The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulfuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in a horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600, and 700 °C). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis), and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer–Emmett–Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash, and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost, thus forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 °C proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations, another biochar application was proposed—as a catalyst.

The present work aims at (a) carbonizing agriculture biomass residue; (b) characterizing the obtained biochar; and (c) exploring its potential use for energy/resource recovery purposes. Six types of biomass were carbonized. The biochar was investigated through scanning electron microscopy with energy dispersive X-ray spectroscopy detector, thermogravimetric (TGA), proximate, ultimate, and Brunauer–Emmett–Teller analyses, along with bulk density, pH, electrical conductivity, and salt content measurements. The results served as input data for multi-criteria, multi-objective decision analysis of biochar, aiming to evaluate its best application prospective. The TGA identified two general stages: devolatilization (stage 2: 180–560 °C), and combustion (stage 3: 560–720 °C). The activation energy of stage 2 decreased with an increasing heating rate, but the opposite trend was observed for stage 3. The biochar CO₂ adsorption suggested possible applications beyond energy conversion technologies. The decision support analysis revealed that peach stones, cherry stones, and grape pomace biochar achieved the most promising results for all evaluated applications (biofuel; catalyst; CO₂ sequestration and soil amendment; supercapacitor) in contrast to colza, softwood, or sunflower husks char.

The main purpose of the present work was to evaluate the efficiency of the gasification process of three different types of agro-forest biomass residue (rapeseed, softwood, and sunflower husks) along with the characterization of size-segregated particulates’ emissions. The experiments were carried out in a drop tube furnace (DTF), using two different gasifying agents (O₂/N₂ and O₂/N₂/CO₂) at atmospheric pressure and a constant temperature of 1000 °C. In focus was the effect of biomass and the gasifying agent on syngas composition (CO, H₂, CH_4, and CO₂), cold gas and carbon conversion efficiency, and on the emissions of by-products, such as particulate matter (PM), known for having negative environmental and health impacts. The collected particulates were characterized by SEM/EDS and XPS analysis. The results reveal that: (i) the introduction of CO₂ increased the production of CO and CH₄ and syngas’ lower heating value (LHV), thus leading to higher cold gas and carbon conversion efficiency; (ii) CO₂ decreased the production of H₂, leading to lower H₂/CO ratio (between 0.25 and 0.9). Therefore, the generated syngas is suitable for the synthesis of higher hydrocarbons, (iii) CO₂ lowered the emissions of char (cyclone) particles but increased the overall PM_10–0.3. Submicron size PM was the dominant fraction (PM_1–0.3) in O₂/N₂ and (PM_1.6–0.3) in O₂/N₂/CO₂. Unimodal PM size distribution was observed, except for sunflower husks gasification in O₂/N₂/CO₂; (iv) the SEM/EDS and XPS analysis confirmed that submicron-sized PM_1–0.3 contain above 80% of carbon associated to soot, due to incomplete oxidation, whereas in cyclone (char) particles, carbon decreased to about 50%. The SEM/EDS results showed that K and Cl are typical constituents of the submicron size PM, whereas the alkaline earth metals were detected mainly in fine and coarse particulates. Detailed analysis of the XPS (C1s) spectra showed that the most common oxygen-containing groups on the PM₁ surface were carbonyl and carboxyl.

The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulphuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600 and 700 ºC). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis) and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer–Emmett–Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost thus, forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 ºC proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations another biochar application was proposed - as catalyst.

Despite the effort done by member states during the last decade, failure in the implementation of the Ambient Air Quality Directive is being continuously registered in many European cities for different air pollutants. One of the biggest concerns in Bulgaria is the exceeded PM10 concentration in the ambient air, measured in all six air quality zones during the winter period. This has induced numerous activities (at the national and European level) focused on the following issues: identification of the level of exceedance of the air quality norms for PM10; the general emission sources; the most prominent omissions and discrepancies in the legislative framework; the level of implementation of the prescribed measures and many others. However, the PM10 exceedance is still of a significant concern in at least 28 municipalities in Bulgaria. Thus, the present work introduces a brief report on the current state of the problem in the country. For that purpose, benchmarking analyses was applied for obtaining the range of discrepancies and the tendencies of the PM10 concentrations, monitored in the ambient air at the affected municipalities. The investigation was carried out using merely officially reported and freely accessible data and covered a relatively short period of time of six years. The latest national and European environmental reports present data confirming the primary role of residential heating and transport during the winter period as well as at the occurrence of particular atmospheric conditions.

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.