Impact of bioremediation strategies on slurry phase treatment of aged oily sludge from a refinery

Aged oily sludge was subjected to long term (90 day) slurry phase treatment (10% w/v oily sludge) using various biodegradation strategies involving intermittent spiking with nutrients (N), surfactant (S) and microorganisms (M), employed singly or in combination. The strategy involving simultaneous addition of N, S, and M (BNMS) resulted in the highest rate (0.0126 day(-1)) and extent of oil degradation (68.4%). However, oil degradation rate from aged sludge was almost half that observed for freshly procured sludge. In addition to removal of maltenes (85.7%), removal of asphaltenes (53.6%) was also achieved during BNMS treatment. Two-dimensional gas chromatograph equipped with time of flight mass spectrometer could resolve the unresolved complex mixture hump observed in both degraded and un-degraded samples and could provide greater insights on compositional changes in residual oil due to biodegradation. Although the BNMS strategy significantly enhanced oil degradation from aged sludge, treatment of fresh sludge would be faster and more cost effective.