Ratna R. Sharma-Shivappa

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.

Microbial pretreatment of cotton stalks by solid state cultivation of Phanerochaete chrysosporium

White rot fungi degrade lignin and have biotechnological applications in conversion of lignocellulose to valuable products. Pretreatment is an important processing step to increase the accessibility of cellulosic material in plant biomass, impacting efficiency of subsequent hydrolysis and fermentation. This study investigated microbial pretreatment of cotton stalks by solid state cultivation (SSC) using Phanerochaete chrysosporium to facilitate the conversion into ethanol. The effects of substrate moisture content (M.C.; 65%, 75% and 80% wet-basis), inorganic salt concentration (no salts, modified salts without Mn(2+), modified salts with Mn(2+)) and culture time (0-14 days) on lignin degradation (LD), solids recovery (SR) and availability of carbohydrates (AOC) were examined. Moisture content significantly affected lignin degradation, with 75% and 80% M.C. degrading approximately 6% more lignin than 65% M.C. after 14 days. Within the same moisture content, treatments supplemented with salts were not statistically different than those without salts for LD and AOC. Within the 14day pretreatment, additional time resulted in greater lignin degradation, but indicated a decrease in SR and AOC. Considering cost, solid state cultivation at 75% M.C. without salts was the most preferable pretreatment resulting in 27.6% lignin degradation, 71.1% solids recovery and 41.6% availability of carbohydrates over a period of 14 days. Microbial pretreatment by solid state cultivation has the potential to be a low cost, environmentally friendly alternative to chemical approaches. Moisture relationships will be significant to the design of an effective microbial pretreatment process using SSC technology.

KI-impregnated oyster shell as a solid catalyst for soybean oil transesterification.

Research on inexpensive and green catalysts is needed for economical production of biodiesel. The goal of the research was to test KI-impregnated calcined oyster shell as a solid catalyst for transesterification of soybean oil. Specific objectives were to characterize KI-impregnated oyster shell, determine the effect of reaction variables and reaction kinetics. The catalyst was synthesized by impregnating KI on calcined oyster shells. X-ray diffraction analysis indicated the presence of portlandite and potassium iodide on the surface and a 31-fold increase in surface as a result of calcination and KI impregnation. Under the conditions tested, ideal reaction variables were 1 mmol g(-1) for catalyst loading, 50 °C for temperature, 10:1 for methanol/oil, and 4h for reaction time. The transesterification followed a first-order reaction (k=0.4385 h(-1)). The option of using oyster shell for the production of transesterification catalysts could have economic benefits to the aquaculture industry in the US.

Microbial pretreatment of cotton stalks by submerged cultivation of Phanerochaete chrysosporium

This study used the fungus, Phanerochaete chrysosporium, to pretreat cotton stalks with two methods, shallow stationary and agitated cultivation, at three supplemental salt concentrations. Pretreatment efficiencies were compared by evaluating lignin degradation, solid recovery and carbohydrate availability over a 14-day period. Shallow stationary cultivation with no salts gave 20.7% lignin degradation along with 76.3% solid recovery and 29.0% carbohydrate availability. The highest lignin degradation of 33.9% at a corresponding solid recovery and carbohydrate availability of 67.8% and 18.4%, respectively, was obtained through agitated cultivation with Modified NREL salts. Cultivation beyond 10 days did not significantly increase lignin degradation during 14 days of pretreatment. Manganese addition during shallow stationary and agitated cultivation resulted in higher solid recoveries of over 80% but lower lignin degradation. Although agitated cultivation resulted in better delignification, results indicate that pretreatment under submerged shallow stationary conditions provides a better balance between lignin degradation and carbohydrate availability.

Heterogeneous catalytic oxidation of lignin into value-added chemicals

Of late there is significant interest in establishing biorefineries for total utilization of lignocellulosic biomass components to produce energy, chemicals and value-added products. Lignin is an abundant and yet underutilized constituent of lignocellulosic biomass that accounts for up to 40% of the energy content. Among several approaches towards value addition of lignin, catalytic oxidation appears to be promising. Hence, the purpose of this report is to provide background information on catalytic oxidation and to update the reader about current research on heterogeneous catalytic oxidation of lignin into value-added products. Additionally, some thoughts are presented to stimulate discussion on lignin oxidation.

Conversion of Cotton Wastes to Bioenergy and Value-Added Products

Cotton accounts for nearly 40% of global fiber production. While approximately 80 countries worldwide produce cotton, the U.S., China, and India together provide over half the worlds cotton. High cotton production is accompanied by generation of tons of cotton waste each year. Large amounts of residue from the field and gins results in not only environmental problems due to disposal issues and cotton diseases and pests, but also difficulties in cultivation due to slow decomposition in the soil. Development of economical and efficient methods for utilizing and/or disposing of cotton waste have been investigated for years, but scale-up and marketing issues need to be resolved. Cotton waste can be used as an energy source through briquetting, pyrolysis, and anaerobic digestion. Studies suggest that composition of cotton waste is similar to other lignocellulosic feedstocks, and it has the potential to be used for bioethanol production. However, proper pretreatment strategies need to be developed to reduce lignin (comprising approximately 30%). Cotton waste can also be processed into industrial products such as animal feed and bedding, soil amendment, and substrate for vegetative growth through various treatments. Enzyme production through utilization of cotton waste as a carbon source is another potential application. A review of the various conversion processes suggests that although cotton waste is suitable for the production of a variety of products, in-depth investigation at the pilot scale is essential to determine process efficacy and economic feasibility.

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.

Hydrolysis of ozone pretreated energy grasses for optimal fermentable sugar production

Ozonated energy grass varieties were enzymatically hydrolyzed to establish process parameters for maximum fermentable sugar production. Conditions for ozonolysis were selected on the basis of maximum delignification and glucan retention after pretreatment. To study the effect of lignin degradation products generated during ozonolysis on cellulolytic enzymes, hydrolysis was carried out for washed and unwashed pretreated solids. Washing the solids significantly (p<0.05) enhanced glucan conversion from 34.3% to 100% while delivering glucose yields of 146.2-431.9 mg/g biomass. Highest fermentable sugars were produced when grasses were ozonated for maximum delignification and washed solids were hydrolyzed using 0.1g/g Cellic® CTec2. In a comparative study on alkaline pretreatment with 1% NaOH for 60 min, Saccharum arundinaceum exhibited the highest glucan conversion with maximum sugar production of 467.9 mg/g. Although ozonolysis is an effective and environmentally friendly technique for cellulosic sugar production, process optimization is needed to ascertain economic feasibility of the process.

Interactions between fungal growth, substrate utilization and enzyme production during shallow stationary cultivation of Phanerochaete chrysosporium on cotton stalks.

Microbial pretreatment of lignocellulosic feedstocks is an environment friendly alternative to physio-chemical pretreatment methods. A better understanding of the interactive fungal mechanisms in biological systems is essential for enhancing performance and facilitating scale-up and commercialization of this pretreatment technique. In this study, mathematical models were developed for describing cellulose and hemicellulose consumption, lignin degradation, cellulase and ligninolytic enzyme production and oxygen uptake associated with the growth of Phanerochaete chrysosporium during a 14-day shallow stationary submerged fungal pretreatment process on cotton stalks. Model parameters were estimated and validated by Statistics Toolbox in MatLab 7.1. Models yielded sufficiently accurate predictions for cellulose and hemicellulose consumption (R²=0.9772 and 0.9837), lignin degradation (R²=0.9879 and 0.8682) and ligninolytic enzyme production (R²=0. 8135 and 0.9693) under both 1-day and 3-day oxygen flushing conditions, respectively. The predictabilities for fungal growth (R²=0.6397 and 0.5750) and cellulase production (R²=0.0307 and 0.3046) for 1-day and 3-day oxygen flushing, respectively, and oxygen uptake (R²=0.5435) for 3-day oxygen flushing were limited.

Sodium Hydroxide Pretreatment of Switchgrass for Enzymatic Saccharification Improvement

Lignocellulose-to-ethanol conversion is a promising technology to supplement corn-based ethanol production. To improve the enzymatic digestibility of recalcitrant lignocellulosic materials, pretreatment is necessary as it alters the structure of lignocellulosic matrix, thereby making the carbohydrates more accessible to enzymes in hydrolysis. In this study, sodium hydroxide (NaOH) pretreatment of switchgrass was explored at 121 oC, 50 oC, and room temperature. Raw switchgrass biomass at a solid : liquid ratio of 0.1 g/ml was pretreated respectively for 0.25 - 1 h, 1 - 48 h, and 1 - 96 h at different NaOH concentrations (0.5, 1.0, and 2.0%, w/v). Pretreatments were evaluated based on total reducing sugar yields in enzymatic hydrolysis, and lignin reductions caused by NaOH attack were investigated. The results showed that, at the optimal conditions (0.1% NaOH, 0.5 h at 121 oC; 1.0% NaOH, 12 h at 50 oC; 2.0% NaOH, 6 h at room temperature), the total reducing sugar yields were respectively 425.4, 453.35, and 406.16 mg/g raw biomass, which were 3.27, 3.49 and 3.12 times that of untreated biomass. Mitigated biomass solubilizations at 50 oC and room temperature contributed to satisfactory sugar recoveries which were comparable to that obtained at 121 oC. NaOH pretreatment was effective in removing lignin barrier. To achieve high biomass digestibilities, at least 50% of the lignin in raw biomass had to be removed.