acid and the second ensures the degradation of the
chlorobenzoic acid.
The Coupling of Anaerobic and Aerobic Treatments Is
Necessary to Mineralize Polychlorinated Compounds
It comes out from the above results that PCB mineralization
can only be achieved by the joint and complementary action
of anaerobic and aerobic communities (Fig. 16.29). In this
last paragraph will be presented experiment examples where
was applied on sediments or soils an anaerobic treatment
that ensures dechlorination followed by an aerobic treatment
that leads to PCB mineralization. The efficiency of such a
biotreatment was demonstrated in laboratory:
(i) With contaminated sediments from the Hudson River
(USA). In a first step, the sediment was put under
anaerobic conditions in sealed flasks, during 20
weeks, in the presence of methanol: tri-, tetra-, penta-,
and hexachlorobiphenyls were reduced and the increase
of mono- and dichlorobiphenyls was observed. In a
second step, the anaerobic cultures were flushed out
with dioxygen and inoculated with an aerobic bacterium isolated from the sediment. After 96 h incubation,
most of the mono- and about 25 % of dichlorobiphenyls
were degraded (Borja et al. 2005).
(ii) On a soil containing Aroclor 1260 (Master et al. 2002)
firstly submitted during 4 months to an anaerobic treatment (initial PCB concentration 59 mg kg
À1 of soil).
This treatment produced dechlorination of the congener
majority (mean chlorine atom number shifting from
6.2 to 5.2) with in particular formation of 2,2
0 ,4,4
0 -
tetrachlorobiphenyl and 2,2
0 ,4,6
0 -tetrachlorobiphenyl.
In contrast, the overall PCB amount did not decrease.
Then, the anaerobic degradation products were
biodegraded by an aerobic treatment under the action
of the strain Burkholderia sp. LB400. After 28 days of
aerobic treatment, the PCB concentration was reduced to
about 28 mg kg
À1 of soil which corresponded to 68 %
disappearance.
(iii) With sediment from the Red Cedar River (Michigan,
USA) contaminated by Aroclor 1242 (70 mg PCB kg
À1
of soil) (Rodrigues et al. 2006). One-year incubation
under anaerobiosis with microorganisms present in
the sediment leads to the elimination of about 32 %
chlorine atoms of Aroclor 1242 (14 % of Aroclor in
weight), essentially at the level of meta substitutions.
After this incubation period under anaerobiosis, the
sediment was placed under aerobic conditions and
two genetically built strains were inoculated: (1)
Burkholderia xenovorans LB400 containing the
biphenyl degradation pathway and genetically modified
to insert the ohb operon enabling growth on orthochlorobenzoate and thus fully mineralize orthochlorobiphenyl and (2) Rhodococcus sp. strain RHA1
modified to insert the fcb operon enabling growth on
para-chlorobenzoate. Both strains grew on PCBs
(growth estimated by counting with epifluorescence
microscopy and by real time PCR) and remained genetically stable during incubation. After 30 days incubation, 57 % of the remaining PCBs were degraded,
whereas only 4 % were eliminated in the absence of
both strains, thus demonstrating that their joint presence was necessary for the degradation of Aroclor
anaerobic dechlorination products. At the end of the
experiment, the content was about 25 mg kg
À1 of soil.
(iv) In a biofilm developed on a granular support made of
anaerobic sludge particles encapsulated by a polymer
and placed in a bioreactor to monitor the fate of Aroclor
1242 (Tartakovsky et al. 2001). In the thickness of the
biofilm built by prokaryotic populations present in the
mud, a dioxygen gradient took place (oxic zone at
surface, anoxic one at depth); this procedure enables
the simultaneous establishment of aerobic and anaerobic conditions. The analyses showed a PCB disappearance of about 80 %. This suggests that an entire PCB
mineralization can be achieved in a system where aerobic and anaerobic conditions are simultaneously
established.
16.7.4.4 Bioremediation of PCB
Contaminated Sites
The most used and efficient process is burning, but it
is costly and produces dangerous compounds such as
polychlorodibenzofuranes and polychlorodibenzodioxines
formed under incomplete PCB burning. Under these
conditions, researches were considered on alternative
treatments involving microorganisms with PCB degradation
capacities (Mhiri and Tandeau de Marsac 1997; Ohtsubo
et al. 2004). However, bioremediation is generally at a
development stage. Proofs of its efficiency and costeffectiveness at large scale are limited. Nevertheless,
experiments conducted by Harkness et al. (1993)
demonstrated the feasibility of contaminated sediment
bioremediation under in situ conditions, and promising
results were also obtained with contaminated soils treated
by composting. As an example, soil contaminated by PCB
whose composition was close to that of Aroclor 1248 was
excavated and mixed with plant wastes to form 19 m
3
biopiles with a volume to surface ratio of 1.5–1.9 (m
2 /m
3 )
(Michel et al. 2001). In bio-hummocks containing 80 %
plant wastes, temperature rose to 60
C after 10 days.
Under these aerobic conditions (monthly reversal of the
bio-hummocks), 40 % PCBs were eliminated after 370-day
treatment (<1 % evaporation). The most easily degraded
congeners contained 1–3 chlorine atoms. However, beyond
4 chlorine atoms, no significant alteration was observed,
which is in agreement with the aerobic biodegradation processes previously described.
16 Applied Microbial Ecology and Bioremediation
715
chlorobenzoic acid.
The Coupling of Anaerobic and Aerobic Treatments Is
Necessary to Mineralize Polychlorinated Compounds
It comes out from the above results that PCB mineralization
can only be achieved by the joint and complementary action
of anaerobic and aerobic communities (Fig. 16.29). In this
last paragraph will be presented experiment examples where
was applied on sediments or soils an anaerobic treatment
that ensures dechlorination followed by an aerobic treatment
that leads to PCB mineralization. The efficiency of such a
biotreatment was demonstrated in laboratory:
(i) With contaminated sediments from the Hudson River
(USA). In a first step, the sediment was put under
anaerobic conditions in sealed flasks, during 20
weeks, in the presence of methanol: tri-, tetra-, penta-,
and hexachlorobiphenyls were reduced and the increase
of mono- and dichlorobiphenyls was observed. In a
second step, the anaerobic cultures were flushed out
with dioxygen and inoculated with an aerobic bacterium isolated from the sediment. After 96 h incubation,
most of the mono- and about 25 % of dichlorobiphenyls
were degraded (Borja et al. 2005).
(ii) On a soil containing Aroclor 1260 (Master et al. 2002)
firstly submitted during 4 months to an anaerobic treatment (initial PCB concentration 59 mg kg
À1 of soil).
This treatment produced dechlorination of the congener
majority (mean chlorine atom number shifting from
6.2 to 5.2) with in particular formation of 2,2
0 ,4,4
0 -
tetrachlorobiphenyl and 2,2
0 ,4,6
0 -tetrachlorobiphenyl.
In contrast, the overall PCB amount did not decrease.
Then, the anaerobic degradation products were
biodegraded by an aerobic treatment under the action
of the strain Burkholderia sp. LB400. After 28 days of
aerobic treatment, the PCB concentration was reduced to
about 28 mg kg
À1 of soil which corresponded to 68 %
disappearance.
(iii) With sediment from the Red Cedar River (Michigan,
USA) contaminated by Aroclor 1242 (70 mg PCB kg
À1
of soil) (Rodrigues et al. 2006). One-year incubation
under anaerobiosis with microorganisms present in
the sediment leads to the elimination of about 32 %
chlorine atoms of Aroclor 1242 (14 % of Aroclor in
weight), essentially at the level of meta substitutions.
After this incubation period under anaerobiosis, the
sediment was placed under aerobic conditions and
two genetically built strains were inoculated: (1)
Burkholderia xenovorans LB400 containing the
biphenyl degradation pathway and genetically modified
to insert the ohb operon enabling growth on orthochlorobenzoate and thus fully mineralize orthochlorobiphenyl and (2) Rhodococcus sp. strain RHA1
modified to insert the fcb operon enabling growth on
para-chlorobenzoate. Both strains grew on PCBs
(growth estimated by counting with epifluorescence
microscopy and by real time PCR) and remained genetically stable during incubation. After 30 days incubation, 57 % of the remaining PCBs were degraded,
whereas only 4 % were eliminated in the absence of
both strains, thus demonstrating that their joint presence was necessary for the degradation of Aroclor
anaerobic dechlorination products. At the end of the
experiment, the content was about 25 mg kg
À1 of soil.
(iv) In a biofilm developed on a granular support made of
anaerobic sludge particles encapsulated by a polymer
and placed in a bioreactor to monitor the fate of Aroclor
1242 (Tartakovsky et al. 2001). In the thickness of the
biofilm built by prokaryotic populations present in the
mud, a dioxygen gradient took place (oxic zone at
surface, anoxic one at depth); this procedure enables
the simultaneous establishment of aerobic and anaerobic conditions. The analyses showed a PCB disappearance of about 80 %. This suggests that an entire PCB
mineralization can be achieved in a system where aerobic and anaerobic conditions are simultaneously
established.
16.7.4.4 Bioremediation of PCB
Contaminated Sites
The most used and efficient process is burning, but it
is costly and produces dangerous compounds such as
polychlorodibenzofuranes and polychlorodibenzodioxines
formed under incomplete PCB burning. Under these
conditions, researches were considered on alternative
treatments involving microorganisms with PCB degradation
capacities (Mhiri and Tandeau de Marsac 1997; Ohtsubo
et al. 2004). However, bioremediation is generally at a
development stage. Proofs of its efficiency and costeffectiveness at large scale are limited. Nevertheless,
experiments conducted by Harkness et al. (1993)
demonstrated the feasibility of contaminated sediment
bioremediation under in situ conditions, and promising
results were also obtained with contaminated soils treated
by composting. As an example, soil contaminated by PCB
whose composition was close to that of Aroclor 1248 was
excavated and mixed with plant wastes to form 19 m
3
biopiles with a volume to surface ratio of 1.5–1.9 (m
2 /m
3 )
(Michel et al. 2001). In bio-hummocks containing 80 %
plant wastes, temperature rose to 60
C after 10 days.
Under these aerobic conditions (monthly reversal of the
bio-hummocks), 40 % PCBs were eliminated after 370-day
treatment (<1 % evaporation). The most easily degraded
congeners contained 1–3 chlorine atoms. However, beyond
4 chlorine atoms, no significant alteration was observed,
which is in agreement with the aerobic biodegradation processes previously described.
16 Applied Microbial Ecology and Bioremediation
715