Browsing by Subject "Biofuel"
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Item Artificial Leaf for Biofuel Production and Harvesting: Transport Phenomena and Energy Conversion(2013-08) Murphy, Thomas Eugene; Berberoglu, HalilMicroalgae cultivation has received much research attention in recent decades due to its high photosynthetic productivity and ability to produce biofuel feedstocks as well as high value compounds for the health food, cosmetics, and agriculture markets. Microalgae are conventionally grown in open pond raceways or closed photobioreactors. Due to the high water contents of these cultivation systems, they require large energy inputs for pumping and mixing the dilute culture, as well as concentrating and dewatering the resultant biomass. The energy required to operate these systems is generally greater than the energy contained in the resultant biomass, which precludes their use in sustainable biofuel production. To address this challenge, we designed a novel photobioreactor inspired by higher plants. In this synthetic leaf system, a modified transpiration mechanism is used which delivers water and nutrients to photosynthetic cells that grow as a biofilm on a porous, wicking substrate. Nutrient medium flow through the reactor is driven by evaporation, thereby eliminating the need for a pump. This dissertation outlines the design, construction, operation, and modeling of such a synthetic leaf system for energy positive biofuel production. First, a scaled down synthetic leaf reactor was operated alongside a conventional stirred tank photobioreactor. It was demonstrated that the synthetic leaf system required only 4% the working water volume as the conventional reactor, and showed growth rates as high as four times that of the conventional reactor. However, inefficiencies in the synthetic leaf system were identified and attributed to light and nutrient limitation of growth in the biofilm. To address these issues, a modeling study was performed with the aim of balancing the fluxes of photons and nutrients in the synthetic leaf environment. The vascular nutrient medium transport system was also modeled, enabling calculation of nutrient delivery rates as a function of environmental parameters and material properties of the porous membrane. These models were validated using an experimental setup in which the nutrient delivery rate, growth rate, and photosynthetic yield were measured for single synthetic leaves. The synthetic leaf system was shown to be competitive with existing technologies in terms of biomass productivity, while requiring zero energy for nutrient and gas delivery to the microorganisms. Future studies should focus on utilizing the synthetic leaf system for passive harvesting of secreted products in addition to passive nutrient delivery.Item Constraints on algal biofuel production(2011-05) Beal, Colin McCartney; Ruoff, Rodney S.; Webber, Michael E., 1971-; Hebner, R. E. (Robert E.); Berberoglu, Halil; Seibert, A F.; King, Carey W.The aspiration for producing algal biofuel is motivated by the desire to replace conventional petroleum fuels, produce fuels domestically, and reduce greenhouse gas emissions. Although, in theory, algae have the potential to produce a large amount of petroleum fuel substitutes and capture carbon emissions, in practice, profitable algal biofuel production has proven quite challenging. This dissertation characterizes the production pathways for producing petroleum fuel substitutes from algae and evaluates constraints on algal biofuel production. Chapter 8 provides a summary of the entire dissertation. The first chapter provides a framework for reporting the production of renewable diesel from algae in a consistent way by using data that are specific and by presenting information with relevant metrics. The second chapter presents a review of analytical tools (i.e., microscopy, spectroscopy, and chromatography) that can be used to analyze the structure and composition of intermediate products in an algal biofuel production pathway. In chapters 3 through 6, the energy return on investment, water intensity, and financial return on investment are presented for three cases: 1) an Experimental Case in which data were measured during five batches of algal biocrude production with a combined processed volume of about 7600 L, 2) a hypothetical Reduced Case that assumes the same energy output as the Experimental Case, with reduced energy and material inputs, and 3) a Highly Productive Case that assumes higher energy outputs than the Experimental Case, with reduced energy and material inputs, similar to the Reduced Case. For all three cases, the second-order energy return on investment was determined to be significantly less than 1, which means that all three cases are energy negative. The water intensity (consumption and withdrawal) for all cases was determined to be much greater than that of conventional petroleum fuels and biofuels produced from non-irrigated crops. The financial return on investment was also found to be significantly less than 1 for all cases, indicating production would be unprofitable. Additionally, it was determined that large-scale algal biofuel production would be constrained by the availability of critical energy and material inputs (e.g., nitrogen and carbon dioxide). The final part of this dissertation presents a first-principles thermodynamic analysis that represents an initial attempt at characterizing the thermodynamic limits for algal biofuel production. In that analysis, the energy, entropy, and exergy is calculated for each intermediate product in the algal biofuel production pathway considered here. Based on the results presented in this body of work, game-changing technology and biotechnology developments are needed for sustainable and profitable algal biofuel production.Item Development of a novel algae biofilm photobioreactor for biofuel production(2012-08) Ozkan, Altan; Berberoglu, Halil; Kinney, Kerry; Katz, Lynn; Kirisits, Mary J.; Lawler, Desmond; Brand, Jerry; Cetiner, SelimAlgae are photosynthetic microorganisms that convert carbon dioxide and sunlight into biomass that can be used for biofuel production. Although they are usually cultivated in suspension, these microorganisms are capable of forming productive biofilms over substrata given the right conditions. This dissertation focuses on algal biofilms and their application in biofuel feedstock production. In particular it reports the construction and performance of an algae biofilm photobioreactor, the physico-chemical surface properties of different algal species and adhesion substrata, and cell-surface interactions based on experimental results and theoretical models. A novel algae biofilm photobioreactor was constructed and operated (i) to demonstrate the proof of concept, (ii) to analyze the performance of the system, and (iii) to determine the key advantages and short comings for further research. The results indicated that significant reductions in water and energy requirements were possible with the biofilm photobioreactor. Although the system achieved net energy ratio of about 6, the overall productivity was low as Botryococcus branunii is notoriously slow growing algae. Thus, further studies were focused on identification of algal species capable of biofilm growth with larger biomass and lipid productivities. Adhesion of cells to substrata precedes the formation of all biofilms. A comprehensive study has been conducted to determine the interactions of a planktonic and a benthic algal species with hydrophilic and hydrophobic substrata. The physico-chemical surface properties of the algal cells and substrata were determined and using these data, cell-substrata interactions were modeled with the thermodynamic, Derjaguin, Landau Verwey, Overbeek (DLVO) and Extended Derjaguin, Landau, Verwey, Overbeek (XDLVO) approaches and critical parameters for algal adhesion were identified. Finally, the adhesion rate and strength of algal species were quantified with parallel plate flow chamber experiments. The results indicated that both cell and substrata surface hydrophobicity played a critical role for the adhesion rate and strength of the cells and XDLVO approach was the most accurate model. Finally, based on these findings the physico-chemical surface properties of ten algal species and six substrata were quantified and a screening was done to determine algae species substratum couples favoring adhesion and biofilm formation.Item Hydrothermal liquefaction of municipal sludge and biosolids(2015-05) Anthony, Joseph Roslyn; Berberoglu, Halil; Wang, YaguoThe conversion of municipal sludge and biosolids into bio-oil via hydrothermal liquefaction (HTL) can simultaneously provide a replacement to non-renewable crude oil while dealing with waste disposal issues. Hydrothermal liquefaction takes advantage of liquid water’s interesting properties at high temperatures near the critical point, which facilitate the break down and reformation of biomass into a more energy dense bio-oil. Several laboratory-scale batch HTL experiments have been conducted with algae, woody biomass and livestock manure, but few have considered municipal sludge or biosolids. Suzuki et al. (1988) and Vardon et al. (2011) conducted studies on the HTL of sludge and biosolids, however neither study explored the effect of processing conditions (1,2). This thesis presents a study that explored how bio-oil composition and yield were affected by residence time, heating rate, initial biomass solids percentage and initial biomass composition. The highest quality bio-oil had a higher heating value (HHV) of 31.46±0.37 MJ/kg with a conversion yield of 39.42±1.4%. The HHV of the bio-oil was increased when the initial biomass had a higher solids concentration or higher HHV. The conversion yield was larger at lower solids percentages and at a heating rate of 270˚C/min. Furthermore, very few continuous HTL systems have been developed even though they may be the most viable option for scaling up. This thesis also presents the design and construction of a continuous HTL system for the processing of municipal sludge and biosolids.Item Polymer applications for improved biofuel production from algae(2011-12) Jones, Jessica Naomi; Poenie, Martin F.; Brand, Jerry; Brodbelt, Jennifer; Georgiou, George; Roy, Krishnendu; Seibert, FrankBiofuel is a renewable and sustainable energy source with near-neutral carbon footprint. Algae are an ideal feedstock for biofuel production because they reproduce quickly and have high oil. Algae can be cultivated in non-arable land, and would not impact the food supply. Unfortunately, processing algae into biofuel is more expensive than land crops due to the large volumes of dilute algal suspension that must be harvested and concentrated. In order to improve algae-based biofuel economics, resins were developed that reduce costs associated with water pumping and transport. Hydrophobic resins were developed for binding oil out of an algal suspension so that the residual biomass could be recovered without solvent contamination. Binding behavior displayed lipid species specificity, and binding capacity was improved by ethanol treatment of the biomass. Algae was harvested by binding to anion exchange resin and directly converted into biodiesel. One-step, room temperature in situ transesterification of algae yielded nearly as much biodiesel as two-step, heated transesterification of dried biomass. Elution with transesterification reagent also regenerated the resin for subsequent algal binding. Functionalized resins were developed with high algal binding capacity at neutral pH. Binding was easily reversed, as treatment with buffer with pH higher than pKa of the resin functional group removed the algae and regenerated the resin for subsequent use. The resin bound 10% of its weight in algae and released it as a 100-fold concentrated suspension. The polymers developed can be scaled up for commercial processes and reduce algal harvesting and concentration costs.Item Rheology of algae slurries(2010-12) Bolhouse, Angel Michele; Berberoglu, Halil; Ferron, RaissaThis thesis reports the rheological properties of algae slurries as a function of cell concentration for three microalgae species: Nannochloris sp.,Chlorella vulgaris, and Phaeodactylum tricornutum. Rheological properties ofalgae slurries have a direct impact on the agitation and pumping power requirements as well as process design for producing algal biofuels. This study measures the rheological properties of eight diff erent concentrations of each species ranging from 0.5 to 80 kg dry biomass/m³. Strain-controlled steady rate sweep tests were performed for each sample with an ARES-TA rheometer using a double wall couette cup and bob attachment. Shear rates ranged from 5 - 270 s⁻¹, corresponding to typical expected conditions. The results showed that Nannochloris sp. slurry behaved as a Newtonian fluid for concentrations up to 20 kg/m³. Samples with concentrations above 40 kg/m³ behaved as a shear thinning non-Newtonian fluid. The effective viscosity increased with increased biomass concentration for a maximum value of 3.3x10⁻³ Pa-s. Similarly, C. vulgaris slurry behaved as a Newtonian fluid with concentrations of up to 40 kg/m³, above which it displayed a shear thinning non-Newtonianf behavior and a maximum eff ective viscosity of 3.5x10⁻² Pa-s. On the other hand, P. tricornutum slurry demonstrated solely Newtonian fluid behavior, with the dynamic viscosity increasing with increasing biomass concentration for a maximum value of 3.2x10⁻³ Pa-s. The maximum observed e ffective viscosity occurred at a concentration of 80 kg/m³ for all three species. Moreover, an energy analysis was performed where a non-dimensional bioenergy transport e ffectiveness was de termined as the ratio of the energy content of the transported algae biomass to the sum of the required pumping power and the harvesting power. The results show that the increase in major losses due to increase in viscosity was overcompensated by the increase in the transported biomass energy. Also, cultivating a more concentrated slurry requires less dewatering power and is the preferred option. The largest bioenergy transport eff ectiveness was observed for the slurries with the largest initial dry biomass concentrations. Finally, the relative viscosity of algae slurries was modeled using a Kelvin-Voit based model for dilute and concentrated viscoelastic par- ticle suspensions. The model, which depends primarily on the packing factor of the algae species, agrees with the measured viscosity with an average error of 18%, while the concentrated particle suspension model was slightly more accurate than the dilute suspension model.