Experiments and Modeling for Investigation of Oily Sludge Biodegradation in a Wastewater Pond Environment

Abstract

Historic operating and abandoned refineries frequently contain ponds or lagoons that contain oily sludge from historic wastewater treatment processes and separator sludge disposal activities that occurred prior to the implementation of regulations forbidding such disposal. These oily sludge-containing wastewater ponds represent a long-term liability at older operating refineries or abandoned refinery sites. Dewatering and solidification/stabilization are the most common technologies used to treat these sludges; however, these approaches are labor, equipment, and material-intensive. For sites where the time required to complete treatment is not a high priority, biodegradation treatment may be effective for final site remedy. The objective of this study was to investigate potential improvements in oily material biodegradation using dispersants and petroleum-degrading microbial consortia, along with the modeling of this system. The oil dispersed with mixing or remaining in the bulk aqueous phase with biodegradation was measured using methods from a dispersant effectiveness test. The experimental results indicated that mixing at levels of 200 rpm or higher resulted in positive effects on both the extent of hydrocarbon dispersion (80 to 90% of oil dispersed) and the biodegradation of the oil phase (50 to nearly 100% degraded), while the modeling results, taken along with the experimental results, indicated smaller dispersed phase droplet sizes and promoted more efficient biodegradation.