Wenqiao Yuan

Microalgae Mass Production Methods

This article reviews the performance, special features, and technical and/or economic barriers of various microalgae mass production methods including open-pond, photobioreactor, and immobilized culture systems. Open ponds are the least expensive among the three systems; however, issues of vulnerable species contamination, low productivity, high harvesting cost, and large volume of water loss have to be addressed. High biomass productivity and cell density, reduced contamination, and better use of CO2 are some advantages of photobioreactor systems, but the prohibitively high construction cost of photobioreactors still limits commercialization of such systems. Immobilized algae culture systems have great potential to obviate the harvesting problem of open ponds and photobioreactors and enhance biomass productivity; however, high material cost and limited choices of algae species require more investigation. Economics of algae biofuel manufacturing are also discussed. Algae biomass productivity, lipid content, and petroleum price are decisive factors in the economic viability of algae biofuels.

PREDICTING THE PHYSICAL PROPERTIES OF BIODIESEL FOR COMBUSTION MODELING

As the use of biodiesel becomes more widespread, researchers have shown a strong interest in modeling thecombustion processes in the engine in order to understand the fundamental characteristics of biodiesel combustion. In theearly phase of the simulation, accurate prediction of the physical properties of biodiesel is critical in the representation ofspray, atomization, and combustion events in the combustion chamber. The objective of this article is to present methods forpredicting key physical properties including critical properties, vapor pressure, latent heat of vaporization, density, surfacetension, and liquid viscosity for biodiesel that can be used for combustion modeling. Predicted results were compared withpublished data where available, and for some properties, errors were less than 1%. While no published data were availableat temperatures above 373 K to check the accuracy of the predictions from the models at the higher temperatures, the trendsin the fuel properties were regarded as representative of what would be expected in the combustion chamber. These modelscould be used in a detailed combustion model such as KIVA to make relative comparisons between fuels.

DIESEL ENGINE PERFORMANCE AND NOX EMISSIONS FROM OXYGENATED BIOFUELS AND BLENDS WITH DIESEL FUEL

Increased pressure from federal and state agencies to improve air quality has resulted in extensive research into the use of biofuels to reduce diesel engine emissions. Oxygenated biofuels such as biodiesel and ethanol blended with diesel fuel are biodegradable, non-toxic, renewable alternatives to imported petroleum diesel, and their use not only creates new markets for domestic agricultural products, but also greatly reduces particulate emissions. Unfortunately, biodiesel has been shown to increase NOX emissions upwards of 10% compared to petroleum diesel. The objective of this investigation was to evaluate the performance and NOX emissions of selected biofuels and blends with petroleum-based diesel fuel in a turbocharged and intercooled diesel engine using a steady-state nonroad ISO 8-mode test schedule. Test fuels included traditional No. 2 diesel and four biofuels comprising 100% soy methyl ester biodiesel, 2% biodiesel, 10% ethanol-diesel fuel, and 5% ethanol in biodiesel. Exhaust NOX emissions were monitored with a Horiba NOX analyzer. Reductions in peak torque varying from less than 0.5% to about 10% were measured with the test fuels and were attributed mainly to reduced energy content. Biodiesel fuel showed a 12% increase in NOX emissions, while 2% biodiesel fuel increased emissions 2.3%. The ethanol-diesel fuel blend reduced NOX emissions by 2.7% and was highly sensitive to load, with increased temperature and NOX emissions at light load. Addition of only 5% ethanol to biodiesel suppressed NOX emissions, with only a 2.6% increase occurring. It was concluded that ethanol could act as an effective NOX emissions reducing additive.

Disruption of microalgal cells using high-frequency focused ultrasound.

The objective of this study was to evaluate the effectiveness of high-frequency focused ultrasound (HFFU) in microalgal cell disruption. Two microalgal species including Scenedesmus dimorphus and Nannochloropsis oculata were treated by a 3.2-MHz, 40-W focused ultrasound and a 100-W, low-frequency (20kHz) non-focused ultrasound (LFNFU). The results demonstrated that HFFU was effective in the disruption of microalgal cells, indicated by significantly increased lipid fluorescence density, the decrease of cell sizes, and the increase of chlorophyll a fluorescence density after treatments. Compared with LFNFU, HFFU treatment was more energy efficient. The combination of high and low frequency treatments was found to be even more effective than single frequency treatment at the same processing time, indicating that frequency played a critical role in cell disruption. In both HFFU and LFNFU treatments, the effectiveness of cell disruption was found to be dependent on the cell treated.

Culture of Microalga Botryococcus in Livestock Wastewater

Botryococcus has been one of the most frequently and extensively studied algae in the world. Its potentially high hydrocarbon content and applicability for wastewater treatment have attracted increasing attention in recent years. This study aimed to produce oil from Botryococcus braunii using livestock wastewater for dual purposes of biofuel production and animal waste nutrient removal. B. braunii was batch-wise cultivated in the laboratory in livestock wastewater containing various nutrient concentrations. Optimal growth of B. braunii occurred in 50% autoclaved wastewater. Dry biomass concentration of up to 2.543 g L-1 was achieved with an oil content of 19.8%wt. The 30-day average biomass and oil productivities were 84.8 and 16.8 mg L-1 day-1, respectively. Growing B. braunii in livestock wastewater also effectively removed nutrients. On average, 88% of total nitrogen and 98% of total phosphorous in wastewater were removed in 14 days. B. braunii was found to be able to co-exist with a wild green alga, Chlorella sp.; the presence of either alga did not negatively affect growth of the other. Dry weights of B. braunii and Chlorella sp. were measured using a spectrophotometer by correlating dry weights of algae with their optical density values. Linear regression equations (R2 > 99.7%) for dry weight versus optical density for both algae were developed. These equations can be used to determine the dry-weight concentration of B. braunii and Chlorella sp. using readily obtained optical density values, regardless of wastewater concentration.

SPRAY, IGNITION, AND COMBUSTION MODELING OF BIODIESEL FUELS FOR INVESTIGATING NOX EMISSIONS

The objective of this research was to develop a detailed numerical spray atomization, ignition, and combustion model for direct-injection diesel engines using KIVA3V code that could be applied to biodiesel fuels for investigating NOx emissions. Several modified or recalibrated submodels were incorporated into KIVA3V, including a KH-RT spray breakup model, a Shell ignition model, and a single-step kinetic combustion model. This modified model was applied to a John Deere 4045T direct-injection diesel engine fueled by a soybean methyl ester, a yellow grease methyl ester, and No. 2 diesel fuel. The output of the model was in close agreement with the experimental measurements of cylinder pressure and heat release rate from this engine. It was predicted from the modeling results that the two biodiesel fuels had shorter ignition delay and higher overall cylinder temperatures than diesel fuel. The in-cylinder spray analysis indicated that the soybean methyl ester had slightly longer penetration than diesel fuel, but the yellow grease methyl ester had shorter penetration than diesel fuel. Fewer particle numbers were predicted for the two biodiesel fuels. Both soybean methyl ester and yellow grease methyl ester had more widespread high-temperature distribution areas than diesel fuel, which could account for the increases in NOx emissions typically measured for biodiesel fuels.

Hydrothermal conversion of big bluestem for bio-oil production: the effect of ecotype and planting location.

Three ecotypes (CKS, EKS, IL) and one cultivar (KAW) of big bluestem (Andropogon gerardii) that were planted in three locations (Hays, KS; Manhattan, KS; and Carbondale, IL) were converted to bio-oil via hydrothermal conversion. Significant differences were found in the yield and elemental composition of bio-oils produced from big bluestem of different ecotypes and/or planting locations. Generally, the IL ecotype and the Carbondale, IL and Manhattan, KS planting locations gave higher bio-oil yield, which can be attributed to the higher total cellulose and hemicellulose content and/or the higher carbon but lower oxygen contents in these feedstocks. Bio-oil from the IL ecotype also had the highest carbon and lowest oxygen contents, which were not affected by the planting location. Bio-oils from big bluestem had yield, elemental composition, and chemical compounds similar to bio-oils from switchgrass and corncobs, although mass percentages of some of the compounds were slightly different.

Modeling bubble dynamics and radical kinetics in ultrasound induced microalgal cell disruption.

Microalgal cell disruption induced by acoustic cavitation was simulated through solving the bubble dynamics in an acoustical field and their radial kinetics (chemical kinetics of radical species) occurring in the bubble during its oscillation, as well as calculating the bubble wall pressure at the collapse point. Modeling results indicated that increasing ultrasonic intensity led to a substantial increase in the number of bubbles formed during acoustic cavitation, however, the pressure generated when the bubbles collapsed decreased. Therefore, cumulative collapse pressure (CCP) of bubbles was used to quantify acoustic disruption of a freshwater alga, Scenedesmus dimorphus, and a marine alga, Nannochloropsis oculata and compare with experimental results. The strong correlations between CCP and the intracellular lipid fluorescence density, chlorophyll-a fluorescence density, and cell particle/debris concentration were found, which suggests that the developed models could accurately predict acoustic cell disruption, and can be utilized in the scale up and optimization of the process.

Computational modelling of NOx emissions from biodiesel combustion

A detailed numerical spray atomisation, ignition, combustion and NOx formation model was developed for direct injection diesel engines using KIVA-3V code that could be applied to biodiesel fuels and this model was used to investigate the NOx emissions mechanisms of biodiesel compared with diesel fuel. In addition, computational modelling was applied to evaluate strategies for reducing NOx emissions from biodiesel combustion. The physical and thermodynamic properties of biodiesel used in the model were based on fatty acid composition. The model was verified with experimental data from an engine fuelled with diesel fuel, soyabean methyl ester, Yellow Grease Methyl Ester (YGME) and genetically modified soyabean methyl ester. Strategies for reducing NOx emissions from biodiesel combustion were evaluated with the aid of the model. Increasing spray cone angle, retarding start of injection, applying Exhaust Gas Recirculation (EGR) and charge air cooling were all effective approaches to reducing NOx emissions from biodiesel fuel.

Microalgal cell disruption in a high-power ultrasonic flow system.

A 2-kW continuous ultrasonic flow system (UFS) was found effective in the disruption of two microalgal strains: Scenedesmus dimorphus and Nannochloropsis oculata. Compared to the control, cell debris concentration of UFS treatments increased up to 202% for S. dimorphus and 112% for N. oculata. Similarly, Nile red stained lipid fluorescence density (NRSLD) increased up to 59.5% and 56.3% for S. dimorphus and N. oculata, respectively. It was also found that increasing ultrasound intensity improved cell disruption efficiency indicated by up to 54% increase in NRSLFD of the two strains. Increasing sonication-processing time to 3-min resulted in 33.0% increase for S. dimorphus and 45.7% increase for N. oculata in NRSLFD compared to the control. Cell recirculation was found beneficial to cell disruption, however, higher initial cell concentration significantly reduced cell disruption efficiency, indicated by 98.2% decrease in NRSLFD per cell when initial cell concentration increased from 4.25 × 10(6) to 1.7 × 10(7)cells ml(-1).