The anaerobic digestion technology has been in existence for centuries and its underlying theory established for decades. It is considered a useful technology for the generation of renewable energy, and provides means to alleviate problems associated with low access to energy. However, a great deal of current research is targeted towards the optimization of this technology under diverse digestion process conditions. This review presents an in-depth analysis of the chemistry of anaerobic digestion and discusses how process chemistry can be used to optimize system performance through identification of methods that can accelerate syntrophic interactions of different microorganisms for improved methanogenic reactions. Recent advances in addition to old research are discussed in order to offer a general but comprehensive synopsis of accumulated knowledge in the theory of anaerobic digestion, as well as an overview of previous research and future directions and opportunities of the AD technology. Achieving a sustainable energy system requires comprehensive reforms in not just economic, social and policy aspects, but also in all technical aspects, which represents one of the most crucial future investments for anaerobic digestion systems.

The processing of sugarcane bagasse as a potential feedstock for efficient energy production has attracted a great deal of attention in the sugarcane industry, which has traditionally inefficiently burned bagasse in boilers for steam and electricity generation. Alternative technologies for more efficient utilisation of bagasse for energy production within the industry has also been hindered by the high degree of complexity involved in bagasse handling and pre-processing before it can be utilised as an energy feedstock. This can be attributed to unfavourable characteristics of mill-run bagasse, which includes low bulk and energy densities, a wide range of particle sizes and shapes as well as high moisture content. Gasification is regarded as one of the most promising energy recovery technologies for the widespread use of biomass because of its higher efficiency when compared to the combustion technology commonly used by the sugarcane industry. There has been a strong drive to identify efficient pre-processing methods that can be applied to bagasse to make it a suitable feedstock for energy production in thermochemical conversion systems. This work provides a comprehensive review on the pre-processing of bagasse for gasification, and the gasification technology options for its conversion into energy, with a particular emphasis on the downdraft gasification technology

Quintessential characteristics of corn cob were investigated in this study in order to determine its gasification potential. Results were interpreted in relation to gasification with reference to existing data from the literature. The results showed that the gasification of corn cob may experience some challenges related to ash fouling, slagging, and sintering effects that may be orchestrated by high ash content recorded for corn cob, which may contribute to increasing concentration of inorganic elements under high temperature gasification conditions, even though EDX analysis showed reduced concentration of these elements. The study also found that the weight percentages of other properties such as moisture, volatile matter, and fixed carbon contents of corn cob as well as its three major elemental components (C, H, and O) including its clearly exhibited fiber cells make corn cob a suitable feedstock for gasification. FTIR analysis revealed the existence of –OH, C–O, C–H, and C=C as the major functional group of atoms in the structure of corn cob that may facilitate formation of condensable and noncondensable liquid and gaseous products during gasification. TGA results indicated that complete thermal decomposition of corn cob occurs at temperatures close to 1000°C at a heating rate of 20°C/min.

The rising global warming concerns and explosive degradation of the environment requires the mainstream utilization of alternative fuels, such as hydroxy gas (HHO) which presents itself as a viable substitute for extracting the benefits of hydrogen. Therefore, an experimental study of the performance and emission characteristics of alternative fuels in contrast to conventional gasoline was undertaken. For experimentation, a spark ignition engine was run on a multitude of fuels comprising of gasoline, Liquefied petroleum gas (LPG) and hybrid blend of HHO with LPG. The engine was operated at 60% open throttle with engine speed ranging from 1600 rpm to 3400 rpm. Simultaneously, the corresponding performance parameters including brake specific fuel consumption, brake power and brake thermal efficiency were investigated. Emission levels of CO, CO₂, HC and NOx were quantified in the specified speed range. To check the suitability of the acquired experimental data, it was subjected to a Weibull distribution fit. Enhanced performance efficiency and reduced emissions were observed with the combustion of the hybrid mixture of LPG with HHO in comparison to LPG: on average, brake power increased by 7% while the brake specific fuel consumption reduced by 15%. On the other hand, emissions relative to LPG decreased by 21%, 9% and 21.8% in cases of CO, CO₂, and unburned hydrocarbons respectively. Incorporating alternative fuels would not only imply reduced dependency on conventional fuels but would also contribute to their sustainability for future generations. Simultaneously, the decrease in harmful environmental pollutants would help to mitigate and combat the threats of climate change.

Biomass has the potential to replace conventional fuels in a number of applications, particularly in biofuel production. It is an abundantly available renewable material with great potential as a feedstock for bioconversion processes for the production of energy, fuels and a variety of chemicals. Due to its biogenic origin, the carbon dioxide released from its combustion process does not impact atmospheric carbon dioxide. Despite these merits, a major problem hindering its widespread use has always been its recalcitrant nature, in terms of its inherent characteristics, which are unfavorable to its use in bioconversion and bio refinery processes. This makes it necessary for biomass to be pretreated before use in any conversion process for maximum product recovery. However, a major issue with regards to biomass pretreatment is the lack of rapid, high throughput and reliable tools for assessing and tracing biopolymer components of biomass relevant to the energy production potential of the biomass. This chapter therefore presents an overview of the pretreatment and characterization of biomass relevant to energy, fuels and chemicals production. The information provided will bequeath readers with the basic knowledge necessary for finding an auspicious solution to pretreatment problems and the production of energy from pretreated biomass.