Elsevier

Algal Research

Volume 23, April 2017, Pages 1-11
Algal Research

Life cycle analysis of a large-scale limonene production facility utilizing filamentous N2-fixing cyanobacteria

https://doi.org/10.1016/j.algal.2017.01.001Get rights and content

Highlights

  • Life cycle analysis was conducted on a hypothetical limonene production facility.

  • Limonene was produced from genetically engineered Anabaena sp. PCC 7120.

  • Higher limonene productivities worsen the environmental profile of the facility.

  • This limonene facility is a promising sustainable solution for biofuels production.

Abstract

Due to the adverse effects of fossil fuel use, it is becoming increasingly important to produce next-generation biofuels from renewable, sustainable sources. Filamentous N2-fixing strains of cyanobacteria have emerged as promising industrial microorganisms capable of producing a range biofuels and chemicals using CO2, water, and sunlight. In this study, a life cycle analysis (LCA) was conducted on a hypothetical production facility that uses a genetically engineered strain of filamentous cyanobacteria to produce the cyclic hydrocarbon limonene. Two scenarios were evaluated in which the only difference between the scenarios was the limonene productivity of the engineered cyanobacteria strain. In Scenario 1, the cyanobacterium was assumed to produce limonene at a rate of 1.8 mg/L/h, resulting in an annual production of 32,727 L/yr of limonene. In Scenario 2, limonene productivity was 55.5 mg/L/h, resulting in annual production of 1,000,000 L/yr. Both scenarios were assumed to produce the same amount of cellular biomass, that was converted to biogas by anaerobic digestion and the biogas was converted by gas turbines into electricity to power the facility. Excess electricity was assumed to be sold to the grid. The major environmental burdens of the facility, which were measured in eco-points and calculated based on the Eco-indicator 99 method, were the cyanobacteria nutrient supply (especially sodium nitrate) and the photobioreactor (PBR) electrical requirements. The lower output of limonene in Scenario 1 meant that less energy was required for product recovery, leaving more electricity for sale to the grid. Even though a higher limonene productivity will worsen the environmental profile of the process, both scenarios described in this study have less of a negative environmental impact than biodiesel production. This study strongly suggests both scenarios of the theoretical limonene production facility described herein holds great potential as a future solution for producing next-generation biofuels directly from solar energy.

Introduction

Developing renewable, sustainable sources of biofuels is necessary to decrease the environmental burden created by the extensive use of fossil fuels. Fossil fuel reserves are finite and the adverse effects of fossil fuel-generated greenhouse gases are well established [1], [2], [3]. Biofuels can be categorized based on the type of feedstock used and/or the type of fuel produced. Each new generation of biofuel has been developed to overcome limitations or disadvantages of prior generations. This categorization has led to 4 generations of biofuels being defined [4]. While each biofuel type has its own advantages and disadvantages, together they have begun to decrease the burden of global fossil fuel consumption.

First generation biofuels were developed in the 1970s and 80s and consist of either: 1) ethanol produced via fermentation of sugar (primarily from sugar cane) or hydrolyzed starch (primarily from corn), or 2) biodiesel produced via trans-esterification of vegetable oil (primarily soybean oil or animal fats). The fuel ethanol process is well established and consists of feedstock pretreatment (milling, crushing, and solubilizing in water), saccharification (converting starch into sugars for the corn ethanol process), fermentation, distillation, and co-product recovery [5], [6]. First generation biofuels have three major disadvantages: production costs, market access, and competition for arable land with food crops. Because 1st generation biofuel feedstocks are also used for food, the feedstock usually accounts for more than 33% of total production costs, and this situation is unlikely to change as the world population and food demand continue to rise [7]. Second generation biofuels are typically defined as ethanol or other biofuels produced from lignocellulosic biomass, and includes a diverse range of by-products, wastes, and dedicated feedstocks [8]. The sustainability of 2nd generation biofuels is limited by land availability and competition for land use [9], [10], [11], [12]

Due to the drawbacks associated with 1st and 2nd generation biofuels, 3rd and 4th generation biofuels have been developed. These are fuels derived from the fixation of CO2 by photosynthetic algae and cyanobacteria [13], where the photosynthetic organism serves as both the photocatalyst and producer of biofuel [14]. At this time, algae and cyanobacteria appear to be the only sources of biofuel capable of meeting the global demand for transportation fuel [15], [16], [17], [18]. While algal oil can potentially be used directly as a fuel, in most cases the oil is subsequently processed through traditional oil refinery or biodiesel technologies into biofuels [19], [20], [21]. Therefore, many researchers now suggest that the definition of 3rd generation biofuels be altered to photoautotrophic conversion of CO2 into oil or algal biomass that is subsequently converted into biofuels [22]. This conversion step is a limitation to 3rd generation biofuels that does not exist with 4th generation biofuels. Fourth generation biofuel is the term used for the production of ‘drop-in’ biofuels directly from genetically engineered algae or cyanobacteria [19], [20], [21]. The benefit of using drop-in biofuels is that they can be mixed with crude derivatives without the need to develop new fuel infrastructures [23].

Heterocyst-forming filamentous cyanobacteria have the ability to fix atmospheric nitrogen, meaning that the cultivation medium does not need a combined nitrogen source, which is a considerable expense. This is one of the reasons that industrial microbiologists have focused on engineering filamentous N2-fixing cyanobacteria to produce next-generation biofuels and high-value chemicals [24], including limonene [25], farnesene [26], myrcene [27], and linalool [28].

The biofuel producing strain of filamentous cyanobacteria evaluated in this study was previously described by Halfmann et al., [25]. In that study, a genetically engineered Anabaena sp. PCC 7120 (herein referred to as LimS-DXP Anabaena) produced limonene (Fig. 1) photosynthetically and it was postulated that this strain could be used for the large-scale production of limonene as a next-generation biofuel. However, production would need to be increased substantially before an economically feasible process could be achieved. Previously, our research group [29] performed an economic feasibility analysis on a theoretical limonene production facility which used the genetically engineered filamentous cyanobacteria as the limonene producer. This study showed that an economically feasible process is currently not possible due to the low limonene productivity of the cyanobacterial strain. However, if productivity was increased, an economically feasible process would be possible. Data from the Halfmann et al., [25] study and our previous study are [29] were used as the basis for substantial parts of this LCA study.

The aim of this study was to evaluate the environmental profile of a hypothetical, next-generation biofuel production facility that uses genetically engineered cyanobacteria to produce limonene [29]. To evaluate the environmental profile of the theoretical production facility, an LCA was conducted. LCA is a method commonly used to evaluated the environmental impacts of a process by quantifying resource demands, energy demands, and the resulting emissions [30]. LCAs have been commonly used to evaluate environmental profiles of algal and cyanobacterial chemical production facilities [30], [31], [32]. In this study, a cradle-to-gate strategy was applied to define the systems boundaries. Scenario 1 was defined based on a hypothetical production facility described by Johnson et al., in which 32,727 L/yr limonene was produced [29]. Scenario 2 was based on a hypothetical facility described by Halfmann et al., that produced 1,000,000 L/yr of limonene [25]. The only difference between Scenario 1 and Scenario 2 was the total annual limonene production, due to different limonene productivities of the engineered cyanobacteria. The environmental profiles of both scenarios were then compared to the conventional production of fossil-based diesel environmental profile. The goal of this study was to provide evidence as to what the expected environmental effect of increased limonene production by the theoretical facility described below will be. Minimizing the negative environmental impact of this facility while maintaining economic feasibility will be essential.

Section snippets

Production system overview

A process flow diagram of the limonene production process is shown in Fig. 2, while Table 1 lists process inputs and parameters for both scenarios. The process includes photobioreactors (PBRs), clean-in-place units (CIPs), a Limonene Recovery Unit, a biomass harvesting unit, an anaerobic digestion (AD) unit, and a wastewater treatment unit [33], [34], [35], [36]. The system requires a CO2 supply as both the primary carbon source for cyanobacteria (sodium bicarbonate from BG-11 also provides

Overall energetic analysis

Table 3 summarizes the overall energy demand for unit processes, co-product allocations, and net energy demand per FU of limonene. Overall energetics of the process can be described as total energy input, net energy input, net energy balance, and net energy ratio as described below:Total energy=Sub‐process energy inputsNetenergy input=Total energy inputbyproduct allocationsNetenergy balance=Netenergy inputenergy inFUof main productNetenergy ratio=Netenergy input/energy inFUof main product

Conclusions

The life cycle analysis described in this study showed that production of limonene by genetically engineered filamentous cyanobacteria is less energy intensive than both fossil fuel based diesel and 3rd generation biodiesel production. Algal biodiesel production is more energy intensive due to the additional steps of drying biomass, separation of lipids, and conversion of lipids into biodiesel. Scenario 1 was found to be more environmentally friendly compared to Scenario 2 because Scenario 1

Declaration of contributions

All authors of this manuscript were involved in the conception and design of the study, acquisition and interpretation of data, and drafting the article and revising it critically.

Acknowledgements

This work was supported by the South Dakota Agricultural Experiment Station under grant [SD00H398-11], by NASA under award [NNX11AM03A], and by the US Department of Energy through contract [DE-EE0003046] to the National Alliance for Advanced Biofuels and Bioproducts (NAABB) and Texas A&M Agrilife Research Hatch (6806).

References (89)

  • P. Lindberg et al.

    Engineering a platform for photosynthetic isoprene production in cyanobacteria, using Synechocystis as the model organism

    Metab. Eng.

    (2010)
  • L. Brennan et al.

    Biofuels from microalgae—a review of technologies for production, processing, and extractions of biofuels and co-products

    Renew. Sust. Energ. Rev.

    (2010)
  • Y. Chisti

    Biodiesel from microalgae

    Biotechnol. Adv.

    (2007)
  • A. Singh et al.

    Mechanism and challenges in commercialisation of algal biofuels

    Bioresour. Technol.

    (2011)
  • K. Dutta et al.

    Evolution retrospective for alternative fuels: first to fourth generation

    Renew. Energy

    (2014)
  • K. Tong et al.

    Optimal design of advanced drop-in hydrocarbon biofuel supply chain integrating with existing petroleum refineries under uncertainty

    Biomass Bioenergy

    (2014)
  • N.G. Schoepp et al.

    System and method for research-scale outdoor production of microalgae and cyanobacteria

    Bioresour. Technol.

    (2014)
  • T. Johnson et al.

    Producing next-generation biofuels from filamentous cyanobacteria: an economic feasibility analysis

    Algal Res.

    (2016)
  • L.F. Razon

    Life cycle energy and greenhouse gas profile of a process for the production of ammonium sulfate from nitrogen-fixing photosynthetic cyanobacteria

    Bioresour. Technol.

    (2012)
  • M. Sara et al.

    Life cycle analysis of potential substrates of sustainable biorefinery

  • J.W. Richardson et al.

    A financial assessment of two alternative cultivation systems and their contributions to algae biofuel economic viability

    Algal Res.

    (2014)
  • Y. Li et al.

    Integration of algae cultivation as biodiesel production feedstock with municipal wastewater treatment: strains screening and significance evaluation of environmental factors

    Bioresour. Technol.

    (2011)
  • H. Kiyota et al.

    Engineering of cyanobacteria for the photosynthetic production of limonene from CO2

    J. Biotechnol.

    (2014)
  • Y. Cao et al.

    Adsorption of butanol vapor on active carbons with nitric acid hydrothermal modification

    Bioresour. Technol.

    (2015)
  • I. Udom et al.

    Harvesting microalgae grown on wastewater

    Bioresour. Technol.

    (2013)
  • R. Davis et al.

    Techno-economic analysis of autotrophic microalgae for fuel production

    Appl. Energy

    (2011)
  • B. Sialve et al.

    Anaerobic digestion of microalgae as a necessary step to make microalgal biodiesel sustainable

    Biotechnol. Adv.

    (2009)
  • Y. Chisti

    Biodiesel from microalgae beats bioethanol

    Trends Biotechnol.

    (2008)
  • E. Ehimen et al.

    Anaerobic digestion of microalgae residues resulting from the biodiesel production process

    Appl. Energy

    (2011)
  • J.W. Richardson et al.

    Financial feasibility analysis of NAABB developed technologies

    Algal Res.

    (2015)
  • D.D. Hsu

    Life cycle assessment of gasoline and diesel produced via fast pyrolysis and hydroprocessing

    Biomass Bioenergy

    (2012)
  • F. Delrue et al.

    An economic, sustainability, and energetic model of biodiesel production from microalgae

    Bioresour. Technol.

    (2012)
  • H. Khoo et al.

    Life cycle energy and CO 2 analysis of microalgae-to-biodiesel: preliminary results and comparisons

    Bioresour. Technol.

    (2011)
  • B.D. Fernandes et al.

    Continuous cultivation of photosynthetic microorganisms: approaches, applications and future trends

    Biotechnol. Adv.

    (2015)
  • J. Rubio et al.

    Overview of flotation as a wastewater treatment technique

    Miner. Eng.

    (2002)
  • J.W. Richardson et al.

    Economic viability of a reverse engineered algae farm (REAF)

    Algal Res.

    (2014)
  • J.W. Richardson et al.

    Economic comparison of open pond raceways to photo bio-reactors for profitable production of algae for transportation fuels in the southwest

    Algal Res.

    (2012)
  • Y. Chisti

    Response to Reijnders: do biofuels from microalgae beat biofuels from terrestrial plants

    Trends Biotechnol.

    (2008)
  • P. Collet et al.

    Life-cycle assessment of microalgae culture coupled to biogas production

    Bioresour. Technol.

    (2011)
  • D. Welkie et al.

    Transcriptomic and proteomic dynamics in the metabolism of a diazotrophic cyanobacterium, Cyanothece sp. PCC 7822 during a diurnal light–dark cycle

    BMC Genomics

    (2014)
  • B. Dien et al.

    Bacteria engineered for fuel ethanol production: current status

    Appl. Microbiol. Biotechnol.

    (2003)
  • E.D. Deenanath et al.

    The bioethanol industry in sub-Saharan Africa: history, challenges, and prospects

    J. Biomed. Biotechnol.

    (2011)
  • P.M. Schenk et al.

    Second generation biofuels: high-efficiency microalgae for biodiesel production

    Bioenergy Res.

    (2008)
  • N. Chernova et al.

    Microalgae as source of energy: current situation and perspectives of use

  • Cited by (23)

    • Volatile organic compounds from microalgae as an alternative for the production of bioenergy

      2022, 3rd Generation Biofuels: Disruptive Technologies to Enable Commercial Production
    • Life cycle assessment, energy balance and sensitivity analysis of bioethanol production from microalgae in a tropical country

      2019, Renewable and Sustainable Energy Reviews
      Citation Excerpt :

      Net energy input covered the energy input of the project (excluding energy credits) by by-products. The negative number of the net energy balance manifested that the energy production from the project was superior than the energy investment and that meant absolute favour for the project scheme [6,11]. Net energy ratio reflects an energetic impact barometer on the overall process energy input.

    View all citing articles on Scopus
    1

    Both authors contributed equally to this work.

    View full text