Switchgrass and Giant Reed Energy Potential when Cultivated in Heavy Metals Contaminated Soils

Harnessing Lignocellulosic Crops for Phytomanagement of Contaminated Soils: A Multi-Country Study

The dwindling availability of agricultural land, caused by factors such as rapid population growth, urban expansion, and soil contamination, has significantly increased the pressure on food production. To address this challenge, cultivating non-food crops on contaminated land has emerged as a promising solution. This approach not only frees up fertile soil for food production but also mitigates human exposure to contaminants. This work aimed to examine the impact of soil contamination with Cd, Pb, Ni, and Zn on the growth, productivity, metal accumulation, and the tolerance of five lignocellulosic non-food crops: switchgrass (Panicum virgatum L.), biomass sorghum (Sorghum bicolor L. Moench), giant reed (Arundo donax L.), African fodder cane (Saccharum spontaneum L. spp. aegyptiacum Willd. Hackel), and miscanthus (Miscanthus × giganteus Greef et Deu.). A two-year pot experiment was conducted in Greece, Italy, and Portugal, following the same protocols and applying various levels of metals: Cd (0, 4, 8 mg kg-1), Pb and Zn (0, 450, 900 mg kg-1), and Ni (0, 110, 220 mg kg-1). The experimental design was completely randomized, with three replicates for each treatment. The results showed that switchgrass and sorghum generally maintained their height and productivity under Cd and Pb stress but were adversely affected by high Zn and Ni concentrations. Giant reed and African fodder cane showed reduced height and productivity at higher Ni and Zn levels. Miscanthus exhibited resilience in height but experienced productivity reductions only at the highest Zn concentration. Heavy metal uptake varied among crops, with switchgrass and sorghum showing high Cd and Pb uptake, while giant reed accumulated the most Cd and Zn. Miscanthus had the highest Ni accumulation. The tolerance indices indicated that switchgrass and sorghum were more tolerant to Cd and Zn at lower concentrations, whereas miscanthus had lower tolerance to Cd but a higher tolerance to Zn at higher concentrations. Giant reed and African fodder cane demonstrated stable tolerance across most heavy metals. Accumulation indices highlighted the effectiveness of switchgrass and sorghum in Cd and Pb uptake, while miscanthus excelled in Ni and Zn accumulation. The cluster analysis revealed similar responses to heavy metal stress between African fodder cane and giant reed, as well as between sorghum and miscanthus, with switchgrass displaying distinct behavior. Overall, the study highlights the differential tolerance and accumulation capacities of these crops, indicating the potential for phytoremediation applications and biomass production in heavy metal-contaminated soils.

Phytoremediation as a viable ecological and socioeconomic management strategy

Phytoremediation is an environmentally friendly alternative to traditional remediation technologies, notably for soil restoration and agricultural sustainability. This strategy makes use of marginal areas, incorporates biofortification processes, and expands crop alternatives. The ecological and economic benefits of phytoremediation are highlighted in this review. Native plant species provide cost-effective advantages and lower risks, while using invasive species to purify pollutants might be a potential solution to the dilemma of not removing them from the new habitat. Thus, strict management measures should be used to prevent the overgrowth of invasive species. The superior advantages of phytoremediation, including psychological and social improvements, make it a powerful tool for both successful cleanup and community well-being. Its ability to generate renewable biomass and adapt to a variety of uses strengthens its position in developing the bio-based economy. However, phytoremediation faces severe difficulties such as complex site circumstances and stakeholder doubts. Overcoming these challenges necessitates a comprehensive approach that balances economic viability, environmental protection, and community welfare. Incorporating regulatory standards such as ASTM and ISO demonstrates a commitment to long-term environmental sustainability, while also providing advice for unique nation-specific requirements. Finally, phytoremediation may contribute to a pleasant coexistence of human activity and the environment by navigating hurdles and embracing innovation.

Statistical optimization of bioethanol production from giant reed hydrolysate by Candida tropicalis using Taguchi design

The economic production of bioethanol as a sustainable liquid fuel is particularly needed and attractive. Giant reed as a low-cost and renewable biomass can be utilized as a sustainable feedstock for bioethanol development. The current research focuses on optimizing the fermentation parameters to increase ethanol concentration while lowering production costs. In this work, the giant reed was hydrolyzed thermochemically using HCl; cellulose and hemicellulose fractions were maximally converted at optimized hydrolysis conditions (5% HCl, 30 min, and 120 °C), resulting in a high sugar concentration (≈ 55 g/L), which were fermented by Candida tropicalis Y-26 for bioethanol production (≈ 15 g/L). Taguchi design was used to optimize the fermentation parameters (temperatures, pH, incubation period, and nitrogen sources). Under optimum fermentation conditions (25 °C; 24 h.; pH 5.5; and ammonium nitrate as a nitrogen source), the ethanol concentration at flask level accomplished ≈ 21 g/L, while its scale-up to bioreactor level contributed ≈ 25 g/L (equivalent to 250 kg ethanol/ton biomass) with ≈ 67% increase than the fermentation under unoptimized conditions. Overall, these findings proved that optimizing the fermentation parameters by Taguchi design and scaling up at a bioreactor could improve bioethanol production from giant reed biomass.