systems and include, among others, Pseudomonas syringae, Ralstonia
solanacearum, Corynebacterium flaccumfaciens, Erwinia spp., and Xanthomonas
spp. [70]. Some species of Xanthomonas, Pseudomonas, and other phytopathogenic
agents such as Herbaspirillum and Acidovorax or Staphylococcus and Pseudomonas
are particularly monitored because they can originate from hospitals’ WW
[71]. Evidence of possible risks are supported by reports involving the use of
recycled freshwater in plant nurseries and greenhouses, concluding that this can be
identified as an important source for the spread of plant pathogens [72]. More studies
on the presence of phytopathogens in treated WW need to be done for assessing the
risks posed by WW irrigation.
4.3 Viral Components of the Sludge Microbiome
In a typical WWTP, the number of viral particles varies from 10
8 ml
À1 to 10
10 ml
À1 ,
10–1,000 times higher than in other aquatic environments [73–75] suggesting that
WWTPs can be considered as an important reservoir of viruses. Despite viruses’
importance in WWTPs and their potential impact on surrounding environments after
discharge, little is known about their diversity, function, and fate throughout the
treatment of a typical WWTP. The few metagenomic studies revealed novel diversity and function of DNA viral communities in the influent, activated sludge,
anaerobic sludge digester, and effluent of a domestic WWTP. The few molecular
studies show that many viruses found in the WWTP are novel, resulting in only
<5–20% of the sequence reads being phylogenetically or functionally assigned
[76]. Viruses of the families Tombusviridae, Geminiviridae, and Nanoviridae were
identified [77, 78]. The most recent studies of the sludge microbiome show an
important underestimation of diversity of sewage sludge viruses infecting humans.
These studies demonstrate the prevalence of respiratory viruses in sewage sludge.
Herpesviruses and coronaviruses were found to be responsible for infections, one of
which is latent and the other acute and can be fatal [8]. Viruses are also predicted to
account for the most significant fraction of human illnesses in sewage-contaminated
water under specific exposure scenarios [79].
4.4 Antibiotic-Resistant Bacteria, Genes, and Mobile Genetic
Elements
WW effluents generally retain a variety of antimicrobial components, antibioticresistant bacteria (ARBs), antibiotic resistance genes (ARGs), as well as mobile
genetic elements even after treatment [23, 30, 80]. In soils, through WW irrigation or
sludge fertilization, antimicrobial compounds can disrupt the structure and activity
of telluric microbial communities [22, 48, 81]. In fact, disturbances of the nitrogen
Environmental, Economic, and Ethical Assessment of the Treated Wastewater and. . .
65
solanacearum, Corynebacterium flaccumfaciens, Erwinia spp., and Xanthomonas
spp. [70]. Some species of Xanthomonas, Pseudomonas, and other phytopathogenic
agents such as Herbaspirillum and Acidovorax or Staphylococcus and Pseudomonas
are particularly monitored because they can originate from hospitals’ WW
[71]. Evidence of possible risks are supported by reports involving the use of
recycled freshwater in plant nurseries and greenhouses, concluding that this can be
identified as an important source for the spread of plant pathogens [72]. More studies
on the presence of phytopathogens in treated WW need to be done for assessing the
risks posed by WW irrigation.
4.3 Viral Components of the Sludge Microbiome
In a typical WWTP, the number of viral particles varies from 10
8 ml
À1 to 10
10 ml
À1 ,
10–1,000 times higher than in other aquatic environments [73–75] suggesting that
WWTPs can be considered as an important reservoir of viruses. Despite viruses’
importance in WWTPs and their potential impact on surrounding environments after
discharge, little is known about their diversity, function, and fate throughout the
treatment of a typical WWTP. The few metagenomic studies revealed novel diversity and function of DNA viral communities in the influent, activated sludge,
anaerobic sludge digester, and effluent of a domestic WWTP. The few molecular
studies show that many viruses found in the WWTP are novel, resulting in only
<5–20% of the sequence reads being phylogenetically or functionally assigned
[76]. Viruses of the families Tombusviridae, Geminiviridae, and Nanoviridae were
identified [77, 78]. The most recent studies of the sludge microbiome show an
important underestimation of diversity of sewage sludge viruses infecting humans.
These studies demonstrate the prevalence of respiratory viruses in sewage sludge.
Herpesviruses and coronaviruses were found to be responsible for infections, one of
which is latent and the other acute and can be fatal [8]. Viruses are also predicted to
account for the most significant fraction of human illnesses in sewage-contaminated
water under specific exposure scenarios [79].
4.4 Antibiotic-Resistant Bacteria, Genes, and Mobile Genetic
Elements
WW effluents generally retain a variety of antimicrobial components, antibioticresistant bacteria (ARBs), antibiotic resistance genes (ARGs), as well as mobile
genetic elements even after treatment [23, 30, 80]. In soils, through WW irrigation or
sludge fertilization, antimicrobial compounds can disrupt the structure and activity
of telluric microbial communities [22, 48, 81]. In fact, disturbances of the nitrogen
Environmental, Economic, and Ethical Assessment of the Treated Wastewater and. . .
65