Removal Performance of SARS-CoV-2 in Wastewater Treatment by Membrane Bioreactor, Anaerobic-Anoxic-Oxic, and Conventional Activated Sludge Processes

The potential risk of SARS-CoV-2 in treated effluent from a wastewater treatment plant (WWTP) is concerned since SARS-CoV-2 is contained in wastewater during COVID-19 outbreak. However, removal of SARS-CoV-2 in WWTP is virtually unknown. The objective of this study is (i) to clarify removal performance of SARS-CoV-2 in a WWTP, (ii) to compare removal performance among different secondary treatment processes, and (iii) to evaluate applicability of PMMoV as the performance indicator for reduction of SARS-CoV-2 in wastewater treatment. Influent wastewater, secondary treatment effluent (before chlorination) and the final effluent (after chlorination) were collected from a WWTP during the 28 May to 24 September of COVID-19 outbreak in Japan. The target WWTP had three parallel treatment systems by conventional activated sludge (CAS), anaerobic-anoxic-oxic (A2O) and membrane bioreactor (MBR) processes. SARS-CoV-2 in both liquid and solid fractions of influent wastewater was concentrated and quantified by RT-qPCR. SARS-CoV-2 in treated effluent was concentrated from 10 L samples to achieve the detection limit as low as 10 copies/L. Log reduction values (LRVs) of SARS-CoV-2 was 2.7 ± 0.86 log 10 in CAS, 1.6 ± 0.50 log 10 in A2O, and 3.6 ± 0.62 log 10 in MBR. The lowest LRV observed during the sampling period was 2.8 log 10 in MBR, 1.2 log 10 in CAS, and 1.0 log 10 in A2O, indicating that MBR had the most stable reduction performance. PMMoV was found to be a good indicator virus to evaluate reduction performance of SARS-CoV-2 independent of the process configurations, because LRV of PMMoV was significantly lower than that of SARS-CoV-2 in CAS, A2O and MBR processes.