Wastewater Treatment with Powdered
Activated Carbon Regenerated by
Wet Air Oxidation
PAUL V. KNOPP, Director of Research and Development
WAYNE B. GITCHEL, Director of Laboratories
Zimpro, Inc.
Rothschild, Wisconsin
INTRODUCTION
Conventional well operated secondary biological waste treatment systems have
served well to meet past water quality regulations; however, the adoption of improved water quality standards along with the increased demands for a relatively
fixed total water resource will require advanced, more sophisticated wastewater treatment systems. Recently, considerable interest has developed in the chemical/physical
treatment process in which raw sewage is treated chemically and settled to remove
suspended matter and in many cases to precipitate and remove phosphorus. The
remaining organic matter which is predominately soluble is removed by physical
adsorption on activated carbon. Such a system is particularly desirable in that the
biological treatment step is eliminated and the effluent quality is equivalent to that
produced by so called "tertiary" treatment processes. Applications of this concept
have been reported by a number of authors (1,2,3,4). For the most part these
applications employ granular carbon beds in the physical adsorption step.
It is well known that powdered activated carbon offers a number of advantages
in wastewater treatment. Powdered carbon is less expensive than granular carbon.
The small particle size of powdered carbon reduces the dependency of adsorption on
intra-particle transport resulting in adsorption rates which approach the theoretical
maximum. Furthermore, in the powdered carbon system, suspended solids in the
feed stream can be tolerated, which in granular systems, could lead to clogging of the
carbon bed with concommitant increase in system head loss. To overcome this difficulty expanded bed operation has been recommended (2). Finally the powdered
activated carbon system employs rather simple unit operations vis. mixing, flocculation and settling which are time honored and relatively well understood systems in
sanitary engineering technology.
Application of powdered carbon systems to wastewater treatment has been
limited by the ability to economically regenerate the powdered carbon. Work carried
out by Zimpro Inc. has shown that the adsorptive properties of powdered carbon can
be successfully restored by partial wet air oxidation. This paper describes the results
of this development work.
Settled primary effluent was processed with powdered activated carbon in a
continuous two stage countercurrent contact system. The spent carbon was regenerated daily and returned to the system for re-use representing approximately 22 regen-
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