Yebo Li

Application of Sequential Aqueous Steam Treatments to the Fractionation of Softwood

The FIRST (Feedstock Impregnation and Rapid Steam Treatment) approach was used in this study to isolate extractives, hemicellulose, lignin, fibers, and cellulosic fines of softwood. With hydrolysis and fermentation of the hemicellulose and cellulosic fines fractions, this approach produces four co-products: extractives, cellulose, lignin, and ethanol. The first unit operation uses aqueous/alcohol to remove and recover the extractive rich fraction. The second unit operation uses steam treatment to destructure the matrix and solubilize a large fraction of the hemicelluloses. The third unit operation uses alkaline delignification to dissolve a lignin fraction. The fourth unit operation uses the refining process to separate fibers from cellulosic fines. The fibers are bleached. The yields of lignin and bleached cellulose were about 20.0 kg and 38.3 kg out of 100 kg initial dry pine, respectively. The recovered hemicelluloses were 23.3 kg (containing 16.1 kg hexoses and 5.0 kg pentoses) and the cellulose fines derived hexoses amounted to 3.4 kg out of 100 kg initial dry pine. When the two liquors containing the hemicellulose sugars and the cellulose fines-derived hexoses were fermented for ethanol production, an ethanol yield of 6.8 kg was obtained.

Lactic Acid Production from Cheese Whey by Immobilized Bacteria

The performance of immobilized Bifidobacterium longum in sodium alginate beads and on a spiral-sheet bioreactor for the production of lactic acid from cheese whey was evaluated. Lactose utilization and lactic acid yield of B. longum were compared with those of Lactobacillus helveticus. B. longum immobilized in sodium alginate beads showed better performance in lactose utilization and lactic acid yield than L. helveticus. In the spiral-sheet bioreactor, a lactose conversion ratio of 79% and lactic acid yield of 0.84 g of lactic acid/g of lactose utilized were obtained during the first run with the immobilized L. helveticus. A lactose conversion ratio of 69% and lactic acid yield of 0.51 g of lactic acid/g of lactose utilized were obtained during the first run with immobilized B. longum in the spiral-sheet bioreactor. In producing lactic acid L. helveticus performed better when using the Spiral Sheet Bioreactor and B. longum showed better performance with gel bead immobilization. Because B. longum is a very promising new bacterium for lactic acid production from cheese whey, its optimum fermentation conditions such as pH and metabolic pathway need to be studied further. The ultrafiltration tests have shown that 94% of the cell and cheese whey proteins were retained by membranes with a mol wt cutoff of 5 and 20 KDa.

Lactic acid recovery from cheese whey fermentation broth using combined ultrafiltration and nanofiltration membranes.

The separation of lactic acid from lactose in the ultrafiltration permeate of cheese whey broth was studied using a cross-flow nanofiltration membrane unit. Experiments to test lactic acid recovery were conducted at three levels of pressure (1.4, 2.1, and 2.8 MPa), two levels of initial lactic acid concentration (18.6 and 27 g/L), and two types of nanofiltration membranes (DS-5DK and DS-5HL). Higher pressure caused significantly higher permeate flux and higher lactose and lactic acid retention (p<0.0001). Higher initial lactic acid concentrations also caused significantly higher permeate flux, but significantly lower lactose and lactic acid retention (p<0.0001). The two tested membranes demonstrated significant differences on the permeate flux and lactose and lactic acid retention. Membrane DS-5DK was found to retain 100% of lactose at an initial lactic acid concentration of 18.6 g/L for all the tested pressures, and had a retention level of 99.5% of lactose at initial lactic acid concentration of 27 g/L when the pressure reached 2.8 MPa. For all the test when lactose retention reached 99–100%, as much as 64% of the lactic acid could be recovered in the permeate.

The Feasibility of Using Cattails from Constructed Wetlands to Produce Bioethanol

This project investigates the feasibility of harvesting the cattails in the constructed wetlands of the North Carolina A&T Farm to be converted into ethanol. Using the cattails to produce renewable energy will add value to the land as well as reduce emissions of greenhouse gases by replacing petroleum products. Pretreatment of the dried cattails with dilute NaOH was followed by solid-liquid separation and enzymatic hydrolysis and fermentation of the solids. Two trials gave an average conversion efficiency of 43.4% for the pretreated solids alone which, in conjunction with the crop yield for the cattails, would give up to 4,012 L ethanol/ha, a favorable comparison with corn stover’s 1,665 L/ha at a 60% conversion rate. Given the high potential – 9,680 L/ha at 60% conversion efficiency for solid and liquid streams – and the social and environmental benefits gained by adding value to the waste management system and reducing carbon emissions otherwise made by gasoline, it is recommended that further studies be made using cattails as a feedstock for bioethanol.

Semicontinuous Production of Lactic Acid From Cheese Whey Using Integrated Membrane Reactor

Semicontinuous production of lactic acid from cheese whey using free cells of Bifidobacterium longum with and without nanofiltration was studied. For the semicontinuous fermentation without membrane separation, the lactic acid productivity of the second and third runs is much lower than the first run. The semicontinuous fermentation with nanoseparation was run semicontinuously for 72 h with lactic acid to be harvested every 24 h using a nanofiltration membrane unit. The cells and unutilized lactose were kept in the reactor and mixed with newly added cheese whey in the subsequent runs. Slight increase in the lactic acid productivity was observed in the second and third runs during the semicontinuous fermentation with nanofiltration. It can be concluded that nanoseparation could improve the lactic acid productivity of the semicontinuous fermentation process.

Availability of crop residues as sustainable feedstock for bioethanol production in North Carolina.

The amount of corn stover and wheat straw that can be sustainably collected in North Carolina was estimated to be 0.64 and 0.16 million dry t/yr, respectively. More than 80% of these crop residues are located in the coastal area. The bioethanol potential from corn stover and wheat straw was estimated to be about 238 million L (63 million gal/yr) in North Carolina. The future location of ethanol plant in North Carolina was estimated based on feedstock demand and collection radius. It is possible to have four ethanol plants with feedstock demand of 400, 450, 500, and 640 dry t/d. The collection radii for these four ethanol plants are 46, 60, 42, and 67 km (28, 37, 26, and 42 miles), respectively. The best location for a bioethanol plant includes four counties (Beaufort, Hyde, Tyrrell, and Washington) with feedstock demand of 500 t/d and collection radius about 26 mile.

Assessment of Crop Residues for Bioethanol Production in North Carolina

The amount of corn stover and wheat straw that can be sustainably collected in North Carolina was estimated to be 0.52 and 0.14 million dry tons/yr, respectively. About 80% of these crop residues were located in the coastal area. The bioethanol potential from corn stover and wheat straw was estimated to be about 200 million liters/yr in North Carolina. The future location of ethanol plant in coastal area of North Carolina was estimated based on feedstock demand and collection radius. The best location for a bioethanol plant is in the north eastern coastal area with feedstock demand of 771 tons/day and collection radius about 41 miles. If multiple ethanol plants are considered, it is possible to have two ethanol plants with feedstock demand of 300 tons/year and two ethanol plants with feedstock demand of 500 tons/year in the coastal area. The collection radiuses for the two ethanol plants with 300 tons/day feedstock demand are 28 and 41 miles and the collection radiuses for the two ethanol plants with 500 tons/day feedstock demand are 31 and 46 miles, respectively.

LACTIC ACID RECOVERY FROM CHEESE WHEY FERMENTATION BROTH USING NANOFILTRATION MEMBRANES

The separation of lactic acid from lactose in the ultrafiltration permeate of cheese whey broth was studied using a cross-flow nanofiltration membrane unit. Experiments to test lactic acid recovery were conducted at 3 levels of transmembrane pressure (1.4, 2.1 and 2.8 MPa), two levels of initial lactic acid concentration (1.7% and 2.7%), and two types of nanofiltration membranes (DS- 5DK and DS-5HL). Higher transmembrane pressure caused significantly higher permeate flux and higher lactose and lactic acid retention ratio (P<0.0001). Higher initial lactic acid concentrations also caused significantly higher permeate flux, but significantly lower lactose and lactic acid retention (P<0.0001). The two tested membranes demonstrated significant differences on the permeate flux and lactose and lactic acid retention. Membrane DS-5DK was found to retain 100% of lactose at an initial lactic acid concentration of 18.6 g/L for all the tested pressures, and had a retention level of 99.5% of lactose at initial lactic acid concentration of 27.0 /L when the transmembrane pressure reached 2.8 MPa. For all the tests when lactose retention reached 99-100%, as much as 64% of the lactic acid in the permeate could be recovered.