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

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.

Ammonia Fiber Expansion (Afex) Treatment of Wheat Straw for Production of Bioethanol

Ammonia Fiber Expansion (AFEX) treatment is a technique that is able to enhance the enzymatic hydrolysis yield of lignocellulosic materials. In this technique, lignocellulosic materials are treated by liquid ammonia under pressure followed by rapid release of pressure that expands the fiber structure and increases enzyme access to lignocellulose polysaccharides. However, the AFEX treatment variables such as the mass ratio of ammonia to lignocellulosic biomass, moisture of lignocellulose (moisture content of biomass), temperature, and residence time need to be evaluated to find the maximum efficiency of this treatment. The efficiency of the AFEX pretreatment was quantified by the yield of released sugars during enzymatic hydrolysis of the AFEX-treated wheat straw. The optimal treatment conditions for wheat straw were found to be: ammonia-to-wheat straw ratio, 1:1; temperature, 95°C; moisture content of wheat straw, 70% (dry weight basis); and residence time, 5 minutes. Under these conditions, almost 89% of the theoretical sugars were released by enzymatic hydrolysis of the AFEX-treated wheat straw. The enzymatic hydrolysis results showed the significance of AFEX pretreatment of wheat straw when compared to untreated wheat straw with released sugars yield of only 26 %.

Ammonia Fiber Expansion (Afex) Treatment of Wheat Straw for Production of Bioethanol

Ammonia Fiber Expansion (AFEX) treatment is a technique that is able to enhance the enzymatic hydrolysis yield of lignocellulosic materials. In this technique, lignocellulosic materials are treated by liquid ammonia under pressure followed by rapid release of pressure that expands the fiber structure and increases enzyme access to lignocellulose polysaccharides. However, the AFEX treatment variables such as the mass ratio of ammonia to lignocellulosic biomass, moisture of lignocellulose (moisture content of biomass), temperature, and residence time need to be evaluated to find the maximum efficiency of this treatment. The efficiency of the AFEX pretreatment was quantified by the yield of released sugars during enzymatic hydrolysis of the AFEX-treated wheat straw. The optimal treatment conditions for wheat straw were found to be: ammonia-to-wheat straw ratio, 1:1; temperature, 95°C; moisture content of wheat straw, 70% (dry weight basis); and residence time, 5 minutes. Under these conditions, almost 89% of the theoretical sugars were released by enzymatic hydrolysis of the AFEX-treated wheat straw. The enzymatic hydrolysis results showed the significance of AFEX pretreatment of wheat straw when compared to untreated wheat straw with released sugars yield of only 26 %.