Environ. Sci. Technol. 2009 43, 9407–9412
Stimulative Effects of Ozone on a Biofilter Treating Gaseous Chlorobenzene CAN WANG, JIN-YING XI,* HONG-YING HU,* AND YUAN YAO Environmental Simulation and Pollution Control State Key Joint Laboratory, Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, PR China
Received June 29, 2009. Revised manuscript received October 28, 2009. Accepted October 28, 2009.
Recalcitrant volatile organic compounds with low biodegradabilities pose challenges for biofiltration technologies. In this study, the effects and mechanism of adding ozone on the performance of a biofilter were investigated. A biofilter treating chlorobenzene was set up and operated continuously for 265 days under different inlet ozone concentrations. Results showed that ozone below 120 mg m-3 could notably enhance the biofilter performance. The average chlorobenzene removal efficiency increased from 40 to 70% and then to 90% while the inlet ozone concentration rose from 0 to 40 mg m-3 and 120 mg m-3. Reducing ozone concentration resulted in a decrease in removal efficiency from 90 to 40%. Further analysis indicated that the thickness and extra-cellular polymer substance content of the biofilm were remarkably reduced while inlet ozone concentration was gradually increased. Meanwhile, the specific surface areas of the filter bed were found to increase from 784 to 820 and 880 m2 m-3. A respiratory quinone profile showed that the dominant quinone shifted from ubiquinone-8 to menaquinone-9(H2) after ozone was added. This indicated that some Gram-positive bacteria with thick cell wall became the dominant species under ozone compression.
Introduction Volatile organic compounds (VOCs) are common air pollutants found in industrial air emissions, such as from chemical manufacturing plants and various hazardous sites (1). Most of those compounds are harmful to human health and cause severe environmental problems (2). Among the various technologies for VOCs treatment, biofiltration is widely considered a cost-effective technology because of its low operating costs and convenient maintenance (3). However, biofilters could not achieve satisfactory performance for some recalcitrant VOCs treatment due to their low biodegradability (4, 5). Some efforts have been proposed to address this challenge. One was that some special microorganisms with good abilities to degrade persistent VOCs were used as dominant microbial species for biofiltration. Jang et al. (6) used Pseudomonas sp. SR-5 to enhance styrene removal efficiency in a biofilter. Yadav et al. (7) and Wang et al. (8) inoculated a strain of * Address correspondence to either author. Phone: (+86-10)62797163 (J.-Y. X.), (H.-Y.H.). Fax: (+86-10)6277-1472 (J.-Y. X.), (H.-Y.H.); E-mail:
[email protected] (J.-Y. X.);
[email protected] (H.-Y.H.). 10.1021/es9019035 CCC: $40.75
Published on Web 11/10/2009
2009 American Chemical Society
white-rot fungi into biofilters and achieved high performance for removing BTEX family compounds. However, these microorganisms could not be applied directly in pilot or fullscale biofilters since the pure cultivation are often costly and difficult (9). Another effort was coming from some pretreatment technologies. Congna et al. (10) used granular activated carbon as a pretreatment unit before biofiltration. This strategy was proposed to reduce the inlet concentration of inhibitory compounds into a biofilter. But the performance of the biofilter was not improved measurably. Moussavi et al. (11) and Wang et al. (12) obtained interesting results, in that ozone-producing ultraviolet (UV) lamps were used as a pretreatment, which transferred some recalcitrant VOCs to more biodegradable products and thus improved the performance of the whole UV-biofilter system. Moreover, a further study showed that the VOCs removal capacity of a biofilter was enhanced by adding UV and the produced ozone of 10-60 mg m-3 by UV irradiation (13). Therefore, it is interesting to know the effects of ozone on the microorganisms in biofilters and its potential to enhance the performance of biofilters. Actually, ozone is a chemical substance that can have a considerable effect on microorganisms arising from its strong oxidation capacity. A few previous papers (14–16) have investigated the affecting mechanisms by ozone using pure microbial cell. The cell viability and membrane permeability were affected by long-term (5-30 min) ozone exposure. Furthermore, Zhang et al. (17) utilized ozone to disintegrate excess activated sludge in wastewater treatment processes. The ozone destroys the zoogloea structures and converts the solid organic components of the sludge into soluble substances, which can be further biologically degraded when the ozonated sludge is returned to the wastewater. Meanwhile, ozone is often regarded a measure to change the sludge properties. Dytczak et al. (18) investigated the extra-cellular polymer substance (EPS) content and floccule shapes of sludge after ozone treatment. The results showed that the sludge floccule structure became stronger, denser, and more ozone-resistant. However, these papers are mainly relevant to wastewater treatment processes. The effects of ozone on the microorganisms in gas-solid phase bioreactors have rarely been reported. Moreover, ozone was a common disinfectant to deactivate microorganisms in wastewater (19). Such deactivation effects are selective, since some species of microorganisms have been reported to be resistant to ozone (18). Yan et al. (20) found out that the “G-bacteria”, a class of special microorganisms isolated from activated sludge, showed high resistance to ozone oxidation. Therefore, it is quite interesting to explore the changes of microbial characteristics in biofilters under ozone injection. Ozone can also be regarded a potential measure to regulate the microbial community in a mixed flora. In this study, a novel method using ozone to improve chlorobenzene removal performance of a biofilter was investigated, by comparison of its performance with and without ozone injection. Also the corresponding mechanisms of ozone treatment on the biofilter were explored. The results of this study may be helpful to provide a new strategy to improve the performance of biofilters and to understand the mechanism of ozone on biofilters.
Materials and Methods Experimental Set-Up and Operation. The experimental setup is shown in Figure 1. The biofilter was cylindrical in shape, 12 cm in diameter and 50 cm in height, which was packed with bamboo as carriers to a depth of 30 cm. More VOL. 43, NO. 24, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Experimental setup for the biofiltration process with and without ozone.
TABLE 1. Summary of Experimental Conditionsa experimental conditions parameter
phase 1
phase 2
phase 3
phase 4
phase 5
period of operation (day) inlet ozone concentrations (mg m-3) inlet chlorobenzene concentration (mg m-3) EBRT of the biofilter (s)
0-50 0 1000 ( 200 122
51-120 40 ( 20 1000 ( 200 122
121-168 120 ( 20 1000 ( 200 122
169-211 80 ( 20 1000 ( 200 122
212-265 0 1000 ( 200 122
a
EBRT: empty bed residence time.
detailed description of the experimental setup can be found in the Supporting Information (SI) Page S-1. The synthetic waste gas stream was generated by evaporating liquid chlorobenzene into the gas stream using a syringe pump (Shanghai Alcott Biotech Co, China). Ozone was produced from a generator and introduced into the biofilter mixed with the gas stream containing chlorobenzene. The detailed operating conditions are summarized in Table 1. Measurement of the Biofilm Thickness. The biofilm thickness of the packing media samples from the biofilter were measured using a three-dimensional manual micromanipulator (Beijing Daheng Laser Equipment Co., Ltd., China). Five pieces of packing media were sampled at a certain height along the biofilter. Four individual measurements were carried out for each piece. The average biofilm thickness from the 20 measurements for each height was calculated at confidence interval of 95%. More details about the analytical method can be found in the SI Page S-2. EPS Content Analysis. The EPS constitutes the main components of microbial aggregates. The biofilm EPS was extracted and analyzed by sonication and heating methods, as described by Comte et al. (21). Finally, the EPS content was expressed as the mass of total organic carbon (TOC) per gram of wet biofilm (mg-TOC g-biofilm-1). All samples on different days were taken from the bottom section of the filter bed (at a distance 5-10 cm from the inlet). The average EPS content from duplicate samples was then calculated. Scanning Electron Microscopy (SEM). Microbial samples were withdrawn from the biofilter, and then fixed and dehydrated as described by Chung et al. (22). Micrographs were obtained from a Sirion model 200 scanning electron microscope (OXFORD Co., Ltd., British). Analysis of Physical Properties of the Filter Bed. The pulse injection technique was used to describe the physical properties of filter beds (23) by using 1,2-dichloroethane (DCE) as the tracer. The time course of the tracer concentration in the outlet of the biofilter was defined as the molecular retention time distribution (MRTD) curve. The average molecular retention time (ν1), the width of the MRTD curve (µ2) and the specific surface area (a) were calculated based 9408
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on the MRTD curves to analyze the physical properties of the filter bed according to eqs 1-3 (SI Page S-3).
∫ tc dt ∑ t c ≈ ∫ c dt ∑ c ∞
ν1 )
µ2 )
∞
0
i gei∆ti
ge
gei∆ti
∞
0
∫
ge
0
(t - ν1)2cgedt
∫
∞
0
(1)
∑ (t - ν ) c ∑ c ∆t 2
≈
cgedt
i
1
gei
( )(
ν1 u-1 lK l a)2 uµ2 K - 1
2
Db δb
)
gei∆ti
(2)
i
(3)
Microbial Quinone Analysis. The microbial community was analyzed using the quinone profile of the biofilms (24), which is represented as the mole fraction of each quinone type in a mixed culture. Packed media samples were pretreated (SI Page S-4) and used for the quinone analysis. The analytical methods for the microbial quinones in the biofilm utilized an improved method as described by Hu et al. (24). Biolog Plates Analysis. The Biolog ECO-microplates were used in this study to analyze the microbial metabolic activities (25). The microbial suspension (SI Page S-5) was used to inoculate the Biolog plates, which were then read during the incubation period. The reading for each well was then corrected by subtracting the value of the water blank, and the average well color development (AWCD) was calculated according to eq 4 (26). Duplicate samples were carried out for one analysis. AWCD )
1 3
31
∑ (R i)1
it
- R0t)
(4)
FIGURE 2. Chlorobenzene removal efficiencies of the biofilter during phase 1 (day 0-50: without ozone injection), phase 2 (day 51-120: with ozone injection 40 ( 20 mg m-3), phase 3 (day 121-168: with ozone injection 120 ( 20 mg m-3), phase 4 (day 169-211: with ozone injection 80 ( 20 mg m-3), phase 5 (day 212-265: without ozone injection): 0 removal efficiency. where Rit and R0t are the absorbances (cm-1) of the sole carbon source i and the water blank at time t (h), respectively.
Results and Discussion Stimulative Effects of Ozone on the Biofilter Performance. Experiments were conducted for 265 days. During the first 50 days (phase 1), the biofilter was operated without ozone injection. The chlorobenzene removal efficiencies fluctuated around 40%. From day 51 to day 120 (phase 2), ozone was injected into the biofilter at a concentration of 20-60 mg m-3 and was completely eliminated in the effluent flow (data not shown). Accordingly, the chlorobenzene removal efficiencies increased to around 70%. From day 121 to day 168 (phase 3), the ozone concentration was increased further to 100-140 mg m-3. The removal efficiencies first fluctuated and then stabilized around 90%. The outlet ozone concentration was detected to be below 5 mg m-3. In order to verify the effects of ozone on the biofilter’s performance, the inlet concentrations of ozone were reduced to 60-100 mg m-3 from day 169 to day 210 (Phase 4) and then was shut down from day 211 to the end of the operation (Phase 5). The removal efficiencies were correspondingly declined to about 80 and 40%. The removal rate (SI Page S-1) was used to show the effects of ozone on the biofilter performance. Figure 3 compared the removal rates during the various phases with respect to inlet chlorobenzene loadings of the biofilter. The biofilter presented different removal characteristics of chlorobenzene in the various phases. In phases 1 and 5, the biofilter demonstrated a gradual decline of removal rate when the inlet loading was increased beyond 30 g m-3 h-1, which likely arose from the inhibitory effects of chlorobenzene. However, the removal rate of the biofilter in phases 2, 3, and 4 kept going up with inlet loading. And the removal rates in these phases (with ozone injection) were clearly higher than those in phases 1 and 5. Furthermore, higher concentration of ozone could result in higher chlorobenzene removal rate. The results in Figures 2 and 3 indicated that ozone markedly improved the chlorobenzene removal performance of the biofilter. However, little is known about why the performance of the biofilter was enhanced. Therefore, the detailed mechanism was then investigated. Examination of Direct Removal of Chlorobenzene by Ozone Oxidation. One possible reason for performance improvement might come from direct removal of chlorobenzene by ozone oxidation. An abiotic experiment (SI Figure S-1) has been conducted by injecting both gaseous chlorobenzene and ozone into a biofilter with the same packing media and at the same moisture condition (nutrient
FIGURE 3. Chlorobenzene removal rates of the biofilter with respect to inlet chlorobenzene loadings during various phases: O data for phase 1 (O3 ) 0 mg m-3); 4 data for phase 2 (O3 ) 40 ( 20 mg m-3); 0 data for phase 3 (O3 ) 120 ( 20 mg m-3); 2 data for phase 4 (O3 ) 80 ( 20 mg m-3); b data for phase 5 (O3 ) 0 mg m-3). addition). The results (SI Figure S-1) showed that the concentrations of chlorobenzene and ozone did not change when the gas stream passed through the filter bed, which indicated that ozone can not directly react with chlorobenzene in the gas phase. Effects of Ozone on Biofilm Properties. Since ozone could not remove chlorobenzene directly in the gas phase, gaseous chlorobenzene should be mainly removed by the biofilm inside the biofilter. Therefore, the effects of ozone on the biofilm properties were investigated. (1) Biofilm Thickness. Figure 4 compares the biofilm thickness results along the height of the biofilter with and without ozone injection. The biofilm thicknesses on day 45 (without ozone injection) were significantly higher than those with ozone injection (days 83 and 155). Ozone is often regarded as a disinfectant and a strong oxidant to inhibit microorganisms in both water and gas phases (18). In this way, the biofilm was probably oxidized by ozone and then became thinner. (2) EPS Content. The morphologies of biofilm with and without ozone injection were further examined by SEM VOL. 43, NO. 24, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Theoretical Parameters Calculated From the MRTD Curves
FIGURE 4. Biofilm thickness along the height of the biofilter with ozone of 0 (Day 45), 40 (Day 83), and 120 mg m-3 (Day 155). analysis, as shown in Figure 5. The biofilm morphology on day 45 (without ozone) was more compact than that on day 135 (with ozone). In Figure 5B, the bacteria were obviously embedded in the EPS when there was no ozone injected. While in Figure 5C, the presence of single sphere bacteria was clearly observed with ozone injection. The biofilm EPS contents and the TOC values in leachate from the biofilter during operation were analyzed in Figure 6. During phase 1, the EPS content increased from 3.5 to 4.9 mg-TOC g-biofilm-1, probably due to the utilization of chlorobenzene as a substrate by the microorganisms. Starting on day 51, ozone was injected into the biofilter and the EPS content was reduced to around 3 mg-TOC g-biofilm-1. Meanwhile, the TOC value in leachate increased from 20 to 35 mg L-1. In phases 3 and 4, further increases in ozone concentration resulted in a continuous decrease of the EPS
parameters
no ozone (day 45)
O3 injection 40 mg m-3 (day 83)
O3 injection 120 mg m-3 (day 155)
ν1 (min) µ2 (min2) a (m2 m-3)
6.8 53.4 784
9.0 40.7 820
9.4 41.8 880
content to 1-2 mg-TOC g-biofilm-1. Accordingly, the TOC value of leachate went up remarkably to about 100 mg L-1. In phase 5, when the ozone injection was shut down, a higher EPS content and a lower leachate TOC were observed. These results indicated that ozone could destroy fractional part of the biofilm EPS. The oxidized EPS was then washed out from the biofilter by sprayed nutrient solution. The results concerning the biofilm properties suggested that ozone could reduce the thickness and the EPS content of the biofilm. Dytczak et al. (27) reported that the EPS content can form a dense gel that resists the transfer of oxygen and nutrients into the biofilm. Therefore, the reduction of EPS content by ozone could promote mass transfer in the biofilm, which would contribute to the performance improvement of the biofilter. Changes in the Specific Surface Area of the Filter Bed. As shown in Figure 4, the biofilm thickness was influenced by ozone. Such effects would result in changes of the specific surface area of the filter bed, which could also affect the performance of biofilter (23). The MRTD curves of the filter bed on some typical conditions, such as without ozone injection, with low concentration ozone injection (40 mg m-3) and with high concentration ozone injection (120 mg m-3), were measured. Based on these MRTD curves, the average molecular retention time (ν1), the width of the MRTD curve (µ2) and the specific surface area (a) were calculated using eqs 1-3 (SI Figure S-2). As shown in Table 2, the increases in specific surface area of the filter bed a with higher ozone concentration, which should be a result of biofilm thickness reduction caused by
FIGURE 5. Micrographs of carrier surface (A) and microorganisms in the biofilter on day 45 (B) and on day 155 (C).
FIGURE 6. EPS content of biofilm and TOC value in leachate during various operating phases. The results are obtained as an average from duplicate samples. Error bars represent standard deviation based on duplicate samples: b data for EPS; O data for TOC. 9410
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FIGURE 7. Development of AWCD during incubation period of microbial samples under various operating phases. The results are obtained as an average from duplicate samples. Error bars represent standard deviation based on duplicate samples: 4 data for Day 45; bdata for Day 83; O data for Day 155; 2 data for Day 260. ozone oxidation. The increase in the specific surface area of the filter bed showed another proof for mass transfer and biofilter’s performance improvements. Changes in the Microbial Characteristics in the Biofilter. Ozone may play a key role in the microbial characteristics because it is a strong oxidizing agent. Thus, it is necessary to investigate the metabolic activity and the microbial community of biofilm in the biofilter. (1) Metabolic Activity. To quantify the microbial metabolic activities in the biofilter, the developments of the AWCD under different operating conditions were investigated as shown in Figure 7. The time period selected for metabolic activity analysis was from 20 to 40 h, a period when the greatest AWCD changes occurred. The slopes of the AWCD curves within this period represented average metabolic activities of the microbial samples. The slope of AWCD curve on day 45 and day 260 (without ozone injection) was remarkably lower than that on days 83 and day 155 (with ozone injection). The slopes of the AWCD curves were calculated to be 0.033, 0.048, 0.044, and 0.032 cm-1 h-1 for the samples on days 45, 83, 155, and 260, respectively. This result suggested that ozone could raise the microbial metabolic activity of the biofilm and the structure of the microbial community might be changed under ozone compression.
(2) Microbial Community. Figure 8 shows the quinone profiles of microorganisms in the biofilter during operation. In phase 1, the fractional content of ubiquinones-8 (UQ-8) increased from day 30 and became the dominant quinones, suggesting that a microbial community adapted for chlorobenzene degradation formed. From day 50, ozone was injected into the biofilter and the quinone profiles exhibited a marked difference. The fractional content of menaquinone9(H2) (MK-9(H2)), which was observed at low fractional content during phase 1, steadily increased and became the dominant quinone species instead of UQ-8. When ozone was stopped injecting into the biofilter, it was interesting to find out that the UQ-8 was again became the dominant species. The changes in the quinone profiles represented the shifts of the microbial community in the biofilter. These results suggested that ozone played a significant role on the microbial community in the biofilter. The menaquinone are common quinone species in Grampositive bacteria, while the ubiquinones are often found in Gram-negative bacteria (24). The Gram-positive bacteria have thicker cell wall (20-80 nm) and higher content of peptidoglycan (40-90% of total dry weight of a cell) than those of Gram-negative bacteria (cell wall thickness: 2-10 nm, peptidoglycan content: 5-10%). These differences make Gram-positive bacteria show stronger tolerance of ozone than Gram-negative bacteria. Mechanisms of Ozone on the Biofilter Performance. Ozone with a concentration of 20-140 mg m-3 showed a remarkable stimulative effect on the performance of a biofilter treating gaseous chlorobenzene. Further insights into the affecting mechanisms by ozone have been investigated. The experimental results obtained in this study suggested that the affecting mechanisms involve both biotic and abiotic responses of the biofilter to ozone injection. Ozone changed the physical properties of the biofilm by reducing the biofilm thickness and oxidizing the surface part of the EPS. The reduction of the biofilm thickness further resulted in a higher specific surface area of the filter bed. All these changes helped to promote the oxygen, nutrient, and pollutant transfer in the filter bed, which enhanced the removal rate of chlorobenzene. On the other hand, ozone significantly influenced the biological characteristics of the microorganisms in the biofilter. The experimental results indicated that ozone affected the microbial community and the microorganism exposure to ozone showed higher metabolic activities. This is another reason for ozone to improve the chlorobenzene removal performance. To compare the aqueous ozone concentration in this study with that where ozone used as a disinfectant, the ozone concentration in the water phase inside the biofilter was calculated. When the highest gaseous ozone concentration reaches as high as 140 mg m-3, the
FIGURE 8. Changes of quinone profiles in the biofilter during operation. VOL. 43, NO. 24, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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corresponding ozone concentration in the water phase is 0.02 mg L-1 (Henry’s Law Constant of ozone is 3.53 mg L-1 kPa-1, 25 °C). The value is much lower than the common ozone concentration range for disinfection (0.1-10 mg L-1). This explains why the ozone in this study did not show apparent disinfection effects on the microorganisms in the biofilter.
Acknowledgments This study was supported by the National Natural Science Foundation of China (Grant No. 50708049). Our thanks go to Prof. James R. Bolton for his suggestion in the revision of the manuscript.
Supporting Information Available A detailed description of the experimental setup, the analytical methods, and parameter illustrations and values in MRTD curve calculation. Figure S-1 displays the data for chlorobenzene reacting directly with ozone, and Figure S-2 shows the data of the MRTD curve. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Hsu, Y. C.; Chen, S. K.; Tsai, J. H.; Chiang, H. L. Determination of volatile organic profiles and photochemical potentials from chemical manufacture process vents. J. Air Waste Manage. Assoc. 2007, 57 (6), 698–704. (2) Delhomenie, M. C.; Heitz, M. Biofiltration of air: a review. Crit. Rev. Biotechnol. 2005, 25 (1-2), 53–72. (3) Kennes, C.; Veiga, M. C. Fungal biocatalysts in the biofiltration of VOC-polluted air. J. Biotechnol. 2004, 113 (1-3), 305–319. (4) Delhome´nie, M. C.; Heitz, M. Elimination of chlorobenzene vapors from air in a compost-based biofilter. J. Chem. Technol. Biotechnol. 2003, 78 (5), 588–595. (5) Hasnaa, J.; Louise, B.; Michele, H. Biofiltration of air contaminated by styrene: effect of nitrogen supply, gas flow rate and inlet concentration. Environ. Sci. Technol. 2000, 34 (9), 1764– 1771. (6) Jang, J. H.; Hirai, M.; Shoda, M. Enhancement of styrene removal efficiency in biofilter by mixed cultures of Pseudomonas sp. SR-5. J. Biosci. Bioeng. 2006, 102 (1), 53–59. (7) Yadav, J. S.; Reddy, C. A. Degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) by the lignin-degrading basidiomycete Phanerochaete chrysosporium. Appl. Environ. Microbiol. 1993, 59 (3), 756–762. (8) Wang, C.; Xi, J. Y.; Hu, H. Y.; Wen, X. H. Biodegradation of gaseous chlorobenzene by white rot fungi. Biomed. Environ. Sci. 2008, 21 (6), 474–478. (9) Yadav, J. S.; Wallace, R. E.; Reddy, C. A. Mineralization of monoand diCBs and simultaneous degradation of chloro- and methylsubstituted benzenes by the white rot fungus Phanerochaete chrysosporium. Appl. Environ. Microb. 1995, 61 (2), 677–680. (10) Congana, L.; William, M. M. Activated carbon load equalization of discontinuously generated acetone and toluene mixtures treated by biofiltration. Enviorn. Sci. Technol. 2005, 39 (7), 2349– 2356. (11) Moussavi, G.; Mohseni, M. Using UV pretreatment to enhance biofiltration of mixtures of aromatic VOCs. J. Hazard. Mater. 2007, 144 (1-2), 59–66.
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(12) Wang, C.; Xi, J. Y.; Hu, H. Y. A novel integrated UV-biofilter system to treat high concentration of gaseous chlorobenzene. Chin. Sci. Bull. 2008, 53 (17), 2712–2716. (13) Wang, C.; Xi, J. Y.; Hu, H. Y.; Yao, Y. Advantages of combined UV photodegradation and biofiltration processes to treat gaseous chlorobenzene. J. Hazard. Mater. 2009, 171 (1-3), 1120– 1125. (14) Komanapalli, I. R.; Lau, B. H. S. Ozone-induced damage of Escherichia coli K-12. Appl. Microbiol. Biotechnol. 1996, 46 (56), 610–614. (15) Komanapalli, I. R.; Mudd, J. B.; Lau, B. H. S. Effect of ozone on metabolic activities of Escherichia coli K-12. Toxicol. Lett. 1997, 90 (1), 61–66. (16) Finch, G. R.; Smith, D. W.; Stiles, M. E. Dose-response of Escherichia coli in ozone demand-free phosphate buffer. Water Res. 1988, 22 (3), 1563–1570. (17) Zhang, G. M.; Yang, J.; Zhang, J. Sludge ozonation: disintegration, supernatant changes and mechanisms. Bioresour. Technol. 2009, 100 (3), 1505–1509. (18) Dytczak, M. A.; Oleszkiewicz, J. A. Performance change during long-term ozonation aimed at augmenting denitrification and decreasing waste activated sludge. Chemosphere. 2008, 73 (9), 1529–1532. (19) Tachikawa, M.; Yamanaka, K.; Nakamuro, K. Studies on the disinfection and removal of biofilms by ozone water using an artificial microbial biofilm system. Ozone: Sci. Eng. 2009, 31 (1), 3–9. (20) Yan, S. T.; Chu, L. B.; Xing, X. H.; Yu, A. F.; Sun, X. L.; Jrucik, B. Analysis of the mechanism of sludge ozonation by a combination of biological and chemical approaches. Water Res. 2009, 43 (1), 195–203. (21) Comte, S.; Guibaud, G.; Baudu, M. Relations between extraction protocols for activated sludge extracellular polymeric substances (EPS) and EPS complexation properties Part I. Comparison of the efficiency of eight EPS extraction methods. Enzyme Microb. Technol. 2006, 38 (1-2), 237–245. (22) Chung, Y. C.; Lin, Y. Y.; Tseng, C. P. Operational characteristics of effective removal of H2S and NH3 waste gases by activated carbon biofilter. J. Air Waste Manage. Assoc. 2004, 54 (4), 450– 458. (23) Xi, J. Y.; Hu, H. Y.; Qian, Y. Effects of adding inert spheres into the filter bed on the performance of biofilters for gaseous toluene removal. Biochem. Eng. J. 2005, 23 (2), 123–130. (24) Hu, H. Y.; Lim, B. R.; Goto, N.; Fujie, K. Analytical precision and repeatability of respiratory quinones for quantitative study of microbial community structure in environmental samples. J. Microbiol. Methods. 2001, 47 (1), 17–24. (25) Garland, J. L.; Mills, A. L. Classification and characterization of heterotrophic microbial communities on the basis of patterns of community-level sole-carbon-source utilization. Appl. Environ. Microb. 1991, 57 (4), 2351–2359. (26) Grove, J. A.; William, A. A.; Murray, M. Y. Changes in the potential functional diversity of the bacterial community in biofilters. Appl. Microbiol. Biotechnol. 2007, 77 (3), 741–747. (27) Dytczak, M. A.; Londry, K.; Siegrist, H.; Oleszkiewicz, J. A. Extracellular polymers in partly ozonated return activated sludge: impact on flocculation and dewaterability. Water Sci. Technol. 2006, 54 (9), 155–164.
ES9019035
