The Application of Detrital Actors in Industrial Systems

Available online at www.sciencedirect.com

ScienceDirect Procedia CIRP 69 (2018) 867 – 871

25th CIRP Life Cycle Engineering (LCE) Conference, 30 April – 2 May 2018, Copenhagen, Denmark

The application of detrital actors in industrial systems Stephen M. Malonea,*, Abigail R. Cohena, Bert Brasa, Marc Weissburgb a

School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Dr., Atlanta, Georgia 30332, USA b School of Biological Sciences, Georgia Institute of Technology, 950 Atlantic Dr., Atlanta, Georgia 30332, USA

* Corresponding author. Tel.: +1-770-853-9137; E-mail address: [email protected]

Abstract Biological systems have evolved to retain and recycle materials via decomposer networks. However, engineered systems are often deficient in the employment of decomposers despite their potential to improve efficiency and sustainability. These systems favor unmitigated growth and exploit natural resources, exporting pollutants to the environment as waste. Reducing this disparity between industrial and natural systems presents the opportunity for greater material and energetic efficiency. This study demonstrates the application of decomposer networks in industrial settings through constructed wetlands and pyrolysis driven biomass upcycling integrated into a steel industry’s water network. The results from this study show a 26.64%, 57.87%, and 28.29% reduction of fresh water, effluent, and costs respectively. However, common sustainable design principles at design conception leave these system-level improvements unrealized. As such, this study points to the need for a predictive tool in sustainable engineering design, incorporating time-dependent flow metrics to more effectively leverage the decomposer role. © Authors. Published by Elsevier B.V. ThisB.V. is an open access article under the CC BY-NC-ND license ©201 207The The Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 25th CIRP Life Cycle Engineering (LCE) Conference. Peer-review under responsibility of the scientific committee of the 25th CIRP Life Cycle Engineering (LCE) Conference

Keywords: Optimization; Industrial Symbiosis; Manufacturing; Ecological Network Analysis

1. Introduction Industrial Ecology is a well-developed field of inquiry that uses high-level principles from ecology to guide the design and analysis of human industrial processes. This method of inquiry often invokes ecologically-based metaphors to provide insight. Industrial Ecologists liken industrial activity today to opportunistic, immature natural systems [3], which are those that have developed quickly in the presence of abundant resources. The organisms within these systems utilize a rapid growth strategy, squandering resources by maximizing material throughput [4]. Similar to the unregulated growth demonstrated by immature natural systems, industrial activity has grown in size since the industrial revolution to meet the increasing demands of exponential population growth. This growth has placed an unmatched strain on the environment through heavy extraction of resources and unmitigated waste generation [5]. By contrast, mature ecological systems have evolved over time to live within the resource constraints of their

environment. These systems embody sustainability through material efficiency, demonstrating intricate decomposing and cycling networks [6]. The majority of organisms that comprise mature ecosystems optimize, rather than maximizing production [7]. By leveraging the organizational properties of mature natural systems, engineers and industry planners should adapt these lessons to guide sustainable development at the systems level. The objective of this study is to demonstrate the often-unrecognized potential of this ecosystem inspired design approach using an industrial case study. Providing a framework in which the ecosystem metaphor could be leveraged during the conceptual idealization phase of engineering design. Nomenclature ENA

Ecological Network Analysis

2212-8271 © 201 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 25th CIRP Life Cycle Engineering (LCE) Conference doi:10.1016/j.procir.2017.11.091

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2. Natural Ecosystems Organization and Dynamics

3. Sustainable Industrial Design: Challenges and Solutions

Life has evolved on Earth for over 3.8 billion years [8]. Over this time, natural ecosystems have evolved through periods of material and energy shortages to sustainable configurations, where organic materials move through functional roles of producers, consumers, and finally returned to the system through decomposers [9]. These natural system configurations are often represented as a pyramid, illustrated in Fig. 1 [10].

3.1. Sustainable Design Challenges Engineering design in the age of connectivity is increasingly complex with endless linkages between commerce, communication, and transportation. Sustainable designs must take into account environmental, social, and economic shareholders from conception. Considerations must include factors such as safety, security, design for manufacturing, environmental impact, serviceability, material efficiency, energy efficiency, end-of-life recovery, and impact to future generations [16]. Confronting this complexity, some industry leaders have embraced sustainable design frameworks and guidelines, recognizing the inherent economic, environmental, and societal benefits. There is a host of general principles from varying sources used within the engineering community to guide ideation phase design [17, 18]. Table 1 demonstrates one example of such principles. Table 1. Example of common design principles [17]

Fig. 1. Functional Roles Configuration

This pyramid reflects the amount of biomass or energy of different functional groups and how energy is transferred between these groups. The base of the pyramid consists of primary producers, such as plants, that use solar energy and nutrients to produce plant biomass that can be utilized by other organisms to supply energy. Nutrients for plants are supplied by decomposing organisms, which feed on dead organic matter, or detritus [11]. Ascending the pyramid, one then encounters primary consumers such as herbivores and omnivores, fed by the producers, and at the top are the carnivore consumers. The movement of energy when one organism consumes another from one trophic level to the next is idealized as a food chain. In reality, organisms may function as both carnivores and herbivores and so consumer interactions are best thought of as a food-web. The decomposer functional role, consisting of decomposers and detrital feeders named detritivores, is vital to natural ecosystems in that they are nature’s core recycling components [12]. Decomposers convert dead organic matter from all trophic levels into inorganic nutrients that fertilize the growth of the producers [13, 14]. These decomposers typically consist of an array of bacteria and fungi that absorb and metabolize up to half of material flows in natural systems, breaking complex tissue into the fundamental components of carbon dioxide, water, and inorganic nutrients that can then be re-introduced into the system [6]. In addition, decomposers are often biochemically specialized to consume organic materials and waste products that are difficult for other organisms to digest [15]. Detritivores assist decomposers in the nutrient cycling and conversion process by breaking down lumps of larger organic material, increasing surface area for the molecular-scale decomposers, and their biomass feeds higher trophic level consumers.

1 2 3 4 5

Design consistent with ecological principles Design for site-specific context Maintain independence of design functional requirements Design for efficiency in energy and information Acknowledge the purposes that motivate design

However, the qualitative framework of such principles, which are used throughout industry, are subjective in nature. As such, designers lack a quantitative benchmark and sustainable design methodology with which they can mitigate environmental burdens. Without such quantitative benchmarking tools, designers are currently unable to model during design conception how a system might perform at a macro level over time, and they cannot monitor and evaluate system performance or sustainability. 3.2. A possible solution to the challenges: the translation of nature’s lessons to industry Ecological Network Analysis (ENA) is a quantitative tool used by Ecologists to study interactions within ecosystems in a holistic manner [19, 20]. ENA derives structural and functional properties of ecological systems using graphs to represent food web interactions. Graphs consist of nodes and edges that represent predator-prey exchanges of material and energy. Some scientists have adapted this approach for use in engineered industrial systems, comparing the structural and functional properties of natural ecosystems to assess the design and performance of these systems [21, 22]. The translation of functional roles found within mature natural ecosystems into industrial system components is accomplished by distilling out basic functions that exist within both industry and nature, such as the consumption of energy and materials, transforming materials and energy into products [3], and breaking down products to make them reavailable. Using ENA to describe and model industrial systems shows strong disparities between human and natural systems [23]. For instance, industrial systems are characterized by a limited number of primary producers and abundance of

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dependent consumers, while the decomposer role is often lacking or absent altogether [21]. The material cycling deficiency has led to dependence on virgin resources, and it has subjected industrial systems to supply chain vulnerability as well as contributed to the global environmental crisis through excess waste generation. By contrast, natural systems that possess a detrital feedback loop through detritivores and decomposers, exhibit improved performance metrics in these domains, such as structural stability and efficiency [24]. Thus, improvements that originate from the decomposer functional role found in natural systems must be leveraged when translating ecosystem structure and flow-based properties to sustainable industrial systems, as these indicators are the some of the major determinants of longevity and profitability amongst corporate industries today [25]. 3.3. A case study highlighting the unrealized potential of detrital actors in industry Within efficient steel manufacturing industries today, freshwater accounts for over 38% of the total material mass used throughout the crude steel production process, totaling 4.12 m3/tonne-crude steel [1]. As a result, steel industries are typically situated in coastal regions, allowing them to import raw materials and to meet the freshwater demand through desalination technologies. A simplified steel material flow network is illustrated in Fig. 2.

steel mill can result in some slight water savings [2], such analysis ignores other ways to save water through reuse of wastewater. Constructed wetlands were modeled that employ plant species with effluent-specific affinities to leverage materials that would otherwise be disposed of as waste, and bring them back into the steel manufacturing process. These wetlands treat and recycle the brine effluent generated through the desalination’s reverse osmosis process and the otherwise discarded effluent generated by the on-site water treatment plant. Malone’s study [2] yielded major improvements to the steel industries freshwater consumption, effluent generation, and cost as demonstrated in Table 2. Thus, the total reductions achieved by combining the traditional optimization with the use of wetlands was 26.64%, 57.87%, and 28.29% reduction when compared to pre-optimization of fresh water, effluent, and freshwater costs respectively. Table 2. Traditional versus ecological optimization results [2] Trad. After Savings

Eco. After Eco. After Savings

Before

Trad. After

Freshwater (m3/hr)

3363.88

2734.86

18.70%

2467.84

26.64%

Effluent (m3/hr)

754.47

584.86

22.48%

317.84

57.87%

16.67%

12,926,777

28.29%

Freshwater Cost 18,027,639 15,023,032 (USD/yr)

Although optimization of the various unit processes within a

Fig. 2. Simplified steel industrial material flow network [2].

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Fig. 3. Steel industrial network with constructed wetlands and pyrolysis [1].

A proposed end-use for the biomass accumulation from the wetlands is utilizing the excess heat expelled to the environment through the blast furnace flue gas to fuel a pyrolysis process. Pyrolysis is the thermal decomposition of biomass into heterogeneous gaseous, liquid, and solid intermediates in an endothermic reaction. The solid product of this reaction, also known as char, can be used as a fuel or soil amendment [26]. The biochar product would then be reintroduced as a feedstock into the steel manufacturing process as illustrated in Fig. 3. If this were to occur, the ecosystem metaphor would be modified as the wetlands would then take the role of a decomposer as well as a detritivore. This is due to the wetlands now decomposing organics to their elemental form, creating new material flows and cycling in the system which otherwise might need to be removed as waste. The inorganic fuel elements of the pyrolysis process that could interfere with the steel-making process are nearly completely contained within the ash of the pyrolysis process and thus easily disposed or used as a feedstock in chemical manufacturing. The remaining contaminants released from the wetland biomass through the pyrolysis process could be treated with traditional technologies such as charcoal filters and dryscrubbing. A parallel assessment found that this approach would decrease the raw coal consumption required in steel manufacturing by 610 kg per day, decreasing the dependence on imports to the system [1].

industrial systems at conception. This approach builds upon the concepts introduced and lessons learned in [2], where an existing system was modified and optimized. By using ENA to provide valuable insight to designers at conception, the sustainable structural and flow-based properties identified in natural systems can be maximized in the resulting humanengineered system. However, ENA has not traditionally been used in conjunction with optimization techniques or to analyze system processes over a dynamic period of time, representing instead the modeled system as steady state [27]. These incompatibilities introduce fundamental issues in utilizing ENA in a traditional manner in systems design, as industrial systems design today encompasses complex, dynamic, and integrative processes. Halnes, Fath and Liljenström [24] recognized this limitation with current ENA methodology applied even to natural systems feedback cycles of certain actors, which occur at different time scales than traditional predation exchanges. This limitation could be addressed with time-delayed differential equations, though currently there is no research to suggest this approach has been developed further [24]. As such, a predictive tool for conceptual systems design must incorporate time-dependent flow metrics combined with industry supplied constraints to more accurately model and optimize complex systems and more effectively leverage the decomposer functional role. 5. Conclusions

4. Moving forward: The construction of a design tool To address these fundamental issues encountered by designers today, the ideation phase of the complex, sustainable industrial systems demands a systematic overhaul through which designers can quantify, operationalize, and monitor system sustainability. Therefore, we propose modifying ENA to develop a tool, providing optimized quantitative insight into the sustainable performance of

In this study, the organizational properties that give way to the material efficiency of natural ecological systems are examined. We introduce the decomposing networks constituted by detrital actors found throughout natural ecosystems but underutilized within the human engineered industrial landscape. An example of the application of this concept is presented through a case study of the steel industry’s water network. This study demonstrates how

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detrital actors within industrial systems, when combined with optimization techniques, could be applied and the associated sustainable improvements. In addition, this case study highlights the benefit of biological augmentation in manufacturing by providing evidence that the inclusion of biological actors may be an effective way to achieve significant sustainable improvements. Methodologies of current sustainable industrial systems design strategies are discussed, focusing on the challenges introduced by the subjective nature of sustainable design principles. This challenge found in industry today leads to a gap between proposed qualitative environmental, social, and economic metrics and the reality of constructed industrial systems. We introduce the notion of a conceptual tool for designers that utilizes rate-dependent differential equations with ecological network analysis as the engine to assist the closing of this gap. The development of such a tool for designers within industry allows for design teams, at the conceptualization phase, to quantify and optimize their designs structural and flow properties to better resemble those found in natural ecosystems in a quantitative manner that maximizes ecosystem parity. 6. Acknowledgements This material is based upon work supported by the National Science Foundation under Grant Nos. CBET1510531and EFMA-1441208. In addition, we would like to thank the Brook Byers Institute for Sustainable Systems for their unwavering support advancing multiple fronts of sustainability research. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or their respective host institutions. References [1] S.M. Malone, A Systems-Based Approach to Sustainable Steel Manufacturing, Mechanical Engineering, Georgia Institute of Technology, Georgia Institute of Technology Library, 2017, p. 87. [2] S.M. Malone, K. Zhang, B. Bras, M. Weissburg, Y. Zhao, H. Cao, Ecologically Inspired Optimization: An Unconventional Approach to Sustainable Industrial Systems, Engineering Special Issue on Green Industrial Processes (In Print) (2017). [3] B.R. Allenby, W.E. Cooper, Understanding industrial ecology from a biological systems perspective, Environmental Quality Management 3(3) (1994) 343-354. [4] E.D. Enger, B.F. Smith, Environmental science : a study of

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