The Geological Characteristics of the Vadose Zone Influence the Impact of Treated Wastewater on the Groundwater Quality (SCA.Re.S. Project 2019-2020)

This study evaluated whether some chemical and microbial contaminants in treated sewageeffluents from two wastewater treatment plants (WWTP) reached the groundwater when they drainedthrough a fractured karst vadose zone (WWTP-K) and a porous vadose zone (WWTP-P). Forty-fivesamples of sewage water (SW), treated water (TW), and monitoring well (MW), collected from WWTPP(24) and WWTP-K (21), were analyzed for a range of microbiological and chemical properties. TheE. coli and Salmonella counts were below the limits outlined in the Legislative Decree 152/06 ineffluents from both types of WWTP. Enteric viruses were found in 37.5% and 12.5% of the SW andTW from WWTP-P, respectively. The percentages of Pepper mild mottle virus isolated were higherin TW (62.5% in WWTP-P, 85.7% in WWTP-K) than in SW and MW. The residual concentrations ofcontaminants of emerging concern (CEC) of each drug category were higher in the MW downstreamof WWTP-K than of WWTP-P. Our results showed that the porous vadose zone was more effectiveat reducing the contaminant loads than the fractured karst one, especially the CEC, in the effluent.The legislation should include other parameters to minimize the risks from treated effluent that isdischarged to soil.