PNNL

Abstract

Quinoline is an N-containing heterocyclic contaminant associated with creosote wastes and may be biologically degraded under aerobic and anaerobic conditions. Quinoline-degrading bacteria were utilized to investigate the rate of quinoline desorption from smectite clay at low surface concentrations and its subsequent mineralization. Fluorescence spectroscopy and 14C-quinoline mineralization techniques were used to compare the observed desorption rates to mineralization rates. Microbial utilization was desorption-rate limiting. Desorption and microbial utilization may be modeled as pseudo-first-order reactions whose first-order rate constant (kobs) is independent of surface concentration. The difference between quinoline disappearance from solution and from the clay surface as observed by fluorescence spectroscopy was comparable to the difference between microbial utilization of the solution and the surface-bound species. The utilization of quinoline from solution was about 30 times more rapid than surface-bound quinoline. The surface-bound species appeared to be protected from microbial attack and, hence, desorption was required prior to utilization. The desorption process is suggested to be a chemical-reaction-controlled process rather than film diffusion controlled, as is typically suggested for an exchange process. The biotransformation of quinoline to 2-hydroxyquinoline, observed in solution by fluorescence spectroscopy, was about five to eight times faster than the subsequent disappearance of 2-hydroxyquinoline. When quinoline was sorbed, however, no 2-hydroxyquinoline was observed in solution or on the surface of the clay. It is suggested that quinoline may be transformed to 2-hydroxyquinoline at the cell surface and that 2-hydroxyquinoline is the species that is transported into the cell prior to further degradation.