Enhanced Enzymatic Hydrolysis of Pennisetum alopecuroides by Dilute Acid, Alkaline and Ferric Chloride Pretreatments

Abstract

In this study, effects of different pretreatment methods on the enzymatic digestibility of Pennisetum alopecuroides, a ubiquitous wild grass in China, were investigated to evaluate its potential as a feedstock for biofuel production. The stalk samples were separately pretreated with H2SO4, NaOH and FeCl3 solutions of different concentrations at 120 °C for 30 min, after which enzymatic hydrolysis was conducted to measure the digestibility of pretreated samples. Results demonstrated that different pretreatments were effective at removing hemicellulose, among which ferric chloride pretreatment (FCP) gave the highest soluble sugar recovery (200.2 mg/g raw stalk) from the pretreatment stage. In comparison with FCP and dilute acid pretreatment (DAP), dilute alkaline pretreatment (DALP) induced much higher delignification and stronger morphological changes of the biomass, making it more accessible to hydrolysis enzymes. As a result, DALP using 1.2% NaOH showed the highest total soluble sugar yield through the whole process from pretreatment to enzymatic hydrolysis (508.5 mg/g raw stalk). The present work indicates that DALP and FCP have the potential to enhance the effective bioconversion of lignocellulosic biomass like P. alopecuroides, hence making this material a valuable and promising energy plant.

A Two-Step Ferric Chloride and Dilute Alkaline Pretreatment for Enhancing Enzymatic Hydrolysis and Fermentable Sugar Recovery from Miscanthus sinensis

“…Solid yields were calculated on the basis of residual total solid of stalk samples after all pretreatments. The cellulose, hemicellulose, and lignin contents were determined gravimetrically according to the standard method of Goering and Van-Soest and calculated on the basis of residual total solid [11,33]. In brief, the neutral detergent fiber (NDF) content was determined gravimetrically by extracting the solid residue of different pretreatments with neutral detergent (ND).…”

“…One-step processes including FP and ALP were conducted in glass bottles by an antoclave. In brief, the dried Miscanthus sinensis samples were added to the glass bottles containing 0.8-4.8% (mass/volume percent concentration, w/v) FeCl 3 solutions and 0.4-1.2% (w/v) NaOH for FP and ALP, respectively [11,22,26,28]. A solid loading rate of 10% was chosen.…”

“…Although a number of pretreatment techniques operated at severe conditions (e.g., steam explosion and hot water pretreatment, 160-240 • C, 5-45 min, pretreatment severity factor (log R 0 ) of 2.8-4.8) were effective at enhancing enzymatic hydrolysis of the pretreated samples, they had high energy consumption and produced enzyme-inhibiting by-products as compared to those observed at mild conditions (e.g., acid pretreatment, 120 • C, 5-45 min, log R 0 of 1.3-2.2) [4,20,21]. Some other processes with less by-product formation and energy requirement (e.g., biological pretreatment at room temperature) can also improve bioconversion, but these processes are typically time-consuming and/or consume sugars of raw stalks during the pretreatment [2,11]. Up to now, there is no one strategy that could well meet all requirements for the ideal pretreatment.…”

“…Lignocellulosic biomass (e.g., corn stalk, wheat straw, and rice straw), which is a sustainable and renewable energy source with reduced net CO 2 emission, has been widely investigated as substrates for ethanol and biogas fermentation [8,9]. In addition to these biomass wastes, energy crops are also potential candidates for biofuel production [10,11]. For instance, Miscanthus sinensis, which is a perennial grass, is throughout most of provinces in China.…”

“…In spite of their successful application for many biomass wastes, acid pretreatments in some other cases failed to significantly enhance the enzymatic hydrolysis of the pretreated stalks [24]. Previous studies have shown that mild acid pretreatment using Lewis acids such as FeCl 3 also enhanced the enzymatic hydrolysis of the pretreated biomass [11,26]. The corrosion problem in traditional acid pretreatments could also be weakened by using Lewis acids.…”