Jingliang Xu

Two-step liquid hot water pretreatment of Eucalyptus grandis to enhance sugar recovery and enzymatic digestibility of cellulose

A two-step liquid hot water pretreatment (TSLHW) was developed with the objective of achieving complete saccharification of both hemicellulose and cellulose of Eucalyptus grandis, thereby avoiding the problems associated with the use of strong acid catalysts. The first step of the pretreatment was studied in the temperature range 180-200 degrees C, and the highest yield of total xylose achieved was 86.4% after 20 min at 180 degrees C. The second-step of the pretreatment was studied in the temperature range 180-240 degrees C and for lengths of time of 0-60 min. The conversion rate of glucan was more sensitive to temperature than time. The optimum reaction conditions for the second step of the pretreatment with minimal degradation of sugars were 200 degrees C for 20 min. the total sugar recovery from E. grandis with the optimized pretreatment and 72 h enzymatic digestion, reached 96.63%, which is superior to the recovery from a single-step pretreatment with hot water or dilute acid.

Metabolic changes of starch and lipid triggered by nitrogen starvation in the microalga Chlorella zofingiensis.

The aim of this research was to study the metabolic changes of starch and lipid biosynthesis in the microalga Chlorella zofingiensis under nitrogen starvation in comparison to nitrogen abundant condition. C. zonfingiensis showed a rapid growth and kept stable chlorophyll content when grown in nitrogen-replete medium, while a severe inhibition of cell growth and a sharp degradation of chlorophyll occurred under nitrogen depletion. Nitrogen-replete C. zonfingiensis cells possessed basal levels of starch and lipid. Upon nitrogen starvation, both starch and lipid increased greatly within cells, but starch synthesis preceded lipid accumulation. After 2 days of stress condition, starch was partially degraded, possibly to support lipid synthesis. It was speculated that starch accumulation acted as a quick response to environmental stress, whereas lipid served as long-term energy storage. Additionally, C. zonfingiensis tends to lower the degree of unsaturation in response to nitrogen starvation which is desirable for biodiesel production.

Artificial neural network-genetic algorithm based optimization for the immobilization of cellulase on the smart polymer Eudragit L-100

Cellulase was covalently immobilized on a smart polymer, Eudragit L-100 by carbodiimide coupling. Using data of central composite design, response surface methodology (RSM) and artificial neural network (ANN) were developed to investigate the effect of pH, carbodiimide concentration, and coupling time on the activity yield of immobilized cellulase. Results showed simulation and prediction accuracy of ANN was apparently higher compared to RSM. The maximum activity yield obtained from RSM was 57.56% at pH 5.54, carbodiimide concentration 0.32%, and coupling time 3.03 h, where the experimental value was 60.87 + or - 4.79%. Using ANN as fitness function, a maximum activity yield of 69.83% was searched by genetic algorithm at pH 5.07, carbodiimide concentration 0.36%, and coupling time 4.10 h, where the experimental value was 66.75 + or - 5.21%. ANN gave a 9.7% increase of activity yield over RSM. After reusing immobilized cellulase for 5 cycles, the remaining productivity was over 50%.

Medium optimization for ethanol production with Clostridium autoethanogenum with carbon monoxide as sole carbon source

Plackett-Burman and central composite designs were applied to optimize the medium for ethanol production by Clostridium autoethanogenum with CO as sole carbon source, and a medium containing (g/L): NaCl 1.0, KH(2)PO(4) 0.1, CaCl(2) 0.02, yeast extract 0.15, MgSO(4) 0.116, NH(4)Cl 1.694 and pH 4.74 was found optimal. The optimum ethanol yields predicted by response surface methodology (RSM) and an artificial neural network-genetic algorithm (ANN-GA) were 247.48 and 261.48mg/L, respectively. These values are similar to those obtained experimentally under the optimal conditions suggested by the statistical methods (254.26 and 259.64mg/L). The fitness of the ANN-GA model was higher than that of the RSM model. The yields obtained substantially exceed those previously reported (60-70mg/L) with this organism.

Effects of different pretreatment methods on chemical composition of sugarcane bagasse and enzymatic hydrolysis.

Different pretreatment processes, including liquid hot water (LHW) pretreatment, sodium hydroxide (NaOH) pretreatment, and their combinative pretreatments, were conducted to improve the enzymatic digestibility and sugar recovery from sugarcane bagasse (SCB). LHW pretreatment solubilized over 82% of xylan and 42% of lignin, after which the SCB presented the poorest enzymatic digestibility. NaOH pretreatment could remove 78% of lignin and retain most of glucan. For combinative pretreatments, the sequence of two procedures had a significant effect on the chemical composition, substrate characteristic and the subsequent enzymatic hydrolysis process. LHW-NaOH pretreatment could solubilize over 92% of xylan and remove 76% of lignin, and the highest total sugar recovery of 73% was achieved after 72 h enzymatic hydrolysis. While NaOH-LHW pretreatment, which could remove nearly 84% of lignin, but only solubilize 71% of xylan, showed the highest enzymatic digestibility. The pretreatment efficiency was: NaOH-LHW>NaOH>LHW-NaOH>LHW.

Cellulase deactivation based kinetic modeling of enzymatic hydrolysis of steam-exploded wheat straw.

Applying mass action law and quasi-steady-state theory, two cellulase kinetic models namely Eqs. (5) and (8) were developed on the basis of the first and second order reactions of enzyme deactivation, respectively. The two models are compared according to analysis of experimental data from enzymatic hydrolysis steam-exploded wheat straw. Both simulation and prediction results show Eq. (8) has much higher accuracy than Eq. (5). Analysis of initial hydrolysis rate is also in accordance with Eq. (8) and against Eq. (5). Fitted values of k(2) (the rate constant of product formation), k(de2) (the rate constant of enzyme deactivation) and K(e) (the equilibrium constant) determined from Eq. (8) are 0.4732 h(-1), 0.4011 L/(hg), and 16.8597 g/L, respectively. The higher the enzyme concentration is, the larger the deactivation rate.

Kinetic study of hydrolysis of xylan and agricultural wastes with hot liquid water.

We investigated the kinetics of hot liquid water (HLW) hydrolysis over a 60-min period using a self-designed setup. The reaction was performed within the range 160-220 degrees C, under reaction conditions of 4.0 MPa, a 1:20 solid:liquid ratio (g/mL), at 500 rpm stirring speed. Xylan was chosen as a model compound for hemicelluloses, and two kinds of agricultural wastes-rice straw and palm shell-were used as typical feedstocks representative of herbaceous and woody biomasses, respectively. The hydrolysis reactions for the three kinds of materials followed a first-order sequential kinetic model, and the hydrolysis activation energies were 65.58 kJ/mol for xylan, 68.76 kJ/mol for rice straw, and 95.19 kJ/mol for palm shell. The activation energies of sugar degradation were 147.21 kJ/mol for xylan, 47.08 kJ/mol for rice straw and 79.74 kJ/mol for palm shell. These differences may be due to differences in the composition and construction of the three kinds of materials. In order to reduce the decomposition of sugars, the hydrolysis time of biomasses such as rice straw and palm shell should be strictly controlled.

Optimization of fed-batch enzymatic hydrolysis from alkali-pretreated sugarcane bagasse for high-concentration sugar production.

Fed-batch enzymatic hydrolysis process from alkali-pretreated sugarcane bagasse was investigated to increase solids loading, produce high-concentration fermentable sugar and finally to reduce the cost of the production process. The optimal initial solids loading, feeding time and quantities were examined. The hydrolysis system was initiated with 12% (w/v) solids loading in flasks, where 7% fresh solids were fed consecutively at 6h, 12h, 24h to get a final solids loading of 33%. All the requested cellulase loading (10 FPU/g substrate) was added completely at the beginning of hydrolysis reaction. After 120 h of hydrolysis, the maximal concentrations of cellobiose, glucose and xylose obtained were 9.376 g/L, 129.50 g/L, 56.03 g/L, respectively. The final total glucan conversion rate attained to 60% from this fed-batch process.

Luxury uptake of phosphorus changes the accumulation of starch and lipid in Chlorella sp. under nitrogen depletion

The aim of this research was to study the effect of phosphorus supply on starch and lipid production under nitrogen starvation using Chlorella sp. as a model. High phosphate level had marginal effect on cell density but increased biomass growth. Massive phosphorus was assimilated quickly and mainly stored in the form of polyphosphate. The algal cells ceased phosphorus uptake when intracellular phosphorus reached a certain level. 5mM phosphate in the culture rendered a 16.7% decrease of starch synthesis and a 22.4% increase of lipid synthesis relative to low phosphate (0.17 mM). It is plausible that phosphate can regulate carbon partitioning between starch and lipid synthesis pathway by influencing ADP-glucose pyrophosphorylase activity. Moreover, high phosphate concentration enhanced the abundance of oleic acid, improving oil quality for biodiesel production. It is a promising cultivation strategy by integration of phosphorus removal from wastewater with biodiesel production for this alga.

Preparation and properties of an immobilized cellulase on the reversibly soluble matrix Eudragit L-100

Abstract To prepare a smart biocatalyst, cellulase was immobilized on the reversibly soluble matrix Eudragit L-100 by non-covalent and covalent methods. Covalent immobilization using carbodiimide coupling exhibited superior enzyme loading and reusability compared with non-covalent immobilization, and the covalent loading was increased by almost 20% through the addition of N-hydroxysuccinimide. The temperature optimum of the cellulase was not improved apparently by immobilization but the pH optimum increased from 4.75 to 5.25. Immobilized cellulase was more active than free cellulase above pH 5.0. Immobilized cellulase was more stable than free cellulase during storage at 4°C, room temperature and 50°C. Km values of immobilized and free cellulase were 85.55 and 73.84 g L−1, respectively. About 50% productivity was retained after five cycles for hydrolysis of steam-exploded straw.