## 4 Economic Feasibility and Other Benefits of the Revalorization of the Phytoremediation Biomass  
Jiang et al. (1994) recently proposed an integrated approach to enhance phytoremediation's financial viability, produce energy, and recover high-value elements. This model assessed the economic viability of phytoremediation and proposed that high-biomass-yield plant species can significantly achieve a financial return from recovering elements such as Ni, Pt, and As, if the phytoremediation is well managed. In addition to phytoextraction, the authors also proposed extensive on-field experimentation to achieve commercialization and further valorization of its by-products (Shi et al., 2018). According to Jiang et al. (1994), threshold values of elemental concentrations in plant biomass (dry weight) for hyperaccumulators are >10,000 ug/g of Mn and Zn, >1000 ug/g of As, Co, Cu, Ni, Se, and Pb, and >100 ug/g of Cd. Van Der Ent et al. (2018) introduced the term agromining to involve technologies growing a metal accumulator plant as a crop and then harvesting the biomass and drying, ashing, and processing it to recover target HMs, such as As, Se, Cd, Cu, Co, La, Mn, Ni, Pb, Tl, and Zn. However, Haller and Jonsson (2018) stated that phytoremediation is not attractive to farmers, especially for subsistence farming in economically vulnerable regions. Van der Ent et al. (2018) stated that a large-scale demonstration of agromining is first needed to work through operational challenges and provide evidence of profitability. For this reason, according to Marques et al. (2018), biomass resulting from phytoremediation could be used as a by-product with added value, namely to produce biomass-derived energy, within a circular economy concept and global sustainable development. Therefore, phytoremediation suggests a sustainable approach to the disposal and effective use of HM-containing biowastes (Han et al., 2018). The revalorization of biomass from phytoremediation has brought new possibilities to generate value-added products. Besides, biomass pyrolysis has been recognized as the most promising thermochemical technique for large-scale electricity and heat recovery from HM-polluted biomass and biofuel synthesis. Therefore, phytoremediation reduces pollution and can be coupled to energy, revenues, and even feedstock production, boosting a circular economy, carbon sequestration, and cogeneration of phytoproducts and highly-valued by-products. According to Ghosh and Maiti (2018), the economics of these approaches to enhance phytoremediation, production energy, and recovery of high-value elements should be assessed. Simultaneously, scientists should also conduct an environmental cost-benefit analysis based on well-designed, large-scale, and long-term field trials. However, metal recovery by phytoremediation must not be the ultimate goal of phytotechnologies. According to Yan et al. (2018), soil function restoration is an important contribution of phytotechnologies to ecosystems. Plants have the ability to absorb ionic compounds in the soil, even at low concentrations, through their root systems, establishing rhizosphere ecosystems to accumulate toxic metals and modulate their availability, thereby reclaiming the polluted soils, stabilizing soil fertility (Shi et al., 2018), enhancing the nutrient cycling in soil, controlling erosion, and providing aesthetic value (Shi et al., 2018). To date, other technologies have been installed to work along phytoremediation. It has been stated that coupling phytoremediation to biochar, biofuel, or heat production gives far-reaching social and economic benefits (Yang et al., 2018). Yang et al. (2018) compared three oil crop rotation systems for effective use and remediation of HM-contaminated agricultural soil and soil conservation. Other authors have used nanotechnology to increase pollutants' dissipation during phytoremediation of polluted soils (Shi et al., 2018), i.e., phytotechnologies have improved the benefits of soil conservation and social and economic benefits.