Jiele Xu

Lime pretreatment of switchgrass at mild temperatures for ethanol production

To improve the enzymatic digestibility of switchgrass at mild temperatures, lime pretreatment of switchgrass was explored at 50 and 21 degrees Celsius, and compared with that at 121 degrees Celsius. The effects of residence time, lime loading, and biomass washing on the sugar production efficiency were investigated. Pretreatments were evaluated based on the yields of biomass-derived sugars in the subsequent enzymatic hydrolysis. Under the best pretreatment conditions (50 degrees Celsius, 24 h, 0.10 g Ca(OH)(2)/g raw biomass, and wash intensity of 100 ml water/g raw biomass), the yields of glucose, xylose, and total reducing sugars reached 239.6, 127.2, and 433.4 mg/g raw biomass, which were respectively 3.15, 5.78, and 3.61 times those of untreated biomass. The study on calcium-lignin bonding showed that calcium ions crosslinked lignin molecules under alkaline conditions, which substantially decreased lignin solubilization during pretreatment, but the resulting high lignin contents of the pretreated biomass did not compromise the improvement of enzymatic digestibility.

Growing duckweed in swine wastewater for nutrient recovery and biomass production.

Spirodela oligorrhiza, a promising duckweed identified in previous studies, was examined under different cropping conditions for nutrient recovery from swine wastewater and biomass production. To prevent algae bloom during the start-up of a duckweed system, inoculating 60% of the water surface with duckweed fronds was required. In the growing season, the duckweed system was capable of removing 83.7% and 89.4% of total nitrogen (TN) and total phosphorus (TP) respectively from 6% swine lagoon water in eight weeks at a harvest frequency of twice a week. The total biomass harvested was 5.30 times that of the starting amount. In winter, nutrients could still be substantially removed in spite of the limited duckweed growth, which was probably attributed to the improved protein accumulation of duckweed plants and the nutrient uptake by the attached biofilm (algae and bacteria) on duckweed and walls of the system.

Pretreatment of switchgrass for sugar production with the combination of sodium hydroxide and lime

Sodium hydroxide (NaOH) and lime (Ca(OH)(2)) were innovatively used together in this study to improve the cost-effectiveness of alkaline pretreatment of switchgrass at ambient temperature. Based on the sugar production in enzymatic hydrolysis, the best pretreatment conditions were determined as: residence time of 6h, NaOH loading of 0.10 g/g raw biomass, NaOH addition at the beginning, Ca(OH)(2) loading of 0.02 g/g raw biomass, and biomass wash intensity of 100ml water/g raw biomass, at which the glucose and xylose yields were respectively 59.4% and 57.3% of the theoretical yields. The sugar yield of the biomass pretreated using the combination of 0.10 g NaOH/g raw biomass and 0.02 g Ca(OH)(2)/g raw biomass was found comparable with that of the biomass pretreated using 0.20 g NaOH/g raw biomass at the same conditions, while the chemical expense was remarkably reduced due to the low cost of lime and the reduced loading of NaOH.

Bermuda grass as feedstock for biofuel production: a review.

Bermuda grass is a promising feedstock for the production of fuel ethanol in the Southern United States. This paper presents a review of the significant amount of research on the conversion of Bermuda grass to ethanol and a brief discussion on the factors affecting the biomass production in the field. The biggest challenge of biomass conversion comes from the recalcitrance of lignocellulose. A variety of chemical, physico-chemical, and biological pretreatment methods have been investigated to improve the digestibility of Bermuda grass with encouraging results reported. The subsequent enzymatic hydrolysis and fermentation steps have also been extensively studied and effectively optimized. It is expected that the development of genetic engineering technologies for the grass and fermenting organisms has the potential to greatly improve the economic viability of Bermuda grass-based fuel ethanol production systems. Other energy applications of Bermuda grass include anaerobic digestion for biogas generation and pyrolysis for syngas production.

Pretreatment of corn stover for sugar production with switchgrass-derived black liquor.

To improve the cost-effectiveness of biomass-to-sugar conversion, sodium hydroxide (NaOH) pretreatment of switchgrass was carried out at 21°C using previously determined optimum conditions (2% NaOH (w/v), 6h), and the spent alkaline liquid (black liquor) was collected and used for pretreatment of corn stover, a feedstock exhibiting a higher susceptibility to NaOH attack, for improved enzymatic hydrolysis at a reduced cost. The results showed that, because of the high pH and the appreciable amount of carbohydrates in the black liquor, sugar production during enzymatic hydrolysis of corn stover pretreated with black liquor was comparable to that of biomass pretreated with 1% NaOH. After black liquor pretreatment at the best residence time (24h), the total reducing sugar, glucose, and xylose yields of corn stover reached 478.5, 287.7, and 145.3mg/g raw biomass, respectively, indicating the viability of this novel pretreatment technology.

Sodium hydroxide pretreatment of genetically modified switchgrass for improved enzymatic release of sugars.

Overcoming biomass recalcitrance to bioconversion is crucial for cellulosic biofuels commercialization. In this study, Alamo switchgrass (Panicum virgatum L.) was genetically transformed to suppress the expression of 4-coumarate-CoA ligase (4CL). The transgenic plants were determined to have lignin content reductions of up to 5.8%. The ratios of acid soluble lignin (ASL) to acid insoluble lignin (AIL) and syringyl/guaiacyl (S/G) in transgenic plants were 21.4-64.3% and 11.8-164.5%, respectively, higher than those of conventional biomass. Both conventional and transgenic plants were pretreated with 0.5%, 1%, and 2% (w/v) NaOH for 15, 30, and 60min at 121°C, followed by enzymatic hydrolysis with commercial cellulases and xylanases. At the optimal conditions, the glucan and xylan conversion efficiency in the best transgenic plants were 16% and 18% higher than the conventional plant, respectively. The results show that down-regulation of 4CL gene promoted enzymatic hydrolysis of plant cell walls following a mild alkali pretreatment.

Dilute sulfuric acid pretreatment of transgenic switchgrass for sugar production.

Conventional Alamo switchgrass and its transgenic counterparts with reduced/modified lignin were subjected to dilute sulfuric acid pretreatment for improved sugar production. At 150 °C, the effects of acid concentration (0.75%, 1%, 1.25%) and residence time (5, 10, 20, 30 min) on sugar productions in pretreatment and enzymatic hydrolysis were investigated, with the optimal pretreatment conditions determined for each switchgrass genotype based on total sugar yield and the amounts of sugar degradation products generated during the pretreatment. The results show that genetic engineering, although did not cause an appreciable lignin reduction, resulted in a substantial increase in the ratio of acid soluble lignin:acid insoluble lignin, which led to considerably increased sugar productions in both pretreatment and enzymatic hydrolysis. At an elevated threshold concentration of combined 5-hydroxyfuranmethal and furfural (2.0 g/L), the overall carbohydrate conversions of conventional switchgrass and its transgenic counterparts, 10/9-40 and 11/5-47, reached 75.9%, 82.6%, and 82.2%, respectively.

DELIGNIFICATION OF SWITCHGRASS CULTIVARS FOR BIOETHANOL PRODUCTION

Three switchgrass cultivars (‘Performer’, ‘BoMaster’, and ‘Colony’ switchgrass) were delignified using NaOH at varying concentrations and residence times at 121 oC for improved sugar production in enzymatic hydrolysis. Because of its greater carbohydrate/lignin ratio and the more substantial lignin reduction upon alkaline attack, ‘Performer’ switchgrass gave greater sugar productions under all the pretreatment conditions investigated. Maximum sugar production from ‘Performer’ was 425 mg/g raw biomass, which was achieved at 1% NaOH and 0.5 h. Sugar production increased with the improvement of delignification until the lignin reduction reached 30%. The more severe pretreatment conditions, which led to greater lignin reductions, did not favor the increase of sugar production because of greater solid losses. Linear models were proven effective in correlating a modified severity parameter log(Mo) to lignin reduction and sugar production of ‘Performer’ switchgrass.

Duckweed starch accumulation for bioethanol production

Duckweed is a small free-floating aquatic plant within the family Lemnacaea. Because of its excellent growth and high protein content, studies on the application of duckweed as a protein source have been widely reported. Research also shows that the starch content of duckweed can be substantially increased by manipulating growing conditions, which makes duckweed a promising starch source for bioethanol production. Our lab-scale study shows that the duckweed starch content was higher at lower temperatures in the nutrient-rich medium and nutrient starvation favors starch accumulation. Therefore, it is expected that, in practical applications under natural conditions, the change of temperature difference between day and night could also potentially affect the duckweed starch content. Our study also shows that nutrient starvation favors starch accumulation.

Pretreatment of Wheat Straw Using the Combination of Sodium Hydroxide and Lime for the Production of Fermentable Sugars

Conversion of lignocellulosic biomass into bioethanol - is an attractive technology but the production cost involved with the process is a main bottleneck in the commercialization of the process. This study deals with the pretreatment of wheat straw using the combination of sodium hydroxide and lime. The pretreatments were evaluated based on the total reducing sugar yield obtained in the subsequent enzymatic hydrolysis. Factors considered in the study were sodium hydroxide loading, lime loading, residence time and biomass particle size. A central composite design was used to evaluate the significance and the interactions of the factors, which shows sodium hydroxide has a significant effect on the total sugar yield. The optimized sugar yield obtained by using Design-Expert 7.0 was 703.243 mg g-1 raw biomass, which was obtained at the combination of 1.10% sodium hydroxide , 0.075 g g-1 lime of raw biomass, 3.30 h residence time and 24.78 mm particle size.