Response of Activated Sludge to Quantitative Shock
Loading Under a Variety of Operational Conditions
P. KR1SHNAN, Project Manager
Roy F. Weston, Inc.
Wilmette, Illinois 60091
A.F. GAUDY, JR., Professor
Bioenvironmental Engineering Laboratories
Oklahoma State University
Stillwater, Oklahoma 74074
INTRODUCTION
The response of biological treatment processes, e.g., activated sludge, to shock
loadings has been of long standing investigational interest in the authors' laboratories.
Understanding and characterization of response to environmental change present very
difficult and complex problems because of the many types of shock and the manner in
which they can be administered as well as the biological heterogeneity of the biomass
eliciting the response. Work in the author's laboratories has encompassed quantitative
shock (i.e., changes in concentration of feed, Sj) as well as qualitative shock (i.e., changes in
the nature of the substrate). The most recent work on shock loadings published from this
laboratory has concerned hydraulic shock (I), "temperatureshock"(2)and "pH shock"(3).
The present report deals with quantitative shock loading in both once-through and cell
recycle systems with the shock administered as a step increase in feed concentration, Sj. In
the last report from this laboratory dealing with the quantitative shock, Thabaraj and
Gaudy showed that in addition to the shock-induced transient and subsequent attainment
of a new steady state in response to an increase in Sj there may also be a secondary response
of an ecological nature which can be more disruptive of treatment efficiency than the
immediate biomass response (4). The present interest centers on the biomass response, and
a systematic study was designed which provided for parallel comparison of once-through
and cell recycle systems, holding mean hydraulic retention time.T, the same in both, and
varying levels of shock substrate and growth rate (M) or mean cell residence time (dc). All of
these factors as well as biomass concentration, X, mass loading rate and others may affect
response patterns. In the steady state prior to the shock, all of these factors contribute to the
uniqueness of the near-term past growth history of the biomass and this determines, along
with the mode of administering the shock, the response patterns which will be manifested.
Grady (5) and Schaezler, et al. (6) have reviewed the work of many researchers and the
general impression among many is that specific growth rate, /J or its reciprocal, sludge age,
0c, as well as mean hydraulic retention time, t, prior to the shock play a significant role in
determining the response. Schaezler, et al. (6) did not show the corroborating experimental
data but they state that in general their results demonstrated that slower growing cultures
responded to increases in Sj better than more rapidly growing systems. Unfortunately they
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