Abdulmannan Rouhani

Hydrothermal carbonization (HTC) converts digestate into hydrochar for potential soil applications. This study characterized hydrochar produced from anaerobic digestate in a single batch at 180 °C for 6 h with sulfuric acid addition to evaluate properties relevant to sustainable circular resource utilization and potential soil amendment use. Analyses included elemental composition, carbon and nitrogen fractions, pH, electrical conductivity, and pore structure. The hydrochar contained 42.70% total organic carbon and macronutrients, including 2.22% N, 0.51% P, 0.67% K, 1.91% Ca, and 0.39% Mg on a dry matter (DM) basis. The pH(H₂O) was 5.75, while electrical conductivity was 42.55 mS·cm⁻¹. Ni (179 mg·kg⁻¹ DM) exceeded the indicative 50 mg·kg⁻¹ benchmark for organic soil improvers under Regulation (EU) 2019/1009, although the source of the elevated Ni was not resolved. Cr (417 mg·kg⁻¹ DM) was not speciated, preventing comparison with the Cr(VI) criterion. N₂ physisorption showed a BET surface area of 31 m²·g⁻¹, limited mesoporosity, and no measurable microporosity. The composition supports investigating carbon and nutrient inputs to soil, while acidity, soluble salts, and elemental constraints need to be evaluated under relevant soil conditions before the potential for sustainable soil application can be assessed.

S: Land contamination by potentially toxic elements, petroleum hydrocarbons, pesticides, and other pollutants represents a major environmental challenge that affects soil health and ecosystem functioning. Amendment-assisted phytoremediation using perennial energy crops has emerged as a promising strategy for restoring contaminated and marginal lands, while soil nematodes are increasingly recognized as sensitive indicators of ecological disturbance and recovery. A comprehensive analysis of published studies was conducted to evaluate nematode responses to potentially toxic elements and hydrocarbons in phytoremediation systems amended with biochar and ash, with particular attention to nematode abundance, diversity, trophic structure, and ecological indices. The review also examined systems involving perennial energy crops, especially Miscanthus × giganteus. Available evidence indicates that nematode responses to contaminants and amendments are strongly context-dependent and influenced by contaminant type, concentration, soil properties, amendment characteristics, and vegetation system. Bacterivorous nematodes frequently exhibit greater tolerance to contamination, whereas omnivores and predators are generally more sensitive indicators of ecological disturbance. Biochar commonly suppresses plant-parasitic nematodes while having variable effects on other trophic groups, depending on feedstock type and application rate. Ash amendments may also exhibit nematicidal effects but can negatively affect community balance at high application rates. In systems involving Miscanthus × giganteus , amendment-induced shifts in nematode communities reflect both soil recovery processes and persistent ecological disturbance. Therefore, nematode communities provide valuable insight into soil ecological functioning and remediation efficiency and represent informative bioindicators for assessing the sustainability of amendment-assisted phytoremediation strategies in contaminated soils.

The agricultural and environmental application of Miscanthus × giganteus biomass ash (MBA) as a soil amendment requires a thorough assessment of its properties, nutrient potential, and associated risks. This study characterizes the elemental composition, pH, cation exchange capacity (CEC), and polycyclic aromatic hydrocarbons (PAHs) content of MBA in comparison with other common biomass ashes (crops, wood, and sewage sludge) referred to the international regulatory standards. The ash exhibits a strong alkaline pH (11.03), suggesting potential to improve soil pH in acid soils, but requires careful controlled application to prevent excessive alkalization. The main nutrients detected include K (5.54%), Ca (2.07%), Mg (0.37%), and P (0.86%), indicating its potential as a soil amendment, though long-term use may cause nutrient imbalances. Micronutrients such as Zn (240.67 mg·kg⁻¹), Mn (297 mg·kg⁻¹), and Cu (33.5 mg·kg⁻¹) are found in concentrations suitable for agricultural use, while potentially toxic elements (PTEs), including Cd, Cr, Ni, and Pb, are below detection limits, thereby reducing the risk of pollution. As (8.3 mg·kg⁻¹) and ΣPAHs (1.63 mg·kg⁻¹) remain within safety thresholds, suggesting a low environmental toxicity of MBA. The low Na content (0.12%) indicates a minimal risk of salinity accumulation, distinguishing MBA from high-sodium biomass ashes. Soil alkalization, disruptions in nutrient balance, and element leaching are risks to be considered. Despite these concerns, its composition is in agreement with established safety guidelines, supporting its feasibility for valorization as a sustainable soil amendment and remediation material. To maximize agronomic benefits and mitigate environmental risks, it is important to utilize the ash, considering site conditions and carry out regular monitoring of the soil.

Wood biomass ash (WBA) from thermal power plants is often landfilled despite its potential as a secondary raw material. This study adopts a circular economy perspective to assess the physicochemical properties, valorization potential, and environmental risks of WBA, aiming to support its use in agriculture and environmental management. Comprehensive characterization included pH, cation exchange capacity (CEC), proximate and elemental composition, and selected organic contaminants, including polycyclic aromatic hydrocarbons (PAHs). The WBA exhibited a strongly alkaline pH (10.55), moderate CEC (4.36 cmol kg⁻¹), and high ash content (78.32%), with lower nutrient content than other biomass ashes. Major elements included Ca (6.84%), K (2.90%), and Si (3.19%), while nitrogen was absent. Potentially toxic elements (PTEs) such as As, Cd, and Ni were below detection limits; Cr, Cu, Pb, and Zn remained within most regulatory thresholds, although Zn exceeded some limits. ΣPAHs were low (0.05 mg·kg⁻¹), indicating minimal environmental concern. Despite reduced nutrient richness, the ash demonstrated suitability as a liming agent and supplementary nutrient source, provided that Zn levels are managed and nitrogen is supplemented. These results support the redirection of WBA from disposal to beneficial use, advancing circular economy goals and contributing to more sustainable and resilient agricultural systems.

Rapid urban development and industrialization have led to severe soil pollution, which has become a major global environmental problem, further intensified by population growth and land-use changes. In urban soils, pollution from past anthropogenic activities can still be detected through its harmful effects on soil quality, ecosystems and human health. This review summarizes the status of potentially toxic elements (PTEs), polycyclic aromatic hydrocarbons (PAHs), and microplastics (MPs) in Türkiye’s urban soils. Across cities, Cd and Pb frequently exceeded national soil-quality thresholds, with industrial hubs and traffic corridors emerging as hotspots. PAH burdens often reached the 'heavily contaminated' category (> 1000 µg kg⁻ ¹ ), with winter maxima linked to heating activities and a dominance of pyrogenic four-ring compounds. Urban MPs were abundant in parks and along roadsides, dominated by fibers and polyethylene, and showed strong variation with land use (recreational > industrial > residential in İstanbul). This evidence illustrates a lack of in-depth understanding of the full extent of soil pollution in targeted areas. The results of this review will help develop practical strategies for soil management, pollution monitoring, and remediation, which will ultimately improve public health and support sustainable development in Türkiye.

Lead–zinc mining activities generate highly degraded soils enriched with potentially toxic elements (PTEs), characterized by acid-generating tailings and low fertility, which collectively inhibit vegetation establishment and ecological recovery. This review synthesizes findings from studies on phytoremediation and assisted phytoremediation in lead-zinc mining regions worldwide. Phytostabilization was the dominant process, with Pb largely immobilized in the roots and showing minimal movement through the plant. In contrast, Zn showed higher mobility, allowing for occasional phytoextraction. Pioneer shrubs and xerophytic grasses effectively stabilized nutrient-poor, metal-rich soils in Mediterranean and North African sites, while deep-rooted woody plants restricted contaminant migration through root immobilization. Genuine hyperaccumulators were rare, suggesting that local metal tolerance rather than hyperaccumulation is the dominant adaptive mechanism. Assisted systems enhanced remediation efficiency: arbuscular mycorrhizal fungi (AMF) and earthworms improved fertility and reduced Pb and Zn mobility, whereas plant growth–promoting rhizobacteria (PGPR) and endophytes stimulated growth but had variable effects on metal mobility. Biochar consistently decreased Pb, Zn, and Cd bioavailability, improved soil pH and nutrient status, and supported vegetation, though its effectiveness depended on feedstock and dose. In conclusion, phytostabilization using tolerant native vegetation, supplemented by microbial or biochar amendments, represents the most reliable and sustainable remediation pathway in lead-zinc mining areas, whereas phytoextraction remains restricted to specific Zn tolerant species.