A Pyridazine-Containing Phthalonitrile Resin for Heat-Resistant and Flame-Retardant Polymer Materials.

In this study, a novel phthalonitrile monomer containing a pyridazine ring, 3,6-bis[3-(3,4-dicyanophenoxy)phenoxy]pyridazine (BCPD) with a low melting point (74 °C) and wide processing window (178 °C), was prepared by a nucleophilic substitution reaction. The molecular structure of the BCPD monomer was identified by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). Poly(BCPD) resins were derived from the formulations by curing at 350 and 370 °C. The thermoset that was post-cured at 370 °C demonstrated outstanding high heat-resistant (glass transition temperature (Tg) > 400 °C, 5% weight loss temperature (T5%) = 501 °C, Yc at 900 °C > 74%) and was flame-retardant (limiting oxygen index (LOI) = 48)). Further, the poly(BCPD) resin simultaneously exhibited a superior storage modulus, which could reach up to 3.8 Gpa at room temperature. Excellent processability and heat resistance were found for phthalonitrile thermosets containing the pyridazine ring, indicating poly(BCPD) resin could be potentially applied as high-temperature structural composite matrices.

Dechlorination of dichloromethane by a biofilter enriched with electroactive bacteria: Performance, kinetics, and microbial community.

Dichloromethane (DCM) is a recalcitrant volatile organic compound that exhibits biological toxicity and bioaccumulation. In this study, gaseous DCM was removed using an electroactive bacterial biofilter (EBB) with graphite rod as the anode and carbon felt as the cathode. The highest removal efficiency (97.09%) was achieved at a cathodic potential of -600 mV (vs. Ag/AgCl). The EBB had a maximum elimination capacity of 79.29 g m-3 h-1 when the inlet load was 96.48 g m-3 h-1. There was no substrate inhibition phenomenon observed in the EBB, and the Michaelis-Menten model was used to describe the kinetics of the EBB. High-throughput sequencing indicated that electroactive genera such as Rhodanobacter sp., Sphingomonas sp., Pseudomonas sp., Chryseobacterium sp., Pseudochrobactrum sp., and Mycobacterium sp. dominated the EBB. The microbial communities were stable and were slightly affected by the DCM inlet concentration. The results can be applied for the effective treatment of recalcitrant volatile organic compounds (VOCs).

Dispersion, olfactory effect, and health risks of VOCs and odors in a rural domestic waste transfer station.

The impact of odorous gases emitted from refuse transfer stations has always been a concern raised by the surrounding residents. The emitted volatile organic compounds (VOCs) and odors were investigated in a rural solid waste transfer station (RSWTS) located in Southwest China. A total of 70 VOCs were identified and quantified. The total VOCs (TVOCs) concentrations varied from 848.38 to 31193.24 µg/m3. Inorganic odor and greenhouse gases concentrations ranged from 39.11 to 470.14 µg/m3 and 1.03-525.42 µg/m3, respectively. Oxygenated compounds contributed the most (58.25%) to the VOCs. Among the oxygenated compounds, ketones, esters, and ethers were the dominant categories, accounting for 67.5%, 12.70%, and 11.85%, respectively. The key odorants included propionaldehyde, hexanaldehyde, propionic acid, acetaldehyde, and disopropyl ether. N-nitrosodiethylamine, acrylonitrile, and 1,3-Butadiene were the three main carcinogens that pose considerable risk to human health. Allyl chloride was the most non-carcinogenic pathogen among the VOCs detected in RSWTS. With diffusion in the downwind direction, the concentration of VOCs decreased gradually, and their risks weakened accordingly. At the sampling site of RSWTS-10, located 100 m away from RSWTS, acrylonitrile and 1,3-Butadiene still presented an unacceptable carcinogenic risk to human health. This study provides new data for assessing the emission characteristics, olfactory effects, and health risks of trace VOCs, especially those released from RSWTS.

Microbial aerosol particles in four seasons of sanitary landfill site: Molecular approaches, traceability and risk assessment.

Landfill sites are regarded as prominent sources of bioaerosols for the surrounding atmosphere. The present study focused on the emission of airborne bacteria and fungi in four seasons of a sanitary landfill site. The main species found in bioaerosols were assayed using high-throughput sequencing. The SourceTracker method was utilized to identify the sources of the bioaerosols present at the boundary of the landfill site. Furthermore, the health consequences of the exposure to bioaerosols were evaluated based on the average daily dose rates. Results showed that the concentrations of airborne bacteria in the operation area (OPA) and the leakage treatment area (LTA) were in the range of (4684 ± 477)-(10883 ± 1395) CFU/m3 and (3179 ± 453)-(9051 ± 738) CFU/m3, respectively. The average emission levels of fungal aerosols were 4026 CFU/m3 for OPA and 1295 CFU/m3 for LTA. The landfill site received the maximum bioaerosol load during summer and the minimum during winter. Approximately 41.39%- 86.24% of the airborne bacteria had a particle size of 1.1 to 4.7 µm, whereas 48.27%- 66.45% of the airborne fungi had a particle size of more than 4.7 µm. Bacillus sp., Brevibacillus sp., and Paenibacillus sp. were abundant in the bacterial population, whereas Penicillium sp. and Aspergillus sp. dominated the fungal population. Bioaerosols released from the working area and treatment of leachate were the two main sources that emerged in the surrounding air of the landfill site boundary. The exposure risks during summer and autumn were higher than those in spring and winter.

Characteristics of microbial aerosol particles dispersed downwind from rural sanitation facilities: Size distribution, source tracking and exposure risk.

Bioaerosols containing pathogens released from waste and wastewater treatment facilities pose potential health risks to workers on-site and residents downwind. In this study, sampling sites were set up at rural garbage stations (GS-1 and GS-2) and sewage treatment station (STS) to investigate the emission and diffusion characteristics of bioaerosols. High-throughput sequencing was utilized to assay the intestinal bacteria population, while the health risks associated with bioaerosols exposure were estimated based on average daily dose rates (DD). Traceability analysis was used to determine the percentages of intestinal bacteria from GS-1, GS-2 and STS. The recorded emission levels of bioaerosols in the air surrounding GS-1, GS-2, and STS were 5053, 6299, and 4795 CFU/m3, containing 1599, 2244, and 2233 CFU/m3 of intestinal bacteria, respectively. Most of the bioaerosols were coarse particles with size larger than 4.7 µm. Methylobacterium, Rhizobium, Pseudomonas, Enterobacteriaceae, and Brucella presented in the air were originally in rural waste and wastewater. STS and GS-2 were potential sources of intestinal bacteria. With increasing distance from the sources, the concentration of bioaerosols decreased gradually. On-site workers and residents were predominantly affected by bioaerosols through inhalation. The exposure risks via inhalation and skin contact for children were much higher than that for adults. The purpose of this study was to provide preliminary data for bioaerosols control and their risks reduction released from rural sanitation facilities.

Trace volatile compounds in the air of domestic waste landfill site: Identification, olfactory effect and cancer risk.

Landfill sites are regarded as sources of volatile compounds (VOCs) and odors emitted to the atmosphere. Surface emissions of VOCs and odors were investigated in a rural domestic waste landfill site located in southwest China. A total of 76 chemical compounds belonging to 3 chemical families were identified and quantified. The total number of VOCs (TVOC) detected ranged from 18.1 to 806.3 mg/m3, while odorous gases and greenhouse gases ranged from 0.4 to 21.2 and 0-100.5 mg/m3, respectively. High emissions were found in the air surrounding the leachate storage pool (LSP) and dumping area (DPA). The dominant species of VOCs were hexaldehyde, m-xylene, propylene oxide, acetophenone, and 2-butanone. The traceability analysis showed that the odors and VOCs diffused to the downwind boundary mainly came from the DPA and LSP. According to the olfactory effect analysis and cancer risk assessment, the main odor-causing gaseous pollutants were hydrogen sulfide, propionic acid, styrene, and 2-pentanone, while benzene, trichlorethylene, and 1,3-butadiene were the dominant carcinogens. This study provides new insights into the emission characteristics, olfactory effects, and cancer risks of VOCs and odors emitted from rural domestic solid waste landfill sites.

Comparison and application of biofilter and suspended bioreactor in removing gaseous o-xylene.

Two bioreactors, suspended-growth bioreactors (SPB) and biofilter (BF), were compared for the performances in removing gaseous o-xylene. Their efficiencies were investigated by varying the o-xylene loadings, gas flow rates, and gas-water ratios. High-throughput techniques were applied for the microbial populations assay. The conversion rate of carbon in o-xylene was calculated, and the relationship between biomass and removal efficiencies was also analyzed. Results indicated that both the SPB and BF could effectively treat gases containing o-xylene. The average removal efficiencies were 91.8% and 93.5%, respectively. The elimination capacity of the BF was much higher than that of the SPB when the intake load was below 150 g m-3 h-1. When the o-xylene loadings were over 150 g m-3 h-1, both the SPB and BF achieved similar o-xylene removal rates. The maximum elimination capacities were 28.36 g m-3 h-1 for the SPB and 30.67 g m-3 h-1 for BF. The SPB was more sensitive to the changes in the gas flow rate. Results of microbial assay indicated that bacteria e.g. Mycobacterium sp. and Rhodanobacter sp. might play important roles in removing o-xylene in the SPB, while the bacteria Pseudomonas sp., Sphingomonas sp., and Defluviicoccus sp., and the fungi Aspergillus sp. and Scedosporium sp., were the o-xylene degraders in the BF. The successful application of the integrated bioreactor in treating gases containing o-xylene exhausted from the electroplating plant indicated that the integration of SPB and BF could be an effective method for removing VOCs with Henry coefficient in the range of 0.01-1.

Effects of substrate fluctuation on the performance, microbial community and metabolic function of a biofilter for gaseous dichloromethane treatment.

Dichloromethane (DCM) is a harmful volatile organic compound that usually originates from pharmaceutical industry. In this study, the treatment of gaseous DCM in a biofilter was investigated by gradually increasing the DCM inlet concentration. Nearly 80% of DCM could be removed when the inlet concentration was lower than 0.30 g m-3. The maximum elimination capacity of 26.6 g m-3·h-1 was achieved at an inlet loading rate of 38.4 g m-3·h-1. However, with the increase in the inlet concentration to more than 0.60 g m-3, the removal efficiency obviously decreased to about 40%. After a starvation period of 2 weeks, the biofilter rapidly recovered its performance. The Haldane model including a substrate inhibition term was applied to describe the kinetics of the biofilter. High-throughput sequencing indicated that DCM-degrading genera, such as Rhodanobacter sp., Hyphomicrobium sp., Rhizomicrobium sp., Bacillus sp., Pseudomonas sp., and Clostridium sp., were dominant in the biofilter in different operation phases. The microbial communities and diversities were greatly affected by the DCM concentration. Microbial metabolic functions were predicted using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The results indicated that xenobiotics biodegradation and metabolism, carbohydrate metabolism, and amino acid metabolism were the three most abundant metabolic pathways of the microbes. The abundances of these metabolic functions were also altered by the DCM concentration.

Nanoarchitectonics Composites of Thermoplastic Starch and Montmorillonite Modified with Low Molecular Weight Polylactic Acid.

Nano montmorillonite (MMT) was modified by low molecular weight polylactic acid (PLA), then, the PLA modified MMT and raw MMT were added into thermoplastic starch (TPS) to prepare biodegradable nanocomposite films, respectively. For both nanocomposite films with raw MMT and modified MMT, the Tmax of degradation was enhanced and the mechanical properties were improved. The composite films containing 4 wt.% MMT displayed tensile strength of 5.06 MPa, approximately 1.4 times of that for the pure TPS films. The tensile strength of composite films containing 4 wt.% modified MMT is 6.74 MPa approximately 2 times of those for pure starch films. On the other hand, the composite film containing 4 wt.% modified MMT displayed elongation at break as high as 34.25%, which is 1.3 times of that of the pure starch film, while the composite films containing raw MMT had reduced elongation at break. This study showed that the MMT modified with PLA could significantly enhance the mechanical properties of TPS, and provides a new method to prepare fully biodegradable starch-based nanocomposites.

[Particle Size Distribution and Population Characteristics of Airborne Bacteria Emitted from a Sanitary Landfill Site].

Sanitary landfill is a commonly-used method for solid waste disposal. In the process of landfilling, e. g. dumping, stacking, pushing, and compacting, a large number of bioaerosols with pathogenic bacteria will be generated. That can result in air pollution and significant harm to human health if these pathogens are released into the air. Sampling sites were set up in a domestic waste sanitary landfill in North China to collect airborne bacteria in the air. Airborne bacteria, particle size distributions, and populations were analyzed, and the influence of meteorological parameters (temperature, relative humidity (RH), and wind speed (WS)) on the emission of airborne bacteria was also investigated. Results showed that the concentrations of airborne bacteria in the working area and the coverage area were (5437±572) CFU·m-3 and (2707±396) CFU·m-3, respectively. The emission level in the leachate treatment area was the highest, with an average of 9460 CFU·m-3. The concentration of airborne bacteria showed clear seasonal variation, being was much higher in summer than that in the other seasons. Redundancy analysis (RDA) demonstrated that RH, temperature, and WS affected the number of airborne bacteria in the air. The peaks in the airborne particle size distribution were 2.1-4.7 µm in the working area and 0.65-2.1 µm in the coverage area. Most of the airborne bacteria released from the leachate treatment processes were larger than 4.7 µm. Moraxellaceae, Bacillus aerius, Arcobacter, and Aeromonas were potential or opportunistic pathogens detected from the airborne bacteria samples. Effective measures should be taken to reduce the amount of bacterial aerosol emitted to the air in landfill working areas and in the leachate of treatment areas. Operators of landfill machinery and leachate treatment facilities should consider personal protection measures and should reduce their exposure to microbial aerosols in order to prevent disease.

The identification, health risks and olfactory effects assessment of VOCs released from the wastewater storage tank in a pesticide plant.

Wastewater generated during pesticide synthesis is a potential source of high concentrations of volatile organic compounds (VOCs) emissions, which would cause adverse effects on human health and the environment. Here, we provided a comprehensive study on concentrations, health risks, and olfactory effects of VOCs emitted from a pesticide wastewater storage tank. A total of 21 VOCs were identified, their concentrations ranged from 0.63 to 5023.83 µg/m3. Chlorinated compounds such as trichloroethylene (mean = 2581.29 µg/m3) and dichloromethane (mean = 2309.55 µg/m3) presented the highest concentrations. Both the cumulative chronic toxicities (514) and cancer risks (1.67 × 10-3) of VOCs were up to three orders of magnitude higher than the occupational safety limits. Trichloroethylene contributed the greatest to the cumulative chronic toxicities (88.41%) and cancer risks (74.91%). Benzene was another compound with a high cancer risk of 3.32 × 10-4. Regarding olfactory effects, triethylamine and diethylamine were the dominant contributors with a relative olfactory perception importance of 39.93% and 34.26%, respectively. The results of fuzzy synthetic evaluation revealed that benzene, diethylamine, trichloroethylene, dichloromethane, and triethylamine were the priority compounds caused the overall pollution levels, health risks, and olfactory effects.

Characteristics and formation mechanism of intestinal bacteria particles emitted from aerated wastewater treatment tanks.

Aeration tanks in municipal wastewater treatment plants (WWTPs) are regarded as sources of bioaerosols, often containing particles and microbes. In this study, intestinal bacteria were investigated from biochemical reaction tanks (BRTs) of six municipal WWTPs. It was observed that 86 CFU/m3 of intestinal bacteria (in average) occurred in the BRTs installed surface aerator, which was higher than those adopted submerged aeration (67 CFU/m3 in average). 62.72% of fine particles were observed in the BRTs supplied oxygen by submerged aerator, while 75.73% of coarse particles emitted during surface aeration. Pseudomonas sp., Serratia sp. and Acinetobacter sp. were identified as pathogenic bacteria presented in the intestinal bacteria population and most of them existed initially in water or sludge, particularly in water surface. The emission level and particle size distribution were significantly correlated with aeration mode adopted by the WWTPs. The bioaerosols particles emitted from surface aeration process was higher than that from submerged aeration process. Meanwhile, the BRTs with submerged aerators released more fine particles, which can get into the alveoli and represented the potential challenge to human health. Canonical correspondence analysis results exhibited that population of intestinal bacteria had a positive correlation with aeration rate and water quality. As the intestinal bacteria in the bioaerosols emitted from the WWTPs may pose a potential risk to onsite operators, aeration tanks in WWTPs should be paid more attention as a source of intestinal bacterial emissions.

Bioaerosols emission and exposure risk of a wastewater treatment plant with A2O treatment process.

The characteristics of bioaerosol emissions from wastewater treatment plants (WWTPs) have attracted extensive attention. The anaerobic-anoxic-oxic (A2O) process, which uses the activated sludge approach to wastewater treatment, is the most widely used process in WWTPs. Concentration, size distribution, population, and exposure risk from bacteria and fungi in bioaerosols of WWTPs using the A2O process were studied in this work. The results showed that the maximum concentration of airborne bacteria (1.00 × 104 Colony Forming Units per cubic meter (CFU m-3)) and fungi (1.44 ×104 CFU m-3) occurred from the facility's aerobic tank, in summer. As one of the main factors affecting bioaerosol exposure risk, particle size distribution was related to season. The study found that particles larger than 3.3 µm in diameter were detected mainly in spring and summer, while particles less than 3.3 µm were detected mainly in autumn and winter, whether bacterial aerosol or fungal aerosol. In addition, pathogenic bacteria were observed in bioaerosols from WWTPs, with 18 of the 65 species of bacteria detected found to be potentially or opportunistically pathogenic, such as Chryseobacterium, Stenotrophomonas, Alcaligenes, Micrococcus, Pantoea, Enterobacter and Escherichia-Shigella. The presence of these pathogens further increased the exposure risk from bioaerosols. The results of an inhalation risk assessment for airborne bacteria and fungi indicated that potential adverse health risks for adults mainly occurred in spring, summer, and autumn. On this basis, it was concluded that WWTP operators should set up effective bioaerosol controls as soon as possible to protect the health of workers, and of residents near the plant.

Airborne bacteria in a wastewater treatment plant: Emission characterization, source analysis and health risk assessment.

Wastewater treatment plants (WWTPs) are major sources of airborne bacteria, which could pose health risks to WWTP workers and surrounding residents. In this study, air samples were collected from various treatment facilities of a typical WWTP. Community compositions of airborne bacteria were identified by high-throughput sequencing technique. SourceTracker was used to determine the percentages of airborne bacteria from wastewater, sludge, ambient air, and other environment. Health risks associated with airborne bacteria were estimated based on the average daily dose rates (ADD) of exposure by inhalation and skin contact. Concentrations of airborne bacteria varied in a wide range of 23-4878 CFU/m3. The main emission sources of airborne bacteria were treatment facilities with aeration, mechanical agitation, and located indoors. For treatment facilities located indoors, higher percentages of airborne bacteria were associated with wastewater and sludge, while more airborne bacteria were originated from the ambient air for outdoor installations. Opportunistic pathogens such as Micrococcus, Bacteroides, Chryseobacterium, Pseudomonas, and Acinetobacter, were detected in airborne bacteria. Inhalation was the main pathway for on-site workers exposure to airborne bacteria. Due to the presence of opportunistic pathogens, strict control measures should be employed in WWTPs to reduce the infection risks.

Chemicals and microbes in bioaerosols from reaction tanks of six wastewater treatment plants: survival factors, generation sources, and mechanisms.

Sampling was conducted from biochemical reaction tanks of six municipal wastewater treatment plants in the Yangtze River and Zhujiang deltas and the Jing-Jin-Ji region to assess their morphology, level, and composition. Morphological observations suggested that particles were scattered amorphously with C, O, and Si as the major elements. Bioaerosols are composed of spatially varying levels of microorganisms and chemicals. As the sampling height increased, the level of the components in the bioaerosols decreased. Wastewater in the biochemical reaction tanks was identified as an important source of bioaerosols using SourceTracker analysis. The aerosolization of film drops produced by bursting of bubbles was the main reason for the generation of bioaerosols. Increasing the aeration rate of water may promote bioaerosol generation. Relative humidity, temperature, wind speed, and solar illumination influenced the survival of bioaerosols. Large particle sedimentation and wind diffusion significantly decreased the atmospheric aerosol concentration. When the sampling point height increased from 0.1 m to 3.0 m, the concentrations of the microorganisms and total suspended particles decreased by 23.71% and 38.74%, respectively. Considerable attention should be paid to the control of total suspended particles and microorganisms in bioaerosols.

Intestinal bacteria in bioaerosols and factors affecting their survival in two oxidation ditch process municipal wastewater treatment plants located in different regions.

Samples from two oxidation ditch process municipal wastewater treatment plants (MWTPs) (HJK and GXQ) in two regions of China were analysed for bacteria, particles, total organic carbon, and water-soluble ions in bioaerosols. Diversity and potential pathogen populations were evaluated by high-throughput sequencing. Bioaerosol sources, factors affecting intestinal bacterial survival, and the relationship between bioaerosols and water were analysed by Source tracker and partial least squares-discriminant, principal component, and canonical correspondence analyses. Culturable bacteria concentrations were 110-846 and 27-579 CFU/m3 at HJK and GXQ, respectively. Intestinal bacteria constituted 6-33% of bacteria. Biochemical reaction tank, sludge dewatering house (SDH), and fine screen samples showed the greatest contribution to bioaerosol contamination. Enterobacter aerogenes was the main intestinal bacteria (> 99.5%) in HJK and detected at each sampling site. Enterobacter aerogenes (98.67% in SDH), Aeromonas sp. (76.3% in biochemical reaction tank), and Acinetobacter baumannii (99.89% in fine screens) were the main intestinal bacteria in GXQ. Total suspended particulate masses in SDH were 229.46 and 141.6 µg/m3 in HJK and GXQ, respectively. Percentages of insoluble compounds in total suspended particulates decreased as height increased. The main soluble ions in bioaerosols were Ca2+, Na+, Cl-, and SO42-, which ranged from 3.8 to 27.55 µg/m3 in the MWTPs. Water was a main source of intestinal bacteria in bioaerosols from the MWTPs. Bioaerosols in HJK but not in GXQ were closely related. Relative humidity and some ions positively influenced intestinal bacteria in bioaerosols, while wind speed and solar illumination had a negative influence.

[Characteristics of Bioaerosols Emitted from WWTP with SBR Treatment Process].

Sampling sites were located in a wastewater treatment plant (WWTP) with a sequencing batch reactor activated sludge process to investigate the characteristics of bioaerosol emissions. The results indicated that bioaerosols were detected from each treatment section of the WWTP, and concentrations of bioaerosols were in the range of 82-1525 CFU·m-3. The coarse screen, aeration tank, and sludge dewatering house were the main sources of bioaerosols. The dominant species in each treatment section was Cyanobacteria, and the other main bacterial taxa were Aeromonas, Peptostreptococcaceae, Moraxellaceae, Chroococcidiopsis, Sphingomonas, Arcobacter, and Acinetobacter. Among the identified bacterial genera, Aeromonas, Arcobacter, Acinetobacter, and Sphingomonas were potential pathogens. Bioaerosol concentration and abundance decreased along the vertical and horizontal directions. Appropriate temperature and relative humidity benefited the survival of bioaerosols in the air (P<0.01), whereas a negative relationship between bioaerosol concentration and wind speed was observed (P<0.05). Although exposure risks caused by bioaerosols were negligible in this study, the accumulation of bioaerosols would increase potential health risks. The bioreactor for odor treatment could effectively reduce bioaerosol emissions.

Bacterial population and chemicals in bioaerosols from indoor environment: Sludge dewatering houses in nine municipal wastewater treatment plants.

Municipal wastewater treatment plants (MWTPs) are regarded as sources of airborne microorganisms. Sludge dewatering house (SDH) is one of the most serious indoor bioaerosol pollution treatment sectors in MWTPs. In this study, properties of bioaerosols from SDHs of nine MWTPs were investigated in China. Results suggested that bioaerosols were generated mainly from the mixed liquor and will be promoted by the mechanical motion of belts of dewatering devices. They will accumulate in the SDHs due to the treatment devices placed inside. Levels of airborne bacteria and chemicals showed regional variations. In Hefei and Yixing, the emissions of total suspended particles (TSP) and airborne bacteria were higher than those in Beijing and Guangzhou. Results of bacterial population showed that bacterial species in bioaerosols from SDHs also presented significant regional disparity; these regional disparities were closely related with the source of bioaerosols in SDHs. Among these identified bacterial species, some common potential pathogens were detected in all SDHs, such as Aeromonas caviae, Flavobacterium sp., and Staphylococcus lentus. Relative humidity (RH) and temperature were the major parameters on bioaerosols to survive. As shown in this study, SDHs in wastewater treatment plants should be provided considerable attention for being an emission source of indoor bioaerosols.

Operational aspects of SO2 removal and microbial population in an integrated-bioreactor with two bioreaction zones.

An integrated-bioreactor, which consisted of a suspended zone and an immobilized zone, was applied to treat gases containing SO2. The removal of SO2 in suspended zone differed slightly from that in immobilized zone. The influences of operational aspects such as SO2 load, temperature, and pH on integrated-bioreactor performance and bacterial community composition were investigated. The synergistic action of the two zones led to effective reduction of SO2, and the total removal efficiencies with the inlet concentration of 91-117 mg/m3, were over 85 % in steady state. Paenibacillus sp. and Lysinibacillus sp. dominated both zones as desulfurization bacteria. Results of polymerase chain reaction-denaturing gradient gel electrophoresis followed by clone library analysis indicated that temporal shifts in bacterial community composition in both zones developed differently. Differences in the concentration of introduced SO2 and supported mode of microorganisms for survival, confirmed that bacterial community composition and abundance significantly differed among individual zones.