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Biodiesel produced from microalgal lipids is being extensively researched as an alternative to petroleum-derived diesel. Literature reports of prior modeling to estimate the likely energy and carbon footprints and manufacturing cost of microalgal biodiesel are inconclusive, with wide ranges for performance measures such as Net Energy Return and manufacturing cost. The goals of this research are to develop an integrated techno-economic life cycle inventory model of microalgal biodiesel production, create a base case that simulates proven manufacturing processes, identify potential barriers to technical, financial, and/or environmental viability, perform sensitivity analyses that identify the input parameters and modeling assumptions that have significant influence on key biodiesel performance indicators (KPI's), and perform case studies involving alternative microalgal properties, manufacturing processes and operating conditions, modeling time-scales, and geographic locations. The model created to meet these objectives, called TELCIM, is the first publicly available, integrated techno-economic life cycle inventory model of microalgal biodiesel manufacture. It consists of a set of interlinked engineering, financial, and life cycle inventory models. It is implemented in Microsoft Excel®, and simulates a five-step manufacturing process consisting of microalgae cultivation, biomass harvesting, lipid extraction, lipid conversion to biodiesel, and anaerobic digestion of residual biomass. Material and energy flows are estimated using mass and energy balances and equipment performance equations. Operating and capital costs are estimated using standard accounting methods, and a cradle-to-gate life cycle inventory of energy and resource consumptions and pollutant releases is compiled. Detailed descriptions of TELCIM's component physical models, along with the derivation of their governing equations, are provided. TELCIM was initially populated with data representing conventional microalgae cultivation and harvesting and vegetable oil extraction and conversion technologies deployed in a southern California location. The Net Energy Return for this case is below 1.0, the minimum threshold for long-term sustainability; the carbon intensity is similar to that of petrodiesel; and the manufacturing cost is uncompetitive with current transportation fuels. Detailed breakdowns show the contributions of each major process step and use category to these performance metrics, allowing identification of the major barriers to viability. Among the biggest obstacles is the large amount of energy used to dry the biomass to the 10% residual moisture content required by the conventional oilseed extraction process. Two types of single-parameter sensitivity analyses are used to identify input parameters that have significant influence on the KPI's. Tornado plots reveal that biological properties including lipid fraction, intracellular water content, and growth rate are among the most influential with respect to one or more of the KPI's. Trend analyses of several of the anaerobic digester operating parameters show that factors affecting biogas production have much stronger influence on the KPI's than factors relating to nutrient recovery. Several variants to the base case were performed, including cases in which the microalga's growth rate and lipid content conform to R & D targets established by the National Alliance for Advanced Biofuels and Bioproducts; a hypothetical wet extraction process allows the drying step to be bypassed; and there is no anaerobic digestion step. The results from these cases suggest that one or more breakthroughs in cell biology and/or process engineering are necessary to make microalgal biodiesel a sustainable large-scale alternative to petroleum diesel. They also show that including anaerobic digestion in the manufacturing scheme improves the KPI's of greatest interest, and delivers an acceptable financial return on incremental investment. TELCIM is a steady-state model, and the climatological data used in the base case represents annual average conditions. The effects of monthly variations in sunlight intensity are simulated under several facility design bases and operating strategies; it appears that designing for maximum sunlight intensity is more cost and energy effective, but necessitates underutilization of available carbon dioxide and reduces the biodiesel production rate. Enhancing the correlation between sunlight intensity and microalgal growth rate to account for the effect of light saturation on photosynthetic efficiency significantly dampens seasonal variations in biomass productivity. Analysis of hourly average versus daily average sunlight intensity indicates that daily average data is sufficiently precise if the long-term average biomass productivity is known; otherwise substantial error can be introduced if biomass productivity is estimated directly from sunlight intensity data, and daily average data is used instead of hourly average data. Five alternative manufacturing locations along the southern rim of the continental United States are simulated using local climatological inputs, including sunlight intensity. The only performance measure that differs significantly among these sites is water intensity, which is predicted to be much lower east of the Rockies due to higher precipitation rates. Several supporting analyses are also presented in the dissertation, including a comparison of the composition of microalgal and soy lipids, which addresses the assumption that conventional oilseed extraction and conversion technologies will be effective with microalgal biomass as a substrate. The mechanisms of oil extraction, and the effects of residual water on extraction efficiency, are explored in an attempt to optimize evaporation energy load and oil yield. The impact of ambient temperature and relative humidity, dryer operating conditions, and dryer control strategies, on the energy burden imposed by biomass drying, are evaluated. And a multi-parameter sensitivity analysis explores the effect of potential interdependencies among biomass growth rate, intracellular water content, and lipid fraction on the KPI's. Additional findings from this research include that microalgal properties affect virtually every step of the manufacturing process; TELCIM can be used to identify optimal strain characteristics for a given processing scheme. The bulk of the energy use and carbon dioxide emissions attributable to the cradle-to-gate manufacturing process occur within the biodiesel plant, but offsite emissions resulting from energy and raw material supply and transportation activities are not negligible. The main driver of Net Energy Return, carbon intensity and unit manufacturing cost is electricity usage, primarily for pumping fluids over long distances. Replacing evaporation losses can impose an enormous water burden, perhaps overwhelming local supplies, especially in the western United States. TELCIM is a deterministic model; for a given set of input data it returns a set of numerical outputs without any measures of uncertainty or error. Recommendations for future work include an uncertainty analysis involving Monte Carlo simulations. They also include enhancing TELCIM to perform life cycle assessments, by assigning specific fates to byproducts and gauging the environmental impacts of resource usages and pollutant emissions. TELCIM can be modified to simulate alternative manufacturing schemes, such as feeding the biogas produced in the digesters to the central power unit, using the algae ponds for secondary wastewater treatment, and separate growth stages in which biomass production and lipid production are alternately promoted. Finally, the case studies simulating alternative manufacturing sites can be enhanced by using local operating and capital cost structures, especially for those sites in the southeastern United States that appear to have a more acceptable water intensity.
Microalgae Cultivation for Biofuels Production explores the technological opportunities and challenges involved in producing economically competitive algal-derived biofuel. The book discusses efficient methods for cultivation, improvement of harvesting and lipid extraction techniques, optimization of conversion/production processes of fuels and co-products, the integration of microalgae biorefineries to several industries, environmental resilience by microalgae, and a techno-economic and lifecycle analysis of the production chain to gain maximum benefits from microalgae biorefineries. Provides an overview of the whole production chain of microalgal biofuels and other bioproducts Presents an analysis of the economic and sustainability aspects of the production chain Examines the integration of microalgae biorefineries into several industries
This comprehensive book details the most recent advances in the microalgae biological sciences and engineering technologies for biomass and biofuel production in order to meet the ongoing need for new and affordable sources of food, chemicals and energy for future generations. The chapters explore new microalgae cultivation techniques, including solid (biofilm) systems, and heterotrophic production methods, while also critically investigating topics such as combining wastewater as a source of nutrients, the effect of CO2 on growth, and converting biomass to methane through anaerobic digestion. The book highlights innovative bioproduct optimization and molecular genetic techniques, applications of genomics and metabolomics, and the genetic engineering of microalgae strains targeting biocrude production. The latest developments in microalgae harvesting and dewatering technologies, which combine biomass production with electricity generation, are presented, along with detailed techno-economic modeling. This extensive volume was written by respected experts in their fields and is intended for a wide audience of researchers and engineers.
Biofuels produced from agricultural starch, sugar and oil crops such as corn, sugarcane, and palm, or first-generation biofuels, are produced at commercial scales worldwide. Though most biofuels are produced with the intent to reduce greenhouse gas (GHG) emissions and fossil fuel dependency, these first-generation biofuels have increasingly been shown to be problematic; achieving little to no reduction in GHG emissions compared to their fossil fuel counterparts, competing with food and feed crops, and causing direct and indirect land use change. Second generation biofuel feedstocks, such as microalgae, are hoped to reduce or eliminate the drawbacks of first-generation feedstocks. This dissertation investigates the environmental impacts of biodiesel production from microalgae, with the main focus on primary energy requirements and life cycle GHG emissions. The dissertation includes a critical review of existing studies; a mass balance model of a simulated microalgae biodiesel production system; a detailed life cycle assessment (LCA) of the production system with a variety of technology options for each step of the production process; and a scenario analysis with alternative utilization scenarios for the primary co-product from the system, lipid-extracted algal biomass residual. In addition to assessing and informing technology choices and strategies for environmentally preferable pathways among current algal biodiesel technologies, this research also addresses an important methodological issue in LCA, co-product allocation, and proposes some possible solutions to reduce the uncertainty caused by this issue. Results of the critical review show that significant variation exists among existing LCA studies of algal biodiesel production, which arises from inconsistency in both parameter assumptions and methodological choices. Even after a meta-analysis was conducted, which corrected for some differences in scope and key assumptions, the reviewed studies show a large range in life cycle primary energy and GHG emissions; 0.2 to 8.6 MJ per MJ of algal biodiesel, and -30 to 320 g of CO2e per MJ of algal biodiesel. This range is so large that very little can be concluded regarding the potential for algal biodiesel to meet the goals of second-generation biofuels, and provides the motivation for development an independent and original model for algal biodiesel production. A mass balance model for an integrated algal oil and biogas system was developed to understand nutrient, water and carbon flows and identify recycling opportunities. The model showed that recycling growth media and recovering nutrients from residual algal biomass through anaerobic digestion can reduce the total demand for nitrogen (N) and phosphorus (P) by 66% and 35%, respectively. Freshwater and carbon dioxide requirements can also be reduced significantly under these conditions. The mass balance model provided the basis for developing a LCA model capable of incorporating multiple technology options and identifying preferable pathways. The LCA found the best performing scenario consists of normal nitrogen cultivation conditions (as opposed to nitrogen deficient conditions which can increase algal lipid content, but decrease overall productivity), a combination of bioflocculation and dissolved air flotation for harvesting algal cells from cultivation media, centrifugation for dewatering of separated algae, oil extraction from wet biomass using hexane solvent, transesterification of algal oil to biodiesel, and anaerobic digestion of biomass residual with the liquid digestate returning to cultivation ponds. This pathway results in a life cycle energy requirement and GHG emissions of 1.08 MJ and 73 g CO2-equivalent per MJ of biodiesel, with cultivation and oil extraction dominating energy use and emissions. This result suggests that current technologies can neither achieve a positive net energy return for algal biodiesel, nor achieve substantial reductions in CO2e emissions compared to petroleum diesel. A comparison between different scenarios for using the major co-product from algae biodiesel production, lipid-extracted algal biomass residual, suggests that utilizing the co-product within the production system for nutrient and energy recovery is preferable than utilizing it outside as animal feed from a life cycle perspective. A number of possible ways to allocate the environmental burdens between co-products were tested. Among them, system expansion and economic allocation return favorable results compared value-based allocation methods; however, there are still unsolved issues when applying system expansion, for example, current practices do not consider future market values in the context of a consequential LCA. This dissertation shows that the near-term performance of biodiesel derived from microalgae does not achieve the significant reductions in fossil energy dependence and GHG emissions hoped for from second-generation feedstocks. Furthermore, there is substantial uncertainty in technology performance and other key modeling parameters that could influence these findings. However, some promising, but still uncertain technologies, such as hydrothermal gasification, have the potential to achieve greater reduction in life cycle GHG emissions and energy consumption.
Microalgae-Based Biofuels and Bioproducts: From Feedstock Cultivation to End Products compiles contributions from authors from different areas and backgrounds who explore the cultivation and utilization of microalgae biomass for sustainable fuels and chemicals. With a strong focus in emerging industrial and large scale applications, the book summarizes the new achievements in recent years in this field by critically evaluating developments in the field of algal biotechnology, whilst taking into account sustainability issues and techno-economic parameters. It includes information on microalgae cultivation, harvesting, and conversion processes for the production of liquid and gaseous biofuels, such as biogas, bioethanol, biodiesel and biohydrogen. Microalgae biorefinery and biotechnology applications, including for pharmaceuticals, its use as food and feed, and value added bioproducts are also covered. This book’s comprehensive scope makes it an ideal reference for both early stage and consolidated researchers, engineers and graduate students in the algal field, especially in energy, chemical and environmental engineering, biotechnology, biology and agriculture. Presents the most current information on the uses and untapped potential of microalgae in the production of bio-based fuels and chemicals Critically reviews the state-of-the-art feedstock cultivation of biofuels and bioproducts mass production from microalgae, including intermediate stages, such as harvesting and extraction of specific compounds Includes topics in economics and sustainability of large-scale microalgae cultivation and conversion technologies
Microalgae are one of the most studied potential sources of biofuels and bioenergy. This book covers the key steps in the production of renewable biofuels from microalgae - strain selection, culture systems, inorganic carbon utilisation, lipid metabolism and quality, hydrogen production, genetic engineering, biomass harvesting, extraction. Greenhouse gas and techno-economic modelling are reviewed as is the 100 year history of microalgae as sources of biofuels and of commercial-scale microalgae culture. A summary of relevant basic standard methods used in the study of microalgae culture is provided. The book is intended for the expert and those starting work in the field.​
Biofuels made from algae are gaining attention as a domestic source of renewable fuel. However, with current technologies, scaling up production of algal biofuels to meet even 5 percent of U.S. transportation fuel needs could create unsustainable demands for energy, water, and nutrient resources. Continued research and development could yield innovations to address these challenges, but determining if algal biofuel is a viable fuel alternative will involve comparing the environmental, economic and social impacts of algal biofuel production and use to those associated with petroleum-based fuels and other fuel sources. Sustainable Development of Algal Biofuels was produced at the request of the U.S. Department of Energy.