Removal of Noro- and Enteroviruses, Giardia Cysts, Cryptosporidium Oocysts, and Fecal Indicators at Four Secondary Wastewater Treatment Plants in Sweden

The aim of this study was to investigate variation in the occurrence and removal of enteroviruses, noroviruses, Giardia cysts, Cryptosporidium oocysts, and the most commonly used fecal indicators in four Swedish secondary wastewater treatment plants (WWTPs). Paired samples were taken from the inlet and outlet of each WWTP. (Oo)cysts and indicators were enumerated with standard methods and viruses with a reverse transcriptase polymerase chain reaction. Giardia cysts and enteroviruses were constantly detected (mean numbers were $10^{3.31}$ cysts and $10^{4.44}$ polymerase chain reaction (PCR) units ${\rm L}^{-1}$ , respectively). Oocysts were found in 5 out of 19 samples (mean number was 20 ${\rm L}^{-1}$ ). Noroviruses were found between November and February, with an average titer of $10^{3.29}\ {\rm L}^{-1}$ . Mean cyst removal was 2.6 log, while noroviruses and enteroviruses were removed by 0.9 and 1.3 log, respectively. There was no correlation between the removals of pathogens and indicators (p > 0.05). Coliphage removal resembled human viral removal better than did F-specific phage.