Biodegradation kinetics of monoterpenes in liquid and soil-slurry systems

Batch experiments were conducted to evaluate the biodegradation rates of limonene, alpha-pinene, gamma-terpinene, terpinolene and alpha-terpineol at 23 degrees C under aerobic conditions. Biodegradation was demonstrated by the depletion of monoterpene mass, CO2 production and a corresponding increase in biomass. Monoterpene degradation in liquid cultures devoid of soil followed Monod kinetics. The maximum specific growth rate (mu(max)) was 0.02 h(-1) and 0.06 h(-1) and the half-velocity constant (K-s) varied from 32 mg/l to 3 mg/l for the limonene and alpha-terpineol respectively. The recovery of monoterpenes by solvent extraction from autoclaved and azide-amended soil-slurry samples decreased over time and ranged from 69% to 73% for 120 h of incubation period. Although a significant fraction of monoterpene hydrocarbon could not be extracted, mineralization of these compounds in the soil-slurry systems took place, as shown by CO2 production. The soil-normalized degradation rates for the hydrocarbon monoterpenes ranged from 0.6 mu g g(-1) h(-1) to 2.1 mu g g(-1) h(-1). A kinetic model - which combined monoterpene biodegradation in the liquid phase and net desorption - was developed and applied to data obtained from soil-slurry assays.