Natural attenuation of oily sludge used for the maintenance of an unpaved road in Arauca (Colombia)

IN this study the biodegradation and leaching of total petroleum hydrocarbons (TPHs) during the natural attenuation (NA) processes of the oily sludge used for the maintenance of unpaved roads were evaluated. The study was conducted on a road located in Arauca (Colombia) and simultaneously in a laboratory setting where rain conditions were simulated by using columns. In the in situ study, three depths (5, 50, and 80 cm) were assessed. The degradation of TPH was evaluated by monitoring physicochemical and microbiological conditions in situ and in the columns during 538 and 119 days, respectively. The pH levels observed during the study were relatively constant and ranged between the optimum values for biodegradation (6.2± 0.9). Water content in situ was low (<14%) and observed concentrations of nitrogen (as ammonia and nitrate) were <30 and <10 mg/kg_dw, respectively, indicating that no mass balance was maintained, both possible factors limiting intrinsic biodegradation. During the in situ study a 95% TPH degradation was observed at 5 cm depth, whereas no degradation was evident at 50 and 80 cm. In the column experiments, TPH concentration in the leachate was < 1 mg/L, indicating that the leaching process did not play a key role in this study.