Hydrogen and Methane Production from Tequila Vinasses in a Novel Hybrid Reactor Containing Biofilm and Suspended Biomass

The alcoholic beverages industry generates vinasses, a liquid waste by-product. Tequila vinasses have a high content of organic matter (28-100 g COD/L and 13-60 g BOD5/L), low pH (3-5 units), and toxic compounds, which made difficult its biological treatment. However, this by-product can be considered for bioenergy production. A novel one-step hybrid bioreactor with suspended and attached biomass was assessed in terms of its hydrogen (H-2) and methane (CH4) production from tequila vinasses. Additionally, the microbial composition of each kind of biomass was determined. The bioreactor was divided into two zones: (i) external zone with biofilm attached to a volcanic rock packed-bed and (ii) internal zone with the growth of suspended biomass. It was operated with a retention time (RT) of 6.9 days, an organic loading rate (OLR) of 2.2 +/- 0.4 kg COD/m(3) day and a pH between 6.5 and 6.9. Under these conditions, the reactor presented a very stable COD removal efficiency of 43 +/- 11% an increase of volatile fatty acids (VFA) concentration from 2,083 to 4,902 mg/L and the biogas produced by the system was biohythane with a content of 79% hydrogen and 11% methane, which is a new report in one-step treatment systems. H-2 and CH4 production rates (PR) and yields obtained were equal to 5.7 mmol H-2/g CODremoved, 126 NmL H-2/L day, and 10.7 NmL CH4/L day. The biofilm and suspended biomass were composed mainly by Clostridium (42 and 43%, respectively) and Bacteroides (21 and 4%, respectively). Only Methanosarcina (9%) was identified in the biofilm. This bacterial composition community corresponds to a new report since for anaerobic treatment of tequila vinasses the presence of Clostridium, Bacteroides, and Methanosarcina simultaneously had not been previously reported. The content of hydrogen (79%) and methane (11%) in the biogas, the COD removal efficiency (43%) and the biomass composition (64% of fermenters and 9% of methanogens) confirmed that this novel reactor configuration and operation allows principally a dark fermentation and some methanogenesis processes, favoring the biohythane production in a one-step system.

Automated summary

This study assessed a novel hybrid bioreactor for bioenergy production from tequila vinasses. The reactor exhibited a stable COD removal efficiency of around 43% and produced biohydrogen with a content of 79% hydrogen and 11% methane.