Melissa Montalbo-Lomboy

Evaluation of microalgae cell disruption by ultrasonic treatment.

Microalgae are a promising feedstock for biofuels because of their capability to produce lipids. Cell disruption is necessary to maximize lipid extraction. Sonication conditions were evaluated for breaking heterotrophic (Schizochytrium limacinum) and autotrophic (Chlamydomonas reinhardtii) microalgae cells. Cell disruption was estimated by Nile red-lipids fluorescence quantification in S. limacinum and by the release of intracellular chlorophyll and carotenoids in green microalga C. reinhardtii. In both species, approximately 800 J/10 mL was the energy input necessary to maximize cell disruption, regardless of the cell concentrations studied. Increasing sonication time produced increasing amount of free radicals, quantified by the formation of hydroxyterephthalate. Sonication energy beyond the level needed for cell disruption induced oxidation of arachidonic acid, a polyunsaturated fatty acid typically found in marine lipids. Careful control of sonication conditions is necessary to maximize oil extraction at the lowest operational cost and to prevent oil from free radical-induced degradation.

Ultrasonic pretreatment of corn slurry for saccharification: a comparison of batch and continuous systems.

The effects of ultrasound on corn slurry saccharification yield and particle size distribution was studied in both batch and continuous-flow ultrasonic systems operating at a frequency of 20 kHz. Ground corn slurry (28%w/v) was prepared and sonicated in batches at various amplitudes (192-320 microm(peak-to-peak (p-p))) for 20 or 40s using a catenoidal horn. Continuous flow experiments were conducted by pumping corn slurry at various flow rates (10-28 l/min) through an ultrasonic reactor at constant amplitude of 12 microm(p-p). The reactor was equipped with a donut shaped horn. After ultrasonic treatment, commercial alpha- and gluco-amylases (STARGEN 001) were added to the samples, and liquefaction and saccharification proceeded for 3h. The sonicated samples were found to yield 2-3 times more reducing sugars than unsonicated controls. Although the continuous flow treatments released less reducing sugar compared to the batch systems, the continuous flow process was more energy efficient. The reduction of particle size due to sonication was approximately proportional to the dissipated ultrasonic energy regardless of the type of system used. Scanning electron microscopy (SEM) images were also used to observe the disruption of corn particles after sonication. Overall, the study suggests that both batch and continuous ultrasonication enhanced saccharification yields and reduced the particle size of corn slurry. However, due to the large volume involve in full scale processes, an ultrasonic continuous system is recommended.

Simultaneous saccharification and fermentation and economic evaluation of ultrasonic and jet cooking pretreatment of corn slurry.

The potential of ultrasonics to replace hydrocooking in corn‐to‐ethanol plants was examined in this study. Batch and continuous experiments were conducted on corn slurry with sonication at a frequency of 20 kHz. Batch mode used a catenoidal horn operated at an amplitude of 144 μmpeak‐to‐peak (p–p) for 90 s. Continuous experiments used a donut horn operating at inner radius amplitude of 12 μmp–p. Jet‐cooked samples from the same ethanol plant were compared with ultrasonicated samples. The highest starch‐to‐ethanol conversion was obtained by the jet‐cooked samples with a yield of 74% of the theoretical yield. Batch and continuous sonication achieved 71.2% and 68% conversion, respectively, however, statistical analysis showed no significant difference between the jet cooking and ultrasonication. On the basis of the similar performance, an economic analysis was conducted comparing jet cooking and ultrasonic pretreatment. The analysis showed that the capital cost for the ultrasonics system was ∼ 10 times higher compared to the capital cost of a hydrocooker. However, due to the large energy requirements of hydrocookers, the analysis showed lower total overall costs for continuous ultrasonication than that for jet cooking, assuming the current energy prices. Because of the high utility cost calculated for jet cooking, it is concluded that ultrasonication poses as a more economical option than jet cooking. Overall, the study shows that ultrasonics is a technically and economically viable alternative to jet cooking in dry‐grind corn ethanol plant.

Rapid dissolution of switchgrass in 1-butyl-3-methylimidazolium chloride by ultrasonication.

The utilization of ultrasonics to rapidly dissolve switchgrass in ionic liquid, 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) was evaluated in this work. The objective of the study focused on determining the effects of various ultrasonic conditions on the recovery of carbohydrate from biomass, lignin removal, and enzymatic hydrolysis. Dried ground switchgrass was added to ionic liquid, then sonicated at a frequency of 20kHz. The experiments were conducted using a catenoidal horn at varying amplitudes of 96μm, 128μm, and 160μm and sonication times of 2, 3, and 4min. Similarly, ground switchgrass was dissolved in ionic liquid assisted by conventional heat treatment at 130°C for 12 and 24h. The results showed good delignification results of 53% for the 24h heat pretreated samples and of 50.8% for ultrasonic assisted samples at 160μm amplitude and 4min. Even in the presence of lignin in the recovered biopolymer, both of heat treated and ultrasonicated samples obtained 100% glucan digestibility after only 3h of enzymatic hydrolysis. Heat pretreated samples exhibited 44-59% lower xylan digestibility compared to ultrasonic pretreated samples (160μm amplitude and 4min sonication time). Scanning electron microscope images displayed significant changes in biomass structure from intact and crystalline of the untreated biomass to disintegrated and amorphous of the treated biomass (heat treated and ultrasonicated). With increasing ultrasonic amplitude the carbohydrate recovery decreased. Also, more than 50% of the hemicellulose fraction was lost during biomass recovery. Overall, it was concluded that ultrasonication was a promising technology to enhance dissolution of lignocellulose in ionic liquid.

Influence of Ultrasonics in Ammonia Steeped Switchgrass for Enzymatic Hydrolysis

The bioconversion of lignocellulosic materials into fuels is of great environmental and economic importance, because of the large amounts of feedstock (est. over 1 billion tons per year), the potentially low cost of this feedstock, and the potentially high net energy balance the overall process. Switchgrass (Panicum virgatum L.) is a candidate dedicated lignocellulosic feedstock in the US. However, lignocellulosic materials, including switchgrass, are hampered by the recalcitrance of lignocellulose to enzymatic degradation into fermentable sugars. Various types of pretreatment have been developed to overcome this recalcitrance. In this study, we examined sequential ammonia-steeping and ultrasound pretreatment of switchgrass. The experimental variables included ultrasound energy dissipation and source amplitude, biomass concentrations, and antibacterial agents. Specifically, the 35-mL samples received either 2000 J or 5000 J, while biomass concentration was at 10% and 30% (mass basis). Antibacterial agents were employed to determine the extent to which sugars were being metabolized by naturally occurring bacteria in the unsterilized pretreated samples. Analytical glucose analysis was conducted to verify the amount of fermentable sugars released and low-vacuum SEM was used to establish the physical effect of ultrasonics on the biomass. The sequential ammonia steeping-ultrasonic pretreatment released about 10% more fermentable sugars than did ammonia steeping alone. However, the net energy balance (additional chemical in free sugars minus energy consumption of ultrasound process) was not favorable - this contrasts with Grewells work using ultrasonics for enhancing sugar release from starches. We recommend further investigations on re-evaluating the design and conditions which could make ultrasonic work better as a lignocellulosic pretreatment.

Ultrasonic Pretreatment of Corn Slurry in Batch and Continuous Systems

The effects of ultrasonication of corn slurry, on particle size distribution and enzymatic hydrolysis was studied for the dry-grind mill ethanol industry. Two independent ultrasonic experiments were conducted at a frequency of 20 kHz; in batch and continuous systems. The ground corn slurry (33% m/v) was pumped at flow rates 10-28 L/min in continuous flow experiments, and sonicated at constant amplitude (20µmpeak-to-peak(p-p)). Ultrasonic batch experiments were conducted at varying amplitudes of 192-320µmp-p. After ultrasonication, StargenTM001 enzyme was added to the samples and a short 3h hydrolysis followed. The treated samples were found to yield 2-3 times more reducing sugar compared to the control (untreated) samples. In terms of energy density, the batch ultrasonic system was found to deliver 25-times more energy than the continuous flow systems. Although the experiments conducted in continuous system released less reducing sugar than the batch system, the continuous system was more energy efficient. The particle size of the sonicated corn slurry (both batch and continuous) was reduced relative to the controls (without treatment). The reduction of particle size was directly proportional to the energy input during sonication. The study suggests that both batch and continuous flow ultrasonic systems enhances enzymatic hydrolysis yield, reduces particle size of corn slurry and could be a potential effective pretreatment for corn slurry.

Ultrasonication of Sugary -2 Corn for Enhanced Enzymatic Hydrolysis

This study investigates the potential application of high powered ultrasonics as a liquefaction pretreatment of sugary-2 corn slurry. Ground sugary-2 corn (Zea Mays L.) slurry was treated with ultrasonics at 20kHz and amplitudes of 192-320µmpp (peak-to-peak) for 5, 10, 15, 20 and 40 seconds. After sonication, enzymes (StargenTM001) were added to the samples to hydrolyze the starch into fermentable sugars. It was found that the reducing sugar released in the treated samples were 6-fold higher than in the non-treated samples. Scanning electron microscopy images revealed that the sugary starch was partially gelatinized during sonication. This observation was confirmed by polarized-light microscopic images, where deformed “Maltese crosses” were found. The swelling rate of sonicated samples was nearly 66 times higher than when applying conventional heating. This result confirms better gelatinization capability of ultrasonics compared to conventional heating. The maximum relative net energy gain (additional chemically released energy) of the sonicated samples was at 5s of sonication time with a power setting between 248-330W. The findings in this study indicated ultrasonics as a promising pretreatment step in sugary-2 corn hydrolysis.

Enhancing biofuel production by ultrasonics

This work evaluated the use of high-powered ultrasonics to enhance biofuel production in terms of efficiency and costs. A wide range of feed stocks, including switch grass, corn stover, and soft wood, were studied. The effect of ultrasonic pretreatment on the removal of lignin for hydrolysis of starches and cellulose to fermentable sugars was studied. It was found that many of the pretreatments were very successful in enhancing lignin removal. For example, time of dissolution of lingo-cellulosic biomass in ionic liquids was reduced from hours to minutes accompanied by a significant decrease in energy consumption compared to mechanical stirring. In addition, it was found that hydrolysis of corn starch could be greatly accelerated utilizing ultrasonics. Economic models showed that the technology, once implemented, would have a payback period of less than one year. The work also focused on biodiesel production. It was seen that ultrasonics accelerated the transesterification process so that soy bean oil could be converted to biodiesel in less than a minute, compared to 45 min using traditional methods. It was shown that yeast grown from glycerin, a co-product of biodiesel production, could be extracted and simultaneously converted to biodiesel with ultrasonics in less than a minute, compared to traditional techniques that require multiple processes and relatively long cycle times (+1 h).

Simultaneous Saccharification and Fermentation of Ultrasonically Treated Corn Slurry

The potential application of ultrasonics as a pretreatment process to enhance saccharification of starch in corn-to-ethanol plants is evaluated in this paper. Due to energy intensive use of steam in hydro-cooking, ultrasonics poses a promising alternative as a pretreatment method. Two independent ultrasonic experiments were conducted at a frequency of 20 kHz; batch and continuous flow treatment. Corn slurry was obtained from a nearby ethanol plant and sonicated in batch mode at amplitude of 144µmpeak-to-peak (p-p) for 90 s using a catenoidal horn with a 10 mm diameter face. In the continuous flow treatment, corn slurry was pumped through a reactor equipped with a Branson Ultrasonics “donut horn”. Jet-cooked samples were obtained from the same ethanol plant and analyzed for comparison in fermentation yield. Ethanol yields in sonicated samples were comparable to jet-cooked samples. The glucose levels decreased with consumption during the initial stage of the fermentation and suddenly dropped after 6 h as the ethanol increased. An economic comparison was also conducted on jet cooking and ultrasonics pretreatment methods. The analysis showed that capital cost for the ultrasonics system was higher compared to the capital cost of hydrocooking. However, due to the relatively large energy demand of jet cookers, the operating costs of the hydrocooker suggest that it is cost effective to use ultrasonics.