Potential of the Biomass of Plants Grown in Trace Element-Contaminated Soils under Mediterranean Climatic Conditions for Bioenergy Production

María Pilar Bernal,Rafael Clemente,Donatella Grippi

doi:10.3390/agronomy11091750

María Pilar Bernal, Rafael Clemente + Show 1 more

Open Access

https://doi.org/10.3390/agronomy11091750

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Abstract

Phytomanagement of trace element-contaminated soils combines sustainable soil remediation with the use of plant biomass for different applications. Consequently, phytostabilization using plant species useful for bioenergy production has recently received increasing attention. However, the water requirement of most of these species is a limitation for their use under Mediterranean climatic conditions. In this work, eight plant species growing naturally in mine soils contaminated by trace elements were evaluated for their use as bioenergy crops using thermochemical (combustion) and biochemical (anaerobic digestion) methods. The higher heating values of the biomass of the plants studied were all within a narrow range (16.03–18.75 MJ kg−1), while their biochemical methane potentials ranged from 86.0 to 227.4 mL CH4 (g VS)−1. The anaerobic degradation was not influenced by the presence of trace elements in the plants, but the mineral content (mainly Na) negatively affected the potential thermal energy released by combustion (HHV). The highest annual energy yields from biogas or combustion could be obtained by the cultivation of Phragmites australis and Arundo donax, followed by Piptatherum miliaceum. Both options can be considered to be suitable final destinations for the biomass obtained in the phytostabilization of trace element-contaminated soils and may contribute to the implementation of these remediation techniques in Mediterranean areas.

Highlights

Mining is one of the industrial activities with the greatest environmental impact [1].The mining district of Cartagena-La Unión (Murcia, southern Spain) was exploited intensely for ores containing silver, lead, zinc and other metallic minerals from ancient times until the definitive cessation of mining activities in 1990
Most of the values did not reach the toxic limits for plants (As 5–20, Cd 5–30, Cu 20–100, Mn 400–1000, Pb 30–300, Zn 100-400; all in mg kg−1 ) [31], with the exception of Zn in most samples and As, Cd and Pb in D. viscosa, P. australis and P. miliaceum
Walker et al [30] evaluated the use of A. halimus plants for combustion and obtained 17.2 and 12.8 MJ kg−1 for stems and leaves, respectively, in agreement with the results found here, but they considered that its energetic use should be limited to plants from non-saline soils

Summary

Introduction

The mining district of Cartagena-La Unión (Murcia, southern Spain) was exploited intensely for ores containing silver, lead, zinc and other metallic minerals from ancient times until the definitive cessation of mining activities in 1990. The landscape with an area of about 50 km was transformed and the old vegetation cover disappeared, along with habitat and numerous species [2]. The dispersion of mining waste into the surrounding environment has led to colonization by spontaneous plant species that show adaptation to soil metal contamination [3]. Non-invasive remediation technologies, such as phytostabilization, can be effective for the in situ stabilization of metals in the contaminated sites of the Cartagena-La Unión mining district [5,6]. The establishment of a self-sufficient vegetative cover reduces the risk of an uncontrolled transfer of pollutants into the surrounding environment. The use of the plant biomass resulting from remediation is still a challenge for the implementation of phytoremediation strategies [7]

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