This study involved collaboration between three centres with expertise in viruses, bacteria and protozoa. The focus of the research was the study of the dissemination and removal of pathogens and faecal indicators in two sewage treatment plants (STP1 and STP2) using tertiary treatments. Samples were collected over a period of five months through the sewage treatment processes. Analysis of the samples revealed that the plants were not efficient at removing the faecal indicators and pathogens tested during the study. From entry point (raw sewage) to effluent level (tertiary treatment effluent water), the experimental results showed that the reduction ratios of human adenoviruses were 1.2 log10 in STP1 and 1.9 log10 in STP2. Whereas for Giardia spp. and Cryptosporidium spp. the reduction ratios were 2.3 log10 for both pathogens in STP1, and 3.0 and 1.7 log10 in STP2, respectively. Furthermore, the presence of faecal indicators and pathogens at different sampling points was evaluated revealing that the tested pathogens were present in reclaimed water. Human adenovirus and Arcobacter spp. showed positive results in infectivity assays for most of the tertiary effluent water samples that comply with current legislation in Spain. The pathogens detected must be evaluated using a risk assessment model, which will be essential for the development of improved guidelines for the re-use of reclaimed water.

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