# Recent Advancements in Anaerobic Digestion and Gasification Technology
## 9 Intensification of Gasification Process  
As mentioned earlier, in anaerobic digestion, intensification focuses on ways to enhance and improve biomass gasification. To optimize the process of gasification, [PERSON] et al. [70] investigated the efficacy of residual char gasification in a gasifier. The study used char made from wood and sewage sludge under different operating conditions in the gasification set-up. The findings showed that the intensifier and additive caused an increase in air flux from 0.11 kg/m\({}^{2}\)s to 0.32 kg/m\({}^{2}\)s as well as in the gasification rate from 0.8 to 2.61 g/min. Consequently, a 72% decrease in the duration of wood char gasification was recorded. This implies that wood char and sewage sludge char are suitable for the intensification of biomass gasification. A continuous fly ash circulation was used as an intensifier or enhancer in industrial dual-fluidized gasification systems. This was evidenced in the study conducted on the effect of ash circulation on the performance of a dual fluidized bed gasification system. In the study, [PERSON] et al. [71] mentioned that ash-forming elements are released from fuel during the gasification of biomass. Hence, these elements are known to have a positive impact on the quality of the gas produced. To assess the impact on the gas quality, the coarse ash was intensified by an injection of untreated olivine in fine particle size and then recirculated. This resulted in a decrease in the tar concentration. From the study, it was revealed that the effect of ash circulation increased with time at a higher rate than in the control experiment. In another study, [PERSON] et al. [72] explored the use of calcium oxide in the steam gasification of sewage sludge to enhance the quality of syngas and hydrogen yield. The calcium oxide (CaO) was in situ to capture CO\({}_{2}\) released directly from the biomass matrix, thereby causing a steam reformation reaction. This process drives the conversion of biomass process in the production of more hydrogen. Thus, the quality of hydrogen in the gas stream was enhanced as high as 70-80% due to CO\({}_{2}\) sorption. Similarly, [PERSON] et al. [73] developed a two-stage sorption that relies on the integration of a CaO-based CO\({}_{2}\)-carrying cycle in the gasification of sewage sludge, thereby intensifying the sludge carbon. During this process, the CO\({}_{2}\) was first captured and stored in the form of CaCO\({}_{3}\) at a higher temperature to gasify the sludge char for carbon monoxide (CO) production. The proposed intensification process resulted in 284.7 NmL of syngas per gram of dry sludge, gross CO/H\({}_{2}\) molar ratio of 2.3, and hydrogen and carbon-rich gas steam at a temperature of 550 \({}^{\circ}\)C and 750 \({}^{\circ}\)C, respectively. The study recommends CaO-based CO\({}_{2}\) as an efficient option for improving carbon during the gasification of sewage sludge. On a similar note, the use of calcium oxide improved the mole ratio of hydrogen from 0.0 to 0.70 and the yield of syngas from 10.70 vol% to 49.40 vol% [74]. As observed, the catalyst enhanced syngas yield because of its effect on the activation energy [21]. To improve the formation of hydrogen, the study used dolomite (MgCO\({}_{3}\)-CaCO\({}_{3}\)) as a catalyst, which was calculated for 4 h at a temperature of 900 \({}^{\circ}\)C. Dolomite, being a natural mineral-based catalyst, enhanced the formation of hydrogen. One advantage of dolomite is that it is inexpensive, abundantly available, and can aid in the removal of tar from producer gas [75]. Findings from a study by [PERSON] et al. [76] revealed that the application of dolomite in MSW gasification reduced the content of tar from 9.71 weight% to 0.0 weight% and increased the syngas production from 0.620 to 1.470 m\({}^{3}\)/kg feedstock. Regarding the content of hydrogen in the syngas, this also increased from 30.6 to 50.2%. In a similar development, transition-metal-based catalysts (copper, iron, and cobalt) are said to be efficient and effective in the steam reformation of tar.