Characterization of aerosol emissions from wastewater aeration basins

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.

Occurrence and transport of SARS-CoV-2 in wastewater streams and its detection and remediation by chemical-biological methods

This paper explains the transmission of SARS-CoV and influences of several environmental factors in the transmission process. The article highlighted several methods of collection, sampling and monitoring/estimation as well as surveillance tool for detecting SARS-CoV in wastewater streams. In this context, WBE (Wastewater based epidemiology) is found to be the most effective surveillance tool. Several methods of genomic sequencing are discussed in the paper, which are applied in WBE, like qPCR-based wastewater testing, metagenomics-based analysis, next generation sequencing etc. Additionally, several types of biosensors (colorimetric biosensor, mobile phone-based biosensors, and nanomaterials-based biosensors) showed promising results in sensing SARS-CoV in wastewater. Further, this review paper outlined the gaps in assessing the factors responsible for transmission and challenges in detection and monitoring along with the remediation and disinfection methods of this virus in wastewater. Various methods of disinfection of SARS-CoV-2 in wastewater are discussed (primary, secondary, and tertiary phases) and it is found that a suite of disinfection methods can be used for complete disinfection/removal of the virus. Application of ultraviolet light, ozone and chlorine-based disinfectants are also discussed in the context of treatment methods. This study calls for continuous efforts to gather more information about the virus through continuous monitoring and analyses and to address the existing gaps and identification of the most effective tool/ strategy to prevent SARS-CoV-2 transmission. Wastewater surveillance can be very useful in effective surveillance of future pandemics and epidemics caused by viruses, especially after development of new technologies in detecting and disinfecting viral pathogens more effectively.

Detection and characterization of bioaerosol emissions from wastewater treatment plants: Challenges and opportunities

Rapid population growth and urbanization process have led to increasing demand for wastewater treatment capacity resulting in a non-negligible increase of wastewater treatment plants (WWTPs) in several cities around the world. Bioaerosol emissions from WWTPs may pose adverse health risks to the sewage workers and nearby residents, which raises increasing public health concerns. However, there are still significant knowledge gaps on the interplay between process-based bioaerosol characteristics and exposures and the quantification of health risk which limit our ability to design effective risk assessment and management strategies. This review provides a critical overview of the existing knowledge of bioaerosol emissions from WWTPs including their nature, magnitude and size distribution, and highlights the shortcoming associated with existing sampling and analysis methods. The recent advancements made for rapid detection of bioaerosols are then discussed, especially the emerging real time detection methods to highlight the directions for future research needs to advance the knowledge on bioaerosol emissions from WWTPs.

What are the disease burden and its sensitivity analysis of workers exposing to Staphylococcus aureus bioaerosol during warm and cold periods in a wastewater treatment plant?

Biological treatment in wastewater treatment plants releases high amounts of pathogenic bioaerosols. Quantitative microbial risk assessment is a framework commonly used for quantitative risk estimation for occupational exposure scenarios. However, the quantitative contributions of health-risk-estimate inputted parameters remain ambiguous. Therefore, this research aimed to study the disease burden of workers exposed to Staphylococcus aureus bioaerosol during warm and cold periods and strictly quantify the contributions of the inputted parameters by sensitivity analysis on the basis of Monte Carlo simulation. Results showed that the disease health risk burden of workers in the warm period was 1.15-6.11 times higher than that of workers in the cold period. The disease health risk burden of workers without personal protective equipment was 23.83-36.55 times higher than that of workers with personal protective equipment. Sensitivity analysis showed that exposure concentration and aerosol ingestion rate were the first and second predominant factors, respectively; the sensitivity partitioning coefficient of the former was 1.17-1.35 times the value of the latter. In addition, no remarkable differences were revealed in the sensitivity percentage ratio between warm and cold periods. The findings could contribute to the mitigation measures for the management of public health risks.

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.

Life-cycle assessment of full-scale membrane bioreactor and tertiary treatment technologies in the fruit processing industry

A life-cycle assessment (LCA) study was completed to assess the environmental impacts of an on-site wastewater treatment system in the fresh-cut fruit processing industry consisting of a membrane bioreactor (MBR), followed by reverse osmosis (RO) and ultraviolet (UV) disinfection. The system boundaries comprised raw materials extraction and processing, transportation, construction, operation, and waste disposal. SimaPro 8.0.4.26 was used as the software tool, supported by two impact assessment methods (ReCiPe v1.11 and TRACI v2.1). Analysis showed that the treatment capacity of the MBR and tertiary technologies contributed the least damage to the ecosystem when compared with the other three scenarios and can provide water for reuse. Treating wastewater in municipal wastewater treatment plants (WWTPs) mitigated eutrophication like the MBR system but resulted in more environmental impacts from climate change and human health when compared with the on-site treatment system. Findings will be informative to stakeholders in the fresh-cut agri-food sector seeking input into selecting the appropriate treatment approach, with water reuse a goal. PRACTITIONER POINTS: Life-cycle analysis was completed on a fruit processing facility using MBR + RO + UV. On site treatment with MBR + RO UV provides least amount of environmental impact. Use of MBR + RO + UV treatment on fruit wastewater allows for water reuse. ReCiPe v1.11 and TRACI v2.1 give similar LCA results, with TRACI recommended for North American analysis.

Systematic Review of Potential Occupational Respiratory Hazards Exposure Among Sewage Workers

Background: Sewage workers have a higher risk of exposure to various potential occupational respiratory hazards found in sewage plants. Although previous studies discuss occupational respiratory hazard concentration impacting sewage workers' respiratory health, the results are scarce and mixed. Hence, there is a need to identify the potential respiratory hazards in sewage plants so as to clarify the short- and long-term respiratory health effects. Therefore, this systematic review (SR) aims to critically review previous studies investigating potential respiratory hazards found at sewage plants and their effects on sewage workers' respiratory health. Methods: An SR was conducted using PubMed, EBSCO Medline, Web of Science, Scopus, and Google Scholar on peer-reviewed studies published between January 1994 and October 2020 evaluating the impact of potential exposure to respiratory hazards and its effects on respiratory health among sewage workers. "Sewage treatment plant," "respiratory hazards," and "respiratory health effects" were the three main search terms chosen in this SR. The inclusion criteria were (1) studies on potential occupational respiratory hazard exposure among sewage workers, (2) manuscripts written in English, and (3) studies published in the peer-reviewed literature. The human observational studies' quality was assessed using the Effective Public Health Practice Project Quality Assessment Tool. Results: We identified 5,660 articles through an initial database search. Only 26 items met the inclusion criteria and were included in this review; 15 human observational studies and 11 environmental assessment studies were conducted in the sewage industries. Most of the human observational studies were rated as moderate quality, two studies were rated as weak quality, and one study with strong quality was identified. Hydrogen sulfide, bioaerosols, particulate matter 2.5 (PM 2.5), and volatile organic compounds (VOC) were found to be potential respiratory hazards. Most of the risks contributed to adverse outcomes on the sewage workers' respiratory health with some inconsistent findings on the relationship between respiratory hazard exposure and respiratory health effects. Conclusion: Our review finds that, although this area is of great importance, quality studies are still lacking. There is a need for additional studies to clarify the effects of respiratory hazard exposure on sewage workers and respiratory health, especially PM 2.5 and VOC.

SARS-CoV-2 in environmental perspective: Occurrence, persistence, surveillance, inactivation and challenges

The unprecedented global spread of the severe acute respiratory syndrome (SARS) caused by SARS-CoV-2 is depicting the distressing pandemic consequence on human health, economy as well as ecosystem services. So far novel coronavirus (CoV) outbreaks were associated with SARS-CoV-2 (2019), middle east respiratory syndrome coronavirus (MERS-CoV, 2012), and SARS-CoV-1 (2003) events. CoV relates to the enveloped family of Betacoronavirus (βCoV) with positive-sense single-stranded RNA (+ssRNA). Knowing well the persistence, transmission, and spread of SARS-CoV-2 through proximity, the faecal-oral route is now emerging as a major environmental concern to community transmission. The replication and persistence of CoV in the gastrointestinal (GI) tract and shedding through stools is indicating a potential transmission route to the environment settings. Despite of the evidence, based on fewer reports on SARS-CoV-2 occurrence and persistence in wastewater/sewage/water, the transmission of the infective virus to the community is yet to be established. In this realm, this communication attempted to review the possible influx route of the enteric enveloped viral transmission in the environmental settings with reference to its occurrence, persistence, detection, and inactivation based on the published literature so far. The possibilities of airborne transmission through enteric virus-laden aerosols, environmental factors that may influence the viral transmission, and disinfection methods (conventional and emerging) as well as the inactivation mechanism with reference to the enveloped virus were reviewed. The need for wastewater epidemiology (WBE) studies for surveillance as well as for early warning signal was elaborated. This communication will provide a basis to understand the SARS-CoV-2 as well as other viruses in the context of the environmental engineering perspective to design effective strategies to counter the enteric virus transmission and also serves as a working paper for researchers, policy makers and regulators.

Size distribution, biological characteristics and emerging contaminants of aerosols emitted from an urban wastewater treatment plant

Air-liquid exchange process could spread pathogens and pharmaceutical emerging pollutants into the air as aerosol particles in an Urban wastewater treatment plants (UWTPs). These particles can later be transported to places where such pollution is unforeseen. In this study, measurements were conducted in the aeration area of a UWTP in northern Taiwan. According to this investigation, nanoparticles are major contributors to both the number and volume concentration of particles. Most fluorescent particles may be bacterial aggregates or fungal species. Moreover, nine common emerging contaminants were analyzed and found in both air and water samples. Among these contaminants, the most abundant chemicals in the air were erythromycin-H₂O (191.45 pg/m³) and methamphetamine (39.02 pg/m³). These results imply that UWTPs could be an emission source of emerging contaminants and bioaerosols, and the potential risk of inhalation exposure should be carefully evaluated.

Reducing bacterial aerosol emissions from membrane bioreactors: The impact of SRT and the addition of PAC and calcium

Bacterial aerosols resulting from membrane bioreactor (MBR) processes, which require excessive aeration in a confined space, are important to investigate because of their possible adverse effects on human health. This study investigated the influence of solid retention time (SRT) on bacterial aerosols from MBRs. Moreover, powdered activated carbon (PAC) and calcium were used to attenuate bacterial aerosol emissions from MBRs. The particulate matter (PM) emitted from the MBRs was reduced by 30.5 and 25.2% at SRTs of 20 and 80 d, respectively, compared to the level emitted at an SRT of 10 d. Total cell counts were similarly reduced at SRTs of 20 and 80 d. Longer SRTs also led to greater reductions in the particle size distribution of the sludge within 10 μm. Several factors in the MBR influenced the behavior of the bacterial aerosol emissions from the MBRs. This study showed that changes in viscosity and particle size induced by the SRT influenced the bacterial aerosol emissions in MBRs. Therefore, SRT was identified as an important design parameter affecting bacterial aerosol emissions in MBR processes. The amounts of particulate matter and bacterial aerosols were reduced in MBRs using PAC and calcium, both of which exerted an immediate effect on the bacterial aerosol emissions in MBRs by increasing the aerosol-particle size.

Nanobubble Technologies Offer Opportunities To Improve Water Treatment

Since first hypothesizing the existence of nanobubbles (NBs) in 1994, the empirical study of NB properties and commercialization of NB generators have rapidly evolved. NBs are stable spherical packages of gas within liquid and are operationally defined as having diameters less than 1000 nm, though they are typically in the range of 100 nm in one dimension. While theories still lack the ability to explain empirical evidence for formation of stable NBs in water, numerous NB applications have emerged in different fields, including water and wastewater purification where NBs offer the potential to replace or improve efficiency of current treatment processes. The United Nations identifies access to safe drinking water as a human right, and municipal and industrial wastewaters require purification before they enter water bodies. These protections require treatment technologies to remove naturally occurring (e.g., arsenic, chromium, fluoride, manganese, radionuclides, salts, selenium, natural organic matter, algal toxins), or anthropogenic (e.g., nitrate, phosphate, solvents, fuel additives, pharmaceuticals) chemicals and particles (e.g., virus, bacteria, oocysts, clays) that cause toxicity or aesthetic problems to make rivers, lakes, seawater, groundwater, or wastewater suitable for beneficial use or reuse in complex and evolving urban and rural water systems. NBs raise opportunities to improve current or enable new technologies for producing fewer byproducts and achieving safer water. This account explores the potential to exploit the unique properties of NBs for improving water treatment by answering key questions and proposing research opportunities regarding (1) observational versus theoretical existence of NBs, (2) ability of NBs to improve gas transfer into water or influence gas trapped on particle surfaces, (3) ability to produce quasi-stable reactive oxygen species (ROS) on the surface of NBs to oxidize pollutants and pathogens in water, (4) ability to improve particle aggregation through intraparticle NB bridging, and (5) ability to mitigate fouling on surfaces. We conclude with key insights and knowledge gaps requiring research to advance the use of NBs for water purification. Among the highest priorities is to develop techniques that measure NB size and surface properties in complex drinking and wastewater chemistries, which contain salts, organics, and a wide variety of inorganic and organic colloids. In the authors' opinion, ROS production by NB may hold the greatest promise for usage in water treatment because it allows movement away from chemical-based oxidants (chlorine, ozone) that are costly, dangerous to handle, and produce harmful byproducts while helping achieve important treatment goals (e.g., destruction of organic pollutants, pathogens, biofilms). Because of the low chemical requirements to form NBs, NB technologies could be distributed throughout rapidly changing and increasingly decentralized water treatment systems in both developed and developing countries.

Real-Time Ultrafine Aerosol Measurements from Wastewater Treatment Facilities

Airborne particle emissions from wastewater treatment plants (WWTP) have been associated with health repercussions but particulate quantification studies are scarce. In this study, particulate matter (PM) number concentrations and size distributions in the ultrafine range (7-300 nm) were measured from two different sources: a laboratory-scale aerobic bioreactor and the activated sludge aeration basins at Orange County Sanitation District (OCSD). The relationships between wastewater parameters (total organic carbon (TOC), chemical oxygen demand (COD), and total suspended solids (TSS)), aeration flow rate and particle concentrations were also explored. A significant positive relationship was found between particle concentration and WWTP variables (COD: r(10) = 0.876, p <.001, TOC: r(10) = 0.664, p <.05, TSS: r(10) = 0.707, p <.05, aeration flow rate: r(8) = 0.988, p <.0001). A theoretical model was also developed from empirical data to compare real world WWTP aerosol number emission fluxes with laboratory data. Aerosol number fluxes at OCSD aerated basins (9.8 × 10⁴ lbs/min·cm²) and the bioreactor (7.95 × 10⁴ lbs/min·cm²) were calculated and showed a relatively small difference (19%). The ultrafine size distributions from both systems were consistent, with a mode of ∼48 nm. The average mass concentration (7.03 μg/cm³) from OCSD was relatively small compared to other urban sources. However, the in-tank average number concentration of airborne particles (14 480 lbs/cm³) was higher than background ambient concentrations.

Evaluating exposure of pedestrians to airborne contaminants associated with non-potable water use for pavement cleaning

Climate change and increasing demography press local authorities to look after affordable water resources and replacement of drinking water for city necessities like street and pavement cleaning by more available raw water. Though, the substitution of drinking by non-drinking resources demands the evaluation of sanitary hazards. This article aims therefore to evaluate the contribution of cleaning water to the overall exposure of city dwellers in case of wet pavement cleaning using crossed physical, chemical and biological approaches. The result of tracer experiments with fluorescein show that liquid water content of the cleaning aerosol produced is about 0.24 g m(-3), rending possible a fast estimation of exposure levels. In situ analysis of the aerosol particles indicates a significant increase in particle number concentration and particle diameter, though without change in particle composition. The conventional bacterial analysis using total coliforms as tracer suggests that an important part of the contamination is issued from the pavement. The qPCR results show a more than 20-fold increase of background genome concentration for Escherichia coli and 10-fold increase for Enterococcus but a negligible contribution of the cleaning water. The fluorescence analysis of the cleaning aerosol confirms the above findings identifying pavement surface as the major contributor to aerosol organic load. The physical, chemical and microbiological approaches used make it possible to describe accurately the cleaning bioaerosol and to identify the existence of significantly higher levels of all parameters studied during the wet pavement cleaning. Though, the low level of contamination and the very short time of passage of pedestrian in the zone do not suggest a significant risk for the city dwellers. As the cleaning workers remain much longer in the impacted area, more attention should be paid to their chronic exposure.

Biogenic acids produced on epoxy linings installed in sewer crown and tidal zones

In this study the biogenic acids generated by microbes on the surface of Bisphenol A epoxy mortar coupons were investigated for up to 30 months. The epoxy coupons were installed in six sewers in three city locations, Sydney, Melbourne and Perth. Coupons were installed in both the crown and the tidal zones of the sewers to capture the effect of location within the pipe on acid production. The coupons were retrieved approximately every 6 months to provide a dynamic analysis of the biogenic acid production. Our results reveal the colonisation of epoxy mortar by the more aggressive acidophilic bacteria occurred within six months to two years of their installation in the sewer pipes. Biogenic acid generation appear to occur homogeneously from the tidal zone to the crown of the sewer pipes. The reduction in the surface pH of the epoxy lining was supported by the successive growth of microbes beginning with fungi followed be neutrophilic and heterotrophic bacteria and finally by the acidophilic bacteria and the corresponding accumulation of organic and sulphuric acids attributed to these organisms. This study also revealed the potential inhibiting effects on the microbes induced by the accumulation of metabolic products on the epoxy surface. The accumulation of organic acids and H2S coincided with the growth and metabolism inhibition of fungi and acidophilic bacteria. These results provide insights into the microbial interaction and biogenic acids production that contribute to lining degradation and corrosion of concrete in sewer pipes.