Waste has been defined as a moveable object with no direct use that is discarded permanently. There are many different kinds of waste, including solid, liquid, gaseous, hazardous, radioactive, and medical. Wastes can also be defined by generator, for example, municipal, commercial, industrial, or agricultural.

Garbage in bags and containers accumulating at curbside. (U.S. EPA. Reproduced by permission.)

Waste Types

A solid waste does not flow like water or gas. Examples include paper, wood, metals, glass, plastic, and contaminated soil. Solid wastes can be hazardous or nonhazardous. Problems associated with nonhazardous solid waste include aesthetic problems (litter and odors), leachate from the infiltration of water through the waste, and off-gases resulting from biodegradation. Nonhazardous solid wastes are commonly handled by recycling, combustion, land-filling, and composting.

Liquid wastes must be transported in containers or through pipes. Examples include sewage, contaminated groundwater, and industrial liquid discharges. In some cases...