Li, P. Zhang: Environmental and Development. Vol. 29(2013), pp. 121-24. (In Chinese)
33