The conception of a circular economy is one of the crucial approaches that could accelerate the processes of achieving sustainable development goals, which challenge all industries and societies. Still, the potential of agricultural waste in this area is not fully covered by technologies. This study aims to develop a full-scale technology for self-sustaining double-stage circularity through the utilization of sunflower agriculture’s waste in bio-fertilizers. The investigation is performed in Bulgaria, as available sunflower husk ashes (SHA) are subjected to analyses regarding their applicability for bio-fertilizer production. The design of the technology and full-scale equipment commissioning process are described. The conditions and results from the adjustment tests are presented and, based on these, the optimal operating parameters are defined. The successful granulation of different samples of SHA at these conditions is performed and the final granular bio-fertilizers are characterized with a content of 30 wt. % K₂O and 5% wt. P₂O. The moisture of the prepared granules is approx. 5 wt. %, and they pass the crushing tests at 2.5 kgf. The biotoxicity of the bio-fertilizer is also analyzed, and the results show its applicability in agriculture. The proposed approach allows the initial sources of K₂O and P₂O from soil feeding the sunflowers to circulate in different industrial technologies and to reenter the soil through bio-fertilizers.

This paper proposes a valorization approach for solid lavender residue, a by-product of the essential oil industry. The biomass residue was carbonized at atmospheric pressure and two temperatures (450 °C and 650 °C), followed by solvothermal modification with zinc ions (Zn²⁺, 3 and 5 mmol). The effects of temperature and Zn²⁺ incorporation on the elemental composition and morphology of the resulting biochar were examined using X-ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, and Scanning Electron Microscopy/Energy-Dispersive X-ray Spectroscopy (SEM/EDS) analyses. The applied Zn²⁺ modification was effective at both concentrations for the biochar obtained at both carbonization temperatures. However, a more uniform metal ion distribution was observed at 3 mmol, while at 5 mmol, a partial particle agglomeration occurred. Progressive degradation of the O–H, C=O, and C–O groups with increasing temperature and the presence of Zn–O-related interactions was observed. The results demonstrated consistent and reproducible trends, suggesting that controlled carbonization combined with Zn²⁺ incorporation can convert lavender residues into modified carbonaceous materials.

The increasing release of pharmaceutical pollutants, particularly antibiotics and analgesics, into aquatic environments poses a significant environmental challenge and necessitates sustainable removal strategies. In this study, lavender-derived biochar was produced by pyrolysis at 450 and 650 °C and subsequently modified with Zn²⁺ (3 and 5 mmol) via a solvothermal method. The resulting materials were evaluated as photocatalysts for the degradation of doxycycline and paracetamol in distilled water under UV-A irradiation. Structural and optical characterization (SEM–EDS, XRD, PL, FTIR) was conducted to elucidate structure–performance relationships relevant to photocatalytic activity. The sample pyrolyzed at 450 °C and modified with 5 mmol Zn²⁺ exhibited the highest photocatalytic performance, achieving degradation efficiencies of 62.78% for doxycycline (k = 0.0032 min⁻¹) and 75.19% for paracetamol (k = 0.0113 min⁻¹). The results demonstrate that controlled Zn incorporation into lavender-derived biochar enhances photocatalytic performance and highlight the role of synthesis parameters in governing catalytic behavior. This work underscores the potential of agro-waste-derived biochar as a functional matrix in sustainable photocatalytic systems.

Tribocatalysis is an emerging approach for the oxidation of organic pollutants using frictional energy. ZnO nanorods were prepared by thermal decomposition of zinc acetate dihydrate and wet-chemically modified with Gd₂O₃, Dy₂O₃, or Er₂O₃. SEM, nitrogen sorption, XRD, ATR-FTIR, Raman spectroscopy, and XPS confirmed the formation of predominantly rod-like ZnO, preservation of its morphology and wurtzite structure after modification, and introduction of nanocrystalline RE₂O₃ phases. Tribocatalytic activity was evaluated under mechanical stirring using the anionic dye Reactive Black 5 (RB5) and the cationic dye Brilliant Green (BG), examining the effects of RE modification, stirring rate, friction pair, scavengers, and catalyst reuse. Removal increased with stirring rate and was consistently higher for RB5. At 800 rpm, Er:ZnO exhibited the highest activity toward both dyes, reaching approximately 81% RB5 removal (k_app ≈ 0.074 h⁻¹) and 56% BG removal (k_app ≈ 0.040 h⁻¹) after 24 h. COD removal reached 53–60% for RB5 and 27–43% for BG, indicating a reduction in the oxidizable organic load consistent with partial mineralization. ATR-FTIR revealed carbonate formation and PTFE transfer to recovered catalysts, highlighting surface changes and secondary contamination. The results demonstrate measurable tribocatalytic activity and show that the benefits of RE modification depend on the target dye.