Waste-derived Technosols for the treatment of soil and water affected by potentially harmful elements

• Autores: Antonio Aguilar Garrido
• Directores de la Tesis: Francisco José Martín Peinado (dir. tes.)
• Lectura: En la Universidad de Granada ( España ) en 2024
• Idioma: inglés
• ISBN: 9788411954099
• Número de páginas: 349
• Títulos paralelos:
  • Tecnosole derivados de residuos para el tratamiento de suelos y aguas afectados por elementos potencialmente contaminantes
• Tribunal Calificador de la Tesis: José Álvarez Rogel (presid.), Annika Jenni Johana Parviainen (secret.), Erika Da Silva Dos Santos (voc.)
• Programa de doctorado: Programa de Doctorado en Ciencias de la Tierra por la Universidad de Granada
• Menciones:
  • Internacional
• Calificación: Sobresaliente Cum Laude
• Enlaces
  • Tesis en acceso abierto en: DIGIBUG
• Resumen

  • The global expansion of the mining industry, in particular sulphide mining, raises serious health and environmental concerns as a major source of potentially harmful elements (PHEs: As, Cd, Cu, Pb, Sb and Zn) released into the environment. Such concerns motivate the search for strategies that reconcile the production of mining resources with the protection of ecosystems, in order to avoid cases such as the Aznalcóllar mining accident, which has caused residual soil pollution and ecosystem degradation in the Guadiamar Green Corridor (GGC) (Iberian Pyrite Belt, SW Spain) that still persists more than 25 years later. On the other hand, the increase in waste production in industrialised countries leads to the proposal of circular economy and zero waste strategies as essential for the ecosystem preservation. In this context, to respond to these two challenges, this PhD thesis comprehensively evaluates the effectiveness of some waste-derived Technosols in the remediation of different environments degraded by sulphide mining, with high levels of PHEs: (i) artificial acid mine drainage, (ii) polluted soils, and (iii) gossan waste.

    In chapter 3, we assessed the acid neutralisation capacity and the removal effectiveness of PHEs of ten inorganic and organic wastes from the main waste-generating activities (urban, mining, and agro-industrial) through their application in a control treatment of an artificial acid mine drainage (AMD). In this way, we can select those wastes that can be used in the production of the Technosols of this PhD thesis. The wastes selected are those with the highest PHEs removal rates and which meet the necessary conditions to cope with pollution by favouring acidity neutralisation and the immbolisation of PHEs, such as carbonate character (carbonated waste from peat bog [CW] and marble cutting sluge [MS]), richness in organic matter (vermicompost from garden waste [VC], composted solid olive-mill by-product [OL], composted sewage sludge [WS]) and iron oxyhydroxides (iron oxyhydroxide sludge [IO]). Carbonated wastes provide pH buffering capacity, organic wastes favour the recovery of biological activity and contribute to soil aggregation, and iron-rich wastes promote the retention capacity of anionic PHEs (i.e. As, Sb). The combination of these wastes with polluted soil to form efficient Technosols for AMD control can be a viable and effective ecotechnology, as they have a very high acidity neutralisation capacity, a strong capacity to immobilise PHEs, and a variable critical load of PHEs, as discussed in chapter 5. However, the responses of the different Technosols indicate that results may differ depending on the dose, type, and combination of waste used; therefore, the final application must be adjusted to solve this problem in each specific situation. Furthermore, given that the presence of a continuous AMD can pose a medium to long term risk due to the saturation of the capacity to retain certain PHEs and the loss of efficacy as a protective barrier over time, if Technosols applied in AMD control, they must be monitored regularly and corrective measures proposed to maintain their functionality.

    In chapter 4, we characterised the six Technosols produced from polluted soil (PS) and a combination of the aforementioned wastes (T1, T2, T3, T4, T5, and T6) and evaluated their effectivennes in the remediation of PHE-polluted soils at physicochemical, biological, and ecotoxicological levels and a microcosm scale (in growth chamber conditions). After two months of surface application of Technosols on polluted soils, we analysed the soil properties, PHEs concentration in total, soluble, and bioavailable fractions, soil enzymatic activities, and growth responses of Trifolium campestre Schreb. and Lactuca sativa L. in both Technosols and underlying polluted soils. All Technosols improved the unfavourable conditions of PS by neutralising acidity, increasing organic carbon content, reducing the mobility of most PHEs, and stimulating both the soil enzymatic activities and growth of T. campestre and L. sativa. Thus, we conclude that these Technosols constitute a potential solution for the remediation of persistently polluted soils that should be applied in large-scale and long-term interventions to reinforce their feasibility as a cost-effective ecotechnology.

    Prior to field installation, to gain a detailed understanding of how PHE-polluted soil causes phytotoxicity, as well as the role of Technosols in mitigating these effects, in chapter 6 we focused on the comprehensive assessment of ecotoxicity through physiological parameters related to phytotoxicity in L. sativa, such as plant growth, photosynthetic capacity, oxidative stress, and antioxidant defence. In this chapter, the evaluation of phytotoxicity reduction is limited to Technosols T4, T5, and T6. The plants of L. sativa grown on T6 and T4 showed a higher growth rate (+90% and +41%, respectively) than PS, whereas no increase occurred in T5. This lower growth of L. sativa in PS and T5 may be due to the higher toxicity resulting from the presence of PHEs. However, lower oxidative stress and impact on net photosynthetic rate was observed in all Technosols compared to PS (+344% in T6, +157% in T4 and +194% in T5). Thus, this ecotechnology can be a potential solution for the remediation of polluted soils, as a widely used plant such as lettuce can be grown on them without experiencing toxicity; although the effectiveness of Technosols depends largely on their components, as some, such as T6, greatly improve conditions while others, such as T5, may not bring similar benefits.

    After evaluating in chapters 4, 5, and 6 the effectiveness of Technosols in the remediation of soils and water affected by PHEs at laboratory and microcosm level; the next step is the application under real conditions of the two best performing Technosols (T4 and T6). This chapter presents the results of the field application of these Technosols on unvegetated patches of polluted soils in the GGC. In particular, this chapter comprehensively evaluates the effectiveness of in situ remediation of polluted soils of Technosols T4 and T6 by analysing the changes that occurred in: i) soil physicochemical properties, ii) PHEs solubility, iii) soil enzymatic activity, iv) soil microbial composition and diversity, and v) vegetation recovery. The two selected Technosols remediated the adverse state of PS, both by their integration into the Technosols and by the effect of their surface application, neutralising acidity, boosting organic carbon levels, minimising the mobility of PHEs, and stimulating soil enzymatic functions. The progressive increase in soil enzyme activity implies an improvement of the microbial community. In addition, this increased microbial diversity favours greater connectivity between microbial species, indicating an acceleration of ecological interactions as evidenced by the increasing presence of plant growth-promoting microorganisms in soils over time, which positively influenced the establishment of a biodiverse and functional vegetation cover with autochthonous plants. Therefore, the integration of Technosols composed of the polluted soil itslef results in a substantial improvement of soil quality together with the recovery of its ecosystem functions, creating a favourable environment for vegetation growth while mitigating the risks associated with PHEs in polluted soils.

    Finally, in chapter 8, we focused on the remediation of mining tailings, such as gossan waste, which is one of the main sources of pollution in sulphide mining. Specifically, the aim of this chapter is to evaluate the potential of a ecotechnology in mining reclamation that combines the crop of the widely tolerant multifunctional legume, Lablab purpureus (L.) Sweet, with two designed Technosols derived from mixing gossan waste (GW) with a combination of organic/inorganic wastes from local industries (TC50 and TC75). In particular, the purpose is to promote favourable conditions in the gossan waste from the São Domingos mine for optimal growth of L. purpureus, as well as to evaluate the safety of this plant for animal consumption. Both Technosols improved physicochemical conditions, nutritional status, and microbiological activity, and reduced the bioavailability of most PHE (except As) of GW. L. purpureus thrived in both Technosols and showed PHEs accumulation mainly in roots, with PHEs concentrations in shoots that are safe for cattle and sheep consumption. Thus, this is a potential plant that, in conjunction with Technosols, constitutes a potential integrated biotechnology approach for the conversion of marginal lands, such as abandoned mining areas, into food production areas under the condition of exhaustive quality and food safety controls.

    In this PhD thesis, we have deepened the knowledge of Technosols applied to real situations, and we have seen that they produce a significant improvement in severely degraded areas affected by PHE-pollution, while we have found some drawbacks or potential risks that need to be further investigated and carefully managed for each specific situation. Furthermore, this thesis can serve as a basis for many future lines of research (e.g. ecotoxicity studies, studies on the improvement of physical properties, long-term monitoring of Technosols applied in the GGC, phytoremediation with species of interest in the region, designed Technosols for salinity problems, potential of Technosols for reconversion in production areas).