Effects of Loading on a Biological
Tertiary Treatment System
H. KIRK WILLARD, Predoctoral Research Associate
D. A. CARLSON, Professor of Civil Engineering
Department of Civil Engineering
University of Washington
Seattle, Washington
INTRODUCTION
Effluents from conventional wastewater treatment facilities contain a variety
of materials which can act as nutrients to the receiving waters. As the effluent
discharges increase in quantity the effect of the nutrient input to the natural receiving waters becomes more evident (1). The wastage of fertilizing materials
has been increasing in the recent past and predictions for the future indicate rapidly increasing amounts of such nutrients will be added to our streams in the decades ahead (2).
Often secondary treatment is insufficient protection for receiving waters,
especially for the discharge from relatively large plants or an accumulation of
treatment plants. Such plants may emit waste streams with 25 mg/l of SS and
have BOD values in the range of 15 to 25 mg/l. These treated waste streams are
still able to exert a significant detrimental effect on the receiving stream. Both
Downing (3) and Reynolds and Yang (4) emphasize the effects of this effluent load,
which is largely waste biomass, as a critical parameter in assessing the performance of conventional waste treatment processes. The removal of sizeable quantities of non-settle able materials from secondary treatment facilities often requires advanced waste treatment processes to effect adequate removal (5).
In an effort to understandhow treatment plants might be more effectively designed, a new treatment system has been studied at the University of Washington.
A schematic drawing of how this system might appear is shown in Figure 1. The
two phases of this system are a biosynthesis step and a biomass reduction or particulate scrubbing unit.   Each stage of this system is carried out biologically.
PARTICULATE SCRUBBING SYSTEM THEORY
The particulate scrubbing phase of our system, composed of an aerated channel with a large surface to volume ratio, provides the proper environment for at-
Aeration Unit
-ionass deduction I'nit
u.C.D. Renoval
Figure 1 - New two-phase waste treatment system.
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