RESPONSE OF PHENOL-ACCLIMATED ACTIVATED SLUDGE
PROCESS TO QUANTITATIVE SHOCK LOADING
A. F. Rozich, Assistant Professor
A. F. Gaudy, Jr., Professor and chairman
Civil Engineering Department
University of Delaware
Newark, Delaware 19711
INTRODUCTION
This report brings together two lines of research in the authors' laboratory, i.e., response of activated sludge processes to shock loadings and the treatment of toxic carbon sources, e.g., phenol. A
recent paper has dealt with the prediction of response to combined hydraulic and quantitative shocks
for systems treating a non-toxic carbon source [1]. Other work has dealt with the modeling and prediction of performance for activated sludge processes treating phenolic waste under non-shock conditions [2].
Both research concerns are of great importance to water pollution control efforts since it is becoming amply clear that biological treatment is depended upon for the bulk of wastewater purification,
and it will be called upon to treat an increasing variety of toxic components. Phenol, and phenolic
compounds, can be expected to constitute an increasingly larger part of the toxic organic loadings as
the use of coal for energy and chemical feed stock increases.
There is a fairly large amount of literature on the subject of shock loads, some of which has been
discussed in a previous paper [1]. Although a lesser amount of work on treatment of phenolics has
been reported, there are ample data to show that the phenol is readily degraded after development of
an acclimated population [3,4]. There is some controversy regarding the need to include an "inhibitory function" in activated sludge models for treatment of phenolic wastes. However, results of a
two-year study in the authors' laboratory led us to conclude that phenol inhibits growth of acclimated
populations, and that predictive modeling equations should include an inhibitory function [2,5]. This
conclusion was based on the results of well over 100 growth studies in our laboratories [5] in which it
was found that the specific growth rate, n, underwent an increase as phenol concentration increased,
but it did not attain an asymptote to some upper value; instead, it went through a peak and a decline
with further increase in phenol concentration. Also, the results of modeling efforts predicted that systems for which an inhibitory function were included would experience sudden and complete failure
when substrate concentrations attained values close to those corresponding to the peak p. level, which
was generally well below /xmax for the system. Also, preliminary experimentation provided some indication that sudden failure could occur. Thus, it appeared that when operating conditions change so
that the activated sludge population is required to increase its specific growth rate, e.g., an increase in
Sj or D (i.e., a quantitative or hydraulic shock loading), there would be a greater likelihood for the
system to fail, due to shock, than there would be for a system treating non-toxic wastes.
An examination of the literature shows that some of the work which has been conducted on phenol metabolism in continuous flow reactors relates to the shock loading response. Yang and Humphrey [6] performed studies on both pure and mixed cultures growing on phenol. They noted a lag in
response time for the growth rate when the cells were subjected to a shock load consisting of an
increase in Sj, and they introduced a delay function in their dynamic model to account for the lag.
Pawlowsky et al. [7] noted the existence of multiple steady states in a chemostat utilizing phenol as
sole source of carbon when the reactor was placed in an unsteady condition by a shock input of phenol. This multiplicity was attributed to wall growth in the reactor. Howell et al. [8] discussed the
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