Yanna Liang

Converting crude glycerol derived from yellow grease to lipids through yeast fermentation

Cryptococcus curvatus, an oleaginous yeast was observed to grow on crude glycerol derived from yellow grease. When cultured in a one-stage fed-batch process wherein crude glycerol and nitrogen source were fed intermittently for 12 days, the final biomass density and lipid content were 31.2 g/l and 44.2%, respectively. When cultured in a two-stage fed-batch operation wherein crude glycerol was supplemented at different time points while nitrogen source addition was discontinued at the middle of the experiment, the biomass density was 32.9 g/l and the lipid content was 52% at the end of 12 days. Compared with other oil feedstocks for biodiesel production, lipid accumulated by C. curvatus grown on glycerol has high concentration of monounsaturated fatty acid, which makes it an excellent source for biodiesel use.

Use of sweet sorghum juice for lipid production by Schizochytrium limacinum SR21.

Stalk juice from sweet sorghum grown in Southern Illinois, USA, was examined for lipid production through microalgal fermentation. Juice concentrations at 100%, 75%, 50%, and 25% led to different biomass, lipid, and docosahexaenoic acid (DHA) production by Schizochytrium limacinum SR21. Biomass dry weight as 9.4g/l at 50% juice concentration was similar to that from pure glucose (10.9g/l). But with a 73.4% lipid content, this dose resulted in higher lipid and DHA production than those from pure glucose. Major fatty acids in cells grown on juice were identical to those fed by other substrates. Among the three sugars - glucose, fructose, and sucrose in sorghum juice, only glucose was utilized for growth. Spent medium after algal removal may be further processed for white sugar production in a traditional way since sucrose content remained the same throughout the algal fermentation process. Algal cells or lipids harvested can be utilized as fish meal, human nutrition supplements, or for biodiesel purpose.

Batch stage study of lipid production from crude glycerol derived from yellow grease or animal fats through microalgal fermentation.

A marine microalga, Schizochytrium limacinum SR21 has been found to grow fast on crude glycerol - a major by-product from the current biodiesel industry. Using crude glycerol derived from restaurant used oils (yellow grease), we have determined that glycerol concentrations of 25 and 35 g/l were the optimal ones for untreated and treated crude glycerol in batch cultures, respectively. Biomass dry weight as 8.3 and 13.3g/l were attained for these two doses, respectively. Higher concentrations of glycerol resulted in decreased cell growth due to substrate inhibition and methanol presence. With 35 g/l, the cellular lipid content was the highest - 73.3% among all the doses tested. Animal fats derived crude glycerol also supported algal growth and lipid production. Results from this study set a solid foundation for our ongoing fed-batch process to achieve maximal crude glycerol utilization and lipid production.

Fermentable sugar release from Jatropha seed cakes following lime pretreatment and enzymatic hydrolysis.

Composition change of Jatropha seed cake samples was evaluated upon lime pretreatment at 100 degrees C with different parameters. With a lime dose of 0.2 g and a water content of 10 ml per gram of cake and a treatment period of 1 h, 38.2+/-0.6% of lignin was removed. However, 65+/-16% of hemicellulose was also lost under this condition. For all the treatments tested, cellulose content was not affected by lime supplementation. Through further examining total reducing sugar (TRS) release by enzymatic hydrolysis after lime pretreatment, we have found that 0.1 g of lime and 9 ml of water per gram of cake and 3 h pretreatment produced the maximal 68.9% conversion of cellulose. Without lime pretreatment, the highest cellulose conversion was 33.3%. One microalgal species, Schizochytrium limacinum SR21 was able to grow on the hydrolyzates and generate a biomass density of 3.2 g/l in 4 days.

Microbial lipid production from pretreated and hydrolyzed corn fiber.

With its high content of carbohydrates and low percentage of lignin, corn fiber represents a renewable feedstock that can be processed to produce biofuels. Through a combination of pretreatment by lime and enzymatic hydrolysis, total reducing sugars of 700 mg/g corn fiber were released. This amount is equivalent to 92.7% of theoretically available sugars in corn fiber. The resulting hydrolysate itself did not support any growth of Cryptococcus curvatus. But with addition of minerals, C. curvatus grew to a cell density of 6.6 g/L in 6 days. Using the adapted cells, rapid sugar consumption and cell growth were observed. This study demonstrated that it is feasible to produce microbial lipids from corn fiber through pretreatment, enzymatic hydrolysis, and fermentation. In addition, C. curvatus is an excellent candidate for this application since it can utilize all major sugars, glucose, xylose, and arabinose with yield of cells and lipids as 0.55 and 0.27 g/g sugars, respectively.

Optimization of Lime Pretreatment of Sweet Sorghum Bagasse for Enzymatic Saccharification

With recent emphasis on development of alternatives to fossil fuels, sincere attempts are being made on finding suitable lignocellulosic feedstocks for biological conversion to fuels and chemicals. Sweet Sorghum is among the most widely adaptable cereal grasses, with high drought resistance, and ability to grow on low quality soils with low inputs. It is a C4 crop with high photosynthetic efficiency and biomass yield. Our research objective is to optimize lime pretreatment of sweet sorghum bagasse for its enzymatic conversion into fermentable sugars for biofuels. Sweet sorghum biomass was ground and passed through a 35 mesh screen. Moisture content of the biomass was approximately 12%. It had 32.3% cellulose, 21.2% hemicelluloses, and 8.3% acid detergent lignin on dry matter basis. Lime pretreatment was provided in atmospheric pressure at 100oC. The lime concentration was varied from 0.05 g/g biomass to 0.2 g/g biomass; reaction time was 1 hour to 3 hours, and liquid loading was varied from 7 to 20 ml lime solution /g biomass sample. Pretreated biomass was hydrolyzed with mixture of two enzymes, Accellerase® 1500 (Cellulase) at 0.24 mL/g of SSB and Accellerase® XC (xylanase) at 0.25 ml/g of SSB, and measured for total reducing sugars by DNS (1,3-dinitrosalicylic acid) reagent.

Optimization of sugar release from sweet sorghum bagasse following solvation of cellulose and enzymatic hydrolysis using response surface methodology

To release sugars effectively from sweet sorghum bagasse (SSB), a cellulose solvent and organic solvent‐based lignocellulose fractionation pretreatment approach was studied using response surface methodology (RSM). Based on RSMs central composite design, a batch experimental matrix was set up to determine the effects of reaction time (20–60 min) and temperature (40–60 °C) on delignification, total reducing sugar yield, glucan digestibility, and overall glucose yields following a pretreatment‐hydrolysis process. The optimum pretreatment conditions of 50 °C and 40 min led to 51.4% delignification, 86% overall glucose yield, and 61% overall xylose yield. An effort has also been made to obtain predictive models to illustrate the correlation between independent and dependent variables using RSM. The significance of the correlations and adequacy of these models were statistically tested for the selected objective functions. The optimum pretreatment condition predicted by the model was 49.1 °C and 39.2 min which matched the experimental data well. Results from this study can be applied to large scale biorefineries using sugars released from SSB for producing various biofuels.

Changes in pore structure of coal caused by coal-to-gas bioconversion

AbstarctMicrobial enhanced coalbed methane (ME-CBM) recovery is critically examined as a viable technology for natural gas recovery from coalbed methane (CBM) reservoirs. Since the majority of gas-in-place (GIP) is stored as an adsorbed phase in fine pores of coal matrix, the nano-pore structure directly influences gas storage and transport properties. Only limited studies have quantified the alteration of the nano-pore structure due to ME-CBM treatment. This study examines the evolution of the pore structure using a combination of small angle X-ray scattering (SAXS), low-pressure N2 and CO2 adsorption (LPGA) and high-pressure methane adsorption methods. The results show that the surface fractal dimension decreases for the two bioconverted coals compared to the untreated coal. After bio-treatment, the mesopore surface area and pore volume decrease with the average pore diameter increases, while the micropore surface area increases with pore volume decreases. Both inaccessible meso-/micropore size distributions decrease after bioconversion, while the accessible micropore size distribution increases, making a portion of closed micropore network accessible. In addition, the methane adsorption capacities increase after bio-treatment, which is confirmed by the increase of micropore surface area. A conceptual physical model of methanogenesis is proposed based on the evolution of the pore structure.

Pyrene Fate Affected by Humic Acid Amendment in Soil Slurry Systems

BackgroundHumic acid (HA) has been found to affect the solubility, mineralization, and bound residue formation of polycyclic aromatic hydrocarbons (PAHs). However, most of the studies on the interaction between HA and PAH concentrated on one or two of the three phases. Few studies have provided a simple protocol to demonstrate the overall effects of HA on PAH distribution in soil systems for all three phases.MethodsIn this study, three doses of standard Elliott soil HA (ESHA), 15, 187.5, and 1,875 μg ESHA/g soil slurry, were amended to soil slurry systems. 14C-pyrene was added to the systems along with non-radiolabeled pyrene; 14C and 14CO2 were monitored for each system for a period of 120 days.ResultsThe highest amendment dose significantly increased the 14C fraction in the aqueous phase within 24 h, but not after that time. Pyrene mineralization was significantly inhibited by the highest dose over the 120-day study. While organic solvent extractable 14C decreased with time in all systems, non-extractable or bound 14C was significantly enhanced with the highest dose of ESHA addition.ConclusionAmendment of the highest dose of ESHA to pyrene contaminated soil was observed to have two major functions. The first was to mitigate CO2 production significantly by reducing 14CO2 from 14C pyrene mineralization. The second was to significantly increase stable bound 14C formation, which may serve as a remediation end point. Overall, this study demonstrated a practical approach for decontamination of PAH contaminated soil. This approach may be applicable to other organic contaminated environments where active bioremediation is taking place.

Impact of TiO2 and ZnO nanoparticles on an aquatic microbial community: effect at environmentally relevant concentrations

Abstract To investigate effects of engineered nanoparticles (ENPs) at environmentally relevant concentrations to aquatic microbial communities, TiO2 at 700 µg/L and ZnO at 70 µg/L were spiked to river water samples either separately or combined. Compared to controls where no ENPs were added, the addition of TiO2 ENPs alone at the tested concentration had no statistically significant effect on both the bacterial and eukaryotic communities. The presence of added ENPs: ZnO or ZnO + TiO2 led to significant shift of the microbial community structure and genus distribution. This shift was more obvious for the bacteria than the eukaryotes. Based on results from single particle – inductively coupled plasma – mass spectrometry (SP-ICP-MS), all ENPs aggregated rapidly in water and resulted in much larger particles sizes than the original counterparts. “Dissolved” (including particles smaller than the size detection limits and dissolved ions) concentrations of Ti and Zn increased, too in treatment groups vs. the controls.