• Energy Research

Due to significant lipid and carbohydrate production as well as other useful properties such as high production of useful biomolecular substrates (e.g., lipids) and the ability to grow using non-potable water sources, algae are being explored as a potential high-yield feedstock for biofuels production. In both natural and engineered systems, algae can be exposed to a variety of environmental conditions that affect growth rate and cellular composition. With respect to the latter, the amount of carbon fixed in lipids and carbohydrates (e.g., starch) is highly influenced by environmental factors and nutrient availability. Understanding synergistic interactions between multiple environmental variables and nutritional factors is required to develop sustainable high productivity bioalgae systems, which are essential for commercial biofuel production. This article reviews the effects of environmental factors (i.e., temperature, light and pH) and nutrient availability (e.g., carbon, nitrogen, phosphorus, potassium, and trace metals) as well as cross-interactions on the biochemical composition of algae with a special focus on carbon fixation and partitioning of carbon from a biofuels perspective.

Due to significant lipid and carbohydrate production as well as other useful properties such as high production of useful biomolecular substrates (e.g., lipids) and the ability to grow using non-potable water sources, algae are being explored as a potential high-yield feedstock for biofuels production. In both natural and engineered systems, algae can be exposed to a variety of environmental conditions that affect growth rate and cellular composition. With respect to the latter, the amount of carbon fixed in lipids and carbohydrates (e.g., starch) is highly influenced by environmental factors and nutrient availability. Understanding synergistic interactions between multiple environmental variables and nutritional factors is required to develop sustainable high productivity bioalgae systems, which are essential for commercial biofuel production. This article reviews the effects of environmental factors (i.e., temperature, light and pH) and nutrient availability (e.g., carbon, nitrogen, phosphorus, potassium, and trace metals) as well as cross-interactions on the biochemical composition of algae with a special focus on carbon fixation and partitioning of carbon from a biofuels perspective.

Meeting the goals set by the Energy Independence and Security Act requires evaluation of all potential feedstock sources including arid and semi-arid portions of the western United States (U.S.). The objective of this study was to assess the lignocellulosic feedstock potential in stream buffers of the inland Pacific Northwest. A 3-yr (2010–2012) experiment was conducted at two sites within each of the three precipitation zones (low, mid, and high). At each site, barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), alfalfa (Medicago sativa L., cultivar Ladak), tall wheatgrass (Agropyron elongatum Podp. cultivar Alkar) (TWG), and a mix of alfalfa and tall wheatgrass (MIX) were planted in a randomized complete block experimental design. Productivity followed precipitation; in the high and mid precipitation zones, the MIX and TWG treatments showed potential production of 3,079 ± 262 l ha−1 and 3,062 ± 235 l ha−1. Productivity in the low zone was inadequate or unreliable as a source of feedstocks. A geographic information system was then used to identify the area available for stream buffers with soil resources that matched the experimental results within each precipitation zone. In 3.7 × 106 ha of dryland cropland, 44 656 ha (1.5%) available within the mid and high precipitation zones is capable of producing 147 million liters of ethanol. This potential contribution is 0.3% of the lignocellulosic ethanol production expected by the year 2022. Though not a substantial contribution, the added benefit of producing energy for on-farm consumption might provide an additional incentive for landowners and managers to install conservation buffers.

Meeting the goals set by the Energy Independence and Security Act requires evaluation of all potential feedstock sources including arid and semi-arid portions of the western United States (U.S.). The objective of this study was to assess the lignocellulosic feedstock potential in stream buffers of the inland Pacific Northwest. A 3-yr (2010–2012) experiment was conducted at two sites within each of the three precipitation zones (low, mid, and high). At each site, barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), alfalfa (Medicago sativa L., cultivar Ladak), tall wheatgrass (Agropyron elongatum Podp. cultivar Alkar) (TWG), and a mix of alfalfa and tall wheatgrass (MIX) were planted in a randomized complete block experimental design. Productivity followed precipitation; in the high and mid precipitation zones, the MIX and TWG treatments showed potential production of 3,079 ± 262 l ha−1 and 3,062 ± 235 l ha−1. Productivity in the low zone was inadequate or unreliable as a source of feedstocks. A geographic information system was then used to identify the area available for stream buffers with soil resources that matched the experimental results within each precipitation zone. In 3.7 × 106 ha of dryland cropland, 44 656 ha (1.5%) available within the mid and high precipitation zones is capable of producing 147 million liters of ethanol. This potential contribution is 0.3% of the lignocellulosic ethanol production expected by the year 2022. Though not a substantial contribution, the added benefit of producing energy for on-farm consumption might provide an additional incentive for landowners and managers to install conservation buffers.

Algae production process is a key cost center in production of biofuels/bioproducts from microalgae. Decline in the growth of algae in outdoor ponds during non-optimal conditions is one of the hurdles for achieving consistently high algal production rates. An optimal controller can be used to overcome this limitation and provide reliable growth in outdoor conditions. A model predictive controller (MPC) was developed to optimize the algal growth, predicted by flux balance analysis, under natural disturbances, embedding within the cost function, the economic and environmental constraints associated with the process. The model, developed in MATLAB, was validated on a 30-L continuous algal culture under light, temperature and a combination of light and temperature disturbances. The MPC proved effective in minimization of a decrease in growth under these natural disturbances. The growth rates with MPC were observed to be 79-116% higher as compared to the non-MPC growth.

Algae production process is a key cost center in production of biofuels/bioproducts from microalgae. Decline in the growth of algae in outdoor ponds during non-optimal conditions is one of the hurdles for achieving consistently high algal production rates. An optimal controller can be used to overcome this limitation and provide reliable growth in outdoor conditions. A model predictive controller (MPC) was developed to optimize the algal growth, predicted by flux balance analysis, under natural disturbances, embedding within the cost function, the economic and environmental constraints associated with the process. The model, developed in MATLAB, was validated on a 30-L continuous algal culture under light, temperature and a combination of light and temperature disturbances. The MPC proved effective in minimization of a decrease in growth under these natural disturbances. The growth rates with MPC were observed to be 79-116% higher as compared to the non-MPC growth.

Bioethanol produced from the lignocellulosic feedstock is a potential alternative to fossil fuels in transportation sector and can help in reducing environmental burdens. Straw produced from perennial ryegrass (PR) and wheat is a non-food, cellulosic biomass resource available in abundance in the Pacific Northwest U.S. The aim of this study was to evaluate the economic viability and to estimate the energy use and greenhouse gas (GHG) emissions during life cycle of ethanol production from PR and wheat straw. Economic analysis of ethanol production on commercial scale was performed using engineering process model of ethanol production plant with processing capacity of 250 000 metric tons of feedstock/year, simulated in SuperPro designer. Ethanol yields for PR and wheat straw were estimated 250.7 and 316.2 l/dry metric ton biomass, respectively, with annual ethanol production capacity of 58.3 and 73.5 × 106 l, respectively. Corresponding production costs of ethanol from PR and wheat straw were projected to be $0.86 and $0.71/l ethanol. Energy and emissions were calculated per functional unit which was defined as 10 000 MJ of available energy in fuel at the pump. Fossil energies were calculated as 4282.9 and 2656.7 MJ to produce one functional unit of ethanol from PR and wheat straw, respectively. The GHG emissions during life cycle of ethanol production from PR and wheat straw were found to be 227.6% and 284.3% less than those produced for 10 000 MJ of gasoline. Results from sensitivity analysis indicated that there is a potential to reduce ethanol production cost by making technological improvements in pentose fermentation and enzyme production. The integrated economic and ecological assessment analyses are helpful in determining long-term sustainability of a product and can be used to drive energy policies in an environmentally sustainable direction.

Bioethanol produced from the lignocellulosic feedstock is a potential alternative to fossil fuels in transportation sector and can help in reducing environmental burdens. Straw produced from perennial ryegrass (PR) and wheat is a non-food, cellulosic biomass resource available in abundance in the Pacific Northwest U.S. The aim of this study was to evaluate the economic viability and to estimate the energy use and greenhouse gas (GHG) emissions during life cycle of ethanol production from PR and wheat straw. Economic analysis of ethanol production on commercial scale was performed using engineering process model of ethanol production plant with processing capacity of 250 000 metric tons of feedstock/year, simulated in SuperPro designer. Ethanol yields for PR and wheat straw were estimated 250.7 and 316.2 l/dry metric ton biomass, respectively, with annual ethanol production capacity of 58.3 and 73.5 × 106 l, respectively. Corresponding production costs of ethanol from PR and wheat straw were projected to be $0.86 and $0.71/l ethanol. Energy and emissions were calculated per functional unit which was defined as 10 000 MJ of available energy in fuel at the pump. Fossil energies were calculated as 4282.9 and 2656.7 MJ to produce one functional unit of ethanol from PR and wheat straw, respectively. The GHG emissions during life cycle of ethanol production from PR and wheat straw were found to be 227.6% and 284.3% less than those produced for 10 000 MJ of gasoline. Results from sensitivity analysis indicated that there is a potential to reduce ethanol production cost by making technological improvements in pentose fermentation and enzyme production. The integrated economic and ecological assessment analyses are helpful in determining long-term sustainability of a product and can be used to drive energy policies in an environmentally sustainable direction.