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BackgroundEmpty fruit bunch (EFB) has many advantages, including its abundance, the fact that it does not require collection, and its year-round availability as a feedstock for bioethanol production. But before the significant costs incurred in ethanol production from lignocellulosic biomass can be reduced, an efficient sugar fractionation technology has to be developed. To that end, in the present study, an NaOH-catalyzed steam pretreatment process was applied in order to produce ethanol from EFB more efficiently.ResultsThe EFB pretreatment conditions were optimized by application of certain pretreatment variables such as, the NaOH concentrations in the soaking step and, in the steam step, the temperature and time. The optimal conditions were determined by response surface methodology (RSM) to be 3% NaOH for soaking and 160°C, 11 min 20 sec for steam pretreatment. Under these conditions, the overall glucan recovery and enzymatic digestibility were both high: the glucan and xylan yields were 93% and 78%, respectively, and the enzymatic digestibility was 88.8% for 72 h using 40 FPU/g glucan. After simultaneous saccharification and fermentation (SSF), the maximum ethanol yield and concentration were 0.88 and 29.4 g/l respectively.ConclusionsDelignification (>85%) of EFB was an important factor in enzymatic hydrolysis using CTec2. NaOH-catalyzed steam pretreatment, which can remove lignin efficiently and requires only a short reaction time, was proven to be an effective pretreatment technology for EFB. The ethanol yield obtained by SSF, the key parameter determining the economics of ethanol, was 18% (w/w), equivalent to 88% of the theoretical maximum yield, which is a better result than have been reported in the relevant previous studies.

It is a complicated task to achieve high level of mixing inside a microchannel because the flow is characterized by low Reynolds number (Re). Recently, the serpentine laminating micromixer (SLM) was reported to achieve efficient chaotic mixing by introducing ''F''-shape mixing units successively in two layers such that two mixing mechanisms, namely splitting/recombination and chaotic advection, enhance the mixing performance in combination. The present paper proposes an improved serpentine laminating micromixer (ISLM) with a novel redesign of the ''F''-shape mixing unit: reduced crosssectional area at the recombination region locally enhances advection effect which helps better vertical lamination, resulting in improved mixing performance. Flow characteristics and mixing performances of SLM and ISLM are investigated numerically and verified experimentally. Numerical analysis system is developed based on a finite element method and a colored particle tracking method, while mixing entropy is adopted as a mixing measure. Numerical analysis result confirms enhanced vertical lamination performance and consequently improved mixing performance of ISLM. SLM and ISLM were fabricated by polydimethylsiloxane (PDMS) casting against SU-8 patterned masters. Mixing performance is observed by normalized purple color intensity change of phenolphthalein along the downchannel. Flow characteristics of SLM and ISLM are investigated by tracing the purple interface of two streams via optical micrograph. The normalized mixing intensity behavior confirms improved mixing performance of ISLM, which is consistent with numerical analysis result.

Culture conditions for the mass production of three green algae, Chlorella sp., Dunaliella salina DCCBC2 and Dunaliella sp., were optimized using a response surface methodology (RSM). A central composite design was applied to investigate the effects of initial pH, nitrogen and phosphate concentrations on the cultivation of microalgae. The optimal growth conditions estimated from the design are as follows: Chlorella sp. (initial pH 7.2, ammonium 17 mM, phosphate 1.2 mM), D. salina DCCBC2 (initial pH 8.0, nitrate 3.3 mM, phosphate 0.0375 mM) and Dunaliella sp. (initial pH 8.0, nitrate 3.7 mM, phosphate 0.17 mM). Culturing the microalgae with the optimized conditions confirmed that the maximum growth rates were attained for these parameters. The optimum CO(2) concentrations of Chlorella sp., D. salina DCCBC2 and Dunaliella sp. were 1.0, 3.0 and 1.0% (v/v), respectively. The specific growth rates (μ) of Chlorella sp., D. salina DCCBC2 and Dunaliella sp. were 0.58, 0.78 and 0.56 day(-1), respectively, and the biomass productivities were 0.28, 0.54 and 0.30 g dry cell wt l(-1) day(-1), respectively. The CO(2) fixation rates of Chlorella sp., D. salina DCCBC2 and Dunaliella sp. were 42.8, 90.9 and 45.5 mg l(-1) day(-1), respectively. Mixotrophic cultivation of Chlorella sp. with glucose increased biomass productivity from 0.28 to 0.51 g dry cell wt l(-1) day(-1). However, D. salina DCCBC2 and Dunaliella sp. were not stimulated by several organic compounds tested.

Jerusalem artichoke is a low-requirement sugar crop containing cellulose and hemicellulose in the stalk and a high content of inulin in the tuber. However, the lignocellulosic component in Jerusalem artichoke stalk reduces the fermentability of the whole plant for efficient bioethanol production. In this study, Jerusalem artichoke stalk was pretreated sequentially with dilute acid and alkali, and then hydrolyzed enzymatically. During enzymatic hydrolysis, approximately 88 % of the glucan and xylan were converted to glucose and xylose, respectively. Batch and fed-batch simultaneous saccharification and fermentation of both pretreated stalk and tuber by Kluyveromyces marxianus CBS1555 were effectively performed, yielding 29.1 and 70.2 g/L ethanol, respectively. In fed-batch fermentation, ethanol productivity was 0.255 g ethanol per gram of dry Jerusalem artichoke biomass, or 0.361 g ethanol per gram of glucose, with a 0.924 g/L/h ethanol productivity. These results show that combining the tuber and the stalk hydrolysate is a useful strategy for whole biomass utilization in effective bioethanol fermentation from Jerusalem artichoke.

The concentration of ethanol produced from lignocellulosic biomass should be at least 40 g l(-1) [about 5 % (v/v)] to minimize the cost of distillation process. In this study, the conditions for the simultaneous saccharification and fermentation (SSF) at fed-batch mode for the production of ethanol from alkali-pretreated empty palm fruit bunch fibers (EFB) were investigated. Optimal conditions for the production of ethanol were identified as temperature, 30 °C; enzyme loading, 15 filter paper unit g(-1) biomass; and yeast (Saccharomyces cerevisiae) loading, 5 g l(-1) of dry cell weight. Under these conditions, an economical ethanol concentration was achieved within 17 h, which further increased up to 62.5 g l(-1) after 95 h with 70.6 % of the theoretical yield. To our knowledge, this is the first report to evaluate the economic ethanol production from alkali-pretreated EFB in fed-batch SSF using S. cerevisiae.

A micromixer is one of the most important components for a chemical and/or diagnostic analysis in microfluidic devices such as a micro-total-analysis-system and a lab-on-a-chip. In this paper, a novel chaotic micromixer is developed in a simple design by introducing obstruction-pairs on the bottom of a microchannel. An obstruction-pair, which is composed of two hexahedron blocks arranged in an asymmetric manner, can induce a rotational flow along the down-channel direction due to the anisotropy of flow resistance. By utilizing this characteristic of the obstruction-pair, four mixing units are designed in such a way that three obstruction-pairs induce three rotational flows which result in a down-welling and a hyperbolic point in the channel cross-section. There can be a variety of micromixer geometries by arranging the mixing units in various sequences along the microchannel, and their mixing performances will differ from each other due to different flow characteristics. In this regard, numerical investigations are carried out to predict and characterize the mixing performances of various micromixers. Also experimental verifications are carried out by a flow visualization technique using phenolphthalein and sodium hydroxide solutions in a polydimethylsiloxane-based micromixer.

To predict double-emulsion formation in a capillary microfluidic device, a ternary diffuse-interface model is presented. The formation of double emulsions involves complex interfacial phenomena of a three-phase fluid system, where each component can have different physical properties. We use the Navier-Stokes/Cahn-Hilliard model for a general ternary system, where the hydrodynamics is coupled with the thermodynamics of the phase field variables. Our model predicts important features of the double-emulsion formation which was observed experimentally by Utada et al. [Utada et al., Science, 2005, 308, 537]. In particular, our model predicts both the dripping and jetting regimes as well as the transition between those two regimes by changing the flow rate conditions. We also demonstrate that a double emulsion having multiple inner drops can be formed when the outer interface is more stable than the inner interface.