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Biorefineries and the food, energy, water nexus — towards a whole systems approach to design and planning
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ScienceDirect Biorefineries and the food, energy, water nexus — towards a whole systems approach to design and planning Elias Martinez-Hernandez1,2 and Sheila Samsatli1 Concerns over securing basic resources to an increasing world population have stressed the importance of critical interactions between the food, energy and water supply systems, as framed by the food-energy-water nexus concept. Current biorefineries producing first generation biofuels from food crops have impacted nexus resources, most notoriously land and food but also water and fossil energy resources required during cultivation and processing. Solutions to the nexus challenges of biorefineries require the search for alternative feedstocks and the application of methods that capture opportunities for synergistic interactions with the nexus. At the process level, more efficient water and energy use and food production could be possible if methods for extensive biomass fractionation, process integration and optimisation are developed. There is also a great opportunity to include the interactions between biomass supply and the nexus sectors in value chain optimisation to find strategic integrations that improve productivity and reduce losses and environmental impacts. By incorporating opportunities into a whole systems approach for design and planning, biorefineries will be able to balance nexus resource trade-offs, deliver their potential for full exploitation of biomass as the only source of renewable carbon and materials, and translate nexus issues into social welfare and sustainable development.
biofuels have undergone extensive scrutiny regarding their sustainability. Diversion of areas of land that are used to produce food to the production of biofuels has caused food price increases and a continuing food vs fuel debate [1]. Current biofuel production systems still rely on fossil-based resources for cultivation and processing. In addition, they also consume large amounts of water, especially during the cultivation stage, which may worsen water stress in some regions [2]. These realities are evidenced by the impact and trade-offs of the promotion of large scale biofuel production [3] and the bioeconomy on the delicate interactions between food, energy and water systems [4]. The Food-Energy-Water (FEW) nexus concept was presented at the 2011 Bonn Conference as an approach to realise UN Sustainable Development Goals by reducing trade-offs and encouraging integration across sectors for sustainable use of resources [5]. The sustainability issues with biofuels are partly due to their production in linear, single output process systems, which make inefficient use of the feedstock, energy and water inputs. A nexus approach is needed for the development of solutions through integrative process systems such as biorefineries and their supply chains.
Addresses 1 Department of Chemical Engineering, University of Bath, Bath BA2 7AY, UK 2 Biomass Conversion Department, Instituto Mexicano del Petro´leo, La´zaro Ca´rdenas 152, Mexico City, 07730, Mexico
In the most advanced sense, a biorefinery is a facility for the sustainable conversion of biomass through integrated, efficient and flexible processing into multiple products including chemicals, food, animal feed and energy products [6]. Biorefineries can be classified according to the type of feedstock (e.g. algal biorefineries, organic waste biorefineries, lignocellulosic biorefineries), the platform technology (biochemical, thermochemical) or the degree of complexity (Type I or single feedstock-single product, Type II or single-feedstock-multiple product, and Type III or multiple feedstock and multiple product). A biorefinery system can belong to one or more of these various classifications, thus in this review the biorefinery type is not distinguished as the focus is on the interactions of any biorefinery with the FEW nexus systems. Advanced biorefineries (Types II and III, as defined before) have promising prospects to address nexus issues by providing food, energy and clean water in a sustainable way while preserving the environment and ecosystems [7]. The concept was developed by analogy to the complex but highly efficient crude oil refineries and the application of process engineering principles in their designs, such as feedstock fractionation for multiple value-added productions and process integration. The present paper reviews how biorefineries can be a potential solution to the FEW
Corresponding author: Martinez-Hernandez, Elias ([email protected])
Current Opinion in Chemical Engineering 2017, 18:16–22 This review comes from a themed issue on Process systems engineering Edited by Mahmoud El-Halwagi, Ka Ming Ng and Dale Keairns
http://dx.doi.org/10.1016/j.coche.2017.08.003 2211-3398/# 2017 Elsevier Ltd. All rights reserved.
Introduction Initially viewed as an environmentally friendly alternative to fossil fuels and a way to increase energy security, Current Opinion in Chemical Engineering 2017, 18:16–22
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Biorefineries and the food, energy, water nexus Martinez-Hernandez and Samsatli 17
nexus issues if extensive biomass fractionation, process integration and optimisation are elegantly developed through synergistic interactions with the nexus components. The nexus challenges of current biorefinery developments are reviewed in ‘Overview of food-energy-water nexus interactions of biorefineries’ section. This is followed by a review of opportunities for process systems engineering (PSE) tools at the biorefinery process level and at the entire biomass value chain for efficient utilisation of FEW resources. The last section presents a prospective for a whole systems approach for biorefinery design and planning.
Overview of food-energy-water nexus interactions of biorefineries Biorefineries producing first generation biofuels are now well established and can be used as a reference for an initial analysis of FEW nexus interactions. Biofuels provide only 4% of global transportation fuels, yet 3% of global water consumption is driven by their production and they use land and crops that could feed 30% of the population suffering food poverty [8]. 5–10% of cultivated land needs to be diverted to produce biorefinery feedstock to meet China’s biofuel target by 2020, consuming the equivalent of Yellow River’s annual water discharge [9]. These realities reflect the importance of systematically analysing the nexus interactions of biorefineries to avoid negative impacts and balance resource trade-offs.
The FEW nexus of biorefineries manifest itself in different ways depending on the biomass, location and process technology, however, all biorefineries will impact water, energy resources and food supply. Figure 1 shows an overview of interactions for current biorefineries which mainly use food crops such as sugarcane, corn and wheat for biofuels. The delicate energy-food interactions have been widely debated, as mentioned earlier, but it should be noted that current biorefineries contribute indirectly to the production of food by recovering animal feed [10]. Interactions with the energy system come from the use natural gas and electricity to run biorefining processes, and this undermines the life cycle energy and carbon emissions balance [11]. This implies an increase in demand for fossil resources, which bioenergy and biofuels seek to replace, an irony that must be avoided or at least minimised. Furthermore, inefficient energy use in biorefineries could lead to increased water use for cooling duties, thus creating an energy-water nexus issue. Water use during crop cultivation may have serious implications on water quality, due to leaching of fertilisers and pesticides into water bodies, and also on water availability for other purposes. For example, to produce 1 L of ethanol, 500–4000 L of water are required during biomass cultivation while the processing water requirements in a typical ethanol plant are 2–10 L, which can cause a ‘drink or drive’ issue [12]. The increased biofuel production has probably already affected water quality because of the large amount of fertilisers used to grow corn in the US [13] and sugarcane in Brazil [14]. Although
Figure 1
Energy Increased water use for energy
Food/land diverted for energy Energy and biofuel products
Polluted water from energy production
Fossil energy for process Energy use for cultivation
Water for process and utilities
Food/feed products
Biorefinery Water effluent, treated water
Feedstock
Water
Food
Water polluted by fertiliser leaching
Water for food or energy crops Current Opinion in Chemical Engineering
Food, energy and water nexus interactions of current biorefineries which mainly use food crops or first generation feedstocks.
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water use for the biorefinery conversion process and utilities can be small compared to its use in the cultivation stage, process water can also add pressure in water stressed locations. A biorefinery annually producing 100 million gallons of bioethanol in the US would use the equivalent of the water needed by 5000 people [13]. Discharge of biorefinery effluents can also affect water quality, which can further reduce freshwater suitable for human consumption. Therefore, growing biofuel crops and installing biorefineries should aim to balance local water constraints, climate and crop requirements. A clear distinction should be made between using dedicated crops and by-products from other activities as feedstocks for biorefining. The distinction affects the allocation of water footprint, and thus, the implications on the nexus. A dedicated crop will have a larger water footprint as all of the water for cultivation is attributable to the system. If the feedstock is a crop residue, then the only a fraction of that water is attributable, but this also depends on how the water footprint is allocated to the residues [15]. The water footprint of bioenergy and biofuels has been assessed in more detail for a variety of dedicated crops elsewhere [16]. From a nexus perspective, the panorama does not look optimistic for current biorefineries. However, the potential of second and third generation feedstocks can help to resolve FEW resource trade-offs through new technologies and their wise integration in biorefineries. By 2050, 75% of biofuel production will come from lignocellulosic biorefineries [17], but their large scale deployment will imply significant carbon, land, energy and water footprints that need to be quantified and minimised. Together with the prospects of new feedstocks and biorefining technologies, water and energy integration and fractionation to recover food products are the pathways to take to address the FEW nexus issues of biorefineries, as reviewed in the following sections.
FEW nexus opportunities at the biorefinery process level Current biorefineries should evolve into more integrated facilities considering on-site energy generation from residues [18], whole crop utilisation [19] and recovery of feed and food ingredients [20], thus solving some of the nexus challenges at the process level. Biorefineries can further contribute to this by using lignocellulosic crops and residues, and recovering protein and other food products. The need for separating biomass fractions for efficient conversion into multiple products creates enough complexity and scope for mass and energy integration [20]. Furthermore, biorefineries can be a model for closing resource loops [21] and circular economy [22,23] for efficient management of waste in synergy with food, energy and water systems. Several PSE efforts to address nexus challenges by exploiting integrative opportunities in biorefineries have been presented in the literature. A new targeting and Current Opinion in Chemical Engineering 2017, 18:16–22
design method has been proposed for the integration of water, achieving up to 85.5% water savings in a lignocellulosic biorefinery [24]. Another approach combines process optimisation and graph-based allocation maps for the integrated treatment of biorefinery effluents [25]. Another contribution presents the optimisation of locating multiple biorefineries while observing local environmental constraints on water availability [26]. Sequential integration of process technologies, energy and water has been applied to a biorefinery using whole corn [27]. Results showed that there are conditions where it is best to use stover for ethanol production, via the thermochemical route, and the grain for food; thus effectively addressing the FEW nexus trade-offs. Technologies and methods for optimal integration of biomass processing, energy and water in biorefineries have been presented in [28]. The water-energy nexus will be highly dependent on the process technology route and the level of energy integration. The thermochemical routes may provide better scope due to the high temperatures, which also reduce freshwater use for cooling. Fischer–Tropsch has shown the best compromise [29], but targets for process design and water-energy nexus need to be identified [30]. Life cycle approaches have also been developed for successive optimisation of the water-energy nexus for various biofuel production pathways [31]. The application of life cycle studies is also important to identify trade-offs between economic, environmental and social objectives of bioenergy and biorefinery systems, which can be resolved using multi-objective optimisation [32–34]. Resource trade-offs in the nexus and ecosystems can also be identified using ecologically based LCA [35]. A more comprehensive review of the potential for life cycle assessment, pinch analysis and mathematical programming to resolve nexus issues has been presented elsewhere [36]. A comprehensive review of water and energy integration methods is presented in [37]. However, to date only a few studies consider the three components of the FEW nexus in an optimisation framework [38]. Therefore, there is a need to develop tools that can find innovative solutions by simultaneously addressing nexus issues and resource trade-offs, and considering nexus integration opportunities. Extensive research exists on the water-energy nexus of biorefineries, with little attention to the food element. Recent developments on algae cultivation as a biorefinery feedstock has encouraging prospects to fully address FEW nexus issues. Algal biorefineries can provide enough biofuel and protein to fully displace fossil transportation fuels and meet up to 24% of the plant protein demands by 2054 [39]. Recent biotechnological advancements will also enable the fractionation of non-food lignocellulosic biomass into sugars, cellulose, hemicellulose, lignin and proteins and their further conversion into food products. For example, non-food cellulose can be www.sciencedirect.com
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converted into starch and cultured meat production can be an alternative to livestock grazing [40]. Food production in biorefineries will provide a positive impact on the food side of the FEW nexus, but acceptance, safety, ethics and health issues would need be resolved first. Another opportunity is the processing of biorefinery residues and wastewater [21,41]. Organic streams can be used to produce energy and chemicals through biochemical technologies such as anaerobic digestion (AD) [42,43]. Integrated waste biorefineries can also treat wastewater for recycling, while also contributing to food production by recovering nutrients [43,44]. Digestate valorisation can further replace freshwater, nutrients and fossil energy through algae cultivation and bioenergy production [45]. Biorefineries can therefore also be a crucial link to close the nutrient cycle, which is also important for a product life cycle, allowing recovery of fertiliser for food and biorefinery feedstock production and avoiding nitrogen leaching to water bodies [46]. Furthermore, the use and fractionation of biorefinery residues can lead to food production if novel technologies for the extraction of proteins, sugars and lignin such as hydrothermal treatment are developed [47]. As the nexus interactions can become critical at the biomass production stage, there is also a search for new biorefinery feedstocks such as O. ficus-indica and E. tirucalli. These plants grow under water-limited conditions and could provide biomass to produce enough biogas to replace natural gas and fertiliser for food production by using between 4 and 15% of global semi-arid land [48]. Synergistic biorefinery interactions with wider food, energy and water systems as well as techno-ecological synergies that favour the preservation of ecosystem services should also be sought [49,50]. The integration of algal biorefineries with other industries such as livestock, lignocellulosic and aquaculture is another opportunity [51], which will require extensive process systems engineering. Another example is the symbiotic integration of solar energy and CO2 valorisation in biorefineries [52]. Other opportunities at the value chain level are reviewed in the following section.
FEW nexus opportunities at the biomass value chain level Biomass supply chains have received a lot of attention over the last 10 years as they are such an important issue for biorefineries because of the large variety of feedstocks that can be converted into many different types of product (energy services, chemicals and commodities) via a large number of pathways. The feedstocks, intermediates and products need to be transported from their sources to where they are needed and their inventory managed in order to ensure demands can be met at all times despite fluctuations in raw material availability and final-product demands. An additional complexity with biomass supply www.sciencedirect.com
chains is that the raw materials are not limited to specific locations (as would be the case for natural gas, for example), and determining where to grow each type of biomass should be based on land and climate suitability. It is a very complex problem to find the best combination of many highly interdependent decisions, such as determining what biomass to grow, where and when, what types of biorefinery to invest in and where they should be located. All of these decisions affect further decisions about transport and storage of resources. The objective is to create more value at each stage of the supply chain and the value may be measured by more than simple economic metrics and may also include environmental and social indicators, such as greenhouse gas emissions and job creation. The following review papers give a good overview of literature in the area of biomass supply chains: [53–55,56]. Mafakheri and Nasiri [53] consider the challenges and issues for biomass supply chain management. Mitchell [54] lists many of the biosystem models that were developed before 2000, describing how some of them have been developed. Meyer et al. [54] categorised biomass supply chain models published between 1997 and 2012 according to the type of optimisation problem (e.g. heuristics or mathematical programming, linear, non-linear, mixed integer), the decisions considered (e.g. planning or operation) and the type of objective function (e.g. economic or multi-objective). The majority were found to be mathematical programming models with a purely economic objective function. Yue et al. [56] also categorised the literature according to type of optimisation problem being solved (supply chain design or operation, single-objective or multi-objective) and also by application area, such as the type of feedstock and what the products of the supply chain are. The requirements of a tool for total chain integration of biorefineries have also been provided in [57]. The biomass supply chain problem is often formulated as an optimisation problem, typically using Mixed Integer Programming (MIP). The spatial aspect of the problem is usually represented by defining a number of nodes or regions and binary variables then represent the existence of a particular type of biorefinery at each node. Continuous variables represent the operation of the network, such as processing rates of the biorefineries, rates of transport of resources, inventory levels, etc. A comprehensive biomass value chain model has been developed by [58,59], which is configured for the UK by using 157 50 km 50 km cells. It is a multi-vector model that includes a very large number of pathways from biomass to products. It determines what biomass (including various arable crops, energy crops, forestry and waste resources) to grow/utilise, where and when, and what are the best products to produce. It simultaneously considers land allocation (accounting for spatial and temporal variations in biomass yields), transport and storage of Current Opinion in Chemical Engineering 2017, 18:16–22
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resources, imports, staged investments and retirements of biorefineries/power plants, afforestation and carbon capture and storage. The different stages of a biomass supply chain are intricately linked with the nexus. For example, the water required for cultivation, processing and conversion of biomass affect agriculture, land use and food production. Conversely, food production competes with bioenergy for land and water. Furthermore, the transport and storage of biomass feedstocks and distribution of products and services require energy and generate emissions. Intensive and poorly planned deployment of bioenergy can affect detrimentally the ecosystem: deforestation, loss of biodiversity and leaching of nutrients and pesticides to bodies of water, to name a few. However, there are also potential synergies that can be exploited. For instance, food crop residues can be used for bioenergy but ensuring that sufficient residue is left on the field to replenish nutrients. Effective planning can lead to better management of forestry resources, improved agricultural practices, water efficiency and sustainable fertiliser use. Along the various stages of the supply chain, strategic integration with the food, water and energy sectors can improve productivity and reduce losses and environmental impacts. There is therefore a great opportunity to include the interactions between biomass supply chains and the FEW nexus in order to develop biorefineries that can transform rural economies, improve and maintain social welfare, enhance energy security and contribute to economic, environmental and social objectives.
Towards a whole systems approach to biorefineries and the FEW nexus Despite the challenging nexus issues inherent to biorefineries, they have the potential to evolve as process systems with enough complexity to balance nexus resource trade-offs through the application of process integration and optimisation at process and value chain levels. These also represent timely opportunities to develop whole systems methods that transform nexus challenges into integrative opportunities. Such a whole systems approach should embrace the FEW nexus as a framework to enhance sustainability of biomass utilisation through the following principles: 1. Extensive fractionation to utilise all biomass components and extract food components already in feedstock 2. Energy and water integration at process, regional and value chain levels 3. Residual waste and wastewater processing with recovery of nutrients to be returned for food and biomass feedstock cultivation and water for reuse and recycle 4. Mix and match local ecosystems, environmental and climate conditions to crop resource requirements and biorefining technologies Current Opinion in Chemical Engineering 2017, 18:16–22
5. Synergistic integration with FEW nexus components along biomass value chains. Biorefinery planning should also aim to tackle interconnected problems present in FEW systems by developing solutions that align with existing regulations and policies [21]. Key issues associated with biorefineries and the FEW nexus along the whole supply chain should also be considered [60].
Conclusions Sustainability issues of biorefineries using first generation feedstock remarked the importance of interaction with other systems such as food and water production. With a nexus approach advanced biorefineries processing a variety of non-food crops and combining established and novel technologies have the potential to shift those negative impacts on the FEW nexus into synergistic integrations. In this review several opportunities for positive FEW interactions of biorefineries have been discussed and can be highlighted as: firstly, production of food ingredients by extraction from feedstock or converting biomass fractions into food ingredients; secondly, use of non-food and water efficient crops; thirdly, processing of crop residues and waste feedstocks to recover energy and other products while recovering clean water and nutrients for food production; and finally, integrating biorefineries with other renewable energy systems and other agricultural and food production systems to recover resources from waste streams to recycle nutrients and water and recover energy. The interactions highlighted could be possible by one combination or another of feedstock-technology-product. In exploring such opportunities for synergistic interactions, a whole systems approach would support the development of advanced biorefineries and resilient value chains. If timely developed and applied during design and planning stages, biorefineries will not only allow balancing of nexus trade-offs, but deliver their promising potential for the sustainable development of our society.
Conflict of interest No conflict of interest.
Acknowledgements The authors would like to acknowledge the Newton Fund and the EPSRC/ RCUK for financial support through the Biomass Value Chains and the Food-Energy-Water Nexus Project (Grant No. EP/P018165/1).
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47. Kazan A, Celiktas MS, Sargin S, Yesil-Celiktas O: Bio-based fractions by hydrothermal treatment of olive pomace: process optimization and evaluation. Energy Convers Manag 2015, 103:366-373 http://dx.doi.org/10.1016/j.enconman.2015.06.084. 48. Mason PM, Glover K, Smith JAC, Willis KJ, Woods J, Thompson IP: The potential of CAM crops as a globally significant bioenergy resource: moving from ‘‘fuel or food’’ to ‘‘fuel and more food’’. Energy Environ Sci 2015, 8:2320-2329 http://dx.doi.org/10.1039/C5EE00242G. 49. Bakshi BR, Ziv G, Lepech MD: Techno-ecological synergy: a framework for sustainable engineering. Environ Sci Technol 2015, 49:1752-1760 http://dx.doi.org/10.1021/es5041442.
36. Garcia DJ, You FQ: The water-energy-food nexus and process systems engineering: a new focus. Comput Chem Eng 2016, 91:49-67 http://dx.doi.org/10.1016/j.compchemeng.2016.03.003. This paper comprehensively outlines the potential application of PSE tools for developing integrated solutions to nexus challenges from a whole systems perspective.
50. Martinez-Hernandez E, Leung Pah Hang MY, Leach M, Yang A: A framework for modeling local production systems with techno-ecological interactions. J Ind Ecol 2016 http:// dx.doi.org/10.1111/jiec.12481.
37. Ahmetovic´ E, Ibric´ N, Kravanja Z, Grossmann IE: Water and energy integration: a comprehensive literature review of non-isothermal water network synthesis. Comput Chem Eng 2015, 82:144-171 http://dx.doi.org/10.1016/ j.compchemeng.2015.06.011.
51. Subhadra B, Grinson-George: Algal biorefinery-based industry: an approach to address fuel and food insecurity for a carbon smart world. J Sci Food Agric 2011, 91:2-13 http://dx.doi.org/ 10.1002/jsfa.4207. Another paper highlighting the potential for algae biorefineries to address the food component of the nexus.
38. Leung Pah Hang MY, Martinez-Hernandez E, Leach M, Yang A: Designing integrated local production systems: a study on the food-energy-water nexus. J Clean Prod 2016, 135:1065-1084 http://dx.doi.org/10.1016/j.jclepro.2016.06.194. 39. Lehahn Y, Ingle KN, Golberg A: Global potential of offshore and shallow waters macroalgal biorefineries to provide for food, chemicals and energy: feasibility and sustainability. Algal Res 2016, 17:150-160 http://dx.doi.org/10.1016/j.algal.2016.03.031. This paper reviews the benefits of algae biorefineries to address nexus and sustainability issues. 40. Chen HG, Zhang YHP: New biorefineries and sustainable agriculture: increased food, biofuels, and ecosystem security. Renew Sustain Energy Rev 2015, 47:117-132 http://dx.doi.org/ 10.1016/j.rser.2015.02.048. This paper reviews how biorefineries could be synergistically integrated with the agricultural sector. 41. Venkata Mohan S, Nikhil GN, Chiranjeevi P, Nagendranatha Reddy C, Rohit MV, Kumar AN et al.: Waste biorefinery models towards sustainable circular bioeconomy: critical review and future perspectives. Bioresour Technol 2016, 215:2-12 http:// dx.doi.org/10.1016/j.biortech.2016.03.130. This paper highlights the importance of further processing biorefinery effluents and residues to improve efficiency of biomass processing and resource use. 42. Meneses-Ja´come A, Diaz-Chavez R, Vela´squez-Arredondo HI, Ca´rdenas-Cha´vez DL, Parra R, Ruiz-Colorado AA: Sustainable energy from agro-industrial wastewaters in Latin-America. Renew Sustain Energy Rev 2016, 56:1249-1262 http://dx.doi.org/ 10.1016/j.rser.2015.12.036. 43. Coma M, Martinez Hernandez E, Abeln F, Raikova S, Donnelly J, Arnot TC et al.: Organic waste as a sustainable feedstock for platform chemicals. Faraday Discuss 2017 http://dx.doi.org/ 10.1039/C7FD00070G. 44. Sawatdeenarunat C, Nguyen D, Surendra KC, Shrestha S, Rajendran K, Oechsner H et al.: Anaerobic biorefinery: current status, challenges, and opportunities. Bioresour Technol 2016, 215:304-313 http://dx.doi.org/10.1016/j.biortech.2016.03.074. 45. Monlau F, Sambusiti C, Ficara E, Aboulkas A, Barakat A, Carre`re H: New opportunities for agricultural digestate valorization: current situation and perspectives. Energy Environ Sci 2015:2600-2621 http://dx.doi.org/10.1039/C5EE01633A. 46. Singh S, Bakshi BR: Accounting for the biogeochemical cycle of nitrogen in input–output life cycle assessment. Environ Sci Technol 2013, 47:9388-9396 http://dx.doi.org/10.1021/ es4009757.
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52. Abate S, Lanzafame P, Perathoner S, Centi G: New sustainable model of biorefineries: biofactories and challenges of integrating bio- and solar refineries. ChemSusChem 2015, 8:2854-2866 http://dx.doi.org/10.1002/ cssc.201500277. An interesting review on opportunities to integrate biomass and CO2 processing with solar energy. 53. Mafakheri F, Nasiri F: Modeling of biomass-to-energy supply chain operations: applications, challenges and research directions. Energy Policy 2014, 67:116-126 http://dx.doi.org/ 10.1016/j.enpol.2013.11.071. 54. Mitchell CP: Development of decision support systems for bioenergy applications. Biomass Bioenergy 2000, 18:265-278 http://dx.doi.org/10.1016/S0961-9534(99)00099-9. 55. De Meyer A, Cattrysse D, Van Orshoven J: A generic mathematical model to optimise strategic and tactical decisions in biomass-based supply chains (OPTIMASS). Eur J Oper Res 2015, 245:247-264 http://dx.doi.org/10.1016/ j.ejor.2015.02.045. 56. Yue D, You F, Snyder SW: Biomass-to-bioenergy and biofuel supply chain optimization: overview, key issues and challenges. Comput Chem Eng 2014, 66:36-56 http://dx.doi.org/ 10.1016/j.compchemeng.2013.11.016. This is a recent review highlighting the opportunities and research needs from a process systems perspective. 57. Budzianowski WM, Postawa K: Total chain integration of sustainable biorefinery systems. Appl Energy 2016, 184:1432-1446 http://dx.doi.org/10.1016/ j.apenergy.2016.06.050. This paper reviews the components of a biorefinery system and its value chain and outlines requirements for a systematic software tool. 58. Samsatli S, Samsatli NJ, Shah N: BVCM: a comprehensive and flexible toolkit for whole system biomass value chain analysis and optimisation — mathematical formulation. Appl Energy 2015, 147:131-160 http://dx.doi.org/10.1016/ j.apenergy.2015.01.078. 59. Samsatli S, Samsatli NJ: A general spatio-temporal model of energy systems with a detailed account of transport and storage. Comput Chem Eng 2015, 80:155-176 http://dx.doi.org/ 10.1016/j.compchemeng.2015.05.019. 60. Azapagic A: Sustainability considerations for integrated biorefineries. Trends Biotechnol 2014, 32:1-4 http://dx.doi.org/ 10.1016/j.tibtech.2013.10.009.
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ScienceDirect Biorefineries and the food, energy, water nexus — towards a whole systems approach to design and planning Elias Martinez-Hernandez1,2 and Sheila Samsatli1 Concerns over securing basic resources to an increasing world population have stressed the importance of critical interactions between the food, energy and water supply systems, as framed by the food-energy-water nexus concept. Current biorefineries producing first generation biofuels from food crops have impacted nexus resources, most notoriously land and food but also water and fossil energy resources required during cultivation and processing. Solutions to the nexus challenges of biorefineries require the search for alternative feedstocks and the application of methods that capture opportunities for synergistic interactions with the nexus. At the process level, more efficient water and energy use and food production could be possible if methods for extensive biomass fractionation, process integration and optimisation are developed. There is also a great opportunity to include the interactions between biomass supply and the nexus sectors in value chain optimisation to find strategic integrations that improve productivity and reduce losses and environmental impacts. By incorporating opportunities into a whole systems approach for design and planning, biorefineries will be able to balance nexus resource trade-offs, deliver their potential for full exploitation of biomass as the only source of renewable carbon and materials, and translate nexus issues into social welfare and sustainable development.
biofuels have undergone extensive scrutiny regarding their sustainability. Diversion of areas of land that are used to produce food to the production of biofuels has caused food price increases and a continuing food vs fuel debate [1]. Current biofuel production systems still rely on fossil-based resources for cultivation and processing. In addition, they also consume large amounts of water, especially during the cultivation stage, which may worsen water stress in some regions [2]. These realities are evidenced by the impact and trade-offs of the promotion of large scale biofuel production [3] and the bioeconomy on the delicate interactions between food, energy and water systems [4]. The Food-Energy-Water (FEW) nexus concept was presented at the 2011 Bonn Conference as an approach to realise UN Sustainable Development Goals by reducing trade-offs and encouraging integration across sectors for sustainable use of resources [5]. The sustainability issues with biofuels are partly due to their production in linear, single output process systems, which make inefficient use of the feedstock, energy and water inputs. A nexus approach is needed for the development of solutions through integrative process systems such as biorefineries and their supply chains.
Addresses 1 Department of Chemical Engineering, University of Bath, Bath BA2 7AY, UK 2 Biomass Conversion Department, Instituto Mexicano del Petro´leo, La´zaro Ca´rdenas 152, Mexico City, 07730, Mexico
In the most advanced sense, a biorefinery is a facility for the sustainable conversion of biomass through integrated, efficient and flexible processing into multiple products including chemicals, food, animal feed and energy products [6]. Biorefineries can be classified according to the type of feedstock (e.g. algal biorefineries, organic waste biorefineries, lignocellulosic biorefineries), the platform technology (biochemical, thermochemical) or the degree of complexity (Type I or single feedstock-single product, Type II or single-feedstock-multiple product, and Type III or multiple feedstock and multiple product). A biorefinery system can belong to one or more of these various classifications, thus in this review the biorefinery type is not distinguished as the focus is on the interactions of any biorefinery with the FEW nexus systems. Advanced biorefineries (Types II and III, as defined before) have promising prospects to address nexus issues by providing food, energy and clean water in a sustainable way while preserving the environment and ecosystems [7]. The concept was developed by analogy to the complex but highly efficient crude oil refineries and the application of process engineering principles in their designs, such as feedstock fractionation for multiple value-added productions and process integration. The present paper reviews how biorefineries can be a potential solution to the FEW
Corresponding author: Martinez-Hernandez, Elias ([email protected])
Current Opinion in Chemical Engineering 2017, 18:16–22 This review comes from a themed issue on Process systems engineering Edited by Mahmoud El-Halwagi, Ka Ming Ng and Dale Keairns
http://dx.doi.org/10.1016/j.coche.2017.08.003 2211-3398/# 2017 Elsevier Ltd. All rights reserved.
Introduction Initially viewed as an environmentally friendly alternative to fossil fuels and a way to increase energy security, Current Opinion in Chemical Engineering 2017, 18:16–22
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Biorefineries and the food, energy, water nexus Martinez-Hernandez and Samsatli 17
nexus issues if extensive biomass fractionation, process integration and optimisation are elegantly developed through synergistic interactions with the nexus components. The nexus challenges of current biorefinery developments are reviewed in ‘Overview of food-energy-water nexus interactions of biorefineries’ section. This is followed by a review of opportunities for process systems engineering (PSE) tools at the biorefinery process level and at the entire biomass value chain for efficient utilisation of FEW resources. The last section presents a prospective for a whole systems approach for biorefinery design and planning.
Overview of food-energy-water nexus interactions of biorefineries Biorefineries producing first generation biofuels are now well established and can be used as a reference for an initial analysis of FEW nexus interactions. Biofuels provide only 4% of global transportation fuels, yet 3% of global water consumption is driven by their production and they use land and crops that could feed 30% of the population suffering food poverty [8]. 5–10% of cultivated land needs to be diverted to produce biorefinery feedstock to meet China’s biofuel target by 2020, consuming the equivalent of Yellow River’s annual water discharge [9]. These realities reflect the importance of systematically analysing the nexus interactions of biorefineries to avoid negative impacts and balance resource trade-offs.
The FEW nexus of biorefineries manifest itself in different ways depending on the biomass, location and process technology, however, all biorefineries will impact water, energy resources and food supply. Figure 1 shows an overview of interactions for current biorefineries which mainly use food crops such as sugarcane, corn and wheat for biofuels. The delicate energy-food interactions have been widely debated, as mentioned earlier, but it should be noted that current biorefineries contribute indirectly to the production of food by recovering animal feed [10]. Interactions with the energy system come from the use natural gas and electricity to run biorefining processes, and this undermines the life cycle energy and carbon emissions balance [11]. This implies an increase in demand for fossil resources, which bioenergy and biofuels seek to replace, an irony that must be avoided or at least minimised. Furthermore, inefficient energy use in biorefineries could lead to increased water use for cooling duties, thus creating an energy-water nexus issue. Water use during crop cultivation may have serious implications on water quality, due to leaching of fertilisers and pesticides into water bodies, and also on water availability for other purposes. For example, to produce 1 L of ethanol, 500–4000 L of water are required during biomass cultivation while the processing water requirements in a typical ethanol plant are 2–10 L, which can cause a ‘drink or drive’ issue [12]. The increased biofuel production has probably already affected water quality because of the large amount of fertilisers used to grow corn in the US [13] and sugarcane in Brazil [14]. Although
Figure 1
Energy Increased water use for energy
Food/land diverted for energy Energy and biofuel products
Polluted water from energy production
Fossil energy for process Energy use for cultivation
Water for process and utilities
Food/feed products
Biorefinery Water effluent, treated water
Feedstock
Water
Food
Water polluted by fertiliser leaching
Water for food or energy crops Current Opinion in Chemical Engineering
Food, energy and water nexus interactions of current biorefineries which mainly use food crops or first generation feedstocks.
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water use for the biorefinery conversion process and utilities can be small compared to its use in the cultivation stage, process water can also add pressure in water stressed locations. A biorefinery annually producing 100 million gallons of bioethanol in the US would use the equivalent of the water needed by 5000 people [13]. Discharge of biorefinery effluents can also affect water quality, which can further reduce freshwater suitable for human consumption. Therefore, growing biofuel crops and installing biorefineries should aim to balance local water constraints, climate and crop requirements. A clear distinction should be made between using dedicated crops and by-products from other activities as feedstocks for biorefining. The distinction affects the allocation of water footprint, and thus, the implications on the nexus. A dedicated crop will have a larger water footprint as all of the water for cultivation is attributable to the system. If the feedstock is a crop residue, then the only a fraction of that water is attributable, but this also depends on how the water footprint is allocated to the residues [15]. The water footprint of bioenergy and biofuels has been assessed in more detail for a variety of dedicated crops elsewhere [16]. From a nexus perspective, the panorama does not look optimistic for current biorefineries. However, the potential of second and third generation feedstocks can help to resolve FEW resource trade-offs through new technologies and their wise integration in biorefineries. By 2050, 75% of biofuel production will come from lignocellulosic biorefineries [17], but their large scale deployment will imply significant carbon, land, energy and water footprints that need to be quantified and minimised. Together with the prospects of new feedstocks and biorefining technologies, water and energy integration and fractionation to recover food products are the pathways to take to address the FEW nexus issues of biorefineries, as reviewed in the following sections.
FEW nexus opportunities at the biorefinery process level Current biorefineries should evolve into more integrated facilities considering on-site energy generation from residues [18], whole crop utilisation [19] and recovery of feed and food ingredients [20], thus solving some of the nexus challenges at the process level. Biorefineries can further contribute to this by using lignocellulosic crops and residues, and recovering protein and other food products. The need for separating biomass fractions for efficient conversion into multiple products creates enough complexity and scope for mass and energy integration [20]. Furthermore, biorefineries can be a model for closing resource loops [21] and circular economy [22,23] for efficient management of waste in synergy with food, energy and water systems. Several PSE efforts to address nexus challenges by exploiting integrative opportunities in biorefineries have been presented in the literature. A new targeting and Current Opinion in Chemical Engineering 2017, 18:16–22
design method has been proposed for the integration of water, achieving up to 85.5% water savings in a lignocellulosic biorefinery [24]. Another approach combines process optimisation and graph-based allocation maps for the integrated treatment of biorefinery effluents [25]. Another contribution presents the optimisation of locating multiple biorefineries while observing local environmental constraints on water availability [26]. Sequential integration of process technologies, energy and water has been applied to a biorefinery using whole corn [27]. Results showed that there are conditions where it is best to use stover for ethanol production, via the thermochemical route, and the grain for food; thus effectively addressing the FEW nexus trade-offs. Technologies and methods for optimal integration of biomass processing, energy and water in biorefineries have been presented in [28]. The water-energy nexus will be highly dependent on the process technology route and the level of energy integration. The thermochemical routes may provide better scope due to the high temperatures, which also reduce freshwater use for cooling. Fischer–Tropsch has shown the best compromise [29], but targets for process design and water-energy nexus need to be identified [30]. Life cycle approaches have also been developed for successive optimisation of the water-energy nexus for various biofuel production pathways [31]. The application of life cycle studies is also important to identify trade-offs between economic, environmental and social objectives of bioenergy and biorefinery systems, which can be resolved using multi-objective optimisation [32–34]. Resource trade-offs in the nexus and ecosystems can also be identified using ecologically based LCA [35]. A more comprehensive review of the potential for life cycle assessment, pinch analysis and mathematical programming to resolve nexus issues has been presented elsewhere [36]. A comprehensive review of water and energy integration methods is presented in [37]. However, to date only a few studies consider the three components of the FEW nexus in an optimisation framework [38]. Therefore, there is a need to develop tools that can find innovative solutions by simultaneously addressing nexus issues and resource trade-offs, and considering nexus integration opportunities. Extensive research exists on the water-energy nexus of biorefineries, with little attention to the food element. Recent developments on algae cultivation as a biorefinery feedstock has encouraging prospects to fully address FEW nexus issues. Algal biorefineries can provide enough biofuel and protein to fully displace fossil transportation fuels and meet up to 24% of the plant protein demands by 2054 [39]. Recent biotechnological advancements will also enable the fractionation of non-food lignocellulosic biomass into sugars, cellulose, hemicellulose, lignin and proteins and their further conversion into food products. For example, non-food cellulose can be www.sciencedirect.com
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converted into starch and cultured meat production can be an alternative to livestock grazing [40]. Food production in biorefineries will provide a positive impact on the food side of the FEW nexus, but acceptance, safety, ethics and health issues would need be resolved first. Another opportunity is the processing of biorefinery residues and wastewater [21,41]. Organic streams can be used to produce energy and chemicals through biochemical technologies such as anaerobic digestion (AD) [42,43]. Integrated waste biorefineries can also treat wastewater for recycling, while also contributing to food production by recovering nutrients [43,44]. Digestate valorisation can further replace freshwater, nutrients and fossil energy through algae cultivation and bioenergy production [45]. Biorefineries can therefore also be a crucial link to close the nutrient cycle, which is also important for a product life cycle, allowing recovery of fertiliser for food and biorefinery feedstock production and avoiding nitrogen leaching to water bodies [46]. Furthermore, the use and fractionation of biorefinery residues can lead to food production if novel technologies for the extraction of proteins, sugars and lignin such as hydrothermal treatment are developed [47]. As the nexus interactions can become critical at the biomass production stage, there is also a search for new biorefinery feedstocks such as O. ficus-indica and E. tirucalli. These plants grow under water-limited conditions and could provide biomass to produce enough biogas to replace natural gas and fertiliser for food production by using between 4 and 15% of global semi-arid land [48]. Synergistic biorefinery interactions with wider food, energy and water systems as well as techno-ecological synergies that favour the preservation of ecosystem services should also be sought [49,50]. The integration of algal biorefineries with other industries such as livestock, lignocellulosic and aquaculture is another opportunity [51], which will require extensive process systems engineering. Another example is the symbiotic integration of solar energy and CO2 valorisation in biorefineries [52]. Other opportunities at the value chain level are reviewed in the following section.
FEW nexus opportunities at the biomass value chain level Biomass supply chains have received a lot of attention over the last 10 years as they are such an important issue for biorefineries because of the large variety of feedstocks that can be converted into many different types of product (energy services, chemicals and commodities) via a large number of pathways. The feedstocks, intermediates and products need to be transported from their sources to where they are needed and their inventory managed in order to ensure demands can be met at all times despite fluctuations in raw material availability and final-product demands. An additional complexity with biomass supply www.sciencedirect.com
chains is that the raw materials are not limited to specific locations (as would be the case for natural gas, for example), and determining where to grow each type of biomass should be based on land and climate suitability. It is a very complex problem to find the best combination of many highly interdependent decisions, such as determining what biomass to grow, where and when, what types of biorefinery to invest in and where they should be located. All of these decisions affect further decisions about transport and storage of resources. The objective is to create more value at each stage of the supply chain and the value may be measured by more than simple economic metrics and may also include environmental and social indicators, such as greenhouse gas emissions and job creation. The following review papers give a good overview of literature in the area of biomass supply chains: [53–55,56]. Mafakheri and Nasiri [53] consider the challenges and issues for biomass supply chain management. Mitchell [54] lists many of the biosystem models that were developed before 2000, describing how some of them have been developed. Meyer et al. [54] categorised biomass supply chain models published between 1997 and 2012 according to the type of optimisation problem (e.g. heuristics or mathematical programming, linear, non-linear, mixed integer), the decisions considered (e.g. planning or operation) and the type of objective function (e.g. economic or multi-objective). The majority were found to be mathematical programming models with a purely economic objective function. Yue et al. [56] also categorised the literature according to type of optimisation problem being solved (supply chain design or operation, single-objective or multi-objective) and also by application area, such as the type of feedstock and what the products of the supply chain are. The requirements of a tool for total chain integration of biorefineries have also been provided in [57]. The biomass supply chain problem is often formulated as an optimisation problem, typically using Mixed Integer Programming (MIP). The spatial aspect of the problem is usually represented by defining a number of nodes or regions and binary variables then represent the existence of a particular type of biorefinery at each node. Continuous variables represent the operation of the network, such as processing rates of the biorefineries, rates of transport of resources, inventory levels, etc. A comprehensive biomass value chain model has been developed by [58,59], which is configured for the UK by using 157 50 km 50 km cells. It is a multi-vector model that includes a very large number of pathways from biomass to products. It determines what biomass (including various arable crops, energy crops, forestry and waste resources) to grow/utilise, where and when, and what are the best products to produce. It simultaneously considers land allocation (accounting for spatial and temporal variations in biomass yields), transport and storage of Current Opinion in Chemical Engineering 2017, 18:16–22
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resources, imports, staged investments and retirements of biorefineries/power plants, afforestation and carbon capture and storage. The different stages of a biomass supply chain are intricately linked with the nexus. For example, the water required for cultivation, processing and conversion of biomass affect agriculture, land use and food production. Conversely, food production competes with bioenergy for land and water. Furthermore, the transport and storage of biomass feedstocks and distribution of products and services require energy and generate emissions. Intensive and poorly planned deployment of bioenergy can affect detrimentally the ecosystem: deforestation, loss of biodiversity and leaching of nutrients and pesticides to bodies of water, to name a few. However, there are also potential synergies that can be exploited. For instance, food crop residues can be used for bioenergy but ensuring that sufficient residue is left on the field to replenish nutrients. Effective planning can lead to better management of forestry resources, improved agricultural practices, water efficiency and sustainable fertiliser use. Along the various stages of the supply chain, strategic integration with the food, water and energy sectors can improve productivity and reduce losses and environmental impacts. There is therefore a great opportunity to include the interactions between biomass supply chains and the FEW nexus in order to develop biorefineries that can transform rural economies, improve and maintain social welfare, enhance energy security and contribute to economic, environmental and social objectives.
Towards a whole systems approach to biorefineries and the FEW nexus Despite the challenging nexus issues inherent to biorefineries, they have the potential to evolve as process systems with enough complexity to balance nexus resource trade-offs through the application of process integration and optimisation at process and value chain levels. These also represent timely opportunities to develop whole systems methods that transform nexus challenges into integrative opportunities. Such a whole systems approach should embrace the FEW nexus as a framework to enhance sustainability of biomass utilisation through the following principles: 1. Extensive fractionation to utilise all biomass components and extract food components already in feedstock 2. Energy and water integration at process, regional and value chain levels 3. Residual waste and wastewater processing with recovery of nutrients to be returned for food and biomass feedstock cultivation and water for reuse and recycle 4. Mix and match local ecosystems, environmental and climate conditions to crop resource requirements and biorefining technologies Current Opinion in Chemical Engineering 2017, 18:16–22
5. Synergistic integration with FEW nexus components along biomass value chains. Biorefinery planning should also aim to tackle interconnected problems present in FEW systems by developing solutions that align with existing regulations and policies [21]. Key issues associated with biorefineries and the FEW nexus along the whole supply chain should also be considered [60].
Conclusions Sustainability issues of biorefineries using first generation feedstock remarked the importance of interaction with other systems such as food and water production. With a nexus approach advanced biorefineries processing a variety of non-food crops and combining established and novel technologies have the potential to shift those negative impacts on the FEW nexus into synergistic integrations. In this review several opportunities for positive FEW interactions of biorefineries have been discussed and can be highlighted as: firstly, production of food ingredients by extraction from feedstock or converting biomass fractions into food ingredients; secondly, use of non-food and water efficient crops; thirdly, processing of crop residues and waste feedstocks to recover energy and other products while recovering clean water and nutrients for food production; and finally, integrating biorefineries with other renewable energy systems and other agricultural and food production systems to recover resources from waste streams to recycle nutrients and water and recover energy. The interactions highlighted could be possible by one combination or another of feedstock-technology-product. In exploring such opportunities for synergistic interactions, a whole systems approach would support the development of advanced biorefineries and resilient value chains. If timely developed and applied during design and planning stages, biorefineries will not only allow balancing of nexus trade-offs, but deliver their promising potential for the sustainable development of our society.
Conflict of interest No conflict of interest.
Acknowledgements The authors would like to acknowledge the Newton Fund and the EPSRC/ RCUK for financial support through the Biomass Value Chains and the Food-Energy-Water Nexus Project (Grant No. EP/P018165/1).
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