Starting from the introduction of sustainable development concepts in the “Brundtland Report” (WCED 1987), there have been many attempts to incorporate sustainability principles into engineering design. For example, the “Hannover Principles” express the view that human systems must be designed to coexist with natural systems, renewable resources should be used, safe and long‐lived products are desired, and elimination of waste is a priority (Das 2005c; McDonough and Braungart 2002). The Augsburg Materials Declaration Research (2002) identifies eight factors that must be considered to achieve sustainable production, including integration of environmentally benign, materials, and manufacturing over all stages of the life cycle; optimization and exploitation of raw materials and natural resources; energy‐efficient production technologies and product distribution; regenerative energy sources; and durability, recyclability, and closed loops. The “‘12’ Principles of Green Engineering” (Anastas and Zimmerman 2003) include design to be inherently safe and benign, design for recycle or a commercial afterlife, energy and mass efficiency, and integration with existing energy and material flows. The Sandestin Green Engineering Principles, developed as an outcome of a multidisciplinary engineering conference, emphasize the need for holistic thinking and the use of environmental impact and integrative analysis tools such as life cycle assessment (LCA; Abraham and Nguyen 2003; Allen and Shonnard 2012; Shonnard et al. 2007). The Sandestin Green Engineering Principles (also referred to as “Sustainable Engineering Principles”; Abraham 2006) were developed based on a starting list of principles complied from a literature review of available sustainability or green‐related principles and declaratory statements, including the Hannover Principles, CERES, the Augsburg Materials Declaration, the Twelve Principles of Green Chemistry, Ahwahnee Principles (1991), and Earth Charter Principles. These sustainability concepts and engineering design principles can be summarized in the statement: The goal of sustainable engineering design is to create products that meet the needs of today in an equitable fashion while maintaining healthy ecosystems and without compromising the ability of future generations to meet their resource needs.

The Sandestin Sustainable Engineering Principles and the 12 Principles of Green Engineering are illustrative of the multiple sets of principles available. They capture similar but also complementary elements of sustainability and engineering design; therefore, these two sets of principles will be described in more detail. Here are the Sandestin Green Engineering Principles (Sustainable Engineering Principles) (Abraham and Nguyen 2003; Shonnard et al. 2007):

Principle 1: Engineer processes and products holistically use system analysis and integrate environmental impact assessment tools. These concepts resonate in a number of Green and Sustainable Engineering principles and are addressed at length in various textbooks, including Green Engineering: Environmentally Conscious Design of Chemical Processes (Allen and Shonnard 2002). The principle points out the importance of systematic evaluation and reduction of human health and environmental impacts of designs, products, technologies, processes, and systems. The use of system‐based techniques such as heat and mass integration techniques is essential to minimize human health and environmental impacts of designs through material and energy optimization. The principle also conveys the importance of not shifting risk (e.g. reducing releases to one environmental medium may increase risk to another medium and/or increase the likelihood of worker exposures and jeopardize worker safety) (Abraham 2006; Shonnard et al. 2007). A well‐known example of the consequences of shifting risk is the use of methyl‐tert butyl ether (MTBE) as a gasoline line additive. MTBE was added to gasoline to reduce emissions of carbon monoxide from automobile tailpipe, thereby protecting human health. Its greater mobility in soil and water environments, however, meant that spills of MTBE could more readily migrate to and disperse in water supplies than spills of gasoline (for more details see http://www.epa.gov/otaq/consumer/fuels/oxypanel/blueribb.htm).

Principle 2: Conserve and improve natural ecosystems while protecting human health and well‐being. This principle expresses the importance of understanding environmental processes for engineers involved in design of chemicals, automobiles, building, and other manufactured goods. There are many examples where a lack of understanding caused severe environmental harm and raised the level of health risk to humans and other forms of life. For example, chlorofluorocarbons (CFCs) were thought to be ideal refrigerants. They replaced dangerous refrigerant fluids like ammonia and made storage of food and building eliminate control far safer. Their benefits to human health and well‐being were clear; however, once the role of CFC in stratospheric ozone destruction chemistry was worked out, it became clear that there were hazards to human health associated with CFC use. Not every engineer needs to be an expert in environmental processes and health effects, but designers should be aware of the potential harm that can be caused and work with multidisciplinary experts to achieve more sustainable solutions (Allen and Shonnard 2012; Das 2005e).

Principle 3: Use of life‐cycle thinking in all engineering activities. This principle complements Principle 1. Every engineered product is created, functions over a useful life, and eventually disposed of to the environment. Life‐cycle thinking can help avoid a narrow outlook on environmental, social, and economic concerns and help make informed decisions. Life‐cycle thinking that gets incorporated into design will help identify design alternatives that minimize environmental impacts at the various life stages. This same kind of thinking can also consider economic and social aspects. The importance of life‐cycle thinking can be illustrated (see Chapter 6).

Principle 4: Ensure that all material and energy inputs and outputs are as inherently safe and benign as possible. This principle complements Principle 3. These characteristics of materials and chemicals must be applied to all stages of a product’s life, from extraction to use and disposal. The following are some questions that must be asked in each stage of the life cycle: Are the materials toxic? Are these inherently benign (in terms of toxicity) materials that can be used as substitutes? Will exposure during manufacturing be a health problem to workers? Does the product pose minimal impact during recycle and disposal? Will an unintentional release of materials quickly degrade in the environment? Properties of materials relevant to safety, beyond toxicity, must also be considered, such as flammability, explosivity, and corrosivity.

Principle 5: Minimize depletion of natural resources. As the world’s population continues to grow and becomes more affluent, natural resources will be used at ever greater rates, and the importance of this principle is raised. An overview of materials, energy, and water use is provided in Chapter 1. Efficient use of nonrenewable energy resources is of primary interest, and development of renewable alternatives for energy and materials should be given a high priority in engineering design.

Principle 6. Strive to prevent waste. Waste not only represents material that takes up space in landfills but more importantly represents a loss of efficiency in a production system that includes many input materials and energy sources. When waste is avoided through design, the environmental impacts associated with the input materials and the energy that went into producing the discarded product are also avoided. The following are some questions that must be asked during design: Are there ways (e.g. procedures, engineering) to improve the yield or efficiency of raw materials? How can the releases or wastes be recycled and reused? Can the product be reused after its normal commercial life, hence minimizing the raw materials needed to manufacture new products? Methods for minimizing wastes, particularly in chemical processes, are discussed at length in various textbooks, including Green Engineering: Environmentally Conscious Design of Chemical Processes (Allen and Shonnard 2002).

Principle 7: Develop and apply engineering solutions, while being cognizant of local geography, aspirations, and cultures. Engineering design are directed toward meeting individual human and societal needs, and in order to better achieve this goal, awareness of the societal context of the design is crucial. An engineering design in one society, such as rapid public transportation systems, may not meet the aspirations and needs in another society, even though the design achieves environmental objectives. The main point is to move each society, though engineering design, toward more sustainable utilization of resources in a way that achieves that society’s or individual’s aspirations (Allen and Shonnard 2012).

Principle 8: Create engineering solutions beyond current or dominant technologies: improve, innovate, and invent (technologies) to achieve sustainability. Sustainability can be a powerful motivation for change in engineering design, technologies, process, and products. This principle emphasizes the importance of being innovative (i.e. “out‐the‐box” thinking) in the development of new technologies. The knowledge gained through considering the many dimensions of sustainability should be reflected in how engineering designs accomplish societal objectives.

Principle 9: Actively engage communities and stakeholders in the development of engineering solutions. There are many examples of stakeholder and community engagement in the development of engineered solutions in a wide range of activities, including city planning, infrastructure development, and production of manufactured goods. One illustrative example is in the Mining Minerals Sustainable Development North America project (IISD 2002) that has been adopted by key members of this industry. Central to these mining project questions is community engagement from project inception to mine closure. During this engagement, the communities surrounding the proposed mine development express their wishes with regard to managing the economic development and any concerns over local environmental consequences.

A second set of engineering design principles, the 12 Principles of Green Engineering, from Anastas and Zimmerman (2003) and Allen and Shonnard (2012), is presented here as follows.

PRINCIPLES OF GREEN ENGINEERING

Principle 1: Designers need to strive to ensure that all material and energy inputs and outputs are as inherently nonhazardous as possible.

Principle 2: It is better to prevent waste than to treat or clean up waste after it is formed.

Principle 3: Separation and purification operations should be designed to minimize energy consumption and materials use.

Principle 4: Products, processes, and systems should be designed to minimize mass, energy, space, and time efficiency.

Principle 5: Products, processes, and systems should be “output pulled” rather than “input pulled” through the use of material and energy.

Principle 6: Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse, or beneficial disposition.

Principle 7: Targeted durability, not immortality, should be a design goal.

Principle 8: Design for unnecessary capacity or capability (e.g. “one‐size‐fits‐all”) solutions should be considered a design flaw.

Principle 9: Material diversity in multicomponent products should be minimized to promote disassembly and value retention.

Principle 10: Design of products, processes, and systems must include integration and interconnectivity with available energy and materials flows.

Principle 11: Products, processes, and systems should be designed for performance in a commercial “afterlife.”

Principle 12: Material and energy inputs should be renewable rather than depleting.

Principle 1: Designers need to strive to ensure that all material and energy inputs and outputs are as inherently nonhazardous as possible. This principle recognizes that significant costs and hazards result from the selection of sources of materials and energy. Additional control systems are required to capture and destroy hazardous materials during production, use, and disposal, all of which add to the cost of the design. If inputs to the system are inherently less hazardous, the risks of failure will be reduced and the amount of resources expended on control, monitoring, and containment will be less.

Principle 2: It is better to prevent waste than to treat or clean up waste after it is formed. The creation of waste in engineered systems adds to the complexity, efforts, and expense of the design. This is especially true for hazardous wastes, which require extraordinary measures for their control, monitoring, transport, and disposal. To reduce waste generation, the design must strive to incorporate as much of the input materials as possible into final products. This strategy can be applied at many scales, for example, at the molecular level in the design of chemical reactions, at larger scales such as in machining of parts, and further in assembly of discrete parts. Any waste that is generated should be considered as raw material to be used again in the current product system or as input to a separate product system.

Principle 3: Separation and purification operation should be designed to minimize energy consumption and materials use. In the chemical and mineral‐processing industries, large‐scale separation processes are among the largest energy‐consuming units and generates a significant proportion of emissions and wastes. Even in industry sectors where the mass of the products produced is not large, separation processes can be significant. In electronics manufacturing, the generation of ultra‐pure water and the creation of ultra‐clean work environments require separation processes with significant costs and energy demands. Design for efficient separation is very important for these industries, and several approaches can be investigated during design. Gains in energy efficiency can be attempted through heat integration by considering all streams needing to gain or lose energy in the process and also outside the process if in close proximity to other facilities. Similarly, pollution can be prevented by considering mass integration, taking waste streams from one process and using them as raw materials for another. In certain instances, products can be induced to self‐separate by adjusting conditions to take advantage of physical and chemical properties of the chemicals. As another example, in mechanical systems, reversible fasteners can be used to encourage the disassembly of manufactured parts at the end of life.

Principle 4: Products, processes, and systems should be designed to maximize mass, energy, space, and time efficiency. Energy and mass efficiency were dealt with in Principle 3, so this discussion will focus on space and time efficiency. Space and time are interrelated in many engineered systems, but most obviously in transport of raw material and products. Reducing the distance between points of use for materials can save time and reduce pollution. Close proximity can facilitate exchanges of waste heat and materials in highly integrated production systems. Colocation of manufacturing and recycle facilities can also lead to efficiency gains in many production systems. Industrial parks near residential areas can lead to sharing of excess heat with communities. However, these proximity opportunities that take advantage of space and time factors also must consider safety concerns due to potential exposure to emissions and industrial accidents. The excess time that a product sits in inventory can run up against storage stability limits and could lead to excess waste generation.

Principle 5: Products, processes, and systems should be “output pulled” rather than “input pushed” through the use of materials and energy. It is well known that some chemical reactions can be “pulled” to completion by removing certain co‐products from the reaction mixture. This chemical phenomenon, which is termed Le Châtelier’s principle, can be applied to engineering design across scales of production. “Just‐in‐time” manufacturing is an example of this principle where only the necessary units are produced in the necessary quantities at the necessary time by bringing production rates exactly in line with demand. Planning manufacturing systems for final output eliminates the wastes associated with over‐production, waiting time, processing, inventory, and resource inputs.

Principle 6: Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse, or beneficial disposition. Entropy and complexity are related concepts when considering engineered systems. Products having a high degree of order and structure are at a low state of entropy. The higher the degree of complexity and structure in a product, the greater is the amount of energy invested to create such structure and complexity. When considering end‐of‐life options for products, the degree of complexity and structure should point the way to proper reuse, recycle, and remanufacturing options. Highly complex parts should be reused if at all possible in order to avoid the investment required to create a replacement part from virgin (newly extracted from nature) resources.

Principle 7: Targeted durability, not immortality, should be a design goal. Many products last much longer than the expected commercial life. There can be multiple impacts from this extended durability. For example, buildings with inefficient energy systems, designed when energy was relatively inexpensive, may become inoperable in times of expensive energy. At a different scale, the challenge in the design of molecules and of manufactured parts is to create products that are durable yet do not persist indefinitely in the environment. Durability means that the products for the intended commercial life and are therefore readily reconfigured or degraded at the end of life into harmless substances that assimilate easily into natural cycles.

Principle 8: Design for unnecessary capacity or capability (e.g. “one size fits all”) solution should be considered a design flaw. Most products are overdesigned to cover a wide application range and settings. Automobiles must be designed to function not only in warm temperatures but also in extremes of cold. However, there are instances where design for “one size fits all” does not make the most sense and is potentially wasteful. For example, a jacket could be designed for the coldest possible climate, but this garment would not be much use for a stroll along the beach on a breezy evening in Florida in the winter. Likewise, lighting of a large classroom, office space, or a room at home with a single light switch would not make as much sense if only one person were in the room at a given time. In such a case, district lighting would save on energy when only one or a few occupants are present in a large space.

Principle 9: Material diversity in multicomponent products should be minimized to promote disassembly and value retention. This design principle has elements in common with Principle 6. Increasing material diversity in products has the effect of making recycling more difficult and expensive because the number of recycling options and their complexity increase as material diversity increases. Different kinds of material and the use of different additives have a strong influence on recycling methods and costs.

Principle 10: Design of products, processes, and systems must include integration and interconnectivity with available materials and energy flows. This design principle states that products, processes, and entire engineered systems should be designed to use the existing infrastructure of material and energy flows. Integration with existing infrastructure can occur at the scale of a unit operation, production line, manufacturing facility, or industrial park. Taking advantage of existing material and energy flows will minimize the need to generate energy and/or acquire and process raw materials. Applications of this principle include the recovery and use of heat from exothermic chemical reactions, the cogeneration of heat and power, and the recovery of electrical energy by regenerative braking in hybrid vehicles.

Principle 11: Products, processes, and systems should be designed for performance in a commercial “afterlife.” Designing components for a second, third, or even longer life is an important strategy in product design. When components are recovered and reused in next‐generation products, the environmental impacts of raw material acquisition from virgin resources and conversion are eliminated. And the overall life cycle environmental impacts are reduced. This strategy is especially important for products that become obsolete prior to component failure, such as cell phones and other electronic devices. Important examples of this principle also include the recovery and recycle of spent copy toner cartridges, the renovation of industrial building for housing and reuse of beverage containers as practiced in Germany, where bottles are more substantial in their construction to allow for collection, washing, sterilization, refilling, and relabeling.

Principle 12: Material and energy inputs should be renewable rather than depleting. The use of nonrenewable raw materials from nature in the design of engineered systems moves the Earth system incrementally toward depletion of finite resources and is therefore unsustainable by definition. All renewable resources (also see Figure ) derive their usefulness and energy from the sun, and as a result these system inputs can be sustainable, if used at a level consistent with their rate of renewable resources in that it can serve not only as an energy source but also as a feedstock for design of material products (AIChE, CWRT 2000; Das 2005g). One important form of a biomass product is liquid transportation fuels. Biofuels are renewable on relatively short timescales, and the cycling of biofuel carbon between the atmosphere, biomass/biofuel, and back to the atmosphere again is readily integrated into natural cycles in a way that might not cause accumulation of CO₂ in the atmosphere. An offshoot of this principle is the importance of design for products and systems that integrate well with natural cycles of elements across the life cycle, from raw material acquisition to end‐of‐life process.

These engineering design principles, in addition to the others mentioned in the beginning of this section, establish a framework for designing more sustainable products and processes. At first, changes in engineering design are likely to be improvements to inherently unsustainable products and systems, but over time it is hoped that these principles will move industry and consumers toward inherently sustainable products and production systems. However, there will be tensions in applying these principles. What if making a process inherently safer requires more energy? What if minimizing water use requires more energy? Engineers are accustomed to addressing trade‐offs between objectives, but methods for doing so require measures of performance. In most engineering designs the measure is cost. In delivering a specified level of performance of a product, technology, or service, the goal is to minimize cost.