Page 52 - Plant-Based Remediation Processes

40 M. Mleczek et al.

which will provide further directions of development for this reclamation method
in case of soils contaminated with heavy metals. A crucial element presented in
this paper and frequently used by opponents of biological methods is related to
the residue after the phytoremediation process.

3.1 Phytoremediation: Yesterday, Today ... Tomorrow

In recent years we have observed an increased interest in hyperaccumulators,
although despite knowledge gained on molecular/cellular uptake mechanisms
of selected trace elements (Jabeen et al. 2009; Memon and Schro ¨der 2009),
their translocation to individual aboveground organs and detoxification, we still
need to deal with the problem of very limited biomass of these plants. Initial
studies concerned herbaceous plants, but due to their low biomass, significantly
contributing to increased costs of practical application of these plants, interest
was quickly shifted to include also woody plants (Yadav et al. 2010). Other
aspects of enhancing the phytoremediation potential are connected, e.g. with
modification of contaminated substrate to facilitate sorption of metals/
metalloids from soil by the plant root system (Wang et al. 2009;Zhaoet al.
2011; Mleczek et al. 2012), the application of microorganisms (Weyens et al.
2010) and short rotation coppice (SRC) as fast growing tree species with a
significant biomass increase (Dimitriou and Rosenqvist 2011). This latter
aspect seems to be of particular interest, as it is connected with the increased
demand for energy from renewable sources, crucial particularly in recent years.
Selected plant taxa from Populus or Salix species are characterised by a
significant increment in biomass, especially in areas with high ground water
levels, and at the same time relatively high capacity to absorb heavy metals/
metalloids (Adegbidi et al. 2001).
Renewable energy sources (RES) are playing an increasingly important role in
the generation of primary energy in the European Union. In the years 2001–2009,
generation of energy from renewable sources increased from 10.6 % to 18.3 %.
Biomass became the main source of renewable energy. In this respect one of the
most important EU documents was the Directive of the European Parliament and
Council no. 2009/28/EC of 23 April 2009 (the 3 20 þ 10 climate and energy
package). New objectives were specified in this package concerning the use of
renewable energy and greenhouse gas emissions. It was assumed that by the year
2020 the share of renewable energy would increase to 20 % (a significant increase
in the use of non-forest biomass in energy generation) in the total balance of energy
consumption in the EU. In such a case biomass from phytoremediation—with the
application of additional measures limiting further heavy metal transport to the
environment—may significantly increase the amount of biomass required to meet
the stipulations of the directive.
In recent years, studies on phytoremediation have focused on the use of
bacteria and mycorrhizal fungi as well as genetic modifications described in