Experimental methods for laboratory-scale ensilage of lignocellulosic biomass

Abstract

Anaerobic fermentation is a potential storage method for lignocellulosic biomass in biofuel production processes. Since biomass is seasonally harvested, stocks are often dried or frozen at laboratory scale prior to fermentation experiments. Such treatments prior to fermentation studies cause irreversible changes in the plant cells, influencing the initial state of biomass and thereby the progression of the fermentation processes itself. This study investigated the effects of drying, refrigeration, and freezing relative to freshly harvested corn stover in lab-scale ensilage studies. Particle sizes, as well as post-ensilage drying temperatures for compositional analysis, were tested to identify the appropriate sample processing methods. After 21 days of ensilage the lowest pH value (3.73 ± 0.03), lowest dry matter loss (4.28 ± 0.26 g. 100 g-1DM), and highest water soluble carbohydrate (WSC) concentrations (7.73 ± 0.26 g. 100 g-1DM) were observed in control biomass (stover ensiled within 12 h of harvest without any treatments). WSC concentration was significantly reduced in samples refrigerated for 7 days prior to ensilage (3.86 ± 0.49 g. 100 g−1 DM). However, biomass frozen prior to ensilage produced statistically similar results to the fresh biomass control, especially in treatments with cell wall degrading enzymes. Grinding to decrease particle size reduced the variance amongst replicates for pH values of individual reactors to a minor extent. Drying biomass prior to extraction of WSCs resulted in degradation of the carbohydrates and a reduced estimate of their concentrations. The methods developed in this study can be used to improve ensilage experiments and thereby help in developing ensilage as a storage method for biofuel production.