Upgrading of anaerobic digestion of tequila vinasse by using an innovative two-stage system with dominant lactate-type fermentation in acidogenesis

Abstract

A novel two-stage anaerobic digestion (AD) process was examined to continuously treat tequila vinasse (TV), the liquid waste from the tequila industry, for a period of 176 days at different volumetric organic loading rates (OLRs) ranging from 2.5 to 12.5 g COD/L/d in the methanogenic stage. The novelty of this configuration relies on promoting a dominant lactate-type fermentation in the acidogenic stage as a strategy to enhance the overall performance of the process, as it leads to a lower loss of substrate in acidogenesis and is thermodynamically advantageous in methanogenesis. The results showed, however, that the soluble end products found in the acidogenic stage included not only lactate (6.3 ± 0.8 g/L) and acetate (0.7 ± 0.1 g/L) but also propionate (3.8 ± 0.6 g/L) and butyrate (2.5 ± 0.6 g/L). Despite this fact, the methanogenic unit was able to handle an OLR as high as 10.1 g COD/L/d, where it showed the highest productivity of 3.2 NL CH4/L/d with a biogas methane content of 83%, suggesting that lactate might promote syntrophic degradation processes. A methane yield of 0.33 NL CH4/g CODremoved or 15.5 NL CH4/LTV and a total COD removal efficiency close to 94% were achieved. In the two-stage process, the production of hydrogen and methane accounted for 1% and 85%, respectively, of the total energy content of the TV, which together yielded 544.5 kJ/LTV or 15.34 kJ/g VSadded. Taken together, the outstanding results obtained prove the potential application of the lactate-type fermentation to upgrade the AD of TV.