Elimination of SARS-CoV-2 along wastewater and sludge treatment processes

Abstract

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is shed in the feces of infected people. As a consequence, genomic RNA of the virus can be detected in wastewater. Although the presence of viral RNA does not inform on the infectivity of the virus, this presence of genetic material raised the question of the effectiveness of treatment processes in reducing the virus in wastewater and sludge. In this work, treatment lines of 16 wastewater treatment plants were monitored to evaluate the removal of SARS-CoV-2 RNA in raw, processed waters and sludge, from March to May 2020. Viral RNA copies were enumerated using reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) in 5 different laboratories. These laboratories participated in proficiency testing scheme and their results demonstrated the reliability and comparability of the results obtained for each one. SARS-CoV-2 RNA was found in 50.5% of the 101 influent wastewater samples characterized. Positive results were detected more frequently in those regions with a COVID-19 incidence higher than 100 cases per 100,000 inhabitants. Wastewater treatment plants (WWTPs) significantly reduced the occurrence of virus RNA along the water treatment lines. Secondary treatment effluents showed an occurrence of SARS-CoV-2 RNA in 23.3% of the samples and no positive results were found after MBR and chlorination. Non-treated sludge (from primary and secondary treatments) presented a higher occurrence of SARS-CoV-2 RNA than the corresponding water samples, demonstrating the affinity of virus particles for solids. Furthermore, SARS-CoV-2 RNA was detected in treated sludge after thickening and anaerobic digestion, whereas viral RNA was completely eliminated from sludge only when thermal hydrolysis was applied. Finally, co-analysis of SARS-CoV-2 and F-specific RNA bacteriophages was done in the same water and sludge samples in order to investigate the potential use of these bacteriophages as indicators of SARS-CoV-2 fate and reduction along the wastewater treatment.

Wastewater and Marine Bioindicators Surveillance to Anticipate COVID-19 Prevalence and to Explore SARS-CoV-2 Diversity by Next Generation Sequencing: One-Year Study

“…In addition, and in contrast to other research conducted on the presence of SARS-CoV-2 in sewage, our study aimed also at exploring the detection of the virus in the marine environment and the capacity of the WWTP to remove the virus (Galicia is well known for its fish, shellfish and aquaculture activities). Our results confirmed the capacity of the biological reactors and the disinfection system in WWTP to eliminate the virus (Balboa et al, 2021;Serra-Compte et al, 2021). The impact in the marine environment was of minor importance and the detection of the virus in seawater and wild and aquacultured mussels can be associated to uncontrolled discharge of wastewater and alleviation from the sewage network.…”

Sources, fates and treatment strategies of typical viruses in urban sewage collection/treatment systems: A review

“…Although the utilization of anaerobic digestion alone was ineffective in the elimination of EV (1 log reduction) and SARS-CoV-2, the combination of mesophilic anaerobic digestion and thermal hydrolysis has been regarded as one of the most effective approaches to virus inactivation [226] . Similarly, the recent work of Serra-Compte et al found the log removal of viruses during traditional digestion to be negative (mean values of −0.17 ± 0.89), while it was 1.69 ± 0.27 for thermal hydrolysis+anaerobic digestion, which is closely related to the inactivation of the viruses by saturated steam at 150–160 °C [227] . For sludge air-drying, the infectivity of viruses declined with the continuous increase in solid content [228] ; moreover, such inactivation was irreversible because of the disintegration of viral particles and release of RNA genomes.…”

Molecular Monitoring of SARS-CoV-2 in Different Sewage Plants in Venice and the Implications for Genetic Surveillance

“…Indeed, to date no viable virions have been isolated from posttreatment wastewater samples testing positive for SARS-CoV-2 by molecular assays, 24 and most studies have confirmed the complete removal of viral RNA traces at the end of an MBR disinfection line. 11 , 20 , 59 …”