Section Two
PHYSICAL/BIOLOGICAL SYSTEMS
5    FLOC-LOADING BIOSORPTION CRITERIA FOR THE
TREATMENT OF CARBOHYDRATE WASTEWATERS
Mervyn C. Goronszy, Executive Technical Manager
Transfield, Inc.
Irvine, California 92715
W. Wesley Eckenfelder, Professor
Environmental and Water Resources Engineering
Vanderbilt University
Nashville, Tennessee 37235
INTRODUCTION
Biosorption is an essential mechanism in the application of biomass selectivity principles for the
control of filamentous sludge bulking. A number of systems incorporating biological selector concepts have been reported over recent years showing variable success.
This paper provides information on biosorption relative to floc-loading and biomass degradable
fraction for a number of readily degradable carbohydrate wastewaters. Procedures which enable
optimum biosorption, regeneration of biomass biosorptive capacity together with degradation kinetics, overall oxygen requirements, and sludge yield are described. Parameters which favour the selection of a non-filmentous biomass are presented.
BIOSORPTION PHENOMENA
Sorption of soluble organic compounds is a fundamental mechanism in the metabolism of substrate
by microorganisms. This phenomenon was originally observed by Porges et al. [1] and Eckenfelder (2)
but little was done with application to process design and operation until recently. Sorption can be
defined as that phenomenon by which a rapid removal of soluble organics occurs upon contact of the
substrate with activated sludge. This reaction is very rapid occurring in a matter of minutes. There is a
limit to the mass of organics which can initially be removed by a unit mass of sludge. This limiting
removal is in fundamental terms a function of the storage capacity of the biomass and the rate of
biological oxidation of the substrate. A maximum removal by biosorption of 0.65 mg COD/mg VSS
from skim milk was found by Porges et al. [1]. This removal was stored in the cell as glycogen which
was metabolized over a three-hour period.
The contact stabilization process was developed to take advantage of the adsorptive and biosorptive
properties of activated sludge [3]. This process achieves 90-95% BOD and suspended solids removal
with only 15-30 minutes mixing of raw sewage with a well-stabilized sludge.
The removal of BOD in the activated sludge process in mediated by two principal mechanisms. The
first is a physical removal by which the particulates, both organics and inerts, are enmeshed and/or
adsorbed by the sludge matrix. Solubilization of adsorbent particulate organics takes place by enzymatic reactions which contribute to the net soluble organic fraction which is then available for
subsequent biological degradation. Removal of soluble organics is a biological phenomenon.
Porges et al. [I], Quirk [4], Eckenfelder [2,5], Goronszy et al. (6), Chang [7], Hager [8], and
Flippen et al. [9] report observations of rapid, soluble organic uptake by activated sludge with a
variety of substrates.
Biosorptive transport mechanisms are especially significant in activated sludge systems which are
configured with plug-flow hydraulics or which incorporate a short retention contacting region in
order to generate similar sorptive transport conditions which occur in plug-flow systems. A high level
of initial absorption can be evident in those systems where a high substrate to biomass availability
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