Residual Gas for Ethanol Production by Clostridium carboxidivorans in a Dual Impeller Stirred Tank Bioreactor (STBR)

Abstract

Recycling residual industrial gases and residual biomass as substrates to biofuel production by fermentation is an important alternative to reduce organic wastes and greenhouse gases emission. Clostridium carboxidivorans can metabolize gaseous substrates as CO and CO2 to produce ethanol and higher alcohols through the Wood-Ljungdahl pathway. However, the syngas fermentation is limited by low mass transfer rates. In this work, a syngas fermentation was carried out in serum glass bottles adding different concentrations of Tween® 80 in ATCC® 2713 culture medium to improve gas-liquid mass transfer. We observed a 200% increase in ethanol production by adding 0.15% (v/v) of the surfactant in the culture medium and a 15% increase in biomass production by adding 0.3% (v/v) of the surfactant in the culture medium. The process was reproduced in stirred tank bioreactor with continuous syngas low flow, and a maximum ethanol productivity of 0.050 g/L.h was achieved.

Biofuels Production and Processing Technology

“…In particular, biomass and ethanol production increased by 15% and 200% using Tween ® 80 in the culture medium, respectively, compared to pure culture medium. In the bioreactor, 106% more biomass was produced compared to serum bottle fermentation, but the same ethanol concentration was achieved [37].…”

“…It can be produced from biomass, coal, animal or municipal solid waste, and industrial CO-rich off-gases [36]. Benevenuti et al [37] carried out a study, using Clostridium carboxidovorans for syngas fermentation, evaluating the effect of different concentrations of Tween ® 80 in the culture medium and the best process conditions were validated in a stirred tank bioreactor (STBR). The study pointed out that the supplementation with Tween ® 80 to the culture medium was characterized by an increasing in biomass and ethanol production during Clostridium carboxidivorans syngas fermentation in serum bottles and validated in a stirred tank bioreactor.…”

Recent Advances in the Technologies and Catalytic Processes of Ethanol Production

“…Syngas fermentation is a biological carbon fixation process that uses a gaseous feedstock, primarily composed of a mixture of CO, CO 2 , and H 2 which is obtained from biomass, coal, animal or municipal solid waste, and industrial CO-rich waste gases, that is a promising approach converted into valuable chemicals and fuels by microorganisms through a hybrid thermo/biochemical process [151,152]. Several Clostridium species are known to produce different bioproducts, but only a few of them use syngas as the sole carbon and energy source [153,154].…”

Impacts of Syngas Composition on Anaerobic Fermentation

“…Besides the major components (CO, H 2 and CO 2 ), biomass-derived syngas may contain additional constituents such as ethylene (C 2 H 4 ), ethane (C 2 H 6 ), acetylene (C 2 H 2 ), tar, ash, char particles, oxygen (O 2 ), ammonia (NH 3 ), nitric oxide (NO), hydrogen sulfide (H 2 S), sulfur dioxide (SO 2 ) and hydrogen cyanide (HCN) [53][54][55]. Tars can be composed of several high-molecular weight molecules that are gas chromatography undetectable, such as 7 carbon and higher ring compounds, heterocycles such as phenol, cresol and pyridine, light aromatic such as toluene, styrene and xylene, light poly-aromatic such as naphthalene, phenanthrene and anthracene, and heavy poly-aromatic such as fluoranthene, pyrene, chrysene, perylene and benzoperylene; however, usually these components are not evaluated individually [48].The composition in terms of these impurities in syngas varies with feedstock type, gasifying agent and operating conditions [56], but the most frequently found compounds are tar, ammonia (NH 3 ), nitric oxide (NO) and hydrogen cyanide (HCN) [53]. Some of these impurities can inhibit acetogenic bacterial activity, even at very low concentrations, by limiting cell growth, enzyme activities or by changing physiochemical conditions (pH, osmolarity, redox potential, etc.)…”