Abstract
The aim of this study was to evaluate the effectiveness of the novel aerobic granular sludge (AGS) wastewater treatment technology in removing faecal indicator organisms (FIOs) compared to the conventional activated sludge (CAS) treatment system. The work was carried out at two full-scale wastewater treatment plants (WWTP) in the Netherlands, Vroomshoop and Garmerwolde. Both treatment plants have a CAS and AGS system operated in parallel. The parallel treatment lines are provided with the same influent wastewater. The concentrations of the measured FIOs in the influent of the two WWTPs were comparable with reported literature values as follows: F-specific RNA bacteriophages at 106 PFU/100 mL, and Escherichia coli (E. coli), Enterococci, and Thermotolerant coliforms (TtC) at 105 to 106 CFU/100 mL. Although both systems (CAS and AGS) are different in terms of design, operation, and microbial community, both systems showed similar FIOs removal efficiency. At the Vroomshoop WWTP, Log10 removals for F-specific RNA bacteriophages of 1.4 ± 0.5 and 1.3 ± 0.6 were obtained for the AGS and CAS systems, while at the Garmerwolde WWTP, Log10 removals for F-specific RNA bacteriophages of 1.9 ± 0.7 and 2.1 ± 0.7 were found for the AGS and CAS systems. Correspondingly, E. coli, Enterococci, and TtC Log10 removals of 1.7 ± 0.7 and 1.1 ± 0.7 were achieved for the AGS and CAS systems at Vroomshoop WWTP. For Garmerwolde WWTP Log10 removals of 2.3 ± 0.8 and 1.9 ± 0.7 for the AGS and CAS systems were found, respectively. The measured difference in removal rates between the plants was not significant. Physicochemical water quality parameters, such as the concentrations of organic matter, nutrients, and total suspended solids (TSS) were also determined. Overall, it was not possible to establish a direct correlation between the physicochemical parameters and the removal of FIOs for any of the treatment systems (CAS and AGS). Only the removal of TSS could be positively correlated to the E. coli removal for the AGS technology at the evaluated WWTPs.
Highlights
Pathogens enter the aquatic environment through municipal wastewater discharges; their occurrence in either treated or raw wastewater may contribute to spreading epidemiological waterborne diseases (Bijkerk et al, 2015; Efstratiou et al, 2017)
F-specific RNA bacteriophages were detected in both wastewater treatment plants (WWTP) at an arithmetic mean concentration of 106 plaque-forming units (PFU)/100 mL; Enterococci were detected at mean concentrations of 105 colony forming units (CFU)/100 mL; and Thermotolerant coliforms (TtC) and E. coli bacteria both at the same order of magnitude (106 CFU/100 mL) in both WWTPs
At the Vroomshoop WWTP, the minimum influent concentrations for all the target organisms were approximately between one to three orders of magnitude lower than the average concentrations. These lower values were measured in samples that were diluted with rain water because they were taken during rainy weather flow (RWF) events, with a flowrate of around 800 m3/h being more than 63% of the operational design average peak flow (Table 1)
Summary
Pathogens enter the aquatic environment through municipal wastewater discharges; their occurrence in either treated or raw wastewater may contribute to spreading epidemiological waterborne diseases (Bijkerk et al, 2015; Efstratiou et al, 2017). Lodder and de Roda Husman (2005) and van Beek et al (2016) reported the presence of noroviruses and enteric viruses in river basins in the Netherlands originating from treated municipal wastewater discharges. F-specific RNA bacteriophages characteristics, such as their isoelectric point, size (22e29 nm), and morphology (Grabow, 2001; Lodder and de Roda Husman, 2005) resemble human viruses such as noroviruses and other enteric viruses (Fauvel et al, 2017). Bacteriophages are easier to detect than human viruses; inexpensive conventional analytical methods can be used to determine them
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