Restrictions on landfill disposal have prompted cities to introduce decentralized refuse-derived fuel (RDF) systems, yet their material-flow performance under actual operating conditions remains insufficiently documented. Three municipal waste treatment facilities were assessed during Yogyakarta City's late-2024 waste-management transition using facility-level material flow analysis and screening-level RDF characterization. The recorded solid organic fraction accounted for 14.8–18.9% of incoming MSW, while an unaccounted mass fraction of 51.7–63.8% remained after mass-balance closure. Facility utilization ranged from 36.7% to 94.9%, while RDF yield remained within a narrower range of 10.2–13.3%. Plastics represented 54.4–91.0% of the RDF, which contained 70.4–78.5% carbon, 2.19–5.50% moisture, and HHV values of 33.2–36.9 MJ/kg. As the assessment was based on a single field campaign at each facility, the results represent cross-sectional rather than long-term performance. The findings identify heterogeneous feedstock, uneven facility loading, incomplete material-flow monitoring, and unverified downstream pathways as key constraints during early decentralized RDF implementation.
Rice straw is an abundant agricultural residue with potential as a ruminant feed, but its low protein content and recalcitrant lignocellulosic structure limit its utilisation. This study evaluated an integrated pretreatment using urea, lime, and molasses to improve the nutritional and physical quality of rice straw. A 3 × 3 × 3 factorial experiment was conducted with urea (0, 3, and 4%), lime (0, 2, and 3%), and molasses (0, 2, and 4%), giving 27 treatment combinations. Pretreatment improved crude protein content and reduced major fibre fractions. Crude protein increased from 3.94% in untreated straw to 7.44% in the 4% urea + 3% lime + 4% molasses treatment (T27), an 88.8% increase. In T27, neutral detergent fibre, acid detergent fibre, and acid detergent lignin decreased from 68.82, 46.47, and 6.12% to 61.16, 41.38, and 3.45%, respectively, representing reductions of 11.1, 10.9, and 43.6%. Mineral enrichment was also evident, with calcium increasing from 0.459% to 2.556%, phosphorus from 0.146% to 0.574%, and zinc from 35.16 ppm to 57.10 ppm. Urea-containing treatments produced softer straw with no visible mould, while microscopic visualisation revealed disruption of the compact fibre structure. The 4% urea + 3% lime + 4% molasses combination was identified as the overall most suitable treatment. However, increasing molasses from 2% to 4% provided limited additional improvement in major feed-quality parameters. Overall, integrated urea–lime–molasses pretreatment offers a promising approach for converting rice straw waste into a nutritionally improved ruminant feed resource.
Direct aqueous carbonation of magnesia-rich feedstocks represents a promising route for permanent CO2 storage via the formation of stable magnesium carbonate. Building on previous work, where brucite formation and limited carbonation efficiencies (15–36%) were observed for two magnesia-carbon refractories, this study investigated whether limited CO2 availability within the liquid phase was the main rate controlling factor. Experiments were conducted in an improved reactor setup at 100 °C and 180 °C at CO2 partial pressures of 20 and 11 bar, respectively, to evaluate the influence of temperature on CO2 solubility and reaction kinetics. Additional experiments with NaHCO3 additives were performed to address the effect of increased initial CO2 availability. By optimizing gas introduction via a dip tube positioned at the stirrer vortex and employing a turbine impeller, carbonation efficiencies increased significantly to 75–93% at 180 °C, representing a 3- to almost 5-fold improvement compared to the 19–23% achieved under similar conditions in the previous reactor setup. Magnesite was identified as the dominant product phase, indicating that improved CO2 mass transfer and dissolution into the aqueous phase eliminated earlier gas-supply limitations. Higher temperatures (180 °C) promoted faster kinetics and more complete carbonation, whereas experiments at 100 °C yielded metastable hydromagnesite. The results indicate that CO2 transfer efficiency governs reaction rates and underscore the reactor design’s critical role in aqueous carbonation. Synopsis Advances in permanent CO2 sequestration via aqueous carbonation to valorize magnesia-rich materials were achieved by highlighting the reactor design’s critical role in CO2 transfer.
Bioleaching of valuable raw materials from spent lithium-ion batteries (LIBs) has gained increasing attention, but challenges remain in scalability, microbial inhibition, and diverse LIB chemistries. A set of experiments was performed to select the best-performing microbial culture and most compatible black mass (BM) for scale up. Batch bioleaching of four types of BM was performed in flasks (50 mL) at 30°C: nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), mobile phones & laptops (ML), and electric bikes & power tools (PS). Different pulp densities (1, 3, and 6% (w/v)) were leached using an adapted environmental enrichment (aEN) and an adapted mixed culture of three acidophiles (aM). aEN achieved high metal recoveries (100% Li, Cu) from all BMs at 1% pulp density, but the leaching efficiencies dropped (except for Li) at 3 and 6% BM. Next, upscaled bioleaching (1 L) of LFP was performed using aEN in bioreactors with either propeller-driven stirring (R) or magnetic stirring (MR). MR provided improved BM mixing and microbial activity, achieving up to 100% solubilization of Li, Al, Mn, Co, and Ni within 10 days, even at high pulp density of 10% (w/v). 16S rRNA analysis revealed a shift in the microbial population during bioleaching in the bioreactor with an increased abundance of Acidithiobacillus spp. Overall, the findings of this study demonstrate that bioleaching is a promising alternative to conventional recycling processes for the recovery of critical metals from BM, particularly effective for LFP-type materials.
