# Green engineering

Green engineering approaches the design of products and processes by applying financially and technologically feasible principles to achieve one or more of the following goals: (1) decrease in the amount of pollution that is generated by a construction or operation of a facility, (2) minimization of human population exposure to potential hazards (including reducing toxicity), (3) improved uses of matter and energy throughout the life cycle of the product and processes, and (4) maintaining economic efficiency and viability. Green engineering can be an overarching framework for all design disciplines.

## History

The concept of green engineering began between 1966 and 1970 during the Organization for Economic Cooperation and Development under the name: "The Ten Ecological Commandments for Earth Citizens". The idea was expressed visually as the following cycle starting with the first commandment and ending with the tenth:
* Respect the laws of nature
* Learn as responsible earth citizens from the wisdom of nature
* Do not reduce plurality richness, abundance of living species
* Do not pollute
* Face earth-responsibility every day for our children and our children's children
* Follow the principle of nature precaution/sustainability in all economic activities!
* Act as you speak!
* Prefer small clever and intelligent problem solutions, including rational and emotional intelligence factors
* Information about environmental damage belongs to mankind - not (only) to privilieged big business
* Listen carefully [to] what your own body tells you about [the] impact of your very personal social and natural environment upon your wellbeing
The idea was then presented by Peter Menke-Glückert at the United Nations Educational, Scientific, and Cultural Conference at Paris in 1968. These principles are similar to the Principles of Green Engineering in that each individual has an intrinsic responsibility to uphold these values. The Ten Ecological Commandments for Earth Citizens is thought by Dr. Płotka-Wasylka to have influenced The Principles of Green Engineering, which has been said to imply that all engineers have a duty to uphold sustainable values and practices when creating new processes.
Green engineering is a part of a larger push for sustainable practices in the creation of products such as chemical compounds. This movement is more widely known as green chemistry, and has been headed since 1991 by Paul Anastas and John C. Warner. Green chemistry, being older than green engineering, is a more researched field of study and began in 1991 with the creation of the 12 Principles of Green Chemistry.

### 12 Principles of Green Engineering

On May 19, 2003, Paul Anastas along with his future wife, Julie Zimmerman created the 12 Principles of Green Engineering. This expanded upon the 12 Principles of Green Chemistry to not only include the guidelines for what an environmentally conscious chemical should be in theory, but also what steps should be followed to create an environmentally conscious alternative to the chemical. Environmentally conscious thought can be applied to engineering disciplines such as civil and mechanical engineers when considering practices with negative environmental impacts, such as concrete hydration. These principles still were centered around chemical processes, with about half pertaining to engineers. There are many ways that both the 12 Principles of Green Chemistry and 12 Principles of Green Engineering interact, referred to by Tse-Lun Chen et al. as "cross connections". Every one Principle of Green Engineering has one or more corresponding "cross connections" to Principles of Green Chemistry. For example, principle 1 of green engineering is "Inherent Rather than Circumstantial", which has cross connections to principles 1, 3, and 8 of green chemistry. The twelve principles introduced by the American Chemical Society are:
* Inherent Rather Than Circumstantial – Designers need to strive to ensure that all materials and energy inputs and outputs are as inherently nonhazardous as possible.
* Prevention Instead of Treatment – It is better to prevent waste than to treat or clean up waste after it is formed.
* Design for Separation – Separation and purification operations should be designed to minimize energy consumption and materials use.
* Maximize Efficiency – Products, processes, and systems should be designed to maximize mass, energy, space, and time efficiency.
* Output-Pulled Versus Input-Pushed – Products, processes, and systems should be "output pulled" rather than "input pushed" through the use of energy and materials.
* Conserve Complexity – Embedded entropy and complexity must be viewed as an investment when making design choices on recycling, reuse, or beneficial disposition.
* Durability Rather Than Immortality – Targeted durability, not immortality, should be a design goal.
* Meet Need, Minimize Excess – Design for unnecessary capacity or capability (e.g., "one size fits all") solutions should be considered a design flaw.
* Minimize Material Diversity – Material diversity in multicomponent products should be minimized to promote disassembly and value retention.
* Integrate Material and Energy Flows – Design of products, processes, and systems must include integration and interconnectivity with available energy and materials flows.
* Design for Commercial "Afterlife" – Products, processes, and systems should be designed for performance in a commercial "afterlife."
* Renewable Rather Than Depleting – Material and energy inputs should be renewable rather than depleting.

## Sustainable Engineering

"Sustainable engineering" and "green engineering" are terms that are often used interchangeably. The main difference between the two being that green engineering is "optimized to minimize negative impacts without exhausting resources available in the natural environment" and sustainable engineering is "more directed toward building a better future for the next generations". The concept of sustainable engineering was awoken due to the amount of resource consumption partaken by humans, and the idea attempts to draw people toward sustainable actions to help the environment. Challenges that exist include the large-scale emissions of greenhouse gases form structural materials, worldwide use of fossil fuels, and finite number of raw and natural resources. In particular, experts look to incorporate sustainable engineering, along with green engineering concepts, into undergraduate engineering curriculums to educate future generations about potential risks to the environment that can be mitigated by engineering theories. The idea of sustainable development became intertwined with engineering and chemistry early in the 21st century. One often cited book that brought the idea of sustainable development to engineers was the publishing of: "Sustainable Infrastructure: Principles into Practice", written by Charles Ainger and Richard Fenner.

## Systems approach

Many engineering disciplines engage in green engineering. This includes sustainable design, life cycle analysis (LCA), pollution prevention, design for the environment (DfE), design for disassembly (DfD), and design for recycling (DfR). As such, green engineering is a subset of sustainable engineering. Green engineering involves four basic approaches to improve processes and products to make them more efficient from an environmental standpoint.
* Waste Reduction - With the human population continuing to grow at a steady rate, so does resource consumption by the human race. As a result of this growth, the increase of waste material becomes a challenge.
* Materials Management - Fossil fuels and raw materials are scarce resources that require proper management to conserve. Materials management covers this management process.
* Pollution Prevention - Greenhouse gas and carbon dioxide emissions remain costly effects of engineering factories and sit at the top of pollution risks. The prevention of these pollutants and others is essential to green engineering principles.
* Product Enhancement - Engineers look to enhance their products to benefit the environment through the utilization of environmental-friendly materials. Such materials include paper, cardboard, wood, and sand for steel and concrete alternatives.
Green engineering approaches design from a systematic perspective which integrates numerous professional disciplines. In addition to all engineering disciplines, green engineering includes land use planning, architecture, landscape architecture, and other design fields, as well as the social sciences(e.g. to determine how various groups of people use products and services. Green engineers are concerned with space, the sense of place, viewing the site map as a set of fluxes across the boundary, and considering the combinations of these systems over larger regions, e.g. urban areas. The life cycle analysis is an important green engineering tool, which provides a holistic view of the entirety of a product, process or activity, encompassing raw materials, manufacturing, transportation, distribution, use, maintenance, recycling, and final disposal. Assessing its life cycle should yield a complete picture of the product. The first step in a life cycle assessment is to gather data on the flow of a material through an identifiable society. Once the quantities of various components of such a flow are known, the important functions and impacts of each step in the production, manufacture, use, and recovery/disposal are estimated. In sustainable design, engineers must optimize for variables that give the best performance in temporal frames.
The system approach employed in green engineering is similar to value engineering (VE). Daniel A. Vallero has compared green engineering to be a form of VE because both systems require that all elements and linkages within the overall project be considered to enhance the value of the project. Every component and step of the system must be challenged. Ascertaining overall value is determined not only be a project's cost-effectiveness, but other values, including environmental and public health factors. Thus, the broader sense of VE is compatible with and can be identical to green engineering, since VE is aimed at effectiveness, not just efficiency, i.e. a project is designed to achieve multiple objectives, without sacrificing any important values. Efficiency is an engineering and thermodynamic term for the ratio of an input to an output of energy and mass within a system. As the ratio approaches 100%, the system becomes more efficient. Effectiveness requires that efficiencies be met for each component, but also that the integration of components lead to an effective, multiple value-based design. Green engineering is also a type of concurrent engineering, since tasks must be parallelized to achieve multiple design objectives.

## Implementation
### Ionic liquids

An ionic liquid can be described simply as a salt in a liquid state, exhibiting triboelectric properties which allow it to be used as a lubricant. Traditional solvents are composed of oils or synthetic compounds, like fluorocarbons which, when airborne, can act as a greenhouse gas. Ionic liquids are nonvolatile and have high thermal stability and, as Lei states, "They present a “greener” alternative to standard solvents". Ionic liquids can also be used for carbon dioxide capture or as a component in bioethanol production in the gasification process.

### Ceramic tiles

Ceramic tile production is typically an energy and water-intensive process. Ceramic tile milling is similar to cement milling for concrete, where there is both a dry and wet milling process. Wet milling typically produces a higher quality tile at a higher cost of energy and water, while dry milling would produce a lower quality material at a lower cost.