Production of chemicals in thermophilic mixed culture fermentation: mechanism and strategy

Abstract

Thermophilic mixed culture fermentation (TMCF) has advantages such as high substrate degradation rate (e.g. 0.5 d⁻¹ of 60 °C vs 0.2 d⁻¹ of 35 °C), hydrogen and methane yields (e.g. 3–4 mol-H₂/mol-glucose at 70 °C vs 1–2 mol-H₂/mol-glucose at 35 °C) and low gas solubility (e.g. H₂ decrease 10% and CH₄ decrease 30%) for the treatment of hot wastewater. However, the low biomass concentration, complexity of metabolites and high-running cost still limit its application to some extent. Here, the typical metabolic reactions in this process are briefly summarized. Then, the recent advances in alkali TMCF, anaerobic membrane bioreactor, individual metabolite production, thermophilic microbial fuel cells and thermophilic syngas fermentation are reviewed. The following separation processes of biogas upgrading, gas stripping and electrodialysis are also reviewed to separate and purify the metabolites in TMCF. Lastly, to meet the demands of better overall performance and lower-running cost, the prospects in the fields of direct interspecies electron transfer, medium chain fatty acids production and energy cost reduction are highlighted, but new strategies in TMCF still need to be developed in the future.

Keywords:

• Thermophilic mixed culture fermentation
• metabolic reactions
• metabolites production
• metabolite separation
• running cost

Disclosure statement

The authors report no conflict of interest.

Additional information

Funding

The authors would like to acknowledge the financial support from National Natural Science Foundation of China (Grant no: 51408530, 51478447 and 51808120), and the Program for Innovative Research Team in Science and Technology in Fujian Province University (IRTSTFJ).