Environmental Engineering FOURTH EDITION

Wastewater Treatment 171

Undisturbed soil

Figure 9-3. Alternative on-site disposal system.

its invention in 1778; others (Reyburn 1969) recognize it as the brainchild of Sir
John Harrington in 1596.2 The latter argument is strengthened by Sir John’s original
description of the device, although there is no record of his donating his name to
the invention. The first recorded use of that euphemism is found in the regulation at
Harvard University, where in 1735 it was decreed that “No Freshman shall go to the
Fellows’ John.”
The wide use of waterborne wastewater disposal, however, concentrated all of the
wastes of a community in one place. Cleanup then requires a major effort, and this
requirement fostered what is known as central wastewater treatment.

CENTRAL WASTEWATER TREATMENT

The objective of wastewater treatment is to reduce the concentrations of specific pol-
lutants to the level at which the discharge of the effluent will not adversely affect the
environment or pose a health threat. Moreover, reduction of these constituents need
only be to some required level. Although water can technically be completely purified
by distillation and deionization, this is unnecessary and may actually be detrimental to
the receiving water. Fish and other organisms cannot survive in deionized or distilled
water.
For any given wastewater in a specific location, the degree and type of treatment
are variables that require engineering decisions. Often the degree of treatment depends
on the assimilative capacity of the receiving water. DO sag curves can indicate how
much BOD must be removed from wastewater so that the DO of the receiving water is
not depressed too far. The amount of BOD that must be removed is an effluent standard

%ir John, a courtier and poet, installed his invention in his country house at Kelson, near Bath. Queen
Elizabeth had one fitted soon afterward at Richmond Palace. The two books that were written about this
innovation bear the strange titles, A New Discourse on a Stale Subject, Calkd the Metanwlphosis of Aja,
and An Anatomie of the MetanwlphosedAjaz“AjAjax” is a play on the words “a jakes,’’ a synonym for water
closet.