3    PAC BIOTREATMENT OF HAZARDOUS COMPOUNDS FROM
AN INTEGRATED OIL REFINERY
N. Gain, Research Fellow
M. Rebhun, Professor
Environmental and Water Resources Engineering
Technion-Israel Institute of Technology
Haifa, 32,000, Israel
INTRODUCTION
Problems encountered in activated sludge treatment of wastewater from an integrated oil refinery
have been reported and discussed earlier by the authors.12 The problems could be classified into three
major categories:
1. Slow rate (kinetics) of the bioprocess due to inhibitory effect of phenolic compounds.
2. "Escape" of biomass in effluent ascribed to poor bioflocculation and frequent high
hydrocarbon content.
The slow kinetics, limiting the removal rate to low values and the biomass "escape"
limiting the MLVSS to below 2,000 mg/L, require long residence times, consequently
large reactor volumes and high costs.
3. Sudden discharges of concentrated phenolic wastes disrupted the process, first by
impairing bioflocculation, followed by complete disruption of the biological process.
The suggested solution, to avoid occasional disturbances, was to intercept and store the
concentrated wastewater streams in separate tanks, discharging gradually from the storage facilities to the main sewerage system at a controlled predetermined flow rate, not
disrupting the bioprocess.
This solution implies significantly higher concentrations of phenols which may cause
further decrease in kinetics and removal rates.
Powdered activated carbon (PAC) addition to activated sludge is suggested in many cases as a
modification being able, potentially, to improve the process, especially in the case of concentrated
industrial wastewater containing refractory, toxic and hazardous compounds. The modification has
been investigated by several workers.3'7 The benefits of PAC in removing toxic adsorbable compounds, such as phenols, have been described810 and the enhancement of activated sludge by PAC
addition in treatment of oil refinery wastewater has been reported.1114
OBJECTIVES AND PROGRAM
The purpose of the combined PAC activated sludge treatment process in this study is to adsorb a
great part of the phenols by the PAC in order to lower their load on the biomass and so to reduce the
inhibitory action expected at high loadings of phenols, particularly cresols and xylenols. The major
objective was, therefore, to study the effect of PAC on substrate removal rate by the biomass, obtain
rate constants, evaluate degree of inhibition and to correlate it with adsorption of the different
phenols by PAC.
The PAC modifies the process and affects its general performance not only through its effect on
inhibitory substances, but also by sharing the total organic load with the biomass. In case of refinery
wastewater the PAC activated sludge combined process involves three simultaneous mechanisms of
removal; namely, stripping, adsorption on PAC, and biological degradation. Therefore, another
major objective was to evaluate quantitatively the fraction of total organics removed by each mechanism. This information is also essential for calculations of biological removal rates constants.
The study program, as dictated by the objectives, included:
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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