Abstract
Energy consumption places growing demands on modern lifestyles, which have direct impacts on the world’s natural environment. To attain the levels of sustainability required to avoid further consequences of changes in the climate, alternatives for sustainable production not only of energy but also materials and chemicals must be pursued. In this respect, syngas fermentation has recently attracted much attention, particularly from industries responsible for high levels of greenhouse gas emissions. Syngas can be obtained by thermochemical conversion of biomass, animal waste, coal, municipal solid wastes and other carbonaceous materials, and its composition depends on biomass properties and gasification conditions. It is defined as a gaseous mixture of CO and H2 but, depending on those parameters, it can also contain CO2, CH4 and secondary components, such as tar, oxygen and nitrogenous compounds. Even so, raw syngas can be used by anaerobic bacteria to produce biofuels (ethanol, butanol, etc.) and biochemicals (acetic acid, butyric acid, etc.). This review updates recent work on the influence of biomass properties and gasification parameters on syngas composition and details the influence of these secondary components and CO/H2 molar ratio on microbial metabolism and product formation. Moreover, the main challenges, opportunities and current developments in syngas fermentation are highlighted in this review.
Highlights
The increasing global demand for natural resources tends to exceed our Earth’s capacity for their regeneration
The results revealed that the calorific value of the producer gas reached a maximum (5.76 MJ/Nm3) when the equivalence ratio was 0.30
Waste wood content was varied from 0 to 30% and the results indicate an increase in H2 and CO2 compositions in producer gas when the waste wood percentage increased, while CO and CH4 compositions were not affected
Summary
The increasing global demand for natural resources tends to exceed our Earth’s capacity for their regeneration. Environmental deterioration such as ocean acidification, greenhouse gas accumulation in the atmosphere and groundwater depletion, is accelerating [1,2] Faced with this scenario, alternative energy and materials sources are needed to meet growing demands as well as society’s environmental and economic concerns. Syngas fermentation fulfills the requirements for their sustainable production, having recently attracted much attention. It can be implemented directly in industries where the high levels of exhaust gases are constantly released, such as cement or steel manufacturing, oil refining and the production of petrochemicals, contributing to the reduction in greenhouse gas emissions [3,4]. Syngas composition depends on how it is produced, i.e., the process, operating conditions and raw materials, among others
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