BIODEGRADATION OF PAINT STRIPPER SOLVENTS IN A MODIFIED GAS LIFT LOOPBIOREACTOR

Paint stripping wastes generated during the decontamination and decomm issioning of former nuclear facilities contain paint stripping organic s (dichloromethane, 2-propanol, and methanol) and bulk materials conta ining paint pigments. It is desirable to degrade the organic residues as part of an integrated chemical-biological treatment system. We have developed a modified gas lift loop bioreactor employing a defined cen sortium of Rhodococcus rhodochrous strain OFS and Hyphomicrobium sp. D M-2 that degrades paint stripper organics. Mass transfer coefficients and kinetic constants for biodegradation in the system were determined . It was found that transfer of organic substrates from surrogate wast e into the air and further into the liquid medium in the bioreactor we re rapid processes, occurring within minutes. Monod kinetics was emplo yed to model the biodegradation of paint stripping organics. Analysis of the bioreactor process was accomplished with BIOLAB, a mathematical code that simulates coupled mass transfer and biodegradation processe s. This code was used to fit experimental data to Monod kinetics and t o determine kinetic parameters. The BIOLAB code was also employed to c om pa re activities in the bioreactor of individual microbial cultures to the activities of combined cultures in the bioreactor. This code i s of benefit for further optimization and scale-up of the bioreactor f or treatment of paint stripping and other volatile organic wastes in b ulk materials. (C) 1997 John Wiley & Sons, Inc.