Trickle-Bed Bioreactors for Acetogenic H2/CO2 Conversion

Abstract

Acetic acid is an essential industrial building block and can be produced by acetogenic bacteria from molecular hydrogen (H2) and carbon dioxide (CO2). When gasses are supplied as substrates, bioreactor design plays an important role for their availability. Trickle-bed bioreactors (TBs) have an enhanced gas-to-liquid mass transfer and cells remain in the system by forming a biofilm on the carriers. So far, TBs have been investigated extensively for bio-methanation processes, whereas studies for their use in acetic acid production are rare. In this study, we evaluated the reproducibility of two parallel TBs for acetic acid production from H2:CO2 (= 70:30) by a mixed culture with a gas flow rate of 3.8 mL min−1 and a medium flow rate of 10 mL min−1. Additionally, the effect of glucose addition during the starting phase on the resulting products and microbial composition was investigated by setting up a third TB2. Partial medium exchanges to decrease the internal acetic acid concentration (AAC) combined with recycling of withdrawn cells had a positive impact on acetic acid production rates with maxima of around 1 g L−1 d−1 even at high AACs of 19–25 g L−1. Initial glucose addition resulted in the accumulation of unwanted butyric acid up to concentrations of 2.60 ± 0.64 g L−1. The maximum AAC of 40.84 g L−1 was obtained without initial glucose addition. The main families identified in the acetogenic TBs were Peptococcaceae, Ruminococcaceae, Planococcaceae, Enterobacteriaceae, Clostridiaceae, Lachnospiraceae, Dysgonomonadaceae and Tannerellaceae. We conclude that a TB is a viable solution for conversion of H2/CO2 to acetate using an anaerobic enrichment culture.

Probing efficient microbial CO2 utilisation through metabolic and process modelling

“…This simplicity allows for a bioprocess using gaseous substrates with low operation and maintenance costs. Other reactors, such as packed bed reactors (Steger et al., 2022 ) or U‐loops (Puiman et al., 2022 ) have even higher gas transfer rates (Nikakhtari & Hill, 2005 ) but are more complex and costly and so were not included in the present work. Based on a thermodynamic and economic assessment of syngas fermentation by Redl et al (Redl, Sukumara, et al., 2017 ).…”

“…Such a study could provide valuable insights and further improvements into gas fermentation‐mediated CO 2 upcycling. Mass transfer models based on experimental data of continuous stirred tank (CSTR) (Liu et al., 2019 ), packed bed (PBR) (Steger et al., 2022 ) or external loop airlift (ELAR) (Puiman et al., 2022 ) reactors have been published. Especially the latter two reactor types are worth considering because of their potential to improve gas transfers (Nikakhtari & Hill, 2005 ).…”

Eight Up-Coming Biotech Tools to Combat Climate Crisis

“…While low CO concentrations significantly improved the overall gas fermentation performance and process stability, more than 50% of the captured CO 2 was converted to ethanol by C. autoethanogenum , independent of CO supplementation [ 19 ]. The highest acetate titers of 40–60 g·L −1 were previously reported for batch-stirred tank reactor systems and continuous trickle-bed reactors using CO 2 and H 2 as substrates [ 20 , 21 , 22 ]. Syngas fermentation based on a mix of CO, CO 2 , and H 2 yielded significantly lower acetate concentrations of 1.0–7.7 g·L −1 [ 23 , 24 ].…”

Microbial Enrichment Techniques on Syngas and CO2 Targeting Production of Higher Acids and Alcohols

“…Microbial communities present a series of benefits derived from their inherent microbial diversity and functional redundancy; however, their high complexity also constitutes one of their major limitations as they often result in decreased product selectivity, requiring further development of community management strategies. So far, application of MMC has been exceptionally promising for the production of methane and acetic acid [ 8 , 9 , 10 , 11 , 12 ], while it has also shown high potential for ethanol production, especially when the medium is supplemented with acetic acid [ 11 , 12 , 13 ]. Production of molecules with higher carbon atoms is mainly investigated in processes based on pure, wild or engineered microbial strains or co-cultures [ 14 , 15 , 16 , 17 ], while there is an emerging interest also in MMC [ 18 , 19 , 20 , 21 ].…”