Published in Scientific Papers. Series E. Land Reclamation, Earth Observation & Surveying, Environmental Engineering, Vol. X
Written by Violina ANGELOVA, Vanya ZAPRYANOVA
There has been carried out comparative research, which allows determining the quantities and the depots of accumulation of heavy metals, macro, and microelements in the vegetative organs of Miscanthus x giganteus, efficacy for phytoremediation, and quality of biomass as renewable energy sources for the combustion process. The field experiment was performed on an agricultural field contaminated by the Non-Ferrous-Metal Works (MFMW) near Plovdiv, Bulgaria. The experimental plots were situated at different distances (0.5, 3.5, and 15 km) from the source of pollution. Macronutrients (N, P, K, Mg, Ca), microelements (Fe, Mn, Cu), and heavy metal (Cd, Pb, Zn) concentrations in plant materials (roots, rhizomes, stems, and leaves) were determined during the three-year research period, two harvest periods (autumn, spring) per year. Heating value, ultimate and proximate analyses were evaluated at the end of the second growing season. Miscanthus x giganteus is tolerant towards heavy metals and can be grown on highly contaminated soils (2671.6 mg/kg of Zn, 2694.8 mg/kg of Pb, and 84.8 mg/kg of Cd). The depot for accumulation follows the order: roots>stems>leaves>rhizomes. The high concentration of heavy metals in the roots and rhizomes and the low translocation factor indicate the possibility of Miscanthus x giganteus to be used in phytostabilization. The obtained results have shown that Miscanthus x giganteus can be a significant source of good quality raw material in the production of solids biofuels. The biomass is of good quality (high carbon (47.85-49.92%) and hydrogen (5.37- 5.59%) content, and low ash (3.18-3.26%), nitrogen (0.05-0.1%), chlorine (0.056-0.085%), and sulphur (0.006- 0.048%) content and high energy potential (17.38-18.32 MJ/kg LHV). The degree of soil contamination did not have a significant influence on heating values, carbon, hydrogen, nitrogen, and sulphur contents but did influence on biomass heavy metal contents. The content of heavy metals in the biomass of Miscanthus x giganteus grown on heavily contaminated soils is significantly higher and exceeds the limit values according to the standard ISO 17225-6:2014. Biomass of Miscanthus x giganteus from highly contaminated soils could be used as a source of energy if the burning of biomass occurs in power plants equipped with purification systems to control dust emissions.
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