communities able to remove toluene and TPH in BES reactors and microcosms that
simulate marine environments (Cruz Viggi et al. 2015; Daghio et al. 2016; Matturro
et al. 2017). In particular, microorganisms of the family Desulfobulbaceae seem to
be the key players since their presence has been reported in several studies (Daghio
et al. 2016, 2018a, b; Matturro et al. 2017). Members of the family
Desulfobulbaceae, called cable bacteria, have been extensively described to couple
sulfide oxidation with reduction of spatially distant oxygen by delivering electrons
over long distances (Müller et al. 2016; Pfeffer et al. 2012; Schauer et al. 2014), and
they might be also involved in electron transfer processes during the hydrocarbon
removal in BES. Hydrocarbons can be oxidized via sulfate reduction (with formation
of sulfide) and the bacteria of the family Desulfobulbaceae could oxidize sulfide to
elemental sulfur on the anode surface and transfer the electrons to the anode (Daghio
et al. 2018a). Elemental sulfur can be reduced to sulfide by members of the
Desulfuromonadaceae forming a cycle (Bond et al. 2002; Daghio et al. 2016,
2018a; Dutta et al. 2009) or being oxidized back to sulfate (Zhang et al. 2014)
regenerating the electron acceptor for sulfate reducers. The effect of the sulfate
reduction during the removal of PAHs (i.e., naphthalene, 2-methylnaphthalene,
and phenanthrene) in marine sediments was assessed (Hamdan et al. 2017). The
performances of the reactors where molybdate was added as an inhibitor of the
sulfate reduction were compared with the results obtained in the reactors without the
inhibition of the sulfate-reducing bacteria. Slightly higher hydrocarbon removal was
observed in the reactors where the sulfate reduction was inhibited. The microbial
community in the MFCs where molybdate was added differed from the community
enriched when the inhibitor was not supplied. Indeed, with molybdate, the enrichment of Desulfuromonas was observed on the anodes, as well as iron reducers of the
genus Geoalkalibacter. A decrease in sulfate concentration, however, was also
observed in the molybdate-supplied reactors (i.e., the sulfate concentration dropped
from 1130 mg/kg of dry sediment to 590 mg/kg of dry sediment after 28 weeks);
therefore, the authors hypothesized a partial inhibition of the sulfate reduction
(Hamdan et al. 2017). Further experiments might help in a more detailed description
of the effects the sulfur cycle can have on the bioelectrochemical processes in
sulfate/sulfide-rich environments.
Pure cultures of G. lovleyi were inoculated in bioelectrochemical reactors for the
reductive dehalogenation of PCE and TCE to cis-DCE that was not further reduced
(Aulenta et al. 2009; Strycharz et al. 2008). Dehalococcoides spp. are the only
microorganisms able to completely reduce TCE to ethene (Maymó-Gatell et al.
2001; West et al. 2008) and they were widely used for the study of the reductive
dehalogenation in BESs (Daghio et al. 2017). Fluorescence in situ hybridization
(FISH) analysis of the microbial communities both on the cathode and in the bulk of
reactors used for bioelectrochemical TCE and 1,2-DCA removal showed the presence of active Dehalococcoides proving their importance during the reductive
dehalogenation in BESs (Aulenta et al. 2009, 2010b; Leitão et al. 2015, 2016). In
particular, a strong enrichment of Dehalococcoides mccartyi was observed in a
bioelectrochemical reactor during 1,2-DCA dehalogenation with an electrode poised
at À300 mV in the presence of AQDS (Leitão et al. 2016). The presence of
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
383
simulate marine environments (Cruz Viggi et al. 2015; Daghio et al. 2016; Matturro
et al. 2017). In particular, microorganisms of the family Desulfobulbaceae seem to
be the key players since their presence has been reported in several studies (Daghio
et al. 2016, 2018a, b; Matturro et al. 2017). Members of the family
Desulfobulbaceae, called cable bacteria, have been extensively described to couple
sulfide oxidation with reduction of spatially distant oxygen by delivering electrons
over long distances (Müller et al. 2016; Pfeffer et al. 2012; Schauer et al. 2014), and
they might be also involved in electron transfer processes during the hydrocarbon
removal in BES. Hydrocarbons can be oxidized via sulfate reduction (with formation
of sulfide) and the bacteria of the family Desulfobulbaceae could oxidize sulfide to
elemental sulfur on the anode surface and transfer the electrons to the anode (Daghio
et al. 2018a). Elemental sulfur can be reduced to sulfide by members of the
Desulfuromonadaceae forming a cycle (Bond et al. 2002; Daghio et al. 2016,
2018a; Dutta et al. 2009) or being oxidized back to sulfate (Zhang et al. 2014)
regenerating the electron acceptor for sulfate reducers. The effect of the sulfate
reduction during the removal of PAHs (i.e., naphthalene, 2-methylnaphthalene,
and phenanthrene) in marine sediments was assessed (Hamdan et al. 2017). The
performances of the reactors where molybdate was added as an inhibitor of the
sulfate reduction were compared with the results obtained in the reactors without the
inhibition of the sulfate-reducing bacteria. Slightly higher hydrocarbon removal was
observed in the reactors where the sulfate reduction was inhibited. The microbial
community in the MFCs where molybdate was added differed from the community
enriched when the inhibitor was not supplied. Indeed, with molybdate, the enrichment of Desulfuromonas was observed on the anodes, as well as iron reducers of the
genus Geoalkalibacter. A decrease in sulfate concentration, however, was also
observed in the molybdate-supplied reactors (i.e., the sulfate concentration dropped
from 1130 mg/kg of dry sediment to 590 mg/kg of dry sediment after 28 weeks);
therefore, the authors hypothesized a partial inhibition of the sulfate reduction
(Hamdan et al. 2017). Further experiments might help in a more detailed description
of the effects the sulfur cycle can have on the bioelectrochemical processes in
sulfate/sulfide-rich environments.
Pure cultures of G. lovleyi were inoculated in bioelectrochemical reactors for the
reductive dehalogenation of PCE and TCE to cis-DCE that was not further reduced
(Aulenta et al. 2009; Strycharz et al. 2008). Dehalococcoides spp. are the only
microorganisms able to completely reduce TCE to ethene (Maymó-Gatell et al.
2001; West et al. 2008) and they were widely used for the study of the reductive
dehalogenation in BESs (Daghio et al. 2017). Fluorescence in situ hybridization
(FISH) analysis of the microbial communities both on the cathode and in the bulk of
reactors used for bioelectrochemical TCE and 1,2-DCA removal showed the presence of active Dehalococcoides proving their importance during the reductive
dehalogenation in BESs (Aulenta et al. 2009, 2010b; Leitão et al. 2015, 2016). In
particular, a strong enrichment of Dehalococcoides mccartyi was observed in a
bioelectrochemical reactor during 1,2-DCA dehalogenation with an electrode poised
at À300 mV in the presence of AQDS (Leitão et al. 2016). The presence of
17 Bioelectrochemical Processes for the Treatment of Oil-Contaminated. . .
383