Types and Amounts of Waste
Waste comes in a bewildering variety of forms but can be categorised in two basic ways. First is its state: gaseous, liquid, or solid, with subcategories of all kinds within these broader categories. Waste can also be of organic origin or composition (animal excrement, wood pulp, plastics) or inorganic (typically metals). Waste may also be categorized by its toxicity. Some waste is relatively harmless, such as used paper. Some is harmless in and of itself but presents environmental hazards if not properly disposed of, such as plastic containers. Some waste, such as human or animal excrement, is not toxic per se, but it presents a health hazard if it contaminates water supplies, for instance. Finally, some waste, such as heavy metals, radioactive materials, or certain chemicals, is highly toxic to human health and the environment. (Nuclear and toxic wastes will receive little discussion here; for a more thorough discussion, see the chapters Nuclear Energy and Toxic Waste, respectively.)
Second, waste can be categorized by its source. There is waste associated with agricultural production, manufacturing, resource extraction, consumption, and human bodily functions. This chapter will largely focus on household waste.
By definition, waste is not useful or wanted, at least in its immediate state. It can be, and often is, recycled into useful material or products, or, in the case of organic wastes, used as compost or burned for energy. Whether reused or not, waste must almost always be removed in a timely fashion from where it is immediately produced—be it the farm, the factory, or the household.