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BackgroundIt is widely believed that reducing the lignocellulosic biomass particle size would improve the biomass digestibility by increasing the total surface area and eliminating mass and heat transfer limitation during hydrolysis reactions. However, past studies demonstrate that particle size influences biomass digestibility to a limited extent. Thus, this paper studies the effect of particle size (milled: 2 mm, 5 mm, cut: 2 cm and 5 cm) on rice straw conversion. Two different Ammonia Fiber Expansion (AFEX) pretreament conditions, AFEX C1 (low severity) and AFEX C2 (high severity) are used to pretreat the rice straw (named as AC1RS and AC2RS substrates respectively) at different particle size.ResultsHydrolysis of AC1RS substrates showed declining sugar conversion trends as the size of milled and cut substrates increased. Hydrolysis of AC2RS substrates demonstrated opposite conversion trends between milled and cut substrates. Increasing the glucan loading to 6% during hydrolysis reduced the sugar conversions significantly in most of AC1RS and AC2RS except for AC1RS-2 mm and AC2RS-5 cm. Both AC1RS-2 mm and AC2RS-5 cm indicated gradual decreasing trends in sugar conversion at high glucan loading. Analysis of SEM imaging for URS and AFEX pretreated rice straw also indicated qualitative agreement with the experimental data of hydrolysis. The largest particle size, AC2RS-5 cm produced the highest sugar yield of 486.12 g/kg of rice straw during hydrolysis at 6% glucan loading equivalent to 76.0% of total theoretical maximum sugar yield, with an average conversion of 85.9% from total glucan and xylan. In contrast, AC1RS-5 cm gave the lowest sugar yield with only 107.6 g/kg of rice straw, about 16.8% of total theoretical maximum sugar yield, and equivalent to one-quarter of AC2RS-5 cm sugar yield.ConclusionsThe larger cut rice straw particles (5 cm) significantly demonstrated higher sugar conversion when compared to small particles during enzymatic hydrolysis when treated using high severity AFEX conditions. Analysis of SEM imaging positively supported the interpretation of the experimental hydrolysis trend and kinetic data.

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Abstract-Sodium hydroxide pretreatment of oil palm mesocarp fiber (OPMF) was carried out with NaOH from 2% to 10% (w/v) at temperature 50 0 C and 70 0 C. The performances of pretreatments were evaluated based on total carbohydrate and reducing sugar including glucose, xylose and arabinose after enzymatic hydrolysis on the pretreated biomass. It was found that the enzymatic hydrolysis had significantly improved when 6% NaOH in 70 0 C applied in the pretreatment process. The highest total reducing sugars produced by means of commercial enzymes was achieved with the overall conversions of glucan and xylan of 87% and 60.73% respectively. The compositions of OPMF in this study are as follows (% g/g dry biomass): glucan, 28.8, xylan, 25.3, arabinan, 1.91, ethanol extractive, 6.32 and ash, 2.60.Index Terms-Enzymatic hydrolysis, glucose, NaOH pretreatment, oil palm mesocarp fiber.

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The degradation of lignin in oil palm empty fruit bunch (EFB) fibers by a low concentration of H2O2 was observed with the assistance of Fenton oxidation with Fe(III), Fe(0), and Fe3O4 as a catalyst. To escalate the oxidation activity toward lignin in the EFB fibers, the uptake of the Fenton reagent on the EFB fibers for in situ Fenton oxidation was optimized with fitted Langmuir and Freundlich adsorption models. The efficiency of assisted Fenton reagents was monitored through controlled parameters of H2O2 concentration, retention time, and increment of Fenton reagents. The delignification was observed with up to 71.2% of lignin degradation compared to 47.2% without the use of the Fenton reagents. The characteristics of EFB fibers after the oxidation process were changed based on the observation of morphological and chemical properties. The oxidation concurrently dislodged part of the silica bodies and disrupted specific functional groups and the crystallinity of the EFB fibers.

The current world demand for succinic acid is around 30 000 tonnes per annum, which is forecast to expand 6-fold by 2015, owing to the introduction of biosuccinic acid. An insight into the practical usage of different biomass derivatives as substrates in the commercial bioproduction of succinic acid is discussed. Lignocellulosic crop stalk waste (corn straw, rice straw, and cotton straw) appears, in this case, to be the most promising form of biomass for commercial succinic acid fermentation. Another example of a low cost carbon source with high availability, crude glycerol, on the other hand, shows comparable potentials as a sustainable commercial carbon source for biosuccinic acid. In terms of the metabolic pathway of succinate-producing microbes, a greater availability of substrate CO2 and a lower oxidation/reduction potential (ORP) of the fermentation broth will trigger the microbial metabolic flux toward the generation of highly reduced metabolites (succinate) in order to regain an intracellular redox balance.