20    BIOTREATMENT INHIBITION BY HAZARDOUS
COMPOUNDS IN AN INTEGRATED OIL REFINERY
Menahem Rebhun, Visiting Professor
Department of Civil Engineering
Virginia Polytechnic Institute
Blacksbury, Virginia 24061
Noah Galil, Research Associate
Technicon-Israel Institute of Technology
Haifa, Israel
INTRODUCTION
Integrated refineries include many cracking processes, particularly catalytic cracking and auxiliary
processes which generate wastewaters with high concentrations of hazardous contaminants such as
various phenolic compounds. All refineries are significant water consumers and consequently large
wastewater producers. In areas with limited water resources, reuse has to be often practiced and
therefore good quality effluent is required. Also, in "water rich" areas, the wastewater has to be
efficiently treated for removal of the hazardous contaminants before discharge to protect the quality
of receiving waters.
Treatment schemes commonly used in refineries include gravity oil-water separation followed by
flocculation and dissolved air flotation. For removal of the dissolved organics biological treatment is
usually necessary. It may be applied either for the pretreated refinery wastewater only, or as joint
treatment with neighboring municipal wastewater.
Biological treatment of refinery wastewater has been reported for many years, with efficient stabilization in the activated sludge process requiring, however, long acclimation periods for the biota to
metabolize the refractory components.' Application of adapted mutant bacterial cultures to the
treatment was suggested by some researchers.2'3 While many report that phenol is a controlling
toxicant in biological treatment,4'5 some researchers report efficient phenol removal at influent
concentration up to 200 mg/L after acclimation, but requiring long reactor residence time to achieve
good biofloc settleability.6 Biodegradability rate of paraffinic and aromatic hydrocarbons was much
lower then of municipal type organic material and adverse effects of hydrocarbons on settling characteristics of the bioflocs were encountered.7
In the present work the biotreatability of wastewater from an integrated oil refinery was studied in
an on-site pilot plant. It was a rather strong wastewater, due to the low specific water consumption,
with significant phenols content and occasional very high phenols concentration. The phenols are
contributed by the cracking process and special gasoline washeries. The specific objectives were to
study the fate of phenols and hydrocarbons and their effect on the biological process, process rates,
biofloc properties and to derive ways to overcome difficulties caused by these pollutants.
EXPERIMENTAL
The present treatment plant in this refinery includes an API type gravity separator followed by
chemical flocculation (CF) and dissolved air flotation (DAF), as shown in Figure 1. High oil, hydrocarbon and suspended solids removals are accomplished by this treatment. To meet effluent discharge
standards and to prepare the effluent for reuse, the reduction of hydrocarbons (including so-called
"soluble hydrocarbons") to low levels, removal of phenols and reduction of BOD are required.
Biological treatment is planned as the next stage for which this study was performed. This research
was performed on an on-site pilot plant (see Figure 2) consisting of an aeration tank, as a bioreactor,
an attached clarifier (volumes: 270 liters and 75 liters, respectively), all the necessary piping, pumps
for biosludge recirculation, flow measurements and regulation devices.
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