17    EVALUATION OF TOXIC ORGANICS REMOVAL BY
SIMULTANEOUS ADSORPTION AND BIODEGRADATION
Frieda Orshansky and Nava Narkis
Environmental and Water Resources Engineering
Technion—Israel Institute of Technology, Haifa 32000, Israel
ABSTRACT
Simultaneous adsorption and biodegradation processes were investigated. Three toxic organic
compounds, nitrobenzene, aniline, and phenol were selected to be studied individually and in
mixtures as a model of polluted toxic industrial wastewaters. Their behavior was assessed separately in adsorption, biotreatment, as well as in combined systems, by physicochemical and
respirometric methods. Powdered activated carbon (PAC) was used as an adsorbent in these experiments. In the adsorption systems, in single, bi- and trisolute solutions, the limiting adsorption
capacities, Q" and b, the energy of adsorption related constants, were determined from the linearized forms of Langmuir adsorption isotherms. Q" values for aniline and phenol were found to
be similar and approximately 2.5 times higher for nitrobenzene. The energy related coefficient b,
was similar for nitrobenzene and phenol, and almost 5 times higher for aniline. The presence of
mineral nutrients, needed for biological processes, significantly decreased the energy related
constants for phenol and aniline, but did not affect this parameter for nitrobenzene. Kinetic characteristics of those three compounds' biodegradation by acclimated microbial cultures were determined in biological systems. The degree of bioresistance of the organics was estimated. PAC
addition to the biological systems affected differently the biooxidation of the three compounds.
The presence of PAC considerably enhanced the microbial respiration in the bioreactor with nitrobenzene, distinctly intensified that of phenol, but reduced it in the reactor with aniline. Different organic removal mechanisms were suggested in simultaneous adsorption and biodegradation
of each of the three compounds, due to their different adsorption characteristics. It was found
that the strong inhibiting effect of the three compounds in highly concentrated mixture on microbial respiration was completely wiped out by adding PAC to the biological reactor. As a result,
the initial COD 3350 mg 0-,/L was reduced to 27.6 mg 0-,/L. The optimal PAC dose was determined by using respirometric data.
The results obtained can be used for the evaluation of simultaneous adsorption and biodegradation as a method for effective removal of toxic organics from industrial wastewaters, under appropriate conditions. The method can be applied for the industrial wastewater treatment alone as
well as for pretreatment, before discharging to the municipal biological treatment plant. The
process is expected to decrease the harmful effect on conventional activated sludge processes
and to prevent the disposal of hazardous materials into the environment.
INTRODUCTION
The problem of the environmental protection from industrial toxic, teratogenic, and carcinogenic pollutants is becoming more and more acute. The traditional approach to industrial wastewaters purification is treating them together with large amounts of domestic sewage in a biological treatment plant, with the idea of their manifold dilution. However, most of the industrial
contaminants are nonbiodegradable at such conditions and have a deteriorating effect on municipal wastewater treatment plant operation and effluents' quality. Thus, the above method provides
"cosmetic" purification and results in incomplete removal of the contaminants. To obtain a
higher and stable treated water quality for a wide range of uses, advanced treatment processes
are required. Activated carbon adsorption proved to be an effective method for residual toxic or-
52nd Purdue Industrial Waste Conference Proceedings, 1997, Ann Arbor Press. Chelsea. Michigan 48118. Printed in
U.S.A.
159