Effect of Lactate Fermentation Type on the Biochemical Methane Potential of Tequila Vinasse

In a two-stage anaerobic digestion (AD) process approach, the relation between the type of fermentation that occurs during the acidogenic stage and methane production potential from tequila vinasse (TV) remains unexplored. This study aimed to investigate the effect of lactate fermentation type on the biochemical methane potential (BMP) of TV. To this end, a series of batch cultures were carried out to perform two sequential lactate-type fermentations, i.e., first (carbohydrates -> lactate + acetate) and second (lactate + acetate -> butyrate + H-2) fermentation, which were further tested for mesophilic BMP using an automatic gas measuring device. Raw TV was also included in the comparison as a control (single-stage AD). During the primary fermentation, 75% of the total fermentable sugars were metabolized into lactate (12.6 g/L) and acetate (6.6 g/L) by the bacterial cluster mainly encompassing Klebsiella, Enterobacter, and Streptococcus, as supported by Illumina MiSeq sequencing analysis. During the secondary fermentation, lactate and acetate were bioconverted into butyrate (5.1 g/L) and hydrogen (115.6 NmL/g VSadded) by Clostridium. During methanogenesis, all tested feedstocks resulted in different BMP performances. The primary lactate fermentation led to the highest BMP (435.9 NmL CH4/g VSadded), methane production rate (105.8 NmL CH4/day), and chemical oxygen demand removal efficiency (92.9%), which were 46.2%, 89.3%, and 8.8%, respectively, higher than those attained from raw TV. Methanobacterium and Methanolinea dominated in the starter granular sludge culture, suggesting the hydrogenotrophic pathway was key for methane formation. This study shows for the first time the viability of the lactate-type fermentation for designing enhanced two-stage TV-fed AD processes.