15    TREATMENT OF Cr(VI) CONTAINING WASTEWATER BY
ADDITION OF POWDERED  ACTIVATED CARBON TO
THE ACTIVATED SLUDGE PROCESS
Sang Eun Lee, Director
Environmental Engineering Department
Korea Institute of Construction Technology
Inchon, Korea
Hang Sik Shin, Assistant Professor
Byeong Cheon Paik, Graduate Student
Department of Civil Engineering
Korea Advanced Institute of Science and Technology
Seoul, Korea
INTRODUCTION
The activated sludge process is one of the most widely used processes for the removal of organic and
inorganic substances from industrial and municipal wastewaters. The disturbances in treatment performances caused by the presence of inhibitory or toxic substances in wastewater and by wide
fluctuations in hydraulic and organic loads often have been encountered in conventional activated
sludge operations. Therefore pretreatment facilities to control such disturbances generally preceded
the activated sludge processes for treatment of various industrial wastewaters. However, since activated carbon is able to mitigate these substances, the addition of powdered activated carbon (PAC) to
activated sludge aeration basin has proved to be a good alternative that could provide a practical and
economical method to achieve a high quality effluent by effectively overcoming the disturbances
rather than employing various pretreatment processes.1'2
Many of heavy metals that have inhibitory or toxic effects on activated sludge microorganism are
present in various industrial wastewaters sometimes in very high concentration and they could upset
the operation of the activated sludge process.3'4 Hexavalent chromium (Cr(VI)) is one of them which
has to be removed from influent to activated sludge processes' and it has been shown that activated
carbon adsorption may be an effective pretreatment method for Cr(VI) containing wastewaters.6'7'8
Therefore, the addition of PAC to the aeration tank of conventional activated sludge processes may
be one possible solution for effective treatment of wastewaters containing certain levels of Cr(VI)
rather than employing the activated carbon adsorption process as pretreatment.
Many researchers have utilized complex wastewaters containing nonbiodegradable and inhibitory
or toxic organic compounds to determine the enhancement of activated sludge performance by
addition of PAC for treatment of such wastes, while there have been only few evaluations of these
processes for removal of specific heavy metals.9 There is also little direct information available about
control parameters representing the effectiveness of PAC for the treatment of wastewaters containing
Cr(VI). The objectives of this study were therefore to evaluate the effect of PAC addition to activated
sludge process for treatment of wastewaters containing Cr(Vl) and to determine the kinetic parameters of the processes with and without PAC addition for treatment of such wastewaters.
EXPERIMENTAL APPARATUS AND METHODOLOGY
Apparatus
Two laboratory scale completely mixed, continuous-flow activated sludge reactors with internal
sludge recycle were used during this study, one with PAC addition and the other without PAC
addition. The schematic diagram of the experimental apparatus is shown in Figure 1. The reactors
were fabricated with acrylic resin and consisted of an aeration part and an internal clarifier zone.
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