Photochemistry and Photobiology, 2015, 91: 68–73
Inspection of Feasible Calibration Conditions for UV Radiometer Detectors with the KI/KIO3 Actinometer Zhimin Qiang*1, Wentao Li1, Mengkai Li1, James R. Bolton2 and Jiuhui Qu1 1
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China 2 Department of Civil and Environmental Engineering, University of Alberta, Edmonton, AB, Canada Received 23 July 2014, accepted 29 September 2014, DOI: 10.1111/php.12356
ABSTRACT
indirectly with challenge microorganisms (5), chemical actinometers (6), fluorescent microspheres (7) or photoelectric detectors (8). In whatever applications of the UV technology, UV radiometers are always a fundamental instrument for irradiance measurements. They are easy to operate and have a fast response. However, the sensitivity of the radiometer detector often declines as a result of aging, for example, an 18% decrease in 1 year was reported to be a typical value for a detector used at 300 nm (9). As a consequence, the radiometers need to be sent back to their manufacturers or a qualified laboratory for recalibrations at least once per year (10), which not only induces an extra cost but also is time-consuming. Chemical actinometers are the other well-established approach to determine the irradiance, with advantages over radiometers such as being able to conform to the reactor geometry and free of periodic calibrations (11). A chemical actinometer is a chemical system that undergoes a light-induced reaction with a known quantum yield (12). Since the first reported actinometer in 1930 (13), different kinds of actinometers in solid, gas and liquid phases have been developed (9). Among those suitable for UV applications, the KI/ KIO3 actinometer stands out for its operational simplicity and high sensitivity, and being free of interference from room light (14). In fact, it has been intensively investigated and applied for the determination of irradiance under a variety of conditions (11,14–17). Recently, Bolton et al. (18) accurately determined the quantum yield of the KI/KIO3 actinometer at 254 nm with the standard tunable laser light source at the U.S. National Institute of Standards and Technology (NIST), and proposed a calibration protocol for UV radiometer detectors by the KI/KIO3 actinometer in a qCBA equipped with a low-pressure UV lamp. The calibration results following this protocol are traceable to NIST. This study aimed to identify the feasible calibration conditions of UV radiometer detectors with the KI/KIO3 actinometer in a qCBA. Based on the calibration principle, the actual irradiance was first determined by the KI/KIO3 actinometer. Afterward, the calibration conditions such as the beaker size, internal diameter (ID) of washer and calibration position were all examined in detail to achieve reliable calibration results. This study could promote the application of the KI/KIO3 actinometer to calibrating UV radiometer detectors at 254 nm in ordinary laboratories.
UV radiometers are widely employed for irradiance measurements, but their periodical calibrations not only induce an extra cost but also are time-consuming. In this study, the KI/ KIO3 actinometer was applied to calibrate UV radiometer detectors at 254 nm with a quasi-collimated beam apparatus equipped with a low-pressure UV lamp, and feasible calibration conditions were identified. Results indicate that a washer constraining the UV light was indispensable, while the size (10 or 50 mL) of a beaker containing the actinometer solution had little influence when a proper washer was used. The absorption or reflection of UV light by the internal beaker wall led to an underestimation or overestimation of the irradiance determined by the KI/KIO3 actinometer, respectively. The proper range of the washer internal diameter could be obtained via mathematical analysis. A radiometer with a longer service time showed a greater calibration factor. To minimize the interference from the inner wall reflection of the collimating tube, calibrations should be conducted at positions far enough away from the tube bottom. This study demonstrates that after the feasible calibration conditions are identified, the KI/KIO3 actinometer can be applied readily to calibrate UV radiometer detectors at 254 nm.
INTRODUCTION Ultraviolet (UV) technology has been used widely for inactivation of pathogenic microorganisms and photochemical oxidation of refractory organic compounds in water and wastewater treatment (1–3). During the UV processes, accurate determination of UV dose (or fluence) is crucially important, especially for quantification of photochemical or photobiological kinetic parameters. The UV dose can be theoretically determined as a result of the irradiance (or fluence rate) multiplied by the exposure time. However, the determination of UV dose in practical applications has never been an easy task. For those with uniform UV irradiation incident from one direction (e.g. in a quasi-collimated beam apparatus [qCBA]), the UV dose can be determined following the protocol proposed by Bolton and Linden (4); in contrast, for those with UV irradiation incident from all directions (e.g. in an enclosed UV reactor), the UV dose can only be quantified
MATERIALS AND METHODS Experimental system and chemicals. Calibration tests were conducted in a standard qCBA equipped with a low-pressure mercury vapor lamp
*Corresponding author email:
[email protected] (Zhimin Qiang) © 2014 The American Society of Photobiology
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Photochemistry and Photobiology, 2015, 91 (85 W, Light Sources Co., CA) emitting monochromatic light at 254 nm (Fig. 1). The length and ID of the collimating tube was 42.0 and 9.0 cm, respectively. The KI/KIO3 actinometer solution, consisting of 0.6 M KI, 0.1 M KIO3 and 0.01 M Na2B4O710H2O, was added to a glass beaker placed on a magnetic stirrer right in the center of the UV beams. A lift platform could adjust the distance from the solution to the UV lamp. A washer was placed on the top of the beaker to constrain the UV light impinging on the solution. It is important that the washer ID should be comparable to that of the active surface of the UV radiometer detector to be calibrated. A Hach DR5000 UV-Vis spectrophotometer (Loveland, CO) was utilized to measure the absorbance of the KI/KIO3 acitnometer solution at 352 nm before and after UV exposure. The detectors of three commercial UV radiometers of different brands (denoted as A, B and C) were calibrated in this study, which had been officially calibrated by qualified authorities about 10, 14 and 28 months before our tests, respectively. All chemicals used were purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. (Beijing, China) with at least analytical grade. All solutions were prepared with ultrapure water produced by a Milli-Q system (Millipore, Bedford, MA). Calibration principle. The KI/KIO3 actinometer solution has negligible absorbance above 330 nm, but absorbs all the light below 290 nm (see Fig. S1). On exposure to 254 nm light, a series of photochemical reactions are initiated in the KI/KIO3 actinometer solution, with the overall reaction given below (14):
hv 8I þ IO 3 þ 3H2 O ! 3I3 þ 6OH
Eact ¼
ðA352 V U253:7 U e352 Acs t ð1 RÞ
coefficient of I3 (e352) is 27 636 M1 cm1, and the quantum yield (Φ) is a function of the solution temperature (T, °C) (18):
/ ¼ 0:71 þ 0:0099 ðT 24Þ
ð3Þ
If the irradiance measured by a UV radiometer is denoted as Erad, the calibration factor (Rcal) of this radiometer calibrated by the KI/KIO3 actinometer can be calculated as follows:
Rcal ¼
Eact Erad
ð4Þ
Calibration conditions. Though the UV light from the qCBA is expected to be collimated, it is inevitably divergent to some extent, and the divergence decreases as the light transmits away from the UV lamp. In this situation, a difference in the beaker size, washer ID or calibration position may all lead to varying results, since the constraints on the UV light will vary. To examine their possible effects, different beaker sizes and washer IDs were tested for the calibration of Radiometer A in Run A, and in Run B, all the three radiometers were calibrated at positions with varying distances to the UV lamp. The calibration conditions for both runs are detailed in Table 1. The protocol proposed by Bolton et al. (18) was adopted, and each calibration test (e.g. T1) was repeated three times.
ð1Þ
The photoproduct, triiodide (I3), has an absorbance peak at 352 nm with a known molar absorption coefficient (see Fig. S1), and thus can be used to measure the absorbance change in the actinometer solution before and after UV exposure. With the quantum yield of the overall reaction accurately determined, the photon flow entering the solution can be quantified. The irradiance at the washer cross section is then determined as the light energy divided by the cross-sectional area and the exposure time, as expressed by Eq. (2):
A0352 Þ
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ð2Þ
where Eact = irradiance determined by the KI/KIO3 actinometer (mW cm2); A0 352 (or A352) = absorption coefficient of the actinometer solution before (or after) exposure (cm1); t = exposure time (s); V = solution volume (mL); Acs = cross-sectional area of the washer hole (cm2); U253.7 = molar photon energy at the emission wavelength of 253.7 nm (471527.65 J einstein1); and R = reflection coefficient of UV light at the water/air interface (0.025), thus (1 R) = fraction of the incident UV light absorbed by the actinometer solution. The molar absorption
RESULTS AND DISCUSSION Irradiance determination and calibration factor For each calibration process (Table 2), four parallel actinometer samples (s1–s4) were exposed for an identical time to increase Table 1. Calibration conditions in Runs A and B.
Test no.
Washer ID (cm)
Beaker size (mL)
Distance to the lamp (cm)
Distance to the tube bottom (cm)
68 68 68 68 68 68
16 16 16 16 16 16
56 62 68 74 80
4 10 16 22 28
Run A: (Radiometer A) T1 1.41 10 T2 1.41 50 T3 2.01 10 T4 2.01 50 T5* – 10 T6* – 50 Run B: (Radiometers A, B and C) T7 1.41 10 T8 1.41 10 T9 1.41 10 T10 1.41 10 T11 1.41 10
*The radiometer was calibrated without a washer. Table 2. Irradiance determined by the KI/KIO3 actinometer.
Figure 1. Schematic diagram of the experimental system.
Sample
A352
A0 352
A352A0 352
Irradiance (mW cm2)
b1 s1 s2 b2 s3 s4 b3
– 0.660 0.663 – 0.664 0.658 –
0.021 0.021* 0.022* 0.021 0.023* 0.024* 0.025
– 0.639 0.641 – 0.641 0.634 – Average 95% Confidence
– 0.0843 0.0846 – 0.0845 0.0836 – 0.0843 0.0004
*Linear interpolation result of A0 352 of the blank tests (b1, b2 and b3).
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the precision of the measurements. Since a thermal oxidation reaction always occurs in the actinometer solution, which slowly generates the background I3, the other three actinometer blanks (b1–b3, without UV irradiation) were tested for the background absorbance (A0 352) at certain time intervals during the calibration process. The absorbance of each actinometer sample before irradiation could thus be determined by interpolating the A0 352 values of the blanks according to the test time. The calculation of irradiance is presented in Table 2, taking the results of a calibration case for example. In this case, V = 5.03 mL, t = 600 s, Acs = 1.57 cm2, and since the solution temperature was stable at 22°C, the Φ was calculated to be 0.690 from Eq. (3). The average irradiance determined by the KI/KIO3 actinometer was 0.0843 mW cm2, while that directly measured by Radiometer A was 0.0735 mW cm2. Therefore, the calibration factor for that test radiometer was 1.15, which indicates that Radiometer A underestimated the UV irradiance by about 13%. This value is slightly higher than the calibration criterion of 10% regulated by the U.S. Environmental Protection Agency (10). In this situation, the radiometer readings should be multiplied by the calibration factor (i.e. 1.15) to obtain the accurate irradiance. Effects of beaker size and washer ID The results of calibrations conducted with different beaker sizes (10 and 50 mL) and washer IDs (1.41 and 2.01 cm) are illustrated in Fig. 2. Note that the irradiances measured by Radiometer A in various tests were statistically identical at 0.0735 mW cm2, indicating that the radiometer detector was placed at the same position during the tests. To this end, the washer in T1–T4 (with a washer) and the solution surface in T5 and T6 (without a washer), which marked the calibration position of the radiometer detector, respectively, in the two cases, were maintained at the same height by adjusting the lift platform. The accurate irradiance was first determined to be 0.0843 mW cm2 with the KI/KIO3 actinometer (10 mL beaker, 1.41 cm washer and 68 cm distance from washer to lamp). Thereafter, the effects of various calibration conditions could be examined through comparing the irradiances determined by the actinometer in these tests with the accurate irradiance.
0.18
1.50 1.15
0.12
1.23 1.10
1.14
Eact
Erad(A)
1.25
1.00
Rcal(A)
0.06
0.50
0.00
Calibration factor
Irradiance (mW cm−2)
1.15
0.00
T1
T2
T3
T4
T5
T6
Figure 2. Effects of beaker size and washer ID on UV irradiance and calibration factor.
The irradiances determined by the actinometer were identical in T1 and T2 at 0.0843 mW cm2, which indicates that with the 1.41 cm washer, the irradiance could be determined accurately in both the 10 and 50 mL beakers. However, when the 2.01 cm washer was used, the irradiance determined in the 10 mL beaker (T3) was slightly lower than that in the 50 mL beaker (T4). This can be ascribed to the absorption effect of the internal beaker wall. As mentioned above, the UV light was divergent in nature. When a washer of a small ID was employed, all the UV light that passed through the washer would successfully reach the actinometer solution regardless of the beaker size, as the cases in T1 and T2. But when the washer ID was enlarged, a small portion of the UV light would reach the internal beaker wall and get partially absorbed, which led to an underestimation of irradiance in T3. In contrast, the result in T4 was not influenced, since the beaker size was enlarged as well. In fact, the IDs of the two employed beakers were 2.23 and 3.81 cm, respectively, with the smaller one being only slightly larger than 2.01 cm of the washer ID. Therefore, only when the beaker was covered by a proper washer could the calibration result not be influenced by the beaker size. When no washer was employed, the irradiance would be overestimated by 7.1% and 9.5% in the cases of 10 (T5) and 50 mL (T6) beakers, respectively, (Fig. 2). This could originate from the reflection effect of the internal beaker wall. Without the constraint by the washer, the slightly divergent UV light would inevitably reach the internal beaker wall, be partially absorbed and the rest reflected. Since the reflected UV light, which could finally be absorbed by the actinometer solution, was not accounted for by the radiometer detector, an overestimated irradiance would be determined by the actinometer. The larger the beaker size, the greater the internal wall reflection and the resulting irradiance overestimation. This kind of internal wall reflection effect was also observed by Wright et al. (19), who reported that an approximately 10% increase in the UV dose with a qCBA could arise from the reflection by the internal wall of the glass vessel. Rather than painting the internal wall black (i.e. the way they took to eliminate the wall reflection), using a washer to directly block the extra UV light is a more practical solution. The proper range of washer ID The results presented above have well demonstrated the indispensability of a washer to the calibration of UV radiometer detectors with the KI/KIO3 actinometer. In fact, a proper washer can also increase the accuracy in the UV dose determination for other photochemical or photobiological experiments conducted in a glass vessel in the qCBA, since the internal wall reflection always exists. To determine the proper range of the washer ID, mathematical analysis was performed to illustrate the impact of the washer ID on the irradiance determination with the actinometer in the qCBA. To reach the actinometer solution surface, the UV light emitted from the lamp first needed to transmit through the collimating tube and then through the washer placed on the top of the beaker, as illustrated in Fig. 3. During this process, the maximum divergence angle of the UV light that passed through the washer (h1) and the maximum incident angle of the UV light that transmitted into the solution rather than onto the beaker wall (h2) could be defined as follows:
Photochemistry and Photobiology, 2015, 91
Figure 3. Illustration of mathematical analysis of UV light transmitting from the lamp to the actinometer solution (distance unit: cm).
h1 ¼ arctan
IDtub þ IDwas 2ðL1 þ L2 Þ
ð5Þ
h2 ¼ arctan
IDbea IDwas 2d
ð6Þ
where IDtub, IDwas and IDbea = internal diameters of the collimating tube, washer and beaker, respectively; L1 = length of the collimating tube; L2 = distance from the tube bottom to the washer; and d = distance from the washer to the solution surface. The distance from the top of the collimating tube to the lamp (L0) was 10 cm. Theoretically, a h2 greater than h1 ensures that no UV light can transmit onto the internal beaker wall and thus no wall absorption or reflection occurs, and only in this situation can the irradiance be determined accurately by the actinometer. For a better illustration, the values of h1 and h2 in each test of Run A are shown in Table 3. The results indicate that the irradiances determination in T1, T2 and T4 were accurate (h2 > h1), while those in other three cases (i.e. T3, T5 and T6) were not accurate (h2 < h1). It is clear that the above predictions agree well with the experimental results presented in Fig. 2, demonstrating that the mathematical analysis can be a reliable way to decide whether the internal wall of the glass vessel interferes with the irradiance determination.
Table 3. Calculation of h1 and h2 in Run A (L1 = 42 cm, L2 = 16 cm, IDtub = 9 cm). Test no. IDwas (cm) d (cm) IDbea (cm) h1 (°) h2 (°)
T1
T2
T3
T4
T5
T6
1.41 2.00 2.23 5.1 11.6
1.41 3.50 3.81 5.1 18.9
2.01 2.00 2.23 5.4 1.4
2.01 3.50 3.81 5.4 14.4
2.23* 2.00 2.23 5.5 0
3.81* 3.50 3.81 6.3 0
*Assuming that a washer, with a same ID as the beaker, was used here.
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When h2 equals h1, a special IDwas (referred to as ID0) can be obtained by combining Eqs. (5) and (6). From the viewpoint of mathematical analysis, an ideal IDwas should be no larger than ID0 so that the corresponding h2 can be greater than h1, to ensure an accurate determination of the irradiance. For the cases of the 10 and 50 mL beakers in Run A, the ID0 values were calculated to be 1.85 and 3.08 cm, respectively. Note that this calculation is based on an ideal condition, that is, before the UV light passes through the washer, all its possible reflections and scatterings are neglected. The real sample irradiation process in a qCBA can be more sophisticated. On the other hand, a too small IDwas will greatly increase the exposure time for a required UV dose. Thus, for practical applications, it is recommended that the proper range of IDwas should be 40–80% of the ID0. Taking the 10 and 50 mL beakers (Run A) as example, the proper ranges of IDwas were calculated to be 0.74–1.48 and 1.23–2.46 cm, respectively. From this respect, the 1.41 cm washer was suitable but the 2.01 cm one was too large for the 10 mL beaker, which agrees well with the experimental results (Fig. 2). It should be noted that when calculating the irradiance in the case that the cross section of the washer is larger than the active surface of the detector, a Petri Factor (PF) should be introduced to account for the nonuniformity of the irradiance at the cross section. The PF is defined as the ratio of the area-averaged irradiance to the irradiance at the cross-section center (4). Since a UV radiometer detector actually measures the central irradiance, the irradiance determined by the KI/KIO3 actinometer should be converted to the central value by dividing by the PF. The PFs of the 1.41 and 2.01 cm washers as a function of the distance to the lamp are presented in Fig. S2. It is clear that the smaller the washer cross section or the greater the distance from washer to lamp was, the closer the PF approached one. Effect of calibration position The results of calibrations conducted at positions with varying distances from the washer to the UV lamp for the three test radiometers are shown in Fig. 4. Compared to the irradiance determined by the actinometer, all three radiometers exhibited an underestimation of 13%, 40% and 50% (corresponding to the calibration factors of 1.16, 1.68 and 2.02), respectively, at a distance of 68 cm to the lamp. It is seen that the detector sensitivity decreased gradually along with the radiometer’s service time. In fact, Radiometers B and C had been used for more than 1 year (ca. 14 and 28 months, respectively) before this calibration, thus underestimated the irradiance to a greater extent than Radiometer A (ca. 10 months of service time). Hence, the two radiometers should be sent back to their manufacturers for adjustment and recalibration. As the distance from the washer (i.e. calibration position) to the lamp increased, the irradiance increased linearly with the reciprocal of the squared distance (see Fig. S3), which is in good agreement with the LSI model (20). In addition, the calibration factors were somewhat underestimated when calibrations were conducted at the two nearer positions (T7 and T8, with 56 and 62 cm distances to the lamp, respectively), but increased and became stable after the distance to the lamp reached 68 cm (i.e. T9–T11) (Fig. 4b). Taking the results in T9 as reference, the calibration factors in T7 were underestimated by 3.4%, 10.1% and 5.9% for Radiometers A, B and C, respectively. These underestimations could arise from the inner wall reflection of the collimating tube; and meanwhile, the distinct angular response of each
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Irradiance (mW cm–2)
0.20
Eact Erad (A) Erad (B) Erad (C)
0.15 0.10 0.05 0.00
Calibration factor
a
2.00 1.50
b
1.90
1.92
1.51
1.54
1.12
1.10
1.00
2.02
2.05
2.06
1.68
1.70
1.70
1.16
1.15
1.17 Rcal (A) Rcal (B)
0.50
Rcal (C)
0.00 56
68 74 62 Distance to the lamp (cm)
80
Figure 4. Effect of calibration position on UV irradiance (a) and calibration factor (b).
detector tended to be responsible for the varying extent of the underestimations. An ideal qCBA should have a collimating tube with its inner wall painted black to avoid any light reflection inside. However, it is a reality that a black surface can still reflect the UV light to some extent, for example, the reflection coefficient of black cotton was measured to be 11.1% (21). Therefore, some UV light would be reflected by the inner tube wall. Furthermore, the qCBA employed in this study had a dismountable stainless steel ring (2 cm height) unpainted at the bottom of the collimating tube, which was likely to enhance the light reflection. The reflected UV light with large divergent angles could be detected by a radiometer if placed close to the tube bottom, but could not enter the actinometer solution, thus leading to the underestimated calibration factors in T7 and T8 (Fig. 4b). In response to the possible reflection of UV light by the inner tube wall, calibrations should be conducted at positions far enough away from the tube bottom. For example, when the 10 mL beaker and the 1.41 cm washer were used, a distance of 16 cm from the washer to the tube bottom was considered far enough for calibrations of UV radiometer detectors. In addition, each radiometer detector has its own distinct angular response to UV irradiation, which ideally should be a cosine function of the incident angle to the detector’s active surface. Because of the diverse designs and manufactures of UV radiometer detectors, their angular responses are rarely the same, so the measured irradiances have certain variations when the UV light does not impinge perpendicularly on the detector panel. Martin et al. (22) tested nine different UV radiometers for measurements of the UV irradiance inside a phototherapy cabinet and found a maximum variation of 50%, which they believe was induced by the different angular responses of the radiometer detectors. Therefore, although the test radiometers were placed at the same position near the collimating tube, they responded diversely to the divergent UV light, thus causing their calibration factors being underestimated to different extents.
CONCLUSIONS This study applied the KI/KIO3 actinometer to calibrate UV radiometer detectors at 254 nm in a qCBA equipped with a low-pressure UV lamp. The results indicate that a washer which constrains the UV light was indispensable, and with a proper washer installed, the beaker size (10 or 50 mL) had little influence on the calibration results. The absorption or reflection of UV light by the internal beaker wall would cause an underestimation or overestimation of the irradiance determined by the KI/ KIO3 actinometer, respectively. The proper range of the washer ID could be determined via mathematical analysis of the irradiation process. For three test radiometers which had been used for about 10, 14 and 28 months, their calibration factors were determined to be 1.16, 1.68 and 2.02, respectively, indicating the gradually decreased detector sensitivity with the service time. When calibrations were conducted at positions close to the bottom of the collimating tube, the inner tube wall reflection would cause an underestimation of the calibration factors, and the extent of underestimation varied with different radiometers due to the distinct angular response of each detector. Hence, calibrations should be conducted at positions far enough away from the tube bottom, for example, with a distance of at least 16 cm when the 10 mL beaker and the 1.41 cm washer were used. In conclusion, under feasible calibration conditions, the KI/KIO3 actinometer can be easily applied to calibrate UV radiometer detectors at 254 nm in a qCBA in ordinary laboratories, which saves the cost and time for periodic detector recalibrations. Acknowledgements—The authors gratefully acknowledge the financial support from the People Programme (Marie Curie Actions) of the European Union’s Seventh Programme FP7/2007-2013 under a REA grant (Agreement No. 318926), the National Natural Science Foundation of China (51221892), and the Ministry of Science and Technology of China (2012AA062606, 2012BAJ25B04).
SUPPORTING INFORMATION Additional Supporting Information may be found in the online version of this article: Figure S1. Absorption spectra of KI/KIO3 actinometer solution before and after 254 nm UV irradiation (Eact = 0.169 mW cm2). Figure S2. Variations in the PFs of two washers with different distances to the lamp. Figure S3. The irradiances determined by the KI/KIO3 actinometer and three test radiometers as a function of 1/L2 (L = distance from washer to lamp).
REFERENCES 1. Sarathy, S. R. and M. Mohseni (2006) An overview of UV-based advanced oxidation processes for drinking water treatment. IUVA News 8(2), 16–27. 2. Guo, M. T., H. Y. Hu, J. R. Bolton and M. G. El-Din (2009) Comparison of low and medium pressure ultraviolet lamps: Photoreactivation of Escherichia coli and total coliforms in secondary effluents of municipal wastewater treatment plants. Water Res. 43, 815–821. 3. Penru, Y., A. R. Guastalli, S. Esplugas and S. Baig (2012) Application of UV and UV/H2O2 to seawater: Disinfection and natural
Photochemistry and Photobiology, 2015, 91
4. 5. 6. 7.
8. 9. 10.
11. 12. 13.
organic matter removal. J. Photochem. Photobiol. A: Chem. 223, 40–45. Bolton, J. R. and K. G. Linden (2003) Standardization of methods for fluence (UV dose) determination in bench-scale UV experiments. J. Environ. Eng. 129, 209–215. Sommer, R., A. Cabaj, T. Sandu and M. Lhotsky (1999) Measurement of UV radiation using suspensions of microorganisms. J. Photochem. Photobiol. B: Bio. 53, 1–6. Rahn, R. O., P. Xu and S. L. Miller (1999) Dosimetry of room-air germicidal (254 nm) radiation using spherical actinometry. Photochem. Photobiol. 70, 314–318. Bohrerova, Z., G. Bohrer, S. M. Mohanraj, J. Ducoste and K. G. Linden (2005) Experimental measurements of fluence distribution in a UV reactor using fluorescent microspheres. Environ. Sci. Technol. 39, 8925–8930. Li, M. K., Z. M. Qiang, J. R. Bolton, W. T. Li and P. Chen (2014) UV disinfection of secondary water supply: Online monitoring with micro-fluorescent silica detectors. Chem. Eng. J. 255, 165–170. Kuhn, H. J., S. E. Braslavsky and R. Schmidt (2004) Chemical actinometry (IUPAC technical report). Pure Appl. Chem. 76, 2105– 2146. USEPA (2006) Ultraviolet Disinfection Guidance Manual for the Final Long Term 2 Enhanced Surface Water Treatment Rule (EPA 815–R–06–007). Office of Water, United States Environmental Protection Agency, Washington, DC. Jin, S. S., A. A. Mofidi and K. G. Linden (2006) Polychromatic UV fluence measurement using chemical actinometry, biodosimetry, and mathematical techniques. J. Environ. Eng. 132, 831–841. Bolton, J. R. (2010) Ultraviolet Applications Handbook, 3rd edn. ICC Lifelong Learn Inc., Edmonton, Canada. Leighton, W. G. and G. S. Forbes (1930) Precision actinometry with uranyl oxalate. J. Am. Chem. Soc. 52, 3139–3152.
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14. Rahn, R. O. (1997) Potassium iodide as a chemical actinometer of 254 nm radiation: Use of iodate as an electron scavenger. Photochem. Photobiol. 66, 450–455. 15. Rahn, R. O., M. I. Stefan, J. R. Bolton, E. Goren, P. Shaw and K. R. Lykke (2003) Quantum yield of the iodate-iodide actinometer: Dependence on wavelength and concentration. Photochem. Photobiol. 78, 146–152. 16. Rahn, R. O., J. R. Bolton and M. I. Stefan (2006) The iodide/iodate actinometer in UV disinfection: Determination of the fluence rate distribution in UV reactors. Photochem. Photobiol. 82, 611–615. 17. Goldstein, S. and J. Rabani (2008) The ferrioxalate and iodide-iodate actinometers in the UV region. J. Photochem. Photobiol. A: Chem. 193, 50–55. 18. Bolton, J. R., M. I. Stefan, P. Shaw and K. R. Lykke (2011) Determination of the quantum yields of the potassium ferrioxalate and potassium iodide–iodate actinometers and a method for the calibration of radiometer detectors. J. Photochem. Photobiol. A: Chem. 222, 166–169. 19. Wright, H., C. Odegaard, S. Hess and K. Bircher (2011) Impacts of reflection on UV dose delivery – Collimated beam apparatus and UV reactors. In Proceedings of Disinfection 2011, pp. 121–126. Water Environment Federation, Alexandria, VA, USA. 20. Blatchley, E. R. III (1997) Numerical modeling of UV intensity: Application to collimated-beam reactors and continuous-flow systems. Water Res. 31, 2205–2218. 21. Li, M. K., Z. M. Qiang, J. R. Bolton and W. W. Ben (2012) Impact of reflection on the fluence rate distribution in a UV reactor with various inner walls as measured using a micro-fluorescent silica detector. Water Res. 46, 3595–3602. 22. Martin, C. J., C. J. Currie and C. J. Pye (1999) The importance of radiometer angular response for ultraviolet phototherapy dosimetry. Phys. Med. Biol. 44, 843–855.
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