Valorization of the Crude Glycerol for Propionic Acid Production Using an Anaerobic Fluidized Bed Reactor with Grounded Tires as Support Material.

This study evaluated the propionic acid (HPr) production from crude glycerol (CG) (5000 mg L) in an anaerobic fluidized bed reactor (AFBR). Grounded tire particles (2.8-3.35 mm) were used as support material for microbial adhesion. The reactor was operated with hydraulic retention times (HRT) varying from 8 to 0.5 h under mesophilic (30 °C) conditions. The HPr was the main metabolite produced, increasing in composition from 66.5 to 99.6% by decreasing the HRT from 8 to 0.5 h. Other metabolic products were 1,3-propanediol, with a maximum of 29.4% with an HRT of 6 h, ethanol, acetic, and butyric acids. The decrease in HRT from 8 to 0.5 h decreased the HPr yield, with a maximum of 0.48 ± 0.06 g HPr g COD and an HRT of 6 h, and favored HPr productivity, with a maximum of 4.09 ± 1.24 g L h and HRT of 0.5 h. In the biogas, the H content increased from 12.5 to 81.2% by decreasing the HRT from 8 to 0.5 h. These results indicate the potential application of the AFBR for HPr production using an immobilized mixed culture.