Microalgae are an attractive way to produce biofuels due to the ability to accumulate lipids and very high photosynthetic yields. This article presents a review of life-cycle assessment studies of microalgae biodiesel production, including an analysis of modeling choices and assumptions. A high variation in GHG emissions (between -0.75 and 2.9 kg CO2eq MJ-1) was found and the main causes were investigated, namely modeling choices (e.g. the approach used to deal with multifunctionality), and a high parameter uncertainty in microalgae cultivation, harvesting and oil extraction processes

Castanheira, Érica

Figueiredo, Filipa

Freire, Fausto

Garcia, Rita

Gonçalves, Margarida S.

Malça, João

Matos, Cristina T.

Oliveira, Ana Cristina

Repositório do LNEG

Energy for Sustainability 2015 Sustainable Cities: Designing for People and the Planet Coimbra, 14 and 15 May 2015 LIFE-CYCLE ASSESSMENT OF MICROALGAE BIODIESEL: A REVIEW Filipa Figueiredo1*, Rita Garcia1, Margarida S. Gonçalves3, Érica Castanheira1, João Malça1,2, Ana Cristina Oliveira3, Cristina T. Matos3, and Fausto Freire1 1: ADAI-LAETA, Dept. of Mechanical Engineering,  University of Coimbra Rua Luís Reis Santos, 3030-788 Coimbra, Portugal e-mail: filipa.figueiredo@dem.uc.pt, rita.garcia@dem.uc.pt, erica@dem.uc.pt, jmalca@dem.uc.pt, fausto.freire@dem.uc.pt web: http://www2.dem.uc.pt/CenterIndustrialEcology/  2: Dept. of Mechanical Engineering, ISEC, Coimbra Polytechnic Institute, Portugal Rua Pedro Nunes, 3030-199 Coimbra, Portugal web: http://www.isec.pt  3: Unidade de Bioenergia, Laboratório Nacional de Energia e Geologia IP, Estrada do Paço do Lumiar, 1649-038 Lisboa, Portugal  e-mail: margarida.goncalves@lneg.pt, cristina.oliveira@lneg.pt, cst.matos@gmail.com web: http://www.lneg.pt/ Keywords: Greenhouse gas emissions, open ponds, photobioreactor (PBR), dry extraction, wet extraction Abstract Microalgae are an attractive way to produce biofuels due to the ability to accumulate lipids and very high photosynthetic yields. This article presents a review of life-cycle assessment studies of microalgae biodiesel production, including an analysis of modeling choices and assumptions. A high variation in GHG emissions (between -0.75 and 2.9 kg CO2eq MJ-1) was found and the main causes were investigated, namely modeling choices (e.g. the approach used to deal with multifunctionality), and a high parameter uncertainty in microalgae cultivation, harvesting and oil extraction processes.                Filipa Figueiredo, Rita Garcia, Margarida S. Gonçalves, Érica Castanheira, João Malça, Ana Cristina Oliveira, Cristina T. Matos and Fausto Freire  2  1. INTRODUCTION  Microalgae have been investigated as a feedstock for biofuels due to fast growth, relatively high lipid content, and their growth is season independent [1]. Moreover, microalgae do not have to compete with food crops for arable land or other agricultural inputs [2], conversely to first generation biofuels [3, 4]. In spite of these advantages, a life-cycle assessment (LCA) is required to ensure that biodiesel produced from algal feedstock does not result in higher life-cycle impacts than fossil diesel and first generation biofuels. The main objective of this article is to present a comprehensive review of LCA studies published in recent years of biodiesel produced from microalgae. An assessment of important aspects, including modeling choices, was conducted to identify the main causes for the high variability of greenhouse gas (GHG) intensity.  2. LIFE-CYCLE CHAIN OF MICROALGAE BIODIESEL  The life-cycle stages of microalgae biodiesel production are shown in Figure 1. Microalgae biodiesel production is not yet clearly established, because technology is in its infancy and there are few commercial scale installations. Figure 1 shows available technologies for each life-cycle stage, as identified in the literature review. Figure 1. Life-cycle chain of microalgae biodiesel, including alternative technologies.  Cultivation of microalgae can be conducted in photobioreactors and/or open ponds. Possible growth media include: (i) fresh water with growth nutrients; (ii) marine water with growth nutrients; and (iii) wastewater. For harvesting, several technologies can be combined. Microalgae may be decanted and/or flocculated followed by a centrifugation or filtration step. Depending on the oil extraction technology, microalgae can also be dried. In the extraction step, oil can be extracted from the microalgae biomass with a solvent (through dry and wet extraction), with supercritical CO2 (dry extraction) or with hydrothermal liquefaction (wet extraction). Conversion into biodiesel can be made with a traditional transesterification reaction (the most common technology in the reviewed studies), or using more recent technologies like ultrasonication with direct transesterification or supercritical methanol (less common). Filipa Figueiredo, Rita Garcia, Margarida S. Gonçalves, Érica Castanheira, João Malça, Ana Cristina Oliveira, Cristina T. Matos and Fausto Freire  3 3. REVIEW OF MICROALGAE BIODIESEL LCA  An online search of articles published (since 2009) with LCA studies of microalgae with detailed information on the methodology, assumptions and data used was conducted. A total of more than 30 studies were assessed, of which a selection of 14 is presented in Table 1. The remaining studies have been excluded due to: lack of transparency and insufficient quantitative information; assessment of only one life-cycle stage of biodiesel production; or the use of wastewater as culture medium (microalgae from wastewater medium have low productivity and lipid content compared with microalgae grown under nitrogen-limited growth conditions). Discussion of results was only detailed for GHG emissions, since this was the only impact category common to all analyzed studies.  3.1. Geographical scope, system boundaries and functional unit The geographical scope of the majority of the reviewed studies was the USA (6 studies), 2 studies for the UK and 2 for China. Remaining studies were from Singapore, Israel, Colombia and Europe. Three alternative life-cycle approaches were adopted. Six out of 14 used a “well-to-gate” approach (ending at the gate of the biodiesel production plant). One study considered a “well-to-pump” approach, which is similar to the “well-to-gate” plus the biodiesel distribution step. Finally, seven studies considered a “well-to-wheels” boundary, also called in the literature “cradle-to-combustion” and “pond-to-wheels”, which includes combustion in a specific vehicle. The definition of the functional unit (FU) in biodiesel LCA depends on the scope and system boundary of the study [18]. The reviewed studies employed functional units based on energy or mass. Ten out of 14 considered 1 MJ or 10 MJ of biodiesel (measured in terms of the lower heating value). 3.3. Multifunctionality The reviewed studies used different approaches to deal with multifunctionality. Six out of 14 studies considered the system expansion method and expanded the system boundaries of microalgae biodiesel to include alternative functions for the co-products. The main alternative functions considered were the use of microalgae biomass for animal feed, fertilization, anaerobic digestion, and/or cogeneration (for electricity and heat production), and the use of glycerin by pharmaceutical industries, displacing fossil glycerin. Three of the revised studies considered different allocation methods: mass, energy and economic (market prices) allocation. Three studies considered a combination of the two described methods (system expansion and allocation) and one study performed a sensitivity analysis of different allocation methods. One study [8] attributed all impacts to the main product.  3.4. GHG emissions Figure 2 presents the GHG emissions reported in the revised studies. Well-to-Gate and Well-to-Wheels GHG emissions of fossil diesel are also shown (red lines), as reference. The GHG emissions of reviewed studies varied from -0.75 to 2.9 kg CO2eq MJ-1. Main causes for this were related to modeling choices (e.g. multifunctionality approach), and the high uncertainty related to the microalgae cultivation, harvesting and the oil extraction processes. Three studies [2, 12, 16] reported negative GHG emissions due to the multifunctionality approach used Filipa Figueiredo, Rita Garcia, Margarida S. Gonçalves, Érica Castanheira, João Malça, Ana Cristina Oliveira, Cristina T. Matos and Fausto Freire  4  (substitution approach) and the accounting of biogenic CO2 absorbed during microalgae growth. More than 50% of the GHG results reported in the microalgae biodiesel LCA studies (many studies included several scenarios) were higher than fossil diesel GHG emissions. Nevertheless, microalgae biodiesel production systems are very recent and technology developments are focused on finding higher production efficiencies. In this context, the reviewed studies present future scenarios with expected GHG emission reductions associated with microalgae biodiesel. The development of less energy-intensive technologies, e.g. for microalgae cultivation and harvesting steps, will provide a reduction of the associated fossil GHG emissions. Figure 2. GHG intensity of microalgae biodiesel. 4. CONCLUSIONS A review of recently published life-cycle assessment studies of microalgae biodiesel production was performed. A high variation in the GHG emissions was found among the various studiews (between -0.75 kg and 2.9 kg CO2eq MJ-1). Main causes for this variability were related to modeling choices and the high parameter uncertainty in microalgae cultivation, harvesting and oil extraction. Microalgae biodiesel production systems are very recent and the quest for the best production technologies is still undergoing. Future LCA studies should also be performed for commercial systems to better support the selection of the most environmentally benign production pathways.  Diesel (WtW)Diesel (WtG)-0,500,511,522,533,5kgCO2eq MJ-100,10,20,30,4kgCO2eq MJ-1Well-to-Wheels studiesWell-to-Gate studiesFilipa Figueiredo, Rita Garcia, Margarida S. Gonçalves, Érica Castanheira, João Malça, Ana Cristina Oliveira, Cristina T. Matos and Fausto Freire   5  Table 1. Review of life-cycle assessment studies of microalgae biodiesel production: relevant model choices and assumptions. Relevant choices and assumptions Hou et al. [5] Passel et al. [6] Brentner et al. [7] Khoo et al. [8] Batan et al. [9] Lardon et al. [10] Yanfen et al. [11] Geographical scale China Israel USA Singapore USA Europe China System boundary Well-to-Wheels (WtW) Well-to-Wheels (WtW) Well-to-Gate (WtG) Well-to-Gate (WtG) Well-to-Pump (WtP) Well-to-Wheels (WtW) Well-to-Wheels (WtW) Microalgae species n.d. Nannochloris and nannochloropsis Scenedesmus dimorphus Nannochloropsis Nannochloropsis Chlorella vulgaris Chlorella vulgaris Microalgae cultivation type OP OP OP and PBR PBR (inoculum) and OP PBR OP OP and PBR Functional unit 1 MJ 1 MJ 10 GJ 1 MJ 1 MJ 1MJ combusted 1000 kg biodiesel Lipid content (%) 45 50 25 25 50 37.9 40 Multifunctionality Mass and energy allocation Energy allocation and Substitution method Market allocation  with Substitution method All impacts attributed to the main product Substitution method Energy allocation Substitution method LCIA method CML 2001 n.d. CED, BEES n.d. IPCC CML 2001 n.d. IA categories ADP,GWP,OLD, POP, AP,EP,HTTP, FAETP, MAETP,TETP GWP, POCP, PM, WD, NER, NOx, SOx CED, GWP, WU, EP, LU ER, GWP NER, GWP ADP,AP,EP,GWP,OLD,HTP,MTP, LU, Ra, POP; CED GWP, AP, POF, NE, soot and ashes Extraction type Dry (hexane) Wet (hexane) Dry (hexane); Supercritical CO2; ultrasonication and  direct transesterification; supercritical methanol Dry (hexane) Dry (hexane) Dry and Wet (hexane) Dry (hexane) Harvesting type Flocculation Auto-flocculation and centrifugation Centrifugation/flocculation /chamber press filtration with drying or not Flocculation and centrifugation Flocculation, centrifugation, vacuum belt dryers or solar dryers Flocculation and drying or only flocculation Sedimentation, flocculation, centrifugation and heat drying      Filipa Figueiredo, Rita Garcia, Margarida S. Gonçalves, Érica Castanheira, João Malça, Ana Cristina Oliveira, Cristina T. Matos and Fausto Freire   6  Table 1. (Continued) Relevant choices and assumptions Stephenson et al. [12] Soh et al. [13] Adesanya et al. [2] Zaimes and Khanna. [14] Sills et al. [15] Pardo-Cardenas et al. [16] Zaimes and Khanna. [17] Geographical scale UK USA UK USA USA Colombia USA System boundary Well-to-Wheels (WtW) Well-to-Gate  (WtG) Well-to-wheels (WtW) Well-to-Gate (WtG) Well-to-Wheels (WtW) Well-to-Gate (WtG) Well-to-Gate  (WtG) Microalgae species Chlorella vulgaris Neochloris oleoabundans; Chlorella sorokiniana; Nannochloropsis oculata; Tetraselmis suecica Chlorella vulgaris n.d. n.d. Chlorella vulgaris Chlorella vulgaris Microalgae cultivation type PBR and OP Laboratorial scale (Erlenmeyer flasks) with Hybrid (PBR+OP) OP Hybrid (PBR+OP) OP OP Functional unit 1 t biodiesel 1 kg biodiesel 1 t biodiesel 1 MJ 1 MJ 1 MJ 1 MJ Lipid content (%) 40 18, 22, 19, 26, 9, 35, 2, 13 n.d. 25 n.d. 30 20-25 Multifunctionality Substitution method and Market price allocation Substitution method Substitution method Market and Energy allocation and system expansion Substitution method Energy allocation Substitution method LCIA method EDIP 2003 GREET* CML 2001 TRACI and CED Eco-Indicator 2002 EDP 2007 n.d. IA categories GWP and ER GWP, EP, CED GWP, ER and WF OLD, GWP, Smog, AP, EP, Carc. NCarc, Re, EcT, EU ED, ED and GWP GWP, AP, EP, POP, ODP, nRE-fossil GWP and ED Extraction type Dry (hexane) Dry (hexane) Dry (hexane) with two cell disrupting processes (mechanical  and enzymatic) Dry and Wet (hexane) Dry  (hexane) and wet (Hydrothermal liquefaction) extraction Dry (hexane, methanol/chloroform and ethanol/hexane) Dry and wet  (hexane) Harvesting type Flocculation and centrifugation Flocculation, Centrifugation and decanted Flocculation centrifugation Flocculation and  chamber filter press Autoflocculation, centrifugation or filter press Flocculation and thermal dryer Flocculation, centrifugation or chamber filter press *GREET is a life-cycle model; ADP: abiotic depletion potential; GWP: global warming potential; OLD: ozone layer depletion; POP: photochemical oxidation potential; AP: acidification potential; EP: eutrophication potential; HTTP: Human toxicity potential; FAETP: fresh water aquatic ecotoxicity potential; MAETP: marine aquatic ecotoxicity potential; TETP: terrestrial ecotoxicity potential; POF: photochemical ozone formation; PM: particulate matter; WD: water dep letion; NER: net energy ratio; CED: cumulative energy demand; WU: water use; LU: land use; ER: energy requirements; MTP: marine toxicity potential; Ra: radiation; NE: nutrient  enrichment; WF: water footprint; Car: carcinogens; NCar: non carcinogens; Re: Respiratory effects; EcT: ecotoxicity; EU: energy use; ED: energy demand; nRe-fossil: non renewable fossil; PBR: photobioreactor; OP: open pond; n.d.: not defined. Filipa Figueiredo, Rita Garcia, Érica Castanheira and Fausto Freire  8 ACKNOWLEDGMENTS This work was funded by FEDER funds through “Programa Operacional Factores de Competitividade” - COMPETE and by the Portuguese Science and Technology Foundation (FCT) projects FCOMP-01-0124-FEDER-029055 (PTDC/EMS-ENE/1839/2012) and FCOMP-01-0124-FEDER-021495 (PTDC/SEN-TRA/117251/2010), and is framed under the Energy for Sustainability Initiative of the University of Coimbra, Portugal, and the MIT-Portugal Program, and supported by the R&D project EMSURE (CENTRO-07-0224-FEDER-002004). REFERENCES [1] M.O.P. Fortier, W. G. Roberts, S. M. Stagg-Williams, B. S. M. Sturm, “Life cycle assessment of bio-jet fuel from hydrothermal liquefaction of microalgae”, Applied Energy, vol. 122, pp. 73–82, 2014.  [2] V. O. Adesanya, E. Cadena, S. A. Scott, A. G. Smith, “Life cycle assessment on microalgal biodiesel production using a hybrid cultivation system”, Bioresource Technology, vol. 163, pp. 343-355, 2014. [3] D. Tilman, R. Socolow, J.A. Foley, J. Hill, E. Larson, L. Lynd, S. Pacala, J. Reilly, T. Searchinger, C. Somerville, R. Williams “Beneficial biofuels—the food, energy, and environment trilemma”. Science, vol. 325 (5938) pp. 270-325, 2009. [4] S. Nonhebel,  “Global food supply and the impacts of increased use of biofuels” Energy, vol. 37(1), pp. 115-121, 2012. [5] J. Hou, P. Zhang, X. Yuan, Y. Zheng, “Life cycle assessment of biodiesel from soybean, jatropha and microalgae in China conditions”, Renewable and Sustainable Energy Reviews, vol. 15, pp. 5081-5091, 2011. [6] H. Passel, H. Dhaliwal, M. Reno, B, Wu, A. B.Amotz, E. Ivry, M. Gay, T. Czartoski, L. Laurin, N. Ayer, “Algae biodiesel life cycle assessment using current commercial data”, Journal of Environmental Management, vol. 129, pp. 108-111, 2013. [7] L. B. Brentner, M. J. Eckelman, J. B. Zimmerman, “Combinatorial Life Cycle Assessment to Inform Process Design of Industrial Production of Algal Biodiesel”, Environmental Science & Tecnology, vol. 45, pp. 7060-7067, 2011. [8] H. H. Khoo, P. N. Sharratt, P. Das, R. K. Balasubramanian, P. K. Naraharisetti, S. Shaik, “Life cycle energy and CO2 analysis of microalgae-to-biodiesel: Preliminary results and comparisons”, Bioresource Technology, vol. 102, pp. 5800-5807, 2011. [9] L. Batan, J, Quinn, B. Willson, T. Bradley, “Net energy and greenhouse gas emission evaluation of biodiesel derived from microalgae”, Environmental Science & Tecnology, vol. 44, pp. 7975-7980, 2010. [10] L. Lardon, A. Hélias, B. Sialve, J-P. Steyer, O. Bernard, “Life-Cycle Assessment of Biodiesel Production from Microalgae”, Environmental Science & Tecnology, vol. 43(17), pp. 6475-6481, 2009. [11] L. Yanfen, H. Zehao, M. Xiaoqian, “Energy analysis and environmental impacts of microalgal biodiesel in China”, Energy Policy, vol. 45, pp. 142-151, 2012. [12] A. L. Stephenson, E. Kazamia, J. S. Dennis, C. J. Howe, A. A. Scott, A. G. Smith, “Life-Cycle Assessment of Potential Algal Biodiesel Production in the United Kingdom: A Comparison of Raceways and Air-Lift Tubular Bioreactors” Energy Fuels, vol. 24, pp. 4062-4077, 2010. Filipa Figueiredo, Rita Garcia, Margarida S. Gonçalves, Érica Castanheira, João Malça, Ana Cristina Oliveira, Cristina T. Matos and Fausto Freire  8  [13] L. Soh, M. Montazeri, B. Z. Haznedaroglu, C. Kelly, J. Peccia, M. J. Eckelman, J. B. Zimmerman, “Evaluating microalgal integrated biorefinery schemes: Empirical controlled growth studies and life cycle assessment”, Bioresource Technology, vol. (151), pp. 19-27, 2014. [14] G. G. Zaimes, V. Khanna, “The role of allocation and coproducts in environmental evaluation of microalgal biofuels: How important?”, Sustainable Energy Technologies and Assessments, vol. 7, pp. 247-256, 2014 [15] D. L. Sills, V. Paramita, M. J. Franke, M. C. Johonson, T. M. Akabas, C. H. Greene, J. W. Tester, “Quantitative Uncertainty Analysis of Life Cycle Assessment for Algal Biofuel Production”, Environmental Science & Tecnology, vol. 47, pp. 687-694, 2013. [16] Y. Pardo-Cárdenas, I. Herrera-Orozco, Á-D. Gonzáles-Delgado, V. Kafarov, “Environmental assessment of microalgae biodiesel production in colombia: comparison of three oil extraction systems”, Journal Ciencia, Tecnología y Futuro, vol. 5(2), pp. 85-100, 2013. [17] G. G. Zaimes, V. Khanna, “Environmental Sustainability of Emerging Algal Biofuels: A Comparative Life Cycle Evaluation of Algal Biodiesel and Renewable Diesel”, Environmental Progress & Sustainable Energy, vol. 32 (4), pp. 926-936, 2013. 

Life-cycle assessment of microalgae biodiesel: a review

Oliveira, A. C.

Laboratório Nacional de Energia e Geologia Repository

http://repositorio.lneg.pt/bitstream/10400.9/3007/1/Figueiredo%20et%20al_2015_LCA%20microalgae%20biodiesel_A%20review.pdf

Life-cycle assessment of microalgae biodiesel: a review

Abstract

Similar works

Full text

Available Versions

Repositório do LNEG

Laboratório Nacional de Energia e Geologia Repository