Biobutanol production from apple pomace: the importance of pretreatment methods on the fermentability of lignocellulosic agro-food wastes

Abstract

Apple pomace was studied as a possible raw material for biobutanol production. Five different soft physicochemical pretreatments (autohydrolysis, acids, alkalis, organic solvents and surfactants) were compared in a high-pressure reactor, whose working parameters (temperature, time and reagent concentration) were optimised to maximise the amount of simple sugars released and to minimise inhibitor generation. The pretreated biomass was subsequently subjected to a conventional enzymatic treatment to complete the hydrolysis. A thermal analysis (DSC) of the solid biomass indicated that lignin was mainly degraded during the enzymatic treatment. The hydrolysate obtained with the surfactant polyethylene glycol 6000 (PEG 6000) (1.96% w/w) contained less inhibitors than any other pretreatment, yet providing 42 g/L sugars at relatively mild conditions (100 °C, 5 min), and was readily fermented by Clostridium beijerinckii CECT 508 in 96 h (3.55 g/L acetone, 9.11 g/L butanol, 0.26 g/L ethanol; 0.276 g/g yield; 91% sugar consumption). Therefore, it is possible to optimise pretreatment conditions of lignocellulosic apple pomace to reduce inhibitor concentrations in the final hydrolysate and perform successful ABE fermentations without the need of a detoxification stage.

Acetone-butanol-ethanol (ABE) fermentation of soluble and hydrolyzed sugars in apple pomace by Clostridium beijerinckii P260

“…Although no significant (p > 0.05) difference was found within different acid or alkali pretreatments, the acid pretreatment groups had a higher glucose production compared with the alkali pretreatment groups on average. A similar result was found in a previous study that alkali (sodium hydroxide and potassium hydroxide) was not as effective as acids (sulfuric acid, hydrogen chloride, and nitric acid) to pretreat apple pomace for the production of hydrolyzed sugars [13]. We further investigated the synergistic cooperation of cellulase and pectinase for the glucose production during hydrolysis.…”

“…As can be seen in Table 2, the contents of degradation products (inhibitors) including HMF and furfural are significantly (p < 0.05) higher in liquids after acid pretreatment and hydrolysis than those in liquids after alkali pretreatment and hydrolysis. A previous study found that the apple pomace hydrolysate obtained after nitric acid pretreatment and enzymatic hydrolysis was not fermentable and the possible reason was the high content of inhibitors generated in the acidic treatment [13]. At last, a total of 9.6 and 9.4 g/L of ABE were generated by consumption of 30.4 and 28.0 g/L of total sugars from ACHS and ALHS, respectively.…”

“…A published study used the soluble sugars in apple pomace to produce butanol [12]. Recently, researchers applied different pretreatments (autohydrolysis, acids, alkali, organic solvent, and surfactant) followed by enzymatic hydrolysis to break down the structural carbohydrates of apple pomace into hydrolyzed sugars, which were further fermented to butanol [13]. Although separate studies on soluble sugars or structural carbohydrates utilization exist, no research has been conducted to evaluate the technical feasibility of comprehensive utilization of all (both soluble and insoluble) carbohydrates in apple pomace to obtain butanol.…”

Development and validation of a HPLC-DAD method for simultaneous determination of main potential ABE fermentation inhibitors identified in agro-food waste hydrolysates

“…The biomasses were ground in a SM100 Comfort rotary mill (Retsch GmbH, Haan, Germany), sieved to a size of 0.5-1.0 mm and stored at room temperature in airtight containers until being used. Moisture, ash, cellulose, hemicellulose, Klason lignin, protein and fat were determined as described by Hijosa-Valsero et al [18]. Starch was determined by polarimetry according to Spanish national regulations [19].…”

“…Thereby, twelve different chemical reagents: acids (H2SO4, HCl, HNO3), alkalis (NaOH, KOH, NH4OH), organic solvents (ethanol, methanol, acetone) and surfactants (Tween 80, PEG 6000, and CTAB) were compared to select the most efficient reagent in each group. Hydrolysis experiments were performed as previously described [18]. The hydrolysates obtained were analyzed for sugars (cellobiose, glucose, xylose, rhamnose and arabinose), organic acids (formic acid, acetic acid and levulinic acid), 5-HMF and furfural, using an Agilent 1200 HPLC equipment (Agilent Technologies) furnished with an Aminex HPX-87H (Biorad, Hercules, CA, USA) and a Refractive Index Detector (RID) G1362A (Agilent Technologies) as described by Hijosa-Valsero et al [18].…”