# Recent Advancements in Anaerobic Digestion and Gasification Technology
## 8 Recent Studies on Gasification Focusing on Syngas Production  
This section presents the selected recent studies conducted by various scholars and researchers on biomass gasification. This is necessary to have an overview and track the trend of research in this regard. On the positive side, the development of the biomass gasification process has contributed to high potential energy efficiency that is environmentally friendly and inexpensive, mostly as a waste-to-energy technology. Therefore, its contributions cannot be neglected, especially for the production of syngas. Currently, on the gradual progress made so far on biomass gasification, it is interesting to mention that some high-profile gasifier units have been installed and are operating in a different part of the world. Table 6 shows a few of the gasification plants installed in selected parts of the world. Reviewing the recent studies on biomass gasification from the literature, the gasification of eucalyptus wood chips in a downdraft gasifier to produce syngas in South Africa was conducted by [PERSON] et al. [59]. The authors sourced the eucalyptus wood chip from the sawmill industry. The eucalyptus wood was gasified using air as the oxidizing agent, and the produced syngas were measured. With the aid of a non-dispersive infra-red \begin{table}
\begin{tabular}{c c c} \hline \hline
**Gasifier Unit** & **Location** & **Capacity** \\ \hline TCG global steam reforming & USA & 136,000 t/year \\ Two-stage thermal process & Norway & 78,000 t/year \\ Fixed-bed dry bottom & USA & 16,000 t/day \\ General Electric & China & 1500 t/day \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The recent operating gasifier units with their capacity and locations [64]. \begin{table}
\begin{tabular}{l c} \hline \hline
**Feedstock for Anaerobic Digestion** & **Source of Waste** \\ \hline Animal waste & Energy crop, livestock manure, remains from harvest and farm mortality, etc. \\ Industrial waste & Diary product waste, processing of food/beverage, pharmaceutical industries, waste from a slaughterhouse, residues from agro-processing, etc. \\ Municipal waste & Sewage sludge, yard trimmings, food waste from restaurants, and organic fraction of \\ MSW. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Feedback of anaerobic digestion by waste classification. sensor and palladium/nickel (Pd/Ni) gas sensor., the volumetric composition of the syngas produced was as follows; hydrogen (22.3-22.5%), carbon monoxide (22.3-24.3%), methane (1.9-2.1%), carbon dioxide (9.8-10.7%), and nitrogen (41.5-42.9%). These syngas produced a higher heating value (HHV) of 6.08 MJ/Nm\({}^{3}\), obtained from hydrogen, carbon monoxide, and methane composition. The study provided evidence that gasification is an alternative for the waste-to-energy conversion. To predict and optimise the rate of syngas production, [PERSON] et al. [65] developed a robust biomass gasification process model. This was possible by incorporating updated biomass reaction kinetics and dense bed hydrodynamics into the Aspen Plus platform. The model was developed using 864 datasets of four input parameters and demonstrated good agreement and best line of fit under a range of operating conditions. This was achieved when comparing the model prediction with the experimental result. An optimal syngas yield from 61.4% to 78.5% by volume was obtained on a dry N\({}_{2}\)-free basis. According to the optimization model result, a maximum syngas production of 78.6 vol% occurred at a temperature of 900 \({}^{\circ}\)C, equivalent ratio (ER) of 0.23, steam-to-biomass (S/B) ratio of 0.21, and moisture content (MC) at 30 wt%. [PERSON] et al. [26] carried out an experimental study on the gasification of cotton stalks to enhance the Boudouard reaction and carbon monoxide production. The parameters studied included carbon dioxide flow rate (50-400 mL/min), carbon dioxide concentration (0-100%), temperature (750-950 \({}^{\circ}\)C), and feedstock particle size of 0.1-8 mm.