Rimozione di Cryptosporidium e Giardia in impianti di potabilizzazione dell’area vasta fiorentina

Five drinking water treatment plants in the Tuscan area, differing in relation to the treatments employed, were monitored for the presence of Cryptosporidium and Giardia (oo)cysts in order to estimate their removal capacity of each works. Twenty-eight water samples (16 from inflow raw water and 12 from outflow drinking water) were analysed during the one-year survey. The US EPA 1623 method was used, obtaining, according to the PHLS quality control system, a recovery rate of 51.3 +/- 22.9% for Cryptosporidium oocysts and 48.8 +/- 20.7% for Giardia cysts. The results showed that both the protozoa were present in surface raw waters: Cryptosporidium in 62.5% and Giardia in 87.5% of the samples. Considering the outflow drinking waters, the removal capacity varied from 100% in the technologically more complex plant (which supplies most of the area), to at least 90% in the remaining four plants, where less complex treatments are carried out. The occurrence of (oo)cysts was not associated with seasonality, turbidity or Clostridium perfringens (Cl. perfringens seems to be related with Cryptosporidium oocysts in surface raw waters; in this respect, our legislation states that the protozoa have to be searched for whenever a water sample is positive for Cl. perfringens). We confirmed the validity of the US-EPA 1623 method in assessing and managing the risk associated with waterborne protozoa, thus a valid tool to safeguard the population from exposure to such pathogens.