Quantification and Analysis of Airborne Bacterial Characteristics in a Nursing Care Institution

ABSTRACT

Indoor air quality has become a critical issue because people spend most of their time in the indoor environment. The factors that influence indoor air quality are very important to environmental sanitation and air quality improvement. This study focuses on monitoring air quality, colony counts, and bacteria species of the indoor air of a nursing care institution. The regular colony counts in two different wards range from 55 to 600 cfu m^?3. Regression analysis results indicate that the bacterial colony counts have close correlation with relative humidity or carbon dioxide (CO₂) but not with carbon monoxide (CO) or ozone (O₃). Real-time PCR was used to quantify the bacterial pathogens of nosocomial infection, including Acinetobacter baumannii, Citrobacter freundii, Escherichia coli, Klebsiella pneumoniae, and methicillin-sensitive Staphylococcus aureus. The most abundant bacteria species in the air of the nursing care institution is E. coli.

IMPLICATIONS Indoor temperature, humidity, ventilation, accumulation of biological pollutants, and potential infection problems will seriously affect the indoor environments. Studying these factors is important to indoor environmental sanitation and air quality improvements. Results of using real-time PCR to evaluate the bacterial pathogens of nosocomial infection for a nursing care institution in Taiwan reveal that the main bacteria species existing in the indoor air is E. coli.     

Indoor and outdoor air quality investigation at schools in Hong Kong

Five classrooms in Hong Kong (HK), air-conditioned or ceiling fans ventilated, were chosen for investigation of indoor and outdoor air quality. Parameters such as temperature, relative humidity (RH), carbon dioxide (CO2), sulphur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), respirable particulate matter (PM10), formaldehyde (HCHO), and total bacteria counts were monitored indoors and outdoors simultaneously. The average respirable particulate matter concentrations were higher than the HK Objective, and the maximum indoor PM10 level exceeded 1000 microg/m3. Indoor CO2 concentrations often exceeded 1000 microl/l in air-conditioning and ceiling fan classrooms, indicating inadequate ventilation. Maximum indoor CO2 level reached 5900 microl/l during class at the classroom with cooling tower ventilation. Increasing the rate of ventilation or implementation of breaks between classes is recommended to alleviate the high CO2 level. Other pollution parameters measured in this study complied with the standards. The two most important classroom air quality problems in Hong Kong were PM10 and CO2 levels.     

Investigation of the concentration of bacteria and their cell envelope components in indoor air in two elementary schools

Bacterial cell envelope components are widely distributed in airborne dust, where they act as inflammatory agents causing respiratory symptoms. Measurements of these agents and other environmental factors are assessed in two elementary schools in a southeastern city in the United States. Muramic acid (MA) was used as a marker for bacterial peptidoglycan (PG), and 3-hydroxy fatty acids (3-OH FAs) were used as markers for Gram-negative bacterial lipopolysaccharide (LPS). Culturable bacteria were collected using an Andersen sampler with three different culture media. In addition, temperature (T), relative humidity (RH), and CO2 were continuously monitored. Concentrations of airborne MA and 3-OH FAs were correlated with total suspended particulate (TSP) levels. Outdoor MA (mean = 0.78-1.15 ng/m3) and 3-OH FA levels (mean = 2.19-2.18 ng/m3) were similar at the two schools. Indoor concentrations of airborne MA and 3-OH FAs differed significantly between schools (MA: 1.44 vs. 2.84 ng/m3; 3-OH FAs: 2.96 vs. 4.57 ng/m3). Although indoor MA levels were low, they were significantly related to teachers' perception of the severity of indoor air quality (IAQ) problems in their classrooms. Concentrations of CO2 correlated significantly with all bacteria measurements. Because CO2 levels were related to the number of occupants and the ventilation rates, these findings are consistent with the hypothesis that the children and teachers are sources of bacterial contamination. Many culturable bacteria present in indoor air are opportunistic organisms that can be infectious for compromised individuals, while both culturable and nonculturable bacterial remnants act as environmental toxins for both healthy and compromised individuals. Measuring the "total bacteria load" would be most accurate in assessing the biotoxicity of indoor air. Chemical analysis of MA and 3-OH FAs, when coupled with the conventional culture method, provides complementary information for assessing biocontamination of indoor air.     

Improving the indoor air quality of respiratory type of medical facility by zeolite filtering

This study investigated the indoor air quality (IAQ) conditions of carbon dioxide (CO₂), carbon monoxide (CO), ozone (O₃), formaldehyde (HCHO), total volatile organic compounds (TVOCs), and bio-aerosols (bacteria and fungi) in a respiratory type of medical facility in Chia-Yi County in southern Taiwan. Among those IAQ conditions, the concentrations of CO, O₃, and HCHO exceeded the regulation values of the Taiwan Environmental Protection Administration (EPA) mostly in the morning. The concentrations of bacteria and fungi did not exceed the regulation values but still posed potential health and environment problems for workers, patients, and visitors. Therefore, self-made silver-coated zeolite (AgZ) was used as a filter material in air cleaners to remove bio-aerosols in the respiratory care ward (RCW), and the removals were still effective after 120 hr. The cumulative bio-aerosol removals for bacteria and fungi were 900 and 1,088 colony-forming units (CFU) g^?1 after 24 hr and were above 3,100 and 2,700 CFU g^?1 after 120 hr. From the research results, it is suggested that AgZ filtering could be used as a feasible engineering measure for hospitals to control their bacteria and fungi parameters in IAQ management. Hospitals should maintain their environmental management and monitoring programs and use different engineering measures to improve different IAQ parameters.

Implications: This study investigated the IAQ conditions in the field at a hospital in Chia-Yi County in southern Taiwan. Although concentrations of most parameters were still within the regulation values, the concentrations of CO, O₃, and HCHO were partially exceeded. We propose a method using an air cleaner with silver-coated zeolite (AgZ) as a possible engineering measure, and there were effective reductions of bacteria and fungi to lower levels with antibacterial effects after 120 hr. Furthermore, this study implies that hospitals should continuously maintain environmental monitoring programs and adopt optimal engineering measures for different needs.     

Simultaneous monitoring of SARS-CoV-2, bacteria,and fungi in indoor air of hospital: a study on Hajar Hospital in Shahrekord,Iran

The novel SARS-CoV-2 outbreak was declared as pandemic by the World Health Organization (WHO) on March 11, 2020. Understanding the airborne route of SARS-CoV-2 transmission is essential for infection prevention and control. In this study, a total of 107 indoor air samples (45 SARS-CoV-2, 62 bacteria, and fungi) were collected from different wards of the Hajar Hospital in Shahrekord, Iran. Simultaneously, bacterial and fungal samples were also collected from the ambient air of hospital yard. Overall, 6 positive air samples were detected in the infectious 1 and infectious 2 wards, intensive care unit (ICU), computed tomography (CT) scan, respiratory patients’ clinic, and personal protective equipment (PPE) room. Also, airborne bacteria and fungi were simultaneously detected in the various wards of the hospital with concentrations ranging from 14 to 106 CFU m^?3 and 18 to 141 CFU m^?3, respectively. The highest mean concentrations of bacteria and fungi were observed in respiratory patients’ clinics and ICU wards, respectively. Significant correlation (p < 0.05) was found between airborne bacterial concentration and the presence of SARS-CoV-2, while no significant correlation was found between fungi concentration and the virus presence. This study provided an additional evidence about the presence of SARS-CoV-2 in the indoor air of a hospital that admitted COVID-19 patients. Moreover, it was revealed that the monitoring of microbial quality of indoor air in such hospitals is very important, especially during the COVID-19 pandemic, for controlling the nosocomial infections.

     

Characterization of Air Quality Problems in Five Finnish Indoor Ice Arenas

ABSTRACT

The air quality in five Finnish ice arenas with different volumes, ventilation systems, and resurfacer power sources (propane, gasoline, electric) was monitored during a usual training evening and a standardized, simulated ice hockey game. The measurements included continuous recording of carbon monoxide (CO), nitric oxide (NO), and nitrogen dioxide (NO₂) concentrations, and sampling and analysis of volatile organic compounds (VOCs). Emissions from the ice resurfacers with combustion engines caused indoor air quality problems in all ice arenas. The highest 1-hour average CO and NO₂ concentrations ranged from 20 to 33 mg/m³ (17 to 29 ppm) and 270 to 7440 µg/m³ (0.14 to 3.96 ppm), respectively. The 3-hour total VOC concentrations ranged from 150 to 1200 µg/m³. The highest CO and VOC levels were measured in the arena in which a gasoline-fueled resurfacer was used. The highest NO₂ levels were measured in small ice arenas with propane-fueled ice resurfacers and insufficient ventilation.

In these arenas, the indoor NO₂ levels were about 100 times the levels measured in ambient outdoor air, and the highest 1-hour concentrations were about 20 times the national and World Health Organization (WHO) health-based air quality guidelines. The air quality was fully acceptable only in the arena with an electric resurfacer. The present study showed that the air quality problems of indoor ice arenas may vary with the fuel type of resurfacer and the volume and ventilation of arena building. It also confirmed that there are severe air quality problems in Finnish ice arenas similar to those previously described in North America.     

Size and seasonal distributions of airborne bioaerosols in commuting trains

Aerobiological studies in commuting trains in northern Taiwan were carried out from August, 2007 until July, 2008. Two six-stage (>7 μm, 4.7～7 μm, 3.3～4.7 μm, 2.1～3.3 μm, 1.1～2.1 μm, 0.65～1.1 μm) cascade impactors of 400 orifices were used to collect viable bacteria and fungi, respectively. The levels of carbon monoxide (CO), carbon dioxide (CO₂), formaldehyde (HCHO), temperature, and relative humidity in the commuting trains were also recorded during the sampling period. Results show that bacterial concentrations ranged from 25 to 1530 CFU m^?3, and averaged 417 CFU m^?3. The fungal concentrations ranged from 45 to 1906 CFU m^?3, and averaged 413 CFU m^?3. Additionally, the highest fractions occurred in the fifth stage (1.1～2.1 μm) for both bacteria and fungi. The respirable fractions, R_b and R_f, for bacteria and fungi were 62.8% and 81.4%, respectively, which are higher than those in other studies. Furthermore, the bacterial concentration reached its highest level in autumn, and its lowest level in winter. However, the fungal concentration was highest in spring and lowest in winter. Though the total bacterial or fungal concentration did not exceed the recommendation standard in Taiwan, the relatively high respirable fraction in commuting trains probably implies a higher adverse health risk for sensitive commuters. This study further conducted multiple regression analysis to determine the relationship of various stage fractions of airborne bacteria and fungi with indoor air pollutants (CO and HCHO) and environmental parameters (CO₂, temperature, and relative humidity). The correlation coefficients of multiple regression analysis for total bacteria and fungi concentrations with indoor air pollutants and environmental parameters were 0.707 (p < 0.00376) and 0.612 (p < 0.00471), respectively. There are currently no formally regulated laws for indoor air quality (IAQ) in Taiwan, and this preliminary study can provide references to the Taiwan government on IAQ management.     

Photocatalytic elimination of indoor air biological and chemical pollution in realistic conditions

The photocatalytic elimination of microorganisms from indoor air in realistic conditions and the feasibility of simultaneous elimination of chemical contaminants have been studied at laboratory scale. Transparent polymeric monoliths have been coated with sol-gel TiO(2) films and used as photocatalyst to treat real indoor air in a laboratory-scale single-step annular photocatalytic reactor. The analytical techniques used to characterize the air quality and analyze the results of the photocatalytic tests were: colony counting, microscopy and PCR with subsequent sequencing for microbial quantification and identification; automated thermal desorption coupled to gas chromatography with mass spectrometry detection for chemical analysis. The first experiments performed proved that photocatalysis based on UVA-irradiated TiO(2) for the reduction of the concentration of bacteria in the air could compete with the conventional photolytic treatment with UVC radiation, more expensive and hazardous. Simultaneously to the disinfection, the concentration of volatile organic compounds was greatly reduced, which adds value to this technology for real applications. The fungal colony number was not apparently modified.     

Air Quality Monitoring During Construction and Initial Occupation of a New Building

Air quality monitoring was conducted during the late construction and early occupation stages of the College of DuPage Student Resource Center (SRC) addition from April 24,1995, to July 20,1995. Chemical contaminants monitored included combustibles; cleaning solvents; and human, furniture, and carpeting effluents. Carbon dioxide, carbon monoxide, ethanol, propane, 3-pentanone, methyl cyclohexane, methyl formate, tetrahydrofuran, methyl methacrylate, and cyclohexane were used as calibration standards for continuous infrared absorption measurements. Indoor water content, outdoor relative humidity, indoor and outdoor temperatures, and indoor airborne particulate matter were measured. After most construction and indoor painting and carpeting were completed, a two-week air-out was performed using a continuous supply of fresh air, without recirculated air. This resulted in a low "case study" level of contaminants. Contaminant levels increased significantly after furniture and people move-ins and student use. Contaminant level changes were observed during typical indoor construction days, before and after a power outage-caused loss of ventilation, and in the presence of carpentry machines. A "naive" sensory panel contributed its "perception" of air quality, and anair quality survey was conducted among new building employees. No significant or consistent effects of indoor contaminants or indoor temperature upon indoor perception were noted. An inverse relationship between indoor air quality perceptions and the outdoor Temperature-Humidity Index was found.     

Effects of ceiling-mounted HEPA-UV air filters on airborne bacteria concentrations in an indoor therapy pool building

The purpose of this study was to assess the effectiveness of a new generation of high-volume, ceiling-mounted high-efficiency particulate air (HEPA)-ultraviolet (UV) air filters (HUVAFs) for their ability to remove or inactivate bacterial aerosol. In an environmentally controlled full-scale laboratory chamber (87 m3), and an indoor therapy pool building, the mitigation ability of air filters was assessed by comparing concentrations of total bacteria, culturable bacteria, and airborne endotoxin with and without the air filters operating under otherwise similar conditions. Controlled chamber tests with pure cultures of aerosolized Mycobacterium parafortuitum cells showed that the HUVAF unit tested provided an equivalent air-exchange rate of 11 hr(-1). Using this equivalent air-exchange rate as a design basis, three HUVAFs were installed in an indoor therapy pool building for bioaerosol mitigation, and their effectiveness was studied over a 2-year period. The HUVAFs reduced concentrations of culturable bacteria by 69 and 80% during monitoring periods executed in respective years. The HUVAFs reduced concentrations of total bacteria by 12 and 76% during the same monitoring period, respectively. Airborne endotoxin concentrations were not affected by the HUVAF operation.     

Indoor and outdoor bioaerosol levels at recreation facilities, elementary schools, and homes

One major deficiency in linking environmental exposure to health effects is the current lack of data on environmental exposure. Therefore, to address this issue, the present study measured the bacterial and fungal concentrations in the indoor and outdoor air from two types of recreation facility (42 bars and 41 Internet cafes), 44 classrooms at 11 elementary schools, and 20 homes under uncontrolled environmental conditions during both summer and winter. No major environmental problems were reported at the four microenvironments being investigated during the entire study period. Bacteria and fungi were found in all the air samples, and the environmental occurrence of individual fungi was in the order of Cladosprium, Penicillium, Aspergillus, and Alternaria. The six parameters surveyed in the present study were all found to influence the indoor and outdoor bioaerosol levels: microenvironment type, sampling time in elementary school classrooms, agar type for measuring the fungal species, seasonal variation, facility location, and summer survey periods. The indoor and outdoor air concentrations of bacteria and fungi found in this study were comparable to those in other reports, with GM values for the total bacteria and total fungi between 10 and 10³ colony-forming units per cubic meter of air (CFU m⁻³). The fungal concentrations found at most of the indoor environments fell within the specified guidelines of the American Conference of Government Industrial Hygienists (ACGIH), between 100 and 1000 CFU m⁻³ for the total fungi. However, the indoor bioaerosol concentrations at most of the surveyed environments exceeded the Korean indoor bioaerosol guideline (800 CFU m⁻³). Consequently, the current findings suggest the need for reducing strategy for indoor microorganisms at the surveyed microenvironments.     

Probabilistic assessment of the potential indoor air impacts of vent-free gas heating appliances in energy-efficient homes in the United States

Use of vent-free gas heating appliances for supplemental heating in U.S. homes is increasing. However, there is currently a lack of information on the potential impact of these appliances on indoor air quality for homes constructed according to energy-efficient and green building standards. A probabilistic analysis was conducted to estimate the impact of vent-free gas heating appliances on indoor air concentrations of carbon monoxide (CO), nitrogen dioxide (NO₂), carbon dioxide (CO₂), water vapor, and oxygen in “tight” energy-efficient homes in the United States. A total of 20,000 simulations were conducted for each Department of Energy (DOE) heating region to capture a wide range of home sizes, appliance features, and conditions, by varying a number of parameters, e.g., room volume, house volume, outdoor humidity, air exchange rates, appliance input rates (Btu/hr), and house heat loss factors. Predicted airborne levels of CO were below the U.S. Environmental Protection Agency (EPA) standard of 9 ppm for all modeled cases. The airborne concentrations of NO₂ were below the U.S. Consumer Product Safety Commission (CPSC) guideline of 0.3 ppm and the Health Canada benchmark of 0.25 ppm in all cases and were below the World Health Organization (WHO) standard of 0.11 ppm in 99–100% of all cases. Predicted levels of CO₂ were below the Health Canada standard of 3500 ppm for all simulated cases. Oxygen levels in the room of vent-free heating appliance use were not significantly reduced. The great majority of cases in all DOE regions were associated with relative humidity (RH) levels from all indoor water vapor sources that were less than the EPA-recommended 70% RH maximum to avoid active mold and mildew growth. The conclusion of this investigation is that when installed in accordance with the manufacturer’s instructions, vent-free gas heating appliances maintain acceptable indoor air quality in tight energy-efficient homes, as defined by the standards referenced in this report.

Implications: Probabilistic modeling of indoor air concentrations of carbon monoxide (CO), nitrogen dioxide (NO₂), carbon dioxide (CO₂), water vapor, and oxygen associated with use of vent-free gas heating appliances provides new data indicating that uses of these devices are consistent with acceptable indoor air quality in “tight” energy-efficient homes in the United States. This study will provide authoritative bodies such as the International Code Council with definitive information that will assist in the development of future versions of national building codes, and will provide evaluation of the performance of unvented gas heating products in energy conservation homes.     

Inter-comparison of air pollutant concentrations in different indoor environments in Hong Kong

Indoor air quality in selected indoor environments in Hong Kong such as homes, offices, schools, shopping malls and restaurants were investigated. Average CO₂ levels and total bacteria counts in air-conditioned classrooms, shopping malls and restaurants were comparatively higher than those measured in occupied offices and homes. Elevated CO₂ levels exceeding 1000 ppm and total bacteria counts resulted from high occupancy combined with inadequate ventilation. Average PM₁₀ levels were usually higher indoors than outdoors in homes, shopping malls and restaurants. The highest indoor PM₁₀ levels were observed at investigated restaurants due to the presence of cigarette smoking and extensive use of gas stoves for cooking. The restaurants and shopping malls investigated had higher formaldehyde levels than other indoor environments when building material, smoking and internal renovation work were present. Volatile organic compounds (VOCs) in both indoor and outdoor environments mainly resulted from vehicle exhaust emissions. It was observed that interior decoration work and the use of industrial solvents in an indoor environment could significantly increase the indoor levels of VOCs.     

Assessment of airborne environmental bacteria and related factors in 25 underground railway stations in Seoul,Korea

This study assessed bacterial concentrations in indoor air at 25 underground railway stations in Seoul, Korea, and investigated various related factors including the presence of platform screen doors (PSD), depth of the station, year of construction, temperature, relative humidity, and number of passengers. A total of 72 aerosol samples were collected from all the stations. Concentrations of total airborne bacteria (TAB) ranged from not detected (ND) to 4997 CFU m^?3, with an overall geometric mean (GM) of 191 CFU m^?3. Airborne bacteria were detected at 23 stations (92%) and Gram-negative bacteria (GNB) were detected at two stations (8%). TAB concentrations of four stations (16%) exceeded 800 CFU m^?3, the Korea indoor bio-aerosol guideline. The results of the study showed that TAB concentrations at the stations without PSD showed higher TAB concentrations than those with PSD, though not at statistically significant levels. TAB concentrations of deeper stations revealed significantly higher levels than those of shallower stations. Based on this study, it is recommended that mitigation measures be applied to improve the indoor air quality (IAQ) of underground railway stations in Seoul, with focused attention on deeper stations.     

Improvement of Air Quality in a Small Indoor Ice Arena by Effective Emission Control in Ice Resurfacers

ABSTRACT

The effectiveness of a new emission control system in the ice resurfacer was tested in an exhaust gas emission laboratory, and the improvement of the air quality in a small, enclosed ice arena was demonstrated in a 4.5-month follow-up study. The emission control system consisted of a lambda sensor-controlled fuel supply and a three-way metallic catalyst that were applied to a propane-fueled resurfacer. In the laboratory tests, the engine emissions of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO ) reduced simultaneously by 91, 90, and 96%, respectively. During the air quality follow-up the median 1-hour average nitrogen dioxide (N0₂) concentration inside the ice arena decreased from 430 ug/m³ (230ppb) to 58 ug/m³ (31 ppb), and that of CO decreased from 4.4 mg/m³ (3.8 ppm) to 1.5 mg/m³ (1.3 ppm). The new emission control system proved to be a feasible, reliable, and effective means to improve the indoor air quality in the ice arena. However, continuous mechanical ventilation was necessary during all business hours in order to achieve and maintain a fully acceptable air quality with this technology.     

Analytical solutions to compartmental indoor air quality models with application to environmental tobacco smoke concentrations measured in a house

This paper derives the analytical solutions to multi-compartment indoor air quality models for predicting indoor air pollutant concentrations in the home and evaluates the solutions using experimental measurements in the rooms of a single-story residence. The model uses Laplace transform methods to solve the mass balance equations for two interconnected compartments, obtaining analytical solutions that can be applied without a computer. Environmental tobacco smoke (ETS) sources such as the cigarette typically emit pollutants for relatively short times (7-11 min) and are represented mathematically by a "rectangular" source emission time function, or approximated by a short-duration source called an "impulse" time function. Other time-varying indoor sources also can be represented by Laplace transforms. The two-compartment model is more complicated than the single-compartment model and has more parameters, including the cigarette or combustion source emission rate as a function of time, room volumes, compartmental air change rates, and interzonal air flow factors expressed as dimensionless ratios. This paper provides analytical solutions for the impulse, step (Heaviside), and rectangular source emission time functions. It evaluates the indoor model in an unoccupied two-bedroom home using cigars and cigarettes as sources with continuous measurements of carbon monoxide (CO), respirable suspended particles (RSP), and particulate polycyclic aromatic hydrocarbons (PPAH). Fine particle mass concentrations (RSP or PM3.5) are measured using real-time monitors. In our experiments, simultaneous measurements of concentrations at three heights in a bedroom confirm an important assumption of the model-spatial uniformity of mixing. The parameter values of the two-compartment model were obtained using a "grid search" optimization method, and the predicted solutions agreed well with the measured concentration time series in the rooms of the home. The door and window positions in each room had considerable effect on the pollutant concentrations observed in the home. Because of the small volumes and low air change rates of most homes, indoor pollutant concentrations from smoking activity in a home can be very high and can persist at measurable levels indoors for many hours.     

Effects of Ceiling-Mounted HEPA-UV Air Filters on Airborne Bacteria Concentrations in an Indoor Therapy Pool Building

Abstract

The purpose of this study was to assess the effectiveness of a new generation of high-volume, ceiling-mounted high-efficiency particulate air (HEPA)-ultraviolet (UV) air filters (HUVAFs) for their ability to remove or inactivate bacterial aerosol. In an environmentally controlled full-scale laboratory chamber (87 m³), and an indoor therapy pool building, the mitigation ability of air filters was assessed by comparing concentrations of total bacteria, culturable bacteria, and airborne endotoxin with and without the air filters operating under otherwise similar conditions. Controlled chamber tests with pure cultures of aerosolized Mycobacterium parafortuitum cells showed that the HUVAF unit tested provided an equivalent air-exchange rate of 11 hr^?1. Using this equivalent air-exchange rate as a design basis, three HUVAFs were installed in an indoor therapy pool building for bioaerosol mitigation, and their effectiveness was studied over a 2-year period. The HUVAFs reduced concentrations of culturable bacteria by 69 and 80% during monitoring periods executed in respective years. The HUVAFs reduced concentrations of total bacteria by 12 and 76% during the same monitoring period, respectively. Airborne endotoxin concentrations were not affected by the HUVAF operation.     

Comparison of indoor and outdoor concentrations of CO at a public school. Evaluation of an indoor air quality model

A field study was carried out to investigate the internal and external carbon monoxide (CO) concentration levels of a public school building in Athens, Greece. Simultaneous measurements of indoor and outdoor CO concentrations were conducted using a non-dispersive infrared analyzer. Measurements of mean hourly CO concentrations inside and outside the sampling room were conducted on a 24-h basis for 13 consecutive days during May and June 1999 and for 14 consecutive days during December 1999. The aim of the study was to investigate the attenuation pattern of external pollution levels within the building. The diurnal concentration variations reported for different days during the week show that indoor CO concentrations are in general lower than the respective outdoor levels, and that the morning peaks of indoor concentrations show a delay of 1 h or less compared to the morning peaks of outdoor concentrations. The measured indoor to outdoor concentration ratios show a seasonal variation. An indoor air quality model for the prediction of indoor concentration levels developed by Hayes (J. Air Pollut. Control Assoc. 39 (11) (1989) 1453; J. Air Waste Manage. Assoc. 41 (2) (1991) 161) is coded as a computer program and evaluated using the experimental data. The model results are in good agreement with the indoor concentration measurements, although in some cases the model cannot respond adequately to sharp outdoor concentration changes. The ratio between measured and predicted daily maximum indoor concentration ranges between 0.88 and 1.23. The regression curve between predicted by the model and measured hourly indoor concentrations, for a continuous period of 96 h, has a slope of 0.64 and a coefficient of determination (R²) of 0.69.     

Analysis of microbiological characteristics of wastewater along the polishing sequence of a treatment plant.

Microbial populations were studied by plate counts and flow cytometry along the polishing sequence of a wastewater plant. The comparison between plate count and flow cytometry showed comparable trends, but plate counts detected less than 10% of the total intact bacteria counted by flow cytometry. Six months monitoring showed that, in spite of the high ozone doses, the disinfection effect of ozonation was insignificant. This is in agreement with the variability of ozone demand, not only related to chemical oxygen demand or total suspended solids. Membrane-intact bacterial population decreased after ozonation, slightly regrew between ozone and biological activated carbon (BAC), and sharply increased after BAC, probably for damaged bacteria regrowth and saprophytes release; BAC effluent had the highest bacterial counts. Preliminary investigations on the effluent microbial composition showed that the beta Proteobacteria subclass is the most represented in the BAC effluent, whereas the alpha subclass is the most sensitive to ozone effect.     

岩溶水系统中微生物迁移机制

对桂林罗锦响水岩岩溶水系统雨前、雨中和雨后水中及悬浮物上携带的细菌数量变化规律分析表明,在雨期,岩溶地下河水质变化对地表水质响应迅速,表现为在一定时期内地下水与地表水中的细菌总数可达到同一个数量级;地下水中TSS与细菌总数的变化具有一致性,即细菌总数随TSS的升降而升降,说明细菌大多是附着在悬浮颗粒物运移的;同时,岩溶区地下河局部存在的溶潭等蓄水构造对污染物具有明显的纳污与稀释效应,是岩溶地下河系统产生自净作用的主要场所。TSS与地下水流速呈正相关,而附着在悬浮颗粒物上的细菌占地下水中细菌总数的比例与流速呈负相关。地下河洞口的堆积物对微生物具有明显的截留作用,其对微生物的吸附和缓慢释放,是导致地下河在很长一段时间内都会受到微生物污染的主要原因。