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

Diffusion behavior and transport risk of bioaerosol particles in a domestic waste landfill site in an arid and cold region of northwestern China

Bioaerosols have attracted increasing attention as novel contaminants because of their potential role in the spread of disease. In this study, sampling sites were established in a landfill in northwestern China with the aim of investigating the emission and diffusion characteristics of bioaerosols. The results revealed that the counts of airborne bacteria released by landfill cover area (LCA) and waste dumping area (WDA) located in the landfill area reached 18 193 ± 30 CFU/m3 and 10 948 ± 105 CFU/m3, respectively. These two aeras were the main sources of bioaerosol generation. Meanwhile, Corynebacterium spp., Bacteroidetes spp., and Pseudomonas spp. were identified as potential pathogens. A Gaussian model was applied to simulate the diffusion of the bioaerosols; the influence distance was calculated as 12 km from the boundary of the landfill site. The potential health risks of bioaerosol exposure to on-site workers and nearby residents were calculated and evaluated in terms of aerosol concentration, particle size, and pathogenic bacteria. The present study promotes the recognition of the emission behavior of microorganisms in aerosol particles and provides a basis for controlling bioaerosol contamination from landfill sites, particularly those located in cold and arid northwestern regions of China.

Bioaerosol emission and exposure risk from a wastewater treatment plant in winter and spring

The potential health risks posed by bioaerosols containing pathogens originating from wastewater treatment plants (WWTPs) have gaining intensive attention. This study designated sampling locations within a WWTP situated in Xi'an, a major city in northwest China. The airborne bacterial concentration, taxonomic composition, and the associated health risks were analyzed in the aeration tanks with bottom microporous aeration system. The Anaerobic-Anoxic-Oxic (AAO) tank emitted significantly higher culturable bacteria (1.58×104 CFU m-3 in spring, 6.69×103 CFU m-3 in winter) compared to Double-ditch (DE) oxidation ditch and aerated grit chamber (AGC) chamber, aligning with 16S rDNA quantification results. The bacterial concentrations are higher in spring than that in winter, with the AAO tank posing the highest exposure risk during the spring season. The dominant genera in the air samples include Cutibacterium, Lawsonella, Acinetobacter, Pseudomonas, and Aeromonas. Among the identified genus, 139 bacterial genera were identified as potential human pathogens like Neisseria, Moraxella, Haemophilus, Escherichia-Shigella and Streptococcus. These pathogens further elevate exposure risks from WWTP bioaerosols. This study provides relevant information on the seasonal health risk variations tied to bioaerosol emissions from diverse aeration tanks with bottom microporous aeration system in the mega city of northwest China, emphasizing the imperative to enhance the management and control measures for bioaerosols originating from the AAO tank.

Bioaerosols emission from source facilities in a wastewater treatment plant: Critical exposure time and sensitivity analysis

Overexposure of sewage workers to bioaerosol released from wastewater treatment plants (WWTPs) can cause serious infections, but practical method for controlling their health risk is lacking. In this study, reverse quantitative microbial risk assessment was used to estimate the daily critical exposure time (CET) of sewage workers exposing to Staphylococcus aureus bioaerosol emitted by three emission sources facilities in a WWTP based on either U.S. EPA or WHO benchmark, and sensitivity analysis was conducted to analyze the influence of various parameters on the outcomes of CET. The results showed that the CET of females was always 1.12-1.29 times that of males. In addition, the CET after wearing face masks was 28.28-52.37 times as long as before. The working time can be determined based on the CET results of male workers wearing face masks exposed to the inverted-umbrella aeration tank (14.73-550.98 min for U.S. EPA benchmark and 55.07-1972.24 min for WHO benchmark). In each scenario, the variable parameter exposure concentration (ec) always showed the most influence on the CET results. After wearing the face masks, the removal fraction by employing face masks also had a significant effect on the results, only second to ec. Therefore, the wearing of face mask is the most convenient and effective measure to prolong the CET. Furthermore, practical methods to reducing bioaerosol concentration in WWTPs exposure are also necessary to extend CET and safeguard worker health. This study enriches the application range of reverse quantitative microbial risk assessment framework and provides theoretical support for stakeholders to establish reasonable working time threshold guidelines, and practical method and novel perspective to protect the on-site health risks of sewage workers exposing to various facilities.

Emission Characteristics of Aerosols Generated during the Micro-Nano Bubble Aeration Process in Wastewater

Micro-nano bubble (MNB) aeration is an emerging technology that considerably enhances the aeration efficiency of wastewater. This study evaluates, for the first time, aerosolization at the water-air interface during MNB aeration. Our results show that the concentration of culturable mixed microorganisms (i.e., bacteria, fungi, and intestinal bacteria) in the in situ MNB generation (MNBs-G) phase is 2170 CFU/m3, 1.38 and 1.58-fold higher than those in medium-bubble aeration (MBA; 1568 CFU/m3) and small-bubble aeration (SBA; 1376 CFU/m3) aerosols, respectively. Conversely, the concentration of culturable mixed microorganisms in the MNB persistent dissolved oxygen (MNBs-O) phase is only 914 CFU/m3. Microbiological analysis shows a lower abundance of bacterial pathogens in MNBs-G (34.12%) and MNBs-O (34.02%) phases than in MBA (39.63%) and SBA (38.87%) aerosols. Acinetobacter is prevalent in MNBs-G (14.76%) and MNBs-O (8.22%) aerosols, whereas Bacillus and Arcobacter are prevalent in MBA (23.96%) and SBA (6.92%) aerosols, respectively. The total concentrations of chemicals [i.e., total organic carbon, water-soluble ions, and metal(loid)s] in aerosols formed via MNB aeration (205.98-373.74 μg/m3) are lower than those in MBA and SBA (398.69-594.92 μg/m3). Compared to MBA and SBA, the MNBs-G phase exhibits higher emissions of 12 elements in aerosols (i.e., NO3-, NO2-, Ca2+, Na+, K+, Mg2+, Zn, Cd, Fe, Mn, As, and Cr), whereas the MNBs-O phase generally shows lower emissions. These findings highlight the potential of optimized MNB aeration technology in considerably mitigating aerosol emissions and thereby advancing environmental sustainability in wastewater treatment.

Transport and risk of airborne pathogenic microorganisms in the process of decentralized sewage discharge and treatment

Sewage treatment processes are a critical anthropogenic source of bioaerosols and may present significant health risks to plant workers. Compared with the specialization and scale of urban sewage treatment, many decentralized treatment models are flexible and extensive. These treatment facilities are usually close to residential areas owing to the pipe network layout and other restrictions. Bioaerosols generated by these facilities may present a serious and widespread occupational and non-occupational exposure risk to nearby residents, particularly the elderly and children. An understanding of the characteristics and exposure risks of bioaerosols produced during decentralized sewage treatment is lacking. We compared bioaerosol emission characteristics and potential exposure risks under four decentralized sewage discharge methods and treatment models: small container collection (SCC), open-channel discharge (OCD), single household/combined treatment (SHCT), and centralized treatment (CT) in northwest China. The OCD mode had the highest bioaerosol production, whereas the CT mode had the lowest. The OCD model contained the most pathogenic bacterial species, up to 43 species, including Sphingomonas, Pseudomonas, Cladosporium, and Alternaria. Risk assessments indicated bioaerosol exposure was lower in the models with sewage treatment (SHCT and CT) than in those without (SCC and OCD). Different populations exhibited large variations in potential risks owing to differences in time spent indoors and outdoors. The highest risk was observed in males exposed to the SCC model. This study provides a theoretical basis and theories for the future joint prevention and control of the bioaerosol exposure risk from decentralized sewage treatment.

Bioaerosols in deodorization covers of wastewater treatment plants: Emission characteristics and health risks

Wastewater treatment plants (WWTPs) are the main source of bioaerosol emissions. The cover of deodorization within WWTPs serves not only to manage odors but also to limit the dispersion of bioaerosols. This study investigated the emission characteristics and exposure risks of bioaerosols inside deodorization covers from a WWTP in Northern China. The results revealed that the concentration of bacteria in bioaerosols ranged from 96 ± 8 to 706 ± 45 CFU/m3, with the highest concentration observed in the biochemical reaction tank. The predominant bacterial genera in bioaerosols within the odor control covers were Cetobacterium, Romboutsia, Bacteroides, Lactobacillus, and Tubricibacter, while the dominant fungal genera included Aspergillus, Alternaria, Fusarium, and Cladosporium. The main water-soluble ions in the air were NH4+, Ca2+, SO42-, and Cl-. SO42- was found to promote the survival of Cetobacterium, Brevibacterium, Fusarium, Penicillium, and Filobasidium, while Cl- exhibited inhibitory effects on most microorganisms in bioaerosols. Source tracker analysis indicated that wastewater was the primary source of bioaerosols in the biochemical reaction tank. The non-carcinogenic risk associated with bioaerosols within deodorization covers was less than 1 (2.34 × 10-9 to 3.08 × 10-2). FunGuild fungal functional prediction suggested that the abundance of animal pathogens was highest in the bioaerosols from the anaerobic sedimentation tank. BugBase phenotypic prediction showed that the abundance of potential pathogens in secondary sedimentation tank bioaerosols was the highest. This study effectively revealed the characteristics and sources of bioaerosols in the sewage and sludge treatment area under the deodorization cover, which provided a theoretical basis for enhancing the management and control of bioaerosols.

Distribution characteristics and potential risks of bioaerosols during scattered farming

In most economically underdeveloped areas, scattered farming and human‒livestock cohabitation are common. However, production of bioaerosols and their potential harm in these areas have not been previously researched. In this study, bioaerosol characteristics were analyzed in scattered farming areas in rural Northwest China. The highest bacteria, fungi, and Enterobacteria concentrations were 125609 ± 467 CFU/m³, 25175 ± 10305 CFU/m³, and 4167 ± 592 CFU/m³, respectively. Most bioaerosols had particle sizes >3.3 μm. A total of 71 bacterial genera and 16 fungal genera of potential pathogens were identified, including zoonotic potential pathogenic genera. Moreover, our findings showed that the scattered farming pattern of human‒animal cohabitation can affect the indoor air environment in the surrounding area, leading to chronic respiratory diseases in the occupants. Therefore, relevant government departments and farmers should enhance their awareness of bioaerosol risks and consider measures that may be taken to reduce them.

The bioaerosols generated from the sludge treatment process: Bacterial and fungal variation characteristics, source tracking, and risk assessment

Bioaerosols generated from sludge treatment processes in wastewater treatment plants (WWTPs) may spread infectious diseases. This study investigated the generation characteristics, source, and associated risks of bioaerosols produced during sludge treatment processes. The results showed that the concentration range of total suspended particles was 49 ± 3 to 354 ± 10 μg/m3, and the primary water-soluble ions in bioaerosols were NH4+, SO42- and Cl-. The bacterial concentration in bioaerosols was 50 ± 5 to 1296 ± 261 CFU/m3, with the highest concentration in the biochemical reaction tank. The dominant bacteria in bioaerosols included Bacteroides, Cetobacterium, Romboutsia, Lactobacillus and Turicibacter, while the dominant fungi were Aspergillus, Alternaria, Cladosporium and Fusarium. Pathogenic microorganisms such as Escherichia and Aspergillus were detected in all treatment processes. The results of principal component analysis showed that the bacterial composition in bioaerosols was similar of different technological processes, while the fungal species composition was different. The dominant microbial composition of sludge and bioaerosols was relatively close. The Source Tracker results indicated that sludge was the main source of airborne bacteria in the sludge dewatering house, as well as the main source of airborne fungi in the plate-frame pressure filtration tank and the sloping plate sedimentation tank. The non-carcinogenic risk in each stage was low (1.22 × 10-9-3.99 × 10-2). However, Bugbase phenotype prediction results showed that the bioaerosols in the anaerobic sedimentation tank may have potential pathogenicity. Therefore, the management and control of bioaerosols from the sludge treatment should be strengthened.

Microbiome recognition of virulence-factor-governed interfacial mechanisms in antibiotic resistance and pathogenicity removal by functionalized microbubbles

The frequent occurrence of epidemics around the world gives rise to increasing concerns of the pollution of pathogens and antibiotic resistant bacteria in water. This study investigated the impacts of virulence factors (VFs) on the removal of antibiotic resistant and pathogenic bacteria from municipal wastewater by ozone-free or ozone-encapsulated Fe(III)-coagulant-modified colloidal microbubbles (O3_free-CCMBs or O3-CCMBs). The highly interface-dependent process was initiated with cell-capture on the microbubble surface where the as-collected cells could be further inactivated with the bubble-released ozone and oxidative species if O3-CCMBs were used. The microbiome sequencing analyses denote that the O3_free-CCMB performance of antibiotic resistant and pathogenic bacteria removal was dependent on the virulence phenotypes related to cell-surface properties or structures. The adhesion-related VFs facilitated the effective attachment between cells and the coagulant-modified bubble-surface, which further enhanced cell inactivation by bubble-released ozone. On the contrary, the motility-related VFs might help cells to escape from the bubble capture by locomotion; however, this could be overcome by O3-CCMB-induced oxidative demolition of the movement structures. Besides, the microbubble performance was also impacted with the cell-membrane structure related to antibiotic resistance (i.e., efflux pumps) and the dissolved organic matter through promoting the surface-capture and decreasing the oxidation efficacy. The ozone-encapsulated microbubbles with surface functionalization are robust and promising tools in hampering antibiotic resistance and pathogenicity dissemination from wastewater to surface water environment; and awareness should be raised for the influence of virulence signatures on its performance.

Bioaerosol-related studies in wastewater treatment plant with anaerobic-anoxic-oxic processes: Characterization, source analysis, control measures

Sewage in wastewater treatment plants (WWTPs) can produce fugitive bioaerosols that pose a health risk to employees and residents. This study aimed to fugitive bioaerosols from two WWTPs with anaerobic-anoxic-oxic (AAO) processes, and bioaerosols control measures were proposed based on the results of these studies. It was found that the bioaerosols were mainly composed of microorganisms from dominant genera such as Romboutsia, Rubellimicrobium, Sphingomonas, Acidea, Cryptotrichosporon and water-soluble ions dominated by SO₄^2-. Moreover, total suspended particulate (TSP), relative humidity (RH), wind speed (WS), Ca²⁺, NH₄⁺, Na⁺, Cl^-, NO₃^-, and K⁺ had positive effects on most dominant genera, while temperature (T) and SO₄^2- had negative effects on most dominant genera. The source analysis showed that the bioaerosols in the indoor treatment facility's fine screen room and sludge dewatering plant mainly originated from sewage or sludge, and those in the aeration tank of the outdoor treatment facility mainly originated from the background air of WWTPs . By combining the characteristics of bioaerosols and the results of source analysis, targeted control measures were proposed from three aspects: source reduction of bioaerosol fugitives, control of bioaerosol propagation, and collection and treatment systems. This study provides the theoretical basis and ideas for controlling bioaerosols in WWTPs with AAO processes.

Dispersion characteristics of bioaerosols during treatment of rural solid waste in northwest China

In rural China, the release of bioaerosols containing pathogens from solid waste dumps poses a potential health risk to the local population. Here, we sampled bioaerosols from rural solid waste-treatment in four provinces of northwest China to investigate their emission and dispersion characteristics in order to provide a scientific basis for control and risk reduction of bioaerosols released from rural sanitation facilities. The airborne bioaerosol concentrations and particle size distributions were calculated using an Anderson six-stage airborne microbial sampler and counting with its internal Petri dish culture. High-throughput sequencing was used to characterize the microbial composition at different sampling sites and to explore possible influencing factors, while the health risk associated with exposure was estimated based on average daily dose-rate. The highest concentration point values of bacteria and fungi in bioaerosols near the solid waste were 63,617 ± 15,007 and 8044 ± 893 CFU/m³, respectively. Furthermore, the highest concentration point values of Enterobacteriaceae was 502 ± 35 CFU/m³. Most bioaerosols were coarse particles larger than 3.3 μm. Potentially pathogenic genera of winter-indicator species detected in the air were primarily Delftia, Rhodococcus and Aspergillus. The composition of solid waste and environmental conditions are important factors in determining the characteristics of bioaerosols. Local residents are exposed to bioaerosols mainly through inhalation. Children are at a particularly high risk of exposure through both inhalation and skin contact. The results of this study show that bioaerosols in the vicinity of rural solid waste dumps pose a health risk to the surrounding population. More suitable risk assessment criteria for rural areas should be established, and corresponding control and protection measures should be taken from three aspects: generation source and transmission pathway, as well as the recipient.

ADMS simulation and influencing factors of bioaerosol diffusion from BRT under different aeration modes in six wastewater treatment plants

Bioaerosols produced by municipal wastewater treatment plants (MWTP) can spread in air, thereby polluting the atmosphere and causing safety hazards to workers and surrounding residents. In this study, the biological reaction tanks (BRTs) of six MWTPs undergoing typical processes in North China, Yangtze River Delta, and the Greater Bay Area were selected to set up sampling points and investigate the production characteristics of bioaerosols. The Atmospheric Dispersion Modelling System method was used to simulate the diffusion of bioaerosols in the MWTPs. The concentrations of bacteria and, specifically, intestinal bacteria in the bioaerosols ranged from 389 CFU/m³ to 1,536 CFU/m³ and 30 CFU/m³ to 152 CFU/m³, respectively, and the proportion of the intestinal bacteria was 8.85%. The concentration of soluble chemicals (SCs) in the bioaerosols was 18.36 μg/m³-82.19 μg/m³, and the main SCs found were Mg²⁺, Ca²⁺, and SO₄^2-. The proportion of intestinal bacteria (75.79%) produced via surface aeration by a BRT attached to large-sized bioaerosol particles was higher than that of a BRT undergoing the bottom aeration process (37.28%). The main microorganisms found in the bioaerosols included Moraxellaceae, Escherichia-Shigella, Psychrobacter, and Cyanobacteria. The generation of bioaerosols exhibited regional characteristics. The wastewater treatment scale, wastewater quality, and aeration mode were the main factors influencing bioaerosol production. Model simulation showed that, after 1 h, the diffusion distance of bioaerosol was 292 m-515 m, and the affected area was 42,895 m²-91,708 m². The diffusion distance and range of the bioaerosols were significantly correlated with the concentration at the bioaerosol source and the aeration mode adopted by the BRTs. Wind speed and direction were two environmental factors that affected the diffusion of bioaerosols. With an increase in the diffusion distance, the concentration of microorganisms, intestinal bacteria, ions, and fine particles in the bioaerosols decreased significantly, resulting in a corresponding reduction in the exposure risk. This study provides new insights to help predict bioaerosol risks at MWTPs and identify safe areas around MWTPs. The study also provides a basis for selecting safe MWTP sites and reducing bioaerosol pollution risks.

Escape and functional alterations of microbial aerosol particles containing Pseudomonas sp. during wastewater treatment

Wastewater treatment plants (WWTP) are considered sources of bioaerosols emission that negatively affects the surrounding atmosphere. This study focused on Pseudomonas sp. Emissions in bioaerosols from a WWTP that adopts the A²O treatment process, and their inactivation through ultraviolet (UV) radiation. High-throughput sequencing was used to assay the microbial population, and functional composition profiles were predicted using 16 S rRNA sequencing data with PICRUSt2. Recorded emission levels of airborne bacteria and Pseudomonas sp. In WWTP were 130 ± 83-6113 ± 3015 CFU/m³ and 0-6431 ± 1945 CFU/m³, respectively. Bioaerosol emissions presented site-related and temporal variation. Over 80% of Pseudomonas sp. Were attached to coarse particles with sizes over 2.1 μm. Bioaerosol concentration and particle-size distribution in the air were closely related to ambient temperature, relative humidity, light intensity, and wind speed. Exposure to 45.67 μW/cm³ UV radiation led to a significant decline in bioaerosol concentrations in the air, and reduction rate reached 89.16% and 95.77% for airborne bacteria and Pseudomonas sp., respectively. The results suggested that UV radiation can be an effective method in reducing bioaerosols. Compared with other bacteria, Pseudomonas stutzeri and Bacillus sp. Are more resistant to UV radiation. The abundance of antibiotic resistance genes noticeably receded when exposed to UV irradiation. The relative abundance of cationic antimicrobial peptide resistance, categorized under human diseases in KEGG (level 3), significantly decreased in Pseudomonas sp. After 120 min of UV irradiation. This study provides a novel insight into the control of bioaerosol emissions carrying pathogenic bacteria.

Quantitative microbial risk assessment with nasal/oral breathing pattern for S. aureus bioaerosol emission from aeration tanks and residual sludge storage yard in a wastewater treatment plant

A large number of pathogenic bioaerosols are generated during the treatment process of wastewater treatment plants (WWTPs), and they can pose potential risks to human health. Therefore, this study systematically analyzed the emission characteristics of Staphylococcus aureus bioaerosols released from an inverted umbrella aeration tank, a microporous aeration tank, and a residual sludge storage yard in a WWTP, and quantitatively evaluated the health risks of four kinds of exposed populations with nasal/oral breathing patterns under optimistic and conservative estimations. The results displayed that the bioaerosol concentration in inverted umbrella aeration tank was higher than that in microporous aeration tank and residual sludge storage yard. Aerosolization ratio in residual sludge storage yard was an order of magnitude lower than that in aeration tanks. Sludge workers were at higher health risks than the other three exposed populations. The health risks of nasal breathers (infection risk: 1.62 × 10^-5-2.56 × 10^-3 pppy; disease burden: 4.24 × 10^-8-6.72 × 10^-6 DALYs pppy) were 0.61-0.63 times higher than those of oral breathers (infection risk: 9.95 × 10^-6-1.59 × 10^-3 pppy; disease burden: 2.61 × 10^-8-4.18 × 10^-6 DALYs pppy). For female field engineers using oral breathing, laboratory technicians, and researchers without personal protective equipment (PPE), infection risk and disease burden had the opposite results, which indicated that satisfying one certain benchmark did not mean absolute safety. In addition, health risks of exposed populations were reduced by an order of magnitude after wearing PPE. This study can provide a reliable theoretical basis for the risk prevention of bioaerosols and supply data support for the strategies of health risk control perspectives for local sewage utilities.

Bioaerosols emission characteristics from wastewater treatment aeration tanks and associated health risk exposure assessment during autumn and winter

Aeration tanks from activated sludge wastewater treatment plants (WWTPs) can release a large amount of bioaerosols that can pose health risks. However, risk characterization of bioaerosols emissions form wastewater treatment plants is currently not systematically carried out and still in its infancy. Therefore, this study investigated emission characteristic of two indicator model bioaerosols Staphylococcus aureus and Escherichia coli, emitted from aeration tanks of a municipal WWTP. Monte Carlo simulation was then used to quantitatively assess microbial risk posed by different aeration modes under optimistic and conservative estimates. Further to this, two different exposure scenarios were considered during 3 days sampling campaign in autumn and winter. Results showed that the bioaerosol concentration from microporous aeration tank (20-262 CFU m^-3) was one order of magnitude lower than rotating disc aeration tank. Average aerosolization rate was 7.5 times higher with mechanical aeration mode. Health risks of exposed populations were 0.4 and 9.6 times higher in winter than in autumn for E. coli and S. aureus bioaerosol, respectively. Health risks of staff members were 10 times higher than academic visitors. Interesting results were observed for academic visitors without personal protective equipment (PPE) respectively exposed to S. aureus and E. coli bioaerosol in autumn and winter: while the derived infection risk met the United States Environmental Protection Agency (U.S. EPA) benchmark under optimistic estimation, the disease risk burden was over the World Health Organization (WHO) benchmark under conservative estimation. These revealed that only satisfying one of the two benchmarks didn't mean absolute acceptable health risk. This study could facilitate the development of better understanding of bioaerosol quantitative assessment of risk characterizations and corresponding appropriate risk control strategies for wastewater utilities.

Seasonal variation of quantitative microbial risk assessment for three airborne enteric bacteria from wastewater treatment plant emissions

Airborne E. coli, fecal coliform, and Enterococcus are all related to sewage worker's syndrome and therefore used as target enteric bioaerosols about researches in wastewater treatment plants (WWTPs). However, most of the studies are often inadequately carried out because they lack systematic studies reports bioaerosols emission characteristics and health risk assessments for these three enteric bacteria during seasonal variation. Therefore, quantitative microbial risk assessment based on Monte Carlo simulation was utilized in this research to assess the seasonal variations of health risks of the three enteric bioaerosols among exposure populations (academic visitors, field engineers, and office staffs) in a WWTP equipped with rotating-disc and microporous aeration modes. The results show that the concentrations of the three airborne bacteria from the rotating-disc aeration mode were 2-7 times higher than the microporous aeration mode. Field engineers had health risks 1.5 times higher than academic visitors due to higher exposure frequency. Health risks of airborne Enterococcus in summer were up to 3 times higher than those in spring and winter. Similarly, health risks associated to E. coli aerosol exposure were 0.3 times higher in summer compared to spring. In contrast, health risks associated with fecal coliform aerosol were between 2 and 19 times lower in summer compared to spring and winter seasons. Data further suggest that wearing of N95 mask could minimize health risks by 1-2 orders of magnitude. This research shed light on seasonal variation of health risks associated with bioaerosol emission from wastewater utilities.

The changing pattern of bioaerosol characteristics, source and risk under diversity brush aerator speed

Bioaerosols containing pathogens released from wastewater treatment plants (WWTP) may pose potential health risks to workers on-site and residents downwind. In this study, sampling points were set up in the wastewater treatment facility to investigate the generation pattern of bioaerosols in the aeration tank section. High-throughput sequencing was utilized to assay the intestinal bacteria population, while the health risks associated with airborne bacteria were estimated based on average daily dose rates. The contribution of wastewater to bioaerosols was evaluated using the traceability analysis. As the rotational speed increased from 200 rpm to 800 rpm, the concentration of culturable bacteria increased from 397 CFU/m³ to 1611 CFU/m³, the proportion of bacteria attached to particles with an aerodynamic diameter larger than 4.7 µm increased from 30.41% to 48.44%, and the Shannon index of air samples increased from 1.032485 to 1.282065. Microbial composition, sources, and health risks of bioaerosols also changed as the rotational speed increased. The results showed that the predominant bacteria in the air at 200 rpm were Bacillus (78.78%), Paenibacillus (11.77%) and Lysinibacillus (1.40%). When the rotating speed reached 800 rpm, the dominant bacteria became Bacillus (55.50%), Acinetobacter (31.01%), and Paenarthrobacter (13.17%). The contribution of the wastewater to bioaerosols increased from 46.49% to 65.10%, in which surface water was the main source of bioaerosols (34.64% on average). Although the contribution of bottom water was lower than that of surface water, its contribution increased more, from 15.36% to 29.31%. The health risk of bioaerosols was 1.28 × 10^-2 on average, which increased with the increase of rotational speed. At the same exposure concentration, children (2.31 × 10^-2) have a higher exposure risk than adults (7.67 × 10^-3). This study is aimed at exploring the variation law of bioaerosols discharged from WWTP with oxidation ditch process and providing preliminary data for reducing its risk.

Bioaerosolization and pathogen transmission in wastewater treatment plants: Microbial composition, emission rate, factors affecting and control measures

Environmental consequences during wastewater management are vital and getting increased attention to interrupt any possible disease transmission pathways. Evidence of bioaerosolization of pathogen from wastewater to atmosphere during wastewater treatment have been highlighted previously. Understanding aerosol-based transmission in wastewater treatment plant (WWTP) is important because of the hazard it presents to the workers involved or to the population around and appears to be very significant during pandemic occurrences. This work aims to evaluate the possibility of pathogenic content of wastewater getting aerosolized during treatment by synthesizing the evidence on the potential aerosol generating treatment phases of WWTP, bioaerosol microbial composition, emission load and the factors affecting the bioaerosol formation. We also present some potential control strategies to take up in WWTP which may be useful to avoid such occurrences. Implementation of Aeration based strategies (use of diffused, submerged aeration, reduction in aeration rate), Improved ventilation based strategies (effective ventilation with adequate supply of clean air, minimizing air recirculation, supplementation with infection control measures such as filtration, irradiation), Improved protection based strategy (periodic monitoring of disinfection efficiency, pathogenic load of wastewater, improved operation policy) and other strategies (provision of buffer zone, wind shielding, water spraying on aerosol, screened surface of treatment units) could be very much relevant and significant in case of disease outbreak through aerosol formation in wastewater environment. Recent progress in sensor-based data collection, analysis, cloud-based storage, and early warning techniques in WWTP may help to reduce the risk of infectious transmission, especially during a pandemic situation.

A state-of-the-art review on WWTP associated bioaerosols: Microbial diversity, potential emission stages, dispersion factors, and control strategies

Wastewater treatment plants (WWTPs) associated bioaerosols have emerged as one of the critical sustainability indicators, ensuring health and well-being of societies and cities. In this context, this review summarizes the various wastewater treatment technologies which have been studied with a focus of bioaerosols emissions, potential emission stages, available sampling strategies, survival and dispersion factors, dominant microbial species in bioaerosols, and possible control approaches. Literature review revealed that most of the studies were devoted to sampling, enumerating and identifying cultivable microbial species of bioaerosols, as well as measuring their concentrations. However, the role of treatment technologies and their operational factors are investigated in limited studies only. Moreover, few studies have been reported to investigate the presence and concentrations of air borne virus and fungi in WWTP, as compared to bacterial species. The common environmental factors, affecting the survival and dispersion of bioaerosols, are observed as relative humidity, temperature, wind speed, and solar illumination. Further, research studies on recent episodes of COVID-19 (SARS-CoV-2 virus) pandemic also revealed that continuous and effective surveillance on WWTPs associated bioaerosols may led to early sign for future pandemics. The evaluation of reported data is bit complicated, due to the variation in sampling approaches, ambient conditions, and site activities of each study. Therefore, such studies need a standardized methodology and improved guidance to help informed future policies, contextual research, and support a robust health-based risk assessment process. Based on this review, an integrated sampling and analysis framework is suggested for future WWTPs to ensure their sustainability at social and/or health associated aspects.

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.

Characterization, factors, and UV reduction of airborne bacteria in a rural wastewater treatment station

Bioaerosols containing pathogens released from wastewater will pose potential health risks to workers on site. The emission of airborne bacteria from a rural wastewater treatment station and their inactivation by ultraviolet were investigated in this study. High-throughput sequencing technique was utilized to assay airborne bacterial population while the health risks associated with airborne bacteria exposure were estimated based on average daily dose rates. The recorded emission level of airborne bacteria in the air surrounding the multi-point inlet contact oxidation bioreactor (MTB) was 4795 ± 1475 CFU/m³, containing 2233 ± 471 CFU/m³ of intestinal bacteria, and most of them (70.3%) was coarse particles with size over 2.1 μm. Wind disturbance had significant effects on the diffusion and particle size distribution of the bioaerosols emitted from MTB. The identified opportunistic pathogens in bioaerosols were Enterobacter sp., Acinetobacter sp., Pantoea sp., Achromobacter sp., and Curtobacterium sp. They were originated in the water and active sludge in MTB. Inhalation was one of the main ways through which onsite workers were exposed to airborne bacteria. Exposure to ultraviolet radiation caused an apparent decrease in the level of bioaerosols in the air, thereby indicating that it can be utilized as an effective method for the reducing of bioaerosols. This study aims to provide preliminary data for the bioaerosols control in rural wastewater treatment process.

The effect of mixing and free-floating carrier media on bioaerosol release from wastewater: a multiscale investigation with Bacillus globigii

Aeration tanks in wastewater treatment plants (WWTPs) are significant sources of bioaerosols, which contain microbial contaminants and can travel miles from the site of origin, risking the health of operators and the general public. One potential mitigation strategy is to apply free-floating carrier media (FFCM) to suppress bioaerosol emission. This article presents a multiscale study on the effects of mixing and FFCM on bioaerosol release using Bacillus globigii spores in well-defined liquid media. Bioaerosol release, defined as percentage of spores aerosolized during a 30 minute sampling period, ranged from 6.09 × 10-7% to 0.057%, depending upon the mixing mode and intensity. Bioaerosol release increased with the intensity of aeration (rotating speed in mechanical agitation and aeration rate in diffused aeration). A surface layer of polystyrene beads reduced bioaerosol released by >92% in the bench-scale studies and >74% in the pilot-scale study. This study discovered strong correlations (R2 > 0.82) between bioaerosol release and superficial gas velocity, Froude number, and volumetric gas flow per unit liquid volume per minute. The Reynolds number was found to be poorly correlated with bioaerosol release (R2 < 0.5). This study is a significant step toward the development of predictive models for full scale systems.

Study of the generation and diffusion of bioaerosol under two aeration conditions

Given that studies on actual sewage treatment plants are often affected by environmental conditions, it is challenging to clearly understand the associated bioaerosol generation and diffusion characteristics during the aeration process. Therefore, to enhance understanding in this regard, in this study, bioaerosol generator was used to simulate bioaerosol generation and diffusion under two aeration modes, i.e., bubble bottom aeration and brush surface aeration. The total concentration range of culturable bacteria in the bioaerosol produced by bubble bottom aeration and that produced by brush surface aeration were 300-3000 CFU/m³. Under bubble bottom aeration, the generated bioaerosol was symmetrically distributed around the source point, whereas under brush surface aeration, it was primarily distributed in the forward direction of the rotating brush surface. These bioaerosols from bubble bottom aeration predominantly consisted of particles with sizes below 3.3 μm, particularly those with sizes in the range 1.1-2.1 μm. On the contrary, the bioaerosols produced via brush surface aeration predominantly consisted of particles with sizes above 3.3 μm. The distribution characteristics of population structure in the two aeration modes were consistent with the distribution characteristics of concentration in the corresponding models. Additionally, the results showed that when the aeration process is unaffected by environmental conditions (particle matters, wind direct, wind speed, etc.), the bioaerosol components originate primarily from the parent sewage or sludge, and do not diffuse far from the source point. Therefore, source reduction (capping or sealing) can be recommended as the primary control strategy for bioaerosols in sewage treatment plants. The adoption of such measures will significantly limit the diffusion of bioaerosols, thereby reducing the potential risks associated with human exposure.

Wastewater treatment plant workers' exposure and methods for risk evaluation of their exposure

Work in wastewater treatment plants (WWTPs) can be associated with respiratory symptoms and diarrhea. The aim of this study was to obtain knowledge about WWTP workers' exposure to airborne bacteria and endotoxin, and the inflammatory potential (TIP) of their exposure, and to evaluate the risk posed by the exposure by 1) calculating a hazard index and relating the exposure to suggested occupational exposure limits (OELs), 2) estimating the potential deposition of bacteria in the airways, 3) relating it to the risk group classification of bacteria by the European Union, and 4) estimating the TIP of the personal exposure. A cohort of 14 workers were followed over one year. Bioaerosols were collected using personal and stationary samplers in a grid chamber house and an aeration tank area. Airborne bacteria were identified using (MALDI-TOF MS), and TIP of exposure was measured using HL-60 cells. A significant effect of season, work task, and person was found on the personal exposure. A hazard index based on exposure levels indicates that the risk caused by inhalation is low. In relation to suggested OELs, 14% and 34% of the personal exposure were exceeded for endotoxin (≥50 EU/m³) and bacteria (≥500 CFU/m³). At least 70% of the airborne bacteria in the grid chamber house and the aeration tank area could potentially deposit in the lower respiratory tract. From the personal samples, three of 131 bacterial species, Enterobacter cloacae, Staphylococcus aureus, and Yersinia enterocolitica are classified within Risk Group 2. Seven additional bacteria from the stationary samples belong to Risk Group 2. The bacterial species composition was affected significantly by season (p = 0.014) and by sampling type/area (p = 0.001). The TIP of WWTP workers' exposure was higher than of a reference sample, and the highest TIP was measured in autumn. TIP of personal exposure correlated with bacterial exposure. Based on the geometric average exposures to endotoxin (9.2 EU/m³) and bacteria (299 CFU/m³) and based on the calculated hazard index, the risk associated with exposure is low. However, since 43 of 106 exposure levels exceed suggested OELs, the TIP of exposure was elevated and associated with bacterial exposure, and WWTP workers were exposed to pathogenic bacteria, a continued focus on preventive measures is important. The identification of bacteria to species level in personal samples was necessary in the risk assessment, and measurement of the microbial composition made the source tracking possible.

Linking aerosol characteristics of size distributions, core potential pathogens and toxic metal(loid)s to wastewater treatment process

Wastewater treatment plants (WWTPs) play important roles in water purification but are also important source of aerosols. However, the relationship between aerosol characteristics and wastewater treatment process remains poorly understood. In this study, aerosols were collected over a 24-month period from a WWTP using a modified anaerobic-anoxic-oxic process. The aerated tank (AerT) was characterized by the highest respiratory fraction (RF) concentrations (861-1525 CFU/m³) and proportions (50.76%-65.96%) of aerosol particles. Fourteen core potential pathogens and 15 toxic metal(loid)s were identified in aerosols. Mycobacterium was the genus that aerosolized most easily in fine grid, pre-anoxic tank, and AerT. High wastewater treatment efficiency may increase the emission of RF and core potential pathogens. The median size of activated sludge, richness of core potential pathogens in wastewater, and total suspended particulates were the most influential factors directly related to the RF proportions, core community of potential pathogens, and composition of toxic metal(loid)s in WWTP aerosols, respectively. Relative humidity, temperature, input and removal of biochemical oxygen demand, dissolved oxygen, and mixed liquor suspended solids could also directly or indirectly affect the aerosol characteristics. This study enhances the mechanistic understanding of linking aerosol characteristics to treatment processes and has important implications for targeted manipulation.

Characteristics and interactions of bioaerosol microorganisms from wastewater treatment plants

Bacteria and fungi are abundant and ubiquitous in bioaerosols from wastewater treatment plants (WWTPs). However, the specificity and interactions of bioaerosol microorganism, particularly of potential pathogens, from WWTPs are still poorly understood. In this study, we investigated 9 full-scale WWTPs in different areas of China for 3 years, and found microbial variations in bioaerosols to be associated with regions, seasons, and processes. Relative humidity, total suspended particulates, wind speed, temperature, total organic carbon, NH₄⁺, Cl^- and Ca²⁺ were the major factors influencing this variation, and meteorological factors were more strongly associated with the variation than chemical composition. In total, 95 and 22 potential bacterial and fungal pathogens were detected in bioaerosols, respectively. The linear discriminant analysis effect size method suggested that Serratia, Yersinia, Klebsiella, and Bacillus were discriminative genera in bioaerosols on the whole, and were also hub niches in the interactions within potential bacterial pathogens, based on network analysis. Strong co-occurrences such as Serratia-Bacillus and Staphylococcus-Candida, and co-exclusions such as Rhodotorula-Cladosporium and Pseudomonas-Candida, were found within and between potential bacterial and fungal pathogens in bioaerosols from WWTPs. This study furthers understanding of the biology and ecology of bioaerosols from WWTPs, and offers a theoretical basis for determining bioaerosol control.

A valuable experimental setup to model exposure to Legionella's aerosols generated by shower-like systems

The mechanism underlying Legionella aerosolization and entry into the respiratory tract remains poorly documented. In previous studies, we characterized the aerodynamic behaviour of Legionella aerosols and assessed their regional deposition within the respiratory tract using a human-like anatomical model. The aim of this study was to assess whether this experimental setup could mimic the exposure to bioaerosols generated by showers. To achieve this objective we performed experiments to measure the mass median aerodynamic diameter (MMAD) as well as the emitted dose and the physiological state of the airborne bacteria generated by a shower and two nebulizers (vibrating-mesh and jet nebulizers). The MMADs of the dispersed bioaerosols were characterized using a 12-stage cascade low-pressure impactor. The amount of dispersed airborne bacteria from a shower was quantified using a Coriolis® Delta air sampler and compared to the airborne bacteria reaching the thoracic region in the experimental setup. The physiological state and concentration of airborne Legionella were assessed by qPCR for total cells, culture for viable and cultivable Legionella (VC), and flow cytometry for viable but non-cultivable Legionella (VBNC). In summary, the experimental setup developed appears to mimic the bioaerosol emission of a shower in terms of aerodynamic size distribution. Compared to the specific case of a shower used as a reference in this study, the experimental setup developed underestimates by 2 times (when the jet nebulizer is used) or overestimates by 43 times (when the vibrating-mesh nebulizer is used) the total emitted dose of airborne bacteria. To our knowledge, this report is the first showing that an experimental model mimics so closely an exposure to Legionella aerosols produced by showers to assess human lung deposition and infection in well-controlled and safe conditions.

Evaluation of Bioaerosol Bacterial Components of a Wastewater Treatment Plant Through an Integrate Approach and In Vivo Assessment

Wastewater carries different pathogenic and non-pathogenic microorganisms that can be dispersed in the surrounding environment. Workers who frequent sewage treatment plants can therefore be exposed to aerosols that contain a high concentration of potentially dangerous biological agents, or they can come into direct contact with contaminated material. This can lead to allergies, infections and occupational health-associated diseases. A characterization of biological risk assessment of bioaerosol exposure is necessary. The aim of this study was to evaluate the application of an interdisciplinary method that combines chemical and biological approaches for the analysis of a bioaerosol derived from a wastewater treatment plant (WWTP) situated in Italy. Sampled filters were analyzed by HPLC-MS/MS spectroscopy that searched for different chemical biomarkers of airborne microorganisms. The analytical quantification was compared to the biological cultural method that revealed an underrated microbial concentration. Furthermore, next generation sequencing analysis was used also to identify the uncultivable species that were not detected by the culture dependent-method. Moreover, the simple animal model Caenorhabditis elegans was used to evaluate the pathogenicity of two isolates—Acinetobacter iwoffii and Micrococcus luteus—that showed multidrug-resistance. This work represents a starting point for the development of a multidisciplinary approach for the validation of bioaerosol exposure on WWTP workplaces.