Effect of bioaugmentation with Paenibacillus spp. and thin slurry recirculation on microbial hydrolysis of maize silage and bedding straw in a plug-flow reactor

Abstract

AbstractIn this work, the effect of bioaugmentation on the hydrolysis and acidogenesis efficiency of bedding straw mixed with maize silage is examined. A plug-flow bioreactor was operated for 70 weeks with maize silage as a reference feedstock and subsequently with an increasing straw content of 30% and 66% (w/w). Bioaugmentation with two Paenibacillus species was conducted at each process condition to investigate the impact on hydrolysis of the recalcitrant lignocellulosic feedstock. A stable acidogenic digestion of the substrates was achieved, during which acetic and butyric acid were accumulated as main byproducts. Specific hydrolysis rates between 258 and 264 gO2 kg−1VS were determined for pure maize silage and maize silage mixed with 30% of straw, while the specific hydrolysis rate decreased to 195 gO2 kg−1VS when a mixture with 66% of straw was applied. Bioaugmentation with Paenibacillus spp. increased the specific hydrolysis rate by up to 41–63% for pure maize silage and the mixture with 30% of straw, while no increase was observed with a mixture of 66% of straw. Acid production, however, was enhanced by 21 to 42% following bioaugmentation for all substrate mixtures. A positive effect on the physiological state of cultures, as recorded with frequency-dispersed polarizability, was seen after bioaugmentation, which remained for two retention times during the continuous fermentation mode. Recirculation of the thin sludge further prolonged the positive effects of bioaugmentation. The results of this work provide a basis to optimize the amount of the bioaugmented microorganisms and hydrolysis of biogenic material with respect to sustainable effects on process performance and costs.