Green Engineering

Introduction to Green Engineering

Green Engineering is the design, commercialization, and use of processes and products, which are feasible and economical while minimizing 1) generation of pollution at the source and 2) risk to human health and the environment. Green engineering embraces the concept that decisions to protect human health and the environment can have the greatest impact and cost effectiveness when applied early to the design and development phase of a process or product.[1] In Green Engineering it is not sufficient to be only green, but other design considerations must also be included, like economics, safety, and others.("Green")

Risk Assessment


Risk assessment is a systematic, analytical method used to determine the probability of adverse effects. A common application of risk assessment methods is to evaluatehuman health and ecological impacts of chemical releases to the environment. Information collected from environmental monitoring or modeling is incorporated into models of human or worker activity and exposure, and conclusions on the possibility of adverse effects are formulated. Almost always, when the results from environmental risk assessment are used, they are incorporated into the decision-making process along with economic, societal, technological, and political consequences of a proposed action estimating environmental risks when the only hazard information available is a chemical structure. Many of these methods have been developed by the US Environmental Protection Agency (US EPA) and its contractors. The methods are routinely used in evaluating pre-manufacture notices submitted under the Toxic Substances Control Act (TSCA). Under the provisions of TSCA, before a new chemical can be manufactured in the United States, a pre-manufacture notice (PMN) must be submitted to US EPA. The PMN specifies the chemical to be manufactured, the quantity to be manufactured and any known environmental impacts as well as potential releases from the manufacturing site. Based on these limited data, the US EPA must assess whether the manufacture or use of the proposed chemical may pose an unreasonable risk to human or ecological health. To accomplish that assessment, a set of tools has been developed that relate chemical structure to potential environmental risks.
The first group of properties that must be estimated in an assessment of environmental risk are the basic physical and chemical properties that describe a chemical's separation between solid, liquid and gas phases. These include melting point, boiling point, vapor pressure and water solubility. Additional molecular properties that are frequently used in assessing the environmental fate of chemicals include octanol-water partition coefficient, soil sorption coefficients, Henry's law constantsand bio-concentration factors. Once the basic physical and chemical properties are defined, series of properties that influence the fate of chemicals in the environment are estimated. These include estimates of the rates at which chemicals will react in the atmosphere, the rates of reaction in aqueous environments, and the rate at which the compounds will be metabolized by organisms. If environmental concentrations can be estimated based on release rates and environmental fate properties, then human exposures to the chemicals can be estimated. Finally, if exposures and hazards are known, then risks to humans and the environment can be estimated. Table 1 identifies the chemical and physical properties that will influence each of the processes that determine environmental exposure and hazard. The table makes clear that a wide range of properties need to be estimated to perform a screening level assessment of environmental risks.
Table 1. Chemical properties needed to perform environmental risk screenings.
Environmental Process
Relevant Properties

Dispersion and fate
Volatility, density, melting point, water solubility, effectiveness of wastewater treatment

Persistence in the environment
Atmospheric oxidation rate, aqueous hydrolysis rate, photolysis rate, rate of microbial degradation, and adsorption

Uptake by organism
Volatility, lipophilicity, molecular size, degradation rate in organism

Human uptake
Transport across dermal layers, transport rates across lung membrane, degradation rates within the human body

Toxicity and other health effects
Dose-response relationships

9 Principles of Green Engineering


1. Engineer processes and products holistically, use systems analysis, and integrate environmental impact assessment tools.

Environmental Impact Assessment (EIA) is a tool used to identify the environmental, social and economic impacts of a chemical processes and products prior to decision-making resulting in a process that generates less toxic byproducts and lowers the overall risk associated with the process. This tool first was contained in the United States in the National Environmental Policy Act of 1969 [2]. EIA determines that toxic intermediates used in the synthesis of chemicals might be eliminated and benign solvents might replace more environmentally hazardous materials. EIA aims to predict environmental impacts at an early stage in project planning and design, find ways and means to reduce adverse impacts, shape projects to suit the local environment and present the predictions and options to decision makers. More detailed tools could be employed at the development stages, where potential emissions and wastes have been identified. Finally, detailed environmental impact assessments would be performed as a process nears implementation. By using EIA both environmental and economic benefits can be achieved, such as reduced cost and time of project implementation and design, avoided treatment/clean-up costs and impacts of laws and regulations. [3]

Key Elements of an Environmental Impact Assessment

(a) Scoping: identify the key issues of concern at an early stage in the planning process. Scoping should be carried out at an early stage in order to aid site selection and identify any possible alternatives. The scoping process should involve all interested parties such as the proponent and planning or environmental agencies and members of the public.
(b) Screening: collect information on preliminary designs for the major pieces of equipment to be used in the process need to be specified for the design options that merit further study. Material flows for both major and minor by-products are estimated. Rough emission estimates, based on analogous processes, might be considered.
(c) Identifying and evaluating alternatives: this includes both alternative sites and alternative techniques. This search must be genuine, well documented and carried out before a choice has been made. Determine a list alternative sites and techniques and the impacts of each alternative that include energy consumption, raw materials consumption, impacts to air and water, solid wastes, human health impacts, toxic effects to ecosystems. If a design alternative appears attractive at this stage, a small-scale pilot plant of the process might be constructed and a detailed process flow sheet for a full-scale process might be constructed.
(d) Mitigating measures dealing with uncertainty: review proposed action to prevent or minimize the potential adverse effects of the project. This would include the various pollution reduction techniques that would be required to minimize emissions to the legal limits. If the uncertainties are great, with the possibility of grave consequences then the development plan is rejected. If there are uncertainties that might me reduced by further studies then the applications delayed until further studies are carried out.
(e) Issuing environmental statements: report a comprehensive document that includes the findings of the EIA. This is the final stage of the EIA process and is now often required by law before a new project can proceed.[5]

A typical EIS can be broken down into two parts with different levels of detail:

1) A comprehensive and concise document drawing together all relevant information regarding the process; Non-Technical Summary (NTS). This is a brief report in non-technical language so that it can easily be understood by the public.
2) A document contains detailed assessment of the significant environmental effects.

2. Conserve and improve natural ecosystems while protecting human health and well- being.


Conservation and improvement of natural ecosystems includes: [7]

a) Fully assess and minimize the potential environmental, human health and social impact of the new materials and technologies prior to use and/or market release (e.g., new chemical components, nonmaterial’s, bio-plastics, etc.)
b) Minimize energy use/ maximize energy efficiency. Design for carbon neutrality when possible to reduce the energy impact of the product throughout its life cycle.
c) Ensure that all material used and or released are as benign and inherently safe as possible before putting products on the market, by applying a precautionary approach to chemical management and by finding safer substitutes for chemicals that persist and accumulate in the environment.
d) Maximize design for reparability, reuse, and durable use, to increase the longevity of the product and thereby reduce consumption of limited material resources.
e) Plan for recyclability of the product. This includes using materials that can be recycled easily into new products to minimizing waste.
f) Minimize use of raw virgin materials, and maximize use of recycled materials, to reduce consumption of limited natural resources.
g) Invest in solutions that go beyond our current dominant technologies to improve, innovate, and invent technologies that achieve sustainability.
h) Actively engage communities in the development of new design solutions that improve the life cycle impact of chemical process and products.

Examples of application of principle 2 across design scales

Design scale
Current practice
Application of principle
Polyacrylic acid
Polylactic acid
Paper coating with petroleum-based polymers
Paper coating with renewable, biodegradable polymers
Polystyrene packaging material
(starch-basedpacking peanut)
Utility energy sales
Energy efficiency
buy-back programs

3. Use life-cycle thinking in all engineering activities.

Life cycle analysis (LCA) is a method for developing quantitative predictions and comprehensive assessment of the environmental impacts of a given chemical process or product. The tools of LCA recognize that products, services, and processes all have a life cycle. To perform a life cycle analysis, the material and energy flows of a process should be considered from the point where raw materials are extracted from the environment. Raw materials then go through a number of manufacturing steps until the product is delivered to a customer. The product is used and then disposed of, recycled, or remanufactured. Traditionally, chemical process designers have been concerned with process life cycles up to and including the manufacturing step. However, that basis is changing because chemical product designers now consider how their products will be recycled. They must consider how their customers will use their products and what environmental hazards might arise. Engineers must become managers for their products and processes throughout their life cycles. Engineers must also increasingly understand the networks of industrial systems that produce the raw materials for processes, use the products of processes, or are markets for the byproducts of processes. Finding productive uses for materials and byproducts is a principle that has been used for decades in manufacturing.

LCA considers the environmental impacts of every aspect of manufacturing, including formation of by-products and use of solvents and auxiliaries uses in industries that extend far beyond chemical manufacturing. If a product is environmentally benign but is made using hazardous or nonrenewable substances, the impacts have simply been moved to another part of the overall life cycle. If, for example, a product or process is energy efficient or even energy generating (e.g., photovoltaics), but the manufacturing process consumes energy to a degree that balances any energy gains, there is no net sustainability advantage. Accordingly, designers should consider the entire life cycle, including those of the materials and energy inputs. [6]

This strategy complements the selection of inherently benign inputs that will reduce the environmental impact across life-cycle stages. Multiple indicators of environmental impacts are used; for example air quality issues, water emissions, solid waste, and resource consumption. The purpose of LCA is to compare alternative products or processes that meet the same function. An example might be alternative fuels to meet a specific transportation requirement (e.g., conventional gasoline versus ethanol). Studies conducted include alternative beneficial uses for industrial hazardous wastes and household waste (e.g., alternatives to landfill).

LCA is intended to aid in the evaluation of alternative manufacturing scenarios. It is especially useful in choosing between process options. For a process to be ‘‘green’’ (or more precisely, to deter-mine which chemical manufacturing option is the ‘‘greenest’’), LCA is necessary. Although still in the development stages, LCA is a tool that has been in development and evaluation for over a decade. LCA alone, however, is inadequate to assess the economic and social impact of a given green technology. Additional factors must be considered; in particular, toxicology and assessment of risk associated with a product and the chemical process used in its manufacture are extremely important. [6]

4. Ensure that all material and energy inputs and outputs are as inherently safe and benign as possible.

Engineers are always striving for inherently safe and benign designs as possible. Chemical engineers want to create processes that won’t lead to toxic byproducts, and electrical engineers design products that are safe for the users. Inherently safe is defined as a process which poses a low risk if something should go wrong. There is never a guarantee that a process or product won’t result in a harmful situation if something does go wrong, but inherently safer designs limit the number and level of risk associated with the design by avoiding the hazards instead of trying to control them.
There are four main methods to achieve inherently safer designs. The first is minimize. A plant and/or process should be reducing the amount of hazardous material present at any given time. This will lessen the risk of something going wrong. The next is substitute. Instead of using a flammable solvent, engineers should consider if something less hazardous can be used, such as water and detergent. The third method is to moderate. Is it possible to use a more diluted substance rather than a concentrated one? And finally, simplify. Instead of designed around a problem, engineers should search for a way to design out the initial hazard.
The idea of inherently safe designs and process originated from an article written by Trevor Kletz titled “What You Don’t Have, Can’t Leak” which was an article based on the lessons from the Flixbrough Diaster in 1974. The Flixbrough Diaster was an explosion at a chemical plant in the village of Flixbrough near North Lincolnshire, England on June 1, 1974. The explosion killed 28 people and seriously injuried 36 others.
The plant had been in operation since 1967 to produce caprolactam, which was used to make nylon. The plant was responsible for oxidizing cyclohexane with air in a series of six reactors to produce a mixture of cyclohexanol and cyclohexanone. In April of 1974, a crack was discovered on the 5th reactor and it was decided that instead of fixing the crack, a 20 inch diameter pipe would be installed to bypass the leaking reactor while the repairs were made so the plant could continue operation.
On Saturday June 1, the bypass pipe burst. In less than one minute, 40 tonnes of cyclohexane leaked out and formed a vapor cloud. The cloud came in contact with an ignition source and exploded. The explosion completely destroyed the entire plant and about 1,800 buildings within a one mile radius of the site. The 28 employees working that day died in the explosion, but if the accident had occurred on a week day, it is estimated that nearly 500 people would have been killed.
The engineers who decided to bypass the problem introduced another risk instead of eliminating one by shutting down the plant to fix the problem initially, so their design was not inherently safe. Today, the Dow's Fire & Explosion Index Hazard Classification Guide helps engineers determine the risk of fire and explosion that their processes have.

5. Minimize depletion of natural resources.

It is known that there is a limit of the amount of natural resources that can be found on the Earth. It is the responsibility of engineers to make products that protect all natural resources and minimize the need and quantity of those resources that will be depleted from the environment.

6. Strive to prevent waste.

In every process there is some amount of waste – no process or product is 100% efficient. Engineers work to design products and processes that are more efficient and have less waste. Examples of products that strive to prevent waste can be found in the **Green Products** section.

7. Develop and apply engineering solutions, while being cognizant of local geography, aspirations, and cultures.

Special consideration must be taken with each project in relation to the cultural and geographical surroundings. A prime example of this is the development of biofuels in developing countries. The article “Biofuels development in Africa: illusion or sustainable alternative?” details some of the considerations that must be made. In the case of biofuel, project needs to match the countries’ sustainable agricultural capabilities in relation to climate and economy.

8. Create engineering solutions beyond current or dominant technologies; improve, innovate, and invent (technologies) to achieve sustainability.

Green engineering is the pursuit of improvement in relation to the environment. Innovation and technology are just that, improvements and advancements in knowledge. Using our technology to solve environmental issues is the core of green engineering.

9. Actively engage communities and stakeholders in development of engineering solutions.

It is important to engage the public and private sectors and promote green awareness in every industry. Seize the Moment is a summary of a workshop lead by the U.S. EPA to encourage environmental stewardship (e.g., green chemistry and green engineering) in the pharmaceutical industry.


Engineering is the application of science in the design, planning, construction, and maintenance of buildings, machines, and other manufactured things. Green Engineering reaches in to all aspects of the environmental movement. Nearly all of the wiki pages are green engineering solutions.


1. "Green Engineering". EPA. Last updated September 13, 2007. Retrieved on March 16, 2009.
2. The National Environmental Policy Act of 1969, as amended, 42 USC Sections 4321-4347. Retrieved on April 18, 2009.
3. ^ "Environmental Impact Assessment.” Retrieved on April 18, 2009.
4. “Environmental Impact” Retrieved on April 20, 2009.
5. “Environmental Impact Statement” Retrieved on April 19, 2009.
6. “Use of the life-cycle assessment (LCA) toolbox for an environmental evaluation of production processes.” Retrieved on April 20, 2009
7. ”Design with Green Engineering.” Allen, D. T.; Shonnard, D. R. AIChE J. 2001, 47 (9), 1906-1910.
8. “Human Health Risk Assessment.” Retrieved on April 20, 2009.
9. “Ecological Risk Assessment” Retrieved on April 20, 2009.
10. “Summary of the Toxic Substances Control Act.” Retrieved on April 22, 2009.
11. “Partition coefficient.” Retrieved on April 22, 2009.
12. "Green Engineering , Process Safety and Inherent Safety: A New Paradigm”. Shonnard, David. Retrieved on April 20, 2009.
13. "Biofuels development in Africa: illusion or sustainable alternative?". ENDA. Retrieved on April 20, 2009.
14. “Seize the Moment : Opportunities for Green Chemistry and Green Engineering in the Pharmaceutical Industry”. EPA. Retrieved on April 20, 2009.