A high solids field-to-fuel research pipeline to identify interactions between feedstocks and biofuel production

Abstract

Background Environmental factors, such as weather extremes, have the potential to cause adverse effects on plant biomass quality and quantity. Beyond adversely affecting feedstock yield and composition, which have been extensively studied, environmental factors can have detrimental effects on saccharification and fermentation processes in biofuel production. Only a few studies have evaluated the effect of these factors on biomass deconstruction into biofuel and resulting fuel yields. This field-to-fuel evaluation of various feedstocks requires rigorous coordination of pretreatment, enzymatic hydrolysis, and fermentation experiments. A large number of biomass samples, often in limited quantity, are needed to thoroughly understand the effect of environmental conditions on biofuel production. This requires greater processing and analytical throughput of industrially relevant, high solids loading hydrolysates for fermentation, and led to the need for a laboratory-scale high solids experimentation platform. Results A field-to-fuel platform was developed to provide sufficient volumes of high solids loading enzymatic hydrolysate for fermentation. AFEX pretreatment was conducted in custom pretreatment reactors, followed by high solids enzymatic hydrolysis. To accommodate enzymatic hydrolysis of multiple samples, roller bottles were used to overcome the bottlenecks of mixing and reduced sugar yields at high solids loading, while allowing greater sample throughput than possible in bioreactors. The roller bottle method provided 42–47% greater liquefaction compared to the batch shake flask method for the same solids loading. In fermentation experiments, hydrolysates from roller bottles were fermented more rapidly, with greater xylose consumption, but lower final ethanol yields and CO2 production than hydrolysates generated with shake flasks. The entire platform was tested and was able to replicate patterns of fermentation inhibition previously observed for experiments conducted in larger-scale reactors and bioreactors, showing divergent fermentation patterns for drought and normal year switchgrass hydrolysates. Conclusion A pipeline of small-scale AFEX pretreatment and roller bottle enzymatic hydrolysis was able to provide adequate quantities of hydrolysate for respirometer fermentation experiments and was able to overcome hydrolysis bottlenecks at high solids loading by obtaining greater liquefaction compared to batch shake flask hydrolysis. Thus, the roller bottle method can be effectively utilized to compare divergent feedstocks and diverse process conditions.

Water-soluble saponins accumulate in drought-stressed switchgrass and may inhibit yeast growth during bioethanol production

“…This fermentation profile was in stark contrast to the switchgrass grown in the normal rainfall year (2010) based on the volume of carbon dioxide produced. These results align with previously reported results [ 17 , 33 ] and provide a baseline for comparing the effects of extraction on yeast fermentation. Water extraction prior to AFEX completely alleviated yeast inhibition in the drought-year (2012) switchgrass, while the non-stress year (2010) showed comparable CO 2 production as the unextracted samples and a shorter lag phase, indicating no nutrient limitation following water extraction (Fig.…”

“…2 ). The reaction conditions for this experiment were previously optimized by Ong et al and Chandrasekar et al [ 17 , 33 ]. There was slightly more glucose and xylose produced from switchgrass that had been extracted after AFEX pretreatment compared to the switchgrass that was extracted before pretreatment, for all solvents (Fig.…”

“…This method has previously been used to successfully differentiate between the drought-year (2012) and non-drought year (2010) switchgrass hydrolysates as they have vastly different fermentation profiles [ 33 ].…”

“…Fermentations of switchgrass hydrolysates into ethanol by yeast were performed as previously described [ 33 ] with modifications. Sterile serum bottles were aliquoted with 4 mL of switchgrass hydrolysate.…”

High yield co-production of isobutanol and ethanol from switchgrass: experiments, and process synthesis and analysis

“…The fermentation experiment in Table 1 was carried out in a respirometer system as described previously, 65 with the following modifications. The starter cultures were grown in YPD aerobically overnight and then inoculated into 4 mL of each hydrolysate in sterile 60 mL Wheaton serum bottles with initial OD 600 values of 0.5.…”