46    A BIOREGENERATED SORPTIVE SLURRY SCRUBBER
Thomas J. Overcamp, Professor
Barth F. Smets, Assistant Professor
Ruth E. Hammervold, Graduate Assistant
C.P.L. Grady Jr., R. A. Bowen Professor and Acting Head
Department of Environmental Systems Engineering
Clemson University
Anderson, South Carolina 29625
INTRODUCTION
Industry is facing the difficult challenge of decreasing emission of hazardous air pollutants (HAPs)
under Title III of the Clean Air Act Amendments. Many of the HAPs emitted are volatile organic
compounds (VOCs) such as solvents used in degreasing, chemical processing, and manufacturing.
Traditional VOC control technologies such as thermal and catalytic oxidation, wet scrubbing with
chemical oxidation, and carbon adsorption can be applied to these emissions. With the possible
exception of the recovery for reuse of an immiscible solvent at high concentrations using carbon
adsorption, these technologies have high capital and operating costs.
For biodegradable compounds in wastewater, biological treatment has wide application.1 In most
cases, biological treatment can mineralize the compounds and destroy their toxic nature.2 If a biodegradable air pollutant can be transferred to water, biological processes have potential application to
air pollution control.
This paper presents an innovative concept to improve the conventional suspended-culture bioscrub-
ber. In this concept, powdered activated carbon (PAC) is added to the biomass slurry circulating in the
bioscrubber. PAC increases the effective solubility of the pollutant. Since the carbon can be regenerated by biological processes, the PAC-biomass slurry can be recirculated.
LITERATURE REVIEW
In a suspended-culture bioscrubber, a suspended-culture of microorganisms, analogous to activated
sludge in wastewater treatment, is circulated between an absorber and an oxidation reactor. The
contaminated gas passes through the absorber where the pollutant is absorbed into water containing
suspended bacteria. Partial oxidization of the pollutant occurs in the absorber and is completed in the
oxidation reactor. Overcamp et al.1 present a simulation model for the performance of such a
bioscrubber. Their predictions indicate such a system has the potential to control pollutants with low
Henry's law coefficients, which are highly soluble in water. Such scrubbers have great potential for the
control of soluble compounds such as methanol, but the efficiency decreases as compounds with a
higher Henry's law coefficient, such as acetone, methyl ethyl ketone, or toluene, are attempted. Data
on methanol removal from an air stream have verified the model for soluble compounds. Based on
analogies to suspended-wastewater treatment processes, this concept has the advantage of achieving
higher efficiencies by changing the operating conditions.4
The solubility of the gaseous pollutant often limits the performance of the conventional bioscrubber.3 Mehta and Calvert,6 Calvert et al.,7 and Kim and Pingel8 have demonstrated that powdered
activated carbon can dramatically increase the absorption into water of a variety of gases including
toluene, benzene, and low molecular weight alkanes. The carbon can be biologically regenerated as in
the PACT process, a proprietary biological treatment process of E. I. Dupont de Nemours, Inc.,
which has use in industrial wastewater treatment. In this process, powdered activated carbon is added
to the suspended-culture activated sludge process. PAC assists the biological process by the adsorption of the contaminants and metabolic byproducts of degradation. The microorganisms regenerate
the carbon to allow reuse in the process.9
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
419