If nutrient and organic loads are not
tremendously heavy in relation to the size of the receiving stream, this
procedure can help to assure that no one stretch gets too strong a dose
of them. It is likely to find good use in the Potomac and elsewhere,
though only as an adjunct to the best available treatment.

* * * * *

"Advanced treatment" and "tertiary treatment" are becoming common terms
nowadays. They refer to any of a considerable array of additional or
intensified processes aimed at attaining levels of purification that
would have cost an impossible price a few years ago. Most of them are
still experimental and often still expensive, and they involve
everything from filtration through powdered coal to flash distillation,
with still others in prospect. Some bypass conventional treatment and
deal with whole raw wastes. More build on conventional treatment and are
designed to remove nutrients and residual organic material from its
effluents. Of these latter approaches, at least one, involving lime
precipitation and other processes to remove nearly all phosphorus and
most remaining organic material, is nearing a stage of development and
economy that may warrant important use. It will be applied first at the
new Piscataway treatment plant of the Washington Suburban Sanitary
Commission in Prince Georges County, Maryland, which will also
incorporate research and demonstration projects in nitrogen stripping
and other things.

[Illustration]

In the long run such advances offer the main hope of clean water for a
superpopulated future America, where volumes of wastes are going to be
enormous and first-rate off-stream treatment is going to have to be the
main way of handling them. Even where wastes can be collected easily for
treatment, however, as in industry or in sewered populated areas, it may
take a good many years to work out varied forms of advanced treatment
adaptable to different sets of circumstances, at prices that communities
can afford to pay--and a willingness to pay what can be paid is going to
have to be a part of the long clean-up job ahead. Undoubtedly continuing
research will work out such forms of treatment, but the research itself
may be quite costly and no one can predict its pace.

Where waste sources are too diffuse to be channeled into collection
systems--as along many agricultural streams heavily polluted through
land runoff and drainage, and also in some urban s