Abstract
Accumulation of carbon dioxide (CO2), associated with global temperature rise, and drastically decreasing fossil fuels necessitate the development of improved renewable and sustainable energy production processes. A possible route for CO2 recycling is to employ autotrophic and hydrogenotrophic methanogens for CO2-based biological methane (CH4) production (CO2-BMP). In this study, the physiology and productivity of Methanobacterium thermaggregans was investigated in fed-batch cultivation mode. It is shown that M. thermaggregans can be reproducibly adapted to high agitation speeds for an improved CH4 productivity. Moreover, inoculum size, sulfide feeding, pH, and temperature were optimized. Optimization of growth and CH4 productivity revealed that M. thermaggregans is a slightly alkaliphilic and thermophilic methanogen. Hitherto, it was only possible to grow seven autotrophic, hydrogenotrophic methanogenic strains in fed-batch cultivation mode. Here, we show that after a series of optimization and growth improvement attempts another methanogen, M. thermaggregas could be adapted to be grown in fed-batch cultivation mode to cell densities of up to 1.56 g L−1. Moreover, the CH4 evolution rate (MER) of M. thermaggregans was compared to Methanothermobacter marburgensis, the CO2-BMP model organism. Under optimized cultivation conditions, a maximum MER of 96.1 ± 10.9 mmol L−1 h−1 was obtained with M. thermaggregans—97% of the maximum MER that was obtained utilizing M. marburgensis in a reference experiment. Therefore, M. thermaggregans can be regarded as a CH4 cell factory highly suited to be applicable for CO2-BMP.
Highlights
IntroductionFossil hydrocarbon utilization has positively promoted our economy and energy infrastructure in the past (Rondinelli and Berry 2000)
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Fossil hydrocarbon utilization has positively promoted our economy and energy infrastructure in the past (Rondinelli and Berry 2000)
A fed-batch pre-screening with the aim to examine biological CH4 production and growth of M. thermaggregans with key process parameters such as inoculation volume, agitation speed, and DS was performed
Summary
Fossil hydrocarbon utilization has positively promoted our economy and energy infrastructure in the past (Rondinelli and Berry 2000). Combustion of fossil hydrocarbons is known to adversely affect our health and the environment, and it contributes to global warming (Hansen et al 2000). Environmental awareness and decreasing fossil energy sources have driven interests in renewable energy and biofuel production. Biofuels are energy carriers that can be produced from biological resources. The utilization of biofuels reduces greenhouse gas emissions by recycling waste and carbon dioxide (CO2). Biofuel production from agricultural resources, in relation to biological waste, could provide independency from the natural gas exploitation business, both to energy suppliers and to energy end consumers. A biofuel-based industry could be integrated into various
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