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

Abstract

This study evaluated whether some chemical and microbial contaminants in treated sewage effluents from two wastewater treatment plants (WWTP) reached the groundwater when they drained through a fractured karst vadose zone (WWTP-K) and a porous vadose zone (WWTP-P). Forty-five samples of sewage water (SW), treated water (TW), and monitoring well (MW), collected from WWTP-P (24) and WWTP-K (21), were analyzed for a range of microbiological and chemical properties. The E. coli and Salmonella counts were below the limits outlined in the Legislative Decree 152/06 in effluents from both types of WWTP. Enteric viruses were found in 37.5% and 12.5% of the SW and TW from WWTP-P, respectively. The percentages of Pepper mild mottle virus isolated were higher in TW (62.5% in WWTP-P, 85.7% in WWTP-K) than in SW and MW. The residual concentrations of contaminants of emerging concern (CEC) of each drug category were higher in the MW downstream of WWTP-K than of WWTP-P. Our results showed that the porous vadose zone was more effective at 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 is discharged to soil.

Factors Influencing Microbial Contamination of Groundwater: A Systematic Review of Field-Scale Studies

“…Effluents from WWTPs, including on-site systems (OSWTS), as a potential point sources of groundwater contamination, were also discussed [52,60,63,65,72] as well as the impacts of untreated wastewater [67,69], septic tanks [58], and a municipal solid waste (MSW) dumpsite [68].…”

“…For example, one study compared the behaviour of microorganisms in porous and fractured aquifers [66]. Another one compared the fate of microorganisms in a porous aquifer and a karst aquifer [72]. Finally, one study involved an aquifer that comprised an unsaturated porous zone and a saturated fractured zone [64].…”

“…Bacterial species or groups were considered in nineteen studies [50,51,[53][54][55][56][57][59][60][61][62][63][64][66][67][68][69][70]73] and five papers reported the behaviour of both bacteria and viruses [52,58,65,71,72].…”

“…With regard to bacterial species, the environmental fate of E. coli was widely studied [50,52,[54][55][56][57]59,60,[63][64][65][66][67][69][70][71][72][73]. Bacillus subtilis endospores [52,57], Campylobacter jejuni [57], and Clostridium perfringens [72] were also reported.…”

“…With regard to bacterial species, the environmental fate of E. coli was widely studied [50,52,[54][55][56][57]59,60,[63][64][65][66][67][69][70][71][72][73]. Bacillus subtilis endospores [52,57], Campylobacter jejuni [57], and Clostridium perfringens [72] were also reported. Many studies focused on the observation of faecal indicator bacteria such as total coliforms [50,63,64,66,[68][69][70][71], faecal coliforms (including thermotolerant coliforms) [51][52][53]57,58,65,66,68], and enterococci (including faecal streptococci and Enterococcus spp.)…”