"Out of sight, out of mind" has been the traditional philosophy of waste disposal. Technologically, it may well be the last thing scientists want to be associated with, so it has received relatively little attention until recent decades, when the negative results of lax policies have shown themselves. Improper sewage disposal results in pollution-related problems--besides being foul and unpleasant, pollution can damage plant and animal communities, contaminate food and water supplies, and spread serious human diseases.

In the 1870s, Louis Pasteur (1822-1895) discovered the existence of microbes, and made the association between pollution and diseases such as cholera and typhoid. Yet it took the better part of a century for practice to come into line with knowledge, and many parts of the world still do not have adequate sanitation.

Sewer systems have been part of the urban scene since ancient times. Latrines and drains were used...