Biodegradability of volatile hydrocarbons of gasoline

The biodegradability under aerobic conditions of volatile hydrocarbons (4-6 carbons) contained in gasoline and consisting of n-alkanes, iso-alkanes, c ycloalkanes and alkenes, was investigated. Activated sludge was used as the reference microflora. The biodegradation test involved the degradation of the volatile fraction of gasoline in closed flasks under optimal conditions . The kinetics of biodegradation was monitored by CO2 production. Final deg radation was determined by gas chromatographic analysis of all measurable h ydrocarbons (12 compounds) in the mixture after sampling the headspace of t he flasks. The degradation of individual hydrocarbons was also studied with the same methodology. When incubated individually, all hydrocarbons used a s carbon sources, except 2,2-dimethylbutane and 2,3-dimethylbutane, were co mpletely consumed in 30 days or less with different velocities and initial lag periods. When incubated together as constituents of the light gasoline fraction, all hydrocarbons were metabolised, often with higher velocities t han for individual compounds. Cometabolism was involved in the degradation of dimethyl isoalkanes.