Anaerobic Fermentation with Ethanol and Lactate as Co-Electron Donors for Medium-Chain Carboxylic Acid Production

Abstract

Developing alternative technologies for producing chemical compounds, previously based on fossil sources, is the first step into a circular economy. Current environmental pressures and the net-zero carbon emission goal require a more efficient waste management technology. Accordingly, using organic waste to produce high-value chemical compounds (e.g., medium- chain carboxylic acids [MCCAs]) is a promising alternative to re-valorize waste and reduce fossil fuel dependency. MCCAs (ranging from six to twelve carbons) are essential industrial chemicals that could be employed in several applications, including as antimicrobial agents, fodder- annexing agents, rubbers, and precursors of aviation fuels. The most commonly used electron donors for microbial MCCA production were ethanol and lactate, which could be available in many waste-fermentation broths (e.g., syngas, liquor-making wastewater, food waste, or acid whey). With expanding application of real waste into microbial MCCA production, it was found that both ethanol and lactate were present in the fermentation broth of some waste (e.g., maize silage, food waste, or acid whey) due to fermentation way of waste. Few studies have focused on the co-utilization of ethanol and lactate for MCCA production. More research was required to understand using ethanol and lactate as co-electron donors for MCCA production and to lay a foundation for further conversion of more real waste into MCCAs. In this dissertation, I studied anaerobic fermentation with ethanol and lactate as co-electron donors for MCCA production. In the first study, I present the process regulation in MCCA production in open cultures with ethanol and lactate as co-electron donors; in the second study, I explored the microbial ecology of the microbiome for MCCA production in a long-term run bioreactor with ethanol and lactate as co- electron donors; in the third study, I investigated the parameter affecting MCCA production with ethanol and lactate with co-substrates.