The process of turning waste into a reusable material.

Able to be maintained at a certain rate or level.

The science of dealing with the occurrence, circulation, distribution, and properties of the waters of the earth and its atmosphere.

Of a natural resource or source of energy existing in finite quantity; not capable of being replenished.

A smelting furnace in the form of a tower into which a blast of hot compressed air can be introduced from below.