Biotreatment of heavy oil wastewater by combined upflow anaerobic sludge blanket and immobilized biological aerated filter in a pilot-scale test

A field pilot study has been constructed in the Liaohe oilfield, China to treat heavy oil wastewater with large amounts of dissolved recalcitrant organic compounds and low nutrient of nitrogen and phosphorus by an upflow anaerobic sludge blanket (UASB) coupled with immobilized biological aerated filters (I-BAFs). By operating the system for 252 days (including the start-up of 128 days), the chemical oxygen demand (COD), ammonia nitrogen (NH3-N) and suspended solid (SS) in the wastewater were removed by 74%, 94% and 98%, respectively. GC–MS analysis indicated that most of alkanes were degraded by the UASB process, while the I-BAF played important roles both in degrading organic compounds and in removing the NH3-N and SS. The bacterial community structural analysis based on the PCR-DGGE technology reveals that the predominant bacteria in the UASB reactor belong to the Bacillales and Rhodobacterales, and that in the I-BAF was identified as uncultured soil bacterium. Our results suggest that the combined biotreatment system has immense potential in large-scale treatment of heavy oil wastewater.

► Heavy oil wastewater was treated by a pilot combined bioreactor.
► The COD, NH3-N and SS in the wastewater can be removed effectively.
► Most of alkanes can be degraded in a UASB process.
► Immobilized-BAF plays an important role for removing the NH3-N and SS.
► Bacterial species belonging to Bacillales and Rhodobacterales were alkane-degraders.