Wastes and Emissions

Manufacturing produces both solid and liquid wastes that must be treated or disposed of so they do not harm the environment. Traditional manufacturing plants produce large quantities of wastes from the following: production scraps, defective products, overproduction, or excess raw materials. Manufacturing additionally produces process wastes, which are materials needed to make a product but that do not become part of the final product. Concentrated acids are common process wastes that must be managed so they do not enter the environment where they would cause immediate damage to ecosystems. Other common process wastes are water, solvents, salts, and metals. The U.S. Environmental Protection Agency (EPA), which oversees the nation’s waste management, has promoted lean manufacturing as a way to reduce these solid and liquid wastes. The table below summarizes the features of lean manufacturing.

An important initial step for manufacturers to take in reducing solid, liquid, and gas wastes is to list all of the materials exiting the factory as

waste. Waste management begins by knowing exactly what waste materials are being produced, the amount of each, and the potential hazard of each waste on the environment. With this list in hand, production engineers follow a stepwise process to reduce the amount of these wastes produced, as follows:

1. Classify all wastes according to hazards they cause in the environment.
2. Identify the wastes produced in the highest volume.
3. Design new production processes to reduce these first, from the most costly waste to the least costly.
4. Identify the wastes produced in lower volumes or intermittently.
5. Study the production process to find ways of reducing the amount of low-volume or intermittent wastes.

Production engineers often create loops in the production process so that high-volume wastes may substitute for low-volume wastes, thus eliminating one waste category and reducing the other. The DuPont Company described a similar process it has used for several years to reduce the wastes that have cost the company the most money. By asking and finding answers to the following questions, companies like DuPont can blend environmental needs (waste reduction) with business needs (lowered costs):

• How can we reuse high-volume wastes?
• How can we modify the production process or the chemistry to reduce or eliminate each waste on the list?

 The Sharp Corporation headquartered in Japan has devised a similar point-by-point plan for its electronics manufacturing plant in Kameyama that addresses several waste issues as well as energy savings. Sharp’s plan comprises the following points:

1. Minimize greenhouse gas emissions.
2. Reduce resource consumption.
3. Reduce energy consumption.
4. Manage and reduce waste discharges.
5. Evaluate health risks of accidental spills of wastes, to humans and to environment.
6. Evaluate the environmental burden of specific solid, liquid, and gas wastes.

Some of the Kameyama innovations consist of reusing excess heat energy made by the plant’s production processes to supply power for the air-conditioning system. The principles of heat energy are further discussed in the sidebar on page 94 “Heat Energy.” In this case heat represents yet another manufacturing waste that can be turned into a reusable resource. Even the innovative Sharp engineers have a difficult time reusing emissions that contain carbon dioxide (CO2) among other gaseous wastes, so for the present, manufacturers depend on emissions-cleaning technology such as scrubbers. Future production processes may someday be entirely redesigned to use biological rather than chemical processes and so eliminate dangerous emissions. This new biology-based manufacturing is called white manufacturing, or white biotechnology.

Traditional manufacturing often uses coal-fired plants to supply the power to run operations. These types of power plants have been linked to the worst emissions that manufacturing has produced since the dawn of the Industrial Revolution. Coal-fired power plants produce electricity by burning coal in a boiler to heat water into steam. The pressurized steam then enters a turbine that runs a generator, which in turn converts kinetic energy (motion) into electricity. These power plants use up large amounts of coal—a plant near Knoxville, Tennessee, burns 14,000 tons (12,700 metric tons) daily—and release a large volume and variety of greenhouse gases, heavy metals, and particles unless their smokestacks have scrubbers. The energy expert Gordon Couch explained to National Geographic in 2006, “When you try to burn coal or convert it to something else, you’ve got to deal with pretty difficult mineral matter. You’ve got sulfur, pyrite, quartz, silica and all kinds of stuff in with the coal.” Power plants must maintain and clean their scrubbers on a regular schedule in order for these devices to clean hazards out of flue gases.

 Coal-fired plants have two options for solving their emissions problems: redesign the manufacturing operations to use alternative energy

Coal-fired power plants in the United States and many other parts of the world generate electricity for millions of people. These plants consume fossil fuels, water, and energy, and they produce emissions, waste ash, and hot water that harm ecosystems when released. Power generation has two options to improve the situation: design cleaner coal combustion or turn to renewable sources for electricity generation.

sources, or convert to the burning of clean coal, also known as low- sulfur coal. Clean coal is equivalent to standard coal with an exception: the burning of clean coal includes various steps and technologies that remove much of the particles, heavy metals, and the greenhouse gases sulfur dioxide and nitrogen oxides. The following table lists technologies that convert traditional coal-burning power plants into clean coal plants.

Critics of clean coal remind the public that the hazards of coal do not disappear by inventing technologies to lower emissions. Coal mining remains a hazardous occupation for miners, often causing environmental diseases such as black lung disease. In 2007 Marilyn Snell wrote on behalf of the Sierra Club that coal is “dirty and destructive: entire mountaintops are removed to get at it; emissions from coal-fired plants contribute to at

least 24,000 premature deaths a year in this country [the United States] alone; and it accounts for 36 percent of our overall releases of carbon dioxide, the main culprit in global warming. Despite the industry’s hype, there’s no such thing as ‘clean coal.’ But new technologies and policies can help reduce coal plants’ deadly emissions, including carbon dioxide, sulfur dioxide, mercury, and nitrogen oxides.” The question surrounding clean coal may be centered more on the willingness of the world to accept a costly new technology to replace the relatively cheap price of dirty coal.

Will the coal industry as the world knows it ever disappear or at least transform itself into a cleaner form of energy generation? Places in the United States have made efforts to wean themselves from coal-generated energy. California in 2007, for example, announced rules that would bar any new municipal utility company from signing a contract with a coalfired power plant. But coal costs one-sixth the price of natural gas and a fraction of today’s fluctuating oil prices, and the United States holds the world’s largest coal reserves. The rest of the world uses coal as its main energy source, especially the fast-growing economies in China and India.

The coal industry will likely survive any attempts to dismantle it. But this industry can help the environment by voluntary means or through strict air pollution laws. The coal industry can pursue clean technologies, low-impact mining methods, or an advanced technology called coal-toliquid in which coal turns into liquid hydrocarbon fuel under extreme heat and pressure. All of these technologies remain to be perfected. The long-term future of the coal industry seems to be rosy even though coal mining and combustion contribute a great deal to air pollution and global warming. Problems associated with coal-fired plants, even plants using the best emissions-control technologies, suggest that clean manufacturing will need a major overhaul rather than small changes to reduce its wastes—the main objective of sustainable manufacturing.