Improving Activated Sludge Treatment with
Powdered Activated Carbon
ALAN D. ADAMS, Applications Supervisor
Pollution Control Venture Department
ICI America, Inc.
Wilmington, Delaware
INTRODUCTION
The activated sludge process is probably the most challenging waste treatment process
to control. In the face of variable hydraulic and organic loads, varying waste characteristics
and increasingly more stringent standards, it is difficult to achieve and maintain a high
quality effluent merely by altering operating procedures. Consequently, the use of physical-
chemical and tertiary treatment methods is becoming more prevalent. For many plants,
however, such improvements may not be feasible for a variety of reasons. These include lack
of funds, inadequate available space and ill defined effluent standards.
Nearly forty years ago, powdered activated carbon was first investigated as an aid to
sewage treatment for overloaded activated sludge plants. Carbon was found to improve
sludge compaction and filtration (1). The use of powdered carbon was virtually ignored
until more recently when the DuPont Company found that direct addition of powdered
carbon to an activated sludge aerator gave tertiary quality effluent without additional
equipment investment (2). Since the fall of 1971, ICI America has moved beyond the
laboratory studies run by DuPont, and has conducted extensive full scale field tests in a
variety of industrial and municipal wastes. These tests have demonstrated that, depending
upon prevailing problems, powdered carbon will:
— improve BOD and COD removals despite hydraulic and organic overloads.
— aid solids settling, decrease effluent solids and yield thicker sludges.
— adsorb dyes and toxic components that are either not treated biologically or are
poisonous to the biological system.
— reduce aerator and effluent foam by adsorption of detergents.
— prevent sludge bulking over broader F/M ranges.
— effectively increase plant capacity at little or no additional capital investment.
— give more uniform plant operation and effluent quality, especially during periods
of widely varying organic or hydraulic loads.
POWDEHED
ACTIVATED
CARBON
Figure I -    Activated sludge process.
Figure 1 depicts a typical activated sludge process. Powdered carbon is added in dry or
slurry form directly into the aerator, or into the effluent channel from the primary clarifier.
Carbon can be added continuously or on a batch basis.
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