Biomass Production a Stronger Driver of Cellulosic Ethanol Yield than Biomass Quality

Abstract

Core Ideas Fermentable sugars were greatest in corn stover > perennial grasses > polycultures. Corn stover had the highest ethanol content. Miscanthus had the highest ethanol yield potential on a per hectare basis. Ethanol yield potential per hectare of switchgrass ≥ corn stover. Biomass yield was the strongest driver of per hectare ethanol yield. Many crops have been proposed as feedstocks for the emerging cellulosic ethanol industry, but information is lacking about the relative importance of feedstock production and quality. We compared yield and sugar content for seven bioenergy cropping systems in south‐central Wisconsin (ARL) and southwestern Michigan (KBS) during three growing seasons (2012 through 2014). The cropping systems were (i) continuous corn stover (Zea mays L.), (ii) switchgrass (Panicum virgatum L.), (iii) giant miscanthus (Miscanthus × giganteus Greef & Deuter ex Hodkinson & Renvoize), (iv) hybrid poplar (Populus nigra × P. maximowiczii A. Henry ‘NM6’), (v) native grass mix, (vi) early successional community, and (vii) restored prairie. A high‐throughput pretreatment and fermentation assay showed corn stover with the highest sugar content (213 g glucose kg−1 [Glc] and 115 g xylose kg−1 [Xyl]) followed by the two monoculture perennial grass treatments (154 [Glc] and 88 [Xyl]) and then the herbaceous polycultures (135 [Glc] and 77 [Xyl]). Biomass production and sugar content were combined to calculate ethanol yields. Miscanthus had the highest per hectare ethanol yields (1957 l ha−1 yr−1 ARL, 2485 l ha−1 yr−1 KBS) followed by switchgrass (1091 l ha−1 yr−1 ARL, 1017 l ha−1 yr−1 KBS) and corn stover (1121 l ha−1 yr−1 ARL, 878 l ha−1 yr−1 KBS). Perennial grass cropping systems (i.e., switchgrass and miscanthus) had higher per hectare ethanol yields at both sites relative to diverse systems that included dicots. Despite feedstock differences in fermentable sugars, biomass production was the strongest driver of per hectare ethanol yield.

Switchgrass and Giant Miscanthus Biomass and Theoretical Ethanol Production from Reclaimed Mine Lands

“…For the two most abundant sugars, GLC2 was lower in switchgrass than in miscanthus (37.4 vs 40.4%), while XYL2 was higher in switchgrass than in miscanthus (24.5 vs 22.0%). Although values were higher in the present study, relative differences among miscanthus and switchgrass glucan and xylan values were similar to those in Sanford et al [59]. Switchgrass glucan and xylan values were higher than those in Schmer et al [11] and Vogel et al [29], and similar to those in Dien et al [43,60] and Adler et al [56], with approximately the same proportions as in the present study in all cases.…”

“…Although species had little to no variation in TEY, TEP was higher for miscanthus using both methods because of higher miscanthus biomass (Table 7 and Fig. 1), which effect has also been reported by Sanford et al [59] and Nichols et al [10] TEP1 and TEP2B, respectively). While species differed for both TEP variables, only TEP2B from the NREL model discriminated among miscanthus lines.…”

“…Switchgrass and miscanthus productivity were comparable with those on other marginal and reclaimed lands under annual applications of 0-60 kg N ha −1 [15,36,48,51,55]. Annual biomass yields of these species on agricultural soils under limited N rates have ranged from 2.5 to 16.0 Mg DM ha −1 for switchgrass [6,15,27,[56][57][58][59] and from 11.9 to 34.6 Mg DM ha −1 for miscanthus [5,27,59]. On marginal land, annual yields with < 67 kg N ha −1 have ranged from 2.0 to 19.0 Mg DM ha −1 for switchgrass [5,6,11,15,16,49,54,55].…”

Diverse lignocellulosic feedstocks can achieve high field‐scale ethanol yields while providing flexibility for the biorefinery and landscape‐level environmental benefits

“…Additionally, the different materials had consistent hydrolysis yields as long as the feedstocks were mainly comprised of grass species. In another study, we evaluated theoretical ethanol yields from different feedstocks on a field basis and found that ethanol yield was determined more by crop yield than by feedstock quality (chemical composition) (Sanford et al, ). This finding supports the practicable idea that biofuel refineries could process multiple different regional feedstock types without experiencing significant impacts on ethanol production.…”

Legume Addition to Perennial Warm‐Season Grass Swards Increases Harvested Biomass

“…An additional benefit of planting a legume crop with no N Fig. For ethanol production, however, the constraint of total biomass yield swamps the effects of biomass quality in herbaceous systems (Sanford et al, 2017). Least-squares (LS) means of biomass yield response in 2012 of (A) big bluestem and (B) switchgrass accessions to fertilizer addition, presented as the difference between yield with fertilizer and without fertilizer.…”