Rice is the most important cereal in Asia. However, it also results in the generation of large quantities of rice-derived residues (i.e., rice straw and rice husk). Due to the residues richness in lignocellulosic components, they potentially have considerable value in material and/or energy production without illegal burning in open fields. This work focused on investigating the thermochemical properties and inorganic/metal element contents of rice straw and rice husk. The former included proximate analysis, calorific value, thermogravimetric analysis (TGA) and energy dispersive X-ray spectroscopy (EDS). The latter covered the ten elements most relevant to their slagging/fouling indices. The results showed that they are suitable for energy use as biomass fuels, but rice husk was superior to rice straw because of the high silica content in the rice husk and the significant contents of potassium, sulfur and phosphorus in the rice straw. Using several slagging and fouling indices, the evaluation results were also consistent with their contents of inorganic elements or oxides. To increase the fuel properties of rice-derived residues, they could be pretreated with alkaline leaching, thus causing lower emissions of particulates and reduced slagging tendency when co-firing them with coal in industrial boilers.

In this study, moso bamboo (Phyllostachys edulis, PE) was pyrolyzed in a high-temperature carbonization furnace to produce porous biochar materials with high carbon contents under different carbonization temperatures (500, 600, 700, 800, and 900 °C) and heating rates (10 and 20 °C/min). Preliminary characterization of the PE precursor was conducted to evaluate its thermochemical properties, including proximate analysis, elemental analysis, and thermal decomposition behavior. The results indicated that PE biomass is a suitable precursor for biochar production at temperatures above 400 °C, owing to its low ash content (80%). The pore structure and thermochemical properties of PE-derived biochars were found to improve with increasing carbonization temperature. Optimal pore characteristics were achieved at 800 °C with a heating rate of 10 °C/min, resulting in a Brunauer–Emmett–Teller (BET) surface area of 496 m²/g and a total pore volume of 0.18 cm³/g. In contrast, biochars produced at a heating rate of 20 °C/min exhibited significantly higher carbon contents (90.7–95.7%) compared with those obtained at 10 °C/min (75.4–89.0%). This phenomenon was attributed to enhanced carbon volatilization associated with the longer residence time during slower heating. Observations from scanning electron microscopy (SEM) were consistent with the development of porous structures in the PE-based biochars.

In line with the principles of the circular economy, this study aimed to develop a pyrolysis-activation regeneration process capable of producing highly porous carbon materials from spent granular activated carbon (GAC), which was generated by a high-tech electronics manufacturing company in Taiwan. Thermogravimetric analysis (TGA) and other thermochemical analyses were first conducted to investigate the thermal decomposition behavior of the spent GAC. Subsequently, the thermal regeneration system was employed to perform the N₂ pyrolysis and CO₂ activation experiments under various process conditions (i.e., 800, 850, and 900 °C for holding 0, 30, and 60 min, respectively). Analytical instruments included a surface area and porosimeter for pore property analysis, scanning electron microscopy (SEM) for porous texture observation, and energy dispersive X-ray spectroscopy (EDS) for surface elemental distribution analysis. The results revealed that the pore properties of thermally regenerated GAC were significantly improved compared to the spent GAC, indicating the effective removal or decomposition of adsorbed organics and deposited substances under the process conditions. Additionally, thermal regeneration via physical activation with CO₂ led to enhanced pore properties compared to simple pyrolysis. The maximum BET surface area achieved exceeded 720 m²/g, which was greater than those of spent GAC (approximately 425 m²/g) and N₂-pyrolyzed GAC (approximately 570 m²/g) under the same regeneration conditions (i.e., 900 °C with a 30 min holding time).

This study explored the potential of reusing eggshell powders as a renewable activating agent for producing porous carbon materials from coffee husk. Carbonization and activation experiments were conducted by heating the samples at a rate of 10 °C/min up to 850 °C under a nitrogen atmosphere. A custom-designed double steel-mesh sample holder was used to hold approximately 2.0 g coffee husk on the top, with varying masses of eggshell at the bottom to achieve eggshells to coffee husk mass ratios of 2:1, 4:1, 6:1 and 8:1. The results demonstrated that CO₂ released from the thermal decomposition of the eggshell powder significantly enhanced pore development at 850 °C. Compared to the pore properties of carbon material produced without eggshell (e.g., BET surface area of 321 m²/g), the activated carbon samples exhibited substantially improved pore properties (e.g., BET surface area in the range of 592 to 715 m²/g). Furthermore, the pore characteristics improved consistently with increasing eggshell content. Observations by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR) confirmed the structural and chemical transformations of the resulting carbon materials. Under optimal carbonization-activation conditions, the resulting carbon materials derived from coffee husk exhibited microporous structures and slit-shaped pores, as indicated by the Type I isotherms and H4 hysteresis loops.

In the present study, slurry digestate from a centralized anaerobic digestion (AD) plant, designed for dairy manure treatment and biogas-to-power generation, was utilized as a precursor for the preparation of porous biochars at elevated temperatures ranging from 550 to 850 °C. Proximate analysis and thermogravimetric analysis (TGA) were conducted to determine the thermochemical characteristics of the dried digestate and to explain its complex nature in relation to the physicochemical properties of the resulting biochars. Despite the substantial ash content of the precursor biowaste (approximately 30 wt%), primarily composed of inorganic compounds from calcium, the pore properties of the digestate-derived biochars had an overall increasing trend with regard to rising pyrolysis temperature. Nevertheless, some inconsistencies were observed between the samples produced at 550 °C and 850 °C, which highlighted the heterogeneous and complex nature of the precursor digestate. These observations can be attributed to active pyrolysis and the charring of the lignocellulosic components. The maximum Brunauer–Emmett–Teller (BET) surface area exceeded 200 m²/g when pyrolysis was performed at 850 °C. Nitrogen (N₂) adsorption–desorption isotherms and scanning electron microscopy (SEM) confirmed that the porous digestate-based biochars predominantly exhibited both type I (microporous) and type IV (mesoporous) characteristics. Furthermore, the analytical results of energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) indicated that oxygen-containing surface functional groups on the resulting biochars were retained after pyrolysis. The surface of the digestate-based biochar was also confirmed to be negatively charged at pH > 3.2.

To reduce greenhouse gas (GHG) emissions, decarbonize coal, and also create a circular economy model, solid recovered fuel (SRF) has been developed as an alternative fuel/energy source in the international community, especially in developed countries with a high dependence on imported energy. This mini review offers updates on the regulatory promotion of the production of SRF, focusing on the reuse of biomass or lignocellulosic waste as a starting material in Japan, South Korea, and Taiwan. In this regard, the status of renewable energy and the policies for bioenergy in Japan, South, and Taiwan are first addressed in this work. It is found that the terms for defining refuse/waste/biomass-derived fuel are different across East Asia. However, SRF is increasingly used for the substitution of fossil fuels in industrial utilities (including boilers, incinerators, and kilns), as well as for steam (heat) utilization and/or power generation. With the international policies of pursuing staged carbon reduction by 2030 and carbon neutrality by 2050, the regulatory promotion of the use of bio-SRF has been actively adopted by these countries or regions. Regarding the quality requirements of SRF and concerns about air pollutant emissions, this work also offers updates on regulatory standards, especially in Taiwan. Finally, prospects for the production of bio-SRF and concerns regarding its use are addressed to support the development of a sustainable and circular society.