A comparison of on-site nutrient and energy recycling technologies in algal oil production |
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| Institution: | 1. Institute of Transportation Studies, University of California, Davis, 1605 Tilia Street, Suite #100, Davis, CA 95616, USA;2. Department of Civil and Environmental Engineering, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA;1. Institute of Systems Sciences, Innovation and Sustainability Research, University of Graz, Merangasse 18/1, A-8010 Graz, Austria;2. Department of Forest and Soil Sciences, BOKU – University of Natural Resources and Life Sciences, Konrad-Lorenz-Strasse 24, A-3430 Tulln, Austria;1. Institute of Hydrobiology, Jinan University, Guangzhou 510632, China;2. Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Science and University of Maryland Baltimore County, Baltimore, MD 21202, United States;3. Arizona Center for Algal Technology and Innovation, Arizona State University, Mesa, AZ 85212, United States;4. Center for Microalgal Biotechnology and Biofuels, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China;1. Key Laboratory of Safety Science of Pressurized System (MOE), School of Mechanical Engineering, East China University of Science and Technology, Shanghai 200237, China;2. State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai 200237, China;3. School of Energy and Power Engineering, University of Shanghai for Science and Technology, Shanghai, China;4. School of Business Society and Technology, Mälardalen University, Västerås, Sweden;5. School of Chemical Science and Engineering, Royal Institute of Technology, Stockholm, Sweden;1. Hanoi University of Science (HUS), Vietnam National University, No. 19, Le Thanh Tong, Hoan Kiem, Hanoi, Viet Nam;2. Institute of Chemistry, Vietnam Academy of Science and Technology (VAST), A18 – No. 18 Hoang Quoc Viet, Cau Giay, Hanoi, Viet Nam;3. International Research Centre for River Basin Environment (ICRE), University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 400-8511, Japan |
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| Abstract: | Research on biofuel production pathways from algae continues because among other potential advantages they avoid key consequential effects of terrestrial oil crops, such as competition for cropland. However, the economics, energetic balance, and climate change emissions from algal biofuels pathways do not always show great potential, due in part to high fertilizer demand. Nutrient recycling from algal biomass residue is likely to be essential for reducing the environmental impacts and cost associated with algae-derived fuels. After a review of available technologies, anaerobic digestion (AD) and hydrothermal liquefaction (HTL) were selected and compared on their nutrient recycling and energy recovery potential for lipid-extracted algal biomass using the microalgae strain Scenedesmus dimorphus. For 1 kg (dry weight) of algae cultivated in an open raceway pond, 40.7 g N and 3.8 g P can be recycled through AD, while 26.0 g N and 6.8 g P can be recycled through HTL. In terms of energy production, 2.49 MJ heat and 2.61 MJ electricity are generated from AD biogas combustion to meet production system demands, while 3.30 MJ heat and 0.95 MJ electricity from HTL products are generated and used within the production system.Assuming recycled nutrient products from AD or HTL technologies displace demand for synthetic fertilizers, and energy products displace natural gas and electricity, the life cycle greenhouse gas reduction achieved by adding AD to the simulated algal oil production system is between 622 and 808 g carbon dioxide equivalent (CO2e)/kg biomass depending on substitution assumptions, while the life cycle GHG reduction achieved by HTL is between 513 and 535 g CO2e/kg biomass depending on substitution assumptions. Based on the effectiveness of nutrient recycling and energy recovery, as well as technology maturity, AD appears to perform better than HTL as a nutrient and energy recycling technology in algae oil production systems. |
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| Keywords: | Algae Anaerobic digestion Hydrothermal liquefaction Nitrogen Phosphorus GHG |
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