Oil palm empty fruit bunch (OPEFB) is an abundant organic waste in Malaysia that is often disposed of through field burning. A previous study has shown that solar-driven steam gasification of OPEFB can produce hydrogen-rich syngas with an energy upgrade factor of 1.2 and a carbon conversion efficiency of 95.1 %. Beyond its potential as a biofuel, OPEFB can also act as a carbon sink, capturing photosynthetically stored carbon. This study explores the potential of amplifying OPEFB's negative carbon emissions through solar-driven gasification, using CO₂ as the gasifying agent. In this work, a Central Composite Design (CCD) approach was employed to assess the influence of temperature (1100–1300 °C) and CO₂/OPEFB molar ratio (1.6–3.0) on H₂/CO molar ratio and energy upgrade factor, with a constant OPEFB flow rate of 1.8 g/min. The results demonstrated that at an energy upgrade factor of 1.4, 94.9 % of the total carbon was converted into syngas with a H₂/CO molar ratio of 0.3. The maximum observed net carbon capture yield of 0.4 g C/g OPEFB was achieved at 1300 °C and a CO₂/OPEFB molar ratio of 3.0. The remaining carbon (94.4–95.7 wt %) was converted into biochar with low heavy metal content, which has potential as a soil enhancer.

Sugarcane bagasse (SCB) is increasingly considered as a potential source for bioenergy or bulk chemicals production. However, efficient pretreatment techniques need to be developed to make full use of its potential. A central composite design was employed to evaluate the effect of temperature (146.4–213.6 °C), NaOH concentration (0.7–2.3 M) and treatment time (3.2–36.8 min) on the hydrothermal pretreatment of SCB. Glucose was the abundant fermentable sugar released in the hydrolysate (4.0 g/L) and its concentration was significantly (p-value < 0.05) affected by temperature and NaOH concentration. Sugars released in the hydrolysate and the remaining cellulose, hemicellulose, and lignin in the pretreated fiber were anaerobically co-digested in batch thermophilic assays (55 °C). Propionate, one of the most promising platform chemicals, was the main metabolite produced (0.5 g/L) and its concentration was significantly affected by temperature and NaOH concentration. Both NaOH concentration and pretreatment duration significantly affected methane composition in the biogas (p-value <0.05 and 0,10 respectively). Defluviitoga, and Methanothermobacter genera were favored in response to alkaline hydrothermal pretreatment at the central point conditions (180 °C, 1.5 M NaOH, 20 min).

Oil palm empty fruit bunch (OPEFB) is an abundant waste that is commonly incinerated, causing environmental pollution. In this study, an alternative waste management approach was investigated to produce value-added syngas from OPEFB using solar steam gasification. The three operating variables were temperature (1100–1300 °C), H₂O/OPEFB molar ratio (1.7–2.9), and OPEFB flowrate (0.8–1.8 g/min). Central composite design (CCD) was conducted to investigate and optimise the effects of these operating variables on H₂/CO molar ratio and solar to fuel energy conversion efficiency (η_{solar to fuel}). The findings revealed that all investigated operating variables were significant. Experimentally, the highest H₂/CO molar ratio (1.6) was obtained at 1300 °C, H₂O/OPEFB molar ratio of 2.9, and OPEFB flowrate of 1.8 g/min, with a high carbon conversion reaching 95.1%. Results from CCD analysis showed that a higher H₂/CO molar ratio (above 1.8) could be reached at 1200 °C, H₂O/OPEFB molar ratio of ≥3.0, and OPEFB flowrate of ≥2.0 g/min. The maximum η_{solar to fuel} of 19.6% was achieved at 1200 °C, H₂O/OPEFB molar ratio of 1.3, and OPEFB flowrate of 1.3 g/min, whereby a favourable energy upgrade factor (1.2) was achieved. The statistical model showed adequacy to predict H₂/CO molar ratio.