Abstract
BackgroundMineral elements present in lignocellulosic biomass feedstocks may accumulate in biorefinery process streams and cause technological problems, or alternatively can be reaped for value addition. A better understanding of the distribution of minerals in biomass in response to pretreatment factors is therefore important in relation to development of new biorefinery processes. The objective of the present study was to examine the levels of mineral elements in pretreated wheat straw in response to systematic variations in the hydrothermal pretreatment parameters (pH, temperature, and treatment time), and to assess whether it is possible to model mineral levels in the pretreated fiber fraction.ResultsPrincipal component analysis of the wheat straw biomass constituents, including mineral elements, showed that the recovered levels of wheat straw constituents after different hydrothermal pretreatments could be divided into two groups: 1) Phosphorus, magnesium, potassium, manganese, zinc, and calcium correlated with xylose and arabinose (that is, hemicellulose), and levels of these constituents present in the fiber fraction after pretreatment varied depending on the pretreatment-severity; and 2) Silicon, iron, copper, aluminum correlated with lignin and cellulose levels, but the levels of these constituents showed no severity-dependent trends. For the first group, an expanded pretreatment-severity equation, containing a specific factor for each constituent, accounting for variability due to pretreatment pH, was developed. Using this equation, the mineral levels could be predicted with R2 > 0.75; for some with R2 up to 0.96.ConclusionPretreatment conditions, especially pH, significantly influenced the levels of phosphorus, magnesium, potassium, manganese, zinc, and calcium in the resulting fiber fractions. A new expanded pretreatment-severity equation is proposed to model and predict mineral composition in pretreated wheat straw biomass.
Highlights
In second-generation bioethanol production, instead of sucrose and starch, lignocellulosic agricultural waste streams are utilized as carbohydrate feed stocks, avoiding the ethical issues associated with turning food into fuel [1]
Potassium was solubilized from the fiber fraction, and silicon became the most abundant mineral element in each fiber fraction
Xylose and arabinose content decreased with high pretreatment-severity, whereas glucose content increased with pretreatment-severity because its recovery was not dependent on pretreatment conditions, and it constituted a larger proportion of the fiber fraction when hemicellulose was solubilized
Summary
In second-generation bioethanol production, instead of sucrose and starch, lignocellulosic agricultural waste streams are utilized as carbohydrate feed stocks, avoiding the ethical issues associated with turning food into fuel [1]. In the context of biorefining of lignocellulosic biomass, mineral elements may accumulate in certain streams, which may challenge the processing, and cause wear and tear of equipment. These may provide opportunities for recovery and recycling of scarce metals, and/or for creating novel high-value applications [10,11,12]. Detailed information about the mineral content of the product streams is an overlooked subject in plant biomass biorefining, and information about the distribution of mineral elements in lignocellulosic biomass streams is sparse in the literature, despite such information being an important prerequisite for designing optimal biorefinery processes. Mineral elements present in lignocellulosic biomass feedstocks may accumulate in biorefinery process streams and cause technological problems, or alternatively can be reaped for value addition. The objective of the present study was to examine the levels of mineral elements in pretreated wheat straw in response to systematic variations in the hydrothermal pretreatment parameters (pH, temperature, and treatment time), and to assess whether it is possible to model mineral levels in the pretreated fiber fraction
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