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. 2021 Sep 1:202:117435.
doi: 10.1016/j.watres.2021.117435. Epub 2021 Jul 15.

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

Albert Serra-Compte  1 , Susana González  2 , Marina Arnaldos  2 , Sabrina Berlendis  3 , Sophie Courtois  3 , Jean Francois Loret  3 , Olivier Schlosser  3 , Adela M Yáñez  4 , Elena Soria-Soria  4 , Mariana Fittipaldi  4 , Gemma Saucedo  5 , Anna Pinar-Méndez  5 , Miquel Paraira  5 , Belén Galofré  5 , Juan M Lema  6 , Sabela Balboa  6 , Miguel Mauricio-Iglesias  6 , Albert Bosch  7 , Rosa M Pintó  7 , Isabelle Bertrand  8 , Christophe Gantzer  8 , Carlos Montero  2 , Xavier Litrico  9
Affiliations

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

Albert Serra-Compte et al. Water Res. .

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.

Keywords: COVID-19; SARS-CoV-2; Sludge; WWTP; Wastewater.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Image, graphical abstract
Graphical abstract
Fig. 1
Fig. 1
Influent wastewater samples from the different targeted WWTP. Y-axis represents the COVID-19 prevalence rate in the corresponding area at the time of sampling. Filled dots represent SARS-CoV-2 RNA positive samples whereas empty dots represent no SARS-CoV-2 RNA occurrence.
Fig. 2
Fig. 2
The graph shows integrated results of all WWTPs monitored. Primary (n=5), secondary (n=30), tertiary (n=2). A) Percentage of positive and negative samples for SARS-CoV-2 RNA occurrence in each water treatment step and B) SARS-CoV-2 RNA log removal in each treatment step comparing influent and effluent concentration in each treatment.
Fig. 3
Fig. 3
The graph shows integrated results of all WWTPs monitored. Activated sludge (n=11), activated sludge plus nutrient removal (n=11), MBR (n=8). A) Percentage of positive and negative samples for SARS-CoV-2 RNA occurrence in each treatment process and B) SARS-CoV-2 RNA log removal in each treatment process comparing influent and effluent concentrations after each treatment.
Fig. 4
Fig. 4
The graph shows integrated results of all WWTPs monitored. Primary sludge (n=6), secondary sludge (n=14), thickened sludge (n=13), digested sludge (n=7), digested sludge plus thermal hydrolysis (n=5) A) Percentage of positive and negative samples for SARS-CoV-2 RNA in sludge samples and B) Boxplot showing first and third quartiles and the median value of SARS-CoV-2 RNA log removal in each sludge matrix comparing influent and effluent samples after each treatment.
Fig. 5
Fig. 5
SARS-CoV-2 RNA and F-specific RNA bacteriophages concentration Log (copies/L) along the different steps of a selected WWTP. n. d. = not detected. Bars represent mean values (n=4) with the corresponding standard deviation.
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