Valorization of Bovine Manure and Molasses by the Production of Lactic Acid and Biomass through Probiotic Anaerobic Cofermentation with <i>Lactobacillus acidophilus</i>, <i>Lactobacillus fermentum</i>, and <i>Bacillus</i> <i>subtilis</i>

Abstract

Lactic acid (LA) and probiotic biomass production were evaluated from bovine manure supported with 12% v/v molasses using three probiotic bacteria, Lactobacillus acidophilus, Lactobacillus fermentum, and Bacillus subtilis, with three inoculum concentrations, 5%, 10%, and 15% v/v. Laboratory-scale tests were carried out in 250-mL flasks (useful volume of 200&nbsp;mL) at 37°C and 120&nbsp;rpm for 72&nbsp;h. During this time, samples were taken every 4&nbsp;h to determine (1)&nbsp;the LA content using titration, (2)&nbsp;cell growth using the poured plate method, and (3)&nbsp;consumption of carbohydrates using the anthrone-sulfuric method. The data obtained were adjusted to the Gompertz generalized four-parameter model to obtain the kinetic parameters of the growth of the bacteria in the residue. With the species L. acidophilus at 10% v/v, the highest LA production yield was obtained, Y(P/S)=0.7 g LA/g carbohydrates, with a concentration of 13.5 g LA/L (p&gt;0.05) and values of μmax=0.161/h and Ks=0.46 g/L. With the same bacteria at 15% v/v, the biomass obtained had the highest concentration of proteins, 32.19% dry weight of proteins (p&gt;0.05). The results showed that bovine manure has the potential to produce LA and biomass, which are products with high nutritional, economic, and energetic value.