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.

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The ever-increasing organic waste generation in Malaysia is a significant contributor to greenhouse gas (GHG) emissions. However, organic wastes can be utilized to produce biogas by anaerobic digestion, which is a promising option for both energy and material recovery from organic wastes with high moisture content. Therefore, this study was formulated to investigate the feasibility of anaerobic co-digestion of three types of organic wastes generated in significantly huge quantities in Malaysia, namely palm oil mill effluent (POME), food waste (FW), and sewage sludge (SWS). The biomethane potential (BMP) test was used to evaluate the biomethane potential from these organic wastes under mesophilic conditions to establish a stable and balanced microbial community, which may lack in mono-digestion, to improve biogas production. Comparative performance was made at different food to microorganism (F/M) ratios to investigate methane production in three groups of assays, namely A, B, and C. In groups A and B, the effect of F/M ratio variation on methane production was investigated, while in group C, the effect of varying the co-substrate mixture on methane yield was examined. The findings showed that the highest methane yields achieved for mono-digestion of POME and SWS in group A were 164.44 mL-CH₄/g-COD_added and 65.34 mL-CH₄/g-COD_added, respectively, at an F/M ratio of 0.8 and 197.90 mL-CH₄/g-COD_added for FW in group B at an F/M ratio of 0.5. In addition, the highest methane yield achieved from the anaerobic co-digestion was at 151.47 mL-CH₄/g-COD_added from the co-digestion of the POME and SWS (50:50) at an F/M ratio of 1.7 in group A. Both AD and AcoD were tested to fit into two kinetic models: the modified Gompertz and the transfer function models. The results showed that the modified Gompertz model had a better fit and was more adjusted to the experimental results for both AD and AcoD. The importance of this research lies in the economics of anaerobically co-digesting these abundance feedstocks and the variations in their characteristics which were found to increase their methane yield and process efficiency in anaerobic co-digestion.

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Small-scale electrical power generation (<100 kW) from biogas plants to provide off-grid electricity is of growing interest. Currently, gas engines are used to meet this demand. Alternatively, more efficient small-scale solid oxide fuel cells (SOFCs) can be used to enhance electricity generation from small-scale biogas plants. Most electricity generators require a constant gas supply and high gas quality in terms of absence of impurities like H ₂S. Therefore, to efficiently use the biogas from existing decentralized anaerobic digesters for electricity production, higher quality and stable biogas flow must be guaranteed. The installation of a biogas upgrading and buffer system could be considered; however, the cost implication could be high at a small scale as compared to locally available alterna-tives such as co-digestion and improved digester operation. Therefore, this study initially describes relevant literature related to feedstock pre-treatment, co-digestion and user operational practices of small-scale digesters, which theoretically could lead to major improvements of anaerobic digestion process efficiency. The theoretical preamble is then coupled to the results of a field study, which demonstrated that many locally available resources and user practices constitute frugal innovations with potential to improve biogas quality and digester performance in off-grid settings.

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The ever-increasing organic waste in Malaysia is one of the major factors of the increase in Green House Gases (GHGs) emissions. Some of the organic wastes, however, can be utilized to produce biogas by anaerobic digestion (AD), which is a promising option for both energy and material recovery from organic wastes with high moisture content. This study was formulated to investigate the feasibility of tri-digestion of three of the major organic wastes which are generated in huge quantities in Malaysia such as Sewage Sludge (SS), Palm Oil Mill Effluent (POME), and Food Waste (FW). Tri-digestion on mixture of these organic wastes was examined to establish a stable and balanced microbial community, which may be lacking in mono-digestion of a single organic waste, to improve biogas production. Batch anaerobic digestion experiment of selected samples was conducted for 33 days under mesophilic condition. The Anaerobic tri-digestion was evaluated and compared with anaerobic mono-digestion for the same samples at different mixing ratios. The experiments were designed in two groups A and B, at food to micro-organisms (F/M) ratios of 1 and 5, respectively. From the results obtained, tri-digestion of the wastes at 80:10:10 (FW:POME:SS) proportion yielded the highest biogas production of 245.04 mL CH4/g-COD at F/M ratio of 1, which was greater than the methane production in mono-digestion of food waste at the same F/M ratio. In addition, tri-digestion showed better methane yield for all the samples at F/M= 1 compared to mono-digestion for an individual substrate. The results were significantly different at F/M=5 for POME and FW as the production of methane during the first half of the test period was not stable, compared to SS which showed consistency and stability at both F/M ratios. From the results obtained, it is evident that tri-digestion of FW, POME and SS is an attractive option to be explored for improving biogas production by AD in Malaysia due to the abundance of these three organic wastes and the mesophilic conditions naturally available.@en