Pascoli Danielle Uchimura, Suko Azra, Gustafson Rick, Gough Heidi L, Bura Renata
School of Environmental and Forest Sciences, University of Washington, Box 352100, Seattle, WA, 98195-2100, USA.
Biotechnol Biofuels. 2021 Jan 7;14(1):9. doi: 10.1186/s13068-020-01839-0.
Ethanol biorefineries need to lower their overall production costs to become economically feasible. Two strategies to achieve this are to reduce costs using cheaper feedstocks or to increase the ethanol production yield. Low-cost feedstocks usually have high non-structural components (NSC) content; therefore, a new process is necessary to accommodate these feedstocks and overcome the negative effects of NSC. This study developed a novel ethanol biorefinery process including a biomass preprocessing step that enabled the use of lower-cost feedstocks while improving ethanol production without detoxification (overliming). Two types of poplar feedstocks were used, low-quality whole-tree chips (WTC) and high-quality clean pulp chips (CPC), to determine if the proposed process is effective while using feedstocks with different NSC contents.
Technical assessment showed that acidic preprocessing increased the monomeric sugar recovery of WTC from 73.2% (untreated) to 87.5% due to reduced buffering capacity of poplar, improved sugar solubilization during pretreatment, and better enzymatic hydrolysis conversion. Preprocessing alone significantly improved the fermentability of the liquid fraction from 1-2% to 49-56% for both feedstocks while overliming improved it to 45%. Consequently, it was proposed that preprocessing can substitute for the detoxification step. The economic assessment revealed that using poplar WTC via the new process increased annual ethanol production of 10.5 million liters when compared to using CPC via overliming (base case scenario). Also, savings in total operating costs were about $10 million per year when using cheaper poplar WTC instead of CPC, and using recycled water for preprocessing lowered its total operating costs by 45-fold.
The novel process developed in this study was successful in increasing ethanol production while decreasing overall costs, thus facilitating the feasibility of lignocellulosic ethanol biorefineries. Key factors to achieving this outcome included substituting overliming by preprocessing, enabling the use of lower-quality feedstock, increasing monomeric sugar recovery and ethanol fermentation yield, and using recycled water for preprocessing. In addition, preprocessing enabled the implementation of an evaporator-combustor downstream design, resulting in a low-loading waste stream that can be treated in a wastewater treatment plant with a simple configuration.
乙醇生物精炼厂需要降低其总体生产成本以实现经济可行性。实现这一目标的两种策略是使用更廉价的原料降低成本或提高乙醇生产产量。低成本原料通常具有较高的非结构性成分（NSC）含量；因此，需要一种新工艺来适应这些原料并克服NSC的负面影响。本研究开发了一种新型乙醇生物精炼工艺，包括生物质预处理步骤，该步骤能够使用低成本原料，同时在无需解毒（过度石灰处理）的情况下提高乙醇产量。使用了两种类型的杨树原料，低质量的整树切片（WTC）和高质量的清洁纸浆切片（CPC），以确定所提出的工艺在使用具有不同NSC含量的原料时是否有效。
技术评估表明，酸性预处理将WTC的单体糖回收率从73.2%（未处理）提高到87.5%，这是由于杨树缓冲能力降低、预处理期间糖的溶解性提高以及酶水解转化率提高。单独预处理显著提高了两种原料液体部分的发酵能力，从1 - 2%提高到49 - 56%，而过度石灰处理将其提高到45%。因此，有人提出预处理可以替代解毒步骤。经济评估表明，与通过过度石灰处理使用CPC（基础案例情景）相比，通过新工艺使用杨树WTC每年可增加乙醇产量1050万升。此外，使用更便宜的杨树WTC而不是CPC时，每年总运营成本节省约1000万美元，并且使用再生水进行预处理使其总运营成本降低了45倍。
本研究开发的新工艺成功提高了乙醇产量，同时降低了总体成本，从而促进了木质纤维素乙醇生物精炼厂的可行性。实现这一结果的关键因素包括通过预处理替代过度石灰处理、能够使用低质量原料、提高单体糖回收率和乙醇发酵产量以及使用再生水进行预处理。此外，预处理能够实施蒸发器 - 燃烧器下游设计，产生低负荷废物流，可在配置简单的废水处理厂进行处理。
