Browsing by Subject "Biofuel"

Now showing 1 - 7 of 7
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    Development of an effective swine manure-based algal cultivation system for biofuel & animal feed production and wastewater treatment
    (2013-03) Hu, Bing
    Microalgae have great potential to replace current crop feedstocks for biofuel and animal feed production. However, the algal industry is still far from being economically applicable. The dissertation was inspired by the idea of integrating algal biomass production and wastewater treatment. The overall objective of the study was to develop an effective algal cultivation system in which inorganic nutrients and organic substances in swine manure could be utilized by robust microalgae strains for the production of algal biomass with high lipids or protein contents. The first step in the study was bioprospecting for mixotrophic microalgae strains that adapted well to diluted swine manure. Through the multi-step screening strategy, two locally isolated microalgae strains, UMN271 and UMN266, were found to be facultative heterotrophic, manure-tolerant, and obviously robust in the algae storage including 98 UTEX strains and 50 indigenous strains. The two strains were identified as Chlorella sp. and Hindakia sp., respectively, through morphological observation and genetic identification, and were utilized for further studies in the dissertation. Since algae growth on highly diluted swine manure was still relatively low, a second step in the study was to assess the limiting factors of using anaerobically decomposed swine manure as nutrient supplement for algae cultivation. In the study, Chlorella sp. (UMN271) and Hindakia sp. (UMN266) were used to investigate the effects of two potential factors, which were trace elements and carbon compounds in swine manure, on algal growth and waste nutrient recovery. The results indicated that the algal growth and nutrient removal rates were independent of trace metal content in diluted swine manure, but were significantly improved when the initial liquid COD content in swine manure was high. Moreover, it was demonstrated that Chlorella sp. (UMN271) was able to utilize acetic, propionic and butyric acids, the main water-soluble organic carbon compounds in digested swine manure, for algal growth, lipid production, and waste nutrient removal. Therefore, it was considered that algal growth in highly diluted swine manure was limited by the deficiency of volatile fatty acids (VFAs). The third step was to modify anaerobic digestion process for liquid swine manure (LSM) rich in VFAs, so that the liquid effluent could be more suitable than the conventionally decomposed LSM effluent as nutrient for the cultivation of Chlorella sp. (UMN271). The results showed that the modified acidogenic digestion successfully promoted VFA concentrations in swine manure. The obtained acidogenically digested LSM supported the growth of Chlorella sp.(UMN271) in a 5-day batch experiment with higher algal growth rates and fatty acid contents in comparison with those on the conventionally decomposed LSM. High removal efficiencies on water-soluble nutrients, including COD, PO4-P, TN and NH3-N, were also observed for the raw, acidogenically digested manure sample (58.02%, 44.74%, 31.58%, and 44.73%, respectively). Finally, the fatty acid profile analysis showed that harvested algal biomass could be used as feedstock to produce high-quality biodiesel. In the fourth step, central composite design (CCD) was used to investigate the influences of two key parameters, namely wastewater dilution rate (DR) and hydraulic retention time (HRT), on algal biomass productivity and waste nutrient removal rates. According to the response surface analyses of the CCD results, statistically valid quadric models for the response variables, including algal biomass productivity and the liquid nutrient removal rates including COD, PO4-P, TN and NH3-N, were obtained. The regression analyses illustrated that both DR and HRT had significant influences on the five response variables. The optimal conditions estimated from the significant second-order quadratic models (p<0.05) were 8-fold DR and 2.26-d HRT. The final step was the development of an effective algal cultivation system for the semicontinuous production of algal biomass and waste nutrient removal. In the study, the predicted optimal conditions were applied in a bench-scale multi-layer photobioreactor (PBR) for algae growth on acidogenically digested swine manure. The 17-day semicontinuous cultivating experiment achieved high and stable algal productivity and nutrient removal rates, which fitted the predictive models well. Moreover, relatively high and stable protein and lipid contents (58.78% and 26.09% of the dry weight, respectively) were observed for the harvested algal sample, indicating the suitability of the algal biomass as ideal feedstock for both biofuel and animal feed production.
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    Effects of economy-wide factors on Brazilian economic growth and biofuels production: an inter-temporal general equilibrium analysis.
    (2011-02) Pinto, Cristina Vinyes
    Disenchantment with the Washington Consensus has led to an emphasis on growth diagnostics. In the case of Brazil, the literature suggests three main factors impeding growth: low domestic savings, a shortage of skilled workers, and a lack of investment in the country's transportation infrastructure. The unique contribution of this study is to show the inter-temporal implications of relaxing these constraints. We fit a multi-sector Ramsey model to Brazilian data, validate its fit to times data, and provide empirical insights into the economy's structural transformation to long-run equilibrium. Then, the sensitivity of these results to relaxing each of these three constraints is investigated in a manner that yields the same long-run level of wellbeing. Analytical concepts adapted from static trade theory are used to provide a detailed explanation of how the economy responds in transition growth to the relaxation of these impediments. Addressing these factors clearly benefits the economy, but they do not launch the economy to a substantially higher growth path. In order to enhance energy security and independence, Brazil has supported the production and use of ethanol. Brazil's leadership in this market reveals complex inter-linkages between ethanol, sugarcane, sugar and fossil fuels. These sectors have been growing an average of 14% per year, while the country's growth rates have been very modest. This paper presents a theoretical framework for understanding the interaction between Brazil's economic growth and the evolution of these sectors as the economy transitions toward long-run equilibrium. Then, the sensitivity of these results is analyzed under two simulations; first, a reduction of the cost of financial intermediation (which the literature identifies as one of the factors affecting Brazil's growth), and second, an increase in ethanol prices by 2.6%, based on the expectation that biofuels' world demand is increasing.
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    Entomological considerations for domestication of pennycress, Thlaspi arvense, as a cash cover crop
    (2024-09) Adjeiwaa, Ellen
    Pennycress (Thlaspi arvense L.), a common annual weed in temperate regions, is being domesticated as a winter cover crop and oilseed crop for the Midwest U.S. corn-soybean rotation. This domestication presents significant agricultural and environmental benefits; however, understanding of the interactions between pennycress and insect herbivore communities and agroecosystems remains limited. This research aimed to fill these knowledge gaps and support the development of integrated pest management (IPM) programs for this emerging crop.First, a comprehensive review was conducted to compile available information on the insect herbivores, natural enemies, and pollinators associated with pennycress, as well as its response to stressors such as defoliation, stem injury, and stand loss. The review highlighted the need for further research to develop effective IPM strategies. Second, field experiments were conducted over two years to assess the impact of artificial defoliation on pennycress biomass, yield components, and oil and protein content. The experiments, which tested various defoliation levels and timings, revealed that significant reductions in biomass, yield and protein content occurred, particularly during critical growth stages such as the rosette and flowering periods. These findings emphasize the importance of timing in managing defoliation to minimize crop loss. Finally, field experiments were performed to evaluate the impact of relay-cropping soybean with pennycress on soybean aphid populations. Across four site-years in Minnesota with relatively low levels of soybean aphid infestation, relay-cropping soybean with pennycress generally reduced soybean aphid densities compared to soybean without pennycress. This suggests that pennycress could serve as a sustainable pest management tool in soybean production, while also enhancing other aspects of economic and environmental sustainability of the corn-soybean rotation system.
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    Fast microwave-assisted thermochemical conversion of biomass for biofuel production
    (2015-12) Xie, Qinglong
    Concerns about diminishing fossil fuels and increasing greenhouse gas emissions are driving many countries to develop renewable energy sources. In this respect, biomass provides a carbon-neutral and sustainable solution. Pyrolysis and gasification belong to thermochemical processes which are currently the most appropriate and widely used among all the biomass utilization technologies. Microwave irradiation can provide heating for biomass pyrolysis and gasification, and has many advantages over conventional heating methods. In this dissertation, microwave heating was used in biomass pyrolysis and gasification for the production of bio-oil and syngas, respectively. In addition, in order to utilize the syngas produced, a single-step process was investigated for converting syngas to dimethyl ether (DME) on various bifunctional catalysts. In Chapter 2, the microwave heating characteristics of various biomass feedstocks and microwave absorbents were examined and compared. Experimental results show that microwave absorbents absorbed the microwave irradiation more effectively than biomass. The addition of these microwave absorbents to biomass feedstock during microwave-assisted thermochemical conversion significantly improved the heating characteristics. Among the three microwave absorbents studied, silicon carbide (SiC) exhibited higher microwave absorbing ability than activated carbon (AC) and graphite (GE), which was mainly attributed to a higher dielectric loss tangent (tan ) value of silicon carbide. In addition, higher microwave absorbing ability and heating rates were achieved when more microwave absorbents were used. Finally, a fast microwave-assisted biomass conversion system was developed. In Chapter 3, fast microwave-assisted catalytic co-pyrolysis of microalgae and scum on HZSM-5 catalyst for bio-oil production was investigated. The effects of co-pyrolysis temperature, catalyst to feed ratio, and microalgae to scum ratio on bio-oil yield and composition were examined. Experimental results show that temperature had great influence on the co-pyrolysis process. The optimal temperature was 550 ºC since the maximum bio-oil yield and highest proportion of aromatic hydrocarbons in the bio-oil were obtained at this temperature. The bio-oil yield decreased when catalyst was used, but the production of aromatic hydrocarbons was significantly promoted when the catalyst to feed ratio increased from 1:1 to 2:1. Co-feeding of scum improved the bio-oil and aromatics production, with the optimal microalgae to scum ratio being 1:2 from the perspective of bio-oil quality. The synergistic effect between microalgae and scum during the co-pyrolysis process became significant only when the effective hydrogen index (EHI) of feedstock was larger than about 0.7. In addition, to better understand the fMAP of microalgae, the different roles of three major components, i.e., carbohydrates, proteins, and lipids, were investigated. Cellulose, egg whites, and canola oil were employed as the model compounds of the three components, respectively. Non-catalytic and catalytic fMAP were carried out to identify and quantify some major products, and several reaction pathways were proposed for the pyrolysis of each model compound based on the data obtained. Moreover, a two-step process of microalgae pyrolysis and downstream catalytic reforming was conducted and compared with the one-step process for bio-oil production. The results show that a lower bio-oil yield and higher bio-oil quality were achieved for the two-step process than the one-step process at the same catalyst to feed ratio. The main advantages of the two-step process lie in catalyst saving and reuse. Furthermore, fast microwave-assisted catalytic pyrolysis of sewage sludge was investigated for bio-oil production, with HZSM-5 as the catalyst. Pyrolysis temperature and catalyst to feed ratio were examined for their effects on bio-oil yield and composition. Experimental results show that microwave is an effective heating method for sewage sludge pyrolysis. Temperature has great influence on the pyrolysis process. The maximum bio-oil yield and the lowest proportions of oxygen- and nitrogen-containing compounds in the bio-oil were obtained at 550 oC. The oil yield decreased when catalyst was used, but the proportions of oxygen- and nitrogen-containing compounds were significantly reduced when the catalyst to feed ratio increased from 1:1 to 2:1. Essential mineral elements were concentrated in the biochar after pyrolysis, which could be used as a soil amendment in place of fertilizer. Results of XRD analyses demonstrated that HZSM-5 catalyst exhibited good stability during the microwave-assisted pyrolysis of sewage sludge. In Chapter 4, the microwave-assisted biomass conversion system developed in Chapter 2 was used in corn stover gasification for syngas production. Three catalysts including Fe, Co and Ni with Al2O3 support were examined and compared for their effects on syngas production and tar removal. Experimental results show that microwave is an effective heating method for biomass gasification. Ni/Al2O3 was found to be the most effective catalyst for syngas production and tar removal. The gas yield reached above 80% and the composition of tar was the simplest when Ni/Al2O3 catalyst was used. The optimal catalyst to biomass ratio was determined to be 1:5–1:3. The addition of steam was found to be able to improve the gas production and syngas quality. Results of XRD analyses demonstrate that Ni/Al2O3 catalyst had good stability during gasification process. Finally, a new concept of microwave-assisted dual fluidized bed gasifier was put forward for the first time in all studies in the literature. To further utilize the syngas produced from biomass gasification, single-step synthesis of DME from syngas on bifunctional catalysts containing Cu-ZnO-Al2O3 and seven different zeolites was investigated in Chapter 5. Various characterization techniques were used to determine the structure, reducibility, and surface acidity of the catalysts. Experimental results show that the zeolite type had great influence on the activity, selectivity and stability of the bifunctional catalyst during the syngas-to-DME process. Zeolite properties including density of weak and strong acid sites, pore structure, and Si/Al distribution were found to affect the CO conversion and DME selectivity of the bifunctional catalyst. In addition, the deactivation of the bifunctional catalyst could be attributed to the sintering of metallic Cu and a loss of the zeolite dehydration activity. In summary, microwave irradiation is an effective heating method for biomass thermochemical conversion for biofuel production. Fast microwave-assisted biomass pyrolysis and gasification, using silicon carbide as the microwave absorbent, were carried out for the production of bio-oil and syngas, respectively. In addition, single-step synthesis of DME from syngas on various bifunctional catalysts was conducted with the aim of fully utilizing the syngas produced from biomass gasification. Although there are still many challenges associated with the production of biofuels via fast microwave-assisted thermochemical conversion, this dissertation offers a valuable insight into the potential of and some basic mechanisms of the technology.
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    Microalgal swimming in fluid environments: experimental and numerical investigations
    (2013-09) Chengala, Ahammed Anwar
    The objective of this research was to examine the effects of small-scale fluid motion on the kinetic behavior and some key physiological aspects of Dunaliella primolecta Butcher (D. primolecta / Dunaliella). D. primolecta, a fast growing microalga, is a promising organism for alternative energy production because of its capability to accumulate significant amount of "lipids", a major prerequisite for commercial production of microalgal oil-derived biofuel. For kinetic response studies of Dunaliella, flow visualization and quantification techniques such as Particle Image Velocimetry (PIV) and Digital Holographic microscopy were employed. The two-dimensional PIV results showed that Dunaliella were influenced by the fluid flow as soon as the local (or ambient) flow velocities surrounding the cells exceeded the individual (flow subtracted) swimming velocity of Dunaliella. Further inspection of the swimming characteristics of Dunaliella under shear flow in a three-dimensional holography revealed that Dunaliella preferred to swim cross-stream (i.e. also the direction of local vorticity) when the shear flow exceeded a critical value, and this resulted in Dunaliella dispersing in a thin two-dimensional horizontal layer. The cell body rotation was absent during this display in shear flow, although the cell body rotation was evident while swimming in stagnant fluid. A physical model was developed that provided a possible explanation for the cell orienting and swimming in the cross-stream direction in a shear flow while cell body remained irrotational. The experimental swimming data also showed good agreement with the computational results. In order to investigate the biochemical composition and some physiological aspects in Dunaliella under different flow conditions, a laboratory bioreactor equipped with speakers was utilized. The fluid flow velocities in the proximity of the cells generated by the speaker bioreactor are observable in natural water ecosystems. The results showed that the flow condition with the highest turbulence investigated favored the growth and lipid accumulation in Dunaliella.
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    Spatial Quantification of the Gap between Farm Field and University Trial Maize Yields in the United States
    (2015-08) Forland, Christine
    Greater crop production will be required to support both an increase in biofuel use and a forecasted doubling of global food demand by 2050. An improved understanding of yield potential and realistic estimates of the magnitude and spatial variability of the gap between actual yield and yield potentials are critical to achieving maximum crop production. This study examines near-term yield potentials and gaps of maize (Zea mays L.) yield data over the years of 2006 to 2011 from two sources: university crop variety trials and the United States Department of Agriculture yield surveys. Yield potentials are analyzed across 32 states through a compiled database of 129,499 trial maize hybrid entries. From the database, 1,102 direct, irrigation-specific, year-to-year, county-to-county yield comparisons are made across 27 states. These 32 and 27 states comprise nearly all United States maize production—99% and 97%, respectively. Trial yield is calculated as the 90th percentile of hybrid yields in a given county in a given year, and farm yield is the USDA-reported county-level yield in that same trial-performing county in that same year. Analysis of the median yield gap values in each state shows a yield gap of 13% to 53% in rainfed maize and a yield gap of 16% to 39% in irrigated maize. The magnitude of these differences between farming and trial yields indicates that maize yields in the United States, particularly rainfed, have considerable room for improvement. Additionally, the 40% range of median rainfed yield gap values and the 23% range of median irrigated yield gap values suggest that the yield gap varies greatly between states. The results of this study are expected to support the production of more accurate biofuel crop projections and identify where yields might be increased, thereby avoiding further land conversion to cropland while reaching the goal of increasing biofuel production and sustaining ample food production.
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    Thermochemical conversion of microalgae for biofuel production
    (2013-02) Du, Zhenyi
    Concerns about diminishing fossil fuels and increasing greenhouse gas emissions are driving many countries to develop renewable energy sources. In this respect, biomass may provide a carbon-neutral and sustainable solution. Microalgae have received growing interest recently because of their high productivity, high oil content and the ability to grow in a wide range of climates and lands. Pyrolysis is a thermochemical process in which biomass is thermally decomposed to a liquid product known as bio-oil. In this dissertation, pyrolysis and hydrothermal conversion techniques were applied to microalgae for biofuel production and an integrated algae-based biorefinery was proposed which includes algal biomass production, hydrothermal pretreatment, catalytic pyrolysis of microalgae into biofuels, and recycling of the wastewater from conversion as low-cost nutrient source for algae cultivation. In Chapter 3, Microwave-assisted pyrolysis (MAP) of Chlorella sp. was carried out with char as microwave reception enhancer. The results indicated that the maximum biooil yield of 28.6% was achieved under the microwave power of 750 W. The bio-oil properties were characterized with elemental, gas chromatography-mass spectrometry (GC-MS), gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric (TG) analysis. The algal bio-oil had a density of 0.98 kg/L, a viscosity of 61.2 cSt, and a higher heating value (HHV) of 30.7 MJ/kg. The GC-MS results showed that the bio-oils were mainly composed of aliphatic hydrocarbons, aromatic hydrocarbons, phenols, long chain fatty acids and nitrogenated compounds, among which aliphatic and aromatic hydrocarbons (account for 22.18 % of the total GC-MS spectrum area) are highly desirable compounds as those in crude oil, iii gasoline and diesel. The results indicate that fast growing algae are a promising source of feedstock for advanced renewable fuels production via MAP. To further elucidate the pyrolysis mechanism of microalgae, the different roles of three major components (carbohydrates, proteins, and lipids) in microalgae were investigated on a pyroprobe. In Chapter 4, cellulose, egg whites, and canola oil were employed as the model compounds of the three components, respectively. Non-catalytic pyrolysis was used to identify and quantify some major products and several pyrolysis pathways of algal biomass were also postulated by analysis and identification of pyrolysis products from the model compounds. Algal bio-oil contains oxygenates and nitrogenates which can lower the heating values and lead to NOx emissions, and thus upgrading processes towards reducing nitrogen and oxygen are necessary. Catalytic pyrolysis was then carried out with HZSM-5 for the production of aromatic hydrocarbons at different temperatures and catalyst to feed ratios. The aromatic yields of all feedstocks were significantly improved when the catalyst to biomass ratio increased from 1:1 to 5:1. Egg whites had the lowest aromatic yield among the model compounds under all reaction conditions, which suggests that proteins can hardly be converted to aromatics with HZSM-5. Lipids, although only accounted for 12.33% of Chlorella, contributed about 40% of aromatic production from algal biomass. Based on the preliminary catalytic pyrolysis results, a detailed catalyst screening study was carrier out to evaluate the performance of different zeolites for the production of aromatic hydrocarbons in Chapter 5. Three zeolites with different crystal structures (H-Y, H-Beta and H-ZSM5) were used to study the effect of catalyst type on the aromatic yield. All three catalysts significantly increased the aromatic yields from pyrolysis of microalgae and egg whites compared with non-catalytic runs, and H-ZSM5 was most effective with a yield of 18.13%. Three H-ZSM5 with silica-to-alumina (Si/Al) ratios of 30, 80 and 280 were used to study the effect of Si/Al ratio on the aromatic yield. The maximum yield was achieved at the Si/Al ratio of 80, which provides moderate acidity to achieve high aromatic production and reduce coke formation simultaneously. Aromatic production increased with the incorporation of copper or gallium to HZSM-5. However, other metals studied either had no significant influence or led to a lower aromatic yield. Based on the results in Chapter 4 and Chapter 5, nitrogenates are very resistant to catalytic conversion and the aromatic hydrocarbon yield from proteins was the lowest among the three major components of microalgae. However, since nitrogen is an essential element for algal growth, recycling of this nutrient will be important to achieving sustainable algal feedstock production. Therefore, hydrothermal pretreatment (HP) was employed to reduce the nitrogen content in Nannochloropsis oculata feedstock by hydrolyzing proteins without requiring significant energy inputs. The effects of reaction conditions on the yield and composition of pretreated algae were investigated by varying the temperature (150−225 °C) and reaction time (10−60 min). Compared with untreated algae, pretreated samples had higher carbon contents and enhanced heating values under all reaction conditions and 6−42% lower nitrogen contents at 200 °C−225 °C for 30−60 min. The pyrolytic bio-oil from pretreated algae contained less nitrogen-containing compounds than that from untreated samples. The bio-oil contained mainly (44.9% GCMS peak area) long-chain fatty acids (C14−C18) which can be more readily converted into hydrocarbon fuels in the presence of simple catalysts. Additionally, the feasibility of using recovered nutrients from HP for cultivation of microalga Chlorella vulgaris was v investigated. Different dilution multiples of 50, 100 and 200 were applied to the recycled process water from HP and algal growth was compared among these media and a standard growth medium BG-11. Algae achieved a biomass concentration of 0.79 g/L on 50× process water after 4 days. Algae removed total nitrogen, total phosphorus and chemical oxygen demand by 45.5-59.9%, 85.8-94.6% and 50.0-60.9%, respectively, on different diluted process waters. The fatty acid methyl ester yields for algae grown on the process water were 11.2% (50×), 11.2% (100×) and 9.7% (200×), which were significantly higher than 4.5% for BG-11 grown algae. In addition, algae cultivated on process water had 18.9% higher carbon and 7.8% lower nitrogen contents than those on BG-11, indicating that they are very suitable as biofuel feedstocks. In summary, HP is a low cost and efficient way to reduce the nitrogen content in microalgae without significant energy inputs. The recovered aqueous nutrients from HP can be recycled for algal cultivation. Pretreated microalgae were very hydrophobic with reduced nitrogen content and retained 73 to 99% lipids of the starting microalgae. These lipids can be easily converted into hydrocarbon fuels in the presence of simple catalysts, such as HZSM5 zeolite.