Removal of human enteric viruses by a full-scale membrane bioreactor during municipal wastewater processing

In the US, human enteric viruses are the main etiologic agents of childhood gastroenteritis, resulting in several hospitalizations and deaths each year. These viruses have been linked to several waterborne diseases, such as acute gastroenteritis, conjunctivitis and respiratory illness. The removal of human enterovirus (EV) and norovirus genogroup II (NoV GGII) was studied in a full-scale membrane bioreactor (MBR) wastewater treatment plant (WWTP) and compared with the removal of human adenovirus (HAdV). In total, 32 samples were quantified using real-time reverse transcription-PCR (RT-PCR) from four separate locations throughout the treatment process; influent, primary settling effluent, membrane influent (which includes the MLSS) and membrane effluent. EV was detected in all 32 samples (100%) with an average concentration of 1.1 × 107 and 7.8 × 101 viruses/L for the membrane influent and membrane effluent, respectively. NoV GGII was detected in 20 of 32 samples (63%) with an average membrane influent and membrane effluent concentration of 2.8 × 105 and 1.2 × 101 viruses/L, respectively. HAdV was detected in all 32 samples with an average membrane influent concentration of 5.2 × 108 and 2.7 × 103 viruses/L in the membrane effluent. Our findings indicate that this particular full-scale MBR treatment was able to reduce the viral loads by approximately 5.1 and 3.9 log units for EV and NoV GGII as compared to 5.5 log units for HAdV. This full-scale MBR system outperformed the removal observed in previous pilot and bench scale studies by 1 to 2 log units. To the best of our knowledge, this is the first study focusing on the removal of EV in a full-scale MBR WWTP using real-time RT-PCR, and on the solid–liquid distribution of EV and NoV GII in secondary biological treatment.

► In this study, average removal values for HAdV, EV and NoV GGII were 5.5 (4.1 to 6.3, range), 5.1 (4.1 to 6.8, range) and 3.9 (3.5 to 4.8, range) log units, respectively by the MBR process.
► HAdV, EV and NoV GGII were removed at approximately 3.0 (2.2 to 3.6, range), 3.6 (1.9 to 4.6, range) and 4.7 (4.6 to 5.1, range) log units throughout the entire treatment process.
► After the membrane influent samples were allowed to settle, 99.8%, 97.1% and 96.0% of HAdV, EV and NoV GII concentration was associated with the settled solids showing a high affinity of the viruses for the suspended solids.