Abstract
Lignocellulosic agricultural side products, like wheat straw, are widely seen as an important contribution to a future sustainable economy. However, optimization of biorefinery processes and exploitation of all side streams are crucial for an economically viable biorefinery. Pretreatment of lignocellulosic raw material, which is necessary for further processing steps, can generate low-value side streams. In this feasibility study, side streams from a liquid hot water (LHW) pretreatment of wheat straw were utilized for the production of polyhydroxybutyrate (PHB) and highly valuable tetraether lipids (TELs). Additional value created by these products can benefit the biorefinery’s economic operation. The utilized wheat straw was pretreated at 120 °C and 170 °C for up to two hours in laboratory and lab scale. The resulting side stream consists mainly of carbohydrates from hemicelluloses and fermentation inhibitors such as acetic acid. In order to achieve a successful production of both products, an acetic acid separation via distillation was necessary. Subsequently, the acetic acid fraction was utilized for the PHB production using cyanobacteria. The carbohydrate-rich fraction was applied in the cultivation of Sulfolobus acidocaldarius and resulted in the successful production of TELs. Both fractions achieved better fermentation yields compared to their corresponding reference media.
Highlights
The world is currently confronted with the progressive depletion of its resources, mainly based on non-renewable feedstocks [1]
A complete process chain starting from wheat straw pretreatment using a liquid hot water process, the fractionation of process the pretreatment wastefrom stream and straw the successful utilization these fractions
A complete chain starting wheat pretreatment using of a liquid hot water forprocess, the cultivation of tetraether lipids (TELs)-producing microorganisms was shown
Summary
The world is currently confronted with the progressive depletion of its resources, mainly based on non-renewable feedstocks [1]. A biorefinery approach involves a multi-step process in which the first step, subsequent to the feedstock selection, typically involves treating the biomass to pre-separate the main components, that is, cellulose, hemicellulose, and lignin, and to make it more amenable for further processing [5] This step is conventionally referred to as pretreatment and can account for up to 20%–40% of the overall production costs, which puts a special focus on its optimization [6]. In terms of the improvement of the process economics, mentioned components in the aqueous side stream can potentially be used as carbon source for microbial fermentation processes In this feasibility study, we exemplarily tested the utilization of this aqueous side stream as substrates for the cultivation of cyanobacteria producing polyhydroxybutyrate (PHB; e.g., [8,9]) as well as for the cultivation of Sulfolobus acidocaldarius, a thermoacidophilic archaeon and producer of highly valuable tetraether lipids (TELs; e.g., [10]). The resulting liquid side streams containing hemicellulose and acetic acid were investigated in terms of their suitability for the recombinant production of PHB and TELs in laboratory experiments
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