Control of Microbial Ecosystems. Even the most advanced
of today's models of biological wastewater treatment systems
fall somewhat short of representing the ecology of the various
microbial populations present in, say, an activated sludge process.
They simulate the interactions between several substrates and
several "consortia" of bacterial species, but not
the interactions among the bacteria and their higher-order predators.
In the long run it is our view that control of such processes,
for the practical purpose of more reliable and cost-effective
treatment of wastewater, will increasingly draw upon understanding
of an ecological, as opposed to merely biochemical, nature.
For we know from earlier research that the practical operational
problem of a bulking sludge can be successfully addressed with
a relatively simple ecological model of the competitive growth
of floc-forming and filamentous species of heterotrophic bacteria.
What, then, can Control Theory do for this ecological system?
It may be, for the time being, that it should do what it normally
does: allow us to understand how to cultivate the right organisms
in the right relative amounts in the right place at the right
time. The distinctive point here is that the humble activated
sludge process of wastewater treatment is one of the very few
ecological systems in which the exercise of control by external
manipulations is both feasible and desirable. It is a laboratory
wherein to experiment, learn, and generalize therefrom to larger,
grander insights. As long ago as the mid-1970s Thomann
pioneer of environmental systems analysis introduced
an independent variable of trophic length, in his case for the
purpose of reducing a burgeoning set of ordinary differential
equations to a more manageable partial differential equation
set. The distribution of toxic contaminants over space-time-trophic
length were to be characterized. For our program, trophic length
may have significance in other ways, in permitting distributed-parameter
control theory to be employed in identifying how "internal
control" in an ecological system is distributed over the
continuum of its constituent species, from the smallest to the
largest. The microbial ecosystem of the activated sludge process
may have too restricted a span of trophic lengths for this notion
to be explored. It might better be addressed through the foodweb
model prepared for studying the ecological integrity of Lake
Lanier, spanning trophic length from bacteria to striped bass
fish from the lowest prey to the topmost predator. This,
however, is to extrapolate well ahead of current capabilities;
yet we wish to retain such ambition within our sights.