Domestic wastewater contains various pathogens, which, if not sufficiently eliminated, may enter the receiving water bodies and cause water-transmitted diseases. Among the waterborne pathogens, viruses may occur, survive and/or decay much differently from bacteria in water. In many cases, the diseases caused by viruses are more severe. Therefore, research efforts are mainly directed at the behavior of viruses in water environments, as well as the elimination of viruses from wastewater. In this paper, an overview of the occurrence of viruses in wastewater is presented, together with their categories, methods of detection and potential to cause waterborne diseases. As wastewater treatment plants are critical nodes for the influx and termination of virus transmission, the behavior of viruses at each stage of treatment is reviewed. Particular attention is paid to the unit operations, which play crucial roles in virus removals, such as coagulation and membrane filtration, and that for virus inactivation, such as chemical disinfection and UV irradiation. Future needs for the development of new technologies for virus elimination, source control, and finding more suitable indicators of viral pathogens are also highlighted.
The investigation on bioaerosol in wastewater treatment plant (WWTP) located in Xi'an was conducted to understand the characteristics of bioaerosol released from wastewater and sludge treatment facilities, since the bioaerosol may pose threat to human health. By means of Andersen impactor sampler collection and colony-counting method, bioaerosol concentrations and size distribution were detected. The risk quotient method was used to evaluate the health risks associated with inhalation of bioaerosol for WWTP staff, based on the average daily dose rates of exposure. The related health risk regarding to Legionella pneumophila was quantitatively calculated by quantitative microbial risk assessment (QMRA), based on the assumption of the percentage. The maximum concentration of airborne bacteria (3,767 ± 280 CFU/m3) and fungi (8,775 ± 406 CFU/m3) occurred from the aerated grit chamber and sludge thickening house, respectively, which all exceeded 500 CFU/m3 as the acceptable guideline proposed by the American Conference of Governmental Industrial Hygienists. The particle size of airborne bacteria was mainly distributed in the first three stages (>3.3 μm), while that of airborne fungi was from the second to the fourth stage (2.1–7.0 μm). HIs of exposure to bioaerosol for adult males and females by inhalation were higher than 1. Meanwhile, the proportion of Legionella pneumophila should be strictly controlled below to as low as 10−8, based on the QMRA approach.
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