Recent developments in bio-energy recovery through fermentation

Abstract

Bio-energy recovery through fermentation is gaining importance because of limited fossil resources. Especially, bio-ethanol and biogas production are applied worldwide and have reached industrial scale. Other options such as bio-hydrogen, microbial fuel cells, and higher alcohol and acid fermentations are still in development. Current fields of intense research are the utilization of lignocellulose substrates, intensification of the recovery of wastes and industrial byproducts for bio-energy recovery, optimization of process control (especially, in anaerobic digestion), and the optimal utilization scenario of byproducts from microbial bio-energy processes (e.g., stillage, digestate). For lignocellulose utilization, the optimal pretreatment technologies (heat, acid, enzyme, steam explosion, mechanical treatment) are being investigated. For methane production, benchmarks for fermentation parameters are presented, and current bottlenecks and deficiencies of the technology are discussed. As biomass is not only needed for energy conversion, but also for other purposes (food production, animal feed, raw material for industry), the conversion efficiency from sunlight via plants to biomass and biofuels has to be enhanced. For this reason, research also focuses on increasing yields, improving conversion technologies, usage of the entire plant biomass, and improving the entire energy conversion system. Mass and energy balances, net energy balances, and combined heat and power usage are also considered. Current research tries to evaluate eco balances, greenhouse gas emissions, and the sustainability of the entire production process, in order to improve the entire conversion systems. In summary, microbial bio-energy conversion systems will be of great importance as part of a future energy mix, until alternative energy sources like direct conversion of sunlight (e.g., photovoltaics), nuclear technology (e.g., fusion), or other future energy sources can replace it.