P2 includes "source reduction," "waste reduction," and "toxics use reduction" (using a less-toxic material and/or reducing the amount of a toxic chemical that is used). All of these strategies are different from "pollution control" or "waste management," which are methods to stop waste chemicals from entering the environment after they have been created.

The waste hierarchy, according to the federal Pollution Prevention Act of 1990, establishes pollution prevention as the best "waste management" options available to industry. First and foremost, "pollution should be prevented or reduced at the source whenever feasible." For wastes that cannot be prevented in the first place, waste recycling, treatment, and disposal are the remaining waste management options, in order of preference.

While the Community Guide to Vehicle Assembly focuses on opportunities for pollution prevention, waste treatment options (i.e., end-of-pipe control technologies) are acknowledged here as part of a waste management strategy used by industry to protect human health and the environment. Specific pollution control technologies for air emissions and wastewater are described below. Industry should improve the performance of these technologies to effectively control waste chemicals from entering the environment after they have been created, while at the same time companies should be encouraged to adopt the more desirable pollution prevention practices.

Incineration
Incineration is a treatment technology used to destroy organic contaminants, typically gaseous, present in the air. Contaminants in the air are burned, often with the use of supplemental fuel, resulting in the combustion products carbon dioxide, carbon monoxide, and unburned hydrocarbon gases. Incineration is most often used to control concentrated air streams - those with a high amount of contaminant - thus minimizing the supplemental fuel required for combustion. In a vehicle assembly facility, incineration is typically used to control air emissions from the Finishing processes of the painting and coating operations; the concentration of contaminants in air emissions from these processes is high due to the use of solvent-based coatings.

Adsorption
Adsorption processes also are used to control hydrocarbon emissions from industrial air streams. Contaminated air is forced through a chamber, or 'bed', filled with an adsorption material (e.g., activated carbon). As the air flows past the material, contaminants adsorb (cling) to the material's surface and are removed from the air. The material that is filled with adsorbed contaminant can be burned to destroy the contaminants, disposed of as solid waste, or reactivated. Reactivation removes contaminants from the material; contaminants removed from the media are collected for recycle/reuse, disposal, or destruction. Not restricted to concentrated air streams, adsorption can be used to control emissions from the Finishing or Assembly processes.

Scrubbing
Scrubbing refers to the removal of air contaminants with a liquid that is placed in direct contact with the contaminated air. Scrubbers often are used in vehicle assembly facilities to capture paint/coating solids that have become suspended in the air due to spray application processes (Priming and Finishing processes). Water typically is used for scrubbing, and it is the physical contact between it and the air contaminant that purifies the air. The contaminated water must be treated using a separation technique (described below).

Neutralization
Neutralization balances wastewater pH, reducing either its acidity or alkalinity. By adding an acid (e.g., sulfuric acid or hydrochloric acid), wastewater which is basic in chemistry can be neutralized; by adding a base (e.g., lime or sodium hydroxide) acidic wastewater can be neutralized. Reactions resulting from these chemical additions may generate insoluble solids that must be removed and disposed of as wastewater treatment sludge. Metals from Anticorrosion wastewaters, for example, often are removed using this neutralization technique.

Separation
Separation processes include the removal of oils and greases, as well as suspended solids which may be present in wastewater. Oils and greases in wastewater are typically the result of cleaning processes, such as those used in the Anticorrosion process. They tend to form an insoluble layer with water, and can be removed by simply skimming them from the wastewater surface. If suspended throughout the wastewater, grease and oil removal becomes more difficult, requiring physical and chemical treatment. Solids suspended in wastewater are typically the result of Priming and Finishing at a vehicle assembly facility. Sprayed paints and coatings not transferred to parts may be captured by a water curtain surrounding the application units. To facilitate water recycling, these solids must be removed by filtration or through the addition of other chemicals which result in precipitation of solids.

Removal of Toxic Substances
The removal of toxic substances (e.g., heavy metals) from wastewater typically is achieved by physical-chemical treatment. Additions of chemicals causes some contaminants to form Solids or clumps of solids. Neutralization is a simple example of chemical treatment. Physical treatment then separates these solids from the water (via various filtration processes) and removes dissolved toxics through adsorption (described above).

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