Virus removal in conventional wastewater treatment process

: Little has been published in the scientific literature on the distribution of pathogenic viruses and on their removal in the different treatment phases in wastewater treatment plants in Italy. Recent advances in molecular biology have reduced analytic costs and allowed the detection of virus directly in the environment. This study evaluates the presence of enteric viruses and their removal in three treatment plants of different sizes and which use different treatment methods. Overall 92 samples were collected during three seasonal campaigns (winter, spring-summer, and autumn). Samples were collected at different phases of the treatment process. Chemical and microbiological analyses were performed. Samples were concentrated by ultrafiltration and tested for the presence of hepatitis A virus, adenovirus, rotavirus, astrovirus, norovirus and enteroviruses. All viruses, excluding the Enteroviruses were detected through biomolecular testing. Enteroviruses, were isolated on BGM cells and subsequently genotyped at the VP1 region. Sixty-two of the 92 samples tested positive for viruses; of these, 21 tested positive for HAV, 4 for adenovirus, 9 for rotavirus, 21 for astrovirus, and 7 for norovirus. Enteroviruses were present on average in 44% of samples collected during the three sampling campaigns. Hepatitis A virus was isolated during the spring-summer period while Astroviruses were identified in all three sampling campaigns. Different enteroviruses were isolated, including four types of Coxsackie B virus variably isolated in all three campaigns, and type 1 Echovirus isolated in the second and third campaigns. All detected polioviruses were of the vaccine-type and were identified as types 1 and 3. Both viral genotypes of Norovirus were identified. Adenoviruses were only sporadically isolated and rotaviruses were identified as type A. As expected, results show a greater prevalence of Enteroviruses and this reflects viral circulation in the population. Regarding the efficacy of the different treatment stages, primary treatment was found to remove only small percentages of viruses, while activated sludge e subsequent sedimentation were found to be more effective.