6.6 Summary
Chlorinated organic compounds are widely used for their specific properties in many
commercial applications, and their physical and chemical properties determine their
general behavior and fate as pollutants. Understanding natural attenuation and COCs
transport and fate processes is one of the first steps in order to optimize chemical
remediation of contaminated groundwater.
Chemical reduction is an effective technique for the remediation of COCs in
groundwater. Due to its core–shell structure, ZVI particles possess unique properties
for soil and groundwater remediation, and the degradation mechanisms include
adsorption, encapsulation, precipitation, and chemical reduction. Since its introduction in permeable reactive barriers, the use of ZVI is the subject of extensive
researches to improve the reactivity, stability, and transport of the particles in
subsurface environment. First, the development of small particles was then necessary to facilitate the delivery of ZVI particles for the treatment of a source of
contamination. As shown by field experiments, the use of mZVI particles appears
as a great option as they are less expensive, exhibit less bactericidal effects, and have
a longer lifetime and a higher removal efficiency compared to nZVI particles. The
use of a polymeric coating or a dispersant proves to be essential to improve both the
stability and the transport of the particles. Then, the use of bimetallic particles,
especially Pd/Fe particles, can be used to increase degradation rates by taking
advantage from hydrodechlorination/hydrogenation reactions due to the generation
of atomic hydrogen. However, the significant improvement in degradation rates has
not been proven yet in field experiments. More recently, sulfidated particles have
been developed as to increase the selectivity and durability of the particles, but field
experiments are required to fully understand their reactivity. Finally, the impact of
iron-based technology on microbial activity needs to be evaluated to combine
efficiently abiotic and biotic degradation. Indeed, long-term studies on the fate and
behavior of iron-based particles on groundwater are still necessary.
It should be noted that COCs chemical reduction by ZVI particles is strongly
impacted by the presence of ions, heavy metals, or other contaminants as well as the
geological/hydrogeological characteristics of the polluted site. Consequently, there
is a need to conduct preliminary studies to select the most suitable method for each
situation, according to the initial site conditions, the performance goals, the implementation, and the cost criteria.
Acknowledgments The authors acknowledge the ADEME AMI SILPHES project and the BRGM
project MULTISCALEXPER PSO3 of D3E division for financial support for writing this chapter.
The case study was supported by ADEME (French Environment and Energy Management Agency)
in the framework of Eco-Industries 2011 program (project DECHLORED, contract
no. 1172C0034) and received financial support by BRGM research division. The authors acknowledge Clément ZORNIG who elaborated and provided the Fig. 6.5.
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
371
Chlorinated organic compounds are widely used for their specific properties in many
commercial applications, and their physical and chemical properties determine their
general behavior and fate as pollutants. Understanding natural attenuation and COCs
transport and fate processes is one of the first steps in order to optimize chemical
remediation of contaminated groundwater.
Chemical reduction is an effective technique for the remediation of COCs in
groundwater. Due to its core–shell structure, ZVI particles possess unique properties
for soil and groundwater remediation, and the degradation mechanisms include
adsorption, encapsulation, precipitation, and chemical reduction. Since its introduction in permeable reactive barriers, the use of ZVI is the subject of extensive
researches to improve the reactivity, stability, and transport of the particles in
subsurface environment. First, the development of small particles was then necessary to facilitate the delivery of ZVI particles for the treatment of a source of
contamination. As shown by field experiments, the use of mZVI particles appears
as a great option as they are less expensive, exhibit less bactericidal effects, and have
a longer lifetime and a higher removal efficiency compared to nZVI particles. The
use of a polymeric coating or a dispersant proves to be essential to improve both the
stability and the transport of the particles. Then, the use of bimetallic particles,
especially Pd/Fe particles, can be used to increase degradation rates by taking
advantage from hydrodechlorination/hydrogenation reactions due to the generation
of atomic hydrogen. However, the significant improvement in degradation rates has
not been proven yet in field experiments. More recently, sulfidated particles have
been developed as to increase the selectivity and durability of the particles, but field
experiments are required to fully understand their reactivity. Finally, the impact of
iron-based technology on microbial activity needs to be evaluated to combine
efficiently abiotic and biotic degradation. Indeed, long-term studies on the fate and
behavior of iron-based particles on groundwater are still necessary.
It should be noted that COCs chemical reduction by ZVI particles is strongly
impacted by the presence of ions, heavy metals, or other contaminants as well as the
geological/hydrogeological characteristics of the polluted site. Consequently, there
is a need to conduct preliminary studies to select the most suitable method for each
situation, according to the initial site conditions, the performance goals, the implementation, and the cost criteria.
Acknowledgments The authors acknowledge the ADEME AMI SILPHES project and the BRGM
project MULTISCALEXPER PSO3 of D3E division for financial support for writing this chapter.
The case study was supported by ADEME (French Environment and Energy Management Agency)
in the framework of Eco-Industries 2011 program (project DECHLORED, contract
no. 1172C0034) and received financial support by BRGM research division. The authors acknowledge Clément ZORNIG who elaborated and provided the Fig. 6.5.
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
371