Development of Phytoremediation and Bioremediation Methods for Removal of Heavy Metals from Contaminated Soils in Armenia

Abstract

Pollution of soils and sediments with heavy metals is one of today's major concerns. This, in the first instance, is due to the wide spreading of these pollutants and their persistence in the environment, as unlike organic compounds, heavy metals do not decay. Especially heavy metal contaminated agricultural soils pose a serious threat to society as heavy metals accumulate in the food chain. The heavy metal problem in Armenia is due to decades of mining activities and the operation of mining related industries. In Kapan, located in the southwest of Armenia, decades of extensive copper mining resulted in severe heavy metal pollution of the agricultural soils in the vicinity of the city. For the first approach natural sorbents will be used that occur on Armenian territory, including perlite, zeolites and diatomite. The second approach makes advantage of a specific feature on practically the entire Armenian territory that is the occurrence of a carbonate layer in the alluvial sediments. The buffer capacity of the carbonate layer can potentially be used to re-precipitate the metals below the root zone that are extracted from the soils by soil flushing. To quantify the problem and for a proper site investigation has to study two major tasks: 1.The current heavy metal fluxes in catchments influenced by anthropogenic activities: The sources of the heavy metal contamination of the soils have to be identified including wet and dry atmospheric deposition. The contribution of the two processes to the total heavy metal fluxes have to be quantified. 2. The spatial distribution of the heavy metals and their speciation have to be evaluated: To tailor remediation measures a detailed knowledge on the heavy metal distribution is crucial. The heavy metal speciation determines their mobility at specific hydrogeochemical conditions and must be known, as well. Especially for the latter point a characterization of the soil types is necessary as the soils define the geochemical environment that in turn affects heavy metal speciation. Moreover, due to the large spatial extend of the heavy metal contaminated soils, only 'in-situ' measures are considered here as promising remediation options. For the problem solution suitable remediation methods were developed. In principal 3 different remediation approaches will be applied. Firstly, removal of the heavy metals from the contaminated topsoil by phytoremediation. This is typically achieved by growing specific plants on the soils which 'bio-concentrate' heavy metals. At the end of a growing season plants are harvested and disposed of. Secondly, Immobilization of the heavy metals. In general, suitable materials with high sorption capacity for heavy metals can be mixed into the soil, such as natural zeolites, perlite, iron oxides, volcanic tuffs etc. Ideally, the bio-availability of the heavy metals is highly reduced. And as a final activity, mobilization of the heavy metals and leaching them into deeper soil zones. Mobility of heavy metals is strongly dependent on the geochemical conditions of the soil. By a tailored change of the geochemical conditions (e.g. pH, redox conditions), heavy metals can be mobilized and transported downward to deeper soil zones.

Full text

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6th European Bioremediation Conference, Chania, Crete, Greece, June 29 – July 2, 2015
Development of Phytoremediation and Bioremediation Methods for Removal of
Heavy Metals from Contaminated Soils in Armenia.
Thomas Schiedek1, Marine Nalbandyan2
1 TU Darmstadt, The Institute of Applied Geosciences, Germany
2 The Institute of Geological Sciences, NAS RA
Corresponding author email: marinen3@yahoo.com
ABSTRACT
Pollution of soils and sediments with heavy metals is one of today’s major concerns. This, in the
first instance, is due to the wide spreading of these pollutants and their persistence in the environment,
as unlike organic compounds, heavy metals do not decay. Especially heavy metal contaminated
agricultural soils pose a serious threat to society as heavy metals accumulate in the food chain.
The heavy metal problem in Armenia is due to decades of mining activities and the operation of
mining related industries. In Kapan, located in the south-west of Armenia, decades of extensive copper
mining resulted in severe heavy metal pollution of the agricultural soils in the vicinity of the city.
For the first approach natural sorbents will be used that occur on Armenian territory, including perlite,
zeolites and diatomite. The second approach makes advantage of a specific feature on practically the
entire Armenian territory that is the occurrence of a carbonate layer in the alluvial sediments. The buffer
capacity of the carbonate layer can potentially be used to re-precipitate the metals below the root zone
that are extracted from the soils by soil flushing.
To quantify the problem and for a proper site investigation has to study two major tasks:
1.The current heavy metal fluxes in catchments influenced by anthropogenic activities: The sources of
the heavy metal contamination of the soils have to be identified including wet and dry atmospheric
deposition. The contribution of the two processes to the total heavy metal fluxes have to be quantified.
2. The spatial distribution of the heavy metals and their speciation have to be evaluated: To tailor
remediation measures a detailed knowledge on the heavy metal distribution is crucial. The heavy metal
speciation determines their mobility at specific hydrogeochemical conditions and must be known, as
well.
Especially for the latter point a characterization of the soil types is necessary as the soils define the
geochemical environment that in turn affects heavy metal speciation. Moreover, due to the large spatial
extend of the heavy metal contaminated soils, only ‘in-situ’ measures are considered here as promising
remediation options.
For the problem solution suitable remediation methods were developed. In principal 3 different
remediation approaches will be applied.
Firstly, removal of the heavy metals from the contaminated topsoil by phytoremediation. This is typically
achieved by growing specific plants on the soils which ‘bio-concentrate’ heavy metals. At the end of a
growing season plants are harvested and disposed of.
Secondly, Immobilization of the heavy metals. In general, suitable materials with high sorption capacity
for heavy metals can be mixed into the soil, such as natural zeolites, perlite, iron oxides, volcanic tuffs
etc. Ideally, the bio-availability of the heavy metals is highly reduced.
And as a final activity, mobilization of the heavy metals and leaching them into deeper soil zones.
Mobility of heavy metals is strongly dependent on the geochemical conditions of the soil. By a tailored
change of the geochemical conditions (e.g. pH, redox conditions), heavy metals can be mobilized and
transported downward to deeper soil zones.