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

Distribution of antibiotic resistance genes and their pathogen hosts in duck farm environments in south-east coastal China

Livestock farms are major reservoirs of antibiotic resistance genes (ARGs) that are discharged into the environment. However, the abundance, diversity, and transmission of ARGs in duck farms and its impact on surrounding environments remain to be further explored. Therefore, the characteristics of ARGs and their bacterial hosts from duck farms and surrounding environment were investigated by using metagenomic sequencing. Eighteen ARG types which consist of 823 subtypes were identified and the majority conferred resistance to multidrug, tetracyclines, aminoglycosides, chloramphenicols, MLS, and sulfonamides. The floR gene was the most abundant subtype, followed by sul1, tetM, sul2, and tetL. ARG abundance in fecal sample was significantly higher than soil and water sample. Our results also lead to a hypothesis that Shandong province have been the most contaminated by ARGs from duck farm compared with other four provinces. PcoA results showed that the composition of ARG subtypes in water and soil samples was similar, but there were significant differences between water and feces samples. However, the composition of ARG subtypes were similar between samples from five provinces. Bacterial hosts of ARG subtypes were taxonomically assigned to eight phyla that were dominated by the Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria. In addition, some human bacterial pathogens could be enriched in duck feces, including Enterococcus faecium, Acinetobacter baumannii, and Staphylococcus aureus, and even serve as the carrier of ARGs. The combined results indicate that a comprehensive overview of the diversity and abundance of ARGs, and strong association between ARGs and bacterial community shift proposed, and benefit effective measures to improve safety of antibiotics use in livestock and poultry farming. KEY POINTS: • ARG distribution was widespread in the duck farms and surroundings environment • ARG abundance on the duck farms was significantly higher than in soil and water • Human bacterial pathogens may serve as the vectors for ARGs.

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.

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.

The dynamics and transmission of antibiotic resistance associated with plant microbiomes

Antibiotic resistance genes (ARGs) have been widely found and studied in soil and water environments. However, the propagation of ARGs in plant microbiomes has attracted insufficient attention. Plant microbiomes, especially the rhizosphere microorganisms, are closely connected with water, soil, and air, which allows ARGs to spread widely in ecosystems and pose a threat to human health after entering the human body with bacteria. Therefore, it is necessary to deeply understand and explore the dynamics and the transmission of ARGs in rhizosphere microorganisms and endophytes of plants. In this review, the transmission and influencing factors of ARGs in the microorganisms associated with plants, especially the influence of root exudates on plant microbiomes, are analyzed. Notably, the role of intrinsic genes of plants in determining root exudates and their potential effects on ARGs are proposed and analyzed. The important role of phyllosphere microorganisms and endophytes in the transmission of ARGs and co-resistance of antibiotics and other substances are also emphasized. The proliferation and transmission of ARGs associated with plant microbiomes addressed in this review is conducive to revealing the fate of ARGs in plant microorganisms and alleviating ARG pollution.

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.

Abundance and cultivable bioaerosol transport from a municipal solid waste landfill area and its risks

Municipal solid waste (MSW) landfills, constituting the third largest anthropogenic sources of bioaerosols, are suspected to be one of the major contributors to adverse health outcomes. A regional modeling of aerosol trajectories based on wind-tunnel observations and on-site monitoring was newly-developed to uncover the impacts of a typical MSW landfill on ambient bioaerosol pollution. Results showed that the horizontal diffusion velocity of bioaerosols reached 4.33 times higher than the vertical velocity under surface calm winds. On-site monitoring revealed that the concentrations of particulate matter (PM) with a diameter of 10 μm were 3.05 times higher than those of PM1.0 in the 2.8-km downwind residential regions near the MSW landfill. With the increase in PM concentration, higher-abundance microorganisms were detected. A number of cultivable bacterial species (Micrococcus endophyticus, Micrococcus flavus, Bacillus sporothermodurans, Salmonella entericaserovar typhi, Rhodococcus hoagie, Blastococcups) and fungal species (Aspergillus niger, Penicillium, Microascus cirrosus, Cochliobolus, Stemphylium vesicarium) were identified in these bioaerosols. Furthermore, distinguished by transmission electron microscopy, a longer-range transported microorganism (E. coli) clinging onto suspended PM was observed, signifying higher exposure risks. Human health risk assessments demonstrate that the residents and occupational workers in the vicinity of MSW landfill endured atmospheric diffusion-induced bioaerosol exposure risks due to open dumping activities in MSW landfill. This study clearly indicates bioaerosol pollution from landfills, and people particularly living nearby the MSW facilities, must decrease outdoor activities during dusty days.

A probabilistic assessment of microbial infection risks due to occupational exposure to wastewater in a conventional activated sludge wastewater treatment plant

Exposure to pathogens during wastewater treatment could result in significant health risks. In this paper, a probabilistic approach for assessing the risks of microbial infection for workers in an activated sludge wastewater treatment plant is presented. A number of exposure routes were modelled, including hand-to-mouth and droplet ingestion of untreated wastewater, droplet ingestion and inhalation of aerosols after secondary treatment, and ingestion of sludge during drying. Almost all workers exposed to untreated wastewater could be infected with the three selected potential pathogens of pathogenic E. coli, Norovirus and Cryptosporidium spp. Hand-to-mouth ingestion is the single most significant route of exposure at the head of works. There is also a risk of infections resulting from ingestion of droplets or inhalation of aerosols at the aeration tanks or contaminated hands at the clarifiers during secondary wastewater treatment. For sludge, the risks of infection with Norovirus was found to be the highest due to accidental ingestion (median risks of 2.2 × 10^-2(±3.3 × 10^-3)). Regardless of the point and route of exposure, Norovirus and Cryptosporidium spp. presented the highest risks. The study finds that occupational exposure to wastewater at wastewater treatment plants can result in significant viral and protozoan infections. This risk assessment framework can be used to establish and measure the success of risk reduction measures in wastewater treatment plants. These measures could include the use of personal protective equipment and adherence to strict personal hygiene.

Per- and polyfluoroalkyl substances in the atmosphere of waste management infrastructures: Uncovering secondary fluorotelomer alcohols, particle size distribution, and human inhalation exposure

Per- and polyfluoroalkyl substances (PFAS) have been applied in numerous industrial and consumer products, the majority of which flow into waste management infrastructures (WMIs) at the end of their life cycles, but little is known about atmospheric releases of PFAS from these facilities. In this study, we addressed this key issue by investigating 49 PFAS, including 23 ionic and 26 neutral and precursor PFAS, in the potential sources (n = 4; within or adjacent to WMIs) and reference sites (n = 2; coastal and natural reserve sites) in urban and rural areas of Hong Kong, China. Duplicate samples of air and size-segregated particulate matter were collected for 48 h continuously using a 11-stage Micro-Orifice Uniform Deposit Impactor (MOUDI). In general, fluorotelomer alcohols (FTOHs) and perfluoroalkane sulfonamides were the predominant PFAS classes found across sampling sites. We also demonstrated the release of several less frequently observed semivolatile intermediate products (e.g., secondary FTOHs) during waste treatment. Except for perfluorooctane sulfonate, the size-segregated distributions of particulate PFAS exhibited heterogeneity across sampling sites, particularly in the WMIs, implying combined effects of sorption affinity and emission sources. A preliminary daily air emission estimation revealed that landfill was a relatively important source of PFAS relative to the wastewater treatment plant. A simplified International Commission on Radiological Protection model was used to estimate lung depositional fluxes, and the results showed that inhaled particulate PFAS were mainly deposited in the head airway while fine and ultrafine particles carried PFAS deeper into the lung alveoli. The cumulative daily inhalation dose of gaseous and particulate PFAS ranged from 81.9 to 265 pg/kg/d. In-depth research is required to understand the health effect of airborne PFAS on workers at WMIs.

Submicron aerosols share potential pathogens and antibiotic resistomes with wastewater or sludge

Generation of size-segregated aerosols is an important eco-environmental problem in wastewater treatment plants (WWTPs), but the characteristics of potential pathogens and antibiotic resistomes in submicron aerosols (PM_1.0) were almost unknown. Here, 16S rRNA gene amplification and shotgun metagenome sequencing were respectively used to study the profiles of potential pathogens and antibiotic resistance genes (ARGs) in PM_1.0 from a full-scale WWTP. Acinetobacter and sul1 were respectively the predominant potential pathogens and ARG subtypes in PM_1.0 from aeration process. A total of 9 potential pathogens and 147 ARG subtypes, were shared among WWTP-PM_1.0, wastewater/sludge, and ambient air. Significant differences of potential pathogens or ARGs were found between WWTP-PM_1.0 and wastewater/sludge, however, wastewater/sludge had more crucial source contribution than the ambient air. Moreover, 13 potential pathogens and 40 ARG subtypes were easily aerosolized in PM_1.0 from at least one of the treatment units. ARGs were mainly harbored by Proteobacteria, and multidrug resistance genes were the most ARG type carried by potential pathogens. Taken together, this study indicates the prevalence of potential pathogens, ARGs, and ARG-carrying potential pathogens in WWTP-PM_1.0, which highlights the potential risk of PM_1.0 in spreading potential pathogens and antibiotic resistomes into the air environments.

Response of constructed wetland for wastewater treatment to graphene oxide: Perspectives on plant and microbe

The wide application of graphene oxide (GO) increases its release into environment with less known on environmental effects. This work investigated 120-day interaction between GO (500 and 5000 μg/L) and constructed wetlands (CWs) planted with Iris pseudacorus. CWs showed the effective retention for GO via mature biofilm but less biodegradation. GO significantly induced enzyme activities (urease, neutral phosphatase, and catalase), which was attributed to increases in ecological association and enzyme abundance. GO decreased microbial biomass on day 30, but it had no impacts on day 120. The microbial community showed gradual self-adaption with time due to protection of antioxidant defense system (L-ascorbate oxidase, superoxide reductase, and glutathione related enzyme). The antioxidant enzymes (superoxide dismutase and peroxidase) and lipid peroxidation of Iris pseudacorus were increased by GO, accompanied by reduction on chlorophyll biosynthesis. Overall, the separate effects of GO on micro-regions and individual bodies in CWs were obvious, but it was acceptable that variations in pollutant removal were not evident due to synergetic role of plant-substrate-microbe. Organic matter and phosphorus removals reached to above 93%, and ammonia and total nitrogen removals in GO groups were reduced by 7-8% and 9-13%, respectively.

Microbiological and Toxicological Hazards in Sewage Treatment Plant Bioaerosol and Dust

Despite the awareness that work in the sewage treatment plant is associated with biological hazards, they have not been fully recognised so far. The research aims to comprehensively evaluate microbiological and toxicological hazards in the air and settled dust in workstations in a sewage treatment plant. The number of microorganisms in the air and settled dust was determined using the culture method and the diversity was evaluated using high-throughput sequencing. Endotoxin concentration was assessed with GC-MS (gas chromatography-mass spectrometry) while secondary metabolites with LC-MS/MS (liquid chromatography coupled to tandem mass spectrometry). Moreover, cytotoxicity of settled dust against a human lung epithelial lung cell line was determined with the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and UHPLC-Q-ToF-UHRMS (ultra-high-performance liquid chromatography-quadrupole time-of-flight ultrahigh-resolution mass spectrometry) analysis was performed to determine the source of cytotoxicity. The total dust concentration in the sewage treatment plant was low and ranged from 0.030 mg m^-3 to 0.044 mg m^-3. The highest microbiological contamination was observed in sludge thickening building and screenings storage. Three secondary metabolites were detected in the air and sixteen in the settled dust. They were dominated by compounds typical of lichen and plants and Aspergillus, Penicillium and Fusarium genera mould. The settled dust from the sludge thickening building revealed high cytotoxicity to human lung epithelial cells A-549 (IC₅₀ = 6.98 after 72 h). This effect can be attributed to a biocidal compound-didecyldimethylammonium chloride (DDAC-C10) and seven toxic compounds: 4-hydroxynonenal, carbofuran, cerulenin, diethylphosphate, fenpropimorph, naphthalene and onchidal. The presence of DDAC-C10 and other biocidal substances in the sewage treatment plant environment may bring negative results for biological sewage treatment and the natural environment in the future and contribute to microorganisms' increasing antibiotics resistance. Therefore, the concentration of antibiotics, pesticides and disinfectants in sewage treatment plant workstations should be monitored.

Characteristics of size-segregated aerosols emitted from an aerobic moving bed biofilm reactor at a full-scale wastewater treatment plant

Aerosol emissions from wastewater treatment plants (WWTPs) have been associated with health reverberation but studies about characteristics of size-segregated aerosol particulate matter (PM) are scarce. In this study, the measurement of particulate number size distribution in the range of < 10 µm, and the collection of PM_10-2.5, PM_2.5-1.0 and PM_1.0, were conducted from an aerobic moving bed biofilm reactor (MBBR) at a full-scale WWTP. MBBR aerosols showed a unimodal number size distribution, with the majority of particles (>94%) in the ultrafine size range (<100 nm). For toxic metal(loid)s or potential pathogens, significant differences were found within MBBR aerosols (PM_10-2.5, PM_2.5-1.0, and PM_1.0), and also between MBBR aerosols and wastewater. Both wastewater and ambient air had important source contributions for MBBR aerosols. The compositions of toxic metal(loid)s in PM_1.0, and the populations of potential bacterial or fungal pathogens in PM_10-2.5 and PM_2.5-1.0, were dominated by that from wastewater. Compared to PM_10-2.5 and PM_2.5-1.0, PM_1.0 had the highest aerosolization potential for the toxic metal(loid)s of As, Cd, Co, Cr, Li, Mn, Ni, U, and Zn, and the genera of Acinetobacter, Pseudomonas and Fusarium. Due to the size-segregated specialty, targeted measures should be employed to reduce the health risks. CAPSULE: The compositions of toxic metal(loid)s in PM_1.0, and the populations of potential pathogens in PM_10-2.5 and PM_2.5-1.0, were dominated by that from wastewater.

Foam shares antibiotic resistomes and bacterial pathogens with activated sludge in wastewater treatment plants

Foaming is a common operational problem that occurs in activated sludge (AS) from many wastewater treatment plants (WWTPs), but the characteristic of antibiotic resistance genes (ARGs) and human pathogenic bacteria (HPB) in foams is generally lacking. Here, we used a metagenomic approach to characterize the profile of ARGs and HPB in foams and AS from full-scale WWTPs receiving pesticide wastewater. No significant difference in the microbial communities was noted between the AS and foam samples. The diversity and abundance of ARGs in the foams were similar to those in the pertinent AS samples. Procrustes analysis suggested that the bacterial community is the major driver of ARGs. Metagenomic assembly also indicated that most ARGs (e.g., multidrug, rifamycin, peptides, macrolide-lincosamide-streptogramin, tetracycline, fluoroquinolone, and beta-lactam resistance genes) were carried by chromosomes rather than mobile genetic elements. Moreover, the relative abundances of HPB, Pseudomonas putida and Mycobacterium smegmatis, were enriched in the foam samples. Nine HPB were identified as carriers of 21 ARG subtypes, of which Pseudomonas aeruginosa could carry 12 ARG subtypes. Overall, this study indicates the prevalence of ARGs, HPB, and ARG-carrying HPB in foams, which highlights the potential risk of foams in spreading ARGs and HPB into the surrounding environments.